FXUS63 KDTX 100502
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1202 AM EST THU DEC 10 2009

.AVIATION...

WIND GUSTS WILL REMAIN MODESTLY LOWER COMPARED TO YESTERDAY, LEAVING 
LAKE EFFECT SNOW SHOWERS AS THE MAIN IMPACT ON AVIATION OPERATIONS, 
AND THAT WILL BE FOCUSED MOSTLY IN THE DETROIT TO PONTIAC AREA. 
TRENDS IN THE LATEST OBSERVATIONS MATCH MODEL SIMULATIONS ADEQUATELY 
TO GIVE US AN IDEA OF THE MAIN BANDS FOCUSING IN THE VICINITY OF THE 
INTERSTATE 96 CORRIDOR. THERE WILL BE SNOW SHOWERS AT OTHER
LOCATIONS BUT JUST NOT WITH THE SAME FREQUENCY OR DURATION OF
IFR/LIFR CEILING AND VISIBILITY. THERE WILL BE A BETTER
OPPORTUNITY FOR SNOW SHOWERS IN THE FLINT TO SAGINAW AREA AFTER
SUNRISE AS THE LOW LEVEL WINDS BACK TOWARD THE SOUTHWEST BUT
INLAND PENETRATION OF THE SNOW SHOWERS WILL ALSO BECOME MORE
LIMITED AND DISRUPTED BY DIURNAL BOUNDARY LAYER FORCING. OVERALL,
THERE WILL BE TREND TOWARD VFR CONDITIONS DURING THE AFTERNOON AND
INTO TONIGHT BUT WITH A RENEWED GUSTINESS TO THE WINDS.

&&

.PREV DISCUSSION...ISSUED 1113 PM EST WED DEC 9 2009 

UPDATE...

WITH WIND GUSTS BELOW HEADLINE CRITERIA, LAKE EFFECT SNOW IS NOW
THE FOCUS OF THE FORECAST OVERNIGHT THROUGH THURSDAY MORNING.
EARLIER UPDATE EXPANDED THE WINTER WEATHER ADVISORY EASTWARD
THROUGH WAYNE, OAKLAND, AND MACOMB COUNTIES TO HEIGHTEN AWARENESS
OF EXPECTED IMPACTS ON OVERNIGHT DRIVING CONDITIONS AND THE MORNING
COMMUTE. WHAT HAS OCCURRED SO FAR HAS MEANT BUSINESS IN TERMS OF
SNOWFALL INTENSITY AND IT WILL CONTINUE ORGANIZING DURING THE
EARLY MORNING HOURS. PROJECTED ACCUMULATIONS IN THE ADVISORY AREA
ARE EXPECTED TO OCCUR MAINLY IN THE 6 HOUR PERIOD BETWEEN MIDNIGHT
AND 6 AM WITH A DIMINISHING TREND AFTER THAT. UNTIL THEN, EXPECT
CONVERGENT BANDING TO CONTINUE ORGANIZING OFF THE SOUTH END OF
LAKE MICHIGAN WITH CONVECTIVE DEPTH EASILY ADEQUATE FOR SURVIVING
THE TRIP INTO OUR AREA. SO FAR, THE LOW LEVEL WIND FIELD IS
CONSIDERABLY MORE CONVERGENT THAT INDICATED BY THE NAM12 AND THE
PATTERN WILL TEND NOT TO MOVE TOO MUCH OFF THE VICINITY OF THE
INTERSTATE 96 CORRIDOR. THE PERSISTENCE OF THE WIND FIELD AND
LONGER DURATION WILL FAVOR THE 2 TO 4 INCH ACCUMULATION EVEN IF
CONVECTIVE DEPTH DIES OFF TOWARD SUNRISE AS SUGGESTED IN THE
MODELS.

PREV DISCUSSION...ISSUED 352 PM EST WED DEC 9 2009 

SHORT TERM...TONIGHT

INTENSE LOW PRESSURE SYSTEM NOW DOWN TO 975 MB AS IT RAPIDLY LIFTS 
NORTHEAST ACROSS NORTHERN LOWER MI THIS AFTERNOON.  COLDER AIR 
WRAPPING BACK AROUND THIS SYSTEM NOW BEGINNING TO INFILTRATE THE 
REGION.  THIS COMBINED WITH WEAK SHORTWAVE ENERGY EMBEDDED WITHIN 
THE EDGE OF THE DEVELOPING CYCLONIC FLOW MAINTAINING SCATTERED/ 
NUMEROUS SHOWERS ACROSS THE AREA.  RAPID COOLING THERMAL PROFILE 
RESULTING IN A SHIFT FROM A RA/SN MIX TO SNOW SHOWERS AT THIS TIME. 

TIGHTENING PRESSURE GRADIENT COMBINED WITH THE STRENGTHENING COLD 
AIR ADVECTION/ISENTROPIC DESCENT WILL MAINTAIN A STRONG WIND FIELD 
THROUGH TONIGHT.  AREA OBSERVATIONS SHOWING HIGHEST GUSTS NOW 
PEAKING OUT IN THE 45-55 MPH RANGE.  THEREFORE CURRENT WIND 
HEADLINES REMAIN ON TARGET AND LEAVE AS IS FOR THIS EVENING.

FOCUS TONIGHT TURNS TOWARD THE DEVELOPMENT AND EASTWARD PENETRATION 
OF LAKE EFFECT SNOW.  A PRONOUNCED INCREASE IN OVERLAKE INSTABILITY 
WILL COMMENCE OVER LAKE MICHIGAN INTO THIS EVENING AS 850 MB 
TEMPERATURES DROP BELOW -10C AND EQUILIBRIUM LEVELS CLIMB UPWARDS 
OF 8-10K FT.  THE IMPRESSIVE THERMODYNAMIC STRUCTURE WORKING IN 
CONJUNCTION WITH THE PASSAGE OF THE SYNOPTIC COLD FRONT...STRONG 
WESTERLY FLOW AND INCREASING LOW LEVEL CONVERGENCE WILL ENSURE 
NUMEROUS SNOW SHOWERS STREAM ACROSS THE STATE THROUGH THE NIGHT.  
FAVORED AREAS FOR SEEING MORE SUSTAINED AND HEAVIER SNOWBANDS/
SQUALLS WILL BE WITHIN THE M-59 AND I-94 CORRIDORS.  THIS WILL 
TRANSLATE INTO 1-3 INCH ACCUMULATIONS...WITH THE HIGHEST AMOUNTS 
TARGETING WASHTENAW/LIVINGSTON COUNTIES.  GIVEN THE POTENTIAL FOR 
THIS TO ARRIVE AS A SHORT DURATION/HIGH INTENSITY WIND DRIVEN BURST 
OF SNOW...WILL GO AHEAD AND ISSUE AN ADVISORY FOR WASHTENAW AND 
LIVINGSTON COUNTIES.  

STRONG COLD AIR ADVECTION WILL RESULT IN LOWS REACHING THE UPPER 
TEENS/LOWER 20S...WHILE WIND CHILL READINGS DROP WELL INTO THE 
SINGLE DIGITS BY THIS TIME.

LONG TERM...THURSDAY THROUGH WEDNESDAY

MAIN LAKE EFFECT SNOW BAND WILL BE DISSIPATING TOMORROW MORNING AS 
LOW LEVEL WINDS BACK TO A SLIGHTLY MORE SOUTHWESTERLY FETCH AND 
CONVERGENCE WEAKENS. A FEW LAKE EFFECT SNOW SHOWERS WILL STILL BE 
POSSIBLE TOMORROW AND FRIDAY THOUGH AS 850 MB TEMPS DROP TO NEAR 
-20C. MAIN LIMITING FACTOR WILL BE THE FACT THAT THE CONVECTIVE 
DEPTH WILL BECOME MORE SHALLOW. BEST LOCATIONS WILL BE ALONG THE M59 
CORRIDOR WITH A WEST-SOUTHWEST FETCH OFF OF THE WIDEST PART OF LAKE 
MICHIGAN. OTHER MAIN STORY WILL BE THE COLD TEMPERATURES AND STRONG 
WINDS. PRESSURE GRADIENT BEHIND EXITING SURFACE LOW WILL REMAIN 
STRONG AS 1030 MB HIGH BUILDS TO THE SOUTHWEST. MIXING UP TO 850 MB 
WILL ALSO ALLOW FOR STRONG GUSTS APPROACHING 40 MPH ON THURSDAY AND 
30 MPH ON FRIDAY. THIS COMBINED WITH HIGH TEMPS IN THE LOW 20S WILL 
PRODUCE WIND CHILLS AROUND 0.  

QUIET WEATHER IS EXPECTED OVER THE WEEKEND AS SURFACE RIDGE CROSSES 
THE AREA ON SATURDAY AND WINDS SHIFT TO A MORE SOUTHERLY 
DIRECTION...CUTTING OFF THE LAKE EFFECT SNOW. WAA WILL RAISE 925 MB 
TEMPS TO NEAR 0C BY SUNDAY AND EXPECT MAX TEMPS TO RISE ABOUT 5 
DEGREES HIGHER EACH DAY THIS WEEKEND. 12Z GFS TRIES TO DEVELOP 
PRECIP ON SUNDAY WITH SOME DECENT ISENTROPIC LIFT BUT HAS BEEN VERY 
INCONSISTENT WITH THE TIMING AND TRACK OF THIS FEATURE SO LEANED 
MORE TOWARD THE ECMWF WITH LOW POPS. FORECAST CONFIDENCE DROPS NEXT 
WEEK AS ANOTHER SOUTHERN STREAM SYSTEM WILL MOVE OUT OF THE 
SOUTHWEST CONUS ON MONDAY AND INTO OUR REGION. ONCE 
AGAIN...SIGNIFICANT DIFFERENCES IN TRACK EXIST BETWEEN THE MODELS. 
THE GFS BRINGS THE DEEP UPPER LOW ACROSS THE US/CANADIAN BORDER 
WHILE THE ECMWF KEEPS IT FURTHER NORTH. AS A RESULT...THE ECMWF 
BRINGS THE SURFACE LOW FURTHER NORTH ACROSS LOWER MICHIGAN. 
NEVERTHELESS...UPPER LEVEL DYNAMICS WILL BE MUCH WEAKER WITH THIS 
SYSTEM. PRECIP TYPE COULD BE PROBLEMATIC AS GFS BUFKIT SOUNDINGS 
SUGGEST A BRIEF CHANGEOVER TO RAIN ON MONDAY. GIVEN UNCERTAINTY ON 
TRACK...WILL NOT MAKE MAJOR CHANGES TO THE FORECAST.

MARINE...

INTENSE LOW PRESSURE SYSTEM WILL RAPIDLY LIFT NORTHEAST AND ACROSS  
NORTHERN LAKE HURON THIS EVENING.  STRONG WESTERLY WINDS WILL 
CONTINUE IN THE WAKE OF THIS SYSTEM AIDED BY AMPLE INSTABILITY 
GENERATED BY MUCH COLDER AIR MOVING ACROSS THE MARINE AREAS.  THIS 
WILL ENSURE GUSTS APPROACH STORM FORCE OVER THE SOUTHERN HALF OF 
LAKE HURON AND ACROSS WESTERN LAKE ERIE INTO TONIGHT...WITH GALE 
FORCE WINDS ELSEWHERE.    

GALES WILL CONTINUE THURSDAY AND FRIDAY AS ARCTIC AIR SETTLES ACROSS 
THE GREAT LAKES WHILE THE PRESSURE GRADIENT REMAINS STRONG AND 
MIXING INCREASES.  THE GRADIENT WILL BEGIN TO RELAX NEXT WEEKEND AS 
A RIDGE OF HIGH PRESSURE BUILDS INTO THE REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...WINTER WEATHER ADVISORY...MIZ068-MIZ069-MIZ070-MIZ075-
     MIZ076...UNTIL 10 AM THURSDAY.

LAKE HURON...
     GALE WARNING...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...UNTIL 10 
     PM FRIDAY.

     GALE WARNING...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON 
     INCLUDING SAGINAW BAY...UNTIL 4 AM FRIDAY.

LAKE ST CLAIR...
     GALE WARNING...UNTIL 4 AM FRIDAY.

MI WATERS OF LAKE ERIE...
     GALE WARNING...UNTIL 4 AM FRIDAY.

     LOW WATER ADVISORY...UNTIL 10 PM THURSDAY.

&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...MR
LONG TERM....AGD
MARINE.......MR

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