FXUS63 KDTX 040445
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1145 PM EST THU DEC 3 2009
.AVIATION...
THE HEAVIEST SNOW SHOWER ACTIVITY WILL LIFT FROM THE FLINT AREA UP
INTO SAGINAW DURING THE MORNING AS THE LOW LEVEL FLOW BACKS MORE TO
THE SOUTHWEST. OCCASIONAL IFR CONDITIONS WILL CONTINUE WITHIN THE
HEAVIEST SNOW SHOWERS. PERSISTENT SOUTHWEST FLOW AND OVER LAKE
INSTABILITY WILL MAINTAIN PERIODIC MVFR CEILINGS AND SNOW
SHOWERS/FLURRIES THROUGH MUCH OF THE AFTERNOON AT FNT AND MBS.
MEANWHILE...A LITTLE DRIER AIR ADVECTING INTO THE DETROIT AREA WILL
KEEP VFR CONDITIONS AT DTW AND DET THROUGH THE MORNING. ONSET OF
DAYTIME HEATING WILL LIKELY SUSTAIN A PERSISTENT STRATO CU FIELD
BASED BETWEEN 4K AND 5K FEET DURING THE AFTERNOON.
&&
.PREV DISCUSSION...ISSUED 955 PM EST THU DEC 3 2009
UPDATE...
SNOW SHOWERS HAVE BEEN ADVANCING ACROSS SOUTHERN MICHIGAN OVER
THE LAST COUPLE OF HOURS /MAINLY ALONG THE M 59 AND I 69
CORRIDORS/. REGIONAL RADARS SHOW VERY INTENSE LAKE EFFECT SNOW
SHOWERS JUST WEST OF GRAND RAPIDS. LAKE EFFECT WILL PERSIST THROUGH
THE NIGHT...AIDED WITH SOME ENHANCEMENT FROM A MID LEVEL SHORT
WAVE ADVANCING INTO CENTRAL LAKE MICHIGAN. DESPITE THE HIGH
RETURNS ON THE WEST SIDE OF THE STATE...THERE HAS BEEN A LACK OF
ORGANIZED BANDING INTO SE MI. RETURNS ON THE DTX RADAR ACTUALLY
INDICATE SOME MESO SCALE VORTICIES WHICH MAY BE DISRUPTING THE
ABILITY TO ORGANIZE INTO A DOMINATE BAND. NONETHELESS...THE LAKE
EFFECT ACTIVITY WILL PERSIST THROUGH THE NIGHT...WITH BACKING FLOW
ASSOCIATED WITH THE SHORT WAVE EXPECTED TO LIFT THE HIGHER
CONCENTRATION OF SNOW SHOWERS INTO THE TRI CITIES TOWARD MORNING.
GIVEN THE POSSIBILITY THAT A MORE PERSISTENT BAND OF SNOW MAY YET
DEVELOP TONIGHT /AND CONSIDERING THE DEGREE OF LOW LEVEL
INSTABILITY/ HAVE KEPT ACCUMULATIONS ALONG THE SAME LINES AS THE
PREVIOUS FORECAST /LESS THAN AN INCH ACROSS THE FAR NORTHERN
DETROIT SUBURBS TO 1 TO 3 INCHES IN THE FLINT AND TRI CITIES
REGION/. THE FORECAST WAS UPDATED MAINLY TO ADJUST FOR TIMING AND
AREAL COVERAGE BASED ON THE LATEST RADAR TRENDS.
PREV DISCUSSION...ISSUED 406 PM EST THU DEC 3 2009
SHORT TERM...TONIGHT
COLD AIR IS CONTINUING TO FUNNEL SOUTHWARD THIS AFTERNOON BEHIND THE
EXITING SURFACE LOW WITH 850 MB TEMPS DROPPING TO -9C BY LATER
TONIGHT. MAIN FORECAST CONCERN OVERNIGHT WILL BE TIMING THE ONSET OF
OF LAKE EFFECT SNOW OFF LAKE MICHIGAN. INSTABILITY WILL BE ABUNDANT
WITH DELTA T'S IN THE UPPER TEENS TO NEAR 20 PRODUCING CAPE VALUES
OF AROUND 700 J/KG. THIS COMBINED WITH A SHORTWAVE TROUGH THAT IS
EXPECTED TO MOVE INTO THE REGION WILL SET THE STAGE FOR A FEW
ORGANIZED SNOW BANDS TO FORM AND DRIFT EASTWARD INTO THE AREA. NAM12
SHOWS THE BEST SURFACE CONVERGENCE AND LOW LEVEL OMEGA WILL NOT MAKE
IT INTO OUR CWA UNTIL 06Z-09Z. A FEW DISORGANIZED SHOWERS ARE ALREADY
BEGINNING TO MOVE INTO THE SOUTHERN CWA AND THIS IS EXPECTED TO
CONTINUE THROUGH THE EARLY EVENING BUT...WITH SURFACE DEWPOINT
DEPRESSIONS AROUND 7C...ANY ACCUMULATIONS WILL BE VERY LIGHT AND
SCATTERED UNTIL THE MAIN BAND MOVES INTO THE AREA LATE TONIGHT.
LONG TERM...LATE TONIGHT THROUGH THURSDAY
A LONGWAVE TROUGH WILL REMAIN IN PLACE ACROSS NORTH AMERICA THROUGH
THE LONG TERM KEEPING A COOL AIRMASS OVER SOUTHEAST MICHIGAN WITH
SEVERAL OPPORTUNITIES FOR SNOW SHOWERS. SHORTWAVE ENERGY ROTATING
AROUND THE CLOSED UPPER LOW OVER ONTARIO WILL ENHANCE LAKE EFFECT
SNOW OFF OF LAKE MICHIGAN INTO THIS WEEKEND. ENERGETIC LAKE EFFECT
SNOW SHOWERS WILL BE UNDERWAY FROM LATE TONIGHT INTO FRIDAY WITH THE
TRAJECTORY SETTING UP GENERALLY NORTH OF I-69 BY MORNING. MODELS
INDICATE A SLUG OF DEEP MOISTURE ASSOCIATED WITH THE MID-LEVEL FRONT
WITH 850MB TEMPERATURES CONTINUING TO FALL TO AT LEAST -12C
THROUGHOUT THE DAY. NAM12 SHOWS A WELL DEFINED SURFACE TROUGH ALONG
THE LAKE MICHIGAN SHORELINE...WEAKENING AS IT LIFTS UP TOWARDS THE
THUMB THROUGH THE AFTERNOON. WE DO EXPECT SOME HIGH INTENSITY SNOW
SHOWERS ALONG AND AHEAD OF THIS FEATURE DURING THE MORNING WITH
SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR POSSIBLE OVER A SMALL AREA
AND SHORT DURATION. FORTUNATELY THE HIGH INTENSITY SNOW SHOWERS WILL
BE TRANSIENT WITH TOTALS OF GENERALLY 1-3 INCHES EXPECTED ALTHOUGH A
FEW REPORTS UP TO 4 INCHES REMAIN POSSIBLE IF THE BAND BECOMES MORE
STATIONARY. SNOW SHOWERS WILL BE MORE SCATTERED TOWARDS DETROIT WITH
ACCUMULATIONS TAPERING OFF TO JUST TRACE AMOUNTS. WE HAVE HELD OFF
ON ANY LAKE EFFECTS SNOW ADVISORIES BUT THIS IS EXPECTED TO BE THE
FIRST ACCUMULATING SNOW OF THE SEASON MAKING THE MORNING COMMUTE
SLICK TOWARDS FNT/MBS. THE EVENING SHIFT WILL KEEP A CLOSE EYE ON
HOW LAKE EFFECT SNOW EVOLVES AND THE NEED TO ISSUE AN ADVISORY
LATER THIS EVENING.
MESOSCALE FEATURES WILL CONTINUE TO IMPACT SNOW POTENTIAL THROUGH
FRIDAY NIGHT AND SATURDAY AS SURFACE TROUGHS MOVING THROUGH THE
BROADER LOW LEVEL CYCLONIC FLOW WILL PROVIDE AN OCCASIONAL FOCUS FOR
SHOWERS. THE FLOW BACKS THROUGH THE COLUMN IN RESPONSE TO THE NEXT
SHORTWAVE PUSHING SOUTH INTO MINNESOTA AND WISCONSIN WITH SNOW
SHOWERS LARGELY BECOMING CONFINED TO WESTERN LOWER AND POSSIBLY THE
SAGINAW VALLEY. HIGH PRESSURE BUILDING NORTH INTO SOUTHEAST MICHIGAN
ON SATURDAY SHOULD ONLY ACT TO STRENGTHEN THE TROUGH DOWNWIND OF
LAKE MICHIGAN AND LIMIT THE INLAND EXTENT OF THE SNOW SHOWERS. HAVE
RAISED POPS SLIGHTLY ACROSS THE SAGINAW VALLEY BUT WILL KEEP WORDING
AT JUST SCATTERED WHILE LOWERING CHANCES OF SNOW ACROSS THE
SOUTHEASTERN COUNTIES.
THE COLDEST TEMPERATURES OF THE SEASON WILL BE ARRIVING OVER THE
WEEKEND WITH HIGHS ONLY REACHING THE LOW 30S ON FRIDAY
AND SATURDAY. WE WILL HAVE TO KEEP AN EYE ON MINS FOR SATURDAY NIGHT
AS HIGH PRESSURE STARTS TO BUILD UP FROM THE SOUTH AND MINS MAY HAVE
A GOOD OPPORTUNITY TO DROP RAPIDLY IF WINDS GO CALM AND SKIES CLEAR
OUT.
UNCERTAINTY INCREASES IN THE FORECAST INTO NEXT WEEK AS MODELS
STRUGGLE WITH HOW TO HANDLE TWO DISTINCT WAVES DROPPING SOUTH ACROSS
THE WESTERN UNITED STATES OVER THE WEEKEND. MODELS ARE GENERALLY IN
AGREEMENT THAT THE FIRST SHORTWAVE WILL APPROACH THE OHIO
VALLEY/GREAT LAKES REGION ON A WEST TO SOUTHWEST FLOW ON MONDAY WITH
THE WHOLE UPPER LEVEL TROUGH SWINGING TOWARDS THE REGION BY
WEDNESDAY. CHANCES OF SNOW ARE IN THE FORECAST FOR BOTH SYSTEMS
WITH ACCUMULATIONS POSSIBLE. ENOUGH UNCERTAINTY IS PRESENT IN
DETAILS...INCLUDING THERMAL PROFILES AND STORM TRACKS TO SPECULATE
ON HOW MUCH ACCUMULATIONS WILL BE AT THIS TIME. MODELS SHOW THE
RAIN/SNOW LINE FLIRTING WITH SOUTHEAST MICHIGAN BUT IT DOES SEEM
LIKELY THAT THE COLD AIR WILL BE FIRMLY IN PLACE...INCREASING THE
CHANCES THAT PRECIPITATION WILL FALL AS SNOW.
MARINE...
SLACKENING PRESSURE GRADIENT WILL ALLOW WESTERLY WINDS TO BRIEFLY
DIMINISH TONIGHT WITH A CORRESPONDING DROP IN WAVE HEIGHT. SOUTHWEST
WINDS WILL THEN STRENGTHEN AGAIN TOMORROW. THIS COMBINED WITH COLD
AIR MOVING OVER THE WARMER WATERS WILL LEAD TO UNSTABLE CONDITIONS
BEGINNING TOMORROW EVENING. ADDITIONAL SMALL CRAFT ADVISORIES WILL
LIKELY BE NEEDED DURING THIS TIME.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....SC
UPDATE.......SC
SHORT TERM...AGD
LONG TERM....KEC
MARINE.......AGD
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
