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was equal to 218.9 mm. Maximum monthly precipitation occurs in January, with 77 mm on average, and no detectable precipitation is observed in the period from May to Septem- ber. The mean annual relative humidity is 55.7%, the average wind speed is 14.7 km/h and the prevailing wind direction is 315° (NW). The mean sea level pressure is equal to 1009 millibars [26]. Figure 1. Location of Bushehr Province in Iran (top left panel) and Dayyer County in Bushehr Province (bottom left panel), supplemented by the map presenting the elevation of the study area (right panel). Location of the Dayyer synoptic station is indicated by the black triangle. Figure 1. Location of Bushehr Province in Iran (top left panel) and Dayyer County in Bushehr

Figure 1 was equal to 218.9 mm. Maximum monthly precipitation occurs in January, with 77 mm on average, and no detectable precipitation is observed in the period from May to Septem- ber. The mean annual relative humidity is 55.7%, the average wind speed is 14.7 km/h and the prevailing wind direction is 315° (NW). The mean sea level pressure is equal to 1009 millibars [26]. Figure 1. Location of Bushehr Province in Iran (top left panel) and Dayyer County in Bushehr Province (bottom left panel), supplemented by the map presenting the elevation of the study area (right panel). Location of the Dayyer synoptic station is indicated by the black triangle. Figure 1. Location of Bushehr Province in Iran (top left panel) and Dayyer County in Bushehr

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Figure 2. A map presenting the domains selected for the implementation of the WRF model. The yellow boxes indicate the domains used in the WRF model. diction of weather in the mesoscale [29]. To run the model, a domain first needs to be defined. Four nested domains were defined following a two-way nesting strategy, with a spatial resolution of 36 (D01), 12 (D02), and 4 km (D03). Each domain had 100 x 100 grid points in the latitudinal and longitudinal directions. The area of each domain is shown in Figure 2. The WRF model offers several solvers of the physical and chemical equations, enabling optimization of the model for a specific weather phenomenon and a study area. For microphysics parameterization, radiation (shortwave/longwave), land surface, surface layer, PBL, and cumulus formation the Thompson six-class microphysics scheme, Dud- hia/RRTM, the Noah Land Surface Model, Monin Obokhov, YSU, and Kain-Fritsch were selected, respectively. In the event of thunderstorms, two of the most important components are vertical velocity (here, a positive sign was assumed for the upward movements, and negative for the downward movements) and wind shear. The vertical velocity w and w are related to each other by the equation:
Figure 2. A map presenting the domains selected for the implementation of the WRF model. The yellow boxes indicate the domains used in the WRF model. diction of weather in the mesoscale [29]. To run the model, a domain first needs to be defined. Four nested domains were defined following a two-way nesting strategy, with a spatial resolution of 36 (D01), 12 (D02), and 4 km (D03). Each domain had 100 x 100 grid points in the latitudinal and longitudinal directions. The area of each domain is shown in Figure 2. The WRF model offers several solvers of the physical and chemical equations, enabling optimization of the model for a specific weather phenomenon and a study area. For microphysics parameterization, radiation (shortwave/longwave), land surface, surface layer, PBL, and cumulus formation the Thompson six-class microphysics scheme, Dud- hia/RRTM, the Noah Land Surface Model, Monin Obokhov, YSU, and Kain-Fritsch were selected, respectively. In the event of thunderstorms, two of the most important components are vertical velocity (here, a positive sign was assumed for the upward movements, and negative for the downward movements) and wind shear. The vertical velocity w and w are related to each other by the equation:
Figure 3. The maps of the geopotential height (HGT) (contours) and the vertical velocity (shaded) of 500 hPa (a), a jet stream (shaded) of 500 hPa (b) the geopotential height (contours), and the vertical velocity (shaded) of 700 hPa (c), a jetstream (shaded) of 300 hPa (d), geopotential height (contours) and vertical velocity (shaded) of 850 hPa (e) and a jet stream (shaded) of 850 hPa (f) on 19 March for 00:00 UTC. The vectors indicate the direction of the wind. convections in the study area, which in turn may be a cause for the formation of a squall line longer than 100 km (Figure 5 (top)). It was already shown that when the mid-level winds are close to geostrophic and show strong vorticity, ideal conditions for frontogenesis formation occurs [34-36].
Figure 3. The maps of the geopotential height (HGT) (contours) and the vertical velocity (shaded) of 500 hPa (a), a jet stream (shaded) of 500 hPa (b) the geopotential height (contours), and the vertical velocity (shaded) of 700 hPa (c), a jetstream (shaded) of 300 hPa (d), geopotential height (contours) and vertical velocity (shaded) of 850 hPa (e) and a jet stream (shaded) of 850 hPa (f) on 19 March for 00:00 UTC. The vectors indicate the direction of the wind. convections in the study area, which in turn may be a cause for the formation of a squall line longer than 100 km (Figure 5 (top)). It was already shown that when the mid-level winds are close to geostrophic and show strong vorticity, ideal conditions for frontogenesis formation occurs [34-36].
Figure 4. The maps of the mean sea-level pressure and vector wind on 19 March for 00:00 (left panel) and 06:00 UTC (right panel). Contours indicate the sea level pressure value, while the arrows represent wind speed (color, and the length of vectors) and direction (arrows on vectors).
Figure 4. The maps of the mean sea-level pressure and vector wind on 19 March for 00:00 (left panel) and 06:00 UTC (right panel). Contours indicate the sea level pressure value, while the arrows represent wind speed (color, and the length of vectors) and direction (arrows on vectors).
Figure 5. Maximum reflectivity (MAX) (top panel, in dBZ as presented in the color scale at right of the top panel) and Plan Position Indicator (PP1) (bottom panel, in m/s as presented in the color scale at right of the bottom panel) from the Bushehr Meteorological Radar on 19 March for 04:00 UTC.
Figure 5. Maximum reflectivity (MAX) (top panel, in dBZ as presented in the color scale at right of the top panel) and Plan Position Indicator (PP1) (bottom panel, in m/s as presented in the color scale at right of the bottom panel) from the Bushehr Meteorological Radar on 19 March for 04:00 UTC.
Figure 6. The vertical profiles of velocity (Pa s!) (shaded) and moisture advection (10~° g Ke"! s-) (streamline) on 19 March for 00:00 UTC. Solid bold black lines indicate the vertical velocity having 0 value, solid black lines indicate the vertical velocity with positive values, and the black dashed lines indicate the vertical velocity with negative values. The scale bar indicates the specific humidity value (g/kg).
Figure 6. The vertical profiles of velocity (Pa s!) (shaded) and moisture advection (10~° g Ke"! s-) (streamline) on 19 March for 00:00 UTC. Solid bold black lines indicate the vertical velocity having 0 value, solid black lines indicate the vertical velocity with positive values, and the black dashed lines indicate the vertical velocity with negative values. The scale bar indicates the specific humidity value (g/kg).
Figure 7. The map from the visible band of MODIS sensor for 3:45 UTC on 19 March 2017 (a), the image of the shelf clouds and CB formed on the studied area taken at 3:15 UTC (b). The red rectangle indicates the study area (image source: authors).
Figure 7. The map from the visible band of MODIS sensor for 3:45 UTC on 19 March 2017 (a), the image of the shelf clouds and CB formed on the studied area taken at 3:15 UTC (b). The red rectangle indicates the study area (image source: authors).
Figure 8. Half hourly pressure (a) and wind variations (b) at the synoptic station of Bandar Dayyer on 18-19 March before mal anflftaw LAR Acrrnt
Figure 8. Half hourly pressure (a) and wind variations (b) at the synoptic station of Bandar Dayyer on 18-19 March before mal anflftaw LAR Acrrnt
Figure 9. The Skew-T chart for 51°10’ E and 27°30’ N for 3:00 UTC of 19 March. The solid black line presents the temperature profile, while the solid blue line presents the dew point temperature profile. The black rectangle indicates the lifted condensation level.
Figure 9. The Skew-T chart for 51°10’ E and 27°30’ N for 3:00 UTC of 19 March. The solid black line presents the temperature profile, while the solid blue line presents the dew point temperature profile. The black rectangle indicates the lifted condensation level.
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Environmental ScienceRemote SensingClimatologySynoptic and Mesoscale MeteorologyStorm surgeSupercell Thunderstorms
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