Issued by NWS Detroit/Pontiac, MI
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS63 KDTX 212017 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 317 PM EST SAT NOV 21 2009 .SHORT TERM...-- Changed Discussion --TONIGHT WITH SURFACE DEW POINTS STILL HOVERING IN THE LOW TO MID 40S AND SKIES MOSTLY CLEARED OUT...FOG APPEARS TO BE A GOOD BET TONIGHT AS ANTI-CYCLONIC FLOW BUILDS INTO LOWER MICHIGAN. EASTERLY FLOW OFF LAKE ERIE WILL HELP CONTRIBUTE SOME ADDITIONAL MOISTURE ACROSS THE SOUTH THIRD OF THE CWA. EVEN WITHOUT THIS MOISTURE...RELATIVELY HIGH CROSSOVER TEMPERATURES SHOULD BE SUFFICIENT FOR FOG WITH MINS FALLING INTO THE UPPER 30S. A QUICK REDEVELOPMENT OF THE LOW STRATUS IS ABOUT THE ONLY FLY IN THE OINTMENT...BUT THE ONLY SIGNIFICANT INVERSION LOOKS TO BE THE SURFACE BASED ONE AND LEANING TOWARD A FOG SCENARIO...WHICH COULD BECOME DENSE.-- End Changed Discussion --&& .LONG TERM...-- Changed Discussion --SUNDAY THROUGH NEXT SATURDAY MID LEVEL RIDGING IS FORECAST TO BUILD ACROSS THE EASTERN GREAT LAKES ON SUNDAY...ALLOWING THE HIGH NOW CENTERED OVER OHIO TO BUILD INTO NORTHERN NEW ENGLAND. THE SURFACE HIGH AND ASSOCIATED UPPER RIDGE IS THEN FORECAST TO SLIDE OFF THE COAST OF NEW ENGLAND ON MONDAY...WITH SURFACE RIDGING PERSISTING ACROSS THE EASTERN GREAT LAKES. WITH NO APPRECIABLE ADVECTION OF LOW LEVEL DRY AIR INTO THE REGION AND GIVEN THE LIMITED MIXING POTENTIAL THIS TIME OF YEAR...DENSE FOG WILL BE THE MAIN WEATHER CONCERN OVER THE NEXT SEVERAL DAYS. GIVEN THE WARM AMBIENT AIRMASS...ONCE FOG IS ABLE TO MIX OUT SUN AFTERNOON...TEMPS SHOULD ACHIEVE THE LOWER 50S. ALTHOUGH THE LOW LEVEL GRADIENT IS FORECAST TO INCREASE SUN NIGHT INTO TUES...THE LOW LEVEL FLOW WILL REMAIN OFF LAKE ERIE. THIS WILL SUPPLY ADDITIONAL LOW LEVEL MOISTURE INTO THE ALREADY MOISTURE RICH BOUNDARY LAYER. WHILE THE TIGHTENING GRADIENT RAISES SOME CONCERNS THAT LOW STRATUS WILL BE FAVORED OVER FOG...MODEL SOUNDINGS AND WIND SPEEDS BELOW 950MB SUGGEST ENOUGH BOUNDARY LAYER DECOUPLING TO ALLOW A CHANCE OF FOG REDEVELOPMENT BOTH SUN NIGHT AND MONDAY NIGHT. WEAK SHALLOW COLD AIR ADVECTION ON MONDAY AND PERSISTENT MID LEVEL SUBSIDENCE WILL STRENGTHEN THE INVERSION. THIS MAY MAKE IT DIFFICULT FOR MORNING FOG/STRATUS TO COMPLETELY MIX OUT DURING THE AFTERNOON. THUS...HAVE KEPT MONDAYS MAX TEMPS MAINLY IN THE UPPER 40S. ATTENTION THEN TURNS TO THE WEATHER SYSTEM EXPECTED TO IMPACT THE STATE BY MID WEEK. THE 12Z MODEL SUITE CONTINUE TO SHOW MID LEVEL TROUGH AMPLIFICATION OVER THE CENTRAL ROCKIES ON MONDAY...EVOLVING INTO A CUT OFF CIRCULATION OVER THE CENTRAL PLAINS BY TUESDAY. BOTH GFS AND NAM HAVE TRENDED SLOWER WITH THIS SYSTEM /MORE TOWARD THAT OF THE ECMWF/. SATELLITE REPRESENTATION OF THIS WAVE /NOW OFF THE COAST OF WASHINGTON STATE/ APPEARS STRONGER THAN WHAT THE GFS INITIALIZED. THESE FACTORS SEEMS TO SUPPORT THE SLOWER ECMWF. WITH THE WAVE STILL OFF THE COAST...MODEL CONFIDENCE IS STILL NOT HIGH. IN LIGHT OF RECENT ECMWF TRENDS HOWEVER...THE BEST CHANCE OF RAIN ASSOCIATED WITH THE WARM CONVEYOR BELT WILL OCCUR BETWEEN TUES NIGHT AND WED. AS THE SYSTEM LIFTS ACROSS MICHIGAN /ROUGHLY IN THE WED TIME PERIOD/ A SECONDARY NORTHERN STREAM WAVE IS FORECAST TO DROP INTO THE NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY FROM CANADA. THERE REMAINS A HIGH DEGREE OF UNCERTAINTY WITH RESPECT TO TIMING AND AMPLITUDE OF THIS WAVE AND WHETHER THERE WILL BE ANY PHASING WITH THE WAVE PRECEDING IT. IN LIGHT OF RECENT MODEL TRENDS...A CHANCE OF PRECIPITATION /ALBEIT LIGHT/ CONTINUES TO LOOK WARRANTED THURS THROUGH FRIDAY. THE MAGNITUDE OF COLD AIR ADVECTION WITH THE NORTHERN STREAM SYSTEM HAS NOT BEEN SHOWN TO BE AS STRONG OVER THE LAST COUPLE OF MODEL CYCLES /THE COLDEST AIR NOW DOES NOT LOOK TO ARRIVE UNTIL THURS NIGHT OR FRIDAY/. SINCE EVEN THE FASTER GFS SOLUTION IS NOW INDICATING THAT THE COLD AIR ADVECTION WILL NOT BE STRONG ENOUGH TO OFFSET THE DEPTH OF ABOVE FREEZING AIR IN THE BOUNDARY LAYER...HAVE REMOVED ALL MENTION OF SNOW ON THANKSGIVING DAY AND JUST CARRIED A MIX THURS NIGHT INTO FRIDAY.-- End Changed Discussion --&& .MARINE...-- Changed Discussion --HIGH PRESSURE WILL REMAIN IN PLACE OVER THE CENTRAL GREAT LAKES THROUGH TOMORROW...RESULTING IN VERY LIGHT WINDS. THERE WILL BE A GRADUAL INCREASE IN SOUTHEAST WINDS MONDAY INTO TUESDAY AS THE HIGH RETREATS EAST AWAY FROM THE AREA. THE PATTERN BECOMES ACTIVE AGAIN MID/LATE NEXT WEEK AS A STRONG SHORTWAVE AND ASSOCIATED JET STREAK DIG INTO THE UPPER MIDWEST AND LEAD TO THE DEVELOPMENT OF A LARGE UPPER LEVEL LOW OVER/NEAR THE REGION. THIS TIME FRAME WILL BRING UNSETTLE WEATHER AND HIGHER WIND AND WAVES. &S-- End Changed Discussion --&& .PREV DISCUSSION...-- Changed Discussion --ISSUED 1201 PM EST SAT NOV 21 2009 AVIATION... REMNANT LOW LEVEL MOISTURE WITH ILL DEFINED LOW LEVEL INVERSION WILL MAKE FOR A DIFFICULT TAF FORECAST...AS THE DEBATE WILL BE LOW STRATUS VS FOG AS CALM/LIGHT WINDS PROMOTE GOOD RADIATIONAL COOLING TONIGHT. SLOW DRYING OF THE COLUMN THIS AFTERNOON SHOULD ALLOW FOR PARTIAL CLEARING...BUT BOUNDARY LAYER COOLING WHEN THE SUN SETS WILL ALLOW FOR EITHER MVFR VSBY`S OR CEILINGS QUICKLY REDEVELOPING...WITH EITHER IFR VSBY`S OR CEILINGS EXPECTED OVERNIGHT WITH AT LEAST A STRONG SURFACE BASED INVERSION SETTING UP AS GENERAL SUBSIDENCE WILL BE THE RULE WITH ANTI-CYCLONIC FLOW BUILDING IN. SOUTHEAST FLOW OFF LAKE ERIE WILL MAKE DTW ESPECIALLY SUSCEPTIBLE FOR POSSIBLE DENSE FOG OR LOW STRATUS TOMORROW MORNING. AS TYPICAL FOR THIS TIME OF YEAR...FOG AND STRATUS WILL LIKELY TAKE ALL MORNING TO BURN OFF/DISSIPATE WITH THE LIGHT WINDS AND LIMITED MIXING.-- End Changed Discussion --&& .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ SHORT TERM...SF LONG TERM....SC MARINE.......SF AVIATION.....SF YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
