000
FXUS63 KGRR 171915
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
332 PM EDT SAT MAY 17 2008
LATEST UPDATE...ALL BUT AVIATION...
.SYNOPSIS...(332 PM EDT SAT MAY 17 2008)
AS COLDER AIR FROM CANADA FILTERS IN...THE WEATHER
WILL REMAIN UNSETTLED OVER THE GREAT LAKES REGION INTO SUNDAY NIGHT.
WHILE MAINLY DRY WEATHER IS EXPECTED FOR THE MIDDLE PART OF NEXT
WEEK...THE COOL PATTERN IS EXPECTED TO PERSIST.
&&
.SHORT TERM...(332 PM EDT SAT MAY 17 2008)
(TONIGHT THROUGH MONDAY NIGHT)
THE MAIN CHALLENGE OVER THE SHORT TERM DEALS WITH THE CHANCE FOR
THUNDERSTORMS AND ANY SEVERE WEATHER POTENTIAL FOR TONIGHT.
THE ATMOSPHERE IS CHARACTERIZED BY LOW FREEZING AND -20 DEG C LEVELS
AND SEVERAL SHORTWAVES EMBEDDED IN A STRONGER NORTHWEST FLOW. ONE
SHORTWAVE AS OVER THE U.P. AND TRACKING SOUTHEAST. THE CONVECTION
AHEAD OF THIS WAVE LOOKS TO IMPACT MAINLY NORTHERN LOWER MICHIGAN.
MY NORTHERN COUNTIES COULD SEE SOME OF THESE STORMS. WITH STEEP MID
LEVEL LAPSE RATES AND STRONGER WINDS ALOFT AND ISOLATED SEVERE
THUNDERSTORM COULD OCCUR. HOWEVER WITH A LACK OF LOW LEVEL
MOISTURE IT APPEARS THE COVERAGE OF STRONGER CELLS WILL BE LIMITED.
GIVEN THE LOW FREEZING LEVEL...ANY THUNDERSTORM THAT DOES FORM COULD
PRODUCE PEA SIZE HAIL. THE STRONGEST SHORTWAVE ARRIVES AFTER 06Z
TONIGHT. THIS FEATURE SHOULD IMPACT MAINLY MY SOUTHERN COUNTIES.
THIS FEATURE IS RATHER ORGANIZED AS IT APPROACHES NRN MN WITH COLD
CLOUD TOPS ON IR IMAGERY. ELEVATED INSTABILITY ARRIVES OVERNIGHT SO
WE COULD SEE A THUNDER THREAT AS THIS WAVE PULLS THROUGH. I WILL
RAISE POPS FOR THE CWA AND MENTION SOME THUNDER THROUGH MIDNIGHT.
I DID NOT CHANGE MUCH WITH THE REST OF THE FORECAST. JUST SOME
MINOR TEMPERATURE CHANCES. WE WILL NEED TO MONITOR THE FROST/FREEZE
THREAT SUN NIGHT IF WE CAN CLEAR OUT AND DIMINISH THE WINDS.
&&
.LONG TERM...(332 PM EDT SAT MAY 17 2008)
(TUESDAY THROUGH FRIDAY NIGHT)
LOOKS LIKE A PATTERN CHANGE FOR THE EXTENDED PERIOD. THE GFS HAS
COME INTO MUCH BETTER AGREEMENT WITH THE ECMWF...WHICH HAS BEEN
PRETTY CONSISTENT RUN-TO-RUN FOR A WHILE NOW. THEY SHOW THE CURRENT
UPPER TROUGH OVER THE GREAT LAKES BEING REPLACED WITH A HIGH
AMPLITUDE RIDGE OVER THE PLAINS AND UPPER MISSISSIPPI VALLEY. AS THE
PATTERN CHANGES A WEAK SHORT WAVE WILL BE PASSING OVERHEAD ON
TUESDAY. WE/RE GOING TO RETAIN THE MENTION OF CHC POPS FOR THIS
FEATURE. AFTER THAT GOES BY A SFC HIGH WILL DEVELOP AND EXTEND FROM
NEAR JAMES BAY SOUTH TO THE DEEP SOUTH. THAT WILL INITIALLY KEEP A
COOL DRY CANADIAN AIRFLOW MOVING INTO THE CWA. THE NE WINDS WILL
PROBABLY KEEP TEMPS BELOW AVERAGE FOR THE MIDDLE OF NEXT WEEK. BUT
AS A SFC LOW IN THE PLAINS DEEPENS AND SOUTH FLOW STRENGTHENS
HEIGHTS WILL GRADUALLY RISE AND SFC TEMPS WILL RESPOND BY CLIMBING
INTO 70S BY SATURDAY. FORECAST SOUNDINGS SHOW A DRY PROFILE OVER THE
REGION AND A CAPPING INVERSION COURTESY OF THE UPPER RIDGE. BECAUSE
OF THIS WE DECIDED TO REMOVE POPS AFTER TUESDAY. THE SFC HIGH TO THE
NORTH SHOULD BE IN CONTROL AND CONVECTION IS EXPECTED REMAIN WEST OF
THE CWA. MEMORIAL DAY WEEKEND ACTUALLY LOOKS WARM AND SOMEWHAT SUNNY
AT THIS POINT.
&&
.MARINE...(332 PM EDT SAT MAY 17 2008)
SCA TONIGHT THROUGH 18Z SUNDAY. WHILE WAVES AND WINDS WERE
UNDER CRITERIA AT THIS TIME...AS COLDER AIR FLOWS IN OVER LAKE MI
VALUES WILL BE INCREASING. ADDED SOME THUNDER TO THE HAZARDOUS
WEATHER OUTLOOK FOR THE NEARSHORE WATERS.
&&
.AVIATION...(132 PM EDT SAT MAY 17 2008)
CU IS BUILDING RAPIDLY ACROSS INTERIOR PORTIONS OF SW LWR. WRN TAF
SITES WILL LIKELY REMAIN RAIN FREE...UNTIL LATER TONIGHT WHEN
ANOTHER SHORT WAVE DROPS SOUTH AND GIVES US A CHANCE OF LIGHT RAIN
AGAIN. STEEP LAPSE RATES WILL GENERATE SOME THUNDER ACROSS INTERIOR
LOWER MICHIGAN THIS AFTERNOON. ADDED VCTS TO THE TAF SITES. THUNDER
THREAT WILL DIMINISH WITH SUNSET. GENERALLY VFR CONDITIONS EXPECTED.
&&
.HYDROLOGY...(332 PM EDT SAT MAY 17 2008)
NO HYDRO ISSUES EXPECTED SINCE ANY RAINFALL THROUGH THIS WEEKEND
WILL BE LIGHT AND NOT SIGNIFICANT ENOUGH TO RESULT IN ANY HYDRO
ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY IN EFFECT TONIGHT THROUGH
18Z SUN.
&&
$$
SYNOPSIS: MJS
SHORT TERM: MJS
LONG TERM: 93
MARINE MJS
AVIATION: 93
HYDROLOGY: MJS
