Severe Thunderstorm Warning 102, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
345 PM EDT SUN OCT 14 2001

FCST CHALLENGE IS TIMING AND COVERAGE OF PCPN EVENTS AS NORTHERN
STREAM UPPER TROUGH AND COLD AIR DIGS IN...AND SEVERAL DISTURBANCES
ROTATE THROUGH THE GREAT LAKES REGION.

INITIAL NORTHERN STREAM SHORTWAVE APPROACHING FROM THE SOUTHWEST
COMBINED WITH SOME SURFACE HEATING HAS CAUSED SCATTERED SHOWERS AND
TSTMS TO DEVELOP ACROSS WI/IL/IN THIS AFTERNOON. A FEW OF THESE HAVE
PROMPTED WARNINGS FOR GOLF BALL SIZE HAIL. CONVECTION SHOULD BE
MOVING EAST/NORTHEAST INTO THE AREA THIS EVENING...BUT WILL LIKELY
WEAKEN AFTER DARK AS FAVORABLE THERMODYNAMICS ARE LOST. STILL...
THUNDER MAY NEED TO BE INCLUDED AT LEAST EARLY ON GIVEN THE LATEST
REPORTS UPSTREAM. MODEL FCST SOUNDINGS ACROSS SW MI TONIGHT EXHIBIT
VERY STEEP LAPSE RATES AS -28C 500MB COLD POOL AND NEGATIVE TILT
UPPER TROUGH COME THROUGH. INVERSION HEIGHTS REMAIN UP AROUND 20K
FEET MOST OF THE NIGHT AS WELL...AND WITH ADDITIONAL VORTICITY
MAXIMA APPROACHING FROM THE WEST LATER ON TONIGHT WILL EXPECT
SCATTERED TO NUMEROUS SHOWERS TO PERSIST.

MODELS INDICATE A DECREASE IN MOISTURE AND LOWERING OF INVERSION
HEIGHTS ON MONDAY... BUT AM NOT CONFIDENT ENOUGH TO RUN WITH A
COMPLETELY DRY FCST ATTM. MODEL TIMING/LOCATION OF SHORTWAVES HAS
NOT BEEN CONSISTENT FROM RUN TO RUN... AND WITH COLD POOL ALOFT SOME
SCATTERED DIURNAL SHOWER DEVELOPMENT MAY OCCUR. WILL CARRY A SMALL
CHANCE POP FOR THE AFTERNOON.

MODELS HAVE COME INTO BETTER AGREEMENT ON THE DEVELOPMENT OF A
POTENT WAVE TO OUR SOUTHWEST ON MONDAY NIGHT... BUT DISAGREE ON
PLACEMENT OF THE SURFACE LOW AS IT TRACKS NORTHEAST. PREFER A MORE
NORTHERN TRACK AS THIS IS A TYPICAL TREND THIS TIME OF YEAR. WITH
THAT IN MIND... WILL RUN WITH HIGH POPS FOR RAIN ACROSS ALL OF THE
CWFA MONDAY NIGHT AND TUESDAY. NOT OUT OF THE QUESTION THAT SOME WET
SNOW COULD MIX IN ON THE NORTHERN PERIPHERY OF THE SYSTEM... BUT
WILL NOT INCLUDE THAT AS A POSSIBILITY YET. MAIN CONCERN FOR THIS
WOULD BE IN THE HIGHER ELEVATIONS OF CENTRAL MICHIGAN WITH A
SLIGHTLY MORE NORTHERN TRACK.

GUIDANCE TEMPERATURES GENERALLY ACCEPTED... ALTHOUGH LOW TEMPS
PROBABLY TOO COOL NEAR THE LAKE GIVEN WESTERLY FLOW AND WATER TEMPS
NEAR 50.

MEADE

EXTENDED FORECAST DISCUSSION...
MEDIUM RANGE MODELS IN FAIR AGREEMENT WITH FEATURES EXPECTED TO
INFLUENCE OUR EXTENDED FORECAST PERIOD. UPPER RIDGING STARTS TO
BUILD IN BEHIND THE EARLY WEEK TROUGH ON WEDNESDAY WITH MODERATE
WARM ADVECTION IN THE MID AND UPPER LEVELS BY AFTERNOON. LOSS OF
CYCLONIC CURVATURE AND WARMING MID LAYER SHOULD HELP SCATTER OUT THE
CLOUD COVER ALLOWING FOR SOME SUNSHINE. WEDNESDAY NIGHT/THURSDAY
MORNING LOOKS TO BE THE COLDEST OF THE UPCOMING WEEK AS SFC HIGH
PRESSURE RIDGE ALLOWS FOR LIGHT WINDS UNDER CLEARING SKIES...WHICH
SHOULD ALLOW FOR WIDESPREAD FROST. SWRLY SFC FLOW INCREASES THURSDAY
AS RIDGE AXIS MOVES EAST. SHORTWAVE WILL RAPIDLY APPROACH FRIDAY IN
THE FAST-MOVING WRLY FLOW PATTERN ACROSS THE NRN U.S. TIMING OF THIS
FEATURE SOMEWHAT UNCERTAIN...WITH 12Z AVN ABOUT 8 TO 12 HOURS FASTER
WITH IT COMPARED TO PREVIOUS 00Z MRF RUN. WILL FOLLOW ENSEMBLES HERE
FOR A COMPROMISE AND BRING IN THE CHANCE FOR SHOWERS FRI AFTERNOON
THROUGH SAT MORNING. LOOKS LIKE MOISTURE WILL BE SCARCE WITH THIS
SYSTEM AND WOULD NOT BE SURPRISED TO SEE IT COME THROUGH THE REGION
DRY. SLIGHTLY COOLER AIR BEHIND IT FOR NEXT WEEKEND...BUT TEMPS WILL
LIKELY BE WITHIN 5 DEGREES OF CLIMATOLOGICAL NORMS (MID TO UPPER
50S/ MID TO UPPER 30S).

GREENE

.GRR...NONE.