Severe Thunderstorm Warning 80, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
405 PM EDT FRI SEP 7 2001

SCATTERED SHRA/TSRA SHOULD CONTINUE INTO THE EVENING HOURS BEFORE
BEST HEATING IS LOST.  LINE OF STORMS OVER WISCONSIN WAS WEAKENING
AS IT PULL AWAY FROM BEST DYNAMICS WITH THE LOW LEVEL JET PUSHING
INTO THE U.P.  STILL... NORTHWESTERN COUNTIES COULD GET CLIPPED BY
THIS ACTIVITY THIS EVENING.  MEANWHILE CURRENT LAPS CAPES OVER FAR
SOUTHERN MI HAS ROCKETED UP TO 2500 J/KG AND SCATTERED INDIANA
CONVECTION SHOULD SPREAD INTO THE CWA THIS EVENING.  NEXT IN THE
SERIES OF SHORT WAVES TO TRACK INTO THE UPPER MIDWEST BY EARLY
MORNING.  LOW LEVEL JET ASSOCIATED WITH THIS FEATURE IS POINTING
TOWARD CENTRAL LAKE MICHIGAN BY DAYBREAK.  WEAK SPEED MAX AT H3
PULLS NORTHWARD ACROSS LAKE MICHIGAN BY MORNING WHICH SHOULD PRODUCE
SOME UPPER DIVERGENCE.  WILL GO WITH LIKELY POPS OVER THE
NORTHWESTERN COUNTIES DUE TO THIS ONE/TWO PUNCH OF PCPN...ELSEWHERE
WILL CARRY CHC POPS.  WITH DEW POINTS HOVERING AROUND 70 TEMPS
SHOULD NOT FALL BLO THIS MARK TONIGHT.

SATURDAY SHOULD BE A SIMILAR DAY AS TODAY WITH SCATTERED CONVECTION
AROUND DURING THE EARLY MORNING WITH THE ABOVE MENTIONED SHORT
WAVE.  THIS WAVE AND ITS LOW LEVEL JET PULLS NORTHEAST INTO LAKE
SUPERIOR BY LATE DAY...WHICH SHOULD ONCE AGAIN SPELL A BREAK IN THE
PCPN FOR SW MI.  AMOUNT OF SUNSHINE WILL AGAIN BE A TOUGH CALL AS
LOW LEVEL MOISTURE CONTINUES TO DEEPEN THRU THE DAY.  THIS WILL HAVE
A MAJOR AFFECT ON THE TEMP FORECAST AS WELL AS THE CHC FOR SCATTERED
CONVECTION REDEVELOPING DURING AFTERNOON HEATING.  WILL GO MIDDLE OF
THE ROAD FOR NOW...TEMPS AROUND 80...MOSTLY CLOUDY/PARTLY
SUNNY...WITH CHC POPS.

SURFACE COLD FRONT FINALLY MAKES IT INTO THE CWA LATE SATURDAY
NIGHT.  LACK OF ANY UPPER SHORT WAVE...LOW LEVEL JET...OR UPPER JET
DYNAMICS WITH THE FRONTAL PASSAGE LEADS ME TO BELIEVE
SHOWERS/THUNDERSTORMS SHOULD BE SCATTERED WITH THE NIGHT TIME
FRONT.  CHC POPS ONCE AGAIN.

BY SUNDAY THE COLD FRONT SHOULD SLIDE EAST AS THE UPPER TROF STILL
LURKS TO OUR WEST.  SUBSIDENCE AND NVA MOVES ACROSS THE REGION EARLY
DURING THE DAY LEADING TO PARTIAL CLEARING BEHIND THE FRONT.  AGREE
WITH ETA/S EVOLUTION OF YET ANOTHER WAVE WRAPPING AROUND THE BASE OF
THE UPPER TROF AND HEADING OUR WAY BY LATE DAY.  WILL CARRY CHC POPS
IN THE FAR SOUTHERN COUNTIES FOR AFTERNOON/EVENING SHOWERS RETURNING
AS GOOD ISENTROPIC LIFT IS SHOWN JUST SOUTH OF THE CWA BY 00Z.  BEST
LIFT MOVES ACROSS THE SOUTHERN PORTION OF THE CWA OVERNIGHT...WHERE
LIKELY POPS WILL BE USED...CHC POPS NORTH.  TEMPS WILL REMAIN
MODERATE AS COOLEST AIR WILL NOT MOVE IN UNTIL UPPER TROF HAS
PASSED.

JK

EXTENDED FORECAST DISCUSSION...
EACH MODEL RUN SLOWS DOWN THE TRAILING WAVE ASSOCIATED WITH LATEST
LONGWAVE TROUGH MOVING THROUGH THE GREAT LAKES.  THE TREND ON MOST
OF THE MODELS IS FOR A SOUTHERN STREAM WAVE TO BE MORE CLOSED OFF
WITH EACH RUN. THIS TREND WOULD MOVE A DECENT SURFACE LOW NORTHEAST
INTO MICHIGAN IN THE MONDAY TIME FRAME.  THE ETA SEEMS STRONGEST
WITH THIS IDEA BUT THE CANADIAN...AVN...AND ETA HAVE ALL BEEN
TRENDING THAT WAY FOR SEVERAL RUNS IN A ROW NOW.  I FEEL STRONGLY A
WAVE WILL FORM ON THE FRONT SUNDAY... THEN MOVE ACROSS LOWER
MICHIGAN DURING MONDAY.  THIS WILL KEEP SOUTHWEST MICHIGAN IN THE
WARM AIR INTO MONDAY EVENING... AND KEEP THE POTENTIAL FOR VERY WET
THUNDERSTORMS GOING THROUGH MONDAY.  WITH SUBTROPICAL AIR IN PLACE
AND A POSSIBLE CLOSED UPPER LOW BRINGING SUBTROPICAL AIR OVER A
FRONTAL SYSTEM NEARLY STATIONARY OVER SOUTHWEST MICHIGAN... THE
THREAT FOR VERY HEAVY RAINFALL EXISTS MONDAY WITH THIS SYSTEM AND WE
WILL HAVE TO MONITOR THIS SYSTEM FOR THAT POTENTIAL.  THE GOOD NEWS
IS RIVER LEVELS ARE STILL LOW. SINCE THE SOUTHERN STREAM SEEMS TO
STAY IN CONTROL OF OUR WEATHER THROUGH THE WEEK... SO HIGH AND LOW
TEMPERATURES WILL BE WARMER THAN THE MRF MOS FORECASTS THROUGH THE
FORECAST PERIOD.  IT STILL SEEMS THERE WILL BE A DRY PERIOD TOWARD
THE MIDDLE OF THE WEEK... BUT THEN ANOTHER NORTHERN STREAM WAVE WILL
INTERACT WITH ANOTHER SOUTHERN STREAM WAVE TO BRING THE CHANCE FOR
MORE SHOWERS AND THUNDERSTORMS FRIDAY. SEEMS AT THIS TIME THAT
SOUTHWEST MICHIGAN WILL BE ON THE SOUTHERN EDGE OF THIS SYSTEM AND
GIVEN WHAT HAS BEEN HAPPENING OF LATE... I COULD SEE SOUTHWEST
MICHIGAN BEING DEEPER IN THE WARM AIR AND MOST OF THE FRIDAY
PRECIPITATION STAYING NORTH OF US.

WDM

.GRR...NONE