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000 FXUS63 KDTX 250907 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 407 AM EST WED NOV 25 2009 .SHORT TERM...TODAY STEADY RAIN ATTM WILL LIFT INTO NORTHERN LOWER MICHIGAN/NORTHERN LAKE HURON EARLY THIS MORNING...AS LOW PRESSURE TRACKS NORTHEAST THROUGH LAKE MICHIGAN. WILL ADJUST THE TIMING OF THE FORECAST AT ISSUANCE BUT GENERALLY EXPECT THIS AREA OF RAIN TO GIVE WAY TO SCATTERED SHOWERS BY AROUND DAYBREAK. THESE SHOWERS WILL THEN CONTINUE ON/OFF THROUGHOUT THE DAY AS THE UPPER LEVEL COLD POOL ASSOCIATED W/ THE UPPER LOW MOVES OVER LOWER MICHIGAN. THE BEST COVERAGE OF SHOWERS WILL TEND TO BE FROM I 69 NORTH...BUT THE DIFFERENCES ACROSS THE AREA WILL BE MINIMAL. TEMPERATURES WILL ESSENTIALLY BE STEADY BETWEEN 45-50 INTO THE MORNING...AND THEN SLOWLY FALL DURING THE AFTERNOON AS COOLER AIR FILTERS INTO THE REGION IN THE WAKE OF THIS LOW PRESSURE SYSTEM. && .LONG TERM...TONIGHT THROUGH TUESDAY AN ACTIVE WEATHER PATTERN IS EXPECTED THROUGH THE LONG-TERM FORECAST WITH A SERIES OF COLD FRONTS GRADUALLY USHERING IN A MUCH COOLER AIRMASS BY THE MIDDLE TO END OF NEXT WEEK. THE FIRST OF THESE COLD FRONTS WILL BE PULLED ACROSS LOWER MICHIGAN FROM LATE TONIGHT INTO THURSDAY AS WINDS SHIFT AROUND TO THE SOUTHWEST BEHIND THE DEPARTING LOW PRESSURE SYSTEM. THIS AREA OF LOW PRESSURE WILL SEEM TO STALL OVER NORTHERN LAKE HURON INTO THURSDAY AS THE UPPER LEVEL TROUGH OVER THE EASTERN UNITED STATES UNDERGOES FURTHER DEEPENING AS IT IS RE-ENFORCED BY THE WAVE APPROACHING FROM NORTH DAKOTA FOLLOWED BY A STRONG UPPER JET DIVING SOUTH FROM NORTHERN ONTARIO. IT IS THIS SECONDARY WAVE DROPPING SOUTH FROM THE ARCTIC THAT WILL BRING OUR FIRST WAVE OF COOLER AIR (850MB TEMPERATURES OF BETWEEN -5 TO -8C) AND OUR FIRST CHANCE AT A MINOR SNOWFALL ON THURSDAY NIGHT. BEFORE THAT TIME...DEEP LAYER MOISTURE IS EXPECTED TO INCREASE INTO TONIGHT AS THE UPPER LEVEL LOW OVER NORTH DAKOTA PIVOTS SOUTHEAST TOWARDS ILLINOIS/INDIANA. MODELS ARE IN GOOD AGREEMENT SHOWING AN AREA OF SHOWERS LIFTING NORTH ACROSS SOUTHEAST MICHIGAN ASSOCIATED WITH THE MID-LEVEL FRONT AND DEFORMATION AXIS...BEFORE THE DRY-SLOT LIFTS NORTH INTO EXTREME SOUTHEAST MICHIGAN BY THURSDAY MORNING. MODELS HAVE TRENDED FURTHER SOUTHEAST WITH THE POSITION OF OF THE CLOSED UPPER LOW BY 12Z THURSDAY WHICH INDICATES A SLOWER ARRIVAL OF THIS DRY-SLOT AND HAVE THEREFORE RAISED POPS TO LIKELY FOR LATE TONIGHT. THERMAL PROFILES WITH TEMPS/DEWPOINTS NEAR 40/UPPER 30S RESPECTIVELY INDICATE THESE SHOWERS WILL REMAIN ALL RAIN. THE ABOVE MENTIONED DRY-SLOT DOES SLIDE NORTH ACROSS OUR EXTREME EASTERN COUNTIES ON THURSDAY MORNING WITH DEEPER MOISTURE GRADUALLY WORKING BACK IN FROM THE WEST DURING THE AFTERNOON. HAVE RAISED THE CHANCES OF RAIN ACROSS THE NORTHWESTERN COUNTIES WHERE IT LOOKS LIKE MOISTURE WILL HOLD ON WITH STEEP MID-LEVEL LAPSE RATES DUE TO OUR PROXIMITY TO THE 500MB COLD POOL. DESPITE THESE COLDER TEMPERATURES ALOFT...HAVE REMOVED THE MENTION OF SNOW FROM THE DAYTIME HOURS ON THANKSGIVING AS BOUNDARY LAYER TEMPERATURES SHOULD REMAIN TOO WARM. THE TRANSITION TO A RAIN/SNOW MIX OR ALL SNOW SHOULD OCCUR ON THURSDAY EVENING AS TEMPERATURES DROP INTO THE MID 30S AND 1000-850MB THICKNESSES DROP TO 1300M OR LESS ACROSS THE WHOLE CWA. BEST CHANCES FOR SNOW APPEAR DURING THE FIRST HALF OF THURSDAY NIGHT WHEN SURFACE TEMPERATURES MAY STILL BE A TOUCH ON THE WARM SIDE TO SEE SNOW STICK TO THE GROUND. WILL LEAVE THE CHANCE OF SNOW IN THE FORECAST FOR NOW BUT ANY ACCUMULATIONS SHOULD BE LIMITED TO A HALF INCH OR LESS. TEMPERATURES ON FRIDAY WILL STRUGGLE TO REACH 40 DEGREES. THIS SYSTEM WILL QUICKLY DEPARTS TO THE EAST WITH RIDGING BUILDING OVER THE AREA BEHIND IT. A SURFACE RIDGE BUILDING NORTH INTO THE STATE SHOULD BRING A DRY DAY ON SATURDAY BEFORE THE NEXT LOW PRESSURE SYSTEM DEVELOPING OVER THE PLAINS ADVANCES TOWARDS THE REGION. MODELS ARE STRUGGLING WITH THE TRACK OF THIS LOW PRESSURE SYSTEM ALONG WITH PATTERN EVOLUTION INTO NEXT WEEK...BUT DO SHOW SOME INDICATION THAT AN OCCLUDED FRONT WILL LIFT INTO MICHIGAN ON SUNDAY...WARRANTING A LOW CHANCE OF SHOWERS. FOLLOWING THIS...THE ECMWF/GEM/12Z GFS ARE ON THE MORE PROGRESSIVE SIDE OF THE MODEL ENVELOPE AND PULL THE ASSOCIATED COLD FRONT THROUGH ON MONDAY WHILE THE NEW 00Z/25 GFS SHOWS THE UPPER LEVEL WAVE CLOSING OFF NEAR THE GULF COAST AND DOES NOT PUSH THE FRONT THROUGH UNTIL LATER IN THE WEEK. DESPITE THESE DIFFERENCES FOR DAYS 6 AND 7...MODELS CONTINUE TO SHOW COLDER AIR BUILDING UP OVER WESTERN CANADA BY EARLY NEXT WEEK...WITH A CHANCE THE NEXT COLD FRONT COULD FINALLY DROP TEMPERATURES DOWN TO BELOW NORMAL. && .MARINE... SOUTHEAST WINDS NEARING 15-20 KNOTS WILL SHIFT TO THE SOUTH AND SOUTHWEST AS LOW PRESSURE TRACKS ACROSS LAKE MICHIGAN INTO NORTHERN LOWER MICHIGAN AND SWINGS A COLD FRONT THROUGH THE AREA. EVEN WITH THE STEADY SOUTHWEST FLOW ATTM...WAVE READINGS REMAIN 1-2 FEET SO DO NOT EXPECT ANY HEADLINES FOR THE NEARSHORE WATERS AS WINDS BECOME OFFSHORE. THE HIGHEST WAVES WILL BE OVER SAGINAW BAY WHERE SOUTHWEST WINDS WILL BE ENHANCED BY FUNNELING...BUT STILL EXPECT 2 TO 4 FOOT TO COVER THESE WATERS. THIS CAN BE ADJUSTED IF NECESSARY AFTER THE WIND SHIFT IF SPEEDS COME UP TOO MUCH. OTHERWISE...THE NEXT COLD FRONT WILL BRING THE CHANE OF SMALL CRAFT CONDITIONS FRIDAY AS THE FLOW BECOME NORTHWEST AT 20 KNOTS OR BETTER. THIS SYSTEM WILL ALSO BRING A MIX OF RAIN/SNOW SHOWERS AS COLDER TEMPERATURES SETTLE INTO THE CENTRAL GREAT LAKES. && .PREV DISCUSSION...ISSUED 1201 AM EST WED NOV 25 2009 AVIATION... A FEW ADJUSTMENTS WERE MADE FOR THE 06Z TAF CYCLE TO SPEED UP THE TIMING OF PRECIPITATION BY 1-2 HOURS. CEILINGS WILL CONTINUE TO LOWER AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT RAIN SHOWERS TO MOVE INTO THE AREA AFTER 06Z AS AN AREA OF LOW PRESSURE LIFTS INTO THE WESTERN GREAT LAKES...WITH MORE STEADY RAIN AND IFR CEILINGS BECOMING PREVALENT AFTER 07Z. CURRENT THINKING IS THAT SHOWERS WILL BECOME ISOLATED/SCATTERED AFTER 16Z TOMORROW...WITH MVFR STRATUS HOLDING THROUGHOUT THE DAY. LOW STRATUS (IFR) IS THEN EXPECTED TO BUILD BACK IN FOR WEDNESDAY NIGHT...WITH SHOWERS AGAIN POSSIBLE LATE. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ SHORT TERM...DG LONG TERM....KEC MARINE.......DG AVIATION.....HLO YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
