Severe Thunderstorm Warning 13, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
300 PM EDT SUN MAY 16 1999

SFC LOW LOCATED IN SOUTHEAST NEBRASKA AT MIDDAY...WITH A COLD FRONT
STRETCHING SOUTHWARD AND A WEAK WARM FRONT EXTENDING EAST INTO THE
SRN GRT LKS REGION. ALOFT...FLAT UPR RIDGING LOCATED OVR THE GRT
LKS...WITH AN UPR TROF MOVG THROUGH THE ROCKIES. THROUGH THE SHORT
TERM PERIOD...SFC LOW LIFTS NORTHEAST DRAGGING A COLD FRONT THROUGH
THE FCST AREA MONDAY NIGHT AND TUESDAY. ALOFT...WESTERN UPR TROF
MOVES NORTHEAST AND FLATTENS RIDGE EVEN FURTHER. WEAK UPR SHORTWAVES
EJECTING NORTHEAST OUT OF THE WESTERN TROF AIDING CONVECTIVE
DEVELOPMENT...LIKE THE ONE MOVG THROUGH THE NORTHERN PLAINS AIDING
CONVECTION IN IOWA ATTM. FCST CONCERNS IN THE SHORT TERM WILL BE
TIMING AND EXTENT OF SHOWER AND THUNDERSTORM DEVELOPMENT.

TWO OF THE THREE SHORT TERM MODELS ONCE AGAIN IN AGREEMENT...NAMELY
THE ETA AND THE AVN. NGM IS ONCE AGAIN THE ODD MODEL OUT...MAINLY DUE
TO TIMING DIFFERENCES. WILL FOLLOW THE ETA THIS GO ARND. QUICKER
MOVEMENT OF THE FEATURES FROM THE ETA/AVN SOLUTIONS NOT THAT HARD TO
BUY GIVEN THAT THE UPR S/WV IS FINALLY ON THE MOVE WITH KICKER
DROPPING INTO THE PACIFIC NW.

AS FOR TONIGHT...CONVECTION OVR IOWA MOVG THIS DIRECTION. TSTM/S MOVG
EASTWARD...PER THE 700-300MB LAYER FLOW. THESE THUNDERSTORMS WILL BE
MOVG AWAY FROM THEIR SUPPORT (WEAK UPR S/WV AND THE LLJ)...SO EXPECT
THAT CONVECTION WILL DIMINISH AS IT MOVES EAST. ANTICIPATE ANOTHER
MCS TO FIRE THIS EVENING OVR IOWA AND MOVE EAST INTO LWR MI AFTER
MIDNIGHT. BETTER CHANCES FOR PCPN WITH THIS ROUND OF CONVECTION. WILL
CARRY 50 POPS SOUTH AND 40 POPS NORTH. BETTER CHANCES TO THE
SOUTH...DUE TO THE PROXIMITY TO THE CONVECTION. A RATHER WARM NIGHT
EXPECTED WITH LOWS RANGING FROM THE UPR 50S NORTH TO THE LOWER 60S
SOUTH.

FOR MONDAY...WEAK S/WV MOVES INTO WI...PROVIDING SYNOPTIC SUPPORT.
RIGHT ENTRANCE REGION ASSOCIATED WITH UPR WAVE ALSO ADDING SOME LIFT.
EXPECT ANOTHER ROUND OF CONVECTION TO MOVE IN DURING THE LATE
AFTERNOON...AFTER LEFTOVER CONVECTION FROM THE MORNING
DISSIPATES/MOVES EAST. WILL CARRY LIKELY POPS (60 PCT) FCST AREA
WIDE. LIKE THE COOLER FAN NUMBERS TOMORROW GIVEN EXTENT OF CLOUDS AND
PROBABILITY OF PRECIPITATION. UPPER 70S SHOULD WORK MOST LOCALES.

WILL UP THE POPS TO CATEGORICAL (80 PCT) FOR MONDAY NIGHT GIVEN
PROXIMITY OF THE MAIN UPR S/WV AND APPROACHING SFC FRONTAL BOUNDARY.
WILL MENTION OCCASIONAL SHOWERS AND THUNDERSTORMS. THREAT FOR SVR
TSTM/S DOES EXIST MONDAY AFTERNOON AND EVENING PER THE DAY TWO
OUTLOOK...MAINLY IN THE FORM OF SVR WIND GUSTS. FLOW WILL BE
UNIDIRECTIONAL FROM THE SOUTHWEST AT ABOUT 40KTS IN THE LWR TROP...SO
SVR SFC GUSTS OF ARND 60 MPH POSSIBLE. THREAT FOR SVR WILL HINGE ON
AMOUNT OF DESTABILIZATION DURING THE DAY TMRW. IF SUNSHINE BREAKS OUT
IN THE AFTERNOON AND JUMPS TEMPS INTO THE 80S...THREAT FOR SVR WILL
INCREASE...BUT AT THIS POINT IT APPEARS MARGINAL.

FOR TUESDAY...FRONT MOVG THROUGH THE FCST AREA IN THE MORNING...WITH
SHOWERS LIKELY THROUGH THE DAY. WILL MENTION A TSTM ALSO POSSIBLE IN
THE MORNING.

IN THE EXTENDED...BECOMING PARTLY CLOUDY TUESDAY NIGHT IN THE WAKE OF
THE EXITING SHORTWAVE...THEN PARTLY CLOUDY AND DRY THE REMAINDER OF
THE WEEK. CHC FOR A SHOWER ON FRIDAY...BUT WILL LEAVE OUT FOR NOW
GIVEN POSN OF MAIN SHORTWAVE TO THE NORTH OF THE REGION.

ZONES TOWARD 400PM EDT.

.GRR...NONE.

DUKESHERER