FXUS63 KDTX 301145
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
645 AM EST MON NOV 30 2009
.AVIATION...
BKN/OVC DECK OF VFR STRATUS /4-6K FT/ WILL REMAIN IN PLACE
THROUGHOUT THE TAF PERIOD GIVEN SUFFICIENT MOISTURE PRESENT BENEATH
THE INVERSION. 10KT WINDS WILL SHIFT FROM NORTHWEST TO SOUTHWEST
THROUGH THE DAY AS A SURFACE RIDGE SLIDES THROUGH. WEAK TROUGH
DROPPING ACROSS NORTHERN LOWER MI MAY LEAD TO A PERIOD OF MVFR
CEILINGS OVERNIGHT. STRONGER FORCING AND DEEPER MOISTURE WILL
REMAIN TO THE NORTH...SO WILL HOLD OFF ON INCLUDING A PRECIP
MENTION AT MBS/FNT WITH THIS TAF ISSUANCE.
&&
.PREV DISCUSSION...ISSUED 353 AM EST MON NOV 30 2009
SHORT TERM...TODAY AND TONIGHT
AIRMASS CONTINUING TO DRY THIS MORNING IN THE WAKE OF THE EARLIER
FRONTAL PASSAGE. LATEST SATELLITE IMAGERY DEPICTING SEVERAL BANDS
OF LAKE EFFECT STREAMING SOUTH-SOUTHEAST ACROSS LAKE HURON. NARROW
WINDOW REMAINS FOR A FEW SNOW SHOWERS TO IMPACT THE EASTERN THUMB
YET THIS MORNING BEFORE THE LOW LEVEL FLOW BECOMES ANTICYCLONIC BY
LATE MORNING. OTHERWISE...THE DEPTH OF THE DRYING WITHIN THE LOW
LEVEL NORTHWEST FLOW WILL ALLOW FOR OCCASIONAL PEAKS OF SUN AT LEAST
THROUGH THE MORNING. DIURNAL STRATUS MAY TEND TO FILL IN AGAIN BY
MID AFTERNOON WITH THE LOW LEVEL THERMAL TROUGH IN PLACE AND A
DEVELOPING WESTERLY FLOW PROVIDING SOME ADDED MOISTURE FLUX OFF
LAKE MICHIGAN. 925 MB TEMPERATURES WILL SETTLE INTO THE -2 TO -3C
RANGE FOR THE DAY...TRANSLATING INTO HIGHS RANGING FROM UPPER 30S
TO LOWER 40S.
WEAK CLIPPER SYSTEM WILL DROP SOUTHEAST WITHIN THE MEAN UPPER LEVEL
NORTHWEST FLOW...REACHING THE NORTHERN GREAT LAKES TONIGHT. THIS
WILL BE ACCOMPANIED BY A NARROW AXIS OF MODEST ISENTROPIC ASCENT AND
FAVORABLE LEFT EXIT REGION UPPER JET DYNAMICS. LATEST MODEL
GUIDANCE TRENDING NORTH WITH THE BETTER FORCING WHILE DISPLAYING
LESS IMPRESSIVE MOISTURE PROFILES. THIS WILL RESULT IN A QUICK SHOT
OF LIGHT PRECIPITATION BETWEEN ROUGHLY 02-08Z TONIGHT...WITH HIGHEST
CHANCES FROM I-69 NORTH. FREEZING LEVELS WILL BEGIN TO CLIMB DURING
THIS TIME AS WARM AIR ADVECTION STRENGTHENS...ALTHOUGH INITIALLY
EVAPORATIVE COOLING WILL HINDER THE THERMAL RESPONSE WHILE WET BULB
TEMPS HOVER BELOW FREEZING. THIS POINTS TOWARD MORE OF A RAIN/SNOW
MIX POTENTIAL WITH ACCUMULATIONS REMAINING MINOR /HALF INCH OR LESS
SAGINAW VALLEY-THUMB REGION/. COLD AIR ADVECTION WILL KICK BACK IN
LATE TONIGHT AS THIS SYSTEM SHIFTS TOWARD SOUTHERN ONTARIO. THIS
WILL ALLOW LOWS TO DIP INTO THE LOWER 30S OUTSIDE OF DETROIT.
LONG TERM...
BIG REVERSAL ON THE MID WEEK STORM SYSTEM.
WATER VAPOR IMAGERY SHOWS RATHER AMPLIFIED UPPER LEVEL RIDGE OVER
SOUTHERN BRITISH COLUMBIA/ALBERTA BEING CHOPPED DOWN AND DISPLACED
TO THE EAST AS UPPER LEVEL TROUGH/COLD POOL ENERGY OVER THE GULF OF
ALASKA COMES ASHORE. 300 MB 160 KNOT JET CORE NOTED AT PANT (ANNETTE
ISLAND AIRPORT AK). UNFORTUNATELY...CAN'T FIND ANY GLARING ISSUES
WITH THE MODEL (NAM/UKMET/GFS) INITIALIZATIONS.
TONIGHT'S ANALYSIS/TRENDS SUPPORT GREATER HEIGHT FALLS TO THE WEST
AND SOUTH...BACK ACROSS THE NORTHERN ROCKIES...THEN SLIDING
SOUTHEAST INTO THE CENTRAL PLAINS. THIS SHOULD PROVE SUFFICIENT TO
CAPTURE/ABSORB THE CUTOFF LOW JUST SOUTH OF ARIZONA.
SUBSEQUENTLY...THE LONGWAVE TROUGH AXIS BECOMES NEUTRALLY TILTED
MUCH FASTER...BY WEDNESDAY NIGHT WITH THE MERGING HEIGHT FALL
CENTERS. THIS WILL LIKELY RESULT IN RAPIDLY DEEPENING LOW PRESSURE
SYSTEM...WHICH WILL BE TRACKING MUCH FARTHER WEST (CERTAINLY WEST OF
THE APPALACHIANS). IN FACT...THE 00Z NAM IS SO FAR TO THE WEST...WE
ARE LOOKING AT A RAIN STORM AS THE SURFACE LOW TRACKS THROUGH THE
CWA. THE RETROGRADING UPPER LEVEL LOW OVER EASTERN CANADA ALLOWS
THIS TO HAPPEN. SO...PRECIPITATION NOW APPEARS LIKELY WEDNESDAY
NIGHT...BUT IN WHAT FORM REMAINS A BIT OF A MYSTERY
(SNOW/RAIN)...AND WILL HAVE TO CARRY A MENTION OF BOTH AT THIS
POINT...DEPENDENT ON THE TRACK AND STRENGTH OF THE DEVELOPING TROWAL.
THE 00Z GFS IS CERTAINLY MORE BULLISH ON A SNOW STORM WITH THE
FAVORABLE TRACK NEAR PITTSBURGH PA AND 850 MB TEMPS HOVERING BETWEEN
-3 TO -6 C DURING THE PEAK LIFT/DEFORMATION. BUT AT THIS
POINT...BASED ON THE MODEL TRENDS AND IT BEING EARLY DECEMBER
(NORTHEAST FLOW OFF LAKE HURON ALSO ADDING SOME HEAT
FLUX)...RELUCTANT TO CALL FOR A STRAIGHT SNOW STORM...ESPECIALLY
WITH PARALLEL RUN OF THE GFS ALSO A BIT WARMER AND FARTHER WEST WITH
THE LOW. WILL HIGHLIGHT THE POTENTIAL FOR ACCUMULATING SNOW IN THE
HWO HOWEVER.
THE FORECAST SHOULD THEN GET BACK ON TRACK BY THE END OF THE WORK
WEEK...AS COLD AIR (850 MB TEMPS OF -12 C) STILL LOOKS TO BECOME
ESTABLISHED OVER LOWER MICHIGAN WITH POSSIBLE LAKE EFFECT/DIURNAL
ENHANCEMENT SNOW SHOWERS DURING FRIDAY WITH THE LOW LEVEL WESTERLY
FLOW.
MARINE...
WEAK SURFACE RIDGING SLIDING THROUGH TODAY WILL ALLOW WINDS TO
DECREASE WHILE SHIFTING FROM NORTHWEST TO SOUTHWEST. THIS WILL
RESULT IN DECREASING WAVE HEIGHTS ALONG THE LAKE HURON NEARSHORE
WATERS TODAY. HOWEVER...WAVE HEIGHTS WILL BUILD AGAIN ACROSS
OUTER SAGINAW BAY TONIGHT AS SOUTHWEST WINDS GUST TO 20 KNOTS.
THEREFORE WILL MAINTAIN THE ADVISORY FOR THIS AREA THROUGH TONIGHT.
WINDS WILL DIMINISH INTO TUESDAY AS HIGH PRESSURE RIDGING BRIEFLY
RETURNS. A RELATIVELY WEAK WIND FIELD WILL REMAIN IN PLACE THROUGH
WEDNESDAY AS A COLD FRONT SLIDES INTO THE REGION.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...OUTER SAGINAW BAY...UNTIL 10 AM TUESDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON...UNTIL 4 PM MONDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....MR
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR
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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
