FXUS63 KDTX 080449
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1149 PM EST MON DEC 7 2009
.AVIATION...
REGIONAL OBSERVATIONS SUGGEST THERE WILL CONTINUE TO BE A FEW AREAS
OF MVFR CEILINGS THROUGH THE MORNING. BULK OF OBSERVATIONS AND
LATEST MODEL SOUNDINGS HOWEVER SUGGEST PREDOMINATELY VFR CONDITIONS
TO PERSIST. A STRENGTHENING STORM SYSTEM WILL APPROACH LATE IN THE
DAY. CEILINGS WILL BEGIN TO LOWER THROUGH THE AFTERNOON AS THIS
SYSTEM APPROACHES. SNOW IS EXPECTED TO DEVELOP ON THE LEAD EDGE OF
THIS STORM SYSTEM THIS EVENING...RAPIDLY TAKING BOTH CEILINGS AND
VISIBILITIES DOWN TO IFR AND LIFR.
&&
.PREV DISCUSSION...ISSUED 932 PM EST MON DEC 7 2009
UPDATE...
A MINOR UPDATE WAS ISSUED JUST TO REMOVE ANY MENTION OF FLURRIES.
WHILE A FEW BREAKS IN THE OVERCAST HAVE DEVELOPED THIS EVENING...A
STRENGTHENING LOW LEVEL INVERSION IS GOING TO MAKE IT DIFFICULT TO
SCATTER OUT ALL OF THE LOW LEVEL MOISTURE. HIGH CLOUDS WILL ALSO
MOVE IN FROM THE SOUTHWEST. SO THE CURRENT LOW TEMP FORECAST LOOKS
REASONABLE.
PREV DISCUSSION...ISSUED 412 PM EST MON DEC 7 2009
SHORT TERM...TONIGHT
AFTER A CONSIDERABLE AMOUNT OF SUNSHINE DURING THE LATE MORNING
HOURS...LOW LEVEL CU FIELD PICKED UP QUICKLY DURING THE AFTERNOON
HOURS...AS SURFACE DEW POINTS CLIMBED INTO THE MID 20S. GENERAL
SUBSIDENCE EXPECTED OVERNIGHT TONIGHT AS WEAK SHORTWAVE RIDGING
BUILDS INTO THE CENTRAL GREAT LAKES. TOUGH CALL ON HOW MUCH CLEARING
TAKES PLACE TONIGHT BEFORE WARM ADVECTION HIGH CLOUDS STREAM IN
TOWARD MORNING AHEAD OF THE NEXT STORM SYSTEM. THE PROBLEM IS
ALTHOUGH THE CLOUDS DO LOOK DIURNALLY ENHANCED...THE STAGNANT WEAK
FRONTAL BOUNDARY OVER CENTRAL/NORTHERN LOWER MICHIGAN FINALLY LOOKS
TO BE SINKING SOUTH AND EVENTUALLY DISSIPATING ALTOGETHER. THIS WEAK
LOW LEVEL CONVERGENCE COUPLED WITH WEST-SOUTHWEST FLOW OFF LAKE
MICHIGAN MAY PROVIDE JUST ENOUGH LOW LEVEL MOISTURE TO MAINTAIN THE
CLOUDS. WITH THE QUESTIONABLE CLEARING...WILL HOLD MINS AROUND
20/LOWER 20S...BUT THE POTENTIAL IS CERTAINLY THERE TO DROP OFF INTO
THE TEENS AS WINDS GO CALM. WILL ALSO NEED TO ACCOUNT FOR A FEW
LINGERING LIGHT SNOW SHOWERS/FLURRIES INTO THE EVENING HOURS. IT
SHOULD BE NOTED...DETROIT (METRO) PICKED UP ITS FIRST MEASURABLE
SNOWFALL OF THE YEAR (TWO TENTHS OF AN INCH THROUGH 18Z).
LONG TERM...TUESDAY THROUGH SUNDAY
FOCUS FOR THE LONG TERM PERIOD REMAINS ON THE DEVELOPING WINTER
STORM FOR TUESDAY NIGHT/WEDNESDAY AND THE SUBSEQUENT PUSH OF MUCH
COLDER AIR BEHIND THIS SYSTEM FOR THE REST OF THE PERIOD. LATEST
WATER VAPOR AND UPPER AIR ANALYSIS SHOWING A POSITIVELY TILTED UPPER
TROUGH ELONGATED FROM SOUTH-CENTRAL CANADA INTO THE PACIFIC
NORTHWEST. STRONG SHORTWAVE CURRENTLY DIVING SOUTHEAST WITHIN THE
BASE OF THIS TROUGH WILL RAPIDLY EJECT EAST-NORTHEAST OVER THE NEXT
36-48 HOURS ACCOMPANIED BY A 160+ KT UPPER JET AND A SURGE OF DEEP
MOISTURE. ASSOCIATED SURFACE LOW WILL DEEPEN WHILE LIFTING
NORTHEAST IN RESPONSE TO THE RAPID HEIGHT FALLS. STILL SOME SLIGHT
DIFFERENCES IN THE EXACT LOW TRACK...WITH THE GFS/ECMWF/UKMET TAKING
THE LOW FROM NEAR CHICAGO AT 12Z WED TO CENTRAL LAKE HURON BY
AFTERNOON. LATEST NAM WITH SUPPORT FROM THE WRFHEMI CARRY A MORE
WESTWARD TRAJECTORY THROUGH MILWAUKEE AND UP INTO MACKINAC ISLAND BY
18Z WED. ALSO WORTH NOTING THE SREF WHICH DISPLAYS A SIZABLE SPREAD
IN THE TRACK TOWARD THE WEST...SUGGESTING AN ADDITIONAL ADJUSTMENT
TO THE WEST CERTAINLY CANNOT BE DISCOUNTED.
WITH ALL THAT SAID...HARD TO FAVOR ONE PARTICULAR SOLUTION/CONSENSUS
JUST YET SEEING HOW THE UPPER JET STRUCTURE STILL MOVING ACROSS
THE EASTERN PACIFIC STILL LACKS GOOD MODEL SAMPLING. REGARDLESS...
OVERALL SETUP STILL POINTS TOWARD TREMENDOUS ISENTROPIC ASCENT/
THETA-E ADVECTION DEVELOPING DOWNSTREAM OF THIS SYSTEM TUESDAY
NIGHT. THIS COMBINED WITH INCREASING UPPER DIFFLUENCE/JET COUPLING
AS THE UPSTREAM WAVE BECOMES NEGATIVELY TILTED WILL RESULT IN AN
EXPANDING AREA OF PRECIPITATION SPREADING ACROSS THE AREA BETWEEN
22-02Z. LATEST GFS AND NAM THERMAL PROFILES SUPPORT A BRIEF PERIOD
OF LIGHT SNOW/SLEET AT ONSET ACROSS THE SOUTH...BEFORE WARM AIR
ADVECTION STRENGTHENS AND QUICKLY MIXES/CHANGES THE PTYPE TO ALL
LIQUID FROM SOUTH TO NORTH THROUGH THE EVENING. THIS WILL KEEP
POTENTIAL SNOW ACCUMS TO AN INCH OR LESS FROM M-59 SOUTH...WITH UP
TO 2 INCHES THROUGH THE I-69 CORRIDOR.
MUCH TIGHTER CALL INTO THE SAGINAW VALLEY WHICH WILL BE ON THE CUSP
OF SEEING THE WARM LAYER NOSING IN OVERNIGHT. SOUNDING DATA AND
PARTIAL THICKNESSES MAINTAIN A LONGER DURATION OF SNOW...ESPECIALLY
UP THROUGH MIDLAND/BAY COUNTIES...WHILE ALSO FOCUSING THE STRONGEST
FORCING WITHIN THIS CORRIDOR. BEST OMEGA DOES REMAIN BELOW THE
BETTER DENDRITIC GROWTH ZONE...WHILE CROSS SECTIONS OVER THIS AREA
DISPLAY MODEST STABILITY. ASSUMING SNOW RATIOS CAN HOLD IN THE
7-8:1 RANGE WITH .60-.75" OF QPF...THIS POINTS TO A MARGINAL
WATCH/WARNING SCENARIO ACROSS THE FAR NORTH. THEREFORE WILL GO
AHEAD AND ISSUE A WATCH FOR MIDLAND/BAY FOR TUESDAY NIGHT.
UNCERTAINTY IN THE LOW TRACK AND PTYPE PROFILE WILL PRECLUDE
ISSUING A HEADLINE ANY FURTHER SOUTH.
COLD AIR WILL SPILL BACK IN LATE WEDNESDAY/WEDNESDAY NIGHT. DRY
SLOT IMPINGING ON THE AREA MAY STRIP THE MOISTURE OUT BRIEFLY ON
WEDNESDAY...BEFORE ADDITIONAL SNOW SHOWERS DEVELOP WITHIN THE
MOISTENING CYCLONIC FLOW AND DEVELOPING COLD AIR ADVECTION INTO
WEDNESDAY EVENING/NIGHT. THE STRENGTH OF THE ADVECTION/ISENTROPIC
DESCENT COMBINED WITH AN ALREADY TIGHT PRESSURE GRADIENT WILL
CREATE WINDY CONDITIONS BY LATE WEDNESDAY. WIND FIELD WILL REMAIN
IMPRESSIVE INTO THURSDAY UNDER CONTINUED STRONG COLD AIR ADVECTION
AND PERSISTENT 30-35 KTS AT 925 MB. THIS WILL LIKELY NECESSITATE A
WIND HEADLINE AS THE EVENT NEARS. ARCTIC AIRMASS WILL SETTLE INTO
THE AREA ON THURSDAY AS 850 MB TEMPERATURES DROP BELOW -18C. THIS
WILL RESULT IN STEADY/FALLING DAYTIME TEMPERATURES IN THE
TEENS/LOWER 20S. LAKE EFFECT/ENHANCED SNOW SHOWERS WILL PERSIST
DURING THIS TIME.
ARCTIC AIRMASS WILL REMAIN FIRMLY ENTRENCHED ACROSS SOUTHEAST LOWER
MI INTO FRIDAY AS 850 MB TEMPERATURES HOVER BELOW -17C. THIS WILL
TRANSLATE INTO HIGHS STRUGGLING TO REACH THE LOW-MID 20S...WITH
UPPER TEENS AGAIN POSSIBLE ACROSS THE NORTH. ANY RESIDUAL LAKE
ENHANCED SNOW SHOWER ACTIVITY WILL DIMINISH THROUGH THE DAY AS LOW
LEVEL ANTICYCLONIC FLOW DEVELOPS. MEAN LONGWAVE TROUGH PARKED OVER
THE CENTRAL CONUS WILL BEGIN TO DAMPEN FRIDAY NGT/SATURDAY...LEAVING
ZONAL FLOW FOR THE WEEKEND. BUILDING HEIGHTS WILL LEAD TO A SLOW
MODERATING TREND IN TEMPERATURES DURING THIS TIME...ALTHOUGH
READINGS LOOK TO REMAIN BELOW NORMAL GIVEN AN UNIMPRESSIVE THERMAL
ADVECTIVE RESPONSE.
MARINE...
A RIDGE OF HIGH PRESSURE MOVING INTO THE CENTRAL GREAT LAKES TONIGHT
WILL PROVIDE LIGHT WINDS. SOUTHEAST WINDS WILL THEN BEGIN TO PICK UP
TOMORROW AHEAD OF A MAJOR STORM SYSTEM. DEEPENING LOW PRESSURE (970S
MB) WILL TRACK NORTHEAST THROUGH LOWER MICHIGAN ON WEDNESDAY.
A GALE WATCH HAS SUBSEQUENTLY BEEN ISSUED FOR ALL MARINE AREAS
WEDNESDAY THROUGH THURSDAY...AND INTO FRIDAY MORNING FOR THE OPEN
WATERS OF LAKE HURON. WESTERLY WINDS WEDNESDAY NIGHT OVER THE OPEN
WATERS ARE EXPECTED TO TOP OUT AROUND 45 KNOTS. WINDS WILL BE SLOW
TO DECREASE AS WE HEAD INTO FRIDAY...AS THE ARCTIC AIRMASS SPILLING
OVER THE WARMER WATERS LEADS TO VERY UNSTABLE LOW LEVEL
PROFILE...ALLOWING WAVE GROWTHS IN EXCESS OF 10 FEET. LAKE EFFECT
SNOW SQUALLS ARE ALSO LIKELY BEHIND THE SYSTEM...ESPECIALLY FROM
LATE WEDNESDAY NIGHT THROUGH THURSDAY.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH...MIZ047-MIZ048...FROM 10 PM TUESDAY TO 10 AM
WEDNESDAY.
LAKE HURON...
GALE WATCH...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...FROM 7 AM
WEDNESDAY TO NOON FRIDAY.
GALE WATCH...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON
INCLUDING SAGINAW BAY...FROM 7 AM WEDNESDAY TO 7 PM THURSDAY.
LAKE ST CLAIR...
GALE WATCH...FROM 7 AM WEDNESDAY TO 7 PM THURSDAY.
MI WATERS OF LAKE ERIE...
GALE WATCH...FROM 7 AM WEDNESDAY TO 7 PM THURSDAY.
&&
$$
AVIATION.....SC
UPDATE.......SC
SHORT TERM...SF
LONG TERM....MR
MARINE.......SF
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
