Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240521
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1221 AM EST TUE FEB 24 2015

.AVIATION...

EXPECT VFR CONDITIONS WITH CLOUDS AOA 10-15KFT INCREASING TONIGHT
THROUGH THE MORNING. LOWER VFR CIGS APPROACHING 6KFT WILL THEN BE
POSSIBLE LATER IN THE DAY AS A SURFACE TROUGH SETTLES INTO THE
AREA. ANY PRECIPITATION ALONG THIS BOUNDARY WILL BE LIMITED TO A
FEW -SHSN AND REALLY NOT IMPACT THE TERMINALS. STRONG SOUTHWEST
WINDS WILL DEVELOP WITH GUSTS TO 30 KNOTS OR SO POSSIBLE. BOTH
WINDS AND CLOUDS WILL DIMINISH LATE IN THE FORECAST PERIOD ONCE
THE NEXT COLD FRONT BEGINS PUSHING SOUTHEAST THROUGH THE AREA.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN SOUTHWEST WINDS...200 DEGREES...GUSTING TO 25-30
  KNOTS TUESDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 403 PM EST MON FEB 23 2015

SHORT TERM... TONIGHT

RECORD SETTING COLD AND VERY DRY AIRMASS IN PLACE OVER SOUTHEAST
MICHIGAN...AS INDICATED BY THE 12Z DTX SOUNDING AND THIS MORNINGS
LOWS. LARGE AREA OF HIGH PRESSURE (1040+ MB) WHICH HAS BEEN
WEAKENING OVER NORTHERN MISSOURI WILL TRANSLATE EAST INTO THE OHIO
VALLEY TONIGHT...ALLOWING FOR SOUTHWEST RETURN FLOW TO KICK IN
OVERNIGHT. HOWEVER...FAVORABLE RADIATING CONDITIONS WILL BE IN PLACE
THIS EVENING AS AN EXTENSION OF THE RIDGE AXIS SLIDES THROUGH...AND
WITH AFTERNOON DEW PTS IN THE -5 TO -10 DEGREE RANGE...SHOULD SEE
TEMPERATURES TAKE A NOSE DIVE BELOW ZERO ACROSS MOST LOCATIONS...IN
LINE WITH LATEST MAV/12Z EURO RAW TEMPS. THE ONLY CONCERN IS LAKE
MICHIGAN CLOUDS WHICH ARE TRYING TO WORK THEIR WAY EAST THIS
AFTERNOON...BUT SUSPECT THEY WILL MOSTLY MIX OUT...EXCEPT TOWARD THE
TRI-CITIES REGION...AS WINDS BECOME SOUTHWEST OVERNIGHT...PROVIDING
BETTER FOCUS/FETCH OF MOISTURE...BUT MAIN AXIS WILL PROBABLY BE JUST
NORTH AND WEST OF MIDLAND/BAY. ALSO...THERE IS STILL ALOT OF DRY AIR
WEST OF LAKE MICHIGAN...SO NOT TOTALLY CONVINCED THERE WILL BE A BIG
SOUTHWEST FLARE UP IN ACTIVITY UNTIL VERY LATE TONIGHT. LOWERED
WINDS THIS EVENING/TONIGHT AS WE ATTEMPT TO DECOUPLE...BUT AS
SOUTHWEST WINDS BEGIN TO INCREASE LATE TONIGHT...WARM
ADVECTION/INCREASING HIGH CLOUDS AT THE VERY LEAST SHOULD ALLOW
ACTUAL TEMPS TO RISE INTO THE SINGLE NUMBERS...AND THUS LOOKS LIKE
WIND CHILLS WILL BOTTOM OUT AROUND 15 DEGREES BELOW ZERO ACROSS MOST
AREAS. BUT WITH THE LIMITED DURATION...HAVE ELECTED NOT TO ISSUE A
WIND CHILL ADVISORY SINCE THIS IS A MARGINAL/BORDERLINE
SCENARIO...ESPECIALLY COMPARED TO THE COLD THAT WE HAVE ALREADY
EXPERIENCED THIS MONTH.

LONG TERM...

THE NEXT UPPER LEVEL JETLET WILL PUNCH SOUTHWARD ACROSS THE
INTERNATIONAL BORDER TONIGHT. THIS FEATURE WILL BE RESPONSIBLE FOR
THE CLIPPER SYSTEM AND ASSOCIATED ABSOLUTE VORTICITY THAT WILL DIVE
DIRECTLY INTO THE CENTRAL GREAT LAKES TUESDAY AFTERNOON. THERE ARE A
FEW ITEMS TO ADDRESS WITH THIS PARTICULAR SYSTEM.

FIRST BIG QUESTION OUT OF THE GATE IS OVERALL WIND POTENTIAL FOR THE
DAY TUESDAY. RECENT MODEL GUIDANCE HAS BEEN BULLISH ON THE PROSPECTS
FOR MODERATE GRADIENT FLOW OCCURING IN THE WARM WARM SECTOR IN
ADVANCE OF THE APPROACHING COLD FRONT. THE SETUP AND
ENVIRONMENT...RESEMBLING THAT OF A GREAT PLAINS SCENARIO... SUPPORTS
A STRAIGHT GEOSTROPHIC EVENT. WINDS ARE FORECASTED TO INCREASE
DURING THE MORNING...ALBEIT UNDER WARM AIR ADVECTION AND WITH VERY
SQUATTY MIXING HEIGHTS OF 2000 FT AGL OR LESS. NATURALLY THIS LEADS
TO SOME HESITATION IN AN AGGRESSIVE WIND FORECAST. RELIED HEAVILY ON
GUIDANCE HERE...EXPECTATIONS ARE FOR SOUTHWESTERLY WINDS OF 30 TO 35
MPH TO DEVELOP DURING THE MORNING HOURS AND SUBSIDING TOWARDS DUSK.

THE PRECIPITATION FORECAST FOR TUESDAY COMES IN TWO PHASES. THE
FIRST WITH AN AREA OF SYNOPTIC MOISTURE AND ISENTROPIC ASCENT DURING
THE MIDDAY TIMEFRAME ALONG THE MAIN MIDLEVEL CONVERGENCE AXIS. THE
PROBLEM FROM A MEASURING OF PRECIPITATION  PERSPECTIVE...IS THE LACK
IN DEPTH OF MOISTURE. PLAN VIEWS SHOW THE 700MB AND 500MB MOISTURE
SLABS OUT OF PHASE DURING THE DAYLIGHT HOURS IN ADDITION TO A STABLE
THERMODYANMIC PROFILE FROM 2 TO 13 KFT AGL. WILL LIKELY WITNESS
HYDROMETEORS OVER THE DAYTIME BUT THERE APPEARS TO BE VERY LITTLE
SUPPORT FOR IMPACTFUL ACCUMULATIONS.

THE SECOND PHASE WILL COME WITH CONVECTIVE SNOW SHOWER POTENTIAL
ALONG THE LEAD EDGE OF THE MAIN NEAR SURFACE ARCTIC AIR COLD FRONT.
THE MAIN COLD SURGE WILL LAG BEHIND THE INITIAL WIND SHIFT...WITH
BULK OF COLD AIR PUSHING ACROSS SOUTHEASTERN MICHIGAN AFTER 00Z
WEDNESDAY. FORECAST SOUNDINGS SHOW A GOOD POTENTIAL THE ADDITIONAL
NEAR SURFACE COLD AIR ADVECTION WILL ALLOW FOR A DEPTH IN STEEP
LAPSE RATES FROM THE SURFACE UP TO ROUGHLY 7000 KFT AGL. WILL NEED
TO WATCH FOR THE POTENTIAL OF A SECONDARY WIND POP AND POSSIBLE SNOW
SQUALL TYPE SCENARIO. NEGATIVES ON SNOWFALL ACCUMULATIONS WILL BE
VERY SHORT DURATION OF FORCING AND SPEED OF MOVEMENT ACROSS THE CWA.

SURFACE RIDGE AXIS IS THEN FORECASTED TO BUILD AGGRESSIVELY INTO THE
REGION FOR THE MIDDLE TO END OF THE WEEK.

QUIET PERIOD IN STORE THURSDAY THROUGH AT LEAST THE BEGINNING OF THE
WEEKEND AS SURFACE HIGH PRESSURE SLIDES ACROSS THE UPPER MISSISSIPPI
RIVER VALLEY.  THIS HIGH PRESSURE WILL MAINTAIN TRANQUIL CONDITIONS
ALONG WITH CONTINUAL BELOW NORMAL TEMPERATURES.  NEXT PERIOD OF
ACTIVE WEATHER LOOKS TO MOVE IN AT THE END OF THE WEEKEND.

MARINE...

WINDS WILL TURN SOUTHERLY AND INCREASE IN STRENGTH LATE TONIGHT AS A
LOW PRESSURE SYSTEM TRACKS ACROSS NORTHERN ONTARIO. WINDS LOOK TO
REACH GALE FORCE BY TUESDAY MORNING ACROSS MUCH OF LAKE HURON AS A
STRONG WIND FIELD PUSHES UP INTO THE AREA AHEAD OF THE LOW. A GALE
WARNING IS IN EFFECT FOR LAKE HURON...INCLUDING SAGINAW BAY...WITH
WIND GUSTS TO 45 KNOTS EXPECTED. GALE WARNINGS HAVE ALSO BEEN ISSUED
FOR LAKE ST CLAIR AND LAKE ERIE GIVEN THE FORECASTED MAGNITUDE OF
GEOSTROPHIC FLOW OVER THE REGION AND REDUCED ROUGHNESS LENGTH OF
ICE. ANOTHER ARCTIC COLD FRONT WILL SWEEP DOWN ACROSS THE CENTRAL
GREAT LAKES TUESDAY NIGHT...FLIPPING WINDS TO THE NORTHWEST. THESE
WINDS WILL REMAIN ELEVATED...BUT AT THIS TIME...GUSTS LOOK TO REMAIN
AROUND 30 KNOTS OVER LAKE HURON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...GALE WARNING FROM 4 AM EARLY THIS MORNING TO 7 PM EST THIS EVENING
     FOR LHZ361>363-421-422-441>443-462>464.

LAKE ST CLAIR...GALE WARNING FROM 4 AM EARLY THIS MORNING TO 7 PM EST THIS EVENING
     FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING FROM 4 AM EARLY THIS MORNING TO 7 PM EST THIS EVENING
     FOR LEZ444.

&&

$$

AVIATION.....DG
SHORT TERM...SF
LONG TERM....CB/SS
MARINE.......CB


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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