Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 311100
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
700 AM EDT FRI OCT 31 2014


.AVIATION...

//DISCUSSION...

VERY FEW ADJUSTMENTS NEEDED TO THE PREVIOUS FORECAST. MVFR
CONDITIONS ASSOCIATED WITH LIGHT PREFRONTAL RAINFALL HAVE OVERSPREAD
THE AREA THIS MORNING. SOUTHWESTERLY WINDS WILL SLOWLY VEER THROUGH
THE DAY UNTIL THE PASSAGE OF THE COLD FRONT THIS MORNING THROUGH
AFTERNOON. IN THE MEANTIME...MVFR CIGS AND PERHAPS A LIGHT FOG
RESTRICTION WILL HOLD BETWEEN THE PREFRONTAL RAIN AND THE COLD FRONT
ITSELF. HIGHER RAINFALL RATES AND A SHIFT TO NORTHERLY WINDS CAN
THEN BE EXPECTED WITH FROPA ALONG WITH DEVELOPING WIND GUSTS TO 30
KNOTS. THE FRONT WILL PASS KMBS AROUND 15Z AND KDTW AROUND 20Z. COLD
ADVECTION WILL KEEP THE BOUNDARY LAYER WELL MIXED THROUGH THE NIGHT
RESULTING IN PERSISTENCE OF BOTH LOW CLOUDS AND WIND GUSTS TO 25
KNOTS OR HIGHER. RAIN SHOWERS WILL MIX WITH AND POSSIBLY CHANGE OVER
TO SNOW AS COLD AIR INFILTRATES FROM NW TO SE THIS AFTERNOON INTO
THIS EVENING.


FOR DTW...WINDS WILL GRADUALLY VEER THROUGH THE DAY, BUT A MORE
CONCERTED TURN TO NORTHERLY WINDS CAN BE EXPECTED WITH COLD FRONTAL
PASSAGE AROUND 20Z. MIXING OF LINGERING RAIN SHOWERS WITH SNOW WILL
BE POSSIBLE AFTER 01Z. NO ACCUMULATION.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5KFT

* MEDIUM CONFIDENCE IN SNOW MIXING WITH RAIN AFTER 01Z.

&&

.PREV DISCUSSION...ISSUED 336 AM EDT FRI OCT 31 2014

SHORT TERM...TODAY AND TONIGHT

TROUGH EXTENDING FROM NORTHEAST CANADA INTO THE WESTERN GREAT
LAKES EARLY THIS MORNING WILL CONTINUE TO AMPLIFY AS A POTENT PV
ANOMALY EMBEDDED WITHIN AGGRESSIVELY DIGS TOWARD THE SOUTHERN
UNITED STATES TODAY. A WEAK 1012MB SURFACE LOW IS EVIDENT WITHIN
THE CORRIDOR OF STRONGEST HEIGHT FALLS OVER NORTHERN LAKE HURON,
BUT WITH THE BETTER DYNAMICS SHIFTING AWAY FROM THE GREAT LAKES
DURING THE FORECAST PERIOD, THE LOW WILL GRADUALLY WEAKEN AND
BECOME INCREASINGLY DISORGANIZED AS IT TRANSLATES ACROSS THE
ONTARIO PENINSULA THIS AFTERNOON.

AS OF 07Z, WIDESPREAD LIGHT SHOWERS WITH EMBEDDED MODERATE BANDING
ARE OBSERVED OVER WESTERN LOWER. THIS AREA OF RAIN IS ASSOCIATED
WITH INCREASING ISENTROPIC ASCENT IMMEDIATELY IN ADVANCE OF THE
DIGGING SHORTWAVE. THERE WILL BE PLENTY OF CONTINUED DYNAMIC SUPPORT
TO MAINTAIN THIS ACTIVITY AS THE PRE-FRONTAL CORRIDOR OF WARM
ADVECTION SHIFTS ACROSS SOUTHEAST MICHIGAN THIS MORNING.

A SECONDARY FOCUS OF PRECIPITATION WILL TAKE SHAPE OVER THE AREA
LATE THIS MORNING THROUGH ABOUT 22Z. THIS ACTIVITY WILL MAINLY BE
DRIVEN BY SFC-500MB LAYER FGEN ASSOCIATED WITH THE SYSTEM COLD
FRONT. UPSTREAM ACTIVITY OVER WISCONSIN AND THE UPPER PENINSULA IS
ALREADY EVIDENT THIS MORNING, BUT WITH MODEL PROGS INDICATING A
NOTEWORTHY TIGHTENING OF THE BAROCLINIC ZONE ALONG WITH ADDED
DAYTIME INSTABILITY, A SOLID INCREASE IN COVERAGE AND INTENSITY IS
EXPECTED, ESPECIALLY FOR FLINT AND POINTS SOUTHEAST, INCLUDING METRO
DETROIT.

IN ADDITION, A MODERATE WIND FIELD WILL BE IN PLACE AROUND THE
WEAKENING SURFACE LOW WHICH SHOULD SUPPORT WIDESPREAD SUSTAINED
WINDS OF 15 TO 20 KNOTS. DIURNAL INSTABILITY WILL SUPPORT GUSTS
INCREASING TO 25 KNOTS. AN ADDED COMPONENT OF SYSTEM RELATIVE
ISENTROPIC DESCENT ASSOCIATED WITH FROPA CENTERED WITHIN A COUPLE
HOURS EITHER SIDE OF 21Z WILL SUPPORT AN ENHANCED POP OF WIND THAT
MAY TOP OUT AS HIGH AS 35 KNOTS. THIS BAND OF ENHANCED GUSTINESS
WILL WORK SOUTHEAST FROM THE SAGINAW VALLEY AROUND 19Z TO DETROIT
METRO AROUND 23Z. IN GENERAL, HOWEVER, MARGINAL BOUNDARY LAYER
GROWTH, ONGOING PRECIP, UNIMPRESSIVE DYNAMIC SUPPORT, AND A
MARGINAL-AT-BEST SYSTEM RELATIVE SETUP PRECLUDE WIND ADVISORY
CONCERNS AT THIS TIME. THE EXCEPTION IS HURON COUNTY WHERE WINDS
COMING OFF OF LAKE HURON WILL SUPPORT GUSTS APPROACHING 40 KNOTS
ALONG THE SHORELINE. SIMILAR CONDITIONS ARE NOT OUT OF THE
QUESTION ALONG THE SOUTHERN/EASTERN SHORES OF INNER SAGINAW BAY,
BUT POTENTIAL REMAINS TOO MARGINAL TO WARRANT A SOUTHWESTWARD
EXTENSION OF THE WIND ADVISORY ATTM.

IN THE WAKE OF THE COLD FRONT, 0-1KM THETA-E LAPSE RATES OVER LAKE
HURON WILL FALL TO AROUND -6C, MODERATE VALUES, BUT IMPRESSIVE FOR
THIS TIME OF YEAR. THE THERMODYNAMIC ENVIRONMENT WILL BE SIMILAR TO
THAT OVER LAKE SUPERIOR EARLY THIS MORNING AND SHOULD YIELD AN
EQUALLY HEALTHY LAKE RESPONSE. AS A RESULT, CATEGORICAL POPS REMAIN
IN PLACE FOR THE APPROPRIATE AREAS THROUGH MOST OF THE NIGHT. AS
COLD AIR MAKES INROADS INTO THE AREA DURING THE AFTERNOON, AND
PARTICULARLY TOWARD SUNSET, A CHANGEOVER TO SNOW IS LIKELY,
ESPECIALLY THOSE AREAS WHERE BOUNDARY LAYER WET BULB TEMPERATURES
ARE FORECAST TO FALL BELOW 0C. WHILE ALL AREAS WILL BE SUBJECT TO AT
LEAST A FEW FLAKES OVERNIGHT, LOCATIONS DOWNSTREAM OF LAKE HURON MAY
SEE A FEW TENTHS OF ACCUMULATION IN SPITE OF THE ANTECEDENT WET
SURFACE. WARM ADVECTION OFF THE LAKE REMAINS A CONCERN, PARTICULARLY
OVER FAR EASTERN AREAS, WHERE LOWS MAY STRUGGLE TO FALL BELOW 35-37F
AND PTYPE WILL STRUGGLE TO CHANGE OVER. CONVERSELY, LOCATIONS WEST
OF US-23 WILL REMAIN REMOVED FROM THE LAKE PLUME AND THE COMBINATION
OF UPPER 20S LOWS AND A STOUT WIND FIELD WILL PRODUCE WIND CHILLS IN
THE UPPER TEENS BY SATURDAY MORNING.

LONG TERM...SATURDAY THROUGH THURSDAY

THE CORE OF COLDEST LOW LEVEL AIR /850MB TEMPS OF -7 TO -10C/ WILL
ROTATE ACROSS LOWER MI DURING THE DAY SATURDAY. LAKE EFFECT
PRECIPITATION IS EXPECTED TO BE ONGOING ACROSS THE SOUTHERN HALF OF
LAKE HURON SAT MORNING UNDER NORTHERLY FLOW. MODEL SOUNDINGS SUGGEST
LAKE INDUCED EQUILIBRIUM LEVELS EXCEEDING 1500 FT. EVEN WITH SOME
HEAT FLUX OFF THE LAKE...THE DEGREE OF COLD AIR /1000-850MB
THICKNESSES DROPPING BELOW 1290M/ SUGGESTS PRECIP WILL BE MAINLY IN
THE FORM OF SNOW. THERE IS SOME CONCERN THAT IF THE DEEP LAYER
SYNOPTIC MOISTURE IS A LITTLE SLOWER TO DEPART...THERE COULD BE SOME
ACCUMULATIONS ACROSS THE EASTERN THUMB. THIS WILL BE SOMETHING FOR
LATER SHIFTS TO MONITOR. LIGHTER INTENSITY SNOW SHOWERS AND/OR
FLURRIES ARE CERTAINLY POSSIBLE FARTHER INLAND. AN AGGRESSIVE PUSH OF
DRY AIR...BACKING LOW LEVEL FLOW AND LOWER INVERSION BASES DUE TO
STRENGTHENING LARGE SCALE SUBSIDENCE WILL NOT ONLY END THE LAKE
EFFECT BUT WILL SUPPORT A CLEARING TREND FROM WEST TO EAST DURING
THE AFTERNOON AND EVENING. SAT HIGHS WILL LIKELY FALL SHORT OF 40
DEGREES OVER MUCH OF THE AREA GIVEN THE DEGREE OF COLD AIR. ENOUGH
DECOUPLING IN THE BOUNDARY LAYER WITH SFC HIGH PRESSURE BUILDING IN
FROM THE WEST SAT NIGHT WILL DROP LOWS WELL DOWN INTO THE 20S.

ALTHOUGH AMPLIFIED...THE LARGE SCALE PATTERN WILL REMAIN PROGRESSIVE
WITH MID LEVEL RIDGING EXPANDING ACROSS THE GREAT LAKES BY THE
END OF THE WEEKEND. THIS AND THE DEPARTURE OF THE SFC HIGH TO THE
EAST WILL ESTABLISH A WARM AIR ADVECTION REGIME ACROSS LOWER
MI...LEADING TO A MODEST WARMING TREND HEADING INTO EARLY NEXT
WEEK. MOIST ADVECTION WILL THEN INCREASE MON NIGHT INTO TUES IN
ADVANCE OF A LONG WAVE TROUGH...SUPPORTING THE NEXT CHANCE FOR
PRECIP /WARM ENOUGH FOR ALL RAIN WITH THIS SYSTEM/. THE MEDIUM
RANGE MODEL SUITE SUGGEST THE NORTHERN STREAM WILL REMAIN
PROGRESSIVE THROUGH NEXT WEEK...WITH THE NEXT MID LEVEL WAVE AND
SHOT AT SOME COLDER AIR ARRIVING LATE IN THE FORECAST PERIOD.

MARINE...GALE WARNINGS REMAIN IN EFFECT FOR ALL MARINE AREAS TODAY
INTO TONIGHT. A PUSH OF ARCTIC AIR WILL CONTINUE TO FUNNEL INTO THE
REGION BEHIND A COLD FRONT ASSOCIATED WITH A LOW PRESSURE SYSTEM
FORECAST TO MOVE FROM NORTHERN LAKE HURON THIS MORNING INTO THE
UPPER OHIO VALLEY BY EVENING. HIGH PRESSURE NUDGING INTO THE WESTERN
GREAT LAKES FROM THE PLAINS WILL SUSTAIN A TIGHT PRESSURE GRADIENT
ALONG THE BACK SIDE OF THE DEPARTING LOW. THIS COMBINED WITH THE
HIGHLY UNSTABLE CONDITIONS OVER THE MARINE AREAS WILL SUPPORT GALE
FORCE WINDS DEVELOPING OVER NORTHERN LAKE HURON THIS MORNING AND THE
SOUTHERN HALF OF THE LAKE BY AFTERNOON. WINDS AND WAVES WILL SLOWLY
DECREASE SATURDAY INTO SATURDAY NIGHT AS HIGH PRESSURE BUILDS IN
FROM THE WEST.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY FROM 2 PM THIS AFTERNOON TO 10 PM EDT THIS EVENING
     FOR MIZ049.

LAKE HURON...GALE WARNING FROM 1 PM THIS AFTERNOON TO NOON EDT SATURDAY FOR
     LHZ363-441-462>464.

     GALE WARNING FROM 2 PM THIS AFTERNOON TO NOON EDT SATURDAY FOR
     LHZ442-443.

     GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR LHZ361.

     GALE WARNING UNTIL 2 AM EDT SATURDAY FOR LHZ362.

     GALE WARNING FROM 1 PM THIS AFTERNOON TO 5 AM EDT SATURDAY FOR
     LHZ421-422.

LAKE ST CLAIR...GALE WARNING FROM 6 PM THIS EVENING TO 10 AM EDT SATURDAY FOR
     LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING FROM 6 PM THIS EVENING TO 10 AM EDT SATURDAY FOR
     LEZ444.

&&

$$

AVIATION.....JVC
SHORT TERM...JVC
LONG TERM....SC
MARINE.......SC


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



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