FXUS63 KDTX 111732
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1232 PM EST FRI DEC 11 2009
.AVIATION...
LAKE EFFECT SNOW SHOWERS ARE GETTING SOME DIURNAL HELP...MAINLY
BETWEEN I 94 AND I 69. WILL CARRY 3SM SNOW SHOWERS FOR FNT...PTK AND
DET THIS AFTERNOON. THERE WILL BE TIMES WHEN VISIBILITIES GET AS
LOW AS 1 TO 2 MILES BRIEFLY IN THE HEART OF THE MOST INTENSE SNOW
SHOWERS. WEST WINDS WILL CONTINUE TO GUST UP TO 30 KTS WHICH MAY
CREATE SOME BLOWING SNOW ISSUES AT THE MORE OPEN SITES LIKE MBS.
BETWEEN 21Z AND 03Z...DRIER AIR MOVES INTO THE REGION ON SOME LOW
LEVEL WARM AIR ADVECTION AS THE SURFACE RIDGE MOVES INTO LOWER MI.
THIS WILL ALLOW SKIES TO BECOME CLEAR AFT 03Z WITH DIMINISHING
WINDS.
&&
.PREV DISCUSSION...ISSUED 1034 AM EST FRI DEC 11 2009
UPDATE...
MAIN UPDATE WAS TO BE MORE PESSIMISTIC THIS AFTERNOON FROM I 94 TO
I 69. 12Z NAM AND 12Z LOCAL WRF INDICATE THE LATE MORNING AND
AFTERNOON INCREASE WITH THE BAND OF LAKE EFFECT OFF OF LAKE MI.
WILL HAVE MOSTLY CLOUDY WITH NUMEROUS LIGHT SNOW SHOWERS IN THIS
AREA. AFTER 21Z...THE MIXED LAYER AND INVERSIONS REALLY CRASH ON
THE MODELS AS THE 925 MB TO 850 MB DRY AIR REALLY ADVECTS INTO
SOUTHERN LOWER MI. ACCUMULATIONS MAY GET UP TO AN INCH IN A FEW
ISOLATED LOCATIONS...BUT SHOULD BE JUST A DUSTING TO HALF INCH IN
MOST LOCATIONS.
TEMPS ARE NEAR OR AT MAXES IN THE SOUTH HALF OF THE FORECAST AREA.
DO NOT EXPECT MUCH OF A RISE THE REST OF THE AFTERNOON...BUT DID
HAVE TO RAISE THEM
PREV DISCUSSION...ISSUED 414 AM EST FRI DEC 11 2009
SHORT TERM...TODAY
THE DEEP ELONGATED POLAR VORTEX OVER CENTRAL AND EASTERN CANADA WILL
SUSTAIN THE ARCTIC AIRMASS OVER MUCH OF THE NORTHERN US TODAY. 850MB
TEMPS ARE FORECAST TO HOVER AROUND -20C OVER CENTRAL MICHIGAN TO
-16C OVER METRO DETROIT. THIS ALONG WITH LATEST MODEL SOUNDINGS
SUPPORT THE SLIGHTLY LOWER MET GUIDANCE TEMPS OF UPPER TEENS NORTH
OF THE M 59 CORRIDOR TO LOW 20S FOR DETROIT AND POINTS SOUTH. A
FAIRLY STRONG WESTERLY GRADIENT WILL REMAIN IN PLACE THROUGH THE
DAY...WITH MODEL SOUNDINGS INDICATING THE POTENTIAL FOR GUSTS TO
REACH 30 TO 35 MPH AT TIMES. COMBINED WITH THE COLD TEMPS...WIND
CHILLS WILL REMAIN BELOW ZERO THROUGH MUCH OF THE DAY.
A WEAK MID LEVEL SHORT WAVE PASSED THROUGH THE STATE EARLIER AND
ALLOWED A FLARE UP IN THE LAKE EFFECT ACTIVITY. THE LAKE EFFECT
BANDS HAVE BEEN IMPACTING MAINLY LOCATIONS ALONG AND NORTH OF THE
I 69 CORRIDOR WHERE LOW LEVEL CONVERGENCE HAS BEEN ENHANCED. THE
INTENSITY OF THE BANDS SHOULD DECREASE DURING THE COURSE OF THE
MORNING AS SUBSIDENCE IN THE WAKE OF THE MID LEVEL WAVE LOWERS
INVERSION HEIGHTS OVER LAKE MICHIGAN. BASED ON THE SURFACE
OBS...WOULD EXPECT A GOOD PORTION OF THE SAGINAW AND GENESEE VALLEYS
HAVE RECEIVED A HALF AN INCH ACCUMULATION OVERNIGHT...WITH LOCALIZED
AREAS POSSIBLY PICKING UP AN INCH OR TWO. LAKE MODIFIED SOUNDINGS
FOR THIS AFTERNOON INDICATE EQUILIBRIUM LEVELS FALLING TO 6K FT...
WHICH SHOULD LIMIT THE INTENSITY OF LAKE EFFECT. NONETHELESS...
ENOUGH INSTABILITY OFF LAKE MICHIGAN WILL CONTINUE TO WARRANT
SCATTERED SNOW SHOWERS THROUGH THE AFTERNOON. WILL ALSO HAVE TO
MONITOR THE POTENTIAL FOR SOME ENHANCED CONVERGENCE SETTING UP ALONG
THE I-696 OR M-59 CORRIDORS LATER IN THE DAY WHICH WOULD PROVIDE A
LITTLE BETTER COVERAGE OF SNOW SHOWERS IN THESE LOCALS.
LONG TERM...FRIDAY NIGHT THROUGH THURSDAY
THE ARCTIC AIRMASS BRIEFLY LOSES ITS GRIP ON THE GREAT LAKES REGION
OVER THE WEEKEND AS HEIGHTS GRADUALLY REBOUND OVER THE EASTERN
UNITED STATES. A BROAD AREA OF HIGH PRESSURE CURRENTLY LOCATED OVER
TENNESSEE WILL BUILD NORTHEAST TOWARDS THE MID-ATLANTIC STATES
THROUGH THE DAY ON SATURDAY. THIS WILL BRING AN END TO EVEN LIGHT
SNOW SHOWERS AS SHALLOW MOISTURE STRIPS AWAY WITH CLEARING SKIES ON
FRIDAY NIGHT AND A GOOD DEAL OF SUN EXPECTED ON SATURDAY. LOW LEVEL
WARM AIR ADVECTION WILL INCREASE FROM LATE FRIDAY NIGHT INTO
SATURDAY AS WINDS BACK AROUND TO THE SOUTHWEST AND 925MB
TEMPERATURES CLIMB ABOUT 10C IN 24 HOURS. AFTER TEMPERATURES IN THE
TEENS ON FRIDAY NIGHT...HIGHS WILL TRY TO REBOUND TO AROUND 30
DEGREES ON SATURDAY.
BY SATURDAY THE ARCTIC VORTEX OVER WESTERN CANADA WILL PIVOT TOWARDS
ONTARIO AND ATTEMPT TO PHASE WITH SHORTWAVE ENERGY ARRIVING FROM THE
PACIFIC OCEAN. A STRONG SURFACE LOW PRESSURE SYSTEM WILL DEVELOP
OVER NORTHERN ONTARIO AHEAD OF THIS VORTEX WITH A TRAILING FRONT
EXTENDING SOUTH TO THE MID-MISSISSIPPI VALLEY. MODELS TRY TO
GENERATE SOME LIGHT QPF AS ISENTROPIC ASCENT INCREASES AHEAD OF THE
FRONT. SYSTEM RELATIVE WINDS SHOW THE ISENTROPIC ASCENT IS NOT REAL
IMPRESSIVE AND WILL CONTINUE TO CARRY JUST A CHANCE POP FOR SUNDAY.
ALTHOUGH ANY PRECIP MAY START AS SNOW...MODELS IN FAIRLY GOOD
AGREEMENT THAT MID-LEVEL DRY AIR WILL ARRIVE BY MID-MORNING WITH ANY
LINGERING SHOWERS SWITCHING OVER TO A LIGHT RAIN AS TEMPS CREEP
ABOVE FREEZING.
THE FRONT ASSOCIATED WITH THE ABOVE MENTIONED LOW PRESSURE SYSTEM
WILL STALL OVER LOWER MICHIGAN AS THE SYSTEM BECOMES INCREASINGLY
WRAPPED UP OVER JAMES BAY. MODELS IN DECENT AGREEMENT THAT THE NEXT
WAVE APPROACHING FROM THE PACIFIC WILL BE STRONGER WITH ANOTHER LOW
PRESSURE SYSTEM TRACKING OUT OF THE PLAINS AND ALONG THE STALLED
FRONTAL BOUNDARY OVER THE GREAT LAKES REGION . CURRENT
GUIDANCE SUGGESTS THIS LOW WILL PASS TO OUR WEST WITH A RAIN/SNOW
MIX POSSIBLE ON MONDAY BEFORE CHANGING BACK TO SNOW SHOWERS ON
MONDAY NIGHT AS THE ARCTIC AIRMASS RETURNS. HAVE TRENDED TEMPS DOWN
A FEW DEGREES FOR TUESDAY AND WEDNESDAY AND WILL BE KEEPING AN EYE
ON LAKE EFFECT PARAMETERS UNDER THE COLD NORTHWEST FLOW AS WE HEAD
INTO EARLY NEXT WEEK.
MARINE...
STRONG WESTERLIES WILL CONTINUE INTO THE WEEKEND AS THE TIGHT
PRESSURE GRADIENT IS MAINTAINED BETWEEN THE LARGE LOW PRESSURE
SYSTEM NEAR THE CANADIAN MARITIMES AND THE SPRAWLING HIGH CRAWLING
ACROSS THE SOUTHERN CONUS. UNSTABLE CONDITIONS OVER THE RELATIVELY
WARM WATERS OF THE GREAT LAKES WILL ENSURE GALES OVER OPEN WATERS
THROUGH THE REST OF THE DAY. THE GRADIENT WILL BEGIN TO RELAX
TONIGHT INTO SATURDAY AS HIGH PRESSURE NUDGES INTO THE UPPER OHIO
VALLEY. THIS WILL END THE GALE FORCE WINDS.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
GALE WARNING...LHZ361-LHZ362-LHZ363-LHZ421-LHZ441-LHZ462-LHZ463-
LHZ464...UNTIL 10 PM FRIDAY.
SMALL CRAFT ADVISORY...LHZ422-LHZ442-LHZ443...UNTIL 10 PM FRIDAY.
LAKE ST CLAIR...
SMALL CRAFT ADVISORY...UNTIL 10 PM FRIDAY.
MI WATERS OF LAKE ERIE...
LOW WATER ADVISORY...UNTIL 5 PM FRIDAY.
SMALL CRAFT ADVISORY...UNTIL 10 PM FRIDAY.
&&
$$
AVIATION.....RBP
UPDATE.......RBP
SHORT TERM...SC
LONG TERM....KEC
MARINE.......SC
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
