Severe Thunderstorm Warning 29, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
505 PM EDT TUE MAY 15 2001

FORECAST CONCERNS REVOLVE AROUND SEVERE WEATHER AND HEAVY RAINFALL
POTENTIAL TONIGHT AND WEDNESDAY. FLOOD WATCH/WARNINGS COVER MOST OF
THE FORECAST AREA THROUGH WEDNESDAY MORNING. SEE FFAGRR AND FFWGRR
FOR FURTHER DETAILS ON HEADLINES.

SFC WARM FRONT REMAINED JUST SOUTHWEST OF THE FORECAST AREA THIS
AFTERNOON...JUST TOUCHING THE MI/IN BORDER AT 20Z. CLEARING BEHIND
THIS MORNING'S MCS ALLOWED SFC TEMPS TO RISE INTO THE 70S AS FAR
NORTH AND EAST AS LDM-MKG-GRR-BTL THIS AFTERNOON. SFC TEMPS IN GRAND
RAPIDS FELL DURING THE LATE AFTERNOON AS SOUTHERLY SFC FLOW BACKED
EASTERLY IN OUTFLOW BOUNDARY FROM CONVECTIVE DEVELOPMENT OVER
MID-MICHIGAN. LATEST KGRR 88-D SHOWED LINE OF THUNDERSTORMS ACROSS
ERN-MOST COUNTIES OF FORECAST AREA MOVING TO THE SSE AROUND 25
KNOTS. THIS CONVECTION WAS ASSOCIATED WITH THE 850 MB WARM FRONT AND
ISENTROPIC LIFT. SOME SMALL HAIL HAS BEEN REPORTED WITH A FEW OF THE
STRONGER CELLS IN THE FORECAST AREA THIS AFTERNOON...WITH SEVERE
CRITERIA HAIL SO FAR CONFINED TO NRN LOWER MI. WILL CLOSELY MONITOR
FOR POTENTIAL HAIL AS THIS LINE SLOWLY CLEARS ERN COUNTIES THIS
EVENING.

ISOLATED CONVECTIVE DEVELOPMENT POSSIBLE THIS EVENING ACROSS
FORECAST AREA AS SFC CONVERGENCE INCREASES ALONG AND N OF THE SFC
WARM FRONTAL BOUNDARY. OUTFLOW BOUNDARIES COULD ALSO INTERACT TO
RESULT IN SOME DEVELOPMENT. HOWEVER...STILL BEING NORTH OF THE SFC
WARM FRONT...DO NOT EXPECT SFC-BASED INSTABILITY TO BE A FACTOR THIS
EVENING.

MAIN CONCERN IS FOR LATER TONIGHT...AFT 06Z AS ANOTHER MCS IS
EXPECTED TO AFFECT THE FORECAST AREA. WILL MONITOR NRN MN AND NWRN
WI FOR DEVELOPMENT OF THIS ACTIVITY THIS EVENING. EXPECT MCS TO MOVE
SEWD ALONG AND N OF THE SFC WARM FRONT AGAIN OVERNIGHT...WITH WRN
LOWER MICHIGAN IN THE ZONE OF MOST CONCERN. SEVERE CRITERIA HAIL
WILL ONCE AGAIN BE POSSIBLE WITH ELEVATED CONVECTION MOVING ACROSS
THE FORECAST AREA. PWAT VALUES REACH AROUND 1.50" BETWEEN 06Z AND
12Z. HEAVY RAINFALL SWATH OF 1 TO 2 INCHES POSSIBLE ASSOCIATED WITH
MCS. DO NOT EXPECT BACK-BUILDING CONVECTION AS WAS THE CASE LAST
NIGHT...THEREFORE DO NOT EXPECT ANOTHER REPEAT OF 3 TO 5 INCH
RAINFALL AMOUNTS. FRONTOGENETICAL FORCING...MID-LEVEL WARM ADVECTION
AND UPPER JET SUPPORT NOT NEARLY AS IMPRESSIVE ACROSS THE FORECAST
AREA TONIGHT. HOWEVER...WITH LOW LEVEL JET FEEDING INTO VERY
MOIST/UNSTABLE AIRMASS OVER MN AND WI...MCS DEVELOPMENT ANTICIPATED.
EXPECT THIS TO MOVE AT A STEADY CLIP SEWD ACROSS THE FORECAST AREA
WITH A 2 TO 4 HOUR PERIOD OF LOCALLY HEAVY RAINFALL...BUT NOT A
PROLONGED PERIOD OF TRAINING INTENSE CELLS. WITH RELATIVELY LOW
FREEZING LEVELS...LARGE HAIL COULD BE ASSOCIATED WITH MORE INTENSE
CELLS AGAIN TONIGHT. SLIGHT RISK FOR SEVERE LOOKS REASONABLE ACROSS
THE FORECAST AREA.

SFC COLD FRONT WILL MOVE ACROSS THE FORECAST AREA AFT 18Z WEDNESDAY.
DEPENDING ON CLEARING BEHIND MORNING MCS...COULD SEE CONVECTIVE
REDEVELOPMENT ALONG THE SFC FRONT DURING THE AFTERNOON. INTERACTION
WITH DEVELOPING LAKE BREEZE IN COOL AIR ADVECTION PATTERN COULD
CONTRIBUTE TO THIS CONVECTIVE DEVELOPMENT INLAND. BEST CHANCES FOR
ADDITIONAL AFTERNOON PCPN WILL BE ACROSS THE ERN HALF OF THE
FORECAST AREA. DO NOT EXPECT THESE CELLS TO REACH SEVERE LEVELS.

GREENE

EXTENDED FORECAST DISCUSSION...
AN ACTIVE PATTERN WILL CONTINUE ACROSS THE GREAT LAKES THROUGH
TUESDAY. A SHORT WAVE WILL PUSH THROUGH ON FRIDAY KICKING OFF MORE
SHOWERS AND THUNDERSTORMS. THE S END OF A SHORT WAVE MAY KICK OFF
MORE PCPN ON SUNDAY...BUT WILL HOLD OFF TO SEE IF IT STAYS N OF THE
CWFA. ANOTHER WEAK SHORT WAVE MOVES INTO THE AREA ON MONDAY WITH A
CHANCE OF SHOWERS AND THUNDERSTORMS...BUT THE BEST CHANCE WILL BE
WITH A STRONGER WAVE ON TUESDAY. PLENTY OF MOISTURE WILL REMAIN IN
THE GRT LKS AREA OR JUST TO OUR S.

DGH

.GRR...FLOOD WATCH TONIGHT AND WEDNESDAY MORNING FOR:
       MASON...LAKE...OSCEOLA...OCEANA...NEWAYGO...MECOSTA...
       MUSKEGON...MONTCALM...IONIA...ALLEGAN...BARRY...EATON...
       KALAMAZOO...CAL3HOUN...AND JACKSON COUNTIES.
    ...MIZ037>039-043>045-050-051-058-064>066-072>074.
    ...FLOOD WARNING THROUGH 10 AM WEDNESDAY MORNING FOR KENT AND
       OTTAWA COUNTIES.