FXUS63 KDTX 081758
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1258 PM EST TUE DEC 8 2009
.AVIATION...
CHALLENGING FORECAST IN STORE AS STRENGTHENING STORM SYSTEM BEGINS
TO AFFECT ALL TAF SITES THIS EVENING. CEILINGS HAVE BEGUN TO LOWER
AS MOISTURE CONTINUES TO STREAM INTO THE AREA FROM THE SOUTHWEST.
SNOW WILL BEGIN TO FALL THIS EVENING TAKING CEILINGS AND
VISIBILITIES DOWN INTO IFR AND BRIEF LIFR CATEGORIES. THE SNOW WILL
MIX WITH RAIN AFTER MIDNIGHT THEN CHANGE OVER TO ALL RAIN FROM SOUTH
TO NORTH AS THE LOW APPROACHES AND BRINGS WARMER AIR INTO REGION.
THE EXCEPTION MAY BE MBS WHICH MAY KEEP A MIX OF PRECIPITATION
THROUGH THE PERIOD. EAST WINDS WILL BE ON THE INCREASE OVERNIGHT
GUSTING TO AROUND 25KTS AND THEN VEER TO THE SOUTHWEST TOMORROW AND
INCREASE AGAIN POSSIBLY GUSTING OVER 30KTS.
&&
.PREV DISCUSSION...ISSUED 442 AM EST TUE DEC 8 2009
SHORT TERM...TODAY
MAIN CONCERN TODAY IS HOW QUICKLY SNOW WILL BEGIN ACROSS THE CWA AS
A STRONG LOW PRESSURE SYSTEM DEVELOPS OVER THE SOUTHERN PLAINS. THE
MODELS DIFFER QUITE A BIT WITH THE ONSET OF SNOW TODAY. THE GFS
DEVELOPS SNOW QUICKLY WITH THE ONSET AROUND 18Z FOR MUCH OF THE CWA.
ON THE OTHER SIDE THE NAM ONLY BRINGS A SMALL AMOUNT OF SNOW ACROSS
THE EXTREME SOUTHERN CWA BY 00Z. THE MAIN FACTOR HOLDING SNOW OFF
UNTIL LATER APPEARS TO BE A DRY LAYER OF AIR AT 850 MB. WHILE THE
GFS OVERCOMES THIS DRY LAYER MUCH QUICKER...A HAND ANALYSIS OF THE
00Z 850 MB CHART SHOWS A DRY POCKET OF AIR FROM CENTRAL ILLINOIS ALL
THE WAY TO NORTHERN LOUISIANA WITH DEW POINT DEPRESSIONS OF 10 TO
20. DESPITE THE KDTX 00Z RAOB SOUNDING SHOWING A FAIRLY MOIST COLUMN
THROUGH 750 MB...THIS DRY AIR TO THE SOUTH WILL ADVECT INTO THE
REGION AS THE LOW DEVELOPS AND HEADS NORTHEAST. IN ADDITION
ISENTROPIC LIFT THIS AFTERNOON LOOKS WEAK AT BEST AS 295K SYSTEM
RELATIVE WINDS ARE PARALLEL TO THE ISOBARS. SINCE THIS DRY LAYER
WILL NEED TO BE OVERCOME BEFORE ANY SNOW BEGINS TO FALL AND WITH
VERY LITTLE HELP FROM ISENTROPIC LIFT OR MID LEVEL
FRONTOGENESIS...THE QUICKER GFS SEEMS A BIT OPTOMISTIC IN OVERCOMING
THIS LAYER SO QUICKLY. THE CURRENT FORECAST LOOKS TO BE A GOOD
COMPROMISE IN THIS CASE WITH SNOW STARTING AROUND 21Z. SINCE A LOT
OF THIS INITIAL MOISTURE WILL BE USED TO OVERCOME THIS DRY LAYER NO
MORE THAN A DUSTING IS EXPECTED THROUGH 00Z AS THE COLUMN MOISTENS
UP AND LIGHT SNOW BEGINS ACROSS THE AREA.
LONG TERM...TONIGHT THROUGH MONDAY
UPPER WAVE LIFTING FROM THE CALIFORNIA COAST TOWARDS THE FOUR
CORNERS REGION WILL RACE ACROSS THE ROCKIES (150-160KT FLOW) BEFORE
LIFTING UP TOWARDS THE GREAT LAKES TONIGHT. DEEPENING SURFACE LOW
WILL LIFT FROM THE CENTRAL PLAINS AND TOWARDS CHICAGO OVERNIGHT. THE
LOW IS EXPECTED TO TRACK ACROSS SAGINAW BAY AND INTO CENTRAL LAKE
HURON BY WEDNESDAY EVENING...WITH GOOD CONSENSUS NOW SHOWN BY THE
GFS/EURO/GEM/UKMET. NAM/UKMET DO REMAIN SLIGHTLY NORTH OF THIS TRACK
HOWEVER...MORE ACROSS NORTHERN LOWER MICHIGAN.
PRECIPITATION WILL INCREASE IN COVERAGE AND INTENSITY OVER SOUTHEAST
MICHIGAN THIS EVENING...AS THE APPROACH OF THE LOW IS ACCOMPANIED BY
A COUPLED JET STRUCTURE...VERY IMPRESSIVE STRONG ISENTROPIC
ASCENT...GOOD FGEN...AND MODERATE MID-LEVEL INSTABILITY. DEEP LAYER
LIFT WILL HAVE GOOD MOISTURE TO WORK WITH...AS SPECIFIC HUMIDITIES
BELOW 600 MB RISE TO BETWEEN 3 AND 5 G/KG BELOW H600. MODELS ALL NOW
SUPPORT A SLIGHTLY EARLIER ONSET OF PRECIPITATION AND ARE ALSO A
LITTLE SLOWER IN BRINGING THE WARM AIR UP INTO THE REGION. THIS HAS
RESULTED IN AN INCREASE IN FORECAST SNOW AMOUNTS FOR THE OVERNIGHT
PERIOD. NOW EXPECTING 1 TO 2 INCHES FROM THE OHIO BORDER TO
M-59...WITH 2 TO 5 INCHES THEN EXPECTED FROM M-59 TO SAGINAW...AND
ABOUT 6 INCHES OVER BAY AND MIDLAND COUNTIES. STRONG WARM AIR
ADVECTION ARRIVING AHEAD OF THE SYSTEM...ESPECIALLY AFTER 1 AM
TONIGHT...WILL ALLOW PRECIPITATION TO GRADUALLY CHANGE OVER TO ALL
RAIN SOUTH OF FLINT BY 7 AM...WITH A RAIN/SNOW MIX OCCURRING LATE AS
FAR NORTH AS SAGINAW. GFS FORECAST SOUNDINGS ALSO SUPPORT SOME SLEET
MIXING IN SOUTH OF FLINT BEFORE THE CHANGEOVER TO RAIN OCCURS. GIVEN
NEW SNOW AMOUNTS AND EXPECTATION FOR SOME SLEET...HAVE ISSUED A
WINTER WEATHER ADVISORY FOR ALL OF THE FORECAST AREA EXCEPT FOR
MIDLAND AND BAY COUNTIES WHERE THE WATCH WAS UPGRADED TO A WARNING.
LOW-END ADVISORY CRITERIA IS FOR 2 INCHES IN 6 HOURS...HOWEVER
WHEREVER WE COME UP SHY WITH THE SNOW ACCUMULATIONS...WE WILL LIKELY
BE SEEING ENOUGH SLEET TO JUSTIFY THE WINTER WEATHER ADVISORY WITH A
MIX ANYWAY. RAIN/SNOW LINE WILL CONTINUE TO LIFT NORTHWARD FOR THE
FIRST HALF OF THE DAY ON WEDNESDAY...WITH MOSTLY SNOW CONTINUING FOR
BAY AND MIDLAND COUNTIES. POWERFUL COLD FRONT WILL THEN BLAST
THROUGH THE AREA DURING THE LATE AFTERNOON/EVENING...PROVIDING A
VERY FAST CHANGEOVER TO ALL SNOW SHOWERS.
GUSTY WINDS ARE EXPECTED TONIGHT AND FOR TOMORROW...THOUGH THEY MAY
LULL FOR A PERIOD RIGHT NEAR THE LOW CENTER AS IT LIFTS ACROSS
CENTRAL MICHIGAN. WINDS WILL FURTHER INCREASE BEHIND THE COLD FRONT
AS IT PUSHES THROUGH. GFS SOUNDINGS DO SUGGEST WE COULD MIX UP TO 45
MPH...AND THIS IS SUPPORTED BY A TIGHT THERMAL GRADIENT...EXISTING
STRONG PRESSURE GRADIENT...AND STRONG ISENTROPIC DESCENT. SINCE THIS
WOULD ONLY SUPPORT A WIND ADVISORY...WILL NOT ISSUE A HIGH WIND
WARNING. VERY COLD AIR WILL SPILL INTO THE REGION BEHIND THE
FRONT...DESPITE GREAT LAKE WATER TEMPERATURES IN THE MID 40S. HIGHS
ON THURSDAY WILL RISE LITTLE FROM OVERNIGHT LOWS...WITH AFTERNOON
TEMPERATURES PEAKING ONLY IN THE LOW 20S (OR EVEN UPPER TEENS OVER
THE TRI-CITIES/THUMB).
PRECIPITATION WILL BECOME DOMINATED BY LAKE EFFECT SNOW PROCESSES
BEHIND THE FRONT WEDNESDAY NIGHT THROUGH FRIDAY. HAVE CONTINUED TO
MENTION SCATTERED SNOW SHOWERS FOR MOST THE AREA...BUT DID TRY
HIGHLIGHT AN ENHANCED AREA OF LAKE EFFECT BETWEEN I-69 AND THE OHIO
BORDER WED NIGHT AND THURSDAY AND EVEN ADDED IN SOME ACCUMULATIONS.
STRONG WESTERLY FLOW ACROSS LAKE MICHIGAN...WITH GOOD MOISTURE DEPTH
(ESPECIALLY INTO THE EARLY AFTERNOON AND THURSDAY) AND LAKE-850
DELTA T VALUES TOPPING OUT AT 27 DEGREES BY 00Z FRI SHOULD PROMOTE
HEALTHY LAKE EFFECT. ALTHOUGH ACCUMULATIONS ON THE EAST SIDE OF THE
STATE ARE STILL HARD TO DETERMINE...00Z GFS BUFKIT OUTPUT SUGGESTS
1-4 INCH ACCUMULATIONS SOUTH OF I-69 FROM WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT. WILL BE PINPOINTING THIS A LITTLE BETTER OVER THE
NEXT FEW DAYS...AS LAKE EFFECT IS MORE OF A MESOSCALE AND SHORTER
TERM ISSUE.
SURFACE HIGH PRESSURE WILL BUILD INTO THE SOUTHERN GREAT LAKES ON
FRIDAY AND CONTINUE TO EXPAND NORTHWARD INTO LAKE HURON THROUGH
SATURDAY. ASIDE FROM GRADUAL DRYING OF THE ATMOSPHERIC COLUMN OVER
THE REGION...WIND FIELDS WILL WEAKEN AND TAKE ON MORE OF A SOUTHERLY
COMPONENT AT H850. THIS SHOULD BRING AN END TO LAKE EFFECT SNOW
SHOWERS BY EVENING. COLD AIR WILL REMAIN IN PLACE HOWEVER...WITH
HIGHS ON FRIDAY IN THE UPPER TEENS TO LOW 20S AND BREEZY WINDS
LIMITING WIND CHILLS INTO THE SINGLE DIGITS TO JUST SLIGHTLY BELOW
ZERO. GFS/EURO NOW BOTH SHOW AN UPPER WAVE RIDING A STRONG JET
STREAK ACROSS THE GREAT LAKES ON SATURDAY NIGHT...THOUGH THEY DIFFER
A BIT WITH THE STRENGTH AND AMPLITUDE. IT LOOKS AS IF ANOTHER COLD
FRONT WILL DROP DOWN ACROSS THE REGION SATURDAY NIGHT AND EARLY
SUNDAY...REINFORCING COLD AIR OVER THE REGION AND GENERATING A FEW
LIGHT SNOW SHOWERS. THERMAL ADVECTION AHEAD OF THE SYSTEM LOOKS
MEAGER...AND ONLY EXPECT HIGHS TO RECOVER A FEW DEGREES INTO THE MID
20S ON SATURDAY. TEMPERATURES WILL REMAIN BELOW NORMAL BEHIND THE
FRONT AS WE HEAD INTO NEXT WEEK.
MARINE...
SOUTHEAST WINDS WILL PICK UP TODAY AHEAD OF A MAJOR STORM SYSTEM
DEVELOPING ACROSS THE SOUTHERN PLAINS. A DEEPENING LOW PRESSURE
(970S MB) WILL TRACK NORTHEAST THROUGH LOWER MICHIGAN ON WEDNESDAY.
THE GUSTY SOUTHEAST WINDS WILL CAUSE SMALL CRAFT ADVISORY CONDITIONS
ACROSS SAGINAW BAY...LAKE ST. CLAIR AND WESTERN LAKE ERIE LATE THIS
AFTERNOON AND EARLY THIS EVENING WITH SMALL CRAFT ADVISORIES HOISTED
FOR THOSE AREAS. GALE FORCE CONDITIONS WILL OCCUR ALONG THE OPEN AND
NEARSHORE WATERS OF LAKE HURON TONIGHT AS THE LOW APPROACHES THE
CENTRAL GREAT LAKES...WITH GALE WATCHES BEING UPGRADED TO GALE
WARNINGS ACROSS THOSE AREAS. GALE FORCE CONDITIONS ARE NOT EXPECTED
UNTIL WEDNESDAY AFTERNOON/EVENING ACROSS SAGINAW BAY/LAKE ST
CLAIR/WESTERN LAKE ERIE...THEREFORE WILL LET THE GALE WATCH CONTINUE
FOR THOSE AREAS AT THIS POINT. GALE FORCE WINDS WILL CONTINUE
THROUGH THURSDAY ACROSS ALL AREAS...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 WARNING...MIZ047-MIZ048...FROM 10 PM TUESDAY TO 10 AM
WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ063-MIZ068-MIZ069-MIZ070-MIZ075-
MIZ076...FROM 7 PM TUESDAY TO 4 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ055-MIZ060-MIZ061-MIZ062...FROM 7 PM
TUESDAY TO 7 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ049-MIZ053-MIZ054...FROM 7 PM TUESDAY
TO 10 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ082-MIZ083...FROM 7 PM TUESDAY TO 1 AM
WEDNESDAY.
LAKE HURON...
STORM WARNING...LHZ361-LHZ362...FROM 1 AM WEDNESDAY TO 1 PM
WEDNESDAY.
STORM WARNING...LHZ363-LHZ421-LHZ441-LHZ442-LHZ443-LHZ462-LHZ463-
LHZ464...FROM 1 AM WEDNESDAY TO 1 AM THURSDAY.
GALE WARNING...INNER SAGINAW BAY...FROM 1 AM WEDNESDAY TO 1 PM
THURSDAY.
LAKE ST CLAIR...
GALE WATCH...FROM 10 AM WEDNESDAY TO 10 AM THURSDAY.
SMALL CRAFT ADVISORY...FROM 4 PM TUESDAY TO 10 AM WEDNESDAY.
MI WATERS OF LAKE ERIE...
GALE WATCH...FROM 10 AM WEDNESDAY TO 10 AM THURSDAY.
SMALL CRAFT ADVISORY...FROM 4 PM TUESDAY TO 10 AM WEDNESDAY.
&&
$$
AVIATION.....DRK
SHORT TERM...KURIMSKI
LONG TERM....HLO
MARINE.......KURIMSKI
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
