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000 FXUS63 KGRR 251201 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 700 AM EST WED NOV 25 2009 LATEST UPDATE...AVIATION... .SYNOPSIS...(431 AM EST WED NOV 25 2009) LOW PRESSURE WILL DRIFT OVER THE GREAT LAKES TODAY AND CONTINUE TO BRING ON AND OFF SHOWERS. THESE SHOWERS WILL BE MOST COMMONPLACE EARLY TODAY...THEN BECOME SCATTERED INTO THE AFTERNOON. MORE NUMEROUS SHOWERS ARE EXPECTED TONIGHT AS AN UPPER LOW MOVES IN. THIS SYSTEM WILL LINGER OVER THE REGION ON THANKSGIVING DAY. AS COOLER AIR IS PULLED OVER THE AREA THE RAIN WILL BECOME MIXED WITH OR CHANGE TO SNOW THURSDAY AFTERNOON AND CONTINUE THURSDAY NIGHT. A LIGHT SLUSHY ACCUMULATION OF SNOW WILL BE POSSIBLE BY EARLY FRIDAY MORNING...BUT TRAVEL SHOULD NOT BE HAMPERED AS ROADWAYS SHOULD REMAIN MAINLY WET. && .SHORT TERM...(431 AM EST WED NOV 25 2009) (TODAY THROUGH FRIDAY) MAIN FORECAST ISSUES WERE DETERMINING RAIN CHANCES TODAY AS DRY SLOT SWINGS THROUGH. IT ALSO APPEARS THE MIXED SNOW COULD BE DELAYED UNTIL THANKSGIVING DAY. HOWEVER ONCE IT ARRIVES SOME AREAS COULD PICK UP A LIGHT ACCUMULATION BY EARLY FRIDAY. LOW PRESSURE WAS CENTERED OVER SE WISCONSIN THIS MORNING AND WILL CONTINUE TO DRIFT NE. RAIN HAS SPREAD OVER MUCH OF THE AREA... HOWEVER THE DRY SLOT WAS PUSHING ACROSS THE SOUTHERN CWA EARLY THIS MORNING. DESPITE THIS DRY WEDGE WILL STILL RAISE POPS FOR TODAY. THIS IS DUE TO AN AREA OF RAIN THAT WAS UNDER THE UPPER LOW THAT WAS OVER NRN IL ATTM. THIS AREA OF RAIN WILL MOVE ACROSS SOUTHERN LAKE MICHIGAN AND THEN OVER THE HEART OF THE CWA THROUGH THE MORNING. ONCE THE UPPER LOW PASSES TO THE NE WEAK UPPER RIDGING...BETWEEN THIS UPPER LOW AND ANOTHER ONE OVER IA...WILL SLIDE OVERHEAD. AS A RESULT THE RAIN SHOULD BECOME SCATTERED INTO THE AFTERNOON. THE IA UPPER LOW WILL SLIDE OVER THE WESTERN GREAT LAKES TONIGHT AND BRING ANOTHER SURGE OF MOISTURE AND LIFT. COOLER AIR ALSO ARRIVES LATE WHICH MAY CAUSE SOME LAKE ENHANCED SHOWERS. SPEAKING OF THE COOLER AIR...THE COLDEST AIR APPEARS TO BE DELAYED UNTIL A SURFACE TROUGH PASSES THROUGH MID DAY THURSDAY. DUE TO THIS HAVE REMOVED THE MENTION OF SNOW TONIGHT AND EARLY THURSDAY. A BETTER CHANCE OF MIXED RAIN AND SNOW COMES THURSDAY AFTERNOON INTO THURSDAY EVENING AS THE ABOVE MENTIONED TROUGH COMES THROUGH AND OPENS THE DOOR TO THE COLDER AIR. TEMPS AND DEWPOINTS SHOULD FALL ONCE THIS TROUGH PASSES. THROUGH MIDNIGHT SOME AREAS COULD PICK UP AS MUCH AS AN INCH OF SNOW ON GRASSY AREAS...ESPECIALLY WHERE SOME HIGHER INTENSITY LAKE EFFECT BANDS SET UP. HOWEVER WE LOSE THE DEEPER MOISTURE IN THE DGZ AFTER MIDNIGHT AND THE PCPN SHOULD TAPER OFF. ALSO ANTICYCLONIC FLOW DEVELOPS BY DAYBREAK FRIDAY PUTTING AN END TO ANY SNOW. A WEAK NORTHERN STREAM WAVES COMES ACROSS FRIDAY AFTERNOON. THIS SYSTEM APPEARS MOISTURE STAVED...SO WILL ONLY CONTINUE THE LOW CHANCE POPS. && .LONG TERM...(431 AM EST WED NOV 25 2009) (FRIDAY NIGHT THROUGH TUESDAY) UPPER LEVEL RIDGING INBETWEEN THE DEPARTING LONGWAVE TROUGH AND THE NEXT ONE DIGGING OVER THE WRN U.S. WILL RESULT IN DRY AND MILD CONDITIONS ON SATURDAY WITH HIGHS IN THE MID 40S. THINGS TURN RATHER COMPLICATED/CHALLENGING FOR SUNDAY THROUGH TUESDAY. A SFC FRONTAL BOUNDARY IS EXPECTED TO MOVE INTO THE REGION FROM THE WEST ON SUNDAY AND SHOULD BRING THE CHANCE FOR A FEW RAIN SHOWERS. UNFORTUNATELY MEDIUM RANGE MODELS DISAGREE ON WHAT HAPPENS AFTER THAT...BUT AN ENSEMBLE APPROACH WOULD SUGGEST THAT THE SFC BOUNDARY WILL EVENTUALLY STALL FROM THE EASTERN GREAT LAKES REGION SOUTH TO THE GULF OF MEXICO AS THE DEEP H5 LONGWAVE TROUGH EDGES SLOWLY EASTWARD. ANY POTENTIAL SHORTWAVES COMING OUT OF THE BASE OF THE LONGWAVE TROUGH OVER TEXAS AND RIDING NORTH NORTHEAST ALONG THE BAROCLINIC ZONE MAY PRODUCE SOME PCPN IN MI. THERE IS EVEN A SUGGESTION THAT A RATHER POTENT AND WET SYSTEM WILL LIFT STRAIGHT NORTH OUT OF THE GULF OF MEXICO TOWARD MI AND INTERACT WITH APPROACHING NRN STREAM ENERGY... BUT CONFIDENCE (AND TIMING) OF THAT HAPPENING IS VERY LOW ATTM. PCPN TYPE SHOULD BE RAIN OR A MIX OF RAIN AND SNOW MONDAY AND TUESDAY...DEPENDING HOW MUCH COLD AIR GETS INTO THE REGION BEHIND THE SFC FRONTAL BOUNDARY. && .AVIATION...(700 AM EST WED NOV 25 2009) IFR CONDITIONS HAD FOR THE MOST PART VACATED THE AREA AS OF 12Z. MOSTLY MVFR CATEGORY CIGS (1500-2500 FT) AND SCATTERED SHOWERS ARE EXPECTED THIS MORNING... WITH VSBYS OCCASIONALLY DIPPING TO 3-5 MILES IN THE SHOWERS. IFR CIGS SHOULD RETURN TO THE AREA FROM THE WEST/SOUTHWEST TOWARD 18Z WITH THE PASSAGE OF THE SFC COLD FRONT/TROUGH... ALTHOUGH CLOUD BASES COULD BE AT OR JUST ABV 1K FEET MAKING IT TECHNICALLY NON IFR. THE NEXT UPPER LOW DROPPING DOWN FROM THE NORTHWEST WILL SPREAD ANOTHER ROUND OF RAIN SHOWERS ACROSS THE AREA TONIGHT AND WE SHOULD REMAIN PREDOMINATELY IN THE IFR CATEGORY. && .MARINE...(431 AM EST WED NOV 25 2009) WINDS AND WAVES WILL BE INCREASING THROUGH THE MORNING HOURS. A SMALL CRAFT ADVISORY IS ALREADY IN EFFECT. HOWEVER EVEN HIGHER WINDS AND WAVES SHOULD DEVELOP LATE TONIGHT INTO THURSDAY AS THE COLD ADVECTION ARRIVES. SCA HEADLINES WILL LIKELY NEED TO BE EXTENDED WITH FUTURE FORECAST PACKAGES. && .HYDROLOGY...(431 AM EST WED NOV 25 2009) MOST AREAS WILL SEE AN ADDITIONAL QUARTER TO HALF INCH OF RAIN FROM TODAY THROUGH MIDNIGHT THURSDAY NIGHT. THE PERSISTENT LIGHT PCPN WILL DO LITTLE TO INFLUENCE AREA RIVERS. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...SMALL CRAFT ADVISORY ST. JOE TO WHITEHALL TODAY AND TONIGHT. && $$ SYNOPSIS: JK SHORT TERM: JK LONG TERM: MEADE AVIATION: MEADE MARINE: JK HYDROLOGY: JK
