Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 312242
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
645 PM EDT SUN AUG 31 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 322 PM EDT SUN AUG 31 2014

A WEAK AREA OF HIGH PRESSURE WILL KEEP MUCH OF THE REGION DRY INTO
THE EVENING. A COLD FRONT WILL APPROACH FROM THE WEST ON LABOR DAY
TRIGGERING SHOWERS AND THUNDERSTORMS. HIGH PRESSURE WILL RETURN
FOR TUESDAY DRYING THE REGION OUT.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 322 PM EDT SUN AUG 31 2014

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE POTENTIAL FOR
SEVERE WEATHER ON MONDAY. OVERALL THE POTENTIAL STILL EXISTS.

ONE POTENTIAL LIMITING FACTOR WILL BE WHAT IMPACTS THE DECAYING
AREA OF THUNDERSTORMS WILL HAVE AS IT MOVES IN FROM THE WEST
MONDAY MORNING. THE HRRR RUC SHOWS THIS SYSTEM WEAKENING WELL
BEFORE IT ARRIVES IN MI...SO I AM THINKING THIS WILL HAVE A
MINIMAL IMPACT ON THE POTENTIAL INSTABILITY MONDAY. THE
COMBINATION OF HEATING AND MOISTURE ADVECTION SUPPORTS CAPE OVER
1500 J/KG ON MONDAY. DEEP LAYER SHEAR INCREASES TOWARD 18Z AS THE
MID LEVEL WAVE CURRENTLY IN WI ARRIVES IN NW LOWER. THE LIFT
ASSOCIATED WITH THIS FEATURE SHOULD TRIGGER STORMS. THE SHEAR WILL
HELP TO INCREASE THE POTENTIAL FOR ORGANIZED CONVECTION AND
RESULTING SEVERE WEATHER. DAMAGING WINDS AND LARGE HAIL A THREAT.
SRH VALUES AROUND 200 M2/S2 DO SUPPORT A RISK FOR TORNADOES.

&&

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 322 PM EDT SUN AUG 31 2014

MEDIUM RANGE MODELS ARE IN DECENT AGREEMENT INTO NEXT WEEKEND...
HOWEVER THERE ARE TIMING DIFFERENCES WITH A STRONG COLD FRONT THAT
COMES THROUGH FRIDAY/FRIDAY NIGHT.

LARGE HIGH PRESSURE IS EXPECTED TO BE SITTING OVER THE EAST SEABOARD
BY MID WEEK.  THIS WILL BRING WARMING SOUTHERLY FLOW TO THE GREAT
LAKES REGION.  IT CONTINUES TO LOOK LIKE THURSDAY WILL BE THE
WARMEST DAY OF THE WEEK WITH 80S FOR HIGHS.  THE RISK FOR SHOWERS
AND STORMS WILL INCREASE ON THURSDAY WITH A COLD FRONT MOVING INTO
THE WESTERN GREAT LAKES. WARM AND MOIST AIR WITH MOVE IN AHEAD OF
THIS FRONT.  IF A LOW LEVEL JET COMES INTO PLAY WE COULD BE LOOKING
AT STRONG TO SEVERE STORMS TOWARD THE END OF THE DAY.

THERE CONTINUES TO BE TIMING DIFFERENCES WITH THE FRONT...BUT THE
GFS SLOWED THE FRONT DOWN...CLOSER TO THE WHAT THE ECMWF HAS SHOWN.
THEREFORE BELIEVE THE FRONT WILL BE COMING THROUGH ON FRIDAY WITH
ADDITIONAL CHANCES FOR SHOWERS AND STORMS.  MUCH COOLER AIR FOLLOWS
THIS STRONG FRONT FOR FRIDAY NIGHT AND INTO NEXT WEEKEND.  H8 TEMPS
DROP TO +7 TO +10C AS COMPARED TO AROUND +19C AHEAD OF THE COLD
FRONT.  THE WEEKEND SHOULD FEATURE HIGHS IN THE UPPER 60S TO MID 70S
WITH MAINLY DRY WEATHER.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 645 PM EDT SUN AUG 31 2014

SCATTERED SHOWERS MAY AFFECT OUR SOUTHEAST TERMINALS (KLAN AND
PERHAPS KBTL/KJXN) DURING THE EARLY TO MID EVENING HOURS TONIGHT
BEFORE DISSIPATING. MAINLY VFR CONDITIONS ARE ANTICIPATED OVERNIGHT
BUT SOME PATCHY MVFR CONDITIONS MAY DEVELOP DURING THE EARLY MORNING
HOURS MONDAY DUE TO LOW CLOUDS AND/OR FOG. CONDITIONS SHOULD THEN
GRADUALLY DETERIORATE TO MAINLY MVFR MONDAY MORNING DUE TO LOW
CLOUDS AND PATCHY FOG.

BY LATE MONDAY MORNING/EARLY AFTERNOON SSW WINDS WILL INCREASE WITH
GUSTS AROUND 20 TO 25 KTS. SCATTERED THUNDERSTORMS WILL ALSO DEVELOP
FROM LATE MONDAY MORNING THROUGH MONDAY AFTERNOON AS INSTABILITY
INCREASES AHEAD OF AN APPROACHING COLD FRONT. SCATTERED SHOWERS AND
THUNDERSTORMS WILL LINGER MONDAY EVENING.

&&

.MARINE...
ISSUED AT 322 PM EDT SUN AUG 31 2014

BEACH HAZARDS AND SCA ISSUED FOR MONDAY

&&

.HYDROLOGY...
ISSUED AT 322 PM EDT SUN AUG 31 2014

HIGH PWAT VALUES SUPPORT LOCALLY HEAVY RAIN ON MONDAY.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM MONDAY MORNING THROUGH MONDAY
     EVENING FOR MIZ037-043-050-056-064-071.

LM...SMALL CRAFT ADVISORY FROM 10 AM TO 10 PM EDT MONDAY FOR
     LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...JK
AVIATION...LAURENS
HYDROLOGY...MJS
MARINE...MJS






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