Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291737
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
137 PM EDT WED JUL 29 2015


.AVIATION...

A COLD FRONT WILL MOVE ACROSS LOWER MICHIGAN THIS AFTERNOON AND
EARLY EVENING. CEILINGS WILL DROP TO BETWEEN 2500-4000 FEET OVER THE
NEXT FEW HOURS AS MOISTURE POOLS AHEAD OF THE FRONT. A LINE OF
SHOWERS AND THUNDERSTORMS...JUST NOW FORMING AT 17Z...WILL FILL IN
AND EXPAND SOUTHWARD. THIS WILL AFFECT SOUTHEAST MICHIGAN TERMINALS
BETWEEN 17-22Z. MOST LIKELY WINDOW REMAINS AS A TEMPO GROUP IN EACH
TAF. A MODEST WIND SHIFT TO THE WEST WILL OCCUR WITH THE
FRONT...FOLLOWED BY MUCH DRIER AIR AND CLEARING SKIES TONIGHT. POST-
FRONTAL AIRMASS WILL NOT BE MUCH COOLER TOMORROW...BUT BREEZY WEST
WINDS ARE EXPECTED WITH GUSTS TO 25 KTS IN THE AFTERNOON AND EARLY
EVENING.

FOR DTW...CEILINGS WILL CONTINUE TO FILL IN AND LOWER THROUGH 19Z.
ALTHOUGH HEIGHT IS A LITTLE UNCERTAIN GIVEN DEVELOPING
CONVECTION...MOST PROBABLE CEILING LOOKS TO BE AT 3500 FEET.
GREATEST WINDOW FOR THUNDERSTORMS TO IMPACT THE TERMINAL WILL BE
BETWEEN 19Z AND 22Z.


//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS BELOW 5000 FT THIS AFTERNOON.

* MEDIUM IN THUNDERSTORMS MID-LATE AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 1210 PM EDT WED JUL 29 2015

UPDATE...
FORECAST STILL ON TRACK AND UPDATE WAS ONLY TO CLEAN UP
CLOUDS/POPS IN THE VERY NEAR-TERM. COLD FRONT NOW PUSHING INTO
WESTERN MICHIGAN SHOULD WORK WITH WARM AND HUMID AIRMASS...TEMPS
IN THE MID/UPPER 80S AND DEWPOINTS PRIMARILY IN THE LOW 70S...TO
TRIGGER SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EARLY
EVENING. COVERAGE STILL EXPECTED TO BE SCATTERED WITH WEAK
FRONTAL FORCING. BETTER DYNAMICS AND HEIGHT FALLS REMAIN NORTH OF
THE AREA. HI-RES MODELS STILL SHOWING HIGHER COVERAGE BUT ARE NOT
HANDLING LACK OF CONVECTION TO OUR WEST WELL. POTENTIAL STILL
EXISTS FOR A FEW STRONGER STORMS THIS AFTERNOON AS ML CAPE VALUES
RISE TO 1000-1500 J/KG. COLD FRONT AND STORMS SHOULD EXIT DURING
THE EVENING.

PREV DISCUSSION...ISSUED 354 AM EDT WED JUL 29 2015

SHORT TERM...TODAY AND TONIGHT

SOUTHERN EDGE OF THE LOWER HEIGHTS EMANATING FROM THE LARGE UPPER
LOW LIFTING INTO WESTERN ONTARIO STEADILY SHIFTING ACROSS THE UPPER
MS VALLEY EARLY THIS MORNING.  WHILE THE GREATER HEIGHT FALLS AND
ASSOCIATED UPPER JET DYNAMICS WILL ACCOMPANYING THE PARENT LOW INTO
SOUTHERN CANADA TODAY...THIS EVOLUTION WILL FORCE A COLD FRONT
THROUGH SE MICHIGAN DURING THE AFTERNOON PERIOD.  A SOLID BUT NARROW
CORRIDOR OF PRE-FRONTAL MOISTURE/THETA-E TRANSPORT WILL SQUEEZE
NORTHEAST AND INTO THE REGION THROUGHOUT THE FIRST HALF OF THE DAY.
CONCURRENT WEAK MID LEVEL DESTABILIZATION AS THIS PROCESS UNFOLDS
WILL PROVIDE AN INITIAL LIMITED OPPORTUNITY FOR ISOLATED CELLS TO
EMERGE ALONG THE LEAD EDGE. LATEST RADAR TRENDS AND HI RES GUIDANCE
WOULD FAVOR THE TRI-CITIES FOR A LOW END POP MENTION FOR POSSIBLE
MORNING ACTIVITY.

GREATEST WINDOW FOR SHOWER/THUNDERSTORM DEVELOPMENT AND EXPANSION
FOCUSED WITH A MID-LATE AFTERNOON FRONTAL PASSAGE /18Z-22Z/.  THE
EXTENSIVE MID/HIGH CLOUD DECK LOOMING JUST UPSTREAM CONTINUES TO
CAST SOME DOUBT AS TO POTENTIAL PRE-FRONTAL DESTABILIZATION...SHOULD
AN EARLY ARRIVING THICKER CANOPY MORE SIGNIFICANTLY UNCUT THE
DIURNAL HEATING PROCESS.  DESPITE THIS...HIGHS OF MID AND UPPER 80S
ON TARGET GIVEN THE RESIDENT AIRMASS.  GIVEN A DEWPOINT CLOSING IN
ON 70 DEGREES...THIS TRANSLATES INTO BALLPARK MLCAPE VALUES IN THE
1500 J/KG RANGE.  FRONTAL CONVERGENCE WILL BE WEAKENING WITH TIME AS
THE BETTER HEIGHT FALLS INITIALLY STREAM TO THE NORTH...BUT APPEARS
ADEQUATE CONSIDERING THE MOISTURE QUALITY AND FAVORABLE DIURNAL
TIMING TO GENERATE AT LEAST A SCATTERED COVERAGE OF CONVECTION
EITHER JUST UPSTREAM OR OVERHEAD WITHIN THE 18Z-22Z PERIOD.  THE
MODEST ASCENT AND LOW BULK SHEAR VALUES /LESS THAN 20 KNOTS/ WILL
HINDER THE PROSPECTS OF SEEING MORE ORGANIZED CONVECTIVE
GROWTH...SIMPLY A LOW END POTENTIAL FOR SOME STRONGER WIND GUSTS TO
DEVELOP WITHIN ANY HEALTHIER CORES.

A SLIGHTLY COOLER BUT SIGNIFICANTLY DRIER POST-FRONTAL ENVIRONMENT
WILL BEGIN TO FILTER IN BY EARLY TONIGHT.  THIS WILL PROVIDE A
NOTEWORTHY DOWNWARD TREND IN HUMIDITY THAT CARRIES RIGHT INTO
THURSDAY.  LOWS TONIGHT IN THE LOWER 60S.

LONG TERM...THURSDAY THROUGH TUESDAY

PRETTY BIG SHIFT IN THE LONGWAVE PATTERN SETTING UP OVER THE END OF
THE WEEK. THE MID LEVEL CLOSED LOW TRACKING ACROSS SOUTHERN CANADA
WILL LIFT NE TO THE HUDSON BAY WHERE IT WILL STALL AND DEEPEN OVER
THE COURSE OF THE WEEKEND WHILE THE RIDGE OVER THE WEST COAST
AMPLIFIES. THIS PATTERN LOOKS TO BE QUITE STUBBORN LEADING TO
TROUGHING OVER THE GREAT LAKES THROUGH THE EXTENDED FORECAST PERIOD.

THURSDAY WILL FEATURE ELEVATED WESTERLY WINDS DUE TO A WELL MIXED
AND DRY POST FRONTAL AIRMASS. CONVERGENT WNW FLOW ALOFT BETWEEN THE
DEVELOPING UPPER LEVEL RIDGE/TROUGH PATTERN...HIGH PRESSURE BUILDING
IN AT THE SFC...COOLING MID LEVELS... AND PWATS DROPPING UNDER 0.75
INCHES...WILL PROMOTE STEEP LL LAPSE RATES. IN ADDITION THE WIND
PROFILE IS DEEP LAYER WESTERLY FLOW WITH SPEEDS UP TO 25 KNOTS DOWN
TO ALMOST 950MB. NOT A HUGE GRADIENT THROUGH THE COLUMN HENCE
SUSTAINED WINDS WILL BE 15-20 KNOTS WITH GUSTS CAPPED OFF A LITTLE
HIGHER AT 25 KNOTS. THESE WINDS ALSO LOOK TO KEEP SOME WARM AIR
STREAMING INTO THE REGION WITH THE RIDGE REMAINING LOW AMPLITUDE.
THIS NEARLY ZONAL FLOW WILL HELP KEEP SOME WARM AIR ADVECTING INTO
THE REGION BEFORE THE TROUGH CAN FURTHER DEEPEN AND DIG INTO THE
AREA.

FRIDAY LOOKS TO REMAIN DRY BUT LOW END POPS WILL BE IN THE FORECAST
THROUGH THE WEEKEND AND INTO NEXT WEEK. THIS IS A LOW CONFIDENCE
FORECAST AS FALL ON THE SOUTHERN PERIPHERY OF THE DEEPENING TROUGH
WITH A SERIES OF SHORTWAVES LIKELY DROPPING THROUGH THE NW FLOW
THROUGH THE REGION. THE AIRMASS LOOKS TO REMAIN DRY AND THE BULK OF
THE ENERGY IN THE PATTERN BRUSHING THE NORTHERN LAKES REGION SO HARD
TO GET TOO EXCITED ABOUT ANY POP CHANCES AT THIS TIME. THE TROUGH
WILL YIELD SOME COOLER TEMPS BUT STILL NEAR NORMAL AROUND 80
DEGREES.

MARINE...

WARM SOUTHERLY FLOW WILL INCREASE AHEAD OF AN APPROACHING COLD FRONT
TODAY. THE STABLE AIRMASS WILL LIMIT THE GUST POTENTIAL WHICH SHOULD
TOP OUT NEAR 20 KNOTS. FLOW WILL REMAIN ELEVATED THROUGH THE NIGHT
AND INTO THURSDAY AS WINDS TURN MORE SOUTHWESTERLY BEHIND THE FRONT.
SMALL CRAFT ADVISORIES FOR WIND MAY BE NEEDED ON THURSDAY AS WINDS
OVER LAND MAY REACH 25 KNOTS WHICH MAY EXTEND INTO NEARSHORE ZONES.
LIGHT GRADIENT WILL SETTLE IN FOR THE EXTENDED PERIOD FAVORING WINDS
10 KNOTS OR LESS FRIDAY AFTERNOON INTO SUNDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....HLO
UPDATE.......HLO
SHORT TERM...MR
LONG TERM....DRK
MARINE.......DRK


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



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