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000 FXUS63 KDTX 232053 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 353 PM EST MON NOV 23 2009 .SHORT TERM...TONIGHT HIGH PRESSURE CONTINUES TO PULL AWAY FROM THE REGION AS A BROAD AREA OF LOW PRESSURE ADVANCES FROM THE PLAINS. A SHORTWAVE LIFTING ACROSS THE MIDWEST IS HELPING TO LIFT AN AREA OF DEEPER MOISTURE NORTH FROM OHIO INTO ONTARIO...CLIPPING EXTREME SOUTHEAST MICHIGAN ON THE WAY. LIGHT RADAR ECHOS HAVE BEEN MOVING NORTH ACROSS OHIO WITH SEVERAL ASOS SITES REPORTING TRACE AMOUNTS ACROSS NORTH CENTRAL OHIO. REPORTS ARE HARDER TO FIND UPSTREAM ACROSS NORTHWESTERN OHIO BUT HAVE ADDED A SLIGHT CHANCE OF LIGHT SHOWERS/SPRINKLES INTO THE FORECAST THROUGH THIS EVENING WITH QPF OF .01 OR LESS. THE FOG FORECAST IS CHALLENGING FOR TONIGHT AS THE DECK OF CLOUD SPREADING NORTH WILL LIMIT COOLING DURING THE EVENING HOURS. HOWEVER NAM/GFS SHOW THESE CLOUDS STARTING TO CLEAR OUT AFTER MIDNIGHT... WHICH WOULD STILL LEAVE PLENTY OF TIME FOR LOW LEVEL MOISTURE TO COME IN OFF LAKE ERIE/HURON UNDER SOUTHEASTERLY FLOW. WILL STILL EXPECT AREAS OF FOG TO DEVELOP LATE WITH PATCHY DENSE FOG POSSIBLE. HAVE RAISED TEMPS A DEGREE OR SO FOR TONIGHT WITH LOWS IN THE UPPER 30S TO NEAR 40 EXPECTED. && .LONG TERM... INTERACTING/MERGING-CONSOLIDATING UPPER WAVES WILL LEAD TO LARGE PV ANOMALY/UPPER LEVEL LOW DEVELOPING AND TRACKING THROUGH THE SOUTHERN GREAT LAKES/OHIO VALLEY...SENDING TEMPERATURES BACK TO NORMAL (IF NOT BELOW)...WITH SNOW POSSIBLE AS WE HEAD INTO THANKSGIVING AND INTO FRIDAY. THE FIRST SHORTWAVE/UPPER WAVE IS CURRENTLY MOVING INTO THE CENTRAL PLAINS...AND WILL PROVIDE SOME GOOD LARGE SCALE/ISENTROPIC ASCENT TUESDAY NIGHT WITH SURFACE LOW/REFLECTION MOVING OVER LAKE MICHIGAN. THE CENTER OF THIS WAVE...AS SEEN ON GFS TROPOPAUSE MAP AND INDICATED BY 12 HR 500 MB HEIGHT FALL CENTER...WILL MOVE THROUGH SOUTHEAST MICHIGAN ON WEDNESDAY....AS THIS SYSTEM CONTINUES TO HEAD OFF TO THE NORTHEAST...OUTPACING THE NEXT UPSTREAM SYSTEM. THE 850-700 MB THETA-E RIDGE AXIS IS NARROW...BUT SHOULD PROVE SUFFICIENT TO GENERATE RAIN TUESDAY NIGHT WITH THE WARM FRONT/MOISTURE ADVECTION...AND HAVE RAMPED POPS TO HIGH LIKELY WITH 12Z UKMET/NAM/GFS ALL ON BOARD. COLD FRONT/FAIRLY STEEP MID LEVEL LAPSE RATES ON WEDNESDAY WILL PROBABLY BE ENOUGH FOR A FEW SHOWERS. THE MORE IMPRESSIVE UPPER WAVE/TROUGH IS CRASHING ASHORE BRITISH COLUMBIA AND LOOKS TO BE DIGGING THROUGH THE PLAINS-MIDWEST AND INTO THE OHIO VALLEY/SOUTHERN GREAT LAKES ON THURSDAY. THE CENTER OF THE COLD CORE (-32 C AT 500 MB/-8 C AT 850 MB) LOOKS TO RESIDE OVER THE NORTHERN OHIO VALLEY...WITH MATURE MID LEVEL DRY SLOT PUNCHING INTO THE CWA...LIKELY LIMITING OUR PRECIPITATION CHANCES DURING THE DAYTIME HOURS (PER 12Z GFS/EUROPEAN) OF THURSDAY. HOWEVER...IT SHOULD BE NOTED...THE TIMING OF THE MERGING UPPER WAVES AND SUBSEQUENT POSITION OF 500 MB LOW REMAIN IN PLAY...AS SECOND UPPER WAVE DROPS SOUTH FROM ONTARIO PROVIDING AN ADDITIONAL COLD INFUSION AS WE HEAD INTO FRIDAY. REGARDLESS...WITH THE 12Z UKMET/NAM BOTH FASTER AND FARTHER NORTH WITH THE 500 MB LOW ON THANKSGIVING AND COLDER (850 MB TEMPS OF -6 TO -7 C NEAR THE OHIO BORDER) IN THE LOW LEVELS...FELT A LOW CHANCE OF BOTH SNOW AND RAIN SHOWERS WERE JUSTIFIED OVER SOUTH TWO THIRDS OF THE CWA DURING THE DAYTIME HOURS. MUCH BETTER CHANCE OF PRECIPITATION (LIKELY IN THE FORM OF SNOW) THURSDAY NIGHT INTO FRIDAY AS WRAP AROUND/DEFORMATION AXIS WORKS THROUGH (WITH LAKE ENHANCEMENT). CLOUDS AND FURTHER LOW LEVEL COLD ADVECTION DURING THE DAY ON FRIDAY WILL MAKE 40 DEGREE MAXES DIFFICULT TO ACHIEVE. WITH RIDGE AXIS SETTLING OVER LOWER MICHIGAN FRIDAY NIGHT...AND ASSUMING SKIES AT LEAST PARTIALLY CLEAR OUT...LOWS IN THE 20S APPEAR TO BE A GOOD BET. A MODEST WARMUP APPEARS ON TAP FOR THE WEEKEND AS RATHER FLAT UPPER LEVEL RIDGE BUILDS INTO THE GREAT LAKES DURING THE FIRST HALF OF THE WEEKEND. POTENTIAL NEXT STORM SYSTEM MAY IMPACT THE AREA SUNDAY OR EARLY NEXT WEEK. SIGNIFICANT DIFFERENCES WITH MEDIUM RANGE MODELS...AS EUROPEAN STILL ADVERTISING MORE OF A SPLIT FLOW PATTERN. NONE-THE-LESS...WITH 12Z UKMET/EUROPEAN AND GFS ALL SHOWING SOME SEMBLANCE OF LOW PRESSURE SYSTEM/SHORTWAVE TRAVERSING THROUGH THE AREA ON SUNDAY...WILL INTRODUCE CHANCE POPS. && .MARINE... SOUTHEASTERLY WINDS WILL CONTINUE AS HIGH PRESSURE EXITS TO THE EAST COAST AND A LOW PRESSURE SYSTEM SLOWLY APPROACHES FROM THE PLAINS. SOUTHEASTERLY WINDS WILL INCREASE TO 15 TO 20 KNOTS ON THE OPEN WATERS ON WEDNESDAY AS THIS AREA OF LOW PRESSURE APPROACHES...WITH THE POSSIBILITY FOR SMALL CRAFT ADVISORIES ON WEDNESDAY NIGHT AS WINDS VEER AROUND TO THE WEST. WAVES SHOULD INCREASE TO 3 TO 5 FEET ON THE SAGINAW BAY ON WEDNESDAY NIGHT BUT WILL HOPEFULLY BE ABLE TO HOLD OFF ON ANY SMALL CRAFT ADVISORIES ELSEWHERE 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. && .PREV DISCUSSION...ISSUED 1251 PM EST MON NOV 23 2009 AVIATION... MVFR STRATUS REMAINS ACROSS THE SAGINAW VALLEY WITH REDUCED VISIBILITIES HOLDING ON IN THIS AREA. THE VISIBILITIES SHOULD CONTINUE TO IMPROVE THIS AFTERNOON AS STRATUS BECOMES BROKEN DURING THE AFTERNOON. ANOTHER AREA OF WIDESPREAD LOW AND MID CLOUDS COVERING OHIO CONTINUES TO STEADILY ADVANCE NORTH TOWARDS SOUTHEAST MICHIGAN. THIS WILL OVERSPREAD THE AREA WITH CEILINGS REMAINING AOB 2000 FEET INTO THIS EVENING. WINDS WILL REMAIN OUT OF THE SOUTHEAST AGAIN TONIGHT WHICH WILL ALLOW LOW LEVEL MOISTURE TO COME INLAND OFF LAKE ERIE AGAIN. THE OVERCAST SKIES MAY HELP TO KEEP AN ACTUAL FOG FROM DEVELOPING UNTIL VERY LATE WHEN MODELS SHOW THE 2000 FOOT DECK EXCITING THE AREA. THIS COULD ALLOW CEILINGS AND VISIBILITIES TO QUICKLY CRATER AND REMAIN LOW INTO TUESDAY MORNING. THE TAFS SHOW A LOW STRATUS DEVELOPING AROUND 8-9Z AND WILL MONITOR FOR DENSE FOG POTENTIAL OVERNIGHT. A FEW SPRINKLES MAY ALSO BE POSSIBLE BUT CONFIDENCE WAS NOT HIGH ENOUGH TO INCLUDE IN THE TAFS AT THIS TIME. SOME IMPROVEMENT CAN BE EXPECTED BY LATE MORNING ON TUESDAY BUT MVFR CLOUDS WILL LIKELY PERSIST THROUGH THE AFTERNOON. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ SHORT TERM...KEC LONG TERM....SF MARINE.......KEC AVIATION.....KEC YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
