Weather pictures & report of July 12 2010

 

MCS (squall line) thunderstorm along convergence line.


Synopsis: at 500 hPa, east of a relaxing trough west of the British Isles, our area in a moderate SW'ly flow of warm and humid potentially unstable air. At surface passage of thermal depression, related convergence line enhanced the instability which started already during the night over France. From the morning on, an MCS thunderstorm entered the SW of Belgium weakening on its western side, but by noon reactivating as squall-line over eastern parts with over there isolated wind damage mostly due to downbursts. Over central Belgium it resulted (again within three days) in a nice shelf cloud. All pictures were taken at Kampenhout (central Belgium), hours in local time (CET). 

 

Surface analysis of July 12 2010 at 0800 CET. Related to a thermal depression over the channel, a convergence line over northwest France which crossed Belgium during the forenoon from SW to NE. (Source chart: Belgocontrol)

 

Loop of 7 surface analyses (of each hour between 0500 - 1200 CET) with weather plots showing the slow movement of the thermal depression. (Source: meteocentre.com)

 

Upper air analysis 500 hPa of July 12 2010 at 1400 CET. Related to a low between Iceland and Greenland, a long wave relaxing trough over the British Isles moving eastwards. On the other hand a collapsing high over Austria. Our area in a strengthening SW'ly airflow. (Source chart: DWD via wetter3)

 

Upper air analysis 850 hPa of July 12 2010 at 1400 CET. Recognizable overhead a moderate SW'ly flow in which the warmest air was already been evacuated to the east (dropping from 17 to 13C).   (Source chart: DWD via wetter3)

 

Upper air analysis of wetbulb temperatures 850 hPa of July 12 2010 at 1400 CET. In moderate SW'ly flow warmest and humid air over the eastern parts of Benelux - western Germany with temperatures over there around 17C. (Source chart: Meteocentre)

 

Loop of forecasted soundings for Brussels of July 12 2010 between 0830-2000 CET. In forenoon unstable from 800 hPa upwards. Furthermore wind speed shows a moderate low level (0-3 km) shear of 30 kt and rather strong deep layer (0-6km) shear of 45 kt. Besides this, SREH 0-3 km was initially moderate with values >150 m/s, but when the MCS came in, this dropped in most places to 100 m/s or less). Together with moderate CAPE this enhanced the risk of large multicells (MCS) eventually preceded by supercells. (Source: RASP)

 

Another loop of forecasted soundings for a 15 hours period (in steps of three hours) of Brussels from July 12 2010, 0500 CET onwards. Included are some thunderstorms indices: surface based CAPE went up to little over 1000 J/kg, KI 33, TT 49, LI -4 = moderate to strong convective potential which may lead to scattered thunderstorms, isolated severe. (Source: weatheronline.co.uk)

 

12/07/2010 0615-1045 CET. Satellite loop in the visual channel. MCS comes in from the north of France. Severe activity (mainly downbursts) was only to be found over the (south)eastern provinces where at the end of this sequence the exploding Cb clouds can be noticed on a NW-SE orientated line. (Source sat picture: Eumetsat via Sat24.com)

 

Still image of the early morning in the visual channel giving a nice view of the MCS over central to northern France. (Source pic: Eumetsat)

 

Radar loop (rainfall rate in mm/hr) of July 12 2010 between 0700-1210 CET. An extensive precipitation belt comes in from the SW. Most intense echo's on a squall line (although this line is not clearly visible on these 125 km radius images) were to be found on the eastern side with over there isolated wind damage. Precipitation tops went up to around 11-12 km. (Source radar picture: Belgocontrol)

 

Corresponding discharges of July 12 2010 between 0615-1215 CET. Besides the extreme west all area's were affected, but the intensity was in most places rather modest, but gradually intensifying when over the northeast. (Source lightning picture: Blids)

 

12/07/2010. 24 hour overview of the discharges over the Benelux: it was quite intense in a narrow band just east and west of central Belgium. (source picture: Buienradar)

 

12/07/2010 0938 WSW. Gradually the typical shape of a shelf cloud began to appear on the western horizon with in the back the control tower of Brussels Airport.

 

12/07/2010 0938 SSW. View of the southern side.

 

12/07/2010 0943 WSW. Evolution of northern side.

 

12/07/2010 0944 WSW.

 

12/07/2010 0945 WNW.

 

12/07/2010 0946 WNW.

 

12/07/2010 0947 NW.

 

12/07/2010 0948 NW.

 

12/07/2010 0949 NNW.

 

12/07/2010 0943 SSW. Evolution southern side.

 

12/07/2010 0946 SSW.

 

12/07/2010 0948 S.

 

To summarize things: time lapse of the events between 0941-0951 CET with view to the west showing the approach and passage of a weakening thunderstorm with shelf cloud and behind turbulent character of the clouds.

 

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