FXUS63 KDTX 222253
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
553 PM EST TUE DEC 22 2009

.AVIATION...

RESIDUAL STRATO CU /BASED AROUND 2500 FT/ IS EXPECTED TO CLEAR OUT 
OF THE DETROIT AREA OVER THE NEXT COUPLE OF HOURS AS DRIER AIR 
CONTINUES TO ADVECT IN FROM THE NORTHEAST. THE LOW LEVEL WIND FIELD 
OVER LAKE HURON IS ALSO FORECAST TO BACK A LITTLE MORE 
NORTH-NORTHWEST TONIGHT WHICH WILL LIMIT THE CHANCES OF
ADDITIONAL LAKE CLOUDS IMPACTING THE TERMINALS. OBSERVATIONS OVER
THE LAST COUPLE OF HOURS HAVE SHOWN DEWPOINTS REALLY STARTING TO FALL
ACROSS SE MI. GIVEN THE DEGREE OF SURFACE DRY AIR ADVECTION...WILL
REMOVE ANY MENTION OF FOG FROM THE TAFS AND MAINTAIN VFR
CONDITIONS THROUGH THE ENTIRE TAF CYCLE.

&&

.PREV DISCUSSION...ISSUED 410 PM EST TUE DEC 22 2009 

SHORT TERM...TONIGHT

A COLD NIGHT IS EXPECTED AS TEMPERATURES DROP INTO THE TEENS 
(OUTSIDE OF THE CITY). THERE IS EVEN POTENTIAL FOR MINS TO DROP INTO 
THE SINGLE NUMBERS IN THE NORMALLY COLDER LOCATIONS...BUT LIGHT 
NORTH/NORTHEAST FLOW COMING OFF LAKE HURON AND HIGH CLOUDS (SOUTH) 
ADD A BIT OF UNCERTAINTY. ALSO...SNOW MELT WITH THE PARTIAL SUNSHINE 
TODAY HAS/WILL CONTRIBUTE TO THE SURFACE MOISTURE...PRIMING US FOR 
POSSIBLE LIGHT FOG OVERNIGHT AS STRONG SURFACE RIDGE BUILDS INTO 
SOUTHEAST MICHIGAN. IN ANY EVENT...WILL FOLLOW THE MAV 
GUIDANCE...WITH THE TRI-CITIES REGION STANDING THE BEST CHANCE OF 
FALLING INTO THE SINGLE NUMBERS. 

ANY FLURRIES/LIGHT SNOW TOWARD THE OHIO BORDER THIS AFTERNOON WILL 
COME TO AN END AS SHEARED OUT UPPER WAVE TRACKING THROUGH THE OHIO 
VALLEY EXITS EAST WITH NORTHWEST CONFLUENT FLOW/GENERAL SUBSIDENCE 
IN CONTROL OVERNIGHT.

LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY

A RIDGE OF HIGH PRESSURE OVER THE CENTRAL GREAT LAKES WILL KEEP THE 
WINDS OUT OF THE EAST AND ENSURE A DRY FORECAST FOR WEDNESDAY AND 
THURSDAY. THE ATMOSPHERE WILL BE DRY ABOVE A STRENGTHENING INVERSION 
BUT THE NAM IS HINTING THAT MOISTURE COMING IN OFF LAKE HURON COULD 
CREATE SOME STRATUS ACROSS THE THUMB. HAVE INCREASED SKY COVER FOR 
THE THUMB TO A PARTLY TO MOSTLY CLOUDY MIX ON WEDNESDAY. FURTHER 
INLAND WE ARE EXPECTED TO START MIXING INTO THE DRIER AIR ALOFT 
EARLY ENOUGH TO PREVENT THE STRATUS FROM FULLY BLANKETING THE AREA 
WITH OVERCAST SKIES. 

STRONG STORM SYSTEM DEVELOPING OVER THE MISSISSIPPI VALLEY REMAINS 
THE FOCUS OF THE FORECAST AS WE HEAD INTO THE CHRISTMAS HOLIDAY. 12Z 
GFS/UKMET/GEM ARE IN GOOD AGREEMENT WITH THE TRACK OF THE SYSTEM 
WITH NO GLARING INITIALIZATION ERRORS. THE NAM IS AN OUTLIER AND 
DOES NOT SHOW THE SURFACE CYCLONE RAPIDLY DEEPENING AS IT LIFTS 
NORTH. THIS SEEMS UNLIKELY GIVEN THE STRONG UPPER LEVEL DIVERGENCE 
THAT WILL OCCUR AS THE TROUGH TAKES ON A NEGATIVE TILT. THE BETTER 
MODEL CONSENSUS SHOWS THE LOW PRESSURE SYSTEM OCCLUDING BY THE TIME 
IT REACHES SOUTHEAST MISSOURI(00Z FRIDAY) THEN CONTINUING TO DEEPEN 
AS IT CURVES WESTWARD BACK OVER IOWA(12Z FRIDAY). STRONG THETA-E 
ADVECTION OCCURS OVER LOWER MICHIGAN BETWEEN 03-09Z ON THURSDAY 
NIGHT WITH PRECIPITATION OVERSPREADING THE AREA FROM SOUTH TO NORTH. 
PRECIPITATION TYPE REMAINS THE BIG CHALLENGE WITH THIS SYSTEM AS THE 
ELEVATED WARM FRONT LIFTS NORTH OVER A COOL BOUNDARY LAYER. 
TEMPERATURES WITHIN THE WARM LAYER ARE EXPECTED TO BE AS HIGH AS
4-5C WHICH WILL LIMIT CHANCES OF SNOW AND MAKE FREEZING RAIN OR
RAIN THE MOST LIKELY PRECIPITATION TYPES. SOME COOLING IS EXPECTED
WITH THE COLUMN AT THE ONSET OF PRECIPITATION DUE TO EVAPORATION
THEN CONTINUING TO COOL THE COLUMN WITH MELTING OVERNIGHT. AT THE
SAME TIME SURFACE TEMPERATURES WILL BE WARMING AND CLIMB ABOVE
FREEZING FOR MOST OF SOUTHEAST MICHIGAN BY CHRISTMAS MORNING...
ALLOWING THE REMAINING PRECIPITATION TO FALL AS RAIN IN THE SOUTH
OR A WET RAIN/SNOW MIX IN THE NORTH ON CHRISTMAS DAY.

AT THIS TIME THE ICING POTENTIAL IS LARGELY DEPENDENT ON THE PUSH OF 
LOW LEVEL WARM AIR APPROACHING WITH THE OCCLUDED FRONT TOWARDS DAWN. 
SURFACE TEMPERATURES WILL NOT BE OVERLY COLD AS WE HEAD INTO 
THURSDAY NIGHT BUT DEWPOINTS IN THE MID TO UPPER 20S ALLOW ROOM FOR 
THE TEMPERATURE TO DROP TO BETWEEN 29-32 AS PRECIPITATION BEGINS. 
CONFIDENCE REMAINS LOW AT THIS TIME IN THE AMOUNT OF ICING AS WE HUG 
THE FREEZING MARK. THE POTENTIAL REMAINS FOR A FEW TENTHS OF AN INCH 
OF ICING AFTER MIDNIGHT WHICH MAY CAUSE SLICK CONDITIONS ON AREA 
ROADWAYS. IMPROVEMENT IS EXPECTED TOWARDS DAWN AS TEMPERATURES CREEP 
ABOVE FREEZING AND RAIN EVEN HELPS TO MELT ANY ICE DURING THE 
MORNING HOURS. THE EXCEPTION TO THIS MAY BE ACROSS THE SAGINAW 
VALLEY WHERE THE COLUMN WILL BE COOLER AND MINOR SNOW ACCUMULATIONS 
OF A COUPLE INCHES ARE POSSIBLE BEFORE A SIZABLE DRY-SLOT MOVES 
OVERHEAD CHRISTMAS AFTERNOON. MODEL QPF IS ALSO IN QUESTION WITH THE 
NAM/GFS BOTH SHOWING BETWEEN A HALF AND ONE INCH OF QPF. WITH 
CONVECTION ONGOING TO THE SOUTH AND THE MOISTURE AXIS LIFTING 
THROUGH RATHER QUICKLY AHEAD OF THE DRY-SLOT...WOULD NOT BE 
SURPRISED TO SEE QPF TOTALS END UP BEING CLOSER TO .3 TO .5 INCH. 

STRONG COLD AIR ADVECTION ARRIVES BY CHRISTMAS NIGHT AS THE NEARLY 
VERTICALLY STACKED SYSTEM LIFTS NORTH OVER WISCONSIN. DEEP MOISTURE 
RETURNS WITH SCATTERED SNOW SHOWERS EXPECTED TO CONTINUE THROUGH THE 
WEEKEND AS THIS SYSTEM LINGERS OVERHEAD. WE WILL BE MONITORING THE 
TRAJECTORY OF BOTH LAKE EFFECT SNOW SHOWERS OFF OF LAKE MICHIGAN AND 
SURFACE TROUGHS MOVING THROUGH THE BROAD CYCLONIC FLOW INTO MONDAY 
THAT COULD ENHANCE SNOW SHOWERS WITH MINOR ACCUMULATIONS POSSIBLE. 
TEMPERATURES WILL RETURN TO BELOW NORMAL FOR THE WEEKEND AND INTO 
THE EARLY PART OF NEXT WEEK.

MARINE...

RIDGING EXTENDING FROM A STRONG HIGH LOCATED OVER ONTARIO WILL 
CONTINUE TO BUILD INTO THE CENTRAL GREAT LAKES THROUGH 
TOMORROW...ALLOWING NORTHERLY WINDS AND SUBSEQUENT WAVES IN EXCESS 
OF 4 FEET TO PERSIST OVER SOUTHERN LAKE HURON. A DEEPENING LOW 
PRESSURE SYSTEM IS THEN EXPECTED TO TRACK UP THE MISSISSIPPI RIVER 
VALLEY THURSDAY AND FRIDAY. THE PRESSURE GRADIENT BETWEEN THE HIGH 
TO THE NORTH AND THIS LOW PRESSURE SYSTEM WILL LEAD TO STRONG 
EASTERLIES BY FRIDAY...WITH GALES LIKELY OVER THE OPEN WATERS OF 
LAKE HURON AND POSSIBLY OVER THE NEARSHORE WATERS AS WELL. 
A GALE WATCH HAS BEEN ISSUED WITH THIS FORECAST PACKAGE FOR ALL OF 
LAKE HURON FOR FRIDAY THROUGH FRIDAY EVENING.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT 
     HURON INCLUDING OUTER SAGINAW BAY...UNTIL 7 PM WEDNESDAY.

     GALE WATCH...LHZ361-LHZ362-LHZ363-LHZ421-LHZ422-LHZ441-LHZ442-
     LHZ443-LHZ462-LHZ463-LHZ464...FROM 7 AM FRIDAY TO MIDNIGHT 
     SATURDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

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

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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).