FXUS63 KDTX 020822
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
322 AM EST WED DEC 2 2009

.SHORT TERM...TODAY

SPLIT UPPER LEVEL FLOW ENCOMPASSING MUCH OF THE CENTRAL CONUS EARLY 
THIS MORNING...CHARACTERIZED BY A POSITIVELY TILTED UPPER TROUGH 
DROPPING ACROSS THE NORTHERN PLAINS AND A STRONG CLOSED LOW ROTATING 
THROUGH TEXAS.  SOUTHEAST LOWER MI WILL REMAIN DOWNSTREAM OF THESE 
SYSTEMS TODAY WITH SOUTHWESTERLY FLOW CONTINUING TO DEEPEN IN 
RESPONSE TO THE UPSTREAM HEIGHT FALLS.  THE CORRESPONDING RESPONSE 
IN THE THERMAL FIELD ALREADY EVIDENT WITH TEMPERATURES AS OF 08Z 
HOLDING IN THE MID 30S TO LOWER 40S.  THIS MILD MORNING START WILL 
AID WEAK WARM AIR ADVECTION /MAINLY EARLY/ AND MODEST MIXING TO 
BRING HIGHS NEAR 50.  

CLOUDS WILL THICKEN THROUGH THE DAY AS MOISTURE SPILLS NORTHEAST OF 
THE CLOSED LOW EJECTING INTO THE TENNESSEE VALLEY.  MOISTURE WILL 
RAPIDLY DEEPEN NORTH OF THIS SYSTEM INTO THE AFTERNOON WITH A GOOD 
SURGE OF THETA-E ADVECTION/ISENTROPIC ASCENT STREAMING INTO THE OHIO 
VALLEY.  THE NORTHWEST PERIPHERY OF THIS MOISTURE AXIS WILL ADVECT 
ACROSS THE FORECAST AREA THROUGH MID-LATE AFTERNOON...ACCOMPANIED 
BY GOOD UPPER DIVERGENCE/FAVORABLE UPPER JET SUPPORT.  LIKELY POPS 
REMAIN WARRANTED ACROSS THE SOUTH PRIOR TO 00Z...TAPERING DOWN TO 
A LOW CHANCE NORTH OF I-69.

&&

.LONG TERM...

MASSIVE UPPER LEVEL TROUGH WILL BE ENCOMPASSING MUCH OF THE CONUS
BY FRIDAY...SENDING TEMPERATURES BELOW NORMAL.

RAIN TONIGHT CHANGING TO SNOW AT THE TAIL END WITH JUST LIGHT 
ACCUMULATIONS EXPECTED IF ANYTHING (SLUSHY HALF AN INCH OVER WESTERN 
HALF OF CWA).

THE 00Z RAOB OUT OF DAVENPORT IOWA REVEALED AN 850 MB TEMP OF +8 C 
WITH LINCOLN ILLINOIS COMING IN WITH AN 850 MB TEMP OF +7 C. 
THUS...THE COLD AIR HAS A LONG WAY TO GO AS THE WESTERN GULF COAST 
LOW LIFTS NORTHEAST. THE 00Z UKMET...REGIONAL GEM...AND NAM STILL 
ADVERTISING THE PREFERRED TRACK THROUGH NORTH CENTRAL OHIO. THE 00Z 
GFS HAS TRENDED WEST...BUT STILL THE FARTHEST EAST. EVEN SO...GFS 
SOUNDINGS/GUIDANCE SUPPORT A MOSTLY RAIN EVENT AS WELL. 

TROUGH AXIS/HEART OF THE COLD AIR (-16 TO -18 C AT 850 MB/-22 TO -24 
C AT 700 MB) OVER THE WESTERN GREAT LAKES LATE THURSDAY WILL BE SLOW 
TO ADVANCE EASTWARD...AND WILL JUST GRADUALLY BEGIN TO MODIFY OVER 
THE WEEKEND AS THE FLOW BECOMES A BIT MORE ZONAL. EVEN SO...THE 
GREAT LAKES REGION LOOKS TO BE ON THE NORTH SIDE OF THE UPPER LEVEL 
JET FOR MUCH OF THE FORECAST PERIOD...THUS ANY WARMUP LOOKS TO BE 
TEMPERED. CYCLONIC FLOW WITH EMBEDDED SHORTWAVES ALONG WITH LAKE 
MICHIGAN ACTIVITY IS EXPECTED TO LEAD TO AT LEAST SCATTERED SNOW 
SHOWERS THURSDAY-SATURDAY...WITH GOOD OPPORTUNITY FOR SOME LOW LEVEL 
CONVERGENCE BAND (I-94/M59) THURSDAY NIGHT-FRIDAY TIME FRAME LEADING 
TO LOCALIZED ACCUMULATIONS AS MOISTURE/INVERSION HEIGHTS EXTEND TO 
700 MB. HAVE UPPED POPS TO HIGH SCATTERED AND WILL PROBABLY HAVE TO 
BE RISEN FURTHER AS WE GET CLOSER AND PIN DOWN EXACT LOCATION.

WITH LACK OF SNOW COVER AND HEAT FLUX OF LAKE MICHIGAN...EXPECTING 
MAXES ABOVE 32 DEGREES EACH DAY DESPITE COLD 925 MB TEMPS OF -6 TO 
-8 C ADVERTISED. LOOKING AT MINS PREDOMINATELY IN THE LOW TO MID 20S 
DUE TO EXTENSIVE CLOUD COVER EXPECTED. HOWEVER...ANY NIGHT WHICH 
CLEARS OUT WILL HAVE THE POTENTIAL FOR TEMPERATURES TO DROP INTO THE 
TEENS. WEAK SURFACE RIDGING/LOWERING INVERSION HEIGHTS COULD ALLOW 
SKIES TO PARTIALLY CLEAR OUT FRIDAY NIGHT AND ESPECIALLY SATURDAY 
NIGHT.

&&

.MARINE...

SOUTHWEST WINDS WILL REMAIN RELATIVELY WEAK TODAY AS A COLD FRONT 
SLIDES INTO THE STATE.  WINDS WILL SHIFT TOWARD THE NORTHEAST WHILE 
INCREASING TONIGHT IN RESPONSE TO A LOW PRESSURE SYSTEM LIFTING 
THROUGH THE OHIO VALLEY.  GUSTS WILL REACH 25-30 KNOTS AT TIMES 
OVERNIGHT INTO THURSDAY.  THE ONSHORE FLOW WILL CREATE ROUGH WAVE 
CONDITIONS WITH WAVE HEIGHTS BUILDING UP TO 10 FEET ON THE NEARSHORE 
WATERS OF LAKE HURON.  THE POTENTIAL EXISTS FOR GUSTS TO BRIEFLY 
REACH GALE FORCE ON SOUTHERN LAKE HURON EARLY THURSDAY MORNING...
BUT THE LIMITED DURATION OF SEEING MARGINAL GALES WILL PRECLUDE 
ISSUING A GALE WARNING AT THIS POINT.    

SLACKENING PRESSURE GRADIENT WILL ALLOW GUSTS TO BRIEFLY DIMINISH 
THURSDAY EVENING...WITH A SUBSEQUENT DROP IN WAVE HEIGHTS INTO 
THURSDAY NIGHT.  SOUTHWEST WINDS WILL THEN STRENGTHEN AGAIN ON 
FRIDAY.  THIS COMBINED WITH COLD AIR MOVING OVER THE WARMER WATERS 
WILL LEAD TO UNSTABLE CONDITIONS FRIDAY.

&&

.PREV DISCUSSION...ISSUED 1149 PM EST TUE DEC 1 2009 

AVIATION...

VFR CONDITIONS WILL BE MAINTAINED THROUGH THE AFTERNOON THANKS TO A 
VERY DRY LOW LEVEL AIRMASS NOW IN RESIDENCE ACROSS THE SOUTHERN 
GREAT LAKES. THE STORM SYSTEM NOW OVER THE GULF COASTAL REGION IS 
FORECAST TO LIFT INTO THE UPPER OHIO VALLEY THIS EVENING...SPREADING 
RAIN AND LOW LEVEL MOISTURE INTO SOUTHEAST MICHIGAN. THIS WILL 
RESULT IN DETERIORATING CONDITIONS AFTER 00Z.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT 
     HURON INCLUDING OUTER SAGINAW BAY...FROM 10 PM WEDNESDAY TO 10 
     PM THURSDAY.

     SMALL CRAFT ADVISORY...INNER SAGINAW BAY...FROM 10 PM WEDNESDAY TO 
     4 PM THURSDAY.

LAKE ST CLAIR...
     SMALL CRAFT ADVISORY...FROM 10 PM WEDNESDAY TO 4 PM THURSDAY.

MI WATERS OF LAKE ERIE...
     SMALL CRAFT ADVISORY...FROM 10 PM WEDNESDAY TO 4 PM THURSDAY.

&&

$$

SHORT TERM...MR
LONG TERM....SF
MARINE.......MR
AVIATION.....SC

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