CONVECTIVE FORECAST
VALID 06Z SAT 14/06 - 06Z SUN 15/06 2003
ISSUED: 13/06 19:43Z
FORECASTER: DAHL

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND NORTHERN FRANCE.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS FRANCE AND THE PRE-ALPINE REGIONS.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL AND SOUTHERN EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE BALTIC STATES.

SYNOPSIS

ZONAL UPPER FLOW PATTERN HAS ESTABLISHED OVER EUROPE ... WITH THE UPPER JET AXIS STRETCHING ACROSS NORTH-CENTRAL INTO EASTERN EUROPE. SEVERAL EMBEDDED WEAK/ILL-DEFINED VORT MAXIMA WILL CROSS THIS REGION DURING SUNDAY PER GME AND GFS. WAVY LOW-LEVEL BAROCLINIC ZONE IS STRETCHING ACROSS N FRANCE ... S GERMANY ... S POLAND INTO W RUSSIA ... AND WILL LARGELY REMAIN IN ITS CURRENT POSITION DURING THE FCST PERIOD.

DISCUSSION

...FRANCE...
ACTIVE SEVERE WEATHER DAY EXPECTED OVER FRANCE AGAIN ... NANCY 12 Z SOUNDING SHOWS CAPE OF 1500 J/KG ... INDICATIONS ARE THAT AN ELEVATED-MIXED LAYER IS PRESENT FARTHER WEST ... SUPPORTING MLCAPE'S ON THE ORDER OF 2500 J/KG ... OR HIGHER. THOUGH CONVECTIVE DEBRIS MAY LINGER OVER PORTIONS OF FRANCE DURING THE FIRST HALF OF THE DAY ... AFTERNOON MLCAPE'S ARE EXPECTED TO CLIMB INTO THE 2000 TO 3000 J/KG RANGE AGAIN ... ESPECIALLY AS SOIL MOISTURE WILL BE VERY HIGH DUE TO CURRENT CONVECTIVE ACTIVITY OVER FRANCE. DEEP-LAYER SHEAR SHOULD INCREASE SOMEWHAT OVER N FRANCE ... AND 30 TO 40 KNOTS 0-6 KM SHEAR MAY BE IN PLACE TOWARDS LATE AFTERNOON. FARTHER S ... WHERE CAPE IS EXPECTED TO BE HIGHEST ... 0-6 KM SHEAR SHOULD ONLY BE ON THE ORDER OF 20 KNOTS.

CONVECTION SHOULD INITIATE TOWARDS EARLY AFTERNOON ALONG OUTFLOW BOUNDARIES LAID OUT BY TONIGHT'S STORMS ... SUPPORTED BY WEAK DCVA-RELATED LIFT COHERENTLY PROGGED BY GFS AND GME AND GENERALLY CONVERGENT LOW-LEVEL FLOW ASSOCIATED WITH A WEAK PRE-FRONTAL SURFACE LOW. ALSO ... TSTMS MAY DEVELOP ALONG WEAK FRONTAL BOUNDARY LYING OVER N FRANCE. ALTOGETHER ... COVERAGE OF THE STORMS COULD RATHER QUICKLY BECOME QUITE HIGH.

SEVERE THREAT APPEARS TO BE DEPENDING ON HOW EFFECTIVELY THE AIRMASS RECOVERS FROM TONIGHT'S CONVECTION AND ON HOW LONG INITIATION WILL BE HELD OFF. INITIAL ACTIVITY WILL HAVE FAIR CHANCES OF BECOMING SUPERCELLULAR OVER CENTRAL AND NORTHERN FRANCE WHERE MARGINAL DEEP-LAYER SHEAR WILL BE PRESENT. LOW-LEVEL HELICITY SHOULD GENERALLY BE RATHER LOW ... BUT IF STORM INFLOW HAPPENS TO BE PARALLEL TO AN OUTFLOW BOUNDARY ... STRONGLY HELICAL AIR WILL BE INGESTED. LOCALLY EXPECTED LARGE CAPE DENSITIES IN THE LOWEST KM ALONG WITH LOW LCL HEIGHTS WOULD CREATE FAVORABLE ENVIRONMENT FOR TORNADOES. HOWEVER ... PRIMARY THREAT SHOULD BE LARGE HAIL WITH ANY SUPERCELL THAT FORMS ... POSSIBLY AS LARGE AS 6 CM IN DIAMETER ... AND DAMAGIN WIND GUSTS. CAPE IS EXPECTED TO WEAKEN GRADUALLY TOWARDS THE NORTH ... WHERE SHEAR WILL BE STRONGER ... AND ALLOVER SEVERE THREAT OVER NORTH FRANCE MAY EFFECTIVELY BE AS HIGH AS OVER CENTRAL FRANCE.

CHANCES OF SUPERCELLS APPEAR TO BE SUBSTANTIALLY LOWER OVER SOUTH FRANCE ... WHERE SHEAR WILL BE MINIMAL ... THOUGH SMALL THREAT OF SUPERCELLS STILL EXISTS IF CELLS INTERACT WITH PRE-EXISTING SMALL-SCALE BOUNDARIES ... WHICH WOULD BE CAPABLE OF PRODUCING VERY LARGE HAIL ... DAMAGING WINDS AND POSSIBLY A TORNADO OR TWO. HOWEVER ... SINCE THIS SCENARIO IS RATHER CONDITIONAL ... A SLGT RISK APPEARS SUFFICIENT ATTM. MAJORITY OF THE STORMS SHOULD BE MULTICELLULAR ... PRODUCING MARGINALLY SEVERE HAIL AND STRONG/DAMAGING WIND GUSTS.

STORMS SHOULD BECOME QUITE NUMEROUS LATE IN THE AFTERNOON/EVENING ... AND MAY FINALLY CONGEAL INTO ONE OR MORE LARGE MCS'S LATE IN THE EVENING/NIGHT AS BOLAM SUGGESTS ENHANCED LOW-LEVEL WAA OVER CENTRAL FRANCE. PRIMARY THREAT WILL THEN SHIFT TOWARDS DAMAGING WIND GUSTS THOUGH ISOLATED MARGINALLY SEVERE HAIL SHOULD STILL BE POSSIBLE.

...PRE-ALPINE REGIONS...
EXPECT A FEW TSTMS TO INITIATE IN THE PRE-ALPINE REGIONS OVER SWITZERLAND ... S GERMANY AND AUSTRIA ALONG OROGRAPHIC FEATURES EARLY IN THE AFTERNOON. THOUGH SHEAR WILL BE MARGINAL FOR SEVERE EVOLUTION ... OROGRAPHIC LOW-LEVEL FLOW PERTURBATIONS AND OTHER FEATURES MAY PRODUCE SUBSTANTIAL LOW-LEVEL SRH ... AND A FEW MESOCYCLONES MAY OCCUR ... ENHANCING THREAT OF LARGE HAIL. MOST STORMS HOWEVER SHOULD BE SUB-SEVERE. GIVEN EXPECTED RATHER HIGH AFTERNOON CAPE VALUES AND INCREASING VERTICAL SHEAR ... A SLGT RISK IS MARGINALLY WARRANTED.

...IBERIA...
HIGH-BASED STORMS ARE EXPECTED TOWARDS LATE AFTERNOON ... THOUGH CAPE SHOULD BE MINIMAL ... LARGE DRY-ADIABATIC SUB-CLOUD LAYER WILL PROMOTE STRONG DOWNDRAFTS ... AND THREAT OF A FEW SEVERE WIND GUSTS EXISTS.

OTHERWISE ... THREAT OF ORGANIZED SEVERE STORMS IS MINIMAL.

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