FXUS63 KDTX 152307
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
607 PM EST TUE DEC 15 2009
.AVIATION...
SCATTERED SNOW SHOWERS WILL DIMINISH TO FLURRIES AND THEN END DURING
THE FIRST PART OF THE FORECAST AS DRIER LOW LEVEL AIR IN THE WAKE OF
A SECONDARY TROUGH WORKS THROUGH LOWER MICHIGAN THIS EVENING. THE
SNOW SHOWERS WILL THE TROUGH ITSELF ARE ALREADY SHIFTING EAST AND
LAKE EFFECT ACTIVITY OFF OF LAKE MICHIGAN IS SHOWING SIGNS OF DRYING
UP PER IR IMAGERY. CEILINGS WILL START OUT LOWER VFR TO MVFR AND
EDGE DOWN INTO MVFR LATE TONIGHT AS INVERSION HEIGHTS LOWER AND THE
REMAINING LOW LEVEL MOISTURE REMAINS TRAPPED AOB 2500 FEET. THESE
CONDITIONS WILL PRETTY MUCH CONTINUE THROUGH THE DAY WEDNESDAY AS
WELL AS WEST/NORTHWEST FLOW PERSISTS.
&&
.PREV DISCUSSION...ISSUED 351 PM EST TUE DEC 15 2009
SHORT TERM...THROUGH TONIGHT
SATELLITE IMAGERY SHOWS AN UPPER LEVEL WAVE PUSHING ACROSS THE
NORTHERN GREAT LAKES THIS AFTERNOON. MID-LEVEL FORCING FROM THIS
FEATURE HELPED TO ENHANCE LAKE EFFECT SNOW THIS AFTERNOON...ALLOWING
WIDESPREAD LIGHT SNOW TO BLANKET MUCH OF SOUTHEAST MICHIGAN.
(PRIMARILY NORTH OF M-59) DRIER AIR ALREADY EVIDENT ON SATELLITE
IMAGERY WILL PUSH INTO THE AREA AND CHIP AWAY AT MOISTURE WITHIN THE
DENDRITIC GROWTH ZONE OVER THE NEXT FEW HOURS. IR ICE ENHANCEMENT
NOW SHOWS THIS TREND OCCURRING OVERHEAD AND TO OUR WEST...WITH THE
EXCEPTION OF A FEW COLDER CLOUD TOPS ASSOCIATED WITH LAKE EFFECT
BANDS OFF LAKE MICHIGAN. DRIER AIR ALONG WITH WANING DYNAMIC
FORCING FROM THE UPPER WAVE WILL ALLOW THE LIGHT SNOW TO TAPER TO
FLURRIES IN THE VERY EARLY EVENING AS LAKE EFFECT CONTINUES. AS
MOISTURE DEPTH DECREASES OVERNIGHT...WE WILL SEE AN END TO THE
FLURRIES AS WELL BY LATE EVENING.
SATELLITE IMAGERY ALSO SHOWS A FEW BREAKS HAVE BEGUN TO DEVELOP IN
THE CLOUD COVER OVER MICHIGAN. THINK WE WILL CONTINUE TO SEE THESE
BREAKS DEVELOP AS WE HEAD INTO THE EVENING...WITH SKIES FILLING BACK
IN WITH STRATUS OVERNIGHT. FORECAST SOUNDINGS FROM THE NAM AND GFS
BOTH MAINTAIN VERY STRONG INVERSIONS HOLDING THROUGH THE NIGHT AND
LOOK SATURATED JUST ENOUGH BELOW THIS INVERSION TO WARRANT A MOSTLY
CLOUDY FORECAST FOR THE OVERNIGHT HOURS. LOWS TONIGHT WILL FALL INTO
THE TEENS...GIVEN THE STRATUS DECK HOLDS.
LONG TERM...WEDNESDAY THROUGH TUESDAY
DEEP DRYING OF THE AIRMASS WILL COMMENCE ABOVE 925 MB INTO WEDNESDAY
AS HIGH PRESSURE BUILDS IN ACROSS THE GREAT LAKES AND NORTHWEST
CONFLUENT UPPER LEVEL FLOW EVOLVES. HOWEVER LINGERING LOW LEVEL
MOISTURE TRAPPED BENEATH THE INVERSION SUPPORTED BY A RESIDUAL MIXED
LAYER/CONTINUED COLD AIR ADVECTION WILL MAINTAIN POCKETS OF STRATUS
THROUGH THE DAY. THE STRENGTH OF THE RESIDENT ARCTIC AIRMASS
SETTLING IN WILL TRANSLATE INTO HIGHS RANGING FROM LOW 20S NORTH TO
UPPER 20S SOUTH...OR 7-10 DEGREES BELOW NORMAL. ANY LINGERING
CLOUDINESS WILL TEMPER THE RADIATIONAL COOLING SLIGHTLY OVERNIGHT...
BUT OTHERWISE LOOKING AT A FAVORABLE SETUP GIVEN THE WEAKENING WIND
FIELD...DEGREE OF MID LEVEL DRYING AND REMAINING SNOWPACK.
THEREFORE WILL CONTINUE TO UNDERCUT GUIDANCE IN MANY LOCATIONS...
WITH READINGS WELL INTO THE TEENS /SINGLE DIGITS POSSIBLE NORTH/.
LITTLE CHANGE IN THE OVERALL THERMAL PROFILE FOR THE THURSDAY/FRIDAY
PERIODS AS THE ANTICYCLONE CENTER SHIFTS NORTH AND SOUTHEAST LOWER
MI SETTLES WITHIN DRY LOW LEVEL NORTHEAST FLOW. A WEAK
SHEARED OUT SHORTWAVE EMBEDDED WITHIN THE BROADER NORTHWEST UPPER
LEVEL FLOW WILL SHIFT THROUGH ON THURSDAY. HOWEVER LIMITED MOISTURE
THROUGH THE COLUMN AND A LACK OF BETTER FORCING WILL PRECLUDE SEEING
ANYTHING MORE THAN SOME INCREASE IN MID CLOUD. SLIGHTLY STRONGER
WAVE WILL ARRIVE ON FRIDAY. BOTH THE GFS AND NAM MAINTAIN A
WEAK RESPONSE AT THE SURFACE WITH AN INVERTED TROUGH AXIS SLIDING
THROUGH...WITH THE LACK OF BETTER MOISTURE AGAIN BRINGING JUST SOME
INCREASE IN CLOUDS AND PERHAPS A FEW FLURRIES. WORTH NOTING THE 12Z
ECMWF WHICH NOW SPINS UP A STRONGER LOW WHILE DEEPENING THE UPPER
TROUGH. THE CORRESPONDING STRENGTHENING OF THE LOW TO MID LEVEL
THERMAL CIRCULATION THEN MAKES THE MOST OF THE MEAGER MOISTURE TO
GENERATE A .1-.2" SWATH OF LIQUID FOR FRIDAY/FRIDAY NIGHT. WILL
MAINTAIN THE GOING DRY FORECAST FOR THIS TIME FRAME AND ALLOW FOR
BETTER SAMPLING OF THIS WAVE BEFORE FAVORING A STRONGER/WETTER
SCENARIO.
COMPLEX PATTERN EVOLUTION FOR THE WEEKEND PERIOD AND BEYOND AS THE
MODELS ATTEMPT TO RESOLVE A HIGHLY BLOCKED FLOW ACROSS EASTERN
CANADIAN. LATEST MODEL GUIDANCE POINTING TOWARD A CLOSED UPPER
LOW STALLING OVER THE CANADIAN MARITIMES...WITH ENERGY EMERGING OUT
OF THE MEAN CENTRAL CANADIAN POLAR VORTEX AND OVER BRITISH COLUMBIA
THIS ENERGY WILL CONSOLIDATE/AMPLIFYING AND DROP SOUTH IN SOME FORM
IN RESPONSE TO THE BLOCKED FLOW DOWNSTREAM. BOTH THE GFS AND ECMWF
BRING A CLOSED LOW INTO THE GREAT LAKES BY TUESDAY...BUT REACH THIS
POINT IN DIFFERENT MANNERS. REGARDLESS OF THE CORRECT SCENARIO...
THE OVERALL PATTERN WILL RESULT IN CONTINUED BELOW NORMAL
TEMPERATURES UNDER A PREDOMINANT NORTHERLY FLOW. DEPENDING ON THE
EXACT ORIENTATION OF THE WIND FIELD...THERE WILL BE AN OPPORTUNITY
FOR SOME LAKE HURON ENHANCED SNOWFALL SATURDAY NIGHT/SUNDAY...
PERHAPS AIDED BY BETTER SYNOPTIC FORCING WITH THE PASSAGE OF AN
INITIAL UPPER TROUGH AXIS (PER 12Z GFS). THE PRESENCE OF THE UPPER
LOW WOULD MAINTAIN A CHANCE OF SNOW SHOWERS WITH GOOD CYCLONIC FLOW/
LAKE ENHANCEMENT INTO EARLY NEXT WEEK.
MARINE...
WINDS AND WAVES WILL INCREASE THIS EVENING AS COLD AIR CONTINUES TO
STREAM OVER THE RELATIVELY WARM LAKE WATERS...AND AS STRONG HIGH
PRESSURE BUILDING INTO THE UPPER MISSISSIPPI RIVER VALLEY PROVIDES A
TIGHT SURFACE PRESSURE GRADIENT. WINDS WILL TURN FROM NORTHWEST TO
WEST THIS EVENING...BUT CONTINUE TO GUST TO AROUND 25 KNOTS THROUGH
LATE TONIGHT. THE WINDS WILL GENERATE LARGE WAVES IN EXCESS OF 4
FEET. HIGH PRESSURE WILL SLIDE EAST AND BECOME CENTERED OVER LAKE
MICHIGAN BY WEDNESDAY AFTERNOON...ALLOWING WINDS AND WAVES TO
DECREASE.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...LHZ422-LHZ442-LHZ443...UNTIL 4 AM WEDNESDAY.
SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 4 PM WEDNESDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....99
SHORT TERM...HLO
LONG TERM....MR
MARINE.......HLO
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
