Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241121
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
621 AM EST WED DEC 24 2014


.AVIATION...

RAIN WILL PIVOT NORTH OF THE AREA AGAIN THIS MORNING WITH FOG AND
OCCASIONAL DRIZZLE SETTLING IN THROUGH MIDDAY OR SO. SHOWERS WILL
INCREASE QUICKLY THIS AFTERNOON INTO THIS EVENING AS LOW PRESSURE
ENCROACHES ON AND THEN MOVES OVER/JUST EAST OF THE TERMINALS. AS
COLDER AIR IS PULLED INTO THIS PASSING SYSTEM...RAIN WILL MIX WITH
AND CHANGE TO SNOW 02Z-06Z...MAINLY MBS...BUT ALSO FNT/PTK AND
PERHAPS YIP/DTW/DET BY END OF THE FORECAST. THIS LOW WILL ALSO BRING
VERY GUSTS WEST TO SOUTHWEST WINDS...CENTERED FROM MID EVENING INTO
THE EARLY MORNING WITH GUSTS OF 35 KNOTS FOR A NUMBER OF HOURS AFTER
THE PASSAGE OF THE LOW. CIGS WILL GENERALLY BOUNCE FROM IFR TO MVFR
WITH VSBYS DOING MUCH THE SAME.

FOR DTW...IFR/LIFR CIGS/VSBYS THIS MORNING WITH FOG AND SOME -DZ.
RATHER STEADY RAIN WILL INCREASE 18Z-20Z AND PERSIST TO 00-02Z
BEFORE BECOMING MORE SHOWERY IN NATURE. LEFTOVER PRECIP WILL MIX
WITH SNOW AFTER 06Z. SOUTHWEST WIND GUSTS TO 35 KNOTS EXPECTED BY
00Z-02Z...THEN DIMINISHING TO 25 KNOTS OVERNIGHT.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS AOB 5000 FEET THROUGHOUT THE TAF PERIOD.

* MEDIUM IN VSBYS AOB 1/2 SM AND CEILINGS AOB 200 FEET THROUGH 18Z.

* MEDIUM TO HIGH FOR WIND GUSTS TO REACH 30 KNOTS FROM 250
  DEGREES...BETWEEN 01Z-05Z.

&&

.PREV DISCUSSION...ISSUED 425 AM EST WED DEC 24 2014

SHORT TERM...TODAY AND TONIGHT

FIRST THINGS FIRST...THE CURRENT DENSE FOG ADVISORY WILL NEED TO BE
GRADUALLY ADJUSTED EARLY THIS MORNING AS AN INCREASE IN THE COVERAGE
OF SHOWERS LEADS TO A TRANSITION AWAY FROM THE CURRENT WIDESPREAD
ONE QUARTER TO ONE HALF MILE VISIBILITY TO SOMETHING CLOSER TO ONE
OR TWO MILES WITH PATCHY DENSE FOG IN THE ONE QUARTER TO ONE HALF
MILE RANGE BY DAYBREAK. GIVEN TRENDS AS OF 4 AM...WILL CANCEL THE
DENSE FOG ADVISORY AS MOST LOCATIONS ARE NOW AOA 1SM WITH LOWEST
VISIBILITIES OF 1/2 TO 3/4 MILE FROM THE THUMB TO SAGINAW VALLEY.

OTHERWISE...A VERY BUSY PERIOD OF WEATHER IS EXPECTED THROUGH
TONIGHT AS RAPIDLY DEEPENING LOW PRESSURE LIFTS JUST EAST OF DUE
NORTH FROM ITS CURRENT POSITION IN WEST CENTRAL TENNESSEE TO FAR
SOUTHEAST LOWER MICHIGAN THIS AFTERNOON AND ON THROUGH LAKE HURON
TONIGHT. BASED ON AN AVERAGE OF THE 00Z MODEL RUNS...THE CURRENT
LOW PRESSURE OF 1002 MB WILL DEEPEN TO 985 MB AS IT CROSSES
SOUTHEAST MICHIGAN. EVENTUALLY...THIS LOW WILL FALL THROUGH THE
980 MB LEVEL WHILE CROSSING LAKE HURON DURING THE EVENING ON ITS
WAY TO NEAR 960 MBS EAST OF HUDSON BAY UPON REACH FULL MATURITY.

WHILE THE MODEL SPREAD ON THE TRACK OF THIS SYSTEM HAS TIGHTENED
CONSIDERABLY IN THE PAST 24 HOURS...THERE REMAINS ENOUGH OF A
DIFFERENCE TO MAKE A FINAL CALL ON HIGH WIND ADVISORY -VS- WARNING
HEADLINES SOMEWHAT DIFFICULT. IN GENERAL...IT APPEARS THE BEST SURGE
OF SOUTH TO SOUTHWEST FLOW ON THE EAST SIDE OF THIS LOW WILL SHIFT
UP THROUGH THE EASTERN LAKES REGION AND BYPASS THE CWA BY A HAIR.

GIVEN THE FACT THAT THE ECMWF AND CANADIAN GEM...DESPITE HAVING HAD
SOME DIFFICULTY...HAVE BEEN THE MOST CONSISTENT MODELS WITH THE
FORECASTED TRACK OF THIS SYSTEM DURING THE PAST SEVERAL DAYS...WILL
LEAN TOWARD THE CURRENT TRACK RIGHT ALONG THE EASTERN EDGE OF THE
CWA...WHICH IS A BIT FURTHER EAST THAN THE REST OF THE MODELS. THIS
WILL LIMIT THE POTENTIAL FOR WIND GUSTS REACHING WARNING CRITERION
AS WIND GUSTS SHOULD GENERALLY REMAIN IN THE SUB 50 MPH RANGE DURING
THE PEAK PERIOD FROM 00Z-06Z. WITH THE TRACK OVER/JUST EAST OF AREA
LATE AFTERNOON AND EARLY EVENING...THERE WILL MOST LIKELY BE A LULL
IN THE WIND FIELDS BEFORE STRONGER SOUTHWEST FLOW WRAPS IN BEHIND
THE LOW PASSAGE. WILL ISSUE A WIND ADVISORY FOR A PORTION OF THE
AREA...MAINLY FOR THIS EVENING AS STRONGEST WINDS WILL BE DELAYED
SLIGHTLY BY THIS "LULL" WITHIN/NEAR THE LOW PRESSURE CENTER AS IT
PASSES. WILL LEAVE THE SAGINAW VALLEY OUT...AND MAY TRIM OUT A FEW
MORE COUNTIES ON THE WESTERN EDGE OF CWA THAT ARE IN CURRENT WATCH
GIVEN A SLIGHTLY MORE EASTWARD TRACK OF THE LOW.

THIS TRACK ALONG/EAST OF EASTERN CWA WILL ALSO OPEN THE DOOR FOR A
SLIGHTLY QUICKER CHANGEOVER TO SNOW...PARTICULARLY OVER THE SAGINAW
VALLEY. IT APPEARS THE CURRENT FORECAST OF AROUND AN INCH OF SNOW
HAS THIS IN HAND PRETTY WELL AS THE CHANGEOVER WILL STILL OCCUR AS
THE HEAVIEST DEFORMATION PRECIPITATION IS LIFTING NORTH OF THE CWA.
WILL ADJUST TIMING OF CHANGEOVER SLIGHTLY AS WELL AS LOWERING THE
OVERALL TEMPERATURE FORECAST THROUGH THE NORTHWEST HALF THE THE CWA
AS MILDEST AIR REMAINS SOUTHEAST OF AREA DURING THE DAY. THIS WILL
LEAD TO A RATHER TIGHT TEMPERATURE GRADIENT FOR HIGHS TODAY FROM
AROUND 40F WESTERN SAGINAW VALLEY TO MID 50S FAR SOUTHEAST CWA.

LONG TERM...

THE DEEP LOW PRESSURE SYSTEM WILL HAVE BEEN PRETTY MUCH EXITED THE
REGION COME CHRISTMAS DAY...WITH ANY LINGER LOW LEVEL CYCLONIC FLOW
QUICKLY BECOMING ANTI-CYCLONIC AS THE DAY WEARS ON. HOWEVER...WITH
THE STRENGTHENING SUBSIDENCE INVERSION...LOW LEVEL MOISTURE/CLOUDS
WILL LIKELY BECOME TRAPPED. LOW LEVEL LAPSE RATES ARE STEEP DURING
THE MORNING HOURS...GENERATING A BIT OF CAPE TO SUPPORT SLIGHT
CHANCE OF SPRINKLES/VERY LIGHT RAIN/SNOW SHOWERS (ALTHOUGH THE
NAM/GFS SOUNDINGS SHOW NO ICE NUCLEI TO SUPPORT SNOW). SURFACE TEMPS
SHOULD BE JUST ON THE POSITIVE SIDE OF FREEZING...BUT NOT TOTALLY
OUT OF THE QUESTION FOR A TOUCH OF FREEZING DRIZZLE 12-14Z.

WARM ADVECTION THURSDAY NIGHT WILL ONLY SERVE TO STRENGTHEN THE LOW
LEVEL INVERSION BETWEEN 1500-2000 KFT...AND ASSUMING THE CLOUDS HAVE
NOT MIXED OUT BY DAY`S END...SHOULD REMAIN LOCKED IN THROUGH THE
NIGHT...AS CLEARLY SUPPORTED BY NAM SOUNDINGS. HOWEVER...PARALLEL
GFS LOWERS THE INVERSION HEIGHT TO 1000 FEET AND ALLOWS FOR
CLEARING. HAVE LEANED TOWARD THE CLOUDIER SOLUTION...ESPECIALLY
NORTH.

ANOTHER POWERFUL STORM SYSTEM ALONG THE BRITISH COLUMBIA COAST EARLY
THIS MORNING WITH UPPER LEVEL ENERGY AT THE BASE OF THE TROUGH
HEADED TOWARD THE NORTHERN CALIFORNIA COAST LATER TODAY AND INTO THE
FOUR CORNERS REGION ON THURSDAY. THE SPLITTING OF UPPER LEVEL
ENERGY/FLOW IS EXPECTED TO LEAD TO A RATHER TAME FRONTAL PASSAGE ON
SATURDAY...WITH ENOUGH WARM AIR (925 MB TEMPS OF 4 C) IN PLACE TO
JUST SUPPORT A CHANCE OF RAIN SHOWERS AS FRONT MOVES THROUGH.
HOWEVER...THE EURO/CANADIAN SOLUTIONS DO SHOW A RIPPLE RIDING ALONG
THE FRONT...SLIDING THROUGH THE AREA SATURDAY EVENING...WHICH WOULD
BE ABLE TO PROLONG SHOWERS AND SUPPORT A CHANGEOVER TO SNOW SATURDAY
NIGHT...BUT THAT REMAINS TO BE SEEN.

PER 00Z EURO...TURNING MUCH COLDER AS WE END THE YEAR...AS IT
APPEARS ARCTIC AIR (SUB 500 DAM 1000-500 MB THICKNESS) WILL FINALLY
SPILL BACK INTO THE CONUS...SLIDING INTO THE ROCKIES/PLAINS AT
FIRST...AND THEN SPREADING EAST NEXT WEEK.

MARINE...

RAPIDLY DEEPENING LOW PRESSURE WILL TRACK UP FROM THE SOUTH TODAY
..BRINGING WITH IT RAIN AND POSSIBLE THUNDERSTORMS. AS THE INTENSE
LOW TRACKS THROUGH LAKE HURON LATE THIS EVENING....GALE FORCE WINDS
ARE EXPECTED TO RAMP WITH GOOD COLD ADVECTION INTO EARLY THURSDAY
MORNING. CONFIDENCE IN GALES OVER THE OPEN WATERS OF LAKE HURON IS
HIGH...AS FEW STRAY GUSTS TO STORM FORCE ARE NOT OUT OF THE
QUESTION. GALE WARNINGS HAVE BEEN ISSUED. A LITTLE CONCERNED ACROSS
LAKE ST CLAIR AND LAKE ERIE...AS THE DURATION OF GALES LOOKS TO BE
SHORT. BECAUSE OF THIS SHORT WINDOW OF GALES...WATER LEVELS ARE ALSO
NOT EXPECTED TO DROP BELOW THE CRITICAL MARK FOR SAFE NAVIGATION.

WINDS WILL DIMINISH DURING THURSDAY AS A RIDGE OF HIGH
PRESSURE BUILDS INTO THE AREA THROUGH THE DAY...WITH LIGHT TO
MODERATE SOUTHWEST WINDS IN STORE FOR FRIDAY AHEAD OF A COLD FRONT
PASSING THROUGH ON SATURDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY FROM 9 PM THIS EVENING TO 5 AM EST THURSDAY FOR
     MIZ049-054-055-062-063.

     WIND ADVISORY FROM 7 PM THIS EVENING TO 3 AM EST THURSDAY FOR
     MIZ069-070-075-076-082-083.

LAKE HURON...GALE WARNING FROM 7 PM THIS EVENING TO 11 AM EST THURSDAY FOR
     LHZ363-421-441>443-462>464.

     GALE WARNING FROM 7 PM THIS EVENING TO 5 AM EST THURSDAY FOR LHZ422.

     GALE WARNING FROM 11 PM THIS EVENING TO 11 AM EST THURSDAY FOR
     LHZ361-362.

LAKE ST CLAIR...GALE WARNING FROM 6 PM THIS EVENING TO 4 AM EST THURSDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING FROM 6 PM THIS EVENING TO 4 AM EST THURSDAY FOR LEZ444.

&&

$$

AVIATION.....DG
SHORT TERM...DG
LONG TERM....SF
MARINE.......SF


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


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