FXUS63 KDTX 222110
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.
&&
.PREV DISCUSSION...ISSUED 1201 PM EST TUE DEC 22 2009
AVIATION...
THE LOW LEVELS WILL CONTINUE TO DRY OUT AS A STRONG SURFACE RIDGE
BUILDS INTO SOUTHEAST MICHIGAN THROUGH TOMORROW...SUPPORTING
PREDOMINATELY CLEAR SKIES (BELOW 12000 FEET) ONCE LOW/MID CLOUDS
EXIT THE SOUTHERN TAFS THIS AFTERNOON. NORTHEAST FLOW OFF LAKE
HURON IS TEMPORARILY MASKING THE DRYING TREND WITH LAKE
CLOUDS...BUT INCREASING ANTICYCLONIC FLOW WILL EVENTUALLY WIN
OUT. HOWEVER...WITH SHALLOW SURFACE MOISTURE...DO THINK LIGHT FOG
IS POSSIBLE LATE TONIGHT...AND WILL MAINTAIN THE LOW MVFR VSBY
MENTION.
&&
.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.
&&
$$
SHORT TERM...SF
LONG TERM....KEC
MARINE.......SF
AVIATION.....SF
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
