FXUS63 KDTX 231736
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.
&&
.PREV DISCUSSION...ISSUED 424 AM EST WED DEC 23 2009
SHORT TERM...TODAY
MOISTURE ON RADAR TO OUR SOUTH AND WEST WILL CONTINUE TO WITHER AND
HIGH PRESSURE WILL ENSURE DRY CONDITIONS AROUND SE MICHIGAN TODAY.
THERE WILL, HOWEVER, BE AN ABUNDANCE OF CLOUDS DURING THE MORNING
HOURS. THERE IS SOME POTENTIAL FOR THE LOWER CLOUDS TO DISSIPATE
AND/OR EXIT TO OUR EAST DURING THE AFTERNOON ALLOWING FILTERED
SUNSHINE TO BOOST HIGH TEMPERATURES TO NEAR 30 BEFORE HIGH CLOUDS
THICKEN AGAIN AHEAD OF THE DEVELOPING PLAINS SYSTEM.
MORNING SATELLITE IMAGERY INDICATES A COMBINATION OF MID CLOUDS AND
STRATUS OVER ALL OF SE MICHIGAN SAVE THE I-96 CORRIDOR, AND THIS IS
EXPECTED TO SLOWLY FILL IN BEFORE SUNRISE. SO, WE WILL START THE
DAYLIGHT HOURS WITH CLOUDY CONDITIONS OVER THE REGION WITH
TEMPERATURES RECOVERING FROM THE TEENS BOTH DUE TO THE INCREASED
CLOUDS AND DIURNAL INFLUENCES. WITH THE HELP OF ADDED MOISTURE FROM
LAKE HURON, THE STRATUS HAS EXPANDED STEADILY INLAND ON NE FLOW
BELOW 925 MB WITH JUST A HINT OF SLOWING SINCE ABOUT 3AM. THIS
SLOWING COULD BE PARTLY AN INFLUENCE OF THE SURFACE RIDGE AXIS THAT
IS ANALYZED ABOUT OVERHEAD. THE KEY TO THE LOW CLOUD EVOLUTION WILL
LIKELY NOW BE TIED TO THE EASTWARD PACE AT WHICH THE SURFACE RIDGE
CAN BE DRIVEN EASTWARD BY THE DEVELOPING PLAINS SYSTEM AND
EFFECTIVELY CARRY THE MOIST LAYER OUT OF THE AREA. THE 00Z MODELS
ARE IN AGREEMENT THAT THIS WILL BE ABOUT MID AFTERNOON OR JUST ABOUT
IN TIME FOR HIGH CLOUDS TO THICKEN IN THEIR PLACE HEADING INTO THIS
EVENING.
LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY
A RIDGE OF SURFACE HIGH PRESSURE WILL REMAIN DRAPED ACROSS
SOUTHEASTERN MICHIGAN THROUGH MIDDAY THURSDAY. THIS WILL ENSURE
QUIET CONDITIONS WITH SOME POSSIBLE MORNING SUNSHINE BEFORE THE
CIRROSTRATUS THICKENS DURING THE AFTERNOON. TEMPERATURES ARE
EXPECTED TO RISE INTO THE LOWER TO MID 30S. MEANWHILE...MID TO UPPER
LEVEL HEIGHTS WILL RISE TREMENDOUSLY OVER THE CENTRAL GREAT
LAKES...IN RESPONSE TO THE DEEPENING STORM SYSTEM ACROSS THE HEART
OF THE COUNTRY. THE RISING HEIGHTS ARE IMPORTANT BECAUSE THE
ANTICYCLONICALLY DRIVEN DRY FEED WILL NOT ONLY BE PRESERVED WELL
INTO THE OVERNIGHT...BUT MORE IMPORTANTLY THE COLUMN WILL UNDERGO A
SECOND ROUND OF HEAVY SUBSIDENCE.
THE 00Z NWP SUITE ARRIVED LARGELY IN CONTINUITY WITH RECENT
THINKING. THE MAIN HIGHLIGHTS WERE THE STRONGER CYCLONE SOLUTION OF
THE ECMWF THROUGH 84 HRS...AND THE PROPENSITY FOR ALL SOLUTIONS TO
WOBBLE THE SURFACE LOW BACK INTO WESTERN IOWA LATE FRIDAY AFTERNOON.
THESE CHANGES ARE NOT OVERLY SIGNIFICANT FOR SOUTHEASTERN
MICHIGAN...HOWEVER...AS THE FORCING EARLY WILL BE DUE TO THE FIRST
TROWAL/THETA E SURGE THAT IS CAST OFF OF THE LARGE VORTEX. THE
TIMING OF THIS SURGE APPEARS TIED TO AN ACTIVE 850MB LAYER PER
BUFKIT SOUNDINGS/THETA E ANALYSIS AND SHOULD ARRIVE ACROSS THE FAR
SOUTHWEST SHORTLY BEFORE 6Z. ALL MODELS SUPPORT A PERIOD OF
MODERATE TO HEAVY PRECIPITATION WITHIN THE OCCLUSION LATE THURSDAY
NIGHT AND FRIDAY MORNING. THERMODYNAMICALLY...THE SETUP LOOKS VERY
GOOD WITH THE ATMOSPHERE ON THE CUSP OF BEING CONVECTIVELY UNSTABLE.
GUIDANCE SUGGESTS THERE WILL BE A VERY BRIEF OPPORTUNITY FOR
SNOW/SLEET AT THE ONSET AS EVAPORATIVE COOLING KEEPS THE NEAR
SURFACE COLUMN COMFORTABLY BELOW FREEZING. THE FORECAST THEN SHIFTS
STRAIGHT TO A RAIN OR FREEZING RAIN FORECAST FOR THE LATTER HALF OF
THURSDAY NIGHT AND FRIDAY MORNING. WHILE THERE STILL REMAINS SOME
UNCERTAINTY WITH OVERALL QPF...THE LIKELIHOOD OF SIGNIFICANT GLAZING
IS STILL AN EXTREMELY TOUGH CALL. THERE ARE A COUPLE OF CONS AGAINST
A SIGNIFICANT GLAZING...NORTHWARD ADVANCING FORCING DUE TO THE
OCCLUSION...A 4 KFT WARM WEDGE WITH TEMPS REACHING 4-5C...AND
EARLIER THURSDAY HIGHS IN THE LOWER 30S. WITH THAT SAID...THE DRY
AIR WILL BE FORMIDABLE AND THE POTENTIAL REMAINS FOR MOST AREAS TO
WITNESS A COUPLE TENTHS OF ICE ACCUMULATION (ESPECIALLY THE HIGHER
TERRAIN OF THE IRISH HILLS).
BOUNDARY LAYER TEMPERATURES ARE EXPECTED TO WARM WELL INTO THE 30S
ON FRIDAY FOR ALL AREAS. THIS WILL CHANGE THE PRECIPITATION OVER TO
AN ALL RAIN FROM SOUTH TO NORTH. A STRONG SURFACE COLD FRONT WILL
THEN CRASH INTO LOWER MICHIGAN FRIDAY AFTERNOON SUPPORTING ALL SNOW.
A BRIEF RESTRENGTHENING OF THE LOW WILL TAKE PLACE NEAR IOWA WHICH
WILL ALLOW FOR THE DEVELOPMENT OF A SECOND TROWAL AXIS NEAR LAKE
HURON. IT IS THIS FEATURE THAT WILL BRING THE POTENTIAL FOR SOME
LIGHT SNOWFALL ACCUMULATIONS ALONG THE EASTERN THUMB SHORELINE
FRIDAY EVENING. FOR THE REST OF THE AREA...THE COLUMN WILL UNDERGO
SIGNIFICANT DRYING SO WIDESPREAD PRECIPITATION IS EXPECTED TO
SHUTDOWN. THE LOW WILL MEANDER ACROSS THE WESTERN LAKES WHILE
FILLING THIS WEEKEND. EMBEDDED SHORTWAVE ENERGY PIVOTING AROUND
THE VORTEX WILL PROVIDE A FOCUS FOR SURFACE REFLECTIONS AND NEAR
SURFACE CONVERGENCE. THEREFORE...OFF AND ON SNOW SHOWERS CAN BE
EXPECTED INTO EARLY NEXT WEEK. THE BEST TIMEFRAME MAY BE ON MONDAY
AS A SIGNIFICANT SURFACE TROUGH SWINGS THROUGH.
MARINE...
AS HIGH PRESSURE SETTLES OVER LAKE HURON AND LOWER MICHIGAN,
NORTHERLY WINDS HAVE SUBSIDED ENOUGH TO ALLOW WAVES TO SETTLE BELOW
5 FEET THIS MORNING. SMALL CRAFT ADVISORIES HAVE BEEN CANCELLED FOR
ALL MARINE AREAS BUT THIS WILL BE SHORT LIVED AS CONDITIONS ARE
EXPECTED TO WORSEN CONSIDERABLY BY THURSDAY NIGHT INTO FRIDAY. THIS
WILL BE DUE TO DEEPENING LOW PRESSURE MOVING UP THE MISSISSIPPI
RIVER VALLEY. THE INCREASED PRESSURE GRADIENT BETWEEN THE HIGH OVER
EASTERN CANADA AND THIS LOW PRESSURE SYSTEM WILL LEAD TO STRONG
EASTERLY WINDS OVER THE GREAT LAKES. AT THE SAME TIME, WARMER AIR
WILL BE DRAWN INTO THE REGION WITH INCREASED STABILITY OVER THE
WATER LIKELY TO KEEP WINDS AROUND 30 KNOTS OVER THE SOUTH HALF OF
LAKE HURON. THE NORTH HALF, HOWEVER, REMAINS UNDER A GALE WATCH AS
THIS IS WHERE THE STRONGEST GRADIENT WIND AND LONGEST FETCH WILL
COMBINE TO POSSIBLY BOOST WIND GUSTS TO 35 KNOTS OR GREATER THROUGH
FRIDAY NIGHT.
&&
.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.
&&
$$
AVIATION.....HLO
SHORT TERM...BT
LONG TERM....CB
MARINE.......BT
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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
