CONVECTIVE FORECAST
VALID 06Z THU 15/05 - 06Z FRI 16/05 2003
ISSUED: 15/05 01:40Z
FORECASTER: VAN DER VELDE

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN RUSSIA, BELARUS

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS BELARUS, WESTERN RUSSIA, ESTONIA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SPAIN, THE BALKAN, TURKEY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS BENELUX, GERMANY, CZECH REPUBLIC, W-POLAND, SWEDEN

SYNOPSIS

UPPER TROUGH FILLED WITH COLD AIR IS DIGGING INTO FAR EASTERN EUROPE WHILE A SHALLOW RIDGE OF HIGH PRESSURE AT SURFACE LEVEL BUILDS AT THE WESTERN SIDE. THE COLD AIR ALOFT BELOW THE UPPER TROUGH WILL PROVIDE INSTABILITY IN THE NORTHERN CENTRAL PART OF EUROPE INTO SCANDINAVIA, WHILE AN UNSTABLE TO HIGHLY UNSTABLE AIRMASS - ESPECIALLY NEAR THE SFC TROUGH OVER RUSSIA/BELARUS - RESIDES EAST OF THE COLD FRONT FROM FINLAND TO GREECE. MOST ASCENDING MOTION (GFS MODEL) IS LOCATED OVER THE COLD FRONT ASSOCIATED WITH VORTICITY ADVECTION ALOFT AND WARM AIR ADVECTION, WITH A MAXIMUM JUST AHEAD OF THE APEX OF THE UPPER TROUGH OVER ERN POLAND/SLOWAKIA/BELARUS APPARENTLY CAUSING A DEEPENING AND TILTING OF THE SFC TROUGH ASSOCIATED WITH THE COLD FRONT OVER RUSSIA. A THERMAL LOW DEVELOPS OVER THE IBERIAN PENINSULA, AND A FRONTAL SYSTEM STARTS AFFECTING EXTREME WESTERN EUROPE AT THE END OF THE FCST PERIOD.

DISCUSSION

...BELARUS, WESTERN RUSSIA, ESTONIA...
12Z PREVIOUS DAY VELIKIE LUKI (ULOL) SOUNDING AHEAD OF THE COLD FRONT OVER RUSSIA CONFIRMS HIGH INSTABILITY, VERY STEEP MIDLEVEL LAPSE RATES AND HIGH STORM-RELATIVE HELICITY VALUES INDICATED BY THE CORRESPONDING GFS 12Z MODEL ANALYSIS. CURRENT 2330Z IR IMAGERY STILL SHOWS CONVECTION ONGOING IN THAT AREA (55N 30E). ALTHOUGH REMNANTS OF THIS ACTIVITY MAY INHIBIT DAYTIME HEATING, GFS INDICATES EVEN HIGHER 30HPA-MLCAPE THAN YESTERDAY ...1000-2000 J/KG RANGE... BUT LESS STEEP LAPSE RATES. SHEAR CONDITIONS ARE STRONG OVER THE COLD FRONT BUT WEAKER INTO THE MOST UNSTABLE AIR, GENERALLY BETWEEN 30-40 KTS 0-6 KM SHEAR (0-1 KM SHR > 20 KTS). THE GFS MODEL INDICATES AN INCREASING TREND IN 0-3 KM SREH TOWARDS VALUES OF MORE THAN 200 M2/S2 OVER A LINEAR AREA ALONG THE COLD FRONT, THE COMBINATION YIELDING AN ENVIRONMENT CONDUCIVE OF STRONG SUPERCELLS. PRESENT THINKING IS THAT - LIKE YESTERDAY - A LINE OF STORMS, PROBABLY A SEVERE SQUALL LINE WITH EMBEDDED SUPERCELLS AND BOW SEGMENTS DEVELOPS, GIVEN THE STRONG LINEAR TRIGGER. AHEAD OF THE LINE THERE IS A POSSIBILITY OF DISCRETE SUPERCELLS - ALTHOUGH THE SHEAR VALUES BECOME LESS FAVORABLE AWAY FROM THE FRONT - THE LOCAL SHEAR AND TRIGGERING ENVIRONMENT ARE LIKELY TO BE LOCALLY AUGMENTED BY OUTFLOW BOUNDARIES FROM PAST CONVECTION. ...LARGE HAIL... WIDESPREAD SEVERE GUSTS INCLUDING POSSIBILITY OF MICROBURST GIVEN THE HIGH MIDLEVEL-SFC THETA-E DIFFERENCE INDICATED BY GFS... A COUPLE OF TORNADOES INCL. AN ISOLATED STRONG TORNADO ARE POSSIBLE UNDER THESE CIRCUMSTANCES. CONVECTION SHOULD DEVELOP BY MID AFTERNOON AND PROGRESS NORTHWARD DURING THE EVENING. SE-FINLAND SHOULD SEE LITTLE ACTIVITY LEFT IN THE EARLY MORNING NEXT DAY.

...BALKAN/TURKEY, SPAIN...
SFC CONVERGENCE UNDER THE THERMAL LOW DEVELOPING OVER SPAIN AND THE COLD FRONT OVER THE BALKAN ARE LIKELY TO TRIGGER THUNDERSTORMS. ISOLATED HIGH-BASED STORMS DEVELOPING HERE CAN DEVELOP STRONG OUTFLOW DUE TO DRY AIR ALOFT AND IN THE BOUNDARY LAYER. MARGINALLY SEVERE HAIL IS A POSSIBILITY AND MOST LIKELY IN THE ELEVATED AREAS.

...BENELUX, GERMANY, CZECH REPUBLIC, W-POLAND, SWEDEN...
COLD UNSTABLE POLAR AIRMASS WITH STEEP LAPSE RATES WILL CAUSE SHOWERY/THUNDERY CONDITIONS ESPECIALLY IN SOUTHERN GERMANY WHERE CAPE´S ARE PROGGED TO BE LARGEST, AND IN SWEDEN UNDER THE CORE OF THE UPPER LOW WHERE ALSO ENHANCED VORTICITY ADVECTION IS FOUND. PAST DAYS HAVE SHOWN THAT WATERSPOUTS/FUNNEL CLOUDS AND EVEN LARGE HAIL LOCALLY OCCURRED (UK, NETHERLANDS) IN THIS AIRMASS, EVEN THOUGH CAPE/SHEAR CONDITIONS DID NOT SEEM ALERTING. THE COLD UPPER LOW WITH VORTICITY OVER SWEDEN SEEMS LIKE A CLASSIC SETUP FOR COLD AIR FUNNELS (THAT DO NOT TOUCHDOWN OFTEN) ...BENELUX COUNTRIES WILL SEE DIMINISHING INSTABILITY DURING THE DAY AS THE RIDGE BUILDS.

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