Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 300412
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1212 AM EDT TUE SEP 30 2014

.AVIATION...

//DISCUSSION...

AVIATION WEATHER IN SE MICHIGAN REMAINS TIED TO THE PASSAGE OF A
STRONG COLD FRONT...NOT AS MUCH WIND AS IN TEMPERATURE...AND THE
RESULTING COLDER AIR MASS SETTLING IN BEHIND THE FRONT. AT PRESS
TIME...THE FRONT ONLY HAD TO MOVE THROUGH THE DTW TERMINAL CORRIDOR
WITH MODEST SPEED BUT SHARP WIND SHIFT TO THE NORTHWEST AND A
PATTERN OF SHOWERS WITH MARGINAL MVFR RESTRICTION. THE RAIN WILL
ONLY LAST A FEW HOURS AND THEN LEAVE WIDESPREAD IFR CEILING THROUGH
THE MID MORNING IN THE DTW AREA...MVFR FARTHER NORTH TOWARD MBS.
CEILING WILL GRADUALLY RISE DURING THE DAY BUT REMAIN LOCKED IN AT
MVFR OVER COOL NORTH WIND.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FEET THROUGH TODAY.

&&

.PREV DISCUSSION...ISSUED 907 PM EDT MON SEP 29 2014

UPDATE...

A STRONG COLD FRONT CONTINUES TO SLIDE THROUGH SE MICHIGAN TONIGHT
AND WILL BRING PRONOUNCED CHANGES TO THE WEATHER IN OUR AREA. THE
FRONT IS NOT PACKING MUCH OF A WIND PUNCH BUT IS BRINGING A SHARP
WIND SHIFT AND TEMPERATURE DECREASE. THE TEMPERATURE DECREASE WAS
MORE DRAMATIC BEFORE SUNSET OVER NORTH SECTIONS WHILE AFTERNOON
TEMPS WERE PUSHING 80...BUT WILL NOW BE MASKED A BIT MORE BY
COOLER READINGS AFTER SUNSET OVER THE REST OF SE MICHIGAN. THE
FORECAST TIMING OF THE FRONTAL PASSAGE LOOKS SOLID IN THE GOING
PACKAGE.

EARLIER IN THE EVENING...THE THERE WAS JUST ENOUGH SURFACE BASED
INSTABILITY GENERATED BY DEWPOINT NEAR 60 TO FIRE OFF SOME
THUNDERSTORMS WITHIN THE FRONTAL ZONE OVER THE SAGINAW VALLEY AND
THUMB. FORCING WAS ALSO BOOSTED BY STRONG DYNAMIC LIFT SUPPLIED BY
THE THE UPPER WAVE...AND THIS WILL BE THE PRIMARY FORCING FOR
SHOWERS FOR THE REST OF THE NIGHT WITHIN THE LOW TO MID LEVEL
THETA-E RIDGE COINCIDENT WITH THE FRONT. THE LOSS OF DAYTIME
HEATING WILL CHALLENGE THE SYSTEM TO PRODUCE MORE THUNDERSTORM
ACTIVITY BUT THE SYSTEM IS STRONG AND PLAN TO MAINTAIN A CHANCE IN
THE FORECAST WITHIN A NEARLY SOLID BAND OF SHOWERS. THE
CATEGORICAL POP FORECAST LOOKS GOOD WITH JUST MINOR REFINEMENT TO
TIMING BEFORE THE PATTERN EXITS SE MICHIGAN BY SUNRISE. THE FRONT
WILL THEN LEAVE CLOUDY AND COOLER CONDITIONS IN PLACE THROUGH
TUESDAY MORNING.

PREV DISCUSSION...ISSUED 344 PM EDT MON SEP 29 2014

SHORT TERM...THROUGH TONIGHT

QUIET AND WARM CONDITIONS ARE EXPECTED THROUGH THE REMAINDER OF THE
AFTERNOON AND INTO THE EVENING BEFORE AN APPROACHING COLD FRONT
USHERS IN BIG CHANGES FOR THE OVERNIGHT HOURS AND ESPECIALLY
TOMORROW.

UPPER TROUGH DROPPING FROM CANADA INTO NORTHERN MICHIGAN WILL DEEPEN
INTO A CLOSED LOW AS IT DROPS ACROSS LOWER MICHIGAN TONIGHT. AT THE
SURFACE...THIS WILL PUSH THE AREA OF SURFACE LOW PRESSURE CENTERED
SOUTH OF ALPENA SOUTHEAST ACROSS LAKE HURON AND INTO ONTARIO
TONIGHT. STRONG SURFACE COLD FRONT WILL TRAIL BEHIND THE
LOW...DROPPING THROUGH SOUTHEAST MICHIGAN THIS EVENING AND OVERNIGHT
(9PM THROUGH 6 AM). STILL LOOKING LIKE A GOOD SHOT FOR RAIN TONIGHT
ALONG THE FRONT WITH UPPER DIFFLUENCE AND GOOD UPPER HEIGHTS FALLS
POSITIONED ABOVE THE FRONT (SOME FGEN AS WELL)...AND AS A MODEST
SURGE OF THETA-E OCCURS. CONTINUE TO THINK THAT THE WINDOW FOR RAIN
SHOWERS AT ANY GIVEN LOCATION IS ONLY 2 TO 4 HOURS WIDE...WHICH
AGREES WELL WITH CURRENT RADAR PRESENTATION OVER NORTHERN MICHIGAN
AND WISCONSIN. (AREAS OF DRIZZLE MAY HOWEVER DEVELOP AFTER THE FRONT
SLIDES THROUGH AND DRIER AIR ALOFT WORKS IN.) SOME THUNDER WILL ALSO
BE POSSIBLE WITH STEEPENING MID-LEVEL LAPSE RATES AND MODEL
CROSS-SECTIONS SHOWING SOME CONVECTIVE INSTABILITY (MOSTLY ALOFT) AS
THE FRONT DROPS THROUGH. THERE WERE SOME THUNDER OVER THE U.P. LATE
LAST NIGHT ALONG THE FRONT.

TEMPERATURE GRADIENT ACROSS THE FRONT RIGHT NOW IS IMPRESSIVE...WITH
LOW 50S RIGHT NOW OVER NORTHERN LOWER MI AND UPPER 70S ACROSS
CENTRAL MI (40S IN THE U.P!). THE TEMPERATURE IN TRAVERSE CITY FELL
FROM 70 TO 58 DEGREES IN ONLY TWO HOURS THIS AFTERNOON AS THE FRONT
DROPPED ACROSS. OUR WARM TEMPS SHOULD HOLD THROUGH THE DAYLIGHT
HOURS BEFORE THE FRONT SLIDES THROUGH...RIGHT AS TEMPERATURES WOULD
COOL ANYHOW. WIND...CLOUDS...AND RAIN SHOULD PREVENT TEMPS FROM
GETTING TOO CHILLY OVERNIGHT...ESPECIALLY WITH BEST COLD AIR
ADVECTION HOLDING OFF UNTIL OVERNIGHT. MIN TEMPS ARE EXPECTED TO RUN
FROM THE MID 40S OVER THE THUMB/SAGINAW VALLEY TO THE MID 50S IN THE
DETROIT HEAT ISLAND.

LONG TERM...

564 DM CLOSED MID LEVEL CIRCULATION CENTERED OVER THE EASTERN
THUMB/SOUTHERN LAKE HURON TUESDAY MORNING WILL PIVOT TO THE EAST
THROUGH THE DAY...ALLOWING A DEEPER NORTHERLY FLOW TO TAKE HOLD
LOCALLY.  A SOLID PERIOD OF COLD AIR ADVECTION ALREADY UNDERWAY
POST-DAYBREAK WILL EASE BY MIDDAY...THE COLDEST CORE OF THIS AIRMASS
/850 MB TEMPS OF 4C/ CENTERING OVERHEAD BY AFTERNOON AND EVENING.
SUBSTANTIAL POST-FRONTAL LOW LEVEL MOISTURE WILL REMAIN TUCKED
BENEATH A BURGEONING INVERSION.  THIS COMBINED WITH STEEPENING LOW
LEVEL LAPSE RATES WILL ENSURE AN EXTENSIVE STRATUS FIELD REMAINS
PREVALENT THROUGHOUT THE DAY.  MOISTURE DEPTH MAY PROVE ADEQUATE
TOWARD GENERATING A FEW POCKETS OF LIGHT RAIN/DRIZZLE...STILL WORTHY
OF A SMALL POP MENTION.  GREATEST POTENTIAL WILL LIKELY EXIST ACROSS
THE THUMB UNDER SOME RENEWED CVA AS A TRAILING PIECE OF VORTICITY
WRAPS BACK AROUND THE EXITING LOW.  THE TIMING/STRENGTH OF THE
ADVECTIVE PROCESS AND THE LACK OF BETTER INSOLATION WILL CONFINE
HIGHS LARGELY IN THE MID AND UPPER 50S.

LOW LEVEL FLOW WILL VEER TO NORTHEASTERLY BY TUESDAY NIGHT AS THE
CENTER OF EXPANDING HIGH PRESSURE WORKS ACROSS ONTARIO.  THE
EXISTING CANOPY OF STRATUS WILL BUDGE LITTLE UNDER THIS SETUP...THE
ADDED CONTRIBUTION OFF LAKE HURON REINFORCING A SUFFICIENTLY
DEEP MOIST SUB-INVERSION LAYER.  LOWS UPPER 40S/LOWER 50S.

HIGH PRESSURE SETTLES IN FOR WEDNESDAY AS A NARROW UPPER RIDGE AXIS
CENTERS OVER THE REGION.  THIS WILL PROMPT A GRADUAL RELEASE OF THE
CLOUD COVER AS THE COMBINATION OF DAYTIME HEATING/MIXING AND
STRENGTHENING MID LEVEL SUBSIDENCE SHRINKS THE EXISTING MOIST LAYER.
A MODERATING AIR MASS GIVEN THE INCREASING THICKNESS FIELD AND SOME
LATE DAY INSOLATION WILL PROVIDE AN INCREMENTAL BOOST TO HIGHS.
850 MB TEMPERATURES ARE PROJECTED TO CLIMB BACK INTO THE 10C RANGE.
THIS WOULD SUPPORT READINGS WITHIN THE 65 TO 70F RANGE...ASSUMING
CLOUD COVER DOES NOT REMAIN PROBLEMATIC WELL INTO THE DAY.

TEMPERATURES WILL RECOVER NICELY FOR THE FIRST HALF OF THURSDAY
AHEAD OF AN APPROACHING COLD FRONT. EXPECT PROBABLY THE LAST RUN AT
80 FOR THE YEAR AS SOUTHERLY DRYING WINDS WILL TRY TO AID
INSOLATION. THE RAIN EVENT THURSDAY NIGHT WILL AVERAGE 0.5 TO 0.75
INCH OF QPF ACROSS THE CWA...WITH LOCALLY HIGHER AMOUNTS. EXPECT A
RAW WEEKEND AS TEMPERATURES DROP STEEPLY AND WINDS PICK UP TO GUST
OVER 25 MPH.

MARINE...

COLD FRONT MOVES THROUGH THE CENTRAL GREAT LAKES TONIGHT. NORTHERLY
WINDS WILL STRENGTHEN BEHIND THIS FRONT LATE TONIGHT AND EARLY
TUESDAY.  WINDS OF 15 TO 20 KNOTS WITH GUSTS TO 25 KNOTS ACROSS
CENTRAL AND SOUTHERN SECTIONS OF LAKE HURON.  THIS WILL PROMPT AN
INCREASE IN WAVE HEIGHTS...WITH APPROPRIATE SMALL CRAFT ADVISORIES
NOW IN PLACE.  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...UNTIL 6 PM TUESDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...HLO
LONG TERM....MR/MM
MARINE.......MR


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