FXUS63 KDTX 260817
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
317 AM EST SAT DEC 26 2009

.SHORT TERM...TODAY

OCCLUDED FRONT HAS LIFTED NORTH OF THE AREA AND TAKEN THE STEADIER 
RAINFALL WITH IT. WITH CAA...PRECIPITATION TYPE WILL CHANGE QUICKLY 
OVER TO SNOW EARLY THIS MORNING...AND EXPECT SCATTERED LIGHT SNOW 
SHOWERS AS ONE OF THE MAJOR VORTICITY CENTERS EMBEDDED WITHIN THE 
LARGE UPPER LOW TO WEST PIVOTS INTO THE WESTERN AND CENTRAL GREAT 
LAKES. THIS ACTIVITY WILL BE RATHER LIGHT WITH LESS THAN AN INCH OF 
ACCUMULATION EXPECTED. ONCE THIS VORT LOBE SHIFTS NORTH THROUGH LAKE 
MICHIGAN...SNOW SHOWERS WILL TAPER OFF BY MIDDAY AS THE UPPER LOW 
REMAINS TO THE WEST THROUGH THE DAY. TEMPERATURES WILL BE COOLER 
TODAY WITH HIGHS NEAR 30. WITH THE COLD AIR JUST NOW OVERSPREADING 
THE REGION...THIS ESSENTIALLY MEANS RELATIVELY STEADY TEMPERATURES
INTO THE AFTERNOON.

&&

.LONG TERM...

SEASONABLY COLD WEATHER WITH A FEW SNOW SHOWERS CAN BE EXPECTED 
DURING THE NEXT COUPLE OF DAYS. 

700-500 MB LOWS/MID LEVEL CIRCULATION REMAINS ON TRACK TO SWING 
THROUGH SOUTHERN LOWER MICHIGAN ON SUNDAY...LEADING TO STEEP LOW 
LEVEL LAPSE RATES/INSTABILITY...WORTHY OF GENERATING AT LEAST 
SCATTERED SNOW SHOWERS. LOW LEVEL WINDS VEERING AROUND TO A MORE 
WESTERLY DIRECTION OFF LAKE MICHIGAN SHOULD ALSO PROVIDE AN ADDED 
BONUS.

MEANWHILE...POLAR VORTEX WILL SINK SOUTHEAST AND BECOME ENTRENCHED 
NEAR SOUTHAMPTON ISLAND IN CANADA ON SUNDAY...WITH AN UPPER 
WAVE/TROUGH EXTENSION SWINGING THROUGH THE EASTERN GREAT LAKES LATE 
MONDAY. LOW LEVEL CONVERGENCE/LOW STATIC STABILITY WITH AN ARCTIC 
FRONT SWINGING SOUTH THROUGH LOWER MICHIGAN DURING MONDAY APPEARS 
FAVORABLE TO GENERATE ANOTHER ROUND OF AT LEAST SCATTERED SNOW 
SHOWERS. LIGHT SNOW ACCUMULATIONS ARE POSSIBLE BOTH DAYS. 925 MB 
TEMPS PROGGED TO FALL TO -12 C OR SLIGHTLY COLDER BY TUESDAY 
MORNING...SETTING UP A COLD NIGHT MONDAY NIGHT (LOW/MID TEENS) WITH 
THE POTENTIAL FOR MINS TO FALL INTO THE SINGLE NUMBERS IF WINDS ARE 
ABLE TO DECOUPLE BY MORNING. THE AIRMASS WILL HAVE A HARD TIME 
RECOVERING ON TUESDAY WITH SURFACE HIGH/RIDGE IN PLACE (MAXES MOSTLY 
IN THE MIDDLE 20S). GENERAL SUBSIDENCE/NORTHWEST CONFLUENT FLOW 
SHOULD ASSURE A DRY DAY...BUT A FLURRY IS ALWAYS A CONCERN WITH 
NORTHWEST FLOW AND POSSIBLY JUST ENOUGH 925 MB MOISTURE.

UPPER LEVEL RIDGE AXIS IS THEN FORECASTED TO SWING THROUGH THE 
CENTRAL GREAT LAKES TUESDAY NIGHT/WEDNESDAY MORNING...WITH 
PREDOMINATELY SPLIT FLOW ADVERTISED OVER THE CONUS...TRENDING TOWARD 
MORE AMPLIFIED/PHASED SCENARIO TOWARD THE END OF THE WORK WEEK. AT 
THIS POINT...IT APPEARS THE NORTHERN STREAM WILL DOMINATE OUR 
WEATHER...WITH MERGING/PHASING OCCURRING JUST A BIT TOO LATE FOR US 
TO EXPECT A BIG SNOWSTORM...BUT A LIGHT ROUND OF SNOW WEDNESDAY 
NIGHT-THURSDAY APPEARS POSSIBLE AHEAD OF A SHORTWAVE TROUGH/SURFACE 
COLD FRONT.

&&

.MARINE...

OCCLUDED FRONT WILL SHIFT THROUGH THE REMAINDER OF LAKE HURON DURING 
THE MORNING...BRINGING AS GRADUAL END TO THE STRONG EASTERLY FLOW AS 
WINDS TURN TO THE SOUTH/SOUTHWEST AND DECREASE SOMEWHAT. WILL EXPIRE 
THE CURRENT HEADLINES ON TIME AS GUSTS OVER NORTHERN LAKE HURON ARE 
ONLY AROUND 30 KNOTS ATTM ANYWAY...AND NEARSHORE CONDITIONS WILL BE 
IMPROVING STEADILY WITH OFFSHORE FLOW OF 10-20 KNOTS. ANY REMAINING 
MIX OF RAIN/SNOW WILL BECOME LIGHT SNOW SHOWERS DURING THE DAY AS 
CAA CONTINUES.

&&

.PREV DISCUSSION...ISSUED 1148 PM EST FRI DEC 25 2009 

AVIATION...

SUBSTANTIAL LOW LEVEL MOISTURE WILL REMAIN IN PLACE THROUGH THE TAF 
PERIOD ENSURING MVFR CEILINGS HOLD DURING THIS TIME.  ANY LINGERING 
LIGHT RAIN WILL END SHORTLY WITH THE PASSAGE OF A COLD FRONTAL 
BOUNDARY.  DRIER MID LEVEL AIR WORKING IN BEHIND THIS FRONT WILL 
KEEP PRECIPITATION CHANCES MINIMAL THROUGH THE MORNING HOURS.  
MOISTURE WILL DEEPEN AGAIN BY SATURDAY AFTERNOON LEADING TO 
SCATTERED SNOW SHOWER DEVELOPMENT.  THE DEVELOPING POST-FRONTAL 
SOUTHERLY WIND FIELD WILL DIMINISH SLIGHTLY OVERNIGHT WITH THE 
GUSTINESS SUBSIDING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

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

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