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000
FXUS63 KGRR 131124
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
724 AM EDT MON MAY 13 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EDT MON MAY 13 2013

THE UPPER TROUGH RESPONSIBLE FOR THE COLD WEATHER ACROSS THE GREAT
LAKES WILL MOVE EAST TODAY ENABLING A WARM UP TO BEGIN. TEMPERATURES
WILL WARM INTO THE 70S AND 80S BY MID WEEK THAT WILL CARRY OVER INTO
NEXT WEEKEND. LOW CHANCES FOR SHOWERS AND THUNDERSTORMS EXIST AS
WELL BUT MOST OF THE WEEK WILL BE DRY.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 330 AM EDT MON MAY 13 2013

FORECAST CONCERNS ARE MINIMAL THIS MORNING AND MAINLY DEAL WITH THE
PASSAGE OF A COLD FRONT TUESDAY NIGHT.

THE FREEZE WARNING WILL EXPIRE AT 8 AM. TEMPERATURES ARE IN THE
UPPER 20S ACROSS THE NRN CWA BUT WILL WARM INTO THE 50S TODAY WITH
ABUNDANT SUNSHINE.

A WARM FRONT WILL APPROACH TONIGHT AND MAY LEAD TO A FEW SHOWERS AS
A RIBBON OF LOW CONDENSATION PRESSURE DEFICITS MOVES ACROSS THE CWA.
A TROUGH AHEAD OF THE NEXT COLD FRONT WILL CROSS LAKE MICHIGAN
TUESDAY AFTERNOON/EVENING. THIS MAY LEAD TO A FEW THUNDERSTORMS.
MODELS SHOW GOOD INSTABILITY AHEAD OF THE TROUGH WITH MUCAPE AROUND
2K J/KG AND LI/S WELL BELOW 0C. MOISTURE MAY BE A LIMITING FACTOR.
HOWEVER THERE IS A STRONG SURGE OF WARM AIR ALOFT WITH H8 TEMPS NEAR
20C APPROACHING AND THIS TYPE OF WAA FREQUENTLY LEADS TO SOME
STORMS. WE/LL CARRY A CHC OF TSRA THROUGH WEDNESDAY AS THE TRAILING
COLD FRONT SHOULD MOVE THROUGH THEN.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 AM EDT MON MAY 13 2013

THE BIG STORY FOR THIS TIME PERIOD WOULD BE A SIGNIFICANT
RAIN/THUNDERSTORM EVENT NEXT WEEKEND.

THE BIGGEST CHANGES I MADE TO THE FORECAST DURING WEDNESDAY NIGHT
THROUGH SUNDAY TIME PERIOD WAS TO DRY OUT THE WEDNESDAY THROUGH
FRIDAY TIME PERIOD AS NOW BOTH THE ECMWF AND GFS ARE SIMILAR ON
BRINGING THE COLD FRONT FARTHER SOUTH DURING THIS TIME PERIOD. I
INCREASED THE POP OVER THE WEEKEND AS BOTH MODELS ARE BRINGING A
LEAD WAVE FROM THE NEXT BIG PACIFIC STORM INTO THE WESTERN GREAT
LAKES. THE PRIMARY SYSTEM WOULD COME IN EARLY THE FOLLOWING WEEK.

MY CONFIDENCE IN THIS FORECAST IS INCREASING DUE TO THE PERSISTENCE
OF THE GFS TO FORECAST THE SAME PATTERN WITH MID WEEK AND WEEKEND
STORM SYSTEMS AND THAT THE ECMWF NOW SEEMS TO BE FOLLOWING THE GFS
WITH BOTH OF THESE FEATURES.

THE OVERALL PATTERN REMAINS AS I HAVE BEEN WRITING ABOUT... THE
UPPER LEVEL FLOW BECOMES MORE ZONAL EARLY NEXT WEEK ONLY TO AMPLIFY
ONCE AGAIN NEXT WEEKEND AS A STRONG PACIFIC STORM ...NOW DEPARTING
JAPAN...CROSSES THE NORTH PACIFIC AROUND 40N...MOVING UNDER THE
SYSTEM STALLED IN THE GULF OF ALASKA IN THE THURSDAY TO FRIDAY TIME
FRAME...THEN HEADS EAST INTO THE WESTERN CONUS DURING THE WEEKEND.
THAT SYSTEM FORCES THE SYSTEM IN FRONT OF IT TO MOVE ACROSS THE
GREAT LAKES OVER THE WEEKEND WHILE IT ALSO IS BUILDING AN UPPER
RIDGE OVER THE CENTRAL PLAINS IN FRONT OF IT. WHAT ALL THIS DOES IS
ALLOWS THE WEDNESDAY SYSTEM COLD FRONT TO GET SOUTH OF INTERSTATE 80
AND IN SO DOING ALLOWS FOR DRY BUT SEASONABLY MILD TEMPERATURES TO
PREVAIL THURSDAY NIGHT INTO FRIDAY. THE SYSTEM THAT BRINGS RAIN TO
THE AREA NEXT WEEKEND IS THAT LEAD WAVE BUT IT IS RATHER WEAK. ON
THE OTHER HAND IT DOES HAVE A COUPLED JET TO HELP THE CAUSE SO WE
SHOULD SEE SOME CONVECTION WITH SIGNIFICANT BUT NOT EXCESSIVE
RAINFALL FROM IT. WHAT WILL BE A MORE SIGNIFICANT EVENT FOR
SOUTHWEST MICHIGAN IS WHEN THE SYSTEM FROM JAPAN GETS HERE EARLY IN
THE FOLLOWING WEEK. THAT MAY HAVE STRONG THUNDERSTORMS AND VERY
HEAVY RAINFALL.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 721 AM EDT MON MAY 13 2013

VFR THROUGH MIDNIGHT. SHOWERS AHEAD OF THE WARM FRONT WILL LIKELY
BRING MVFR VSBY TOWARD 10Z TO THE WESTERN TAF SITES AND THAT WILL
REACH THE EASTERN TAF SITES AFTER 12Z. I DO NOT EXPECT
THUNDERSTORMS AS THERE IS AN INVERSION JUST ABOVE 15000 FT AGL
THAT WILL LIMIT HOW HIGH THE ECHO TOPS CAN GET.

&&

.MARINE...
ISSUED AT 330 AM EDT MON MAY 13 2013

HIGH PRESSURE OVER THE LAKE WILL RESULT IN NW WINDS 5-15 KNOTS TODAY
AND WAVES LESS THAN 3 FEET.


&&

.FIRE WEATHER...
ISSUED AT 330 AM EDT MON MAY 13 2013

DEW POINTS WILL DROP INTO THE TEENS THIS AFTERNOON AS GOOD MIXING
CONDITIONS DEVELOP. THIS WILL RESULT IN MIN RH VALUES AROUND 20
PERCENT OVER THE NRN HALF OF THE CWA.

&&

.HYDROLOGY...
ISSUED AT 330 AM EDT MON MAY 13 2013

NO HYDRO CONCERNS TODAY AS APPRECIABLE RAIN IS NOT EXPECTED IN THE
NEAR TERM.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR MIZ037>040-
     043>046-050>052-056>059-064>067-071>074.

LM...NONE.
&&

$$

SYNOPSIS...93
SHORT TERM...93
LONG TERM...WDM
AVIATION...WDM
FIRE WEATHER...93
HYDROLOGY...93
MARINE...93