Issued by NWS Grand Rapids, MI
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000 FXUS63 KGRR 201147 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 745 AM EDT SAT SEP 20 2008 LATEST UPDATE...AVIATION... .SYNOPSIS...(345 AM EDT SAT SEP 20 2008) A COLD FRONT WILL DROP SOUTH SOUTHEAST ACROSS LOWER MICHIGAN TODAY. HOWEVER MOISTURE WITH THIS SYSTEM IS VERY LIMITED AND THERE IS JUST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM THIS AFTERNOON AND EVENING NORTHEAST OF GRAND RAPIDS. BEHIND THE COLD FRONT A LARGE HIGH PRESSURE RIDGE WILL BUILD IN TO OUR EAST NORTHEAST AND PRODUCE FAIR WEATHER SUNDAY AND MONDAY. && .SHORT TERM...(345 AM EDT SAT SEP 20 2008) (TODAY THROUGH MONDAY AFTERNOON) THERE IS JUST A SLIGHT CHC OF A SHOWER OR TSTORM THIS AFTN AND EARLY EVE... PRIMARILY OVER OUR NE CWFA IN AN AREA OF (RELATIVELY) SLIGHTLY HIGHER 925-850 MB MEAN RH AND WEAK PVA. 00Z GFS GUIDANCE CONTINUES TO INDICATE SOME INSTABILITY WILL DEVELOP THIS AFTN WITH LI/S DOWN TO -4 AND SB CAPES REACHING 1000 J/KG. HOWEVER FCST SOUNDINGS ARE QUITE DRY AND STRONGER PVA PASSES NORTH OF OUR CWFA. THEREFORE WE EXPECT DRY CONDITIONS WILL PREVAIL ACROSS THE VAST MAJORITY OF OUR CWFA. MAX TEMPS WILL REACH THE 70S. CANADIAN HIGH PRESSURE WILL PRODUCE DRY WX SUNDAY AND MONDAY. THERE REALLY ISN/T MUCH OF A PUSH OF COOLER AIR TO SPEAK OF BEHIND THE COLD FRONT. TEMPS WILL BE SLIGHTLY COOLER BUT STILL NEAR NORMAL SUNDAY... AND WILL AVG SLIGHTLY ABOVE NORMAL MONDAY WITH LARGE DIURNALS ANTICIPATED WITH MOSTLY CLEAR SKIES AND THE DRY AIRMASS IN PLACE. && .LONG TERM...(345 AM EDT SAT SEP 20 2008) (MONDAY NIGHT THROUGH FRIDAY) HIGH PRESSURE WILL BE IN PLACE BOTH AT THE SURFACE AND ALOFT TO BEGIN THE LONG TERM PERIOD MONDAY NIGHT. RIDGING WILL HANG ON INTO TUESDAY NIGHT PROVIDING DRY WEATHER THE FIRST FEW PERIODS OF THE LONG TERM FORECAST. WEDNESDAY IS WHERE SOME DIFFERENCES BEGIN TO POP UP. LATEST MODEL RUNS INDICATE SHORTWAVE ACTIVITY TRYING TO PUSH INTO THE MEAN RIDGE POSITION OVER THE GREAT LAKES. AT THE SURFACE A COLD FRONT TRIES TO PUSH INTO THE RIDGE AS WELL ON WEDNESDAY. AT THIS POINT DID NOT ADD POPS. WOULD LIKE TO SEE SOME CONSISTENCY WITH THIS FEATURE BEFORE ADDING POPS. CURRENTLY POPS ARE IN THE FORECAST FROM THURSDAY INTO FRIDAY UNDER THE ASSUMPTION THAT THE FRONT WOULD BE COMING THROUGH DURING THIS TIME FRAME. LATEST RUNS NOW HAVE RIDGING IN PLACE MUCH OF THIS TIME FRAME WITH THE EARLIER FRONTAL PASSAGE. AGAIN...GIVEN MODEL VARIABILITY NOT MAKING CHANGES IN THE WED-FRI TIME FRAME YET. TEMPERATURES SHOULD BE NEAR TO ABOVE NORMAL THROUGH THE PERIOD. && .MARINE...(345 AM EDT SAT SEP 20 2008) WINDS WILL GRADUALLY VEER TO THE NW AND EVENTUALLY NORTHEAST BEHIND THE COLD FRONT. DESPITE THE MODEST COLD AIR ADVECTION... THE OFFSHORE COMPONENT SHOULD RESULT IN HIGHER WAVES BEING MAINLY WEST OF OUR NSH AREA OF RESPONSIBILITY. HOWEVER SOME 3 TO POTENTIALLY 4 FOOTERS COULD AFFECT BIG AND LITTLE SABLE POINTS FOR A WHILE THIS AFTN AND EVE WHEN WINDS ARE NORTHERLY. && .AVIATION...(745 AM EDT SAT SEP 20 2008) SOME LIGHT FOG EXISTS IN SPOTS ACROSS THE GRR FORECAST AREA. THIS FOG SHOULD BURN OFF QUICKLY...BY 14Z. SOME SCATTERED CUMULUS DEVEOPMENT IS POSSIBLE TODAY...UP AROUND 5000FT. ABOVE THAT...CIRRUS LEVEL MOISTURE UP AROUND 20000-25000FT SHOULD BE PREVALENT. A COLD FRONT IS DROPPING SOUTH FROM THE UPPER PENINSULA THIS MORNING AND SHOULD MOVE INTO SOUTHWEST LOWER MICHIGAN THIS AFTERNOON. A FEW THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AND EVENING ACROSS CENTRAL LOWER MICHIGAN UP TOWARD KMOP...BUT THEY SHOULD STAY NORTH OF THE TAF SITES. THE FRONT WILL SLIP SOUTH TONIGHT...BRINGING IN SLIGHTLY COOLER AIR ALONG WITH THE THREAT OF SOME FOG AND LOW CLOUDS. BROUGHT SOME MVFR CEILINGS INTO KLAN OVERNIGHT...AND SOME MVFR FOG AT MOST OTHER SITES. THE THREAT FOR LOWER CEILINGS AND FOG BEHIND THE FRONT OVERNIGHT IS THE MAIN ISSUE IN THESE TAFS AND WILL CONTINUE TO BE MONITORED. && .HYDROLOGY...(345 AM EDT SAT SEP 20 2008) VERY LITTLE IF ANY RAINFALL THROUGH THE UPCOMING WEEK WILL CONTINUE TO BE VERY CONDUCIVE TO A GRADUAL LOWERING IN RIVER LEVELS ACROSS OUR HSA. ONLY THREE SITES ON THE KALAMAZOO RIVER ARE STILL ABOVE FLOOD STAGE AND THEY CONTINUE TO SHOW WATER LEVELS ON THE DECLINE. COMSTOCK PARK ON THE GRAND RIVER SHOWS A SLOW RISE AND IS EXPECTED TO PEAK LATER TODAY JUST A LITTLE BELOW FLOOD STAGE. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: LAURENS SHORT TERM: LAURENS LONG TERM: DUKE MARINE: LAURENS AVIATION: DUKE HYDROLOGY: IOD/LAURENS
