Weather pictures & report of May 25-26 2009

 

Large multi-cell (MCS) & supercell thunderstorms ahead and along convergence line.


Synopsis: at 500 hPa initially a cut-off low north of Spain and a relaxing upper trough west of Eire, amalgamating and its axis crossing Belgium during the night of May 26-27. Ahead advection of warm and humid (Tw 850 hPa up to 17°C), potentially deep unstable air from SSW with also a convergence line within a shallow thermal low which crossed Belgium during the night of May 25-26. During the daylight period of May 25, a long living MCS affected the Ardennes, the next night a supercell and MCS affected the west and center of Belgium. A few pics of lightning were made at Steenokkerzeel, hours in local time. 

 

Surface analysis of May 25 at 1400 CET. An incoming thermal low over the south of France, a retreating high near Denmark. The black line over south of Belgium concerned an MCS. (Source chart: Met Office - UKMO)

 

Upper air analysis 500 hPa of May 25 at 1400 CET. Approaching cut-off low north of Spain & trough west of Eire and a ridge over Germany slowly moving eastwards. (Source chart: DWD via wetter3)

 

Upper air analysis 850 hPa of May 25 at 1400 CET. Very warm air present over western parts of central Europe with temperatures around 15°C, bit more to the west only 9°C, so quite a sharp contrast. (Source chart: DWD via wetter3)

 

25/05/2009 1015-2130 CET. Satellite loop in the visual channel. MCS reactivating over the Ardennes, by the evening some smaller cells arrived over the extreme west of Belgium. (Source sat picture: Eumetsat via Sat24.com)

 

25/05/2009. Satellite picture taken around 1320 CET (visual channel). It shows a detail of the exploding MCS over the southwest of the Ardennes. (Source: Image courtesy of MODIS Rapid Response Project at NASA/GSFC)

 

25/05/2009. Satellite picture taken around 1510 CET (visual channel). Couple hours later, the MCS spread out its cloud shield over entire Belgium. However the active part was situated over the northwest of province Luxembourg and south of province Liège, while the rest encountered some high and medium level cloudiness with locally a few drops of rain   (Source: Image courtesy of MODIS Rapid Response Project at NASA/GSFC)

 

25/05/2009. Satellite picture taken around 1412 CET (infra-red channel with temperature scale). It shows the MCS over the Ardennes with on the southeastern side two overshooting tops with temperatures close to -70°C. (Source: NOAA)

 

Radar loop between 1235-2130 CET. Precipitation tops went up to around 15 km. The cell over the Ardennes produced locally hailstones with a diameter of 4 cm. Observations on some official weather stations showed at St-Hubert a gust of 37 kt, and at Mont-Rigi 9 mm rainfall. (Source radar picture: Belgocontrol)

 

Loop of discharges reaching Earth's surface between 1200-2200 CET. (Source picture: Blids)

 

Surface analysis of May 26 at 0200 CET. Thermal low with trough (black line) over the west of Belgium.(Source chart: Met Office - UKMO)

 

Upper air analysis 850 hPa of May 26 at 0200 CET. Cooler air started to invade Belgium. (Source chart: DWD via wetter3)

 

Forecasted sounding of Vlissingen May 25 at 2000 CET. A deep potential unstable layer above 850 hPa, which clearly needed a trigger for ignition. Due to the nightly cooling, lift must come from dynamical processes like the passage of a thermal low or through and indeed both came along. Here ahead of these features with in the lowest levels still weak easterly winds, but starting from 850 hPa veering to SW and increasing in speed. (Source picture: weeronline)

 

Forecasted sounding of Vlissingen May 26 at 0200 CET. Even a bit more unstable now as indicated by a slightly larger amount of most unstable CAPE, now reaching almost 2000 J/kg. If showers would form these would be the big ones in form of MCS type. Above all the shear (in speed and velocity) increased as well. With a forecasted helicity in a small area over western Belgium temporary up to 250 m²/s² (no clear indication on these progtemps), low level shear 0-3 km tempo up to 30 kt, deep layer shear 0-6 km up to 40 kt, there was even a chance of having supercells (with tornado) or bowecho. (Source picture: wofrance)

 

Observed sounding of Beauvechain May 26 around 0100 CET. The real state of the atmosphere showed that the calculated progtemps were quite good. Below 925 hPa, a rather strong inversion, above a deep unstable layer up to tropopause which was situated at 185 hPa corresponding with a height of 12,5 km. Air remained even saturated above the tropopause and this up to a height of 15 km, the result of spreading out Cirrus of overshooting tops. On the right some interesting values like the thunderstorm indices. (Source picture: Belgocontrol)

 

Mean sea level pressure map including the weather plots of 0300 CET. Around that time the squall-line passed Brussels, indicating the thermal low situated of over the south of Holland. (Source map: Meteocentre).

 

26/05/2009 0115-0400 CET. Satellite loop in the infra-red channel. Initially three MCS thunderstorms over the Benelux amalgamating to one big one. (Source sat picture: Eumetsat via Sat24.com)

 

26/05/2009. Satellite picture taken around 0405 CET (infra-red channel with temperature scale). It shows that the core of the MCS was at that time located over the mid Netherlands. (Source: NOAA)

 

Radar sequence between 2130-0555 CET. Again precipitation tops went up to 15 km. Around 0000 UTC, the cell over Hainaut & Oost-Vlaanderen was a supercell producing hailstones with diameter between 4 and 10 cm. It was later taken over by a very fast moving squall-line speeding up to around 55 kt. At 0100 UTC, the radar encountered briefly the severe precipitation belt of the squall-line, as result loosing even "its sight". (Source radar picture: Belgocontrol)

 

26/05/2009 0210 CET. The cell over Oost-Vlaanderen shows signs of a hook echo. Closer inspection of the radar images reveals that most of the time no real hook echo form was present, but a so-called "pendant echo" form. This could be related to a variant of a supercell, namely a so-called "hybrid supercell-multicell". This type of cell is most effective in producing very large hail and presumable such cell was responsible for some impressive sized hailstones on its entire track. Just before entering Belgium even hailstones with a diameter of 12 cm were measured in Raillencourt-Sainte-Olle (northern France). (Source picture: Belgocontrol).

 

26/05/2009 0135 CET. Zooming in on the pendant shape echo we can discover a weak echo region, an area where the inflow and updraft causes less intense precipitation reflectivity  (Source picture: Belgocontrol).

 

26/05/2009 0135 CET. Making a vertical cut between the two plus signs
(Source picture: Belgocontrol).

 

26/05/2009 0135 CET. Shows the weak echo region where the inflow is quite strong and
no precipitation falls to the ground
(Source picture: Belgocontrol).

 

26/05/2009 0135 CET. And also a bounded weak echo region where the updraft is quite strong
with high reflectivity (possible hail) trailing well above the ground level
(Source picture: Belgocontrol).

 

Hail with the largest diameter did fall in the extreme northwest of province Antwerp, namely in a place called Verrebroek. According the radar images did occur around 0305 CET. Measurements on the field, and this after a while and thus some melting could take place, it still came out to an impressive 9,2 cm. Prevailing form of the large stones were typical squeezed ball-ellipsoid or so-called "oblate". (Source picture: VRT library).

 

Hail trajectory with the red stars being reports on the field of stones of at least 4 cm diameter. The brightest red star is situated in Verrebroek. (Source: weerwoord).

 

26/05/2009 0230 CET. The squall line that affected the center of Belgium in detail, it later evolved to a a bow echo (Source picture: Belgocontrol).

 

26/05/2009. Windprofiler between 0220-0320 CET up to 15 km shows remarkable strong winds of 50 kt at 4 km height (Source picture: Belgocontrol).

 

26/05/2009. And these strong winds reached the surface around 0300 CET as downburst of the rear inflow jet (Source picture: Belgocontrol).

 

26/05/2009. Map of the wind gust (in kt) which occurred between 0200-0800 hr. The gusts over central parts of Belgium were linked to the squall-line. On one of the wind meters at Brussels Airport (located Steenokkerzeel) a gust of 58 kt was observed.

 

26/05/2009. Map of total precipitation (in mm) between 0200-0800 hr. A small area over Oost-Vlaanderen had the most of it as two heavy thundery showers passed by. Over the center of Belgium, the squall moved that fast, that no big amounts did fall.

 

Loop of discharges reaching Earth's surface between 2200-0415 CET. Around 30000 strikes were measured by the Belgian SAFIR, of which around half of it cloud-to-ground strokes. (Source picture: Blids)

 

Some metars (hours in UTC) of Florennes (EBFS), Charleroi (EBCI), Brussels (EBBR), Antwerp (EBAW) and Woensdrecht (EHWO) in Holland. Especially the station in the Netherlands gave some detailed info how things were during the passage of the squall line. Since 2009 no special reports anymore for the Belgian stations, so some luck in needed (like EBAW) to get a clue about the force of this storm.


EBFS 252325Z 09005KT 9999 SCT150 20/16 Q1009 BLU
EBFS 252355Z 10004KT 9999 BKN150 20/16 Q1009 BLU
EBFS 260025Z 18008G37KT 9999 -TSRA FEW027 SCT125 BKN150 21/15 Q1011 BLU
EBFS 260055Z 27014KT 9999 FEW012 BKN027 BKN090 15/14 Q1010 BLU
EBFS 260125Z 26007KT 9999 VCTS FEW120 SCT027 BKN120 14/13 Q1010 BLU
EBFS 260155Z 25005KT 9999 BKN120 14/13 Q1010 BLU
EBFS 260225Z 17004KT 9999 BKN120 14/13 Q1011 BLU


EBCI 252350Z 02003KT CAVOK 19/16 Q1008 RMK TEMPO 22015G30KT 3200 TSRA
EBCI 260020Z 05004KT 030V090 CAVOK 19/16 Q1009 RMK TEMPO 22015G30KT 3200 TSRAGR
EBCI 260050Z 26014G27KT 240V310 6000 -TSRA SCT006 BKN015CB BKN042 14/14 Q1010 RMK REGR TEMPO 4000 TSRA BKN005
EBCI 260120Z 25006KT 210V300 9999 -TSRA FEW006 FEW015CB 14/13 Q1010 RMK TEMPO 4000 TSRA BKN005
EBCI 260150Z 23007KT 9999 -RA FEW008 14/12 Q1010 RMK RETS NOSIG
EBCI 260220Z VRB02KT 9999 FEW008 14/12 Q1009 NOSIG
EBCI 260250Z 16006KT 130V190 9999 FEW008 14/12 Q1010 NOSIG



EBBR 252350Z 02003KT CAVOK 18/16 Q1008 RMK TEMPO 2000 +TSRA BKN015CB
EBBR 260020Z VRB02KT CAVOK 19/16 Q1008 RMK TEMPO 2000 +TSRA RMK BKN015CB
EBBR 260050Z VRB01KT 9999 VCTS FEW015CB 19/16 Q1008 RMK TEMPO 2000 +TSRA BKN015CB
EBBR 260120Z 30012KT 9999 TSRA BKN015CB 14/13 Q1010 RMK RETSRAGR NOSIG
EBBR 260150Z 23005KT 190V260 9999 -TSRA SCT015CB 15/13 Q1009 RMK RETSRA BECMG NSW
EBBR 260220Z 25006KT 9999 -SHRA FEW015CB 15/14 Q1009 RMK RETSRA NOSIG
EBBR 260250Z VRB01KT CAVOK 15/14 Q1008 NOSIG
EBBR 260320Z 16009KT CAVOK 15/14 Q1008 NOSIG

EBAW 252250Z AUTO 03007KT CAVOK 20/15 Q1009 EBAW 252220Z AUTO 04007KT CAVOK 20/15 Q1009
EBAW 252350Z AUTO 05008KT CAVOK 20/15 Q1008 EBAW 252320Z AUTO 05007KT CAVOK 20/15 Q1009
EBAW 260050Z AUTO 08004KT CAVOK 20/15 Q1008 EBAW 260020Z AUTO 07007KT CAVOK 20/15 Q1008
EBAW 260120Z AUTO 23028G53KT 200V260 2500 +SHRA SCT001/// SCT003/// BKN019/// 14/13 Q1012
EBAW 260150Z AUTO 33006KT 9999 -SHRA FEW019 15/13 Q1009 RMK RESHRA
EBAW 260220Z AUTO 10004KT 040V120 7000 SHRA FEW003 SCT007 BKN031 14/13 Q1008 RMK RESHRA
EBAW 260250Z AUTO 16005KT 110V210 9999 -SHRA SCT025 15/13 Q1008 RMK RESHRA
EBAW 260320Z AUTO 33004KT 280V010 9999 -SHRA NCD 15/13 Q1006
EBAW 260350Z AUTO 17013KT 140V200 CAVOK 15/14 Q1008



EHWO 252347Z AUTO 06005KT 9000NDV -RAUP FEW015TCU OVC100 18/16 Q1008 BLU
EHWO 252355Z AUTO 06005KT 9000NDV -RA FEW015TCU OVC100 18/16 Q1008 RMK BL
EHWO 260001Z AUTO 07005KT 7000NDV -RA FEW048 SCT054 OVC100 18/16 Q1008 WHT
EHWO 260013Z AUTO 04004KT 7000NDV -SHRA FEW043 SCT063 BKN084 18/16 Q1008 WHT
EHWO 260025Z AUTO 05003KT 6000NDV -SHRA FEW013 SCT045 BKN052 18/16 Q1008 RMK WHT
EHWO 260039Z AUTO 08006KT 5000NDV -TSRA FEW015CB SCT066 OVC100 18/16 Q1007 WHT
EHWO 260046Z AUTO 07009KT 6000NDV -TSRA FEW034 SCT080 OVC100 18/16 Q1007 WHT
EHWO 260055Z AUTO 08009KT 6000NDV -TSRA FEW015CB OVC100 18/16 Q1007 RMK WHT
EHWO 260101Z AUTO 11005KT 8000NDV -DZ TS FEW015CB OVC100 18/16 Q1007 BLU
EHWO 260114Z AUTO 12003KT 7000NDV TS BR FEW015CB BKN074 OVC081 18/16 Q1007 WHT
EHWO 260125Z AUTO 20010G41KT 4200NDV -TSRA FEW015CB BKN073 OVC079 18/17 Q1009 RMK GRN
EHWO 260129Z AUTO 19021G41KT 1900NDV +TSRA FEW014 FEW015CB SCT019 BKN045 15/13 Q1011 YLO
EHWO 260133Z AUTO 18019G41KT 2600NDV +TSRA FEW009 BKN015CB BKN020 15/14 Q1012 YLO
EHWO 260138Z AUTO 17013G28KT 3800NDV TSRA FEW009 FEW015CB SCT022 BKN044 15/14 Q1010 GRN
EHWO 260143Z AUTO 17009G20KT 5000NDV TSRA FEW009 FEW015CB SCT045 BKN054 15/14 Q1010 WHT
EHWO 260147Z AUTO 17006KT 4600NDV TSRA FEW015CB SCT050 BKN056 15/14 Q1009 GRN
EHWO 260148Z AUTO 16003KT 5000NDV -TSRA FEW015CB BKN058 BKN067 15/14 Q1009 RERA WHT
EHWO 260155Z AUTO 13003KT 6000NDV -TSRA FEW015CB SCT061 BKN076 14/14 Q1008 RMK RERA WHT
EHWO 260156Z AUTO 10004KT 8000NDV -TSRA FEW015CB SCT082 BKN095 14/14 Q1008 RERA BLU
EHWO 260209Z AUTO 04006KT 9000NDV -TSRA FEW056 BKN096 14/14 Q1008 BLU
EHWO 260210Z AUTO 03006KT 7000NDV -TSRA FEW052 BKN096 14/14 Q1008 WHT
EHWO 260215Z AUTO 05006KT 4800NDV -TSRA FEW015CB SCT077 BKN097 14/14 Q1008 GRN
EHWO 260225Z AUTO 07007KT 4400NDV -TSRA FEW015CB OVC097 14/14 Q1008 RMK GRN
EHWO 260231Z AUTO 07006KT 5000NDV -TSRA FEW010 FEW015CB BKN093 OVC100 14/13 Q1008 WHT
EHWO 260244Z AUTO 11006KT 7000NDV -SHRA FEW009 OVC091 14/14 Q1007 RETS WHT
EHWO 260248Z AUTO 16005KT 8000NDV -SHRA FEW009 SCT042 BKN091 14/14 Q1007 RETS BLU
EHWO 260255Z AUTO 20005KT 9000NDV SHRA FEW040 SCT054 OVC094 14/14 Q1007 RMK RETS BLU
EHWO 260302Z AUTO 20007G22KT 7000NDV RA FEW018 SCT050 BKN055 15/15 Q1007 WHT
EHWO 260307Z AUTO 21009G22KT 8000NDV -TSRA FEW015CB SCT050 BKN067 16/15 Q1007 RERA BLU
EHWO 260313Z AUTO 21010KT 9999NDV TSRA FEW014 SCT072 OVC092 16/15 Q1007 BLU
EHWO 260325Z AUTO 23013G23KT 9999NDV -TSRA FEW015CB SCT064 BKN075 16/15 Q1006 RMK RERA BLU
EHWO 260329Z AUTO 25014KT 9999NDV -TSRA FEW038 SCT080 BKN089 16/15 Q1006 BLU
EHWO 260350Z AUTO 11007KT 9999NDV OVC110 15/15 Q1005 RETS BLU

 

Below screenshots of some meteo parameters measured at Brussels Airport during the passage of the squall-line.
Hours in UTC. (Source all screenshots: Belgocontrol)
 

Brussels Airport observations of the wind at runway 25L. Speed in kt (red) and direction in degrees (pink), every 3 seconds (on top), 2 minutes (middle), 10 minutes (bottom). At 00:56:00 the 3 seconds wind was 120 degrees 01 kt, next minute veering to 240 with from 00:57:54 onwards speed exceeding 20 kt, from 00:58:12 exceeding 30 kt, from 01:00:27 topping 40 kt, tempo decreasing to 30 kt, but between 01:01:12 and 01:01:15 topping to 53 kt, from  01:02:24 on decreasing below 40 kt, from 01:05:00 below 30 kt.

Not depicted:
on ruway 02, the wind speed peaked 40 kt, between 00:58:33-00:58:36
on runway 07L, the wind speed peaked 49 kt between 00:58:39-00:58:42
on runway 25R, the wind speed peaked 58 kt between 01:00:51-01:00:54.

 

Brussels Airport observations of the temperature (°C), at 1,5 m (white) and surface (pink) revealing a remarkable drop of more than 6°C within minutes.   

 

Brussels Airport observations of mean sea level pressure (hPa), perhaps even more remarkable with a rise of 4,4 hPa. 

 

Brussels Airport observations of the precipitation (mm), intensity (on top) and total amount (bottom). The rain rate peaked above 100 mm/h, but it lasted around 4 minutes, afterwards rate decreased. Total amount of rain was 12 mm. 

 

To summarize things, this quite fascinating satellite loop between May 24 1415 CET and May 26 1345 CET (infra-red channel enhanced with color to accentuate the coldest spots). It shows the long living and very interesting cell which affected the Ardennes with an unpredictable track. Furthermore the exploding MCS over France & the Benelux area (Source: Meteosat via K. Hamid).

 

26/05/2009 0344 NNE. When most of the precipitation on the backside of the squall-line was cleared, a couple pictures of discharges (all CG's) could be made. This strike was at approx 40 km.

 

26/05/2009 0353 NNE. The best shot, distance of this long vertical discharge was between 15-20 km, with its impact at 20 km, location was Puurs just northwest of Mechelen.

 

26/05/2009 0357 NNE. Discharge at approx 75 km.

 

26/05/2009 0400 NNE. Discharge at approx 75 km.

 

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