Weather pictures & report of September 10 2011

 

Supercell thunderstorms between thermal trough and cold front


Synopsis: at 500 hPa: between a relaxing upper trough northwest of Ireland and a ridge over the continent, our area in a moderate SW'ly flow of warm and humid potentially unstable air. Between the evening and early night passage of  a thermal trough followed by a cold front. Along the thermal trough no activity due to too dry air upper in the lower levels and the presence of a low level inversion. In between the thermal trough and cold front, over the northwest of Belgium, the inversion was cleared by the lift of the upcoming cold front releasing the potentially deep instability in form of supercells (and multicells) with isolated damage due to large hail (up to 5 cm diameter) and strong winds. It gave a nice lightning show at the location where the pictures were made, namely at Kampenhout (central Belgium) with the hours in local time (CET).

 

Surface analysis of September 10 2011 at 2000 CET. Related to a deep low northwest of Ireland a thermal trough followed by cold front crossing the Low Countries between the evening and early night. (Source chart: Belgocontrol)

 

Loop of 9 surface analyses of each hour starting from September 10 at 1700 CET with weather plots showing the movement of the thermal trough with behind the thundery outbreaks. (Source: meteocentre.com)

 

Upper air analysis 500 hPa of September 10 2011 at 1400 CET. Between a relaxing upper trough northwest of Ireland and a ridge over the continent, the Low Countries in a moderate SW'ly flow. (Source chart: DWD via wetter3)

 

Upper air analysis 850 hPa of September 10 2011 at 1400 CET. Between the low northwest of Ireland. and and ridge over the continent, the Low Countries in a moderate SW'ly flow of warm air. (Source chart: DWD via wetter3)

 

Loop of forecasted soundings for Brussels of September 10 2011 between 1130-2000 CET. An unstable airmass is present above 2 km height but also too dry below 5 km height to form showers and above all also capped by an inversion around 1 km. Directional and speed shear were moderate. (Source: RASP)

 

Another loop of forecasted soundings for a 12 hours period (in steps of three hours), but this time of Deurne (Antwerp) from September 10 2011, 1400 CET onwards. Included are some thunderstorms indices: surface based CAPE was during the evening still well above 1500 J/kg, dropping fast towards midnight.  KI 29, TT 52, LI -10 = moderate to strong convective potential which may lead to occasional thunderstorms, isolated severe. Directional shear was moderate with values of around 115 m²/s², low level shear was 30 kt, deep layer shear 40 kt. Due to the moderate CAPE and moderate to strong low level shear / deep layer shear, multicells could be expected with even risk for some supercells. (Source: weatheronline.co.uk).

 

Observed sounding released at Beauvechain on September 11 at 0020CET. It reveals instability above 800 hPa till the tropopause (at 217 hPa) but also a strong inversion around 850 hPa which couldn't be cleared, thus no shower activity over the center and east of Belgium. (Source: Belgocontrol)

 

Forecasted vertical profile and surface temperature for St-Niklaas (province Oost-Vlaanderen) of September 10 from 1400 CET and the following 48 hours. Legend of upper map: green-brown-white is humidity in steps of 10% with darkest green being 90% or more, wind in kt, temperatures each 5°C. First 6 hours rather dry air below 15000 ft, afterwards humidity increased till the upper levels (38000 ft). Furthermore first 9 hours some directional shear mainly below 10000 ft. A rise in temperature between 15-18UTC in the lower levels indicating the passage of the thermal trough (in the warmer airmass). (Source: Belgocontrol)

 

10/09/201 1730-2000 CET. Satellite loop in the visual channel. Supercell thunderstorms forming over the extreme northwest of Belgium as a small feature this due to the rather large scale of this images. (Source picture: Eumetsat via Belgocontrol)

 

10/09/201 1730-2400 CET. Satellite loop in the infra-red channel. Supercell and multicell thunderstorms forming over the extreme northwest of Belgium and further exploding over Holland.. (Source picture: Eumetsat via Belgocontrol)

 

Still image of NOAA at 2056 CET with a closer look on the huge anvil over southwest Holland holding some supercells and multicells.

 

Radar loop (reflectivity in dBZ) of September 10-11 2011 between 1800-0100 CET. Besides multicells also formation of some supercells, often splitting over the (north)west of Belgium with the pink colors indicating (large) hail. Near Maldegem (north of province Oost-Vlaanderen) stones of 5 cm diameter were reported. (Source radar picture: Belgocontrol)

 

Corresponding discharges of September 10 2011 till midnight. All in the last 6 hours of the day, a huge activity of electricity with almost 39000 discharges mainly within clouds. (Source lightning picture: Buienradar)

 

Some metars in UTC. Translation: copy paste each obs via metar-decoder
 

Ostend Airport (EBOS)
EBOS 101450Z 19006KT 150V220 9999 FEW025 25/21 Q1005 NOSIG
EBOS 101520Z 19010KT 9999 FEW025 25/20 Q1004 NOSIG
EBOS 101550Z 28010KT 9999 FEW025 20/17 Q1005 TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101620Z 27007KT 9999 FEW025 SCT040 19/17 Q1005 TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101650Z 28009KT 9999 FEW020CB SCT040 20/17 Q1004 TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101720Z 26010KT 9999 -TS FEW020CB SCT045 19/17 Q1005 TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101750Z 26012KT 9999 FEW020CB SCT045 19/16 Q1005 RETS TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101820Z 25011KT 9999 -TS FEW020CB SCT045 18/16 Q1005 TEMPO 23018G35KT 3000 TSRA SCT020CB
EBOS 101850Z 25011KT 9999 FEW020CB SCT045 18/16 Q1006 RETS NOSIG
EBOS 101920Z 24007KT 9999 FEW020CB SCT045 18/16 Q1005 RETS NOSIG


Deurne (EBAW)
EBAW 101820Z 14005KT 9999 FEW045CB 23/20 Q1004 NOSIG
EBAW 101850Z 13005KT 9999 FEW045CB 22/19 Q1004 NOSIG
EBAW 101920Z 17006KT 9999 FEW045CB 25/20 Q1005 NOSIG
EBAW 101950Z 30012KT 260V320 9999 FEW025CB BKN030 22/17 Q1006 NOSIG
EBAW 102020Z 30011KT 9999 FEW030 20/16 Q1006 NOSIG
EBAW 102050Z 29009KT 9999 BKN027 20/16 Q1006 NOSIG


Woensdrecht (EHWO)
EHWO 101755Z AUTO 17001KT 9999 SCT110 OVC170 24/20 Q1004 BLU
EHWO 101825Z AUTO 00000KT 9999 TS FEW015CB OVC150 22/20 Q1004 BLU
EHWO 101855Z AUTO 06005KT 9999 TS FEW015CB BKN069 BKN079 22/20 Q1004 BLU
EHWO 101903Z AUTO 32012G29KT 9999 TS FEW013 FEW015CB SCT018 BKN058 22/20 Q1004 WHT
EHWO 101908Z AUTO 28015G32KT 9999 TS FEW013 SCT018 FEW020CB BKN025 23/17 Q1005 WHT
EHWO 101915Z AUTO 29014KT 9999 -TSRA FEW010 FEW021CB SCT030 BKN036 21/16 Q1005 BLU
EHWO 101925Z AUTO 28012G22KT 2100 TSRA FEW009 FEW015CB BKN040 BKN045 19/17 Q1005 YLO
EHWO 101931Z AUTO 30012KT 3900 +TSRA FEW012 FEW015CB BKN040 BKN046 18/17 Q1005 GRN
EHWO 101935Z AUTO 30014KT 8000 +TSRA FEW015CB BKN032 BKN042 18/17 Q1005 BLU
EHWO 101945Z AUTO 27008KT 0500 -TSRA FEW015CB SCT039 BKN045 18/18 Q1005 RERA RED
EHWO 101949Z AUTO 24006KT 9999 +TSRA FEW015CB BKN039 OVC045 18/18 Q1005 BLU
EHWO 101955Z AUTO 21005KT 6000 TSRA SCT015CB SCT031 BKN036 BKN042 18/18 Q1006 WHT
EHWO 102008Z AUTO 27009KT 9999 TS SCT015CB SCT040 BKN044 OVC051 18/18 Q1005 RERA WHT
EHWO 102012Z AUTO 28010KT 9999 TS BKN037 BKN042 OVC047 18/18 Q1005 RERA BLU
EHWO 102025Z AUTO 26007KT 9999 TS FEW015CB OVC033 19/18 Q1006 BLU
EHWO 102055Z AUTO 22005KT 9999 TS FEW015CB BKN030 OVC034 18/17 Q1006 BLU
EHWO 102125Z AUTO 22004KT 9999 FEW043 BKN050 BKN055 18/17 Q1006 BLU



10/09/2011 2045 NW. Cloud-to-cloud discharges at distance somewhere between 30-40 km.

 

10/09/2011 2053 NNW. Cloud-to-cloud discharge at distance >40 km.

 

10/09/2011 2055 NNW. Cloud-to-air discharge at distance >40 km.

 

10/09/2011 2058 NNW. Cloud-to-cloud discharge at distance >40 km.

 

10/09/2011 2058 NNW. Cloud-to-cloud discharge at distance >40 km.

 

10/09/2011 2059 NNW. Intra cloud discharge at distance >40 km.

 

10/09/2011 2137 N. Intra cloud discharge at distance >40 km.

 

10/09/2011 2138 N. Intra cloud and cloud -to-air discharges at distance >40 km.

 

10/09/2011 2140 N. Intra cloud and cloud -to-cloud discharges at distance >40 km.

 

10/09/2011 2143 N. Intra cloud and cloud -to-cloud discharges at distance >40 km.

 

10/09/2011 2145 N. Intra cloud and cloud -to-cloud discharges at distance >40 km.

 

10/09/2011 2050 NNW. Short video in real time showing the activity of electricity.

 

Supercell storm in a time-lapse between 2052-2148 CET captured with a 20 second exposure time and an interval of 3 seconds speeded up to 15 frames per seconds. The almost horizontal stripes are landing aircraft at Brussels Airport.

 

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