FXUS63 KDTX 070239
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
939 PM EST SUN DEC 6 2009
.UPDATE...
LIGHT SNOW SHOWERS AND FLURRIES HAVE BEEN ONGOING ALONG A STALLED
FRONTAL BOUNDARY OVER CENTRAL MICHIGAN. LOW LEVEL LIFT SHOULD
SUSTAIN THIS THROUGH THE NIGHT. UPPER JET SUPPORT WILL STRENGTHEN THE
LOW LEVEL FORCING IN ADVANCE OF A MID LEVEL SHORT WAVE /NOW OVER
EASTERN KANSAS/. THIS WILL ENHANCE THE COVERAGE OF SNOW SHOWERS
ACROSS THE SAGINAW VALLEY AND THUMB TOWARD MORNING. THE STRONGEST
LIFT AND BEST CHANCE FOR LIGHT ACCUMULATIONS WILL HOWEVER REMAIN
JUST NORTH OF THE FORECAST AREA. FARTHER SOUTH...LOW LEVEL DRY AIR
AND LACK OF LIFT THROUGH 12Z WILL KEEP CONDITIONS RELATIVELY
PRECIP FREE. GIVEN THE CLOUD COVER AND CURRENT TEMPS IN THE
SAGINAW VALLEY/THUMB... INCREASED OVERNIGHT MINS A FEW DEGREES.
OTHERWISE...NO OTHER MAJOR CHANGES WERE MADE TO THE FORECAST.
&&
.PREV DISCUSSION...ISSUED 601 PM EST SUN DEC 6 2009
AVIATION...
A SURFACE FRONT LOCATED JUST NORTH OF MBS WILL REMAIN NEARLY
STATIONARY THROUGH THE NIGHT. THE BULK OF THE SNOW SHOWER ACTIVITY
AND MVFR CEILINGS HAVE SHIFTED JUST NORTH OF MBS. THE 18Z MODEL
SUITE INDICATE THESE LOWER CEILINGS REMAINING TO THE NORTH OF MBS
THROUGH THE NIGHT AND MORNING ON MON. MEANWHILE...MUCH DRIER LOW
LEVEL AIR TO THE SOUTH OF THIS BOUNDARY WILL KEEP THE REST OF THE
TAF SITES VFR THROUGH MON MORNING. A SHORT WAVE TROUGH WILL THEN
LIFT ACROSS SOUTHERN MICHIGAN ON MONDAY...BRINGING SOME LOWER
CEILINGS TO THE AREA BY AFTERNOON ALONG WITH OCCASIONAL LIGHT SNOW
SHOWERS OR FLURRIES.
PREV DISCUSSION...ISSUED 343 PM EST SUN DEC 6 2009
SHORT TERM...TONIGHT AND TOMORROW
STRONG UPPER LEVEL SHEAR AXIS ACROSS THE GREAT LAKES REGION WITH
WEAK FRONTAL BOUNDARY STRUNG ACROSS NORTHERN LOWER MICHIGAN.
PREDOMINATELY WESTERLY UPPER LEVEL CONFLUENT FLOW THIS AFTERNOON
WITH GIVE WAY TO RISING HEIGHTS/WEAK SHORTWAVE RIDGING THIS
EVENING...THUS WEAK FRONTAL BOUNDARY WILL WEAKEN FURTHER...WITH
MODEST 850 MB FGEN REMAINING ALONG AND JUST NORTH OF SAGINAW BAY.
THE LOW LEVEL CONVERGENCE ZONE WILL HANG OUT AROUND THE TRI-CITIES
REGION...WORTHY OF MAINTAINING SOME LIGHT SNOW MENTION.
ATTENTION THEN TURNS TO THE SHEARING OUT ENERGY COMING OUT OF THE
EASTERN ROCKIES...WHICH WILL LIFT THROUGH THE SOUTHERN GREAT LAKES
TOMORROW. WILL NEED TO RELAY ON ISENTROPIC ASCENT AND TEPID MOISTURE
ADVECTION FOR MOST OF THE CWA. MUCH OF THE LIFT LATE TONIGHT INTO
TOMORROW MORNING WILL BE USED UP TO SATURATE THE LOW LEVELS (SFC-850
MB)...LEADING TO SOME COOLING AT 850 MB...AS TEMPS FALL BACK TO -9 C
TO PERHAPS AROUND -10 C (PER GFS). THUS...THINK WE ARE LOOKING AT
MAINLY FLURRIES/SCATTERED LIGHT SNOW SHOWERS FOR MOST OF THE CWA.
THE EXCEPTION BEING UP ACROSS THE FAR NORTH (MIDLAND/BAY/HURON)...AS
THE STALLED FRONTAL BOUNDARY/LOW LEVEL CONVERGENCE ZONE PROVIDES A
BETTER FOCUS. SUSPECT WE WILL GRIND OUT ABOUT AN INCH OVER THE TWO
PERIODS. LATEST MAV TEMPERATURE GUIDANCE...WHICH MATCH INHERITED
FORECAST LOOK OK...AND NO ADJUSTMENTS MADE.
LONG TERM...MONDAY NIGHT THROUGH SUNDAY
BIG CONCERN IN THE EXTENDED FORECAST REMAINS STRONG WINTER STORM THAT
WILL LIFT INTO/OVER THE AREA TUESDAY NIGHT THROUGH WEDNESDAY. WHILE
SOME MODEL VARIABILITY REMAINS...CONSENSUS IS HONING IN ON A TRACK
OF THE SURFACE LOW RIGHT ACROSS THE CWA ON WEDNESDAY...AND WILL KEEP
THE FORECAST SHAPED TO AGREE WITH THIS SCENARIO. THIS MAKES FOR A
DIFFICULT FORECAST AS SNOW CHANGES TO RAIN OVER THE SOUTHEAST 1/2 TO
3/4 OF THE CWA LATE TUESDAY NIGHT INTO WEDNESDAY...COMPLICATING SNOW
ACCUMULATIONS FOR A GOOD PORTION OF THE AREA. IN FACT...GIVEN THIS
FORECAST TRACK...ONLY THE SAGINAW VALLEY WOULD REMAIN PRIMARILY SNOW
THROUGHOUT THE EVENT TUESDAY NIGHT/WEDNESDAY.
THE INITIAL PORTION OF THIS STORM...AS WAS NOTED YESTERDAY...WILL BE
A HEALTHY SLUG OF GULF MOISTURE SURGING NORTH INTO THE AREA JUST IN
ADVANCE OF THE MAIN STORM SYSTEM AS A WAVE WITHIN THE SUBTROPICAL
JET OVER MEXICO/GULF OF MEXICO IS ENVELOPED BY THE MAIN PACIFIC WAVE
LIFTING OF OF THE SOUTHWEST CONUS MEAN UPPER TROUGH. THIS WILL FALL
PRIMARILY AS SNOW LATE TUESDAY EVENING TO AROUND DAYBREAK WEDNESDAY
BEFORE THE TRANSITION TO RAIN OR A MIX OF RAIN/SNOW RAPIDLY EVOLVES
WEDNESDAY MORNING AS MILD AIR WRAPS INTO THE AREA ALONG/SOUTHEAST OF
THE SURFACE LOW TRACK. GIVEN THE MOISTURE INVOLVED...THIS WILL LEAD
TO 2 TO 4 INCHES OF SNOW OVER MUCH OF THE AREA WITH LIGHTER AMOUNTS
MORE IN THE 1 TO 2 INCH RANGE FROM DETROIT SOUTH WHERE RAIN WILL MIX
IN EARLIER AND ALSO OVER THE THUMB WHERE THE BEST SURGE OF MOISTURE
HOLDS OFF UNTIL DAYBREAK AND BEYOND.
ON WEDNESDAY...THE CENTER OF THE STORM SYSTEM WILL TRACK OVER THE
AREA...WITH SNOW CHANGING TO PRIMARILY RAIN FROM THE OHIO BORDER
INTO THE THUMB...BUT REMAINING LARGELY SNOW OVER THE FAR NORTHWEST
CWA. HENCE...ADDITIONAL SNOWFALL AMOUNTS WILL VARY FROM NIL SOUTH OF
M 59 TO A FEW MORE INCHES OVER THE THUMB BEFORE A CHANGEOVER TO
PERHAPS 3 OR 4 MORE INCHES NORTHWEST INTO THE SAGINAW VALLEY WHERE
TOTALS COULD CLIMB TO 8 OR SO INCHES IF LITTLE OR NO RAIN MIXES IN.
GIVEN THE DYNAMIC COOLING THAT WILL BE ASSOCIATED WITH SUCH STRONG
INTENSIFICATION OF THE SYSTEM AS IT PASSES OVER THE AREA...ACTUALLY
FEEL RATHER CONFIDENT ABOUT THIS QUADRANT OF THE SYSTEM REMAINING
PRETTY MUCH ALL SNOW.
BY LATE WEDNESDAY AFTERNOON/EVENING...COLDER AIR WILL RUSH BACK
ACROSS THE WHOLE CWA AS THE SURFACE LOW CONTINUES NORTH/NORTHEAST
INTO NORTHERN LOWER MICHIGAN/LAKE HURON. SO...WHILE THE HEAVIEST
PRECIPITATION WILL BE SHIFTING NORTH OF THE AREA...PERIODS OF SNOW
WILL CONTINUE AS A TRAILING TROUGH HELPS TO ENHANCE THE QUICKLY
DEVELOPING LAKE EFFECT/ENHANCED ACTIVITY THAT DEVELOPS IN COLD
WESTERLY FLOW IN THE WAKE OF THE SYSTEM. THIS WESTERLY FLOW WILL
BE VERY GUSTY AS WELL AS THE SURFACE LOW CONTINUES TO INTENSIFY
OVERNIGHT AS IT MOVES NORTH OF LAKE HURON.
THE COLD AIR THAT IS USHERED INTO THE AREA BEHIND THIS STORM WILL
PRETTY MUCH REMAIN IN PLACE THROUGH THE REST OF THE FORECAST ONLY
MODERATING SLIGHTLY DURING THE UPCOMING WEEKEND.
MARINE...
WINDS WILL BE ON A DOWNWARD TREND AS WE HEAD INTO TOMORROW AS A
RIDGE OF HIGH PRESSURE BUILDS INTO THE GREAT LAKES REGION.
THE LIGHT WINDS WILL BE SHORT LIVED HOWEVER...AS A VERY STRONG LOW
PRESSURE SYSTEM TRACKS THROUGH THE CENTRAL GREAT LAKES ON WEDNESDAY.
BOTH EASTERLY GALES AHEAD OF THE SYSTEM...AND WESTERLY GALES BEHIND
THE SYSTEM APPEAR LIKELY ON THURSDAY...AS THE LOW DEEPENS TO 980 MB
OR POSSIBLY LOWER. THE WINDS WILL BE SLOW TO DECREASE AS WE HEAD
INTO FRIDAY...AS THE ARCTIC AIRMASS SPILLING OVER THE WARMER WATERS
LEAD TO VERY UNSTABLE LOW LEVEL PROFILE...LEADING TO INCREASED WAVE
GROWTH IN EXCESS 10 FEET.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
UPDATE.......SC
AVIATION.....SC
SHORT TERM...SF
LONG TERM....DG
MARINE.......SF
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
