FXUS63 KDTX 102355
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
655 PM EST THU DEC 10 2009

.AVIATION...

STRONG WESTERLY WINDS WILL CONTINUE TO CARRY COLD AIR INTO THE 
REGION TONIGHT AND FRIDAY. SPEEDS WILL DROP DOWN TO AROUND 20 KNOTS 
DURING THE NIGHT AND HELP ALLEVIATE THE BLOWING SNOW THAT HAS 
REDUCED VISIBILITY AT TIMES. THIS AIR WILL BE DRY AS WELL, WHICH 
WILL OPEN UP SOME SKY ESPECIALLY IN THE DETROIT AREA AND FOR THE 
MAJORITY OF THE TIME AT MBS. FNT AND PTK WILL BE IN AND OUT OF THE 
CLOUDS AND RESIDUAL LAKE EFFECT SNOW SHOWERS THROUGH THE NIGHT AND 
INTO THE MID MORNING HOURS AFTER SUNRISE. WIND GUSTS ARE EXPECTED TO 
RUN BACK UP TO 30 KNOTS DURING FRIDAY BUT WITH VFR CONDITIONS THE 
VAST MAJORITY OF THE TIME OVER THE AREA.

&&

.PREV DISCUSSION...ISSUED 357 PM EST THU DEC 10 2009 

SHORT TERM...THIS AFTERNOON AND TONIGHT

A DRY...ARCTIC AIRMASS INFILTRATED THE REGION TODAY WHICH HAS TAKEN 
A MASSIVE TOLL ON UPSTREAM LAKE EFFECT ACTIVITY. THIS IS EVIDENCED 
NICELY BY RECENT KGRR REFLECTIVITY TRENDS WHICH SHOWS A RAPID 
EASTWARD PROGRESSION/DISSIPATION OF THE LAKE MICHIGAN CONVECTION 
(HIRES WRF SIMULATIONS HAVE EXCELLENT TIMING). THE PRIMARY REASONING 
FOR THE WEAKENING LES IS THE SHRINKING CONVECTIVE DEPTHS DUE TO THE 
TOTAL LACK OF MOISTURE IN THE PARENT AIRMASS. IN ADDITION...MODEL 
SOUNDINGS OVERNIGHT BRING A LOWERING SUBSIDENCE INVERSION WHICH WILL 
LIMIT CONVECTIVE DEPTHS EVEN MORE. GIVEN THE DEEP CYCLONIC FLOW AND 
AMOUNT OF INSTABILITY OVER THE LAKES WILL NEED TO KEEP A LIGHT SNOW 
SHOWER MENTION OVERNIGHT. ADDITIONAL SNOWFALL ACCUMULATIONS TONIGHT 
WILL REMAIN AT AN INCH OR LESS. THE AREA WITH THE GREATER POTENTIAL 
TO OBSERVE AN ACCUMULATION WILL BE ACROSS THE CENTRAL PORTIONS OF THE 
CWA AS THE WIND TRAJECTORIES HOLD WEST SOUTHWESTERLY OVERNIGHT.

SKIES TONIGHT ARE EXPECTED TO THIN...AND WILL CARRY PARTLY CLOUDY 
CONDITIONS. THE LOW TEMPERATURE FORECAST IS AN INTERESTING ONE AS 
DEWPOINTS HAVE ADVECTED INTO THE SINGLE DIGITS ABOVE ZERO TO NEAR 
ZERO. EXPECTING THE MIXED WESTERLIES OF 20 MPH OR OVER WILL KEEP 
TEMPERATURES RELATIVELY BUOYED. HOWEVER...GIVEN THE FRESH SNOW AND 
PUNCH OF THE COLD AIR HAVE TAKEN A COUPLE/FEW DEGREES OFF INHERITED 
VALUES. LOOKING AT LOWS IN THE SINGLE DIGITS ABOVE ZERO ACROSS THE 
NORTH AND SOUTH...WITH AROUND 10 FOR THE CENTRAL PORTIONS OF THE 
CWA/HEAT ISLAND. WIND CHILL VALUES WILL BE VERY COLD IN THE -5 TO 
-15F RANGE.

LONG TERM...FRIDAY THROUGH THURSDAY

LAKE EFFECT SNOW WILL TAPER OFF TOMORROW MORNING AS MOISTURE AND 
INSTABILITY DECREASE. ONLY EXPECTING A FEW LEFTOVER SNOW SHOWERS 
ALONG THE I69 CORRIDOR...DISSIPATING BY TOMORROW AFTERNOON. SURFACE 
RIDGE AXIS WILL MOVE OVER OUR AREA ON FRIDAY NIGHT AND WINDS WILL 
SHIFT TO A MORE SOUTHERLY DIRECTION. POTENTIAL EXISTS FOR DECENT 
RADIATIONAL COOLING SATURDAY MORNING AS WINDS DECREASE BUT WILL 
LARGELY BE DEPENDENT ON CLOUD COVER. NAM RH FIELDS SUGGEST A FEW 
HIGH CLOUDS WILL BE STREAMING IN AT THAT TIME SO DID NOT LOWER MIN 
TEMPS MUCH. MAX TEMPS WILL REBOUND INTO THE LOW 30S ON SATURDAY WITH 
SOUTHERLY WINDS AND 950 MB TEMPS WARMING TO -3C. 

NEXT CHANCE FOR WIDESPREAD PRECIP WILL BE ON SUNDAY MORNING IN 
ASSOCIATION WITH DECENT WAA ON THE BACKSIDE OF EXITING HIGH 
PRESSURE. 00Z ECMWF HAS COME INTO BETTER AGREEMENT WITH THE GFS IN 
SHOWING GOOD ISENTROPIC LIFT SO BUMPED UP POPS FOR SUNDAY. VERY 
LITTLE UPPER LEVEL SUPPORT FOR THIS PRECIP THOUGH AND GIVEN THE 
LIMITED DURATION...NOT EXPECTING MUCH IN TERMS OF ACCUMULATIONS. 
ALSO BUMPED UP LOW TEMPS FOR SUNDAY NIGHT AS WARMER AIR CONTINUES TO 
MOVE INTO THE AREA.

ANOTHER SOUTHERN STREAM SYSTEM WILL COME ONSHORE OVER 
CALIFORNIA AND MOVE NORTHEAST INTO OUR REGION ON MONDAY WHILE 
ATTEMPTING TO PHASE WITH THE UPPER LOW OVER CANADA. THE TRACK OF 
THIS CANADIAN LOW WILL LARGELY DETERMINE WHETHER THIS SYSTEM PASSES 
OVER US AND GENERATES PRECIP OR MOVES TOO FAR NORTH. 12Z GFS WEAKENS 
THE UPPER LOW AND SHIFTS IT OFF TO THE EAST WHILE THE ECMWF 
MAINTAINS A STRONGER LOW OVER MANITOBA...SENDING THE PRECIP FARTHER 
SOUTH INTO OUR AREA. ECMWF SOLUTION IS PREFERRED AFTER LOOKING AT 
HOW THE MODELS INITIALIZED AND SEEING THAT THE GFS IS INITIALLY TOO 
WEAK WITH THE LOW COMPARED TO THE EURO. FORECAST SOUNDINGS SUGGEST 
THAT A MIX OF RAIN AND SNOW WILL BE POSSIBLE DURING THE DAY ON 
MONDAY AS SURFACE TEMPERATURES RISE INTO THE LOWER 40S ACROSS THE 
SOUTHERN HALF OF THE CWA. MUCH COLDER AIR WILL FILTER IN BEHIND THE 
SYSTEM AS A 1040 MB HIGH SLIDES ACROSS THE NORTHERN PLAINS. THIS 
WILL MAKE LAKE EFFECT SNOW OFF OF LAKE HURON A CONCERN BUT GIVEN HOW 
FAR OUT IN TIME IT IS AND THE UNCERTAINTY OVER THE EXACT WIND 
DIRECTION...WILL MAINTAIN LOW POPS. BEYOND THAT...THE EXTENDED 
PERIOD WILL BE RELATIVELY QUIET WITH MAINLY ZONAL FLOW.

MARINE...

STRONG WESTERLIES WILL CONTINUE INTO THE WEEKEND AS THE TIGHT 
PRESSURE GRADIENT IS MAINTAINED BETWEEN THE LARGE LOW PRESSURE 
SYSTEM NEAR THE CANADIAN MARITIMES AND THE SPRAWLING HIGH CRAWLING 
ACROSS THE SOUTHERN CONUS. UNSTABLE CONDITIONS OVER THE RELATIVELY 
WARM WATERS OF THE GREAT LAKES WILL ENSURE GALES OVER OPEN WATERS 
THROUGH FRIDAY. THE TIGHTENED PRESSURE GRADIENT WILL WEAKEN LATE 
THIS WEEKEND AS A SURFACE RIDGE FINALLY ROTATES INTO SOUTHEASTERN 
MICHIGAN.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     GALE WARNING...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...UNTIL 10 
     PM FRIDAY.

     GALE WARNING...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON 
     INCLUDING SAGINAW BAY...UNTIL 4 AM FRIDAY.

LAKE ST CLAIR...
     GALE WARNING...UNTIL 4 AM FRIDAY.

MI WATERS OF LAKE ERIE...
     GALE WARNING...UNTIL 4 AM FRIDAY.

     LOW WATER ADVISORY...UNTIL 10 PM THURSDAY.

&&

$$

AVIATION.....BT
SHORT TERM...CB
LONG TERM....AGD
MARINE.......CB

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