Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171047
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
647 AM EDT FRI OCT 17 2014

.AVIATION...

//DISCUSSION...

MVFR CEILINGS SHOULD GRADUALLY RISE AND BREAK FOR A PERIOD AFTER
SUNRISE AS A SURFACE WARM FRONT LIFTS UP INTO THE AREA. LINGERING
MOISTURE WILL THEN ALLOW MVFR CU TO QUICKLY FILL BACK IN. A STRONG
COLD FRONT WILL APPROACH THE AREA THIS AFTERNOON AS LOW PRESSURE
MOVES FROM WISCONSIN INTO MICHIGAN. THIS WILL ALLOW GUSTY SOUTHWEST
WINDS TO DEVELOP IN THE AFTERNOON AHEAD OF THE FRONT. SHOWERS AND
LOWER CEILINGS WILL ACCOMPANY THE FRONT AS IT PUSHES THROUGH THIS
EVENING...ALONG WITH AN ABRUPT WIND SHIFT TO THE WEST. ISOLATED
THUNDERSTORMS ARE ALSO POSSIBLE BETWEEN 5 PM AND 2 AM...BUT TIMING
AND CONFIDENCE ARE TOO LOW TO WARRANT A MENTION IN THE TAFS. MVFR
CEILINGS AND SCATTERED SHOWERS WILL THEN CONTINUE OVERNIGHT BEHIND
THE FRONT...AND INTO SATURDAY.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET MUCH OF THE TAF PERIOD.

&&

.PREV DISCUSSION...ISSUED 349 AM EDT FRI OCT 17 2014

SHORT TERM...TODAY AND TONIGHT

THE UPPER LOW THAT HAS PLAGUED THE AREA FOR MUCH OF THE WEEK WILL
CONTINUE TO LIFT NORTH THROUGH EASTERN ONTARIO AND WESTERN QUEBEC
TODAY. THIS WILL OPEN THE DOOR FOR ANOTHER UPPER LOW....NOW SEEN
SPINNING ON WATER VAPOR OVER NORTHERN MINNESOTA...TO DROP INTO
SOUTHEAST MICHIGAN BY THIS EVENING. THE SYSTEM SHOULD OPEN UP AS IT
DOES...AND WILL EVENTUALLY PHASE WITH THE LOW OVER ONTARIO/QUEBEC
TONIGHT PER GFS UPPER PV FORECAST.

SURFACE LOW/TROUGH AHEAD OF THE INCOMING SYSTEM WILL TRACK FROM
WISCONSIN TO LOWER MICHIGAN THIS AFTERNOON. AN ELEVATED WARM FRONT
IS ALREADY LIFTING THROUGH SOUTHEAST MICHIGAN PER MODEL DATA.
MOISTURE AND WEAK ISENTROPIC ASCENT WITH THIS FEATURE ARE EXPECTED
TO GENERATE A FEW LIGHT SHOWERS NORTH AND EAST OF FLINT THIS
MORNING. THE REST OF THE AREA SHOULD SEE MAINLY AREAS OF DRIZZLE AS
WEAK ASCENT CONTINUES BEHIND THE INITIAL BAND OF BETTER ISENTROPIC
ASCENT. WE SHOULD SEE A QUICK SURGE OF WARMER AND DRIER AIR
(PARTICULAR SOUTH OF THE I-69 CORRIDOR) DURING THE LATE MORNING AND
AFTERNOON AS THE SURFACE FRONT NOSES UP INTO SOUTHEAST MICHIGAN. THE
TROUGH WILL WORK ACROSS SOUTHEAST MICHIGAN THIS EVENING WITH A
STRONG COLD FRONT TRAILING BEHIND IT. THIS SHOULD BRING A BETTER
CHANCE FOR SHOWERS VERY LATE TODAY AND TONIGHT. A FEW THUNDERSTORMS
WILL ALSO BE POSSIBLE AS A HEALTHY H500 COLD POOL /-22C/ STEEPENS
MID-LEVEL LAPSE RATES AFTER 5 PM TONIGHT. A FEW LIGHTNING STRIKES
HAVE ALREADY BEEN OBSERVED UNDER THE COLD POOL OVER MINNESOTA...AND
ADDED A SMALL THUNDER MENTION DESPITE WEAK SUPPORT FROM MODEL
FORECAST SOUNDINGS. GUSTY WINDS WILL DEVELOP AHEAD OF THE
FRONT...AND THEN STAY GUSTY OVERNIGHT FROM THE NORTHWEST AS THE
BOUNDARY LAYER REMAINS WELL MIXED.

MAX TEMPS TODAY SHOULD REACH INTO THE UPPER 50S TO MID 60S THIS
AFTERNOON AS WARM AIR CONTINUES TO LIFT UP INTO THE AREA BUT CLOUD
COVER LIMITS HEATING FROM SUNSHINE. CLOUDS AND WINDS OVERNIGHT WILL
PREVENT TEMPERATURES FROM BECOMING TOO CHILLY...IN THE 40S...DESPITE
THE INFLUX OF COLD AIR.

LONG TERM...

DEEP NORTHWEST FLOW WILL ENVELOP SOUTHEAST MICHIGAN ON SATURDAY IN
THE WAKE OF A STRONG EARLY MORNING FRONTAL PASSAGE.  A FIRM COLD AIR
ADVECTIVE COMPONENT WILL BRING 850 TEMPERATURES BELOW FREEZING
DURING THE DAYLIGHT PERIOD.  THIS PROCESS IN COMBINATION WITH SOME
RESIDUAL WRAPAROUND LOW LEVEL MOISTURE WILL SUSTAIN A HEALTHY
STRATUS DECK THROUGH MUCH OF THE DAY.  THIS WILL CONTAIN HIGHS
WITHIN THE UPPER 40S/LOWER 50S RANGE...OR ROUGHLY 10 DEGREES BELOW
AVERAGE FOR MID OCTOBER.  A SLIGHTLY GUSTY 10-15 KNOT NORTHWEST WIND
WILL CONTRIBUTE THIS NOTEWORTHY COOLING TREND.  SFC-850 MB LAPSE
RATES WILL STEEPEN AS THE NORTHERN PORTIONS OF A TRAILING WAVE
DIGGING INTO THE EXPANDING MEAN TROUGH EJECTS SOUTHEAST INTO THE
NORTHERN OHIO VALLEY.  THIS MAY PROVIDE JUST ENOUGH ASCENT TO
GENERATE A FEW LIGHT SHOWERS.

FLOW BECOMES INCREASINGLY ANTICYCLONIC SATURDAY NIGHT AT THE EDGE OF
BUILDING HIGH PRESSURE.  THIS WILL KICK ANY LINGERING LOW LEVEL
THERMAL TROUGH EASTWARD AND PRESENT A GREATER POTENTIAL FOR A
CLEARING TREND AS INCREASING MID LEVEL SUBSIDENCE WORKS INTO THE
INVERSION AND THE LOW LEVEL FLOW BACKS TO WESTERLY.  ASSUMING A
WINDOW OF MOSTLY CLEAR SKY DOES EMERGE...THE EXISTING AIRMASS WILL
SUPPORT SUB-FREEZING LOWS IN MANY LOCALES SUNDAY MORNING.  SURFACE
RIDGING TUCKED BENEATH LOW AMPLITUDE MID LEVEL NORTHWEST FLOW WILL
TRANSLATE INTO BENIGN WEATHER CONDITIONS FOR SUNDAY.  TEMPERATURE
RECOVERY WILL BE CAPPED BY THE COLD MORNING START AND LACK OF ANY
THERMAL ADVECTION...DESPITE A HIGHER DEGREE OF INSOLATION RELATIVE
TO SATURDAY.  THIS AGAIN POINTS TO HIGHS OF LOWER 50S AT BEST.

STRENGTHENING SHORTWAVE TRANSLATING THROUGH THE NORTHWEST FLOW WILL
LIFT ACROSS THE REGION ON MONDAY.  A PROGRESSIVE WING OF ISENTROPIC
ASCENT NOTED IN SOME DEGREE ON ALL MODEL GUIDANCE ARRIVES SUNDAY
NIGHT...GREATEST ASCENT AND CORRESPONDING LOWER CONDENSATION
PRESSURE DEFICITS CURRENTLY ELONGATED THROUGH NORTHERN AND CENTRAL
LOWER MI.  THIS WILL LIKELY LEAVE SOUTHERN SECTIONS OF THE FORECAST
AREA AT THE EDGE OF BOTH ADEQUATE FORCING AND MOISTURE QUALITY FOR
THIS INITIAL PUSH.  GREATER POTENTIAL WILL EXIST AREAWIDE ON MONDAY
AS THE MORE CONSOLIDATED FORCING ARRIVES WITH THE INBOUND COMPACT
VORTICITY.  THIS WAVE THEN BECOMES THE MAIN CATALYST FOR WHAT
BECOMES A HIGH AMPLITUDE TROUGH/CLOSED LOW CONFIGURATION OVER THE
EAST COAST...FAVORING A COOL AND DRY PATTERN FOR SE MICHIGAN TO
FINISH THE WORK WEEK.

MARINE...

A MODEST PRE-FRONTAL SOUTHWEST FLOW WILL REMAIN IN PLACE TODAY.
WINDS WILL INCREASE TONIGHT IN THE WAKE OF STRONG COLD FRONTAL
PASSAGE.  THE ADDED INSTABILITY AS THIS COLDER AIR MOVES ACROSS THE
WARMER WATERS WILL LEAD TO WIND SPEEDS OF 20 TO 25 KNOTS BY LATE
TONIGHT AND EARLY SATURDAY.  THE POTENTIAL REMAINS FOR FREQUENT
GUSTS UP TO GALES OVER MUCH OF CENTRAL AND SOUTHERN LAKE HURON AND
A GALE WATCH REMAINS IN EFFECT THROUGH THIS TIME.  WINDS WILL
DECREASE SATURDAY NIGHT INTO SUNDAY AS A RIDGE OF HIGH PRESSURE
BUILDS INTO THE REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING OUTER SAGINAW BAY...FROM 1 AM SATURDAY TO 4 AM
     SUNDAY.

     GALE WATCH...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...FROM 1 AM
     SATURDAY TO 8 PM SATURDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

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

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



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