257
FXUS63 KDTX 071654
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1150 AM EST SAT NOV 7 2009
AVIATION
DRY AIRMASS IS PROVIDING VFR CONDITIONS ACROSS TAF SITES. SURFACE
GRADIENT AHEAD OF A WEAK COLD FRONT WILL CONTINUE TO PRODUCE STRONG
AND GUSTY SOUTHWEST FLOW THROUGH THE AFTERNOON. SOME SCATTERED CU
MAY FORM WITH THE COLD FRONT PASSAGE. SURFACE RIDGING BEHIND FRONT
WILL BRING LIGHT AND VARIABLE WINDS OVERNIGHT WHICH WILL BECOME
SOUTHEASTERLY SUNDAY MORNING AS THE RIDGE SLIDES TO THE EAST.
PREV DISCUSSION
ISSUED 329 AM EST SAT NOV 7 2009
SHORT TERM...TODAY AND TONIGHT
THE LATEST SURFACE ANALYSIS SHOWS A 982MB LOW OVER NORTHERN MANITOBA
WITH A TROUGH AXIS EXTENDING FROM MINNESOTA INTO THE CENTRAL PLAINS.
THIS LOW IS ASSOCIATED WITH A MID LEVEL SHORT WAVE OVER SOUTHERN
MANITOBA...WHICH IS FORECAST TO LIFT INTO NORTHERN ONTARIO TODAY.
THIS WILL SEND THE TROUGH AXIS THROUGH SE MI LATE THIS AFTERNOON.
MODEL SOLUTIONS CONTINUE TO STRUGGLE WITH MOISTURE DEVELOPMENT ALONG
AND AHEAD OF THE SURFACE TROUGH. THE 00Z GFS WAS DRASTICALLY TOO
MOIST FROM THE SFC THROUGH 925MB BASED ON UPSTREAM SOUNDINGS. THE
NAM HAD A MUCH BETTER INITIALIZATION OF THE LOW LEVEL MOISTURE...BUT
CONTINUES TO INDICATE UPSTREAM LOW CLOUD DEVELOPMENT WHICH IS NOT
SUPPORTED BY LATEST OBSERVATIONS. GIVEN THE GENERAL LACK OF LARGE
SCALE ASCENT AND APPARENT LACK OF MOISTURE...THE SURFACE TROUGH
SHOULD PASS THROUGH LATE TODAY WITH LITTLE FANFARE. IN FACT...
CONDITIONS UPSTREAM SUGGEST A FAIR AMOUNT OF SUNSHINE TODAY. DESPITE
LIMITED MIXING DEPTHS...THE SOUTHERLY GRADIENT WILL SUPPORT FREQUENT
GUSTS IN THE 25 TO 30 MPH RANGE THIS AFTERNOON. THIS WILL ADVECT THE
WARM SURFACE TEMPS OBSERVED UPSTREAM YESTERDAY INTO SE MI...ALLOWING
AFTERNOON HIGHS TO RISE INTO THE 60S /A GOOD 10 DEGREES ABOVE
NORMAL/.
WEAK HIGH PRESSURE WILL BUILD ACROSS SOUTHERN MICHIGAN TONIGHT
FOLLOWING THE PASSAGE OF THE SURFACE TROUGH. SURFACE DRY AIR
ADVECTION...CLEAR SKIES AND A WEAKENING GRADIENT WILL FOSTER BETTER
RADIATIONAL COOLING CONDITIONS DURING THE OVERNIGHT. THUS...HAVE
UNDERCUT MOS GUIDANCE A COUPLE DEGREES /CARRYING LOWS IN THE UPPER
30S TO LOWER 40S/.
LONG TERM...SUNDAY THROUGH FRIDAY
HIGH PRESSURE WILL EXPAND INTO THE GREAT LAKES ON SUNDAY...ALLOWING
FOR A CONTINUATION OF WELL ABOVE NORMAL TEMPERATURES. HIGHS IN THE
LOW TO MID 60S WILL RUN MORE THAN 10 DEGREES ABOVE NORMAL. CLOUD
COVER WILL START TO INCREASE LATE AS SOUTHERLY FLOW AHEAD OF THE
NEXT LOW PRESSURE SYSTEM BEGINS TO ADVECT LOW/MID LEVEL MOISTURE
NORTHWARD INTO MICHIGAN. MODEL SOUNDINGS SHOW MORE POTENTIAL FOR LOW
STRATUS DEVELOPING SUNDAY NIGHT AS OPPOSED TO SHALLOW GROUND FOG AS
SURFACE DEWPOINTS MAKE A RUN AT 50 DEGREES. WILL THEREFORE HOLD
PLENTY OF CLOUD COVER IN THE FORECAST OVERNIGHT...KEEPING MIN
TEMPERATURES IN THE UPPER 40S TO NEAR 50. WILL KEEP AN EYE ON
MOISTURE PROFILES OVER THE NEXT FEW MODEL CYCLES HOWEVER TO MAKE
SURE FOG IS NOT WARRANTED INSTEAD.
SURFACE LOW PRESSURE WILL LIFT UP INTO THE WESTERN GREAT LAKES
SUNDAY NIGHT AHEAD OF A WEAK UPPER WAVE MOVING EAST THROUGH CENTRAL
CANADA AND THE NORTHERN PLAINS. THIS UPPER WAVE WILL DEEPEN BEFORE
IT PUSHES INTO THE GREAT LAKES MONDAY/MONDAY NIGHT...AS UPPER PV
ANOMALY DROPS INTO THE SYSTEM FROM THE NORTH PER LATEST GFS
FORECAST. SURFACE FRONTAL BOUNDARY ACCOMPANYING THE SYSTEM WILL PUSH
INTO NORTHWEST MICHIGAN BY MONDAY AFTERNOON...THEN ACROSS SOUTHEAST
MICHIGAN MONDAY NIGHT. SOME INTERESTING DYNAMICS NOW LOOKING TO SET
UP IN ASSOCIATION WITH THIS SYSTEM IT PUSHES ACROSS LOWER MICHIGAN
SUNDAY NIGHT PER LATEST MODEL GUIDANCE. MODELS NOW SHOW GOOD LOW/MID
LEVEL FGEN OVER SOUTHEAST MICHIGAN MONDAY NIGHT AS STRONG HIGH
PRESSURE DEVELOPING OVER THE UPPER MIDWEST HELPS TO INTENSIFY THE
WIND FIELD/CONVERGENCE ALONG THE FRONTAL BOUNDARY. ALSO LOOKING AT
RIGHT ENTRANCE FORCING FROM A CANADIAN JET STREAK...AND INSTABILITY
FROM A LOW-LEVEL JET. WITH MODELS ALSO SHOWING A PW SURGE TO OVER AN
INCH AND A WITH THE ANTICIPATION OF A MORE DYNAMIC SYSTEM...HAVE
INCREASED POPS TO HIGH CHANCE OVERNIGHT. THUNDER HAS ALSO BEEN ADDED
TO THE FORECAST AS CROSS-SECTIONS REVEAL A PRETTY DEEP LAYER OF
CONVECTIVE INSTABILITY. ALL MODELS HAVE SLOWED THE EASTWARD
PROGRESSION OF THE UPPER TROUGH ONCE IT REACHES THE GREAT
LAKES...WHICH MAKES SENSE GIVEN A TREND TOWARDS A DEEPER AND MORE
AMPLIFIED SYSTEM. WITH THE TROUGH AND LOW-LEVEL FRONTAL BOUNDARY NOW
EXPECTED TO LINGER OVER THE GREAT LAKES INTO TUESDAY...HAVE
INCREASED POPS INTO TUESDAY AFTERNOON. FURTHER REFINEMENTS TO
POPS/QPF/WIND SPEEDS FOR MONDAY NIGHT/TUESDAY WILL LIKELY BE NEEDED
IF MODELS CONTINUE TO TREND TOWARDS A DEEPER MORE DYNAMIC SYSTEM.
STRONG HIGH PRESSURE TO OUR WEST LOOKS TO MIGRATE ACROSS MICHIGAN
LATE TUESDAY AND WEDNESDAY...PROVIDING A RETURN TO DRY WEATHER WITH
MORE SEASONABLE TEMPERATURES. MODELS HAVE BEEN STRUGGLING TO RESOLVE
THE SYNOPTIC PATTERN FOR THE END OF NEXT WEEK...AND HAVE OPTED TO
KEEP THE INHERITED DRY FORECAST. WILL BE ON THE LOOKOUT FOR THE NEXT
LOW PRESSURE SYSTEM TO AFFECT US SOMETIME DURING THE FRIDAY-SUNDAY
PERIOD...HOWEVER MODELS REMAIN WILDLY DIVERGENT WITH REGARD TO
TIMING.
MARINE...
WINDS GUSTS IN THE 25 TO 30 KNOT RANGE WILL PERSIST ACROSS LAKE
HURON THROUGH THE MORNING. WINDS WILL BEGIN TO DIMINISH LATER THIS
MORNING AS WARM AIR LIMITS THE MIXING DEPTHS OVER THE WATER. THE
GRADIENT WILL ALSO BEGIN TO RELAX IN THE AFTERNOON IN ADVANCE OF A
WEAK SURFACE TROUGH. WINDS WILL FURTHER DIMINISH TONIGHT AS WEAK
HIGH PRESSURE ADVANCES ACROSS LAKE HURON.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...LHZ422-LHZ442-LHZ443...UNTIL NOON SATURDAY.
SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 4 PM SATURDAY.
LAKE ST CLAIR...
SMALL CRAFT ADVISORY...UNTIL NOON SATURDAY.
MI WATERS OF LAKE ERIE...
SMALL CRAFT ADVISORY...UNTIL NOON SATURDAY.
AVIATION.....DRC
SHORT TERM...SC
LONG TERM....HLO
MARINE.......SC
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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
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