Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291732
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
132 PM EDT MON SEP 29 2014


.AVIATION...

//DISCUSSION...
LOW PRESSURE TRACKING ACROSS MICHIGAN WILL DRIVE A COLD FRONT DOWN
THROUGH SOUTHEAST MICHIGAN TERMINALS BETWEEN 01Z AND 08Z TONIGHT.
FORCING ASSOCIATED WITH THIS SYSTEM WILL BE CONFINED CLOSE TO THE
FRONT...AND WILL RESULT IN A 2-4 HOUR WINDOW CHARACTERIZED BY
RAIN...MVFR (POSSIBLY IFR) CEILINGS...AND AN ABRUPT WIND SHIFT TO
THE NORTHWEST. COLD AIR AND LOW-LEVEL MOISTURE WILL FILL IN BEHIND
THE FRONT...LOWERING CEILINGS TO IFR/LOW MVFR AND ALLOWING AREAS OF
DRIZZLE TO DEVELOP. CEILINGS WILL GRADUALLY RISE TOMORROW
AFTERNOON...BUT ARE EXPECTED TO REMAIN LOCKED IN AT MVFR.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE WITH CEILINGS BELOW 5000 FEET BETWEEN 07-18Z.

&&

.PREV DISCUSSION...ISSUED 315 AM EDT MON SEP 29 2014

SHORT TERM...TODAY AND TONIGHT

A SURFACE COLD FRONT IS SHOWN STRETCHING FROM WRN NEBRASKA...ACROSS
THE UP OF MICHIGAN...AND INTO SRN QUEBEC AS OF 07Z. THERE IS A VERY
TIGHT LOW LEVEL BAROCLINIC ZONE ALONG THIS BOUNDARY AS EVIDENT BY
YESTERDAYS HIGHS IN THE 70S AND 80S SOUTH OF THE FRONT AND 40S AND
50S NORTH. RECENT SURFACE ANALYSES HAVE SHOWN THE DEVELOPMENT OF A
WEAK LOW ALONG THE BOUNDARY OVER CNTL UPPER MI. THIS SFC REFLECTION
HAS DEVELOPED WITHIN THE ENTRANCE REGION OF THE UPPER JET MAX AND
AHEAD OF A MID LEVEL TROUGH NOW ROTATING ACROSS NW ONTARIO AND SRN
MANITOBA.

THE WATER VAPOR LOOP HAS ALREADY BEEN SHOWING THIS MID LEVEL WAVE
AMPLIFYING AS IT TRACKS TOWARD THE E-SE. THIS IS IN SUPPORT OF THE
ENTIRE 00Z MODEL SUITE WHICH SHOW THIS WAVE UNDERGOING RAPID
DEEPENING AS IT TRACKS INTO NRN LOWER MI THIS EVENING...EVENTUALLY
EVOLVING INTO A COMPACT CLOSED MID LEVEL LOW OVER LAKE HURON BY 12Z
TUES. THE CORRESPONDING MID LEVEL HEIGHT FALLS WILL OVERSPREAD SE MI
TONIGHT ALONG WITH A NARROW AXIS OF STRONG DIFFERENTIAL CYCLONIC
VORTICITY ADVECTION. SE MI IS ALSO EXPECTED TO RESIDE IN THE
EXIT REGION OF A CYCLONICALLY CURVED UPPER JET MAX WITHIN THE BASE
OF THE UPPER TROUGH...ENHANCING LARGE SCALE UPPER DIVERGENCE. THE
00Z MODEL SUITE HAVE A REASONABLE HANDEL ON THE LOW-MID LEVEL
MOISTURE PLUME NOW STRETCHING ACROSS THE NRN GREAT LAKES...WHICH IS
FORECAST TO NARROW AS IT WORKS INTO SE MI TONIGHT. THE MOISTURE
LOOKS TO BE ENOUGH TO RESULT IN A BRIEF PERIOD /2 TO 4 HOURS/ OF
SHOWERS CONSIDERING THE STRONG LARGE SCALE ASCENT. THIS BRIEF WINDOW
WHEN THE FORCING AND MOISTURE WILL ALIGN IS EXPECTED TO OCCUR ALONG
AND JUST BEHIND THE SFC FRONT WHICH THE HI RES SOLUTIONS SUGGEST
WILL BE DRIVEN INTO THE TRI CITIES AROUND 00Z AND ACROSS METRO
DETROIT AROUND 06Z. MODEL CROSS SECTIONS SHOW SOME WEAK CONVECTIVE
INSTABILITY AS RAPID COOLING ALOFT STEEPENS MID LEVEL LAPSE RATES.
IN LIGHT OF THE BRIEF YET INTENSE PERIOD OF LARGE SCALE
ASCENT...SOME ISOLATED THUNDERSTORMS CAN NOT BE RULED OUT.

LIKE THE LAST SEVERAL MORNINGS...THERE WILL BE SOME FOG AROUND TO
START THE DAY. MODEL SOUNDINGS AND THE RECENT IR SUGGEST THIS
MOISTURE IS QUITE SHALLOW AND WILL MIX OUT FAIRLY QUICKLY THIS
MORNING. THE LACK OF MUCH CLOUD COVER AHEAD OF THE COLD FRONT AND
SUBTLE LOW LEVEL WARM AIR ADVECTION IN THE PREFRONTAL AIRMASS WILL
BOOST DAYTIME HIGHS TO THE UPPER 70S/AROUND 80. STRONG LOW LEVEL
COLD AIR ADVECTION TONIGHT WILL RAPIDLY DROP TEMPS INTO THE 40S
FOLLOWING FROPA. CHANCE POPS WILL BE CONTINUED THROUGH DAYBREAK TUES
AS EXTENSIVE POST FRONTAL STRATUS WITHIN THE DEEPENING INVERSION MAY
RESULT IN SOME DRIZZLE.

LONG TERM...

MUCH COOLER WEATHER ON TUESDAY...AS 500 MB LOW/COLD POOL (0 C AT 700
MB) SLOWLY EXITS THE CENTRAL GREAT LAKES REGION. STEEP LOW LEVEL
LAPSE RATES...COUPLED WITH NORTHERLY FLOW OFF LAKE HURON SHOULD
ASSURE CLOUDY SKIES ACROSS SOUTHEAST MICHIGAN...WITH EVEN ENOUGH LOW
LEVEL SATURATION/CAPE TO POTENTIALLY CAUSE A FEW LIGHT
SHOWERS/SPRINKLES. PRONOUNCED SUBSIDENCE INVERSION IN PLACE TUESDAY
NIGHT EXPECTED TO TRAP LOW LEVEL MOISTURE TO MAINTAIN MOSTLY CLOUDY
SKIES THROUGH THE NIGHT. WITH SURFACE HIGH/RIDGE IN PLACE AND UPPER
LEVEL RIDGE OVERHEAD ON WEDNESDAY...MAY PROVE DIFFICULT TO MIX OUT
THE LOW LEVEL MOISTURE/CLOUDS...ESPECIALLY OVER THE THUMB REGION.

UPPER LEVEL LOW OVER THE GREAT BASIN EARLY THIS MORNING WILL BE
INFUSED BY UPPER LEVEL LOW/COLD POOL OFF THE BRITISH COLUMBIA
COAST...LEADING TO LONGWAVE TROUGH ENCOMPASSING WESTERN NORTH
AMERICA TUESDAY-WEDNESDAY. GOOD MOISTURE ADVECTION WILL TRANSLATE
NORTHEAST INTO THE GREAT LAKES REGION AS WE HEAD INTO
THURSDAY...WITH PW VALUES RISING ABOVE 1.5 INCHES. TIMING OF THE
850-700 MB THETA-E RIDGE AXIS AHEAD OF THE COLD FRONT LOOKS TO BE
THURSDAY EVENING...SUPPORTING HIGH LIKELY POPS AS AGRESSIVE HEIGHT
FALLS TAKE OVER TO END THE WORK WEEK. THERE IS EVEN A SLIGHT
CHANCE OF THUNDERSTORMS WITH THE COLD FRONT..AS SHOWALTER INDEX
PROGGED TO GO SLIGHTLY BELOW ZERO THURSDAY EVENING...PER 00Z EURO.

MARINE...

A COLD FRONT WILL SLIDE THROUGH THE CENTRAL GREAT LAKES TONIGHT.
SOLID NORTH WINDS OF 15 TO 25 KNOTS WILL FOLLOW BEHIND THE COLD
FRONT INTO TUESDAY MORNING. WITH THE COLD ADVECTION AND STRONGER
WINDS...WAVES WILL BUILD IN EXCESS OF 4 FEET OVER CENTRAL AND
SOUTHERN LAKE HURON...AND SMALL CRAFT ADVISORIES HAVE BEEN ISSUED.
WINDS WILL QUICKLY DIMINISH BY TUESDAY NIGHT AS HIGH PRESSURE BUILDS
BACK INTO THE REGION. LIGHT WINDS AND LOW WAVES WILL PERSIST
WEDNESDAY AND THURSDAY.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
     FROM PORT AUSTIN TO PORT SANILAC...FROM 1 AM TUESDAY TO 6 PM
     TUESDAY.

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

&&

$$

AVIATION.....HLO
SHORT TERM...SC
LONG TERM....SF
MARINE.......SF


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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