Issued by NWS Grand Rapids, MI
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000 FXUS63 KGRR 292018 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 345 PM EDT SAT AUG 29 2009 LATEST UPDATE...ALL SECTIONS EXCEPT AVIATION... .SYNOPSIS...(345 PM EDT SAT AUG 29 2009) LOW PRESSURE OVER THE EASTERN GREAT LAKES WILL CONTINUE TO SUPPLY CHILLY AIR AND SCATTERED SHOWERS TONIGHT. HOWEVER THE LOW WILL DRIFT EAST AND THE WEATHER WILL GRADUALLY IMPROVE SUNDAY INTO THE FIRST PART OF THE WORK WEEK. SUNSHINE WILL RETURN LATER SUNDAY. THEN TEMPERATURES WILL WARM TO AROUND 70 BY MONDAY. && .SHORT TERM...(345 PM EDT SAT AUG 29 2009) (TONIGHT THROUGH MONDAY NIGHT) WE WILL SEE SYNOPTIC SHOWERS PIVOTING AROUND A SHORT WAVE THAT WILL COME ACROSS THE REGION OVERNIGHT. THESES SHOWERS WILL BE ENHANCED BY LAKE MICHIGAN AS A H8 THERMAL TROUGH CROSSES THE LAKE. THE MEAN LAYER WINDS PIVOT FROM 295-300 THIS EVENING TO 340-345 AFTER MIDNIGHT SO WILL CARRY THE HIGHEST POPS DOWNSTREAM FROM THIS FLOW TONIGHT. THE SHORT WAVE WILL BE MOVING INTO THE EASTERN PORTION OF THE STATE BY SUNDAY MORNING. THERE COULD BE A FEW LINGERING SHOWERS OVER THE EASTERN CWA...BUT THESE SHOULD MOVE OUT BY MID DAY. THE LAKE EFFECT SHOWERS SHOULD CONTINUE HOWEVER. THE FLOW REMAINS 340-345 ALL DAY...SO SHOWERS WILL HUG THE COAST AND MAINLY COME INLAND OVER ALLEGAN AND VAN BUREN COUNTIES. DRIER AIR...SUBSIDENCE AND ANTICYCLONIC FLOW GRADUALLY SETTLES IN AS THE WAVE EXITS...SO THE LAKE EFFECT SHOULD SLOWLY DIMINISH IN INTENSITY AND COVERAGE THROUGH THE AFTERNOON. OTHERWISE MUCH DRIER AIR ARRIVES FROM NORTHERN ONTARIO AND WE WILL SEE A CLEARING TREND FROM NW TO SE INTO THE AFTERNOON. WITH THE AFTERNOON SUNSHINE TEMPS SHOULD WARM COMPARED TO TODAY/S READINGS...INTO THE MID AND UPPER 60S. PATCHY FROST COULD BE POSSIBLE ACROSS THE NORTHERN PORTIONS OF THE CWA SUNDAY NIGHT. THE MUCH DRIER AIR MASS WILL ALLOW FOR MOSTLY CLEAR SKIES AND GOOD RADIATIONAL COOLING CONDITIONS. AREAS AWAY FROM LAKE MICHIGAN AND NORTH OF HIGHWAY 20 COULD SEE LOWS DIP INTO THE 30S. WE WILL BE UNDER HIGH PRESSURE MONDAY AND MONDAY NIGHT WITH THE DRY AIR MASS STILL IN PLACE. THIS WILL ALLOW FOR A LARGE DIURNAL TEMPERATURE SWING. TEMPS WILL RECOVER TO AROUND 70 ON MONDAY...AND DIP BACK TO THE LOW AND MID 40S MONDAY NIGHT UNDER MOSTLY CLEAR SKIES. && .LONG TERM...(345 PM EDT SAT AUG 29 2009) (TUESDAY THROUGH SATURDAY) THE MID RANGE MODELS ARE IN GOOD AGREEMENT OVER THE LONG TERM WITH DRY WEATHER UNDER HIGH PRESSURE. ONLY SMALL TWEAKS MADE TO GRIDS. TEMPERATURES WILL BE BELOW NORMAL TUESDAY AND TUESDAY NIGHT. THEY WILL WARM TO AROUND NORMAL WEDNESDAY THROUGH SATURDAY. NORMALS ARE IN THE MID 50S FOR LOWS AND IN THE MID TO UPPER 70S FOR HIGHS. && .AVIATION...(100 PM EDT SAT AUG 29 2009) AS A LOW PRESSURE SYSTEM SLOWLY MOVES EAST JUST TO THE NORTH OF THE FORECAST AREA... MVFR CONDITIONS OF 1500 TO 2500 FOOT CEILINGS... ARE SEEN ACROSS ALL THE TAF SITES BUT JXN... WHERE THE LOWER CEILINGS ARE MOVING IN. SCATTERED LIGHT RAIN SHOWERS WILL BE COVERED BY VCSH WORDING AS THE RAIN OCCURRENCES AT TAF SITES WILL COVER FAR LESS THAN HALF THE TIME. EXPECT MVFR CEILINGS TO PERSIST INTO THE EVENING WITH THE POSSIBILITY OF LIGHT SHOWERS THROUGH THE NIGHT. SHOWERS SHOULD END BY THE MORNING. HOWEVER... A LAKE EFFECT BAND MAY PERSIST RIGHT ALONG THE COAST OF LAKE MICHIGAN THROUGH THE MORNING SUNDAY. ACROSS THE INTERIOR OF LOWER MICHIGAN SUNDAY... SKIES SHOULD BECOME MOSTLY SUNNY. && .MARINE...(345 PM EDT SAT AUG 29 2009) SMALL CRAFT HEADLINES WILL BE MAINTAINED AS THE LAKE WILL REMAINED CHURNED UP THROUGH SUNDAY EVENING. NORTH TO NORTHWEST WINDS WILL CONTINUE TO BRING UNSEASONABLY COOL AIR ACROSS THE LAKE MAKING FOR UNSTABLE CONDITIONS AND WAVES AS HIGH AS TEN FEET. STILL CANNOT RULE OUT AN ISOLATED WATERSPOUT AS CLOUD DEPTH AND INSTABILITY PEAKS OVERNIGHT. THE THREAT SHOULD END BY MID MORNING ON SUNDAY AS DRIER AIR BEGINS TO MOVE IN...AND THE CLOUD DEPTH BECOMES INCREASINGLY SHALLOW. WE WILL SEE A DIMINISHING TREND IN THE WINDS AND WAVES SUNDAY EVENING INTO SUNDAY NIGHT AS HIGH PRESSURE APPROACHES. MONDAY APPEARS TO BE A CONTINUED SUBSIDING TREND. && .HYDROLOGY...(345 PM EDT SAT AUG 29 2009) NO HYDROLOGY PROBLEMS EXPECTED THROUGH THE UPCOMING WEEK. ANY RAINFALL THAT OCCURS THIS WEEKEND WILL REMAIN ON THE LIGHT SIDE WITH RELATIVELY SHALLOW MOISTURE IN PLACE. && .CLIMATE...(345 PM EDT SAT AUG 29 2009) THE FOLLOWING IS THE RECORD COOLEST MAX TEMPS WE HAVE SEEN ON AUG 30. AS LONG AS WE SEE CLEARING INTO THE AFTERNOON ON SUNDAY...THESE RECORDS SHOULD BE SAFE. SUN AUG 30TH MKG 58 IN 1915 GRR 63 IN 1967 AND 1915 LAN 60 IN 1915 && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...SMALL CRAFT ADVISORY ALL ZONES THROUGH LATE SUNDAY NIGHT. && $$ SYNOPSIS: JK SHORT TERM: JK LONG TERM: IOD AVIATION: IOD MARINE: JK HYDROLOGY: JK CLIMATE: JK
