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000 FXUS63 KDTX 242317 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 617 PM EST TUE NOV 24 2009 .AVIATION... UPSTREAM OBSERVATIONS AND GFS/NAM MODEL FORECAST SOUNDING DATA SUPPORTS MVFR CEILINGS AT 3000-4000 FEET FOR THE NEXT SEVERAL HOURS BEFORE THE CLOUD DECK LOWERS AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT SHOWERS TO MOVE INTO THE AREA AFTER 06Z AS THIS AREA OF LOW PRESSURE LIFTS INTO THE WESTERN GREAT LAKES...WITH MORE OF A STEADY RAIN AND IFR CEILINGS BECOMING PREVALENT AFTER 09Z-10Z. THERE IS POTENTIAL FOR CEILINGS TO DROP TO LIFR BETWEEN 09Z-15Z AS WELL...HOWEVER THE PROBABILITY IS NOT HIGH ENOUGH TO WARRANT A PREVAILING IFR GROUP AT THIS TIME. WILL RE- ASSESS CONTINUALLY HOWEVER...AND COULD ADD SOME TEMPO GROUPS IF WARRANTED IN THE NEXT PACKAGE. CURRENT THINKING IS THAT SHOWERS WILL BECOME ISOLATED/SCATTERED AFTER 16Z TOMORROW...WITH LOW STRATUS (IFR) BUILDING BACK IN LATE WEDNESDAY NIGHT. && .PREV DISCUSSION...ISSUED 325 PM EST TUE NOV 24 2009 SHORT TERM...TONIGHT VERTICALLY STACKED LOW PRESSURE SYSTEM CURRENTLY SEEN ON WATER VAPOR IMAGERY MOVING ACROSS THE MIDWEST WILL LIFT NORTHEAST ACROSS THE REGION TONIGHT. VERY LITTLE LOW LEVEL WAA SEEN AHEAD OF THE APPROACHING SYSTEM AS EVIDENCED BY THE WEAK ISENTROPIC LIFT FORECAST OVER THE AREA. HOWEVER...RIDGE OF HIGH THETA-E WILL MOVE INTO THE REGION TONIGHT AND THIS...COUPLED WITH STRONG CVA ALOFT AND THE ASSOCIATED OCCLUDED FRONT...WILL LEAD TO A GOOD CHANCE OF RAIN. MODELS HAVE SHOWN A REMARKABLE AMOUNT OF CONSISTENCY WITH THIS SCENARIO AND HAVE RAISED POPS ACCORDINGLY. ONLY ISSUE WILL BE TIMING. NAM RH FIELDS AND BUFKIT SOUNDINGS SHOW THE BEST SATURATION ACROSS MOST OF THE CWA WILL NOT OCCUR UNTIL AROUND 09Z SO LEFT SLIGHTLY LOWER POPS ACROSS PORTIONS OF THE THUMB. RAISED MIN TEMPS SLIGHTLY ABOVE MOS GUIDANCE GIVEN THE ABUNDANCE OF LOW LEVEL MOISTURE AND CLOUD COVER EXPECTED OVERNIGHT WITH VALUES GENERALLY IN THE MID 40S. LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY THE MID LEVEL WAVE NOW OVER THE MO/IA BORDER WILL QUICKLY LIFT NORTH ACROSS THE STATE ON WEDNESDAY AS A DEEPENING UPPER WAVE DIVES FROM SOUTH CENTRAL CANADA INTO THE MIDWEST. THIS SECONDARY WAVE IS ALSO FORECAST TO DEVELOP INTO A CLOSED CIRCULATION BEFORE ROTATING ACROSS THE NORTHERN OHIO VALLEY/SOUTHERN GREAT LAKES ON THANKSGIVING. OVERALL...THE 12Z MODEL SUITE WERE WELL INITIALIZED WITH THESE UPSTREAM WAVES AND ARE IN REASONABLY GOOD AGREEMENT INTO THANKSGIVING BEFORE SOME TIMING DIFFERENCES ARISE. LARGE SCALE ASCENT IS FORECAST TO QUICKLY LIFT INTO THE NORTHERN LAKES REGION WED MORNING...WITH MID LEVEL MOISTURE BECOMING DEPLETED OVER SOUTHERN MICHIGAN. NONETHELESS...RESIDUAL LOW LEVEL MOISTURE AND BOUNDARY LAYER CONVERGENCE SHOULD SUSTAIN SOME DRIZZLE AND/OR LIGHT RAIN SHOWERS INTO THE EVENING. IN LIGHT OF THE COLD POOL ALOFT PASSING THROUGH SE MI IN THE AFTERNOON...ANY LINGERING MID LEVEL MOISTURE ALOFT MAY PRODUCE SOME HIGHER INTENSITY SHOWERS. MAX TEMPS ON WED /APPROACHING 50/ SHOULD OCCUR DURING THE MORNING AS LOW LEVEL COLD AIR ADVECTION FROM THE SOUTHWEST WILL LEAD TO SLOWLY FALLING TEMPS DURING THE AFTERNOON AND EVENING. STRONG MID LEVEL HEIGHT FALLS ASSOCIATED WITH THE APPROACH OF THE SECONDARY UPPER LOW WILL OVERSPREAD SE MI LATE WED NIGHT INTO THURS MORNING. MODEL SOUNDINGS ALSO SHOW DEPTH OF MOISTURE INCREASING... ENOUGH TO MAINTAIN A FAIRLY HIGH CHANCE OF PRECIPITATION. MODEL SOUNDINGS AND CRITICAL THICKNESSES SUGGEST ALL PRECIP WILL REMAIN IN THE FORM OF RAIN THROUGH EARLY THURS MORNING. WITH THIS SYSTEM ORIGINATING IN CANADA...IT WILL ADVECT MUCH COLDER AIR INTO THE REGION IN COMPARISON TO THE WED SYSTEM. A TIGHT CIRCULATION IS EXPECTED AROUND THIS UPPER LOW...WITH THE COLDEST AIR ACTUALLY SLIDING INTO THE OHIO VALLEY THURS MORNING...THEN ADVECTING INTO MICHIGAN FROM SOUTH TO NORTH DURING THE DAY. WHILE MODEL THERMAL PROFILES CONTINUE TO SUPPORT A MIX OR POSSIBLE CHANGE OVER TO SNOW DURING THE COURSE OF THE DAY THURS...THERE IS GOOD AGREEMENT THAT PRECIPITATION WILL BE LIMITED BY THE MID LEVEL DRY SLOT. AS THE UPPER LOW SLIDES TO EAST OF THE REGION THURS EVENING THROUGH FRIDAY MORNING...MID LEVEL DYNAMICS ASSOCIATED WITH THE DEFORMATION REGION AND MUCH HIGHER MID LEVEL MOISTURE WILL ADVANCE ACROSS SE MI. MODEL THICKNESS PARAMETERS CONTINUE TO SUGGEST A POSSIBLE MIX...ALTHOUGH NOCTURNAL COOLING IN THE BOUNDARY LAYER MAY BE MORE SUPPORTIVE OF SNOW. DESPITE THE LOW QPF ON MODEL OUTPUT...THE POTENTIAL MID LEVEL DYNAMICS LOOK STRONG ENOUGH TO GIVE PERHAPS THE FIRST MINOR SNOW ACCUMULATIONS OF THE SEASON. THE UPPER AIR PATTERN ACROSS NORTH AMERICA IS EXPECTED TO BE PROGRESSIVE THROUGH THE WEEKEND...LEADING TO A SLIGHT MODERATION IN TEMPERATURES. THE SPREAD AMONG THE MEDIUM RANGE MODELS WITH RESPECT TO THE UPPER PATTERN EARLY NEXT WEEK REMAINS VERY LARGE. POOR MODEL CONTINUITY AND LARGE SPREAD AMONG ENSEMBLE MEMBERS LEAD TO A LOW CONFIDENCE FORECAST SUNDAY THROUGH NEXT TUESDAY. OVERALL...THE BULK OF SOLUTIONS INDICATE THE DEVELOPMENT OF A SLIT FLOW REGIME BY EARLY NEXT WEEK. THE STRONG SUB TROPICAL JET SUPPORTS THOSE SOLUTIONS WITH A SLOWER AND STRONGER SOUTHERN STREAM WAVE. LATER MODEL TRENDS WILL HAVE TO BE MONITORED FOR THE POTENTIAL OF THE SOUTHERN STREAM WAVE TO PHASE WITH NORTHERN STREAM ENERGY...WHICH MAY LEAD TO AN EASTERN US STORM SYSTEM BY THE END OF THE LONG TERM. MARINE... SOUTHEASTERLY WINDS WILL CONTINUE AS HIGH PRESSURE EXITS TO THE EAST COAST AND A LOW PRESSURE SYSTEM SLOWLY APPROACHES FROM THE PLAINS. WINDS WILL INCREASE TO 15 TO 20 KNOTS ON THE OPEN WATERS OF LAKE HURON BY TOMORROW AS THIS AREA OF LOW PRESSURE APPROACHES. WAVES SHOULD INCREASE TO 3 TO 5 FEET BUT WILL BE ABLE TO HOLD OFF ON ANY SMALL CRAFT ADVISORIES UNTIL THE PASSAGE OF A STRONGER COLD FRONT ON FRIDAY. THIS SYSTEM WILL BRING COOLER TEMPERATURES WITH THE POSSIBILITY FOR A MIX OF RAIN AND SNOW SHOWERS BY THURSDAY. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....HLO SHORT TERM...AGD LONG TERM....SC MARINE.......AGD YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
