194
FXUS63 KGRR 042257
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
655 PM EDT SAT JUL 4 2009
LATEST UPDATE...AVIATION...
SYNOPSIS
(628 PM EDT SAT JUL 4 2009)
LOW PRESSURE WILL MOVE SOUTHEAST OF LOWER MICHIGAN THIS EVENING AND
ALLOW SKIES TO CLEAR OUT ACROSS THE AREA. A WEAK COLD FRONT WILL
MOVE ACROSS LOWER MICHIGAN SUNDAY EVENING. THERE COULD BE A FEW
ISOLATED SHOWERS OR THUNDERSTORMS WITH THIS FRONT LATE SUNDAY
AFTERNOON INTO SUNDAY EVENING BUT MOST AREAS WILL REMAIN DRY.
SHORT TERM
(628 PM EDT SAT JUL 4 2009)
(TONIGHT THROUGH MONDAY NIGHT)
ONLY FORECAST ISSUE IN THE NEAR TERM IS FOR SLIGHT CHANCE POPS
SUNDAY AFTERNOON/EVENING.
WE HAVE GONE AHEAD AND UPDATED THE ZONES AND GRIDS TO PULL OUT THE
SHOWER MENTION FOR TONIGHT. MAIN AREA OF RAINFALL FROM CHICAGO TO
NORTHERN INDIANA IS MOVING AWAY FROM THE AREA. ISOLATED SHOWER
THREAT HAS PRETTY MUCH ENDED ACROSS THE CWFA WITH SKIES CLEARING AND
ANY DIURNAL INSTABILITY NOW ON THE WANE.
CURRENT DEW POINTS ARE IN THE UPPER 40S TO MID 50S...AND THE 12Z
GUIDANCE HAS TRENDED A BIT DRIER IN THE LOWER LEVELS...SO DROPPED
THE MENTION OF FOG OVERNIGHT. THERE STILL COULD BE SOME LIGHT FOG
ACROSS THE SOUTHERN FORECAST AREA WHERE DEW POINTS WILL BE HIGHER.
FOR SUNDAY AND SUNDAY NIGHT...ISOLATED SHOWERS AND THUNDERSTORMS
EXPECTED TO ATTEND THE PASSAGE OF SLOW MOVING FRONT BEGINNING UP
NORTH IN THE LATE AFTERNOON AND THE REST OF THE FORECAST AREA IN THE
EVENING. MOISTURE AND INSTABILITY ARE LIMITED BUT THERE IS GOOD LOW
LEVEL CONVERGENCE ALONG THE FRONT WHICH MAY BE ABLE TO TRIGGER A FEW
SHORT LIVED UPDRAFTS.
FAIR WEATHER UNDER WEAK SFC RIDGING FOR MONDAY AND MONDAY NIGHT.
LONG TERM
(307 PM EDT SAT JUL 4 2009)
(TUESDAY THROUGH SATURDAY)
MAIN FCST CONCERN IN THE LONG TERM WILL BE PCPN POTENTIAL FROM LATE
TUE NIGHT THROUGH FRI NIGHT.
UPPER CONFLUENT FLOW IS EXPECTED TO BE OVERHEAD TUE MORNING IN
BETWEEN THE UPPER LOW TO OUR EAST AND THE UPPER RIDGE TO OUR WEST.
THIS SHOULD BRING A DRY AND MILD DAY TO THE AREA FOR TUE. UPPER
RIDGE AXIS WILL SLOWLY SHIFT TOWARD THE AREA BY WED.
DEVELOPING WARM FRONT TO OUR WEST AND SOUTHWEST COULD BECOME AN
ISSUE BEGINNING ON TUE NIGHT. MOST OF THE GLOBAL MODELS INDICATE THE
RIDGING WILL BE STRONGER AND KEEP MOST OF ANY STORM/MCS ACTIVITY TO
OUR NORTH FROM THE TUE NIGHT THROUGH THU TIME FRAME. GFS HAS BEEN
INDICATING ON AND OFF FOR A FEW DAYS NOW THAT A SERIES OF MCS
ACTIVITY COULD AFFECT THE AREA LATE TUE NIGHT THROUGH WED NIGHT WITH
THE WARM FRONT IN THE AREA.
WITH THE CONSENSUS FOR NOW SHOWING MAINLY DRY CONDITIONS AND THE
CONVECTIVE FEEDBACK ISSUES OF THE GFS...WE WILL HOLD THE DRY FCST
FOR NOW. WE WILL ADD IN A CHC OF SHOWERS AND STORMS FOR THE FRI AND
FRI NIGHT TIME FRAME AS THERE HAS BEEN GOOD RUN TO RUN CONTINUITY
SHOWING THIS FRONT COMING THROUGH AS A STRONGER WAVE HELPS TO BREAK
DOWN THE RIDGE. DRY CONDITIONS SHOULD RETURN ON SAT AS THE FRONT
SINKS SOUTH OF THE AREA.
TEMPS WILL GRADUALLY WARM FROM TUE THROUGH FRI. WE COULD SEE TEMPS
REACH 90 BY FRI AFTERNOON...AHEAD OF THE COLD FRONT WITH H850 TEMPS
INCREASING TO AROUND 20C. TEMPS WILL COOL OFF INTO THE LOWER 80S FOR
SAT BEHIND THE FRONT.
AVIATION
(655 PM EDT SAT JUL 4 2009)
MAIN ISSUE WILL BE THE EXTENT OF THE FOG THAT DEVELOPS TONIGHT.
OTHERWISE I EXPECT VFR CIGS/VIS THROUGH SUNDAY NIGHT.
SKIES ARE CLEARING THIS EVENING AND WITH THE SURFACE RIDGE OVERHEAD
TONIGHT I WOULD EXPECT NEARLY CLEAR SKIES AND LIGHT WINDS. SINCE
THERE WAS NO RAIN TODAY...IT SEEMS TO ME THE ODDS FOR DENSE FOG
FORMATION ARE RATHER LOW OVERNIGHT. EVEN SO...SOME LIGHT MIST
(BR) IS POSSIBLE TOWARD SUNRISE AT MOST TAF SITES.
VFR CONDITIONS WILL PREVAIL SUNDAY. ANY CU WOULD WIDELY SCATTED AND
ACTUALLY MODEL SOUNDING FROM NAM LOOK RATHER UNFAVORABLE FOR CU
SUNDAY AFTERNOON. ANY CLOUDS WITH FRONT WOULD BE HIGH BASED SO THEY
WERE NOT PUT IN THE TAF.
MARINE
(1250 PM EDT SAT JUL 4 2009)
AN ISOLATED THUNDERSTORM IS POSSIBLE SUNDAY EVENING. OTHERWISE
TRANQUIL WEATHER EXPECTED THROUGH THE WEEKEND WITH LIGHT WINDS AND
WAVES. PATCHY FOG WILL BE POSSIBLE LATE TONIGHT.
HYDROLOGY
(1250 PM EDT SAT JUL 4 2009)
NO WIDESPREAD RAIN EXPECTED UNTIL AT LEAST WEDNESDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LM...NONE.
SYNOPSIS: OSTUNO/NJJ
SHORT TERM: OSTUNO/NJJ
LONG TERM: NJJ
AVIATION: WDM
MARINE: OSTUNO
HYDROLOGY: OSTUNO
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