Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210350
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1150 PM EDT MON APR 20 2015


.AVIATION...

CEILINGS HEIGHTS UPSTREAM HAVE BEEN LIFTING AS DRIER AIR PUSHES INTO
THE AREA IN THE WAKE OF THIS EVENINGS LIGHT RAIN SHOWERS. A POOL OF
DEEPER COLD AIR WILL OVERSPREAD SRN MI TONIGHT. THIS WILL LIFT
INVERSION BASES AND TOGETHER WITH THE DRIER AIR WILL MAINTAIN VFR
CEILINGS INTO THE AFTERNOON. WINDS SPEEDS WILL CONTINUE TO DECREASE
DURING THE EARLY MORNING UNDER CONTINUED COOLING IN THE BOUNDARY
LAYER. RAPID DEEPENING OF THE DAYTIME MIXED LAYER AIDED BY THE DEPTH
OF THE COLD POOL ALOFT WILL LEAD TO STRONG SW WINDS LATE IN THE
MORNING THROUGH TUES AFTERNOON. THE CURRENT SET OF TAFS ACCOUNTS FOR
SOME POTENTIAL FOR STRONG CONVECTIVE WIND GUSTS OUT OF AFTERNOON
SHOWERS ON TUES...WHICH STILL LOOKS REASONABLE.

FOR DTW...THERE IS A CLEARING TREND NOTED UPSTREAM WHICH WILL LIKELY
MAKE INROADS INTO METRO PRIOR TO DAYBREAK. WITH THE LIFTING
INVERSION HEIGHTS AND THIS DRIER AIR...LINGERING CEILINGS AT OR
BELOW 5000 FT SHOULD BE LIMITED. WINDS SHOULD INCREASE RATHER
DRAMATICALLY WITH THE ONSET OF DAYTIME HEATING...ROUGHLY AROUND 14Z.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CEILINGS AT OR BELOW 5000 FT THIS MORNING AND AFTERNOON.

* LOW IN WIND GUSTS EXCEEDING CROSS WIND THRESHOLDS TUESDAY
  AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 1003 PM EDT MON APR 20 2015

UPDATE...

A BAND OF LIGHT SHOWERS WILL CONTINUE TO LIFT NORTHEAST ACROSS
MAINLY THE NORTHERN HALF OF THE FORECAST AREA THROUGH 06Z. THESE
SHOWERS ARE ASSOCIATED WITH A MID LEVEL SHORT WAVE FEATURE SHOWN
ON THE WATER VAPOR LOOP NOW ROTATING ACROSS SRN MI. THE FORCING
HAS BEEN WEAKENING SUBSTANTIALLY OVER SE MI...SO THE REMAINING
SHOWERS HAVE BEEN VERY LIGHT. THE OVERALL TREND WITH THE FORECAST
OF DECREASING COVERAGE OF SHOWERS OVERNIGHT LOOKS GOOD AS THE
FORCING EXITS TO THE NE OVER THE NEXT 2 TO 4 HOURS. A LITTLE BIT
OF SUBSIDENCE IN THE WAKE OF THIS FEATURE HAS BEEN PROMOTING SOME
CLEARING ACROSS NRN IL/FAR SRN LAKE MI. A LITTLE BETTER RESERVOIR
OF LOW LEVEL MOISTURE SHOULD KEEP CONDITIONS MOSTLY CLOUDY ACROSS
THE NRN HALF OF THE FORECAST AREA THROUGH THE NIGHT. SOUTH OF I-69
HOWEVER...CURRENT SATELLITE TRENDS DO SUGGEST SOME POSSIBLE
CLEARING LATE TONIGHT. AN UPDATE WILL BE ISSUED TO FURTHER LOWER
POPS AFTER 06Z AND DECREASE OVERNIGHT CLOUD COVERAGE ACROSS THE
SRN HALF OF THE FORECAST AREA.

PREV DISCUSSION...ISSUED 346 PM EDT MON APR 20 2015

SHORT TERM...TONIGHT

MUCAPES DID REACH 500 TO 800 J/KG EARLIER THIS AFTERNOON (PER LAPS
DATA)...WHICH WAS ABLE TO SUPPORT A COUPLE THUNDERSTORMS OVER
SOUTHEAST MICHIGAN. BULK OF CONVECTIVE ACTIVITY HAS PUSHED
EAST...AND CONTINUED DRYING BEHIND THE COLD FRONT WILL OCCUR...AS
SURFACE DEW PTS CRASH INTO THE 40S. WITH THAT COLDER/DRY AIR PUSH
IS SOME GUSTY WINDS...AS SOME PEAK WINDS OF 35 TO 45 MPH CAN BE
EXPECTED FOR ANOTHER COUPLE OF HOURS AS WE EXIT PEAK HEATING.
NOTED PEAK WIND AT DTW OF 42 KNOTS AT 1855Z. NAM/GFS MODEL
SOUNDINGS/LOW LEVEL RH FIELDS SUGGEST WE ARE GOING TO PARTIALLY
CLEAR OUT TONIGHT...BUT UPSTREAM OBSERVATIONS EXTENDING BACK WEST
OVER THE WESTERN GREAT LAKES/UPPER MISSISSIPPI RIVER VALLEY TO NOT
LOOK VERY ENCOURAGING...AND PREFERENCE WAS TO INCREASE THE CLOUD
COVER FORECAST FOR TONIGHT WITH THE COLD CYCLONIC FLOW. ALSO...AS
850 MB TEMPS FALL INTO THE MID NEGATIVE SINGLE NUMBERS OVER LAKE
MICHIGAN...SOME LAKE MICHIGAN MOISTURE/INSTABILITY CONTRIBUTION IS
NOT OUT OF THE QUESTION. HAVE CARRIED ISOLATED-SCATTERED LIGHT
RAIN SHOWER MENTION TO ACCOUNT FOR LINGERING ACTIVITY LATE THIS
AFTERNOON/EARLY THIS EVENING AND THEN THE POSSIBLE ACTIVITY TOWARD
MORNING. DESPITE CLOUDS...COLD ADVECTION EXPECTED TO SEND MINS
INTO THE UPPER 30S TO LOWER 40S.

LONG TERM...

A BROAD UPPER LEVEL TROUGH WITH A CLOSED LOW IN CLOSE PROXIMITY TO
THE GREAT LAKES REGION WILL KEEP SOUTHEASTERN MICHIGAN UNDER THE
INFLUENCE OF COLD CYCLONIC FLOW THROUGHOUT THE MIDWEEK PERIOD.
NATURE OF INDIVIDUAL SHORTWAVES ROTATING AROUND THIS UPPER LEVEL
FEATURE KEEPS THE SPECIFIC TIMING CONFIDENCE INHERENTLY LOW.

MAGNITUDE OF COLD AND DRY AIR ADVECTION FROM TONIGHT WILL
PRECONDITION THE ATMOSPHERE AND ALLOW FOR THE GROWTH OF A DEEP
DIURNAL NEAR SURFACE MIXED LAYER ON TUESDAY. FORECAST SOUNDINGS
SUGGEST MIXING HEIGHTS REACHING AS HIGH AS 6 TO 7 KFT AGL BY THE
AFTERNOON HOURS. GEOSTROPHIC FLOW IN THE REGION WILL REMAIN ELEVATED
WITH THE LOW HEIGHT ANOMALY OVER CENTRAL ONTARIO WHICH SUPPORTS
WIDESPREAD WESTERLY WIND GUSTS LATE TUESDAY MORNING/TUESDAY
AFTERNOON IN EXCESS OF 30 KNOTS. COMBINATION OF SHORTWAVE ENERGY
WORKING THROUGH THE TROUGH AXIS AND SPOKES OF ENHANCED MIDLEVEL
CONVERGENCE/SATURATION WILL BRING THE POTENTIAL FOR RAIN SHOWERS BY
TUESDAY MORNING. POTENTIAL MEDIUM IMPACT WEATHER SCENARIO MAY
UNFOLD...CONTINGENT ON OVERALL EFFICIENCY OF INDIVIDUAL CONVECTIVE
CIRCULATIONS OF THE SHOWERS TO ENHANCE DOWNWARD MOMENTUM TRANSPORT.
AFOREMENTIONED FORECAST DISCUSSION MADE REFERENCE TO A CLASSIC
INVERTED V STRUCTURE...WHICH SUGGESTS SOME POSSIBILITY THAT
WINDGUSTS COULD REACH 50 MPH. FUTURE SHIFTS CAN ASSESS THE
FEASIBILITY OF A POSSIBLE WIND ADVISORY FOR WEDNESDAY AFTERNOON.

PERSISTENT CYCLONIC FLOW AROUND UPPER LEVEL CLOSED LOW WILL BRING
ANOTHER DAY OF COLD AND SHOWERY TO SOUTHEASTERN MICHIGAN ON
WEDNESDAY. A SECONDARY SURGE OF COLD AIR ADVECTION IS FORECASTED
BETWEEN 15-18Z. THE CAA SHOULD WORK AGAINST DIURNAL HEATING...WITH
HIGHS SOME 7 TO 10 DEGREES COOLER THAN THE DAY BEFORE. HIGHS ON
WEDNESDAY ARE ONLY EXPECTED TO REACH THE MIDDLE TO UPPER 40S. BETTER
MESSAGE TO COMMUNICATE IS THAT WIND CHILLS FOR MANY AREAS WILL NOT
CLIMB OUT OF THE 30S.

THE REGION WILL STILL BE UNDER THE INFLUENCE OF LONGWAVE TROUGHING
ON THURSDAY BEFORE WEAK UPPER LEVEL RIDGING BUILDS IN FOR THE START
OF THE WEEKEND.  THIS TROUGH WILL CONTINUE TO LEAD TO COOLER TEMPS
THURSDAY BEFORE TEMPERATURES MODERATE A TINY BIT BACK INTO THE 50S
BY THE WEEKEND.  AT THIS POINT THE ONLY POTENTIAL FOR POSSIBLE
PRECIP IN THE EXTENDED WOULD BE ON SATURDAY...ALTHOUGH MOST MODELS
ARE KEEPING THE BULK OF THE PRECIP SOUTH OF THE CWA WITH THE
EXCEPTION OF THE 12Z ECMWF.

MARINE...

STRONG SOUTHWESTERLY WIND FIELD IS NOW IN PLACE WITH WINDSPEEDS AREA
WIDE RANGING BETWEEN 25 AND 35 KNOTS. SMALL CRAFT ADVISORIES REMAIN
IN EFFECT FOR ALL NEARSHORE ZONES. BREEZY WESTERLY WINDS WILL
PERSIST THROUGH MIDWEEK AS CONDITIONS REMAIN RELATIVELY STATIC WITH
LOW PRESSURE PARKED OVER THE GREAT LAKES. ADDITIONAL SMALL CRAFT
ADVISORIES FOR WIND WILL LIKELY BE NEEDED ON TUESDAY AND POSSIBLY
ONCE MORE ON WEDNESDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 11 PM EDT TUESDAY FOR LHZ421-422-441>443.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 11 PM EDT TUESDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT TUESDAY FOR LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
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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