Severe Thunderstorm Warning 9, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
933 PM EDT WED APR 30 2003

INGREDIENTS ARE STILL THERE FOR A STRONG RETURN OF THE CONVECTION
...BEGINNING AROUND MIDNIGHT.  ALOFT OVER MI...THERE IS THE RIGHT
ENTRANCE REGION OF A 250 MB JET...PROVIDING FAVORABLE UPPER LEVEL
DIVERGENCE.  FURTHER DOWN THROUGH THE ATMOSPHERE...A 40 TO 50 KNOT
850 MB JET IS EXPECTED TO FORM UPSTREAM THIS EVENING...AND THEN
ARRIVE IN SOUTHWEST LOWER MICHIGAN AFTER MIDNIGHT.  ALREADY THIS
FEATURE WAS HELPING TO TRIGGER THE STORMS UPSTREAM ACROSS EASTERN IA
AND THE WINCHESTER IL PROFILER HAS PICKED IT UP WITH 850 MB WINDS
FROM THE SOUTHWEST AT 40 KNOTS.  WITH A LOW LEVEL NORTHEAST FLOW
ACROSS THE AREA TONIGHT...THE ARRIVAL OF THE LOW LEVEL JET WILL
BRING ON HIGH HELICITY VALUES.  HOWEVER THE CONVECTION IS EXPECTED
TO BECOME MORE ELEVATED AS IT APPROACHES SOUTHWEST LOWER MI AND
THEREFORE THE PRIMARY THREATS WOULD BE HAIL AND SOME HIGH WIND.
IN ADDITION...HEAVY RAIN IS EXPECTED.  THE LATEST RUC SHOWS
DIFFLUENT 1000/500 MB THICKNESS VALUES AFTER MIDNIGHT WITH NEARLY
UNIDIRECTIONAL FLOW THROUGH A DEEP LAYER.  A SHARP 850 MB THETA E
RIDGE ARRIVES AS WELL SO RAINFALL AMOUNTS OF 2 INCHES IN A FEW
PLACES APPEARS LIKELY  FLASH FLOOD GUIDANCE FROM THE RIVER FORECAST
CENTER SUGGESTS AMOUNTS OF AROUND 3 INCHES IN 3 HOURS ARE NEED
TO INITIATE SOME FLASH FLOODING SO NO WATCH WILL BE ISSUED AT
THIS TIME.

.GRR...NONE.

MJS

MIZ037>040-043>046-050>052-056>059-064>067-071>074-011000-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
845 PM EDT WED APR 30 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE SOUTHWEST QUARTER OF LOWER
MICHIGAN.

.DAY ONE....TONIGHT

THE STORM PREDICTION CENTER HAS PLACED MOST OF SOUTHWEST LOWER
MICHIGAN IN THE SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT.
SPECIFICALLY...THIS AREA IS SOUTH OF A WHITEHALL TO  MOUNT PLEASANT
LINE.  WHILE THE THUNDERSTORMS HAVE DIMINISHED EARLY THIS EVENING
...THEY ARE EXPECTED TO REDEVELOP AROUND MIDNIGHT FROM THE SOUTHWEST.
THE STRONGEST STORMS COULD PRODUCE HAIL UP TO AN INCH IN DIAMETER
AND WINDS TO 60 MPH.  ALSO...WHERE THE STORMS PERSIST...LOCALLY
EXCESSIVE RAIN COULD RESULT IN URBAN AND POOR DRAINAGE FLOODING.
LOCALLY 2 INCHES OF RAIN COULD FALL.  THE STORMS WILL BE MOVING EAST
NORTHEAST AT 35 MPH.  ONCE THE STORMS RETURN...THEY ARE EXPECTED TO
PERSIST THROUGH MUCH OF THE NIGHT.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A FEW THUNDERSTORMS MAY LINGER ON THURSDAY MORNING...BUT THESE
STORMS ARE NOT EXPECTED TO BE SEVERE. HIGH PRESSURE WILL BRING A DRY
WEEKEND...ALTHOUGH FROST AND FREEZING TEMPERATURES WILL BE POSSIBLE
AT NIGHT. A CHANCE OF SHOWERS AND THUNDERSTORMS WILL RETURN EARLY
NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS A DISTINCT POSSIBILITY AFTER MIDNIGHT.

MORE INFORMATION MAY BE OBTAINED AT THE FOLLOWING URL:
WWW.CRH.NOAA.GOV/GRR

MJS