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000
FXUS63 KGRR 210723
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
323 AM EDT TUE MAY 21 2013

LATEST UPDATE...
SYNOPSIS/SHORT TERM/LONG TERM/FIRE WEATHER/HYDRO/MARINE

.SYNOPSIS...
ISSUED AT 323 AM EDT TUE MAY 21 2013

LOW PRESSURE OVER MINNESOTA THIS MORNING WILL SLOWLY MOVE ACROSS THE
GREAT LAKES REGION THROUGH WEDNESDAY NIGHT.  THIS SYSTEM WILL
PRODUCE PERIODS OF SHOWERS AND THUNDERSTORMS.  MUCH COOLER AIR WILL
ARRIVE BY THURSDAY AS THE RAIN GRADUALLY COMES TO AN END.

THE END OF THE WEEK AND INTO THE HOLIDAY WEEKEND LOOKS MAINLY DRY.
TEMPERATURES SHOULD GRADUALLY WARM TO AROUND NORMAL VALUES BY
MEMORIAL DAY.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 323 AM EDT TUE MAY 21 2013

A BAND OF SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE CWA EARLY
THIS MORNING.  THIS AREA WAS DRIVEN BY A WEAKENING LOW LEVEL JET AS
WELL AS UPPER DIVERGENCE FROM THE UPPER JET.  THE UPPER FORCING WILL
ALSO WEAKEN EARLY THIS MORNING.  SO EXPECT THE PCPN TO GRADUALLY
BREAK UP AND ANY STORMS WILL GRADUALLY WEAKEN TOWARD DAYBREAK.

FEEL THE THREAT FOR SEVERE WEATHER HAS DIMINISHED TODAY...ALTHOUGH
IT CAN NOT BE COMPLETELY RULED OUT.  THE SURFACE LOW BECOMES BAGGIER
AS IT MOVES ACROSS WISCONSIN AND NO LONGER SUPPORTS A FOCUSED LOW
LEVEL JET.  MEANWHILE THE RIGHT ENTRANCE REGION OF THE UPPER JET
WILL BE FOCUSED TO OUR SOUTH OVER IL/IN.  SO ANY STRONG DYNAMIC
FORCING IS MUCH WEAKER TODAY AS COMPARED TO YESTERDAY.  HOWEVER WE
ARE PROGGED TO BECOME RATHER UNSTABLE...ESPECIALLY OVER THE EASTERN
CWA.  THE WILD CARD WILL BE HOW LONG THE DEBRIS CLOUDS HOLD IN...AND
WHETHER WE CAN REALIZE THIS INSTABILITY.  IF WE CAN BREAK OUT AND
THE MORNING CONVECTIVE LEAVES A FEW BOUNDARIES...SEVERE POTENTIAL
WILL INCREASE ESPECIALLY EAST OF U.S. 131.

FEEL ANY RISK OF SEVERE STORMS WILL WIND DOWN QUICKLY THIS EVENING
AS THE SURFACE LOW BRINGS IN DEEP MOISTURE...BUT DIMINISHING
INSTABILITY.  STRONG INDICATION THAT A VORT MAX WILL ROTATE AROUND
THE UPPER LOW AND MOVE INTO LOWER MI LATE TONIGHT.  THIS SHOULD
BRING AN EXPANDING AREA OF SHOWERS AND STORMS TO SW MI AFTER
MIDNIGHT...BUT SEVERE STORMS ARE NOT EXPECTED.

THE DEEP MOISTURE LINGERS OVER THE CWA WED AND WED NIGHT.  WE WILL
HAVE TO WATCH HOW THIS UNFOLD AS THE RISK TURNS TO THE POTENTIAL FOR
HEAVY RAIN.  IF THESE RAINS WERE TO FOCUS IN ONE PARTICULAR AREA...
LOCALIZED FLOODING COULD OCCUR.

THE SURFACE LOW AND IT/S COLD FRONT FINALLY EXITS THE CWA ON
THURSDAY.  STILL LOOKS LIKE QUITE A WET DAY OVER THE SOUTHERN CWA.
HOWEVER CLEARING SHOULD ARRIVE FOR NORTHERN AREAS BY LATE IN THE
DAY.  TEMPS WILL BE MUCH COOLER...WITH MID 60S IN AREAS THAT SEE
SOME SUN...BUT ONLY UPPER 50S IN THE WETTER SOUTH.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 323 AM EDT TUE MAY 21 2013

THERE ARE TWO SIGNIFICANT WEATHER ISSUES WE ARE TRACKING. THE FROST
ISSUE UP NORTH SATURDAY MORNING AND THE THREAT OF SHOWERS AND
THUNDERSTORMS SATURDAY INTO SUNDAY.

THE LARGE SCALE PICTURE FEATURES TROUGHS ON BOTH COASTS OVER THE
WEEKEND WITH A LARGE SCALE MEAN RIDGE OVER CENTRAL NORTH AMERICA
FROM TEXAS NORTH INTO CENTRAL CANADA.  THE PACIFIC SYSTEM THAT
CLOSES OFF A LOW OVER THE PACIFIC NORTHWEST SENDS A SHORTWAVE OVER
OVER THE TOP OF THE RIDGE AND CREATES A WAVE ON THE FRONT THAT IF
THE ECMWF FROM THE 12Z RUN WERE CORRECT WOULD BRING RAIN AND THE
THREAT OF THUNDERSTORMS TO THE AREA SATURDAY INTO SUNDAY.  THE GFS
KEEPS THIS SYSTEM SOUTH OF THE AREA.  BASED ON CONTINUITY OVER THE
PAST FEW DAYS I AM FAVORING THE DRY SOLUTION OF THE GFS.

THAT WOULD ALLOW FOR COLDER TEMPERATURES FRIDAY NIGHT /SATURDAY
MORNING AND MAINTAIN THE THREAT FOR FROST. IT WOULD ALSO MEAN PARTLY
SUNNY SKIES AND COOL TEMPERATURE THROUGH THE MEMORIAL DAY WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1150 PM EDT MON MAY 20 2013

SHOWERS AND THUNDERSTORMS WILL OVERSPREAD LOWER MICHIGAN BETWEEN
06Z AND 08Z. THESE STORMS SHOULD BRING AREAS OF MVFR CONDITIONS
AND POSSIBLY BRIEF IFR THROUGH 10 TO 12Z. THEN SCATTERED SHOWERS
AND THUNDERSTORMS ARE EXPECTED FOR MUCH OF TUESDAY.

&&

.MARINE...
ISSUED AT 323 AM EDT TUE MAY 21 2013

SOUTHERLY FLOW WILL GRADUALLY WEAKEN OVER THE NEXT COUPLE OF DAYS AS
A SURFACE LOW MOVES TOWARD THE LAKE.  HOWEVER NORTHERLY WINDS WILL
INCREASE ON THE BACK SIDE OF THE LOW.  WE MAY NEED A SCA BY THURSDAY.

&&

.FIRE WEATHER...
ISSUED AT 323 AM EDT TUE MAY 21 2013

THE AREA WILL SEE PERIODS OF RAIN THROUGH THURSDAY.  OVER AN INCH OF
RAIN IS LIKELY KEEPING THE FIRE RISK LOW.

&&

.HYDROLOGY...
ISSUED AT 323 AM EDT TUE MAY 21 2013

PERIODS OF HEAVIER RAIN IS EXPECTED BY LATE TONIGHT AND SHOULD
LINGER UNTIL THURSDAY.  IF THIS SETS UP OVER THE SAME AREAS WE MAY
SEE LOCALIZED FLOODING.  A FLOOD WATCH MAY NEED TO BE CONSIDERED IF
A FOCUSED AREA OF HEAVY RAIN IS EXPECTED.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...OSTUNO
FIRE WEATHER...JK
HYDROLOGY...JK
MARINE...JK