Weather pictures & report of May 20 2012

 

Multicell thunderstorm (MCS alike) along convergence line.


Synopsis: at 500 hPa, Belgium north of a cut off low which approached a bit on its movement eastwards. The air became moister and warmer in the lower levels, while becoming colder in the upper levels. It lead to instabililty mainly due to diurnal heating and most showers did form along a weak convergence line. At my location hardly 2 mm rain was collected with for an hour or so not too close rumbles of thunder. All pictures were taken at Kampenhout (central Belgium), hours in local time (CET). 

 

Surface analysis of May 20 2012 at 2000 CET. Complex depression with centers over mid France and southern Germany with Belgium in a weak NE'ly flow. Previous night a warm front passed Belgium with behind warmer moister potentially unstable air. A weak convergence line could be detected over the Benelux enhancing the instability. (Source chart: Belgocontrol)

 

Loop of 9 surface analyses of May 20 2012 (of each hour between 1400 - 2200 CET) with weather plots. (Source: meteocentre.com)

 

Upper air analysis 500 hPa of May 20 2012 at 1400 CET. Cut off low over Spain, ridge over Russia extending towards the Northsea. Belgium in a weak SE'ly flow. (Source chart: DWD via wetter3)

 

Upper air analysis 850 hPa of May 20 2012 at 1400 CET. Recognizable again the cut off low, but a bit more north (over France) and the ridge over Russia extending towards the Northsea. Also here over Belgium a weak flow from the SE advecting some warmer air present over Germany (11°C). (Source chart: DWD via wetter3)

 

Upper air analysis 850 hPa of May 20 2012 at 1400 CET. Here we take a look at Tw at 850 hPa which was around 13°C. (Belgium was lying in the class zone of 12-16°C) (Source chart: Meteocentre.com)

 

Loop of forecasted soundings for Brussels of May 20 2012 between 0830-2000 CET. Instability is present from around 900 hPa upwards, initially an inversion was present till early afternoon, cleared by the rising surface temperature. (Source: RASP)

 

Another loop of forecasted soundings for a 12 hours period (in steps of three hours) of Brussels from May 20 2012, 1100 CET onwards. Included are some thunderstorms indices: surface based CAPE went up to around 1400 J/kg, KI 27, TT 50, LI -5 = moderate convective potential which may lead to scattered thunderstorms. SREH was rather weak < 50 m²/s², in combi with the not too strong CAPE, the environment would be favorable for multicell thunderstorms.(Source: weatheronline.co.uk)

 

20/05/2012 1630-2030 CET. Satellite loop in the visual channel. Exploding multicell thunderstorms over the Ardennes moving NW-awards. Several times overshooting tops can be detected. (Source sat picture: Eumetsat via Sat24.com)

 

Radar loop (rainfall rate in mm/hr) of May 20 2012 between 1400-2310 CET. Developing storms moving from SE to NW with the most intense cores holding a lot of rain or even large hail. Precipitation tops went up to 12 km. (Source radar picture: Belgocontrol)

 

20/05/2012. Amount of discharges between 1645-1845 over the Benelux with the most recent ones in red dots. (Source picture: Blids)

 

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

Brussels

EBBR 201420Z 36004KT 290V060 9999 SCT023 21/14 Q1006  NOSIG=
EBBR 201450Z 01005KT 330V060 9999 SCT029 21/14 Q1006 TEMPO 4000 TSRA BKN014CB=
EBBR 201520Z 02005KT 340V040 9999 -TS SCT029CB 20/14  Q1006 TEMPO 4000 TSRA BKN014CB=
EBBR 201550Z VRB03KT 8000 SCT029CB 19/14 Q1006 RETS  TEMPO VRB15G25KT 4000 TSRAGR BKN014CB=
EBBR 201620Z 17007KT 9999 -TSRA SCT032CB 17/12 Q1006  TEMPO VRB15G25KT 4000 TSRAGR BKN014CB=
EBBR 201650Z 22003KT 150V260 8000 -TSRA SCT029CB BKN042 16/13 Q1006 TEMPO 4000 TSRA BKN020CB=
EBBR 201720Z 27006KT 8000 RA SCT029CB BKN040 15/13 Q1005 RETS NOSIG=
METAR EBBR 201750Z 30004KT 180V340 9999 -RA FEW013 FEW029CB 16/14 Q1005 NOSIG=
EBBR 201820Z 29003KT 9999 -RA FEW013 15/13 Q1005 NOSIG=
EBBR 201850Z 32003KT 280V350 9000 NSC 16/13 Q1005 NOSIG=
 

Charleroi

EBCI 201320Z 30005KT 270V340 9999 BKN024CB 20/14 Q1006 TEMPO 3000 TSGR=
EBCI 201350Z 02004KT 8000 -TSRA SCT024CB 21/14 Q1006 RESHRA TEMPO 3000 TSGR=
EBCI 201420Z 06005KT 9999 FEW024CB 20/13 Q1006 RETS TEMPO 3000 TSGR=
EBCI 201450Z 04007KT 010V070 6000 -SHRA SCT035CB 18/14 Q1006 TEMPO 3000 TSGR=
EBCI 201520Z /////KT 1600 TSRA BKN012 BKN020CB 14/13 Q1006 TEMPO 3000 TSGR=
EBCI 201550Z 17004KT 140V210 5000 -TSRA SCT014 BKN020CB 14/13 Q1006 TEMPO 3000 TSGR=
EBCI 201620Z 26005KT 9999 SCT018CB 15/14 Q1005 RETS RETSRA TEMPO 3000 TSRA=




 

20/05/2012 1702 NNE. The huge anvil came slowly in from the south with the last breaks over the far north.

 

20/05/2012 1807 S. Some rumbles were heard these non exciting clouds.

 

20/05/2012 1829 SW. The rain shaft was arriving, still nothing exciting.

 

20/05/2012 1830 NNW. Some Cu cloudiness forming in rows on opposite side.

 

20/05/2012 1839 NE. Perhaps a more interesting part of the shower?

 

20/05/2012 1927 NW. Or is this view the most exciting of all with a building Cu in a massive dark Cb without much structure? Anyhow, the first significant thundery situation of the season was a rather boring show. Things can only be better next time...hopefully. 

 

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