000
FXUS63 KDTX 032114
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
414 PM EST WED DEC 3 2008
.SHORT TERM...THIS AFTERNOON AND TONIGHT
RADAR IMAGERY FOR THE IMMEDIATE VICINITY HAS BEEN VERY QUIET TO THIS
POINT WITH PRECIPITATION REMAINING ACROSS NORTHERN LOWER MICHIGAN.
THIS ENHANCED AREA OF 700-500MB FGEN FORCING...ALIGNED NORTHEAST TO
SOUTHWEST ALONG THE LEAD U/L JETLET WILL SETTLE/FILL SOUTHEASTWARD
INTO THE NORTHERN PORTIONS OF THE CWA DURING THE NEXT FEW HOURS.
THE MAIN POLAR JET CORE IS EXPECTED TO STRENGTHEN THIS EVENING AS
THE SHORTWAVE FEATURE OF INTEREST DIGS/SLIDES THROUGH IOWA AND INTO
WISCONSIN. DUE TO THE AGEOSTROPHIC RESPONSE...A SECONDARY BATCH OF
STRONGER MIDLEVEL FGEN AND RESULTANT PRECIPITATION WILL DEVELOP OVER
PORTIONS OF NORTHERN INDIANA...(SHOWING UP RATHER NICELY IN THE
UPSTREAM IWX RADAR AND SATELLITE). THIS IS ALSO EXPECTED TO FILL IN
QUICKLY OVER THE NEXT COUPLE OF HOURS AFFECTING MUCH OF CWA DURING
THE THE 5-10 PM TIMEFRAME. WITH ALL SITES RECORDING AFTERNOON SURFACE
TEMPERATURES IN THE MID 30S AT MINIMUM HAVE INCLUDED A CHANCE OF
RAIN AT THE ONSET FOR THE NORTHERN PORTIONS/WHILE MAINTAINING AN ALL
RAIN MENTION EARLY FOR THE METRO AREA. ALONG THE RIVERS...SEVERAL
OBSERVATIONS HAVE EVEN CHECKED IN WITH MID 30 DEWPOINTS. STILL
EXPECTING NORTHERN AREAS/IRISH HILLS TO QUICKLY CHANGE OVER TO ALL
SNOW DUE TO THE HIGHER ELEVATION AND EVAPORATIONAL COOLING. THERE
ARE ALOT ISSUES GOING AGAINST SIGNIFICANT ACCUMULATIONS...WHICH
INCLUDE MODEST FORCING...WARMER SURFACE TEMPERATURES AT THE
START...TRANSIENT BEHAVIOR OF THE SYSTEM...AND INFLUX OF DRY
MIDLEVEL AIR THIS EVENING. THE GFS/NAM THIS MORNING ARRIVED WITH
DIFFERING SOLUTIONS BUT LATEST CHECK OF OBSERVATIONAL DATASETS GIVE
THE EDGE TO THE GFS. THEREFORE...DID CUT SNOWFALL ACCUMULATIONS A
TOUCH FROM EARLIER FORECASTS. LESS THAN INCH IS EXPECTED FOR WAYNE
AND MONROE COUNTIES...WITH A GENERAL 1 TO 2 INCHES POSSIBLE FOR
SURROUNDING AREAS.
DESPITE THE WARMER TEMPERATURES...CONDITIONS THIS EVENING WILL FEEL
RATHER BREEZY AND DAMP CONDITIONS. TEMPERATURES TONIGHT WILL DROP
WITH THE PASSAGE OF THE FRONT SETTLING INTO THE MID TO UPPER 20S BY
TOMORROW MORNING.
&&
.LONG TERM...THURSDAY THROUGH WEDNESDAY
A VERY COLD AIRMASS WILL CONTINUE TO SPREAD OVER THE REGION ON THURSDAY
WITH TEMPERATURES HOLDING STEADY OR SLIGHTLY FALLING DURING THE DAY.
850MB TEMPERATURES FALL TO AROUND -15C AND EARLY HIGHS WILL BE IN THE
UPPER 20S TO NEAR 30. AVAILABLE MOISTURE WILL BE A LIMITING FACTOR
FOR ANY ACCUMULATING SNOW WITH THE MID LEVEL DRY SLOT IN PLACE OVER
SOUTHERN LOWER MICHIGAN AHEAD OF THE NEXT APPROACHING UPPER LEVEL
TROUGH. THE AVAILABLE SHALLOW MOISTURE WITH CYCLONIC FLOW AND COLD
AIR ADVECTION WILL BE SUFFICIENT HOWEVER TO GENERATE SCATTERED
LIGHT SNOW SHOWERS WITH THE BEST COVERAGE TOWARDS THE SAGINAW
VALLEY DURING THE DAY. BY LATE AFTERNOON...THE INCREASING MOISTURE
DEPTH COMBINED WITH STRONG INSTABILITY OVER LAKE MICHIGAN WILL
LEAD TO INCREASING LAKE EFFECT SNOW SHOWERS FROM THURSDAY NIGHT
INTO FRIDAY MORNING. BOTH THE NAM AND GFS INDICATE MINOR QPF
AMOUNTS ALONG THE I-94 TO I-96 CORRIDOR. HIGH PRESSURE BUILDING
OVER THE OHIO VALLEY WILL ACT TO ENHANCE CONVERGENCE AND SNOW
SHOWERS IN THIS AREA AND HAVE RAISED POPS WITH MINOR ACCUMULATIONS
POSSIBLE IN MAINLY LIVINGSTON/WASHTENAW/WESTERN OAKLAND COUNTIES.
AS THIS SERIES OF SHORTWAVES DEPARTS THE REGION LATE FRIDAY...A
REINFORCING SHORTWAVE WILL DIVE TOWARDS THE UPPER MIDWEST...BRINGING A
FAST MOVING CLIPPER WITH IT. ISENTROPIC ASCENT WITH CONDENSATION
PRESSURE DEFICITS APPROACHING 0 MB BY SATURDAY MORNING CONTINUE TO
SUPPORT SNOW ON SATURDAY WITH MINOR WIDESPREAD ACCUMULATIONS OF 1 TO 2
INCHES. THIS CLIPPER USHERS IN ANOTHER SHOT OF ARCTIC AIR WITH HIGHS
RUNNING 10 TO 15 DEGREES BELOW NORMAL THROUGH THE WEEKEND. SUNDAY NIGHT
COULD BE A PARTICULARLY COLD NIGHT WHERE CLOUDS CLEAR OUT WITH
HIGH PRESSURE BUILDING OVERHEAD. FEW CHANGES WERE MADE TO THE
FORECAST LOWS WHICH HAVE BEEN TRENDING COLDER ON THE MEX GUIDANCE.
FORECAST CONFIDENCE DECREASES INTO NEXT WEEK AS MODELS CONTINUE TO
EXHIBIT POOR RUN TO RUN CONTINUITY. THE COLD REGIME IS EXPECTED TO
CONTINUE WITH THE MAIN QUESTION REGARDING THE EVOLUTION OF THE NEXT
LONGWAVE TROUGH. THE 00Z/03 ECMWF SHOWED THIS TROUGH DEVELOPING MUCH
FURTHER TO THE WEST WHICH ALLOWED A LOW PRESSURE SYSTEM TO TRACK FROM
THE GULF COAST TO THE CENTRAL GREAT LAKES BY WEDNESDAY...INSTEAD OF AN
EAST COAST TRACK THAT MANY OTHER SOLUTIONS ARE SHOWING. FOR NOW THE
FORECAST WILL CONTINUE TO CARRY JUST LOW CHANCES OF SNOW UNTIL WE GET A
BETTER HANDLE ON THE STORM TRACK.
&&
.MARINE...
CANCELLED THE SMALL CRAFT ADVISORIES FOR SAGINAW BAY AS WINDSPEEDS
HAVE DECREASED GIVEN THE RELAXED PRESSURE GRADIENT. EXTENDED SMALL
CRAFT ADVISORIES INTO THIS EVENING FOR LAKE ST CLAIR AND THE
MICHIGAN WATERS OF LAKE ERIE WITH MIXED SOUTHWESTERLY FLOW IN
ADVANCE OF THE COLD FRONT. EXTENDED THE SMALL CRAFT ADVISORIES INTO
TOMORROW MORNING FOR THE LAKE HURON NEARSHORE WATERS WITH RESIDUAL
WAVES AND THE INCREASED NORTHWESTERLY FETCH.
WINDS WILL THEN SLOWLY BACK TOWARD THE SOUTHWEST ON FRIDAY AND
SATURDAY AND REMAIN STRONG ENOUGH FOR UNFAVORABLE MARINE CONDITIONS
THIS WEEKEND.
&&
.PREV DISCUSSION...ISSUED 106 PM EST WED DEC 3 2008
AVIATION...
TWO CHANGES WERE MADE TO THE TAF FORECASTS WITH THE FIRST
DELAYING THE START TIME OF SNOWS LATE THIS AFTERNOON/EARLY
EVENING. THE SECOND WAS TO REMOVE LIFR CONDITIONS FOR
VISIBILITIES/CEILINGS AT ALL TAF SITES EXCEPT KMBS. THUS FAR...THE
ONLY ACTIVITY HAS BEEN VIRGA WITH THE LARGE AREA OF SNOW AFFECTING
NORTHERN PORTIONS OF LOWER MICHIGAN OVER TO SOUTHERN WISCONSIN.
RADAR ECHOS ARE EXPECTED TO FILL IN OVER NORTHERN
ILLINOIS/NORTHERN INDIANA THIS AFTERNOON WHILE TRACKING
NORTHEASTWARD. AMPLE MOISTURE IS EXPECTED TO MOVE IN ALLOWING FOR
A QUICK BURST OF IFR CONDITIONS. SURFACE WINDS WILL ABRUPTLY
CHANGE TO THE NORTHWEST WITH THE PASSAGE OF THE COLD FRONT. DRY
AIR WILL ALLOW CEILINGS TO SCATTER OVERNIGHT BEFORE FILLING TO
MVFR LATE TOMORROW MORNING.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON...UNTIL 10 AM THURSDAY.
LAKE ST CLAIR...
SMALL CRAFT ADVISORY...UNTIL 10 PM WEDNESDAY.
MI WATERS OF LAKE ERIE...
SMALL CRAFT ADVISORY...UNTIL 10 PM WEDNESDAY.
&&
$$
SHORT TERM...CB
LONG TERM....KEC
MARINE.......CB
AVIATION.....CB
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