404
FXUS63 KDTX 091230
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
730 AM EST TUE FEB 9 2010
AVIATION
CONDITIONS WILL QUICKLY DETERIORATE THIS MORNING AS LIGHT SNOW
DEVELOPS IN ADVANCE OF AN APPROACHING WINTER STORM. A STEADY LIGHT
TO MODERATE SNOW WILL THEN CONTINUE INTO TONIGHT AS THIS STORM
SHIFTS THROUGH THE OHIO VALLEY. CONDITIONS WILL LOWER INTO
PREVAILING IFR AND REMAIN THERE THROUGH THE NEXT 24 HOURS. A
PERIOD OF LIFR REMAINS POSSIBLE...TARGETING ROUGHLY THE 00-06Z
TIME WINDOW ESPECIALLY AT PTK AND THE DETROIT AREA. BLOWING SNOW
BECOMES A CONCERN BY WEDNESDAY MORNING AS NORTHERLY WINDS
STRENGTHEN IN RESPONSE TO THE DEEPENING LOW PRESSURE SYSTEM. GUSTS
WILL REACH 25 KNOTS AT TIMES.
PREV DISCUSSION
ISSUED 416 AM EST TUE FEB 9 2010
SHORT TERM...TODAY THROUGH WEDNESDAY
WINTER STORM WARNINGS AND WINTER WEATHER ADVISORIES REMAIN IN EFFECT
FROM TUESDAY INTO WEDNESDAY MORNING. PLEASE SEE THE WINTER STORM
WARNING/WINTER WEATHER ADVISORY /WSWDTX/ FOR EXACT TIMES AND
ACCUMULATIONS.
THE DEVELOPING WINTER STORM IS ON OUR DOORSTEP AT THIS POINT WITH AN
INVERTED SURFACE TROUGH EXTENDING FROM THE LOWER MISSISSIPPI VALLEY
TO WEST OF LAKE MICHIGAN. THIS LOW PRESSURE SYSTEM WILL DEEPEN AS IT
LIFTS TO CENTRAL OHIO BY 00Z AHEAD OF THE LEADING SHORTWAVE TRACKING
FROM ARKANSAS TO THE OHIO VALLEY. AS WE PROGRESS THROUGH THE
NIGHT...THE UPPER LOW APPROACHING MISSOURI WILL SWING EASTWARD
ACROSS THE OHIO VALLEY. THE SURFACE LOW WILL OCCLUDE OVER NORTHEAST
OHIO BEFORE GETTING ABSORBED BY A MUCH STRONGER LOW PRESSURE SYSTEM
DEVELOPING ALONG THE MID-ATLANTIC COAST. THE 00Z MODELS ARE
CONSISTENT WITH THE 12Z NWP PACKAGE IN KEEPING THE UPPER LOW 100
MILES OR MORE FURTHER SOUTH THAN PREVIOUSLY ADVERTISED OVER THE LAST
2-3 DAYS. IMPLICATIONS OF THE FURTHER SOUTH TRACK ARE THAT THE
STRONGEST LARGE SCALE FORCING IS FOCUSED FROM THE APPALACHIANS TO
THE EAST COAST...INSTEAD OF PIVOTING NORTH INTO SOUTHEAST MICHIGAN.
AS A RESULT...THIS SNOWSTORM WILL BE CHARACTERIZED BY A PROLONGED
PERIOD OF MODERATE LIFT AND SNOWFALL INTENSITIES.
THE 00Z DTX SOUNDING SHOWED A DRY LAYER BELOW 700MB. SINCE THEN
REGIONAL RADARS HAVE STARTED TO FILL IN...INDICATING THAT CLOUDS
ARE LOWERING AND THE ATMOSPHERE IS MOISTENING. OBSERVATIONS NEAR
LAKE HURON ALSO SHOW A STRATUS DECK COMING IN OFF THE LAKE UNDER
NORTHEASTERLY FLOW. DESPITE THE DRY AIR IN PLACE...SNOW IS EXPECTED
TO RAPIDLY EXPAND NORTHWARD INTO THE AREA REACHING LENAWEE/MONROE
COUNTIES BY 7AM...THE M-59 CORRIDOR BY 11 AM...THEN EXPANDING
THROUGH THE THUMB THIS AFTERNOON. ISENTROPIC ASCENT INCREASES THIS
MORNING AND CONTINUES THROUGH THE DURATION OF THE EVENT AS THE
TROWAL AXIS LIFTS NORTH OVER LAKE ERIE. A MID-LEVEL DEFORMATION
AXIS ALSO SETS UP FROM THIS AFTERNOON INTO THIS EVENING WITH
MODELS IN AGREEMENT PLACING THIS FEATURE NEAR THE I-69 CORRIDOR.
AT LEAST 2 G/KG SPECIFIC HUMIDITY IS AVAILABLE UP TO ABOUT 750MB
FROM 18Z-06Z BEFORE GRADUALLY TAPERING OFF FROM NORTH TO SOUTH.
MODEL QPF RANGES FROM .70 NEAR THE OHIO BORDER TO .35 IN
MIDLAND/BAY COUNTIES. WITH THAT IN MIND AND MODELS SHOWING SNOW
RATIOS BETWEEN 12:1 TO 15:1...THE FORECAST CONTINUES TO CALL FOR
WIDESPREAD ACCUMULATIONS OF 5 TO 9 INCHES IN THE WARNING AND 3 TO
6 INCHES IN THE ADVISORY. A FEW LOCALLY HIGHER AMOUNTS REMAIN
POSSIBLE...MAINLY WITHIN THE WARNING AREA.
WE CONTINUE TO RELY ON LAKE ENHANCEMENT TO ACHIEVE THE FORECASTED
ACCUMULATIONS IN THE THUMB REGION. NAM 12 SHOWS TWO FAVORED AREAS OF
CONVERGENCE SETTING UP DOWNWIND OF LAKE HURON...ONE EXTENDING FROM
OSCODA SOUTH TO CASEVILLE ON THE WEST SIDE OF THE THUMB...AND THE
OTHER ON THE EAST SIDE OF THE THUMB FROM RICHMONDVILLE SOUTH TO
LAKEPORT. ALTHOUGH LAKE INSTABILITY IS MARGINAL WITH EQUILIBRIUM
LEVELS ONLY REACHING ABOUT 4000 FEET AFTER MIDNIGHT...EXPECT THIS TO
PROVIDE ENOUGH ENHANCEMENT TO SEE A BOOST IN SNOW SHOWERS AND
PROVIDE GENERALLY 1 TO 3 INCHES MORE THAN WHAT THE SYNOPTIC SYSTEM
WOULD ACCOUNT FOR. MODEL QPF IS THE LOWEST ALONG THE TIP OF THE
THUMB WITH ONLY ABOUT A QUARTER INCH OF LIQUID...BUT MODELS NEVER
HANDLE LAKE EFFECT QPF VERY WELL. WE WILL HAVE TO MONITOR THE THUMB
REGION CAREFULLY AND MAY NEED TO LOWER THE SNOW FORECAST IF LAKE
ENHANCEMENT DOES NOT MATERIALIZE. CONFIDENCE IN THE FORECAST IS
LOWEST IN THIS REGION. THESE SNOW SHOWERS ARE EXPECTED TO CONTINUE
THROUGH WEDNESDAY MORNING BEFORE BECOMING LIGHT DURING THE AFTERNOON
AS DRIER AIR PUSHES SOUTH ACROSS LAKE HURON.
BLOWING SNOW DOES BECOME A CONCERN FROM LATE TUESDAY NIGHT INTO
WEDNESDAY AS WINDS INCREASE BEHIND THE DEPARTING SYSTEM. NORTH TO
NORTHWESTERLY SUSTAINED WINDS OF 15 TO 25 MPH WITH GUSTS TO 30 MPH
CAN BE EXPECTED FOR MUCH OF THE DAY ON WEDNESDAY. THE BLOWING SNOW
MAY CAUSE SOME DRIFTING AND ALSO MAKE IT HARDER TO KEEP EAST-WEST
ORIENTED ROADS WITH GOOD EXPOSURE CLEAR OF SNOW.
LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY
WEAK UPPER TROUGHING WILL REMAIN IN PLACE IN THE WAKE OF THE WINTER
STORM FOR WEDNESDAY NIGHT/THURSDAY. AIR MASS WILL SEE A RAPID
REDUCTION IN MOISTURE DEPTH DURING THIS TIME...BUT A RESIDUAL
SATURATED LAYER LOCATED COINCIDENT WITH THE BETTER DENDRITE GROWTH
REGION WILL SUPPORT SOME ADDITIONAL LIGHT SNOW SHOWERS/FLURRIES
DURING THIS TIME. WEAK SURFACE HIGH PRESSURE WILL THEN NOSE INTO
THE GREAT LAKES FOR FRIDAY UNDER WEAK CONFLUENT UPPER LEVEL
NORTHWEST FLOW. PATTERN THROUGH THE END OF THE WEEK SUPPORTS
CONTINUED BELOW NORMAL TEMPERATURES WITH THE OPPORTUNITY FOR SOME
GOOD RADIATIONAL COOLING GIVEN THE FRESH SNOWPACK AND DIMINISHING
WIND FIELD/CLEARING SKIES.
FLOW WILL MAINTAIN A PREDOMINANT NORTHWESTERLY COMPONENT INTO NEXT
WEEKEND AS THE DEPARTING WINTER STORM SETTLES ACROSS THE CANADIAN
MARITIMES WITH THE PERIPHERY EXTENDING WESTWARD INTO THE NORTHEAST
CONUS. AT LEAST ONE SHORTWAVE EMBEDDED WITHIN THE FLOW WILL DROP
SOUTHEAST EITHER ACROSS OR JUST SOUTH OF THE REGION OVER THE
WEEKEND. THE ASSOCIATED WEAK FORCING WOULD BRING A LOW END CHANCE
FOR SNOW...ALTHOUGH POOR MODEL CONSENSUS ON TIMING/PLACEMENT/
STRENGTH OF THIS WAVE WILL DICTATE THAT FEW CHANGES BE MADE DURING
THIS TIME FRAME. A DEEPER NORTHERLY FLOW LOOKS TO EVOLVE IN THE
WAKE OF THIS SYSTEM FOR EARLY NEXT WEEK AS THE MEAN NORTHEAST TROUGH
AMPLIFIES WHILE BUILDING SOUTHWEST. THIS PATTERN WILL ENSURE COLDER
TEMPERATURES REMAIN IN PLACE WHILE BRINGING AN INCREASING CHANCE OF
SNOW.
MARINE...
A DEEPENING LOW PRESSURE SYSTEM LIFTING ACROSS THE OHIO VALLEY
WILL BRING INCREASING NORTHERLY WINDS THROUGH WEDNESDAY. GUSTS WILL
REACH GALE FORCE AT TIMES ACROSS LAKE HURON TONIGHT AND WEDNESDAY.
NORTHWEST WINDS WILL GRADUALLY DIMINISH WEDNESDAY NIGHT AND THURSDAY
AS THE LOW PULLS EAST AND HIGH PRESSURE SLOWLY BUILDS TOWARD THE
WESTERN GREAT LAKES. PREVAILING NORTHWEST FLOW WILL HOLD IN THE
10-15 KNOT RANGE INTO NEXT WEEKEND.
DTX WATCHES/WARNINGS/ADVISORIES
MI...WINTER STORM WARNING...MIZ060-MIZ061-MIZ068-MIZ069-MIZ070-MIZ075-
MIZ076-MIZ082-MIZ083...UNTIL 10 AM WEDNESDAY.
WINTER STORM WARNING...MIZ055-MIZ062-MIZ063...FROM 2 PM TUESDAY TO
1 PM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ047-MIZ048-MIZ053...FROM NOON TUESDAY
TO 7 AM WEDNESDAY.
WINTER WEATHER ADVISORY...MIZ049-MIZ054...FROM 4 PM TUESDAY TO 1 PM
WEDNESDAY.
LAKE HURON...
GALE WARNING...LHZ362-LHZ363-LHZ421-LHZ422-LHZ441-LHZ442-LHZ443-
LHZ462-LHZ463-LHZ464...FROM 7 PM TUESDAY TO 7 PM WEDNESDAY.
LAKE ST CLAIR...
BRISK WIND ADVISORY...FROM 4 PM TUESDAY TO 4 PM WEDNESDAY.
MI WATERS OF LAKE ERIE...
BRISK WIND ADVISORY...FROM 4 PM TUESDAY TO 4 PM WEDNESDAY.
AVIATION.....MR
SHORT TERM...KEC
LONG TERM....MR
MARINE.......MR
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
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