231
FXUS63 KDTX 202340
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
640 PM EST FRI NOV 20 2009
AVIATION
SUSTAINED AREA OF LOW LEVEL MOISTURE TRAPPED BENEATH A STRONG
INVERSION WILL MAINTAIN A PERSISTENT STRATUS DECK THROUGHOUT THE TAF
PERIOD. CONDITIONS PREDOMINATELY IN MVFR THIS EVENING /IFR AT PTK/
WITH A TREND TOWARD IFR AT ALL TERMINALS OVERNIGHT AS THE INVERSION
HEIGHT LOWERS. A DIMINISHING WIND FIELD WOULD ALSO SUGGEST SOME
POTENTIAL FOR FOG OVERNIGHT...BUT THE BKN/OVC CANOPY OF STRATUS
SHOULD LIMIT THE VISIBILITY RESTRICTIONS TO MAINLY MVFR/BRIEF IFR.
CEILINGS WILL SLOWLY RISE IN RESPONSE TO WEAK DAYTIME MIXING ON
SATURDAY...BUT PLENTY OF LOW LEVEL MOISTURE WILL ENSURE MVFR STRATUS
HOLDS THROUGH THE AFTERNOON.
PREV DISCUSSION
ISSUED 313 PM EST FRI NOV 20 2009
SHORT TERM...TONIGHT
LOW LEVEL MOISTURE (AIDED BY THE WESTERLY FLOW OFF LAKE MICHIGAN)
LOOKS TO REMAIN TRAPPED OVER SOUTHEAST MICHIGAN...MAINTAINING CLOUDY
SKIES THROUGH THE NIGHT...PREVENTING MUCH OF A DIURNAL SPREAD IN
TEMPERATURES...AND WILL MAINTAIN THE MIN TEMPS IN THE LOWER
40S/AROUND 40...IN LINE WITH LATEST MAV GUIDANCE.
500 MB SHORTWAVE RIDGING THIS AFTERNOON IN PLACE OVER THE CENTRAL
GREAT LAKES WILL BE REPLACED BY THE BROAD TROUGHING CURRENTLY OVER
THE WESTERN GREAT LAKES WITH THE MAIN UPPER WAVE OVER IOWA TRACKING
ALONG THE SOUTHERN MICHIGAN BORDER. EVEN SO...BOTH NAM/GFS
INDICATING ONLY MODEST LIFT AND A FAILURE TO SATURATE MUCH ABOVE
850/800 MB...AND WILL THUS MAINTAIN A DRY FORECAST WITH THE LACK OF
CLOUD DEPTH (AFTER AFTERNOON SPRINKLES/DRIZZLE CONTINUES TO COME TO
AN END)...BUT WOULD NOT BE SHOCKED IF A FEW SPRINKLES REDEVELOP
OVERNIGHT. DID ADD SOME PATCHY FOG TO THE ZONES HOWEVER AND
CONCERNED ABOUT THE LOW CLOUD CLEARING TREND OVER WESTERN LOWER
MICHIGAN AT THE PRESENT TIME. IF THIS WORKS EAST...WE CAN EXPECT A
BIT MORE WIDESPREAD FOG AND COLDER TEMPERATURES OVERNIGHT. SUSPECT
ONCE THE SUN SETS THE LOW STRATUS WILL BUILD BACK TO THE WEST A
BIT.
LONG TERM...SATURDAY THROUGH NEXT FRIDAY
A MID LEVEL WAVE NOW SHOWN OVER THE UPPER MISSISSIPPI VALLEY WILL
TRACK ACROSS THE STATE ON SATURDAY. LIFT ASSOCIATED WITH THIS WAVE
IS NOT EXPECTED TO BE VERY STRONG. THE 12Z UPPER AIR ANALYSIS DID
SHOW AN AREA OF HIGHER MID LEVEL MOISTURE ACROSS WISCONSIN...WHICH
IS FORECAST TO SLIDE ACROSS LOWER MI IN ADVANCE OF THE UPPER WAVE ON
SATURDAY. MODEL SOUNDINGS INDICATE RESIDUAL LOW LEVEL MOISTURE ALONG
WITH THE MID LEVEL MOISTURE WILL RESULT IN A FAIRLY CLOUDY START TO
THE DAY SATURDAY. MID LEVEL RIDGING ADVANCING INTO THE WESTERN GREAT
LAKES SAT AFTERNOON IN THE WAKE OF THE SHORT WAVE WILL HELP
SCOUR OUT THE MID LEVEL MOISTURE LATE IN THE DAY. SHALLOW WARM AIR
ADVECTION WILL ALSO HELP WEAKEN THE INVERSION. THESE FACTORS MAY
ALLOW FOR SOME BREAKS IN THE CLOUD COVER /OR AT LEAST SOME THINNING
OF THE CLOUDS/ LATE IN THE DAY. THIS ALONG WITH THE MILD LOW LEVEL
AIRMASS LINGERING OVER THE REGION SHOULD BE ABLE TO BOOST MAX TEMPS
INTO THE 50S ON SATURDAY.
THE 12Z MODEL SUITE WERE WELL INITIALIZED WITH THE UPPER WAVE NOW
OVER TEXAS AND CONTINUE TO SHEAR THIS WAVE APART AS IT TRACKS ACROSS
THE EASTERN US LATE SUN INTO MON. THIS WILL LEAVE WEAK HIGH PRESSURE
IN PLACE ACROSS THE EASTERN GREAT LAKES. GIVEN THE RELATIVE HIGH LOW
LEVEL MOISTURE ACROSS THE REGION /SURFACE DEWPOINTS FROM THE UPPER
30S TO LOWER 40S/...FOG AND/OR LOW CLOUDS MAY BE PROBLEMATIC SAT
NIGHT/SUN MORNING AND AGAIN SUN NIGHT/MON MORNING. A LIGHT EASTERLY
FLOW IS ALSO FORECAST TO DEVELOP...WITH MOISTURE FLUX OFF LAKE ERIE
ENHANCING THE FOG/LOW CLOUD POTENTIAL. THE PREVIOUS FORECAST SHIFT
ADDED A MENTION OF FOG FOR THESE TIME PERIODS AND THE LATEST MODEL
GUIDANCE REMAINS SUPPORTIVE OF THIS. TEMPERATURES WILL REMAIN ON THE
MILD SIDE THROUGH THE REST OF THE WEEKEND INTO EARLY NEXT WEEK.
SINCE ANY MORNING FOG OR LOW CLOUDS WILL LIKELY TAKE INTO THE
AFTERNOON TO MIX OUT GIVEN THE LOW SUN ANGLE...HAVE KEPT MAX TEMPS
ON THE CONSERVATIVE SIDE /NEAR 50/ SUN AND MON.
THE 12Z MODEL SUITE CONTINUE TO SHOW DISCREPANCIES WITH RESPECT TO
TIMING AND AMPLITUDE OF A MID LEVEL WAVE FORECAST TO ADVANCE INTO
THE PACIFIC NORTHWEST TOWARD THE END OF THE WEEKEND...THEN INTO THE
CENTRAL US EARLY NEXT WEEK. THE 12Z ECMWF/CANADIAN/UKMET ALL SHOW
MUCH MORE AMPLIFICATION WITH THIS WAVE AS IT TRAVERSES THE ROCKIES
ON MONDAY IN COMPARISON TO THE GFS. THE MORE AMPLIFIED SOLUTIONS
THEN CUT THE UPPER LOW OFF OVER THE CENTRAL PLAINS TUES INTO
WED...WHILE THE GFS CUTS THE SYSTEM OFF OVER THE WESTERN GREAT LAKES
DURING THIS TIME PERIOD. WITH THE SUPPORT OF THE CANADIAN AND UKMET
AND GIVEN THE STILL LARGE SPREAD AMONG GFS ENSEMBLE MEMBERS /A FEW
OF WHICH ARE IN LINE WITH THE ECMWF/...WILL LEAN THE FORECAST TOWARD
THE SLOWER AND MORE AMPLIFIED ECMWF. THIS WILL SUPPORT CONTINUED DRY
AND MILD WEATHER THROUGH TUESDAY...WITH INCREASING CHANCES OF RAIN
BY WED/WED NIGHT. THE ECMWF DOES CONTINUE TO INDICATE SOME PHASING
OF NORTHERN STREAM ENERGY BY THURS...BRINGING A MUCH COLDER AIRMASS
INTO THE GREAT LAKES /WARRANTING THE CHANCE OF SNOW THURS AND FRI/.
MARINE...
WESTERLY WINDS OF 10 TO 20 KNOTS WILL CONTINUE TO DIMINISH THIS
EVENING AND TONIGHT...BECOMING LIGHT SATURDAY AND SUNDAY AS HIGH
PRESSURE BECOMES FULLY ESTABLISHED OVER THE CENTRAL GREAT LAKES
DURING THE WEEKEND. THIS HIGH WILL SLOWLY RETREAT EARLY NEXT
WEEK...BUT SURFACE RIDGING WILL PERSIST ON MONDAY...MAINTAINING
LIGHT WINDS FOR AT LEAST ANOTHER DAY.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
AVIATION.....MR
SHORT TERM...SF
LONG TERM....SC
MARINE.......SF
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
CLICK HERE TO GO TO PREVIOUS BULLETINS.
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