Issued by NWS Grand Rapids, MI
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000 FXUS63 KGRR 202310 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 610 PM EST FRI NOV 20 2009 LATEST UPDATE...AVIATION... .SYNOPSIS...(300 PM EST FRI NOV 20 2009) A LARGE HIGH PRESSURE SYSTEM THAT EXTENDS FROM NORTH CAROLINA TO UTAH EARLY THIS AFTERNOON WILL MOVE SLOWLY NORTHEAST THROUGH THE WEEKEND. THE CENTER OF THE SURFACE HIGH WILL BE OVER MICHIGAN SATURDAY AND TO THE EAST OF MICHIGAN ON SUNDAY. LIGHT WINDS WILL RESULT IN FOG DURING THE EARLY MORNING HOURS OF SATURDAY...SUNDAY AND MONDAY. TEMPERATURES WILL REMAIN ABOVE NORMAL INTO MID WEEK...THEN AROUND THANKSGIVING COLDER AIR FROM CENTRAL CANADA MAY BRING A TOUCH OF WINTER TO THE AREA. && .SHORT TERM...(300 PM EST FRI NOV 20 2009) (TONIGHT THROUGH SUNDAY NIGHT) THE PRIMARY ISSUES FOR THE SHORT TERM FORECAST ARE... CAN THE CLOUDS ACTUALLY CLEAR WITH THE SURFACE HIGH MOVING OVER THE WEEKEND? ALSO... WITH LIGHT WINDS AND TRAPPED LOW LEVEL MOISTURE... WILL THERE BE FOG EACH MORNING? CURRENTLY (245 PM) CLOUDY SKIES PREVAIL ACROSS MOST OF THE CWA. HOWEVER THERE IS A SHORTWAVE TRACKING SOUTHEAST FROM CENTRAL WI AND IT HAS MIXED OUT THE LOW CLOUDS OVER LAKE MICHIGAN RATHER DRAMATICALLY SINCE 1 PM. THE QUESTION THEN BECOMES CAN THAT MIXING FROM THE SHORTWAVE CLEAR THE LOW CLOUDS OVER LOWER MICHIGAN THIS EVENING? SEEMS LIKE THAT IS ALREADY HAPPENING OVER OUR NW LAKE SHORE COUNTIES. SOME OF OUR WEB CAMS SHOW SOME PARTIAL SUNSHINE AT 245 PM. SO I AM THINKING YES... THE LOW CLOUDS SHOULD IN FACT MIX OUT FOR AWHILE THIS EVENING. OF COURSE THERE IS CONSIDERABLE MID CLOUD COVER ASSOCIATED WITH THE SHORTWAVE... SO I BELIEVE MOSTLY CLOUDY STILL SEEMS LIKE A GOOD FORECAST OVERNIGHT. THE OTHER ISSUE IS FOG. THE WINDS THROUGH 5000 FT REALLY DECREASE AFTER 09Z SATURDAY MORNING. GIVEN HOW MOIST THE MODEL SOUNDINGS ARE THROUGH 850 MB... ANY SIGNIFICANT COOLING WILL LEAD TO FOG FORMATION AND LOW CLOUDS. SO I INCREASED THE CLOUD COVER TO OVERCAST DURING THE EARLY MORNING HOURS AND BROUGHT SOME FOG INTO THE PICTURE. THE SHORTWAVE WILL BE SLOW TO MOVE ACROSS LOWER MICHIGAN...NOT EXITING OUR AREA UNTIL LATE SATURDAY EVENING. GIVEN THE MIXING THAT HAPPENED OVER WI TODAY... I BELIEVE WE WILL SEE THAT HERE SATURDAY. SO SKIES WILL NOT BE TOTALLY OVERCAST. LIGHT WINDS WILL LEAD TO MORE FOG SUNDAY MORNING AND WITH THE SOUTHEAST WINDS BRINGING IN HIGHER SURFACE DEW POINTS AND EVEN GREAT THREAT FOR FOG MONDAY MORNING. PARTLY SUNNY SKIES SHOULD PREVAIL SUNDAY AFTERNOON ONCE THE LOW CLOUDS AND FOG MIX OUT. && .LONG TERM...(322 PM EST FRI NOV 20 2009) (MONDAY THROUGH FRIDAY) THE MAIN CHANGE TO THE EXTENDED PERIOD WAS TO INCLUDE ALL SNOW SHOWERS ACROSS THE CWA THANKSGIVING DAY RATHER THAN THE MIX OVER THE SRN CWA. THE FORECAST REMAINS ON TRACK FROM YESTERDAY. THE ECMWF CONTINUES TO LAG THE ECMWF AND GEM IN MOVING THE NEXT UPPER LOW THROUGH THE GREAT LAKES. THAT/S LIKELY BECAUSE THE ECMWF AND GEM CUT OFF THE LOW WHILE THE GFS DOESN/T. THE DIFFERENCE THAT MAKES IS THAT THE GFS IS COLDER QUICKER THAN THE OTHER MODELS. GIVEN THAT I DON/T REALLY SEE THE UPPER JET STRUCTURE I/D LIKE TO SEE IF THE SYSTEM WAS GOING TO CUT OFF...I/LL LEAN TOWARD THE GFS SOLUTION. TEMPS WILL BE ABOVE AVERAGE MONDAY AS SHORT WAVE RIDGING MOVES OVER THE CWA AHEAD OF THE LOW. BUT CHANCES OF RAIN WILL INCREASE AS THE SFC LOW MOVES FROM THE NRN PLAINS TOWARD THE CENTRAL LAKES AND OCCLUDES. COLDER AIR WILL WORK INTO THE REGION FROM THE SW AS THE LOW MOVES NORTHEAST INTO ONTARIO. IT/S POSSIBLE THAT WE COULD SEE MIXED SHRASN TUESDAY NIGHT DEPENDING ON HOW MUCH COLD AIR WORKS SOUTH BEHIND THE LOW. NOT CONFIDENT ENOUGH TO PUT IT IN THE GRIDS BUT WE/LL KEEP AN EYE ON IT. LOOKS LIKE THE REAL COLD SURGE WILL COME IN ON THANKSGIVING WHICH WILL BE AFTER PEAK TRAVEL. THE GFS CONTINUES TO SHOW H8 TEMPS NEAR -11C MOVING ACROSS THE CWA. THAT WOULD BE COLD ENOUGH FOR LAKE EFFECT SNOW TO DEVELOP. THE COLD AIR LINGERS THROUGH FRIDAY BEFORE WARMING DEVELOPS NEXT WEEKEND. && .AVIATION...(610 PM EST FRI NOV 20 2009) MVFR/IFR CONDITIONS TO CONTINUE TONIGHT AS LIGHT WINDS AND ABUNDANT LOW LEVEL MOISTURE WILL RESULT IN LOW VSBYS AND CIGS OVERNIGHT. SOME SLOW IMPROVEMENT EXPECTED DURING THE DAY ON SATURDAY WITH MVFR AND THEN IFR BY LATE AFTERNOON. && .MARINE...(300 PM EST FRI NOV 20 2009) HIGH PRESSURE AND LIGHT WINDS WILL MEAN THE ONLY REAL ISSUE FOR THE NEAR SHORE THIS WEEKEND WILL BE FOG. WEB CAMS SUGGEST THERE IS SOME LIGHT FOG OUT THERE NOW. OTHERWISE LIGHT WINDS WILL MEAN SMALL WAVES THROUGH THE WEEKEND. && .HYDROLOGY...(300 PM EST FRI NOV 20 2009) DRY WEATHER IS EXPECTED INTO MONDAY. AS A RESULT THERE ARE NO SIGNIFICANT HYDRO ISSUES. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: WDM SHORT TERM: WDM LONG TERM: 93 AVIATION: OSTUNO MARINE: WDM HYDROLOGY: WDM
