Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 282323
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
723 PM EDT TUE OCT 28 2014

.AVIATION...

//DISCUSSION...

COLDER AIR WILL BEGIN A MORE CONVINCING SURGE INTO SE MICHIGAN NOW
THAT WE ARE POST SUNSET AND WILL CONTINUE THROUGH THE NIGHT.
EXPECT WIND GUSTS TO DROP OFF WITH EVENING DECOUPLING BUT
SUSTAINED WIND TO HOLD IN THE 10-15 KNOT RANGE. POTENTIAL WILL BE
MONITORED FOR GUSTS TO RETURN OVERNIGHT DURING THE PEAK OF COLD
AIR TRANSPORT...AND ARE EXPECTED TO REACH 20 KNOTS BY MID
WEDNESDAY MORNING WITH THE HELP OF SURFACE HEATING. STRATOCU
ACCOMPANYING THE COLDER AIR WILL REMAIN VFR WITH GREATER COVERAGE
IN THE MBS AREA UNTIL OVERSPREADING ALL OF SE MICHIGAN DURING
WEDNESDAY.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE ON CEILING BELOW 5000 FT WEDNESDAY.

&&

.PREV DISCUSSION...ISSUED 347 PM EDT TUE OCT 28 2014

SHORT TERM...THROUGH TONIGHT

THE COLD FRONT IS JUST ABOUT TO EXIT SE MI AS OF PRESS TIME WHICH
HAS BROUGHT ABOUT AN ABRUPT END TO THE RAIN SHOWERS THIS AFTERNOON.
A NOTABLE DRY SLOT HAS MOVED OVER THE STATE IN THE WAKE OF THIS
COLD FRONT QUICKLY SCOURING OUT THE CLOUD FIELD AS SUBSIDENCE BEHIND
THE FRONT HELPS BRING THIS AIRMASS DOWN. AN ALREADY GUSTY WIND FIELD
WILL HAVE AN OPPORTUNITY TO RAMP UP SLIGHTLY IN THIS WELL MIXED
LAYER. MODEL SOUNDINGS ADVERTISE MIXING DEPTHS TOWARD 850MB WHICH
TAPS INTO WINDS NEARS 30 KNOTS. THOUGH A FEW HOURS LATER THAN
EXPECTED...GUSTS INTO THE UPPER 20S /KNOTS/ HAVE BECOME MORE
CONSISTENT OVER THE WESTERN PART OF THE STATE AND WILL MAKE IT EAST
FOR A FEW HOURS BEFORE SUNSET HELPS REDUCE THESE HIGHER GUSTS. WINDS
WILL STILL REMAIN ELEVATE TONIGHT AT OR ABOVE 10 KNOTS.

FOR THE OVERNIGHT...MODELS ARE MIXED ON WHETHER TO REINTRODUCE A LOW
CLOUD DECK OR NOT. THINK WITH THE DEGREE OF DRY AIR AND SUBSIDENCE
WE SHOULD STAY MOSTLY CLEAR THROUGH THE NIGHT. A SECONDARY COLD
FRONT WILL DROP INTO NORTHERN MI BY MORNING WHICH SHOULD HELP SOME
CLOUDS START REAPPEARING BY MORNING OVER THE SAGINAW VALLEY. CAA
WILL CAUSE 850MB TEMPS TO FALL FROM 14C THIS MORNING...TO AROUND -2C
BY WEDNESDAY MORNING. THIS...IN COMBINATION WITH THE CLEARING SKIES
WILL HELP DROP TEMPS DOWN TO AROUND 40 EVEN WITH THE WINDS STAYING
ELEVATED.

LONG TERM...

SEASONABLY COOL AIRMASS INFILTRATING THE GREAT LAKES TODAY WILL BE
SOLIDLY IN PLACE TO START THE LONG TERM PERIOD ON WEDNESDAY MORNING.
COLD ADVECTION WILL HAVE ALREADY PEAKED BY SUNRISE, LEAVING SE
MICHIGAN UNDER THE INFLUENCE OF DEEP LAYER CYCLONIC FLOW IN THE
PRESENCE OF 850MB TEMPERATURES OF -2C TO 4C. DIURNAL HEATING AT THE
SURFACE WILL FAVOR RESPECTABLE BOUNDARY LAYER GROWTH TO AS HIGH AS
850MB, RESULTING IN GUSTY WINDS TO 20 KTS AND A SOLID COVERAGE OF
STRATOCU. IN ADDITION, THE WELL-MIXED WESTERLY FLOW CAN BE EXPECTED
TO ELICIT A RESPONSE OFF THE LAKES, BUT 0-1KM THETA-E LAPSE RATES
ARE MARGINAL AT BEST, SUPPORTING NOTHING MORE THAN A STRAY LAKE
SHOWER MAKING INTO THE WESTERN CWA DURING THE DAY. NOTHING WORTH
CARRYING A POP FOR. HIGHS WILL STRUGGLE INTO THE UPPER 40S TO AROUND
50 DEGREES.

SHORTWAVE RIDGING IN ADVANCE OF JET ENERGY CURRENTLY STREAMING
ONSHORE IN THE PACNW RACES ACROSS THE MIDDLE MS/OHIO VALLEYS WILL
SUPPORT WEAKLY ANTICYCLONIC FLOW THURSDAY NIGHT, SUPPORTIVE OF SOME
BREAKUP OF STRATOCUMULUS. THIS WILL IN TURN PROVIDE THE OPPORTUNITY
FOR OVERNIGHT LOWS TO FALL NEAR FREEZING. HOWEVER, THIS IS GENERALLY
THE SEASON TO TEMPER LOW TEMPERATURE EXPECTATIONS DUE TO STRATOCU
COVERAGE UNCERTAINTY. FOLLOWED THE LATEST SREF GUIDANCE WHICH
SUGGESTS 36-39 FOR MOST SPOTS.

AFOREMENTIONED PACNW SHORTWAVE WILL PROPAGATE SOUTH OF THE GREAT
LAKES ON THURSDAY. FORCING WILL BE MARGINAL AT BEST, CALLING INTO
QUESTION THE RATHER AGGRESSIVE NAM12 QPF DEPICTIONS THURS AFTERNOON
INTO THURSDAY NIGHT. CROSS-SECTION ANALYSIS REVEALS A STATICALLY
STABLE LAYER IN THE MID-LEVELS WHICH SUPPORTS A MUTED RESPONSE.
SUSPECT THE NAM IS OVERSIMULATING A RESPONSE TO MODEST LOW-LEVEL
INSTABILITY. FOLLOWED THE GLOBAL SUITE ATTM AND HELD OFF ON
MENTIONING POPS UNTIL THURSDAY NIGHT WHEN FORCING INCREASES AHEAD OF
THE MUCH MORE POTENT CANADIAN WAVE.

A MID LEVEL WAVE ORIGINATING FROM NORTHERN CANADA WILL PLUNGE DOWN
TOWARD THE GREAT LAKES ON FRIDAY. THIS SYSTEM WILL MEET SOME REMNANT
MOISTURE ALREADY IN PLACE FROM A PREVIOUS LOW. WIDESPREAD RAIN AND
THEN RAIN/SNOW MIX WILL SPREAD ACROSS THE AREA FOR HALLOWEEN. AS
WETBULB TEMPS DROP BELOW ZERO C AFTER 21-00Z...SOME LIGHT
ACCUMULATIONS MAY RESULT ON GRASSY AND ELEVATED SURFACES. WINDS WILL
REMAIN QUITE GUSTY DURING THE EVENT AS WELL. APPARENT TEMPS WILL BE
IN THE LOW 30S FRIDAY EVENING AND NEAR 20F SATURDAY MORNING. THE
REMAINDER OF THE EXTENDED PERIOD WILL BE MAINLY DRY WITH TEMPS WELL
BELOW NORMAL.

MARINE...

MODERATE TO FRESH SOUTHWEST WINDS WITH WIND GUSTS TO AROUND 30 KNOTS
WILL GRADUALLY VEER TO NORTHWESTERLY BY WEDNESDAY. UNTIL
THEN...SMALL CRAFT ADVISORIES REMAIN IN EFFECT FROM SAGINAW BAY TO
HARBOR BEACH. INCREASED INSTABILITY DUE TO COLD AIR WILL SUPPORT
WIND GUSTS TO NEAR-GALES. NORTHWEST WINDS WILL THEN SUBSIDE
WEDNESDAY NIGHT INTO THURSDAY BEFORE TURNING NORTHERLY AND RAMPING
UP AGAIN DURING THE DAY ON FRIDAY. GUSTS TO GALES WILL BE POSSIBLE
OVER CENTRAL LAKE HURON AND THE EXPOSED NEARSHORE WATERS OF THE
THUMB DURING THIS TIME WITH SIGNIFICANT WAVE HEIGHTS OF 4 TO 8 FEET
POSSIBLE OVER SOUTHERN LAKE HURON...INCLUDING NEARSHORE WATERS.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...SMALL CRAFT ADVISORY UNTIL 8 AM EDT WEDNESDAY FOR LHZ421-422-441.

LAKE ST CLAIR...NONE.

MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....BT
SHORT TERM...DRK
LONG TERM....JVC/MM
MARINE.......JVC


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