Severe Thunderstorm Warning 93, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
312 PM EDT SUN AUG 6 2000

FORECAST CONCERNS TODAY ARE OBVIOUSLY WITH POTENTIAL FOR SEVERE
CONVECTION THIS EVENING. FEEL THIS TOPIC HAS BEEN BEATEN TO DEATH
OVER THE PAST FEW DISCUSSIONS... SO WON/T SPEND TOO MUCH TIME ON
THINGS. FOR MORE INFO... READ THE PAST FEW DISCUSSIONS AND OUTLOOK
INFO FROM SPC. IN A NUTSHELL... IT STILL APPEARS THAT CONVECTION
WILL BE POSSIBLE ACROSS THE FORECAST AREA THIS EVENING... WITH THE
BEST POTENTIAL OVER THE SOUTHEAST CWFA WHERE THE BEST INSTABILITY
WILL BE IN PLACE. LAKE MICHIGAN IS HELPING TO CLEAR CU ACROSS A GOOD
CHUNK OF THE FORECAST AREA... AND IT SHOULD CONTINUE TO HELP KEEP
THINGS A BIT MORE STABLE NORTH AND WEST OF A BEH TO RQB LINE.
INSTABILITY... DEEP LAYER SHEAR... AND LOW LEVEL HELICITY DO SUPPORT
THE POSSIBILITY OF TORNADIC SUPERCELLS... ALTHOUGH THE SHEAR PROFILE
IS MOST SUPPORTIVE OF A SQUALL LINE/LEWP OVER TIME. TIME FRAME FOR
CONVECTION RUNS FROM AROUND 23Z TO 06Z... ALTHOUGH MUCH WILL DEPEND
ON WHETHER WE ARE DEALING WITH DEVELOPING CONVECTION OR ACTIVITY
ADVECTING INTO THE AREA (OR A COMBINATION OF BOTH).

DRIER AIR AND SUBSIDENCE WILL WORK INTO THE AREA BEHIND THE FRONT
LATE TONIGHT... SETTING THE STAGE FOR A PLEASANT MONDAY. MOISTURE
PROGS AND FORECAST SOUNDINGS DON/T SUPPORT CU DEVELOPMENT ON
MONDAY... AND MID AND UPPER LEVEL MOISTURE ARE NIL... SO A MOSTLY
SUNNY FORECAST LOOKS GOOD. IT WILL BE BREEZY... WITH A DECENT
GRADIENT AND GOOD MIXING HELPING TO CREATE SOME GUSTY WEST WINDS
THROUGH THE AFTERNOON.

THE FRONTAL BOUNDARY TO OUR SOUTH WILL START TO WORK BACK TOWARD US
LATE MONDAY NIGHT AND TUESDAY AS THE NEXT WAVE STARTS TO MOVE OUT OF
THE PLAINS. THE MODELS ARE NOT IN PARTICULARLY GOOD AGREEMENT WITH
THE HANDLING OF THE WARM FRONT... AND HAVE DISPARATE QPF SOLUTIONS
AS A RESULT. PREFER THE ETA/S HANDLING OF THINGS... ALTHOUGH DON/T
HAVE MUCH CONFIDENCE IN THINGS EITHER WAY. THE AVN DEVELOPS AN MCS
OVER NW IA MONDAY NIGHT... AND MOVES IT EAST ALONG THE WARM FRONT
AND THROUGH OUR AREA ON TUESDAY. MEANWHILE... THE ETA DEVELOPS ITS
MCS FURTHER SOUTH... AND DOESN/T BRING NEARLY AS MUCH PCPN INTO
LOWER MI ON TUESDAY. AT THIS POINT... WILL COVER THE SCENARIO WITH
CHANCE POPS OVER THE WEST LATE MONDAY NIGHT... AND CHANCE POPS OVER
THE ENTIRE CWFA ON TUESDAY. WILL LIKELY GO WITH PARTLY SUNNY SKIES
ON TUESDAY... SINCE PLAYERS IN THE CLOUD COVER FORECAST... SUCH AS
MCS DEBRIS... ARE UNCERTAIN AT THIS POINT.

FORECAST TEMPERATURES WILL BE A BLEND OF NGM AND OLD AVN MOS NUMBERS.

TRH

.EXTENDED FORECAST...
AVN BRINGS A SURFACE LOW INTO THE NRN GREAT LAKES REGION TUE NIGHT
DRIVING A COLD FRONT INTO LOWER MI. WITH HIGH DEWPOINT AIR SURGING
BACK TO THE NORTH AHEAD OF THIS FRONT AND STEEP LAPSE RATES IN PLACE
EXPECT SCATTERED SHOWERS AND THUNDERSTORMS TUE NIGHT. WILL KEEP
CHANCE OF PCPN INTO WED AS LOW MOVES ACROSS NRN LWR. SIGNIFICANT
TIMING DIFFERENCES BY THE END OF THE WEEK WITH THE MRF MUCH SLOWER
PUSHING THE TROUGH TO THE EAST THAN THE ECMWF.  MRF ENSEMBLES SHOW
THAT THE OPERATIONAL MRF IS FARTHER TO THE WEST WITH THE RIDGE OVER
THE CENTRAL PLAINS AND WITH THE TROUGH IN THE NE U.S. THAN MOST
MEMBERS. THUS WILL GO WITH A MORE PROGRESSIVE SOLUTION.  CHANCE OF
THUNDERSTORMS FOR THU AS MODELS INDICATE UPPER WAVE SWINGING INTO
THE BASE OF THE UPPER TROUGH.  STRONG SURFACE HIGH BUILDS INTO
THE REGION FOR A DRY FRIDAY AS TROUGH SHIFTS EAST.

GRAHAM

.GRR...NONE.

MIZ051-052-056>059-064>067-071>074-070400-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
643 PM EDT SUN AUG 6 2000

...SEVERE THUNDERSTORM WATCH IN EFFECT UNTIL MIDNIGHT FOR PORTIONS
OF SOUTHWEST LOWER MICHIGAN...

SEVERE THUNDERSTORM WATCH  652 IS IN EFFECT UNTIL MIDNIGHT FOR
BARRY... KALAMAZOO... ALLEGAN... KENT... OTTAWA... GRATIOT...
MONTCALM... BRANCH... CALHOUN... CLINTON... EATON... INGHAM...
IONIA... AND JACKSON COUNTIES.

AT 640 PM... DOPPLER RADAR SHOWED AN AREA OF VERY STRONG
THUNDERSTORMS IN NORTHEAST ILLINOIS...NORTHWEST INDIANA... AND
SOUTHERN LAKE MICHIGAN.  THESE STORMS WERE MOVING EAST NORTHEAST
AT 30 MPH AND WILL MOVE INTO THE WATCH AREA BY 700 PM.

THESE STORMS WILL BE CAPABLE OF PRODUCING WIND GUSTS OF 70 TO 80 MPH.

PEOPLE IN SOUTHWEST LOWER MICHIGAN SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER AND SEEK SAFE SHELTER SHOULD IT ARRIVE.  THE
SAFEST PLACE TO BE DURING SEVERE WEATHER IS IN A REINFORCED
STRUCTURE.