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000
FXUS63 KDTX 100511
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1211 AM EST WED FEB 10 2010

.AVIATION...

WHILE SOME BRIEF PERIODS OF MODERATE SNOW WILL CONTINUE...LIGHT SNOW
WILL REMAIN PREDOMINATE AT THE TAF SITES THROUGH 09 OR 10Z BEFORE
THE FORCING ASSOCIATED WITH THE OHIO VALLEY STORM SYSTEM EXITS TO
THE EAST OF THE AREA. CEILINGS WILL REMAIN PRIMARILY IN THE MVFR
RANGE /WITH A FEW AREAS OF LINGERING IFR/ THANKS TO SOME FEED OF
DRIER AIR NEAR THE SURFACE UNDER GUSTY NORTHEASTERLY WINDS WHICH
SHOULD PERSIST THROUGH THE MORNING. GUSTY NORTHEAST WINDS WILL VEER
TO THE NORTH BY 12Z AND CONTINUE INTO THE AFTERNOON WITH FREQUENT
GUSTS OVER 20 KNOTS. THIS WILL CREATE A PROLONGED PERIOD OF BLOWING
AND DRIFTING SNOW.

&&

.PREV DISCUSSION...ISSUED 1043 PM EST TUE FEB 9 2010

UPDATE...

LATEST THOUGHTS REGARDING THE WINTER STORM IMPACTING SOUTHEASTERN
MICHIGAN. THE BIGGEST CHANGE WILL BE TO UPGRADE TO A WINTER STORM
WARNING FOR SAGINAW AND TUSCOLA COUNTIES.

A CLASSIC REALIGNMENT OF THE ISOBARS ON THE 290K SURFACE IS TAKING
PLACE THIS EVENING IN RESPONSE TO THE PASSING...WEAK MIDLEVEL
THERMAL LOW SCRAPING THE IN/OH/MI STATELINES. OBSERVATIONALLY...THIS
IS EVIDENT IN THE LATEST KDTX RADAR IMAGERY AS REFLECTIVITIES HAVE
INCREASED WHILE SWITCHING MORE TO A EAST/WEST ORIENTATION. WHILE
THIS DOES NOT SIGNIFY AN INCREASE IN THE BACKGROUND FORCING...IT
INCREASES CONFIDENCE FOR A PROLONGED PERIOD OF ISENTROPIC LIFT
THROUGH THE HEART OF THE CENTRAL CWA.

GIVEN THE VERY BROAD DEFORMATION FORCING IMMEDIATELY NORTH OF THE
ANOMALY AND THE AFOREMENTIONED ISENTROPIC LIFT...MODERATE SNOWS WILL
PERSIST ACROSS MUCH OF SE MICHIGAN THROUGH 8-10Z. ADDITIONAL QPF
TONIGHT SHOULD RANGE BETWEEN .2 AND .3 INCHES...WHICH YIELDS AN
ADDITIONAL 3 TO 4 INCHES AT 15:1. INCREASED RADAR RETURNS HAVE
OVERLAPPED SHIAWASSEE AND SOUTHERN SAGINAW/TUSCOLA COUNTIES
THROUGHOUT THE EVENING HOURS. LATEST REPORTS IN THAT AREA GIVES
SNOWFALL ACCUMULATIONS OF BETWEEN 3 AND 5 INCHES. GIVEN THESE
TRENDS...WILL UPGRADE TO A WINTER STORM WARNING FOR SAGINAW AND
TUSCOLA COUNTIES. WHAT NEEDS TO BE STRESSED IS THAT SURFACE WINDS
HAVE ALREADY BEEN GUSTING WELL OVER 30 MPH ACROSS THE NORTHERN
CWA. THERE IS LIKELY SIGNIFICANT BLOWING AND DRIFTING THAT IS
OCCURRING. SOME UNCERTAINTY EXISTS AS TO WHETHER LENAWEE/MONROE
AND SOUTHERN WAYNE/WASHTENAW COUNTIES WILL SNEAK OUT OF THE
FOCUSED LIFT. RECENT NAM/RUC/LOCAL HIRES WRF GIVES DECENT
POTENTIAL FOR ANOTHER 6 HRS OF ACCUMULATING SNOWFALL ESPECIALLY
ACROSS THE NORTHERN PARTS OF THE COUNTIES.

THE EASTERN THUMB AND SHORELINE OF LAKE HURON HAS MISSED OUT ON A
BULK OF THE ACTION TO THIS POINT. NWP GUIDANCE SUGGESTS THE
GIGANTIC MIDLEVEL THETA E RIDGE AND STRONGEST DEFORMATION FORCING
WILL LIFT NORTHEASTWARD AND CENTER THERE OVERNIGHT.
THUS...EXPECTING THE MODERATE SNOW TO SETUP YET AND THEN LAG
ACROSS HURON/SANILAC/ST CLAIR COUNTIES INTO THE MORNING. HIRES
MODEL GUIDANCE IS POINTING ONCE AGAIN TO SOME LAKE ENHANCEMENT
TOMORROW MORNING FOR THE HURON SHORELINE DOWN INTO MACOMB COUNTY.
CONFIDENCE IN THIS DEVELOPING REMAINS LOW WITH A GLARING LACK OF
AGREEMENT IN THE DETERMINISTIC SOLUTIONS. WILL ALLOW FOR CONTINUED
OBSERVATION OF TRENDS OVERNIGHT AND WILL REFRAIN FROM ANY CHANGES
TO THOSE HEADLINES/AMOUNTS.

PREV DISCUSSION...ISSUED 401 PM EST TUE FEB 9 2010

SHORT TERM...THIS AFTERNOON AND TONIGHT

WINTER STORM WARNINGS AND WINTER WEATHER ADVISORIES REMAIN IN EFFECT
UNTIL WEDNESDAY MORNING. PLEASE SEE THE WINTER STORM WARNING/WINTER
WEATHER ADVISORY /WSWDTX/ FOR EXACT TIMES AND ACCUMULATIONS.

THE WINTER STORM IS UNDERWAY FOR SE MI. LIGHT SNOW HAS PERSISTED
SINCE THIS MORNING WITH AREAS OF LOCALLY HEAVIER SNOW MOVING THROUGH
AT TIMES. THIS HAS LEAD TO SNOWFALL TOTALS OF 3-4 INCHES NEAR THE
OHIO BORDER DECREASING NORTHWARD TO ABOUT 2 INCHES UP THROUGH
SAGINAW.

MODELS STILL HAVE A GOOD HANDLE ON THIS DEEPENING SURFACE LOW
CURRENTLY LOCATED OVER SOUTHWEST OHIO WITH ITS ASSOCIATED UPPER LOW
LAGGING SLIGHTLY TO THE WEST OVER SOUTHERN ILLINOIS. THIS UPPER LOW
IS FORECAST TO TRACK DUE EAST TOWARD THE ATLANTIC COAST BY WED
AFTERNOON WHICH PHASES IT WITH THE STRONG 180KT SOUTHERN BRANCH OF
THE JET STREAM. THIS CAUSES THE SURFACE LOW TO OCCLUDE AND WEAKEN
ON THE NORTH SIDE OVER THE GREAT LAKES AND RESTRENGTHEN TO THE
SOUTH NEAR THE MID-ATLANTIC STATES. THIS KEEPS THE BEST LARGE
SCALE ASCENT TO OUR SOUTH...BUT WE WILL STILL BE IN A REGION OF
MODERATE LIFT AND DECENT SNOWFALL INTENSITIES AS THE MID LEVEL
DEFORMATION BAND SETS UP AND PIVOTS OVER SE MI. LATEST MODELS
CONTINUE TO PLACE THIS FEATURE ACROSS THE I-69 CORRIDOR AROUND
00Z-06Z. ISENTROPIC ACCENT ALSO INCREASES OVER THE AREA AS THE
TROWEL AXIS LIFTS NORTH THIS AFTERNOON. THE GFS/NAM/ECMWF AND RUC
ALL AGREE WITH THE GENERAL STRENGTH AND LOCATION OF THIS STORM.
MODEL QPF CONTINUE TO RANGE FROM .4 IN THE SAGINAW VALLEY UP TO .7
NEAR THE OHIO BORDER. THIS IN CONJUNCTION WITH SNOW RATIOS BETWEEN
12:1 TO 15:1 KEEPS THE CURRENT FORECAST IN LINE WITH PREVIOUS
THINKING OF 5-9 INCHES IN THE WARNING AREA AND 3-6 IN THE NORTH
WHERE WE ARE UNDER A WINTER WEATHER ADVISORY.

NORTHEAST WINDS MAKE LAKE ENHANCEMENT A POSSIBILITY OVER THE
EASTERN THUMB REGION OVERNIGHT AND TOMORROW. NAM12 SHOWS A
CONVERGENT BAND SETTING UP AROUND 03Z. THE LOCATION OF THIS BAND
WILL MOST LIKELY RAISE SNOWFALL TOTALS IN THIS REGION WHICH HAD BEEN
TAKEN INTO ACCOUNT FOR STORM TOTALS. THESE WINDS WILL INCREASE...GUSTING
UP TOWARD 30KTS...AND BECOME MORE NORTHERLY OVERNIGHT. THIS WILL
CREATE PERIODS OF BLOWING SNOW AND MAY CAUSE DRIFTS TO FORM.

LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY

THE EXPIRATION TIMES LOOK GOOD ON THE CURRENT PACKAGE OF WINTER
HEADLINES. THEY WILL BE NEEDED INTO WEDNESDAY AS SNOW IS EXPECTED TO
LINGER THROUGH AT LEAST THE FIRST HALF OF THE MORNING AFTER SUNRISE,
AND EVEN LONGER IN THE THUMB WHERE LAKE EFFECT WILL REMAIN INVOLVED,
ALTHOUGH IT WILL BE MORE MODEST BY THEN COMPARED TO THE POTENTIAL
TONIGHT. THE LARGER SCALE PATTERN OF SNOW WILL ALSO BE ON THE
DECLINE, BUT WHAT IS LEFT WILL COMBINE WITH STRONG NORTH WINDS
AND BLOWING SNOW THAT WILL RESULT IN HAZARDOUS CONDITIONS DURING
THE MORNING HOURS AND INTO THE EARLY AFTERNOON IN THE THUMB
REGION.

MODEL DATA ON THE WEAKENING TROWAL/OCCLUSION FORCING LOOKS GOOD
DURING THE MORNING. IT SHOULD BE WELL UNDERWAY BY SUNRISE AND WILL
CONTINUE TO WEAKEN AND SHRINK TOWARD THE EAST AS THE UPPER LEVEL
CIRCULATION MOVES TOWARD THE ATLANTIC COAST. THIS WILL LEAVE A
GENERAL WEAK DEFORMATION PATTERN IN THE MID LEVELS THAT WILL HELP
SUPPORT LIGHT SNOW OR FLURRIES OVER THE REGION AS THE STORM SYSTEM
RUNS ITS COURSE. AS THIS OCCURS, THE NORTH WINDS ON THE HEELS OF THE
SYSTEM WILL BE STRONGLY ONSHORE INTO THE THUMB FROM LAKE HURON.
SURPRISINGLY, THE LAKE EFFECT POTENTIAL LOOKS LIMITED BY WARM AIR
MOVING IN FROM ONTARIO IN THE FORM OF SINGLE DIGIT 850 MB
TEMPERATURES. MODEL FORECAST SOUNDINGS SHOW COLDER AIR BELOW THAT,
CLOSER TO -13C CENTERED AROUND 900 MB, BUT THAT JUST INDICATES
EQUILIBRIUM LEVELS AROUND 3500 FEET DURING THE PEAK OF THE ONSHORE
FLOW. GIVEN THIS MODEST CONTRIBUTION, THE ADDITIONAL INCH OR TWO
LOOKS GOOD IN OUR GOING FORECAST FOR THE THUMB WITH AN ADDITIONAL
INCH OR LESS OVER THE REST OF SE MICHIGAN ON WEDNESDAY.

NOTHING MORE THAN A FLURRY IS THEN EXPECTED FROM THE MID LEVEL
MOISTURE LINGERING OVER THE AREA WEDNESDAY NIGHT. THIS CLOUD COVER
WILL DO MORE TO TAKE THE EDGE OFF OF THE NORTHWEST WINDS AND ANY
COLDER AIR CARRIED INTO THE REGION. LOW LEVEL TEMPERATURE FIELDS IN
THE MODEL DATA SHOW THIS NICELY AS A WARM SHADOW OF THE GREAT LAKES,
WHICH WILL BE REFLECTED AS A RELATIVELY NARROW 5 TO 10 DEGREE
DIURNAL TEMPERATURE RANGE RIGHT INTO THURSDAY. IT DOES LOOK LIKE
THE CLOUDS WILL START TO BREAK UP DURING THURSDAY AFTERNOON DUE TO
WEAKLY CONFLUENT FLOW ALOFT AND WEAK NORTHWEST FLOW IN THE LOW
LEVELS BUT CONFIDENCE IS NOT THAT GREAT UNTIL THURSDAY NIGHT INTO
FRIDAY WHEN A SHORT WAVE RIDGE ALOFT AND SURFACE HIGH PRESSURE
TAKE GREATER CONTROL. AT LEAST IT WILL BE DRY THROUGH THE END OF
THE WEEK.

A WAVE FROM CENTRAL CANADA IS THEN EXPECTED TO SET OFF A NEW ROUND
OF LARGER SCALE HEIGHT FALLS OVER THE GREAT LAKES ON FRIDAY INTO
SATURDAY. IT IS NO SURPRISE THAT THE LATEST GLOBAL MODELS HAVE A
WIDE VARIETY OF OPINIONS ON THE SMALL SCALE DETAILS DURING THIS
TIME, MAINLY ON THE LEAD WAVE. THEY ARE IN CLOSER AGREEMENT ON THE
PRESENCE OF THE COMPACT CLOSED CIRCULATION MOVING INTO THE GREAT
LAKES AROUND SATURDAY, BUT THERE IS ENOUGH SPREAD IN THE TIMING OF
THIS SYSTEM TO DO LIKEWISE WITH THE CHANCE OF SNOW DURING THE
WEEKEND. IF IT IS NOT FOR THIS WAVE, IT WILL BE FOR THE PRESENCE OF
THE LARGE SCALE UPPER LOW/TROUGH OVER THE GREAT LAKES. DEEP
NORTHWEST FLOW IN THE LOW LEVELS ASSOCIATED WITH THIS PATTERN WILL
KEEP TEMPERATURES ON THE COLD SIDE OF NORMAL INTO EARLY NEXT WEEK.

MARINE...

DEEPENING LOW PRESSURE WILL TRACK ACROSS OHIO THIS EVENING AND INTO
LAKE ERIE OVERNIGHT. THIS WILL STRENGTHEN THE NORTHEASTERLY
GRADIENT OVER LAKE HURON...LEADING TO FREQUENT GUSTS UP TO 35 KNOT
GALES. THESE WINDS WILL CONTINUE INTO WEDNESDAY AFTERNOON BEFORE
HIGH PRESSURE BUILDS IN FROM THE WEST AND RELAXES THE GRADIENT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING...MIZ055-MIZ062-MIZ063...UNTIL 1 PM WEDNESDAY.

     WINTER STORM WARNING...MIZ053-MIZ054-MIZ060-MIZ061-MIZ068-MIZ069-
     MIZ070-MIZ075-MIZ076-MIZ082-MIZ083...UNTIL 10 AM WEDNESDAY.

     WINTER WEATHER ADVISORY...MIZ047-MIZ048...UNTIL 7 AM WEDNESDAY.

     WINTER WEATHER ADVISORY...MIZ049...UNTIL 1 PM WEDNESDAY.

LAKE HURON...
     GALE WARNING...LHZ362-LHZ363-LHZ421-LHZ422-LHZ441-LHZ442-LHZ443-
     LHZ462-LHZ463-LHZ464...UNTIL 7 PM WEDNESDAY.

LAKE ST CLAIR...
     BRISK WIND ADVISORY...UNTIL 4 PM WEDNESDAY.

MI WATERS OF LAKE ERIE...
     BRISK WIND ADVISORY...UNTIL 4 PM WEDNESDAY.

&&

$$

AVIATION.....SC/MR
UPDATE.......CB
SHORT TERM...DRK
LONG TERM....BT
MARINE.......DRK/SC

YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).