FXUS63 KDTX 232053
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
353 PM EST WED DEC 23 2009
.SHORT TERM...TONIGHT
LOW-LEVEL STRATUS HAS NEARLY DISSIPATED THIS AFTERNOON...SAVE FOR A
SMALL AREA STILL LINGERING SOUTH OF SAGINAW BAY. AFTER SOME CLEARING
THIS EVENING...WILL SEE CLOUD COVER INCREASE BY LATE THIS EVENING
AND OVERNIGHT AS MID LEVEL MOISTURE LIFTS UP INTO LOWER MICHIGAN IN
ADVANCE OF STRONG LOW PRESSURE TRACKING UP THE MISSISSIPPI RIVER
VALLEY. ALSO EXPECT SOME LOW STRATUS TO DEVELOP ACROSS THE THUMB
OVERNIGHT AS WINDS OFF LAKE HURON TURN EASTERLY AND ALLOW LOW-LEVEL
MOISTURE TO FILL IN UNDERNEATH A STRONG INVERSION NEAR 2500 FEET.
FORECAST FOR THE OVERNIGHT PERIOD REMAINS DRY AS HIGH PRESSURE
STRETCHED ACROSS THE NORTHERN GREAT LAKES PROVIDES GENERAL
SUBSIDENCE. LIGHT PRECIPITATION CONTINUES TO GENERATE THIS AFTERNOON
ALONG AN OLD FRONTAL BOUNDARY LYING ACROSS INDIANA AND WESTERN OHIO.
GFS/NAM BOTH INDICATE THIS BOUNDARY WILL LIFT GRADUALLY NORTHWARD
INTO SOUTHERN LOWER MICHIGAN LATE TONIGHT...AS SOUTHERLY FLOW
INCREASES ON THE SOUTH END OF THE FRONT. BOTH MODELS INDICATE A
DECREASE IN BAROCLINICITY THIS EVENING AND OVERNIGHT AS THIS
OCCURS...AND GIVEN TRENDS IN PRECIPITATION UPSTREAM (MOSTLY ONLY
TRACE AMOUNTS SINCE EARLY AFTERNOON) WILL NOT CARRY ANY
SNOW...SLEET...OR FREEZING RAIN MENTION FOR AREAS NEAR THE OHIO
BORDER.
TEMPERATURES WILL REMAIN FAIRLY MILD RELATIVE TO LAST NIGHT...WITH
MIN TEMPERATURES RANGING FROM THE UPPER TEENS TO MID 20S.
&&
.LONG TERM...THURSDAY THROUGH NEXT WEDNESDAY
MODELS CONTINUE TO BE SIMILAR WITH THE OVERALL EVOLUTION OF THE
STORM OVER MO AND IA. THERE IS SOME CONSISTENCY WITHIN RUNS AS
WELL. WILL LEAD AWAY FROM GFS WITH SOME OF THE DETAILS...WHICH
EVACUATES THE DRY AIR OVER SE LOWER MICHIGAN A BIT TOO QUICKLY. THE
GFS ALSO HANDLES THE EVOLUTION OF THE SYSTEM A BIT DIFFERENT THAN
THE OTHER MODELS IN SOME PART DUE TO THE CONVECTION ON THE SOUTH END
OF THE SYSTEM.
THURSDAY WILL BE DRY AS THE DRY WEDGE BETWEEN 2000 AND 8000 FEET IS
MAINTAINED WITH JUST ENOUGH OF A NORTHERLY COMPONENT TO THE EAST
FLOW. STILL ENOUGH MOISTURE BELOW 2-3K FT AND THEN ABOVE 10K FT TO
HAVE MOSTLY CLOUDY SKIES.
MODEL TRENDS CONTINUE TO PUSH THE START OF THE PRECIPITATION BACK
CLOSER TO 12Z FRIDAY. WILL BE PUSHING THE START BACK BY 3 HOURS OR
SO OFF OF PREVIOUS FORECAST. THAT WILL ALLOW THE SOUTHERLY
COMPONENT OF THE EAST FLOW TO PUSH TEMPERATURES UP EVEN MORE FROM
850 MB AND BELOW. MORE WARMER AIR AND LATER START WILL LIMIT THE
POTENTIAL OF SIGNIFICANT ICE ACCUMULATIONS...MUCH LESS THAN .25
INCH...AND THUS NO WATCH ISSUANCE.
OLD TROWEL FROM THE OCCLUSION PUSHES THROUGH LOWER MICHIGAN FROM 12Z
TO NEAR 18Z. GOOD DEEP DEFORMATION AND FGEN FROM 850 TO 500 MBS...
SOME LEFT OVER ISENTROPIC LIFT FROM THE WEAKEN TROWEL...AND THE
RIGHT REAR ENTRANCE OF THE JET MAX ROTATING AROUND THE NORTH SIDE OF
THE UPPER LOW...ALL MEAN 100 PERCENT CHANCE OF PRECIPITATION
CHRISTMAS MORNING INTO EARLY AFTERNOON. 850 TEMPS WARM TO AROUND
+4C BY 12Z FRIDAY WHILE SURFACE TEMPS WILL BE AROUND 32 DEGREES AT
THE START OF THE PRECIP. THAT WILL GIVE EVERYONE IN SOUTHEAST
MICHIGAN A FEW HOURS OF FREEZING RAIN BEFORE CHANGING OVER TO ALL
RAIN DURING CHRISTMAS MORNING. THERE ARE A COUPLE OF COMPETING
ELEMENTS TO GET A HOLD OF THE AMOUNT OF GLAZING FROM THIS EVENT.
DRY EASTERLY FLOW WILL KEEP DEW POINTS BELOW FREEZING AND THUS THE
WET BULB WILL ALSO BE BELOW FREEZING. HOWEVER...RAIN WILL BE FALLING
THROUGH A SUBSTANTIAL LAYER OF +4 TO +5C AIR WITH SURFACE TEMPS
AROUND 32. EXPECT THAT WILL LEAD TO ENOUGH GLAZING FOR AN ADVISORY
TYPE OF EVENT...AND MOST LIKELY AROUND A TENTH OF AN INCH OF ICE.
BY LATE FRIDAY MORNING SURFACE TEMPS WILL WARM INTO THE MID
30S...ENDING THE FREEZING RAIN. THERE IS ANOTHER OLD TROWEL FROM
THE SURFACE OCCLUDED FRONT THAT MOVES THROUGH DURING FRIDAY
AFTERNOON WITH LESS SUPPORT FROM DEEP MOISTURE...JET MAXES...
DEFORMATION...FGEN OR ISENTROPIC LIFT. EXPECT SOME NUMEROUS SHOWERS
FROM THIS WEAKER SURGE OF FORCING. THE WARM LAYER AROUND 5K FEET IS
RETREATING BY THEN...ENOUGH IN THE TRI CITIES TO POSSIBLY START
MIXING WITH SNOW. THAT TREND CONTINUES INTO THE EVENING AND
OVERNIGHT HOURS. AFTER THE OCCLUDED FRONT MOVES THROUGH...DEEPER AND
COLDER AIR FILTERS ACROSS THE FORECAST AREA FROM SW TO NE. THIS WILL
CHANGE THE SCT RAIN SHOWERS TO SCT SNOW SHOWERS.
DRY SLOT IS PRONOUNCED ON SATURDAY. AGAIN WILL LEAN AWAY FROM THE
GFS WHICH IS FASTER BRINGING THE UPPER LOWER OVER THE SOUTHERN GREAT
LAKES. ENOUGH DRY AIR AND LOW ENOUGH TO THE SURFACE TO EXPECT SOME
SUN ON SATURDAY...AND WILL JUST CARRY A CHANCE OF FLURRIES.
AS THE UPPER LOW MOVES OVER THE SOUTHERN LAKES...MORE COLD AIR MOVES
INTO THE REGION AND WINDS TURN TO THE NORTHWEST. THIS WILL BRING A
PROLONGED PERIOD OF CLOUDS...SCT SNOW SHOWERS AND BELOW AVERAGE
TEMPS FROM SATURDAY NIGHT TO MONDAY NIGHT. BY TUESDAY THAT UPPER
LOW PUSHES EAST AND A SURFACE RIDGE SETS UP OVER THE REGION FOR
DRIER CONDITIONS ON TUESDAY AND WEDNESDAY.
&&
.MARINE...
FAIRLY TRANQUIL MARINE CONDITIONS WILL CONTINUE INTO THURSDAY AS
HIGH PRESSURE REMAINS STRETCHED OVER THE NORTHERN GREAT LAKES. WINDS
WILL HOWEVER MAKE A GRADUAL SHIFT TO THE EAST AND INCREASE OVERNIGHT
IN ADVANCE OF THE NEXT SYSTEM. A TIGHTER PRESSURE GRADIENT WILL
DEVELOP OVER THE CENTRAL GREAT LAKES BY THURSDAY NIGHT AS A STRONG
LOW PRESSURE SYSTEM LIFTS UP THE MISSISSIPPI RIVER VALLEY. THIS WILL
BRING STRONG EAST WINDS...WITH GUSTS TO 30 KNOTS LIKELY DEVELOPING
ACROSS ALL NEARSHORE MARINE AREAS THURSDAY NIGHT AND CONTINUING INTO
FRIDAY NIGHT.
WARMER AIR BEING DRAWN INTO THE REGION ALONG WITH HIGHER STABILITY
OVER THE RELATIVELY WARMER WATERS SHOULD KEEP WIND GUSTS LIMITED TO
AROUND 30 KNOTS OVER THE SOUTHERN HALF OF LAKE HURON...ALTHOUGH
ISOLATED GUSTS TO GALE FORCE ARE POSSIBLE. ACROSS NORTHERN LAKE
HURON...A STRONGER PRESSURE GRADIENT AND LONGER FETCH MAY BOOST WIND
GUSTS TO 35 KNOTS OR GREATER THROUGH FRIDAY NIGHT. THEREFORE...THE
GALE WATCH REMAINS IN EFFECT FOR THE NORTHERN HALF OF LAKE HURON
FROM LATE THURSDAY NIGHT THROUGH FRIDAY EVENING.
&&
.PREV DISCUSSION...ISSUED 1236 PM EST WED DEC 23 2009
AVIATION...
MVFR STRATUS CONTINUES TO BREAK UP THIS AFTERNOON AS WINDS
CONTINUE TO UNDERGO A GRADUAL TURN FROM NORTH TO EAST...REDUCING
MOISTURE FLUX OFF OF LAKE HURON. WILL SEE A MVFR CEILINGS LIFT AT
FNT OVER THE NEXT 1-2 HOURS...HOWEVER EASTERLY FLOW OFF OF LAKE
ST CLAIR AND SAGINAW BAY WILL ALLOW STRATUS TO HOLD INTO THE
AFTERNOON AT MBS AND INTO THE EVENING AT DET. DRY VFR CONDITIONS
WITH EASTERLY WINDS UNDER 10 KNOTS ARE EXPECTED OVERNIGHT AND INTO
THURSDAY BEFORE A LARGE LOW PRESSURE SYSTEM LIFTING INTO THE
MIDWEST BRINGS DETIORATING CONDITIONS ON THURSDAY NIGHT. OUTLOOK
FOR THIS STORM...EXPECT A WINTRY MIX WHICH MAY INCLUDE A PERIOD
OF FREEZING RAIN AND SLEET TO OCCUR THURSDAY NIGHT...BEFORE A
TRANSITION TO RAIN OCCURS BY LATE FRIDAY MORNING.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
GALE WATCH...LHZ361-LHZ362...FROM 4 AM FRIDAY TO MIDNIGHT SATURDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
SHORT TERM...HLO
LONG TERM....RBP
MARINE.......HLO
AVIATION.....HLO
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