Mesoscale Convective Systems

In Indonesia, the rate of diabetes sufferers continues to increase, so this is deemed necessary to pay attention to by the Indonesian people in particular, for this reason this research is not the first to be conducted. Predicting diabetes can be done using various methods through various algorithms which are quite diverse, therefore it is necessary to conduct research on the algorithms used. To obtain new information, the Decision Tree algorithm with Naïve Bayes was tested using the Rapid Manner

A significant source of uncertainty in Numerical Weather Prediction (NWP) models arises from the parameterization of sub-grid scale convection, whose inherent nature of complexity is amplified while applied to tropical regions where weather systems are controlled by many intricate factors. However, as the model resolution becomes finer, it is possible to switch off the convection parameterization, although it is still unclear at what resolution this can be achieved. Ambiguity arises due to the inter-linking of various parameterization schemes within a model, and efficiency of one scheme depends on the output of another. In order to explore these issues, an intense convective episode with very heavy precipitation over the coastal Arabian Sea associated with the passage of OCKHI, one of the very severe cyclonic storms, is chosen as a case study. A set of distinct numerical simulations are carried out using Consortium for Small-scale Modelling (COSMO) to assess the direct and indirect impacts of dynamical downscaling on the treatment of convection. Results obtained from the present investigation indicate dynamical downscaling together with switching off the convection parameterization could simulate the magnitudes of CAPE, one of the proxies for characterizing the occurrence of tropical convection, more realistically. But the downscaling did not improve the rainfall prediction, which were seen to deteriorate in the absence of convection parameterization.

During the afternoon of 23 October 2022, a mesoscale convective system (MCS) developed and intensified over the English Channel and tracked north-northeastward into southern England, producing widespread damaging winds and at least three moderate to strong tornadoes in Hampshire. In general, atmospheric temperature and moisture profiles from radiosonde observations and NOAA satellites indicated a high potential for severe thunderstorm, straight line wind, and tornado occurrence over southern England. Radar and satellite observed coincidently high rain rates and very low storm-top temperatures as well as prominent trends in MCS organization and intensity that suggested damaging outflow wind.

O objetivo principal do presente trabalho foi observar a capacidade do modelo BRAMS e sua sensibilidade em simular a ocorrência de sistemas Zona de Convergência do Atlântico Sul-ZCAS, com a finalidade de observar o comportamento do fenômeno e sua interação com a escala interanual. Foram selecionados dois eventos de ZCAS: de 02 a 06 de dezembro de 2009 (durante a fase El Niño) e de 27 a 31 de dezembro de 2010 (durante a fase La Niña). A análise da mesoescala revela importantes variações dinâmicas relacionadas à ZCAS para ambos os casos. Todas as variáveis apresentam coerência e o BRAMS conseguiu simular bem a área principal de atuação da ZCAS, tanto para o caso de El Niño (2009) quanto para o caso de La Niña (2010).

Nocturnal bow echoes can produce wind damage, even in situations where elevated convection occurs. Accurate forecasts of wind potential tend to be more challenging for operational forecasters than for daytime bows because of incomplete understanding of how elevated convection interacts with the stable boundary layer. The present study compares the differences in warm-season, nocturnal bow echo environments in which high intensity [.70 kt (1 kt ' 0.51 m s 21)] severe winds (HS), low intensity (50-55 kt) severe winds (LS), and nonsevere winds (NS) occurred. Using a sample of 132 events from 2010 to 2018, 43 forecast parameters from the SPC mesoanalysis system were examined over a 120 km 3 120 km region centered on the strongest storm report or most pronounced bowing convective segment. Severe composite parameters are found to be among the best discriminators between all severity types, especially derecho composite parameter (DCP) and significant tornado parameter (STP). Shear parameters are significant discriminators only between severe and nonsevere cases, while convective available potential energy (CAPE) parameters are significant discriminators only between HS and LS/NS bow echoes. Convective inhibition (CIN) is among the worst discriminators for all severity types. The parameters providing the most predictive skill for HS bow echoes are STP and most unstable CAPE, and for LS bow echoes these are the V wind component at best CAPE (VMXP) level, STP, and the supercell composite parameter. Combinations of two parameters are shown to improve forecasting skill further, with the combination of surfacebased CAPE and 0-6-km U shear component, and DCP and VMXP, providing the most skillful HS and LS forecasts, respectively.

As a part of the Tropical Cyclone Rapid Intensification Project (TCRI), observations were made of the rapid intensification of Hurricane Sally (2020) as it passed over the Gulf of Mexico. High-altitude dropsondes and radar observations from NOAA's Gulfstream IV, radar observations from WP-3D aircraft, the WSR-88D ground radar network, satellite images, and satellite-detected lightning strikes are used to apply recently developed theoretical knowledge about tropical cyclone intensification. As observed in many other tropical cyclones, strong, bottom-heavy vertical mass flux profiles are correlated with low (but positive) values of low-to midlevel moist convective instability along with high column relative humidity. Such mass flux profiles produce rapid spinup at low levels and the environmental conditions giving rise to them are associated with an intense midlevel vortex. This low-level spinup underneath the midlevel vortex results in the vertical alignment of the vortex column, which is a key step in the rapid intensification process. In the case of Sally, the spinup of the low-level vortex resulted from vorticity stretching, while the spinup of the midlevel vortex at 6 km resulted from vorticity tilting produced by the interaction of convective ascent with moderate vertical shear. SIGNIFICANCE STATEMENT: The purpose of this study is to investigate the rapid intensification of Hurricane Sally as it was approaching the Florida Panhandle. We do that by analyzing an unprecedented dataset from the NOAA WP-3D and Gulfstream-IV aircraft, together with ground-based radar and satellite data. We find that both the dynamics (vorticity structure and evolution) and thermodynamics (instability index, saturation fraction, heating/mass flux profiles) need to be considered in diagnosing intensification processes. Further field projects with continuous high-altitude dropsondes and research are needed to see if these are applicable to other reformation events as well as genesis.

Verification of high-impact weather is needed by the Meteorological Centres, but how to perform it still presents many open questions, starting from which data are suitable as reference. This paper reviews new observations which can be considered for the verification of high-impact weather, and provides advice for their usage in objective verification. Two highimpact weather phenomena are considered: Thunderstorm and fog. First, a framework for the verification of high-impact weather is proposed, including the definition of forecast and observations in this context and creation of a verification set. Then, new observations showing a potential for the detection and quantification of high-impact weather are reviewed, including remote sensing datasets, products developed for nowcasting, datasets derived from telecommunication systems, data collected from citizens, reports of impacts and claim/damage reports from insurance companies. The observation characteristics which are relevant for their usage in forecast verification are also discussed. Examples of forecast evaluation and verification are then presented, highlighting the methods which can be adopted to address the issues posed by the usage of these non-conventional observations and objectively quantify the skill of a high-impact weather forecast. 1 Introduction Verification of forecasts and warnings issued for high-impact weather is increasingly needed by operational centres. The model and nowcast products used in operations to support the forecasting and warning of high-impact weather such as thunderstorm cells also need to be verified. The World Weather Research Programme (WWRP) of the World Meteorological Organisation

In this study we investigate convective environments and their corresponding climatological features over Europe and the United States. For this purpose, National Lightning Detection Network (NLDN) and Arrival Time Difference long-range lightning detection network (ATDnet) data, ERA5 hybrid-sigma levels, and severe weather reports from the European Severe Weather Database (ESWD) and Storm Prediction Center (SPC) Storm Data were combined on a common grid of 0.258 and 1-h steps over the period 1979-2018. The severity of convective hazards increases with increasing instability and wind shear (WMAXSHEAR), but climatological aspects of these features differ over both domains. Environments over the United States are characterized by higher moisture, CAPE, CIN, wind shear, and midtropospheric lapse rates. Conversely, 0-3-km CAPE and low-level lapse rates are higher over Europe. From the climatological perspective severe thunderstorm environments (hours) are around 3-4 times more frequent over the United States with peaks across the Great Plains, Midwest, and Southeast. Over Europe severe environments are the most common over the south with local maxima in northern Italy. Despite having lower CAPE (tail distribution of 3000-4000 J kg 21 compared to 6000-8000 J kg 21 over the United States), thunderstorms over Europe have a higher probability for convective initiation given a favorable environment. Conversely, the lowest probability for initiation is observed over the Great Plains, but, once a thunderstorm develops, the probability that it will become severe is much higher compared to Europe. Prime conditions for severe thunderstorms over the United States are between April and June, typically from 1200 to 2200 central standard time (CST), while across Europe favorable environments are observed from June to August, usually between 1400 and 2100 UTC.

The climatology of (severe) thunderstorm days is investigated on a pan-European scale for the period of 1979–2017. For this purpose, sounding measurements, surface observations, lightning data from ZEUS (a European-wide lightning detection system) and European Cooperation for Lightning Detection (EUCLID), ERA-Interim, and severe weather reports are compared and their respective strengths and weaknesses are discussed. The research focuses on the annual cycles in thunderstorm activity and their spatial variability. According to all datasets thunderstorms are the most frequent in the central Mediterranean, the Alps, the Balkan Peninsula, and the Carpathians. Proxies for severe thunderstorm environments show similar patterns, but severe weather reports instead have their highest frequency over central Europe. Annual peak thunderstorm activity is in July and August over northern, eastern, and central Europe, contrasting with peaks in May and June over western and southeastern Europe. The...

The occurrence of environmental conditions favorable for severe convective storms was assessed in an ensemble of 14 regional climate models covering Europe and the Mediterranean with a horizontal grid spacing of 0.44°. These conditions included the collocated presence of latent instability and strong deep-layer (surface to 500 hPa) wind shear, which is conducive to the severe and well-organized convective storms. The occurrence of precipitation in the models was used as a proxy for convective initiation. Two climate scenarios (RCP4.5 and RCP8.5) were investigated by comparing two future periods (2021–50 and 2071–2100) to a historical period (1971–2000) for each of these scenarios. The ensemble simulates a robust increase (change larger than twice the ensemble sample standard deviation) in the frequency of occurrence of unstable environments (lifted index ≤ −2) across central and south-central Europe in the RCP8.5 scenario in the late twenty-first century. This increase coincides wit...

The occurrence of environmental conditions favorable for severe convective storms was assessed in an ensemble of 14 regional climate models covering Europe and the Mediterranean with a horizontal grid spacing of 0.44°. These conditions included the collocated presence of latent instability and strong deep-layer (surface to 500 hPa) wind shear, which is conducive to the severe and well-organized convective storms. The occurrence of precipitation in the models was used as a proxy for convective initiation. Two climate scenarios (RCP4.5 and RCP8.5) were investigated by comparing two future periods (2021–50 and 2071–2100) to a historical period (1971–2000) for each of these scenarios. The ensemble simulates a robust increase (change larger than twice the ensemble sample standard deviation) in the frequency of occurrence of unstable environments (lifted index ≤ −2) across central and south-central Europe in the RCP8.5 scenario in the late twenty-first century. This increase coincides wit...

Cumulus parameterizations in weather and climate models frequently apply mass-flux schemes in their description of tropical convection. Mass flux constitutes the product of the fractional area covered by convection in a model grid box and the vertical velocity in cumulus clouds. However, vertical velocities are difficult to observe on GCM scales, making the evaluation of mass-flux schemes difficult. Here, the authors combine high-temporal-resolution observations of in-cloud vertical velocities derived from a pair of wind profilers over two wet seasons at Darwin with physical properties of precipitating clouds [cloud-top heights (CTH), convective–stratiform classification] derived from the Darwin C-band polarimetric radar to provide estimates of cumulus mass flux and its constituents. The length of this dataset allows for investigations of the contributions from different cumulus cloud types—namely, congestus, deep, and overshooting convection—to the overall mass flux and of the infl...

O presente estudo apresenta uma aplicação do modelo de mesoescala WRF à simulação de um episódio de vento intenso e persistente que ocorre com frequência irregular no reservatório de Guapé, MG. Tal evento altera a rotina da população na região, fazendo com que, por exemplo, a embarcação que faz a travessia entre as cidades de Guapé e Capitólio interrompa o serviço. Durante um destes episódios, ocorrido em 22 de setembro de 2016, foram realizadas medidas utilizando um LIDAR Zephir ZP300 e uma torre anemométrica, e estes dados foram posteriormente utilizados para validar as simulações. Para a avaliação dos resultados, foram comparadas pressão, temperatura, umidade e velocidade do vento simuladas e observadas. A análise dos perfis verticais de velocidade simulados sugere a presença de um jato de baixos níveis, posicionado em torno de 500 m acima da superfície, gerado por um gradiente de temperatura pós-frontal, cuja parte inferior teria sido acelerada pelo relevo e pela variação de rugosidade superficial terra-água. Mais estudos encontram-se atualmente em andamento para que se possa sugerir à população e às autoridades locais algum tipo de ação preventiva. Palavras-chave: jatos de baixos níveis, reservatórios de centrais hidroelétricas, relevo complexo, modelo WRF.

Satellite imagery and rain gauge data are combined to create mesoscale detail in the initial states of relative humidity (RH) and surface moisture availability (M) for a mesoscale model simulation. The most profound impact of inserting the mesoscale initial fields was the development of a strong vertical circulation transverse to an intensifying cold front that triggered an intense frontal rainband similar to a severe squall line that was observed to develop explosively. This paper explores the causative factors leading to the formation of this intense circulation and the sensitivity of the model to the mesoscale initial fields. A substantial gradient in the initialized RH and M fields occurred across the cold front in the region where the observed frontal squall line formed. In contrast to the control run, the model simulations that incorporated the mesoscale initial analysis displayed considerable daytime warming just ahead of the front. This warming was due principally to a reduction in the RH (and, hence, low-level cloud cover) east of the front, although an increase in the cross-frontal M gradient did contribute about 25% of the warming. Increased sensible heat fluxes at the expense of decreased latent heat fluxes led to a much deeper and well-mixed prefrontal boundary layer, a more erect frontal surface, and an updraft jet just ahead of the front. A density current-like flow developed in the cold air immediately behind the front only in the presence of this cross-frontal gradient in sensible heating. Much improved forecasts of the location and timing of the frontal squall line and other precipitation systems resulted from the mesoscale initial analysis. The initial RH and M fields possessed sufficient resolution and consistency with the model dynamics to have a positive influence on the forecasts for a period of at least 12 h. This study provides evidence that differential cloud cover and evapotranspiration fields can have important impacts on frontal behavior when strong synoptic dynamics are present. Future research should attempt to improve the modeling of evapotranspiration processes, develop more objective satellite-based humidity analysis techniques, and obtain in situ mesoscale data for verification of the retrieved atmospheric and soil moisture fields.

Nocturnal bow echoes can produce wind damage, even in situations where elevated convection occurs. Accurate forecasts of wind potential tend to be more challenging for operational forecasters than for daytime bows because of incomplete understanding of how elevated convection interacts with the stable boundary layer. The present study compares the differences in warm-season, nocturnal bow echo environments in which high intensity [.70 kt (1 kt ' 0.51 m s 21)] severe winds (HS), low intensity (50-55 kt) severe winds (LS), and nonsevere winds (NS) occurred. Using a sample of 132 events from 2010 to 2018, 43 forecast parameters from the SPC mesoanalysis system were examined over a 120 km 3 120 km region centered on the strongest storm report or most pronounced bowing convective segment. Severe composite parameters are found to be among the best discriminators between all severity types, especially derecho composite parameter (DCP) and significant tornado parameter (STP). Shear parameters are significant discriminators only between severe and nonsevere cases, while convective available potential energy (CAPE) parameters are significant discriminators only between HS and LS/NS bow echoes. Convective inhibition (CIN) is among the worst discriminators for all severity types. The parameters providing the most predictive skill for HS bow echoes are STP and most unstable CAPE, and for LS bow echoes these are the V wind component at best CAPE (VMXP) level, STP, and the supercell composite parameter. Combinations of two parameters are shown to improve forecasting skill further, with the combination of surfacebased CAPE and 0-6-km U shear component, and DCP and VMXP, providing the most skillful HS and LS forecasts, respectively.

Convective cell identification methods, besides their operational utility, are useful to identify cells, to understand cell interactions within multicell thunderstorms, and to distinguish between convective and stratiform regions within mesoscale convective systems. The method developed in this note was utilized for research on cell interactions within the 9 August 1991 Convection and Precipitation/Electrification (CaPE) multicell thunderstorm. A critical component of such research is an objective method to accurately depict all significant convective cells within an evolving multicell thunderstorm. While conventional methods based upon radar reflectivity can be successfully used in identifying cells, especially when the cells are in their growth stage, the methods are not as useful during the later stages of cell growth. This is because updraft and precipitation cores are not collocated at these advanced stages, and thus the reflectivity (precipitation) core may not be a good indicator of convectively active regions. The method presented in this note uses four objective criteria to define and identify convective cells within multicell thunderstorms. These criteria are chosen from a prestorm proximity sounding using the air parcel theory. The four objective criteria and their threshold values for the CaPE storm included in parentheses are 1) a threshold updraft W d (ϳ8 m s Ϫ1), 2) a threshold cloud-layer depth D d (ϳ4.9 km), 3) a threshold updraft area A d (ϳ1 km 2), and 4) cell origin within the planetary boundary layer indicated by the W pbl (ϳ3 m s Ϫ1) contour. Since the method is based upon upward motion and not reflectivity factor, multiple Doppler radar data are required to utilize this method.

A significant, convectively induced windstorm known as a derecho occurred over parts of Utah, Wyoming, Idaho, and Colorado on 31 May 1994. The event was unusual in that it occurred not only in an environment of relatively limited moisture, but also one with a thermodynamic profile favorable for dry microbursts in the presence of moderate midtropospheric flow. The development and evolution of the severe wind-producing convective system is described, with emphasis on the synoptic and mesoscale features that may have contributed to its strength and maintenance. A very similar derecho that affected much the same region on 1 June 2002 is more briefly introduced. Questions are raised regarding the unique nature of these events and their potential utility in achieving an increased understanding of the mechanics of derecho-producing convective systems in more moisture-rich environments.

The term elevated convection is used to describe convection where the constituent air parcels originate from a layer above the planetary boundary layer. Because elevated convection can produce severe hail, damaging surface wind, and excessive rainfall in places well removed from strong surface-based instability, situations with elevated storms can be challenging for forecasters. Furthermore, determining the source of air parcels in a given convective cloud using a proximity sounding to ascertain whether the cloud is elevated or surface based would appear to be trivial. In practice, however, this is often not the case. Compounding the challenges in understanding elevated convection is that some meteorologists refer to a cloud formation known as castellanus synonymously as a form of elevated convection. Two different definitions of castellanus exist in the literature-one is morphologically based (cloud formations that develop turreted or cumuliform shapes on their upper surfaces) and the other is physically based (inferring the turrets result from the release of conditional instability). The terms elevated convection and castellanus are not synonymous, because castellanus can arise from surface-based convection and elevated convection exists that does not feature castellanus cloud formations. Therefore, the purpose of this paper is to clarify the definitions of elevated convection and castellanus, fostering a better understanding of the relevant physical processes. Specifically, the present paper advocates the physically based definition of castellanus and recommends eliminating the synonymity between the terms castellanus and elevated convection.

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An isolated heavy-rain-producing thunderstorm was unexpectedly initiated in the afternoon of 9 August 2011 near the central urban area of the Beijing metropolitan region (BMR), which occurred at some distance from BMR’s northwestern mountains and two preexisting mesoscale convective systems (MCSs) to the west and north, respectively. An observational analysis shows the presence of unfavorable quasigeostrophic conditions but a favorable regional environment for the convective initiation (CI) of thunderstorms. A nested-grid cloud-resolving model simulation of the case with the finest 1.333-km resolution is performed to examine the CI of the thunderstorm and its subsequent growth. Results reveal that the growth of the mixed boundary layer, enhanced by the urban heat island (UHI) effects, accounts for the formation of a thin layer of clouds at the boundary layer top at the CI site and nearby locations as well as on the upslope sides of the mountains. It takes about 36 min for the latent...

Mesoscale Convective Complex (MCC) was first introduced in 1980 through research on infrared (IR) satellite images by Maddox. The MCC phenomenon can caused rain with a long period of time. This study aims to determine the atmospheric conditions when MCC occurred in East Kalimantan and surroundings area on December 26, 2021. The research data used in this study is Himawari-8 satellite data to display cloud top temperatures and convective cloud distribution using the CCO method and image interpretation using RGB method. Analysis of atmospheric conditions was also carried out on air humidity, vertical velocity, and reflectivity in the atmosphere obtained from weather radar data from the Stasiun Meteorologi Sultan Aji Muhammad Sulaiman - Sepinggan. Based on the results of the analysis, MCC was identified as a mature phase on December 26, 2021 at 12.00 UTC. Airmass RGB analysis shows the presence of clouds which are known as Cb clouds through CCO analysis as well as warm air masses with ...

Convective wind gusts (CGs) are usually related to thunderstorms, and they may cause great structural damage and serious hazards, such as train derailment, service interruption, and building collapse. Due to the small-scale and nonstationary nature of CGs, reliable CG nowcasting with high spatial and temporal resolutions has remained unattainable. In this study, a novel nowcasting model based on deep learning-namely, CGsNet-is developed for 0-2 h lead times of quantitative CG nowcasting, achieving minutekilometer-level forecasts. CGsNet is a physics-constrained model established by training on large corpora of average surface wind speed (ASWS) and radar observations; it can produce realistic and spatiotemporally consistent ASWS predictions in CG events. By combining the gust factor (1.77, the ratio of the observed peak wind gust speed (PWGS) to the ASWS) with the ASWS predictions, the PWGS forecasts are estimated with a spatial resolution of 0.01 • × 0.01 • and a 6 min temporal resolution. CGsNet is shown to be effective, and it has an essential advantage in learning the spatiotemporal features of CGs. In addition, quantitative evaluation experiments indicate that CGsNet exhibits higher generalization performance for CGs than the traditional nowcasting method based on numerical weather prediction models. CGnowcasting technology can be applied to provide real-time quantitative CG forecasts.

Convective wind gusts (CGs) are usually related to thunderstorms, and they may cause great structural damage and serious hazards, such as train derailment, service interruption, and building collapse. Due to the small-scale and nonstationary nature of CGs, reliable CGs nowcasting with high spatial and temporal resolutions has remained unattainable. In this study, a novel nowcasting model based on deep learning-namely, CGsNet-is developed for 0-2 h of quantitative CGs nowcasting, first achieving minute-kilometer-level forecasts. CGsNet is a physics-constrained model established by training on large corpora of average surface wind speed (ASWS) and radar observations, it can produce realistic and spatiotemporally consistent ASWS predictions in CGs events. By combining the gust factor (1.77, the ratio of the observed peak wind gust speed (PWGS) to the ASWS) with the ASWS predictions, the PWGS forecasts are estimated with a spatial resolution of 0.01°× 0.01°and a 6-minute temporal resolution. CGsNet is shown to be effective, and it has an essential advantage in learning the spatiotemporal features of CGs. In addition, quantitative evaluation experiments indicate that CGsNet exhibits higher generalization performance for CGs than the traditional nowcasting method based on numerical weather prediction models. CGs nowcasting technology can be applied to provide real-time quantitative CGs forecasts and alerts the damaging wind events in meteorological services. 1 Introduction Convective wind gusts (CGs) are nontronadic, straight-line winds (Mohr et al., 2017; Yu and Zheng, 2020). They predominantly occur in Eastern China in the warm summer months (Yang et al., 2017), and they are usually associated with thunderstorm clouds, in particular squall lines and supercells, which generate conditions conducive to the appearance of whirlwinds and squalls (Kolendowicz et al., 2016). Severe convective gusts are caused either by mesoscale cold pools associated with horizontal pressure gradients large enough to produce high wind speeds in the absence of strong downdrafts or by local-scale downbursts that create strong divergent horizontal winds near the ground (Wakimoto, 2001). These severe convective gusts may cause 1

This study investigated the characteristics of extreme precipitation events associated with mesoscale convective systems (MCSs) in East China (the area east of 96°E) during 2016–17. Over the entire region, 204 events were first identified and classified into synoptic, tropical, MCS, small-scale-storm (SSS), and unclassified types. For 73 MCS-type events, further division and analysis were conducted according to the organizational modes. Results show that MCS-related events occurred most frequently near southern Fujian Province and from April to October with a peak in July. The area of occurrence shifted from the south in spring to the north in summer before going back to the south in autumn. The events occurred most commonly from afternoon to early evening, matured around late afternoon, and ended before dark. Among MCS subcategories, the longest average duration was seen in the multiple-MCS cases. Of the 15 selected multiple-MCS events, 11 were defined as early-maturing type with p...

On 8-9 March 1992, a long-lived squall line traversed the state of Kansas, producing hail and damaging winds. It was shown previously that this squall line was part of a synoptic-scale rainband 2000 km in length that was associated with a cold front aloft (CFA). The present study is concerned with the detailed mesoscale structure of this squall line and its relationship to the CFA. Examination of synoptic-scale cross sections based on rawinsonde ascents, and a mesoscale cross section of winds derived from dual-Doppler radar measurements, shows that the squall line was exactly coincident with the ''nose'' of the CFA. The dual-Doppler analysis also shows that the inflow of air to the squall line was elevated, drawing in air from the potentially unstable layer within the weak warm frontal-like feature that was being occluded by the CFA. The stability analysis of the air in the pre-squall-line environment shows that when the CFA overtook the surface position of the drytrough, the thermal and moisture structure of the atmosphere was such that a moderate amount of lifting provided by the CFA could have released convective instability within an elevated layer approximately 1-2 km above ground. The mesoscale structure of the squall line, derived from the radar reflectivity and dual-Doppler wind fields, differs substantially from the ''leading line/trailing stratiform'' conceptual model for midlatitude squall lines. The lack of a strong cold pool, and the presence of strong low-level shear, indicates that the squall line described here was able to persist in its mature stage in an environment that was ''greater than optimal'' in terms of the balance of the vorticity of the cold pool to that of the low-level shear. However, in view of 1) the weakness of the surface cold pool, 2) the elevated inflow and convergence associated with the convection, and 3) the collocation of the large rainband in which the squall line was embedded and the CFA, it seems likely that the CFA (rather than the cold pool) provided the driving force for the squall line.

The role of earlier forecast errors on subsequent convection forecasts is evaluated for a northern Great Plains severe convective event on 11–12 June 2013 during the Mesoscale Predictability Experiment (MPEX) by applying the ensemble-based sensitivity technique to Weather Research and Forecasting (WRF) Model ensemble forecasts with explicit convection. This case was characterized by two distinct modes of convection located 150 km apart in western Nebraska and South Dakota, which formed on either side of an axis of high, lower-tropospheric equivalent potential temperature . Convection forecasts over both regions are found to be sensitive to the position of this axis. The convection in Nebraska is sensitive to the position of the western edge of the axis near an upstream dryline, which modulates the preconvective prior to the diurnal maximum. In contrast, the convection in South Dakota is sensitive to the position of the eastern edge of the axis near a cold front, which also modulates...

On Pentecost Monday, 9 June 2014, a severe linearly organized mesoscale convective system (MCS) hit Belgium and western Germany. This storm was one of the most severe thunderstorms in Germany in decades. The synoptic-scale and mesoscale characteristics of this storm are analyzed based on remote sensing data and in situ measurements. Moreover, the forecast potential of the storm is evaluated using sensitivity experiments with a regional climate model. The key ingredients for the development of the Pentecost storm were the concurrent presence of low-level moisture, atmospheric conditional instability, and wind shear. The synoptic and mesoscale analysis shows that the outflow of a decaying MCS above northern France triggered the storm, which exhibited the typical features of a bow echo like a bookend vortex and a rear-inflow jet. This resulted in hurricane-force wind gusts (reaching 40 m s−1) along a narrow swath in the Rhine–Ruhr region leading to substantial damage. Operational numer...

On November 11, 2017, extreme weather in the form of very heavy rain has occurred in Pontianak. Based on surface observations data from Supadio Meteorological Station, the amount of rainfall reached 187.4 mm / day and caused flooding in several areas in Pontianak. As a result, a number of flights were cancelled on November 12, 2017 due to flooding in the airport runway. This study aims to examine the causes of very heavy rain using the WRF-ARW model and the results of Himawari-8 satellite images which are processed using Python Programming. Based on the output of the WRF-ARW model with the resolution 3 km, it shows some weather parameters that have potential for bad weather in Pontianak, namely the existence of shear line in West Kalimantan and the eddy circulation in this region which can trigger convective cloud accumulation in Pontianak, the wet RH in the 850-500 mb layer ranges from 70-90%, the CAPE ranges from 1000-2000 J/kg, and the air pressure decreases between 03.00 UTC until 06.00 UTC with a 1.7 mb tendency. In addition, the results of the Himawari-8 Satellite Image show that the cloud peak temperature is very low at-75.8 0 C at 08.33 UTC. Therefore, based on the WRF-ARW and Himawari-8 Satellite results, those support the occurrence of very heavy rain in Pontianak.

ECMWF provides the ensemble-based extreme forecast index (EFI) and shift of tails (SOT) products to facilitate forecasting severe weather in the medium range. Exploiting the ingredients-based method of forecasting deep moist convection, two parameters, convective available potential energy (CAPE) and a composite CAPE–shear parameter, have been recently added to the EFI/SOT, targeting severe convective weather. Verification results based on the area under the relative operating characteristic curve (ROCA) show high skill of both EFIs at discriminating between severe and nonsevere convection in the medium range over Europe and the United States. In the first 7 days of the forecast ROCA values show significant skill, staying well above the no-skill threshold of 0.5. Two case studies are presented to give some practical considerations and discuss certain limitations of the EFI/SOT forecasts and how they could be overcome. In particular, both convective EFI/SOT products are good at provi...

Rapid acceleration of cloud-top outflow near vigorous storm updrafts can be readily observed in Geostationary Operational Environmental Satellite-14 (GOES-14) super rapid scan (SRS; 60 s) mode data. Conventional wisdom implies that this outflow is related to the intensity of updrafts and the formation of severe weather. However, from an SRS satellite perspective, the pairing of observed expansion and updraft intensity has not been objectively derived and documented. The goal of this study is to relate GOES-14 SRS-derived cloud-top horizontal divergence (CTD) over deep convection to internal updraft characteristics, and document evolution for severe and nonsevere thunderstorms. A new SRS flow derivation system is presented here to estimate storm-scale (<20 km) CTD. This CTD field is coupled with other proxies for storm updraft location and intensity such as overshooting tops (OTs), total lightning flash rates, and three-dimensional flow fields derived from dual-Doppler radar data....

Verification of forecasts and warnings of highimpact weather is needed by the meteorological centres, but how to perform it still presents many open questions, starting from which data are suitable as reference. This paper reviews new observations which can be considered for the verification of high-impact weather and provides advice for their usage in objective verification. Two high-impact weather phenomena are considered: thunderstorm and fog. First, a framework for the verification of high-impact weather is proposed, including the definition of forecast and observations in this context and creation of a verification set. Then, new observations showing a potential for the detection and quantification of high-impact weather are reviewed, including remote sensing datasets, products developed for nowcasting, datasets derived from telecommunication systems, data collected from citizens, reports of impacts and claim/damage reports from insurance companies. The observation characteristics which are relevant for their usage in forecast verification are also discussed. Examples of forecast evaluation and verification are then presented, highlighting the methods which can be adopted to address the issues posed by the usage of these non-conventional observations and objectively quantify the skill of a high-impact weather forecast.

The kinematics and thermodynamics of wake lows have been extensively examined in the literature. However, there has been relatively little focus on the widespread, sometimes very strong winds associated with wake lows. Some wake lows are, essentially, severe local storms, producing widespread and sometimes intense damage, similar to that of a derecho, but they occur in environments supporting elevated convection, a phenomenon not often perceived as a significant wind damage threat. Three significant wake lows that affected Alabama and/or Georgia, producing widespread (25 000–50 000 km2) wind damage, and local wind gusts near 25 m s−1, are reviewed in detail. The environments and morphology of the wake lows are addressed, using radar, surface, and upper-air data.

Vertical profiles of temperature, relative humidity, cloud particle concentration, median mass dimension, and mass content were derived using instruments on the NOAA P-3 aircraft for 37 spiral ascents/descents flown within five mesoscale convective systems (MCSs) during the 2015 Plains Elevated Convection at Night (PECAN) project, and 16 spiral descents of the NOAA P-3 within 10 MCSs during the 2003 Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The statistical distribution of thermodynamic and microphysical properties within these spirals is presented in context of three primary MCS regions—the transition zone (TZ), enhanced stratiform rain region (ESR), and the anvil region (AR)—allowing deductions concerning the relative importance and nature of microphysical processes in each region. Aggregation was ubiquitous across all MCS zones at subfreezing temperatures, where the degree of ambient subsaturation, if present, moderated the effectiveness of this process via subl...

Numerous studies have shown that atmospheric models with high horizontal resolution better represent the physics and statistics of precipitation in climate models. While it is abundantly clear from these studies that high-resolution increases the rate of extreme precipitation, it is not clear whether these added extreme events are ''realistic''; whether they occur in simulations in response to the same forcings that drive similar events in reality. In order to understand whether increasing horizontal resolution results in improved model fidelity, a hindcast-based, multiresolution experimental design has been conceived and implemented: the InitiaLIzed-ensemble, Analyze, and Develop (ILIAD) framework. The ILIAD framework allows direct comparison between observed and simulated weather events across multiple resolutions and assessment of the degree to which increased resolution improves the fidelity of extremes. Analysis of 5 years of daily 5 day hindcasts with the Community Earth System Model at horizontal resolutions of 220, 110, and 28 km shows that: (1) these hindcasts reproduce the resolution-dependent increase of extreme precipitation that has been identified in longer-duration simulations, (2) the correspondence between simulated and observed extreme precipitation improves as resolution increases; and (3) this increase in extremes and precipitation fidelity comes entirely from resolved-scale precipitation. Evidence is presented that this resolution-dependent increase in precipitation intensity can be explained by the theory of Rauscher et al. (2016), which states that precipitation intensifies at high resolution due to an interaction between the emergent scaling (spectral) properties of the wind field and the constraint of fluid continuity.

This paper studies a damaging hail storm that occurred on 6 June 2015 in the complex topography of Switzerland. The storm persisted for several hours and produced large hail resulting in significant damage. Storms of comparable severity occur on average only three times per year within the entire Swiss radar domain, but are rare events at this exact location, according to a set of over 400,000 automatically identified storms. A multitude of datasets, partly novel for central Europe, is now available to study the storm in great detail capturing its impacts, severity and development. The data we use include radar-based hail products, crowd-sourced hail reports, and insurance loss data. These independent datasets permitted a verification of both hail occurrence and hail size estimations by radar. The crowd-sourced reports agree well with radar-based hail observations and insurance data. Model data (ERA-Interim reanalysis, regional COSMO-2 analysis and WRF simulations) and radio-sounding data showed, that conditions were favourable for thunderstorm development due to an unstable and moist atmosphere over Switzerland, brought about by an interplay of large-scale pattern and local processes. Advection ahead of a cold front west of Switzerland and local evapotranspiration lead to high lower-tropospheric moisture. The large-scale flow and topographically induced Alpine pumping resulted in strong directional wind shear, and contributed to the longevity and severity of this storm. The cold front was not relevant for the vertical lifting. Using model simulations with very high resolution, we identified mountain wind systems and cold-air outflow as possible triggering and propagation mechanisms of this hail storm.

Updraft vertical velocity is an important dynamical quantity which is strongly related to storm intensity and heavy precipitation. It can be calculated by direct observations, NWP model, and geostationary satellites which can provide the possibility of measuring this quantity with high temporal resolution. This research analyzed updraft velocity based on six derived parameters from INSAT3-D and high temporal and spatial resolution simulations of WRF model in the west and southwest of Iran. The interrelationship among the derived variables was investigated from the immature to mature stages of convective cells in Mesoscale Convective Systems (MCS). Updraft velocity was calculated based on a theoretical framework and real observations. The was a large results discrepancy among the results. This finding was in company with previous studies which concluded that updraft velocity is the resultant of other bulk buoyancy forces and environmental variables. Also, the estimated updraft veloci...

The artificially created region around the “Land between the Lakes” (LBL) in Kentucky represents unique land use and land cover (LULC) heterogeneities. Over a distance of 100 km, the LULC comprises artificially created open water bodies (i.e., two parallel large run-on-river dams separated by the LBL), mountainous terrain, forest cover, and extensive agricultural land. Such heterogeneities increase (decrease) moisture supply and sensible heat, resulting in a differential air mass boundary that helps to initiate (inhibit) convection. Hence, the LBL can potentially modify precipitation formation. Historical anecdotes reveal a tendency for storms to dissipate or reintensify near the LBL. The specific scientific question pursued in this study is therefore the following: Has the unique development of two parallel run-on-river reservoirs and the surrounding LULC heterogeneity modified storm patterns in the region? Ten storm events during the growing season were selected. Two additional ev...

During the wintertime, easterly (E) to southeasterly (SE) flow in the Hawaiian coastal waters is frequent. These wind regimes alter the location and magnitude of channel and tip-jet accelerations and the orientation and horizontal extent of the wake zones from east-northeast (ENE) trade wind conditions. The differences are the result of changes in orographic blocking by the Big Island and Maui with respect to the prevailing wind. During an E wind event, the fastest winds over the ‘Alenuihāhā Channel (> 9 m s−1) occur in the channel exit with sinking of the inversion, which rises again downstream. Although the upstream wind speed is similar to typical summer ENE trade winds (7–8 m s−1), the maximum channel wind speed is 3–4 m s−1 slower in the exit. The SE flow is characterized by maximum (~6 m s−1) northeasterly (NE) channel winds along Maui’s south shore and at the channel exit. These winds are the result of orographic blocking on the eastern end of Maui as the northwestern tail...

Reanalysis near-surface wind fields from multiple reanalyses are potentially an important information source for wind energy applications. Inter-comparing reanalyses via employing independent observations can help to guide users to useful spatio-temporal scales. Here we compare the statistical properties of wind speeds observed at 210 traditional meteorological stations over Germany with the reanalyses' near-surface fields, confining the analysis to the recent years (2007 to 2010). In this period, the station time series in Germany can be expected to be mostly homogeneous. We compare with a regional reanalysis (COSMO-REA6) and two global reanalyses, ERA-Interim and ERA-20C. We show that for the majority of the stations, the Weibull parameters of the daily mean wind speed frequency distribution match remarkably well with the ones derived from the reanalysis fields. High correlations (larger than 0.9) can be found between stations and reanalysis monthly mean wind speeds all over G...