Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171729
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1229 PM EST WED DEC 17 2014


.AVIATION...

//DISCUSSION...MOISTURE WILL REMAIN LOCKED UNDER AN INVERSION
THIS AFTERNOON...RESULTING IN OVERCAST SKIES THAT GRADUALLY RISE
FROM MVFR TO VFR DURING THE LATE AFTERNOON AND EVENING AS THE
MIXED LAYER INCREASES IN DEPTH AND SOME DRIER AIR TRIES TO WORK
IN. TIMING OF WHEN CEILINGS WILL RISE ABOVE 3000 FEET IS UNCERTAIN
HOWEVER...AS FLOW OFF LAKE MICHIGAN ADDS SOME ADDITIONAL LOW-LEVEL
MOISTURE. THE BEST CHANCE FOR FLURRIES OR LIGHT SNOW SHOWERS WILL
BE NORTH OF DET. AS FLOW TURNS MORE NORTHWESTERLY TONIGHT AND LAKE
EFFECT BECOMES LESS FAVORABLE...A FEW BREAKS IN THE CLOUDS ARE
EXPECTED. CEILINGS SHOULD THEN LOWER BACK TO MVFR AFTER MIDNIGHT
AS INVERSION HEIGHTS LOWER AND A SURFACE TROUGH DROPS DOWN FROM
NORTHERN MICHIGAN.

WESTERLY GUSTS TO AROUND 25 KNOTS WILL GRADUALLY TAPER OFF DURING
THE LATE AFTERNOON AND EVENING AS LOW PRESSURE OVER SOUTHERN ONTARIO
AND QUEBEC CONTINUES TO MOVE AWAY FROM THE AREA...WEAKENING THE
SURFACE PRESSURE GRADIENT.

FOR DTW...WESTERLY GUSTS BETWEEN 20 AND 25 KNOTS WILL CONTINUE
THROUGH THE AFTERNOON BEFORE SUBSIDING IN THE EVENING. A FEW STRAY
SNOWFLAKES ARE STILL POSSIBLE TODAY...BUT SHOWERS ARE EXPECTED TO
REMAIN NORTH OF DTW. CEILINGS ARE EXPECTED TO RISE TO VFR FOR THE
EVENING BEFORE DROPPING BACK DOWN TO MVFR AFTER MIDNIGHT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FEET THROUGH THE TAF PERIOD.

&&

.PREV DISCUSSION...ISSUED 350 AM EST WED DEC 17 2014

SHORT TERM... TODAY AND TONIGHT

AFTER 3 DAYS OF MAX TEMPERATURES IN THE 40S AND LOWER 50S...NORMAL
DECEMBER AIR IS SURGING BACK INTO SE MICHIGAN FOR TODAY. THIS WILL
LIMIT HIGH TEMPERATURES TO THE LOWER AND MID 30S LEADING INTO LOWS
TONIGHT IN THE MID 20S. LIGHT SNOW WILL LINGER NEAR THE TRI CITIES
AND NORTHERN THUMB...MAINLY DURING THE MORNING...WITH LITTLE MORE
THAN A FLURRY OVER THE REST OF SE MICHIGAN.

LIGHT SNOW ONGOING OVER THE SAGINAW VALLEY AND NORTHERN THUMB BEFORE
SUNRISE IS TIED TO AN AXIS OF DEFORMATION IN THE LOW TO MID LEVELS.
THIS FORCING WILL CONTINUE TO SHEAR INTO MORE OF A WEST TO EAST
ORIENTATION DURING THE MORNING WITH THE STRONGEST DYNAMIC FORCING
DISPLACED FROM THE MOISTURE AXIS. THIS WILL MAINTAIN STEADY BUT
LIGHT PRECIPITATION OVER THE NORTHERN GREAT LAKES AND LEAVE THE TRI
CITIES AND NORTHERN THUMB ON THE SOUTHERN FRINGE OF THE PATTERN. AT
THE SAME TIME...DRY AIR WILL CONTINUE TO SLIDE OVER THE REST OF SE
MICHIGAN AS STRONG SUBSIDENCE OCCURS BETWEEN THE DEFORMATION AXIS
ASSOCIATED WITH THE TRAILING UPPER TROUGH AND NORTH FLANK OF THE
UPPER JET AXIS THAT IS CENTERED WELL SOUTH OF THE GREAT LAKES. THIS
WILL ONLY ALLOW WEAK LAKE MICHIGAN ACTIVATION WHICH WILL STRUGGLE TO
MOVE THIS FAR EAST IN ANY FORM GREATER THAN FLURRIES WHILE THE LOW
LEVEL THERMAL TROUGH IS OVERHEAD.

THE UPPER TROUGH WILL SLIDE QUICKLY EASTWARD BY TONIGHT AND LEAVE
TRAILING CYCLONIC OVERHEAD THAT WILL ALLOW A MODEST UPTICK IN
ACTIVITY OFF LAKE MICHIGAN AND HURON EARLY BEFORE WARMER AIR BEGINS
TO MOVE OVER THE SOUTHERN GREAT LAKES. THERE IS GOOD MODEL AGREEMENT
INDICATING 850 MB TEMPERATURE WARMING FROM NEAR -13C AT MID
AFTERNOON TO THE -8C TO -6C RANGE AFTER MIDNIGHT. BOTH THIS AND THE
GENERAL VEERING OF THE LOW LEVEL FLOW WILL KEEP LAKE EFFECT SNOW
SHOWERS OVER SW LOWER AND NORTHERN INDIANA AND PERHAPS JUST BRUSHING
THE NORTHERN THUMB TONIGHT.

LONG TERM...THURSDAY THROUGH TUESDAY

THE ONLY REAL CONCERN ON THURSDAY WILL BE THE LAKE EFFECT SNOW
SHOWERS BRUSHING THE EASTERN THUMB WITH A NORTH NORTHWEST FLOW OFF
LAKE HURON. WHILE THIS TRAJECTORY IS FAVORABLE FOR SNOWFALL OVER
CANADA...THERE APPEARS TO BE ENOUGH OF A FAVORABLE COMPONENT TO THE
WIND DIRECTION TO MAINTAIN THE CHANCY POPS INHERITED BY THE PREVIOUS
FORECAST. WITH THE MOSTLY UNFAVORABLE TRAJECTORY SNOWFALL
AMOUNTS...IF THERE ARE ANY...WILL BE FAIRLY LIGHT WITH A FEW TENTHS
OF AN INCH POSSIBLE.  HIGH PRESSURE THEN BUILDS IN ACROSS THE GREAT
LAKES REGION ON FRIDAY AS THE MOS GUIDANCE SUGGESTS CLEARING SKIES
LATE THURSDAY NIGHT AND INTO FRIDAY. HOWEVER MODEL SOUNDINGS
INDICATE SUBSIDENCE FROM THE HIGH WILL ONCE AGAIN TRAP MOISTURE
BETWEEN 900 AND 950 MB WHICH WILL MEAN LOW STRATUS WILL ONCE AGAIN
PLAGUE THE CENTRAL GREAT LAKES REGION.  THEREFORE BACKED OFF ON THE
CLEARING SKIES DURING THIS PERIOD AND WENT MORE PESSIMISTIC THAN THE
PREVIOUS FORECAST.

THIS HIGH WILL KEEP THE CENTRAL GREAT LAKES DRY DURING THE WEEKEND
AS A LOW PRESSURE SYSTEM TRACKS THROUGH THE SOUTHEASTERN CONUS.
ALTHOUGH THE SUPER BLEND PAINTS CHANCY POPS ACROSS MUCH OF THE
CWA...MAINLY SATURDAY AND SATURDAY NIGHT...THE NWP MODELS KEEP
THINGS DRY WITH THE AFOREMENTIONED DRY HIGH PRESSURE IN PLACE.
GIVEN THE WET BIAS OF THE SUPER BLEND WILL REMOVE POPS DURING THE
WEEKEND AND GO WITH A DRY FORECAST.  NEAR NORMAL TEMPERATURES ARE
EXPECTED DURING THIS TIME WITH HIGHS IN THE LOW TO MID 30S AND LOWS
IN THE MIDDLE TO UPPER 20S.

THE NEXT SYSTEM OF CONSEQUENCE DEVELOPS OVER THE NORTHERN PLAINS ON
MONDAY AND TRACKS OVER THE WESTERN GREAT LAKES ON TUESDAY.  THIS
SYSTEM LOOKS TO HAVE FAIRLY GOOD DYNAMICS WITH A DEEP 500 MB TROUGH
AND A DECENT LOW LEVEL JET.  IT LOOKS LIKE SOUTHEAST MICHIGAN WILL
BE ON THE WARM SIDE OF THIS SYSTEM ON TUESDAY...WITH MAINLY LIQUID
PRECIPITATION EXPECTED AT THIS POINT IN THE FORECAST.

MARINE...

COLD AIR ADVECTION AND STRONG WESTERLY WINDS ARE INCREASING IN THE
WAKE OF A COLD FRONT THAT PASSED THROUGH THE CENTRAL GREAT LAKES
EARLY THIS MORNING. MIXING DEPTHS UP TO AROUND 900MB WILL TAP INTO
THE STRONGEST FLOW WHICH IS ONLY FORECAST TO BE AROUND 35 KNOTS AT
THAT LEVEL. IT SHOULD NOT TAKE TOO MUCH TO BRING SOME HIGHER GUSTS
DOWN THOUGH WITH SUSTAINED FLOW PUSHING 20 KNOTS. WILL CONTINUE
SMALL CRAFT ADVISORIES FOR ALL NEARSHORE ZONES FOR THESE ELEVATED
WINDS. WAVES WILL ALSO REACH CRITERIA IN SOME OF THE LAKE HURON
ZONES BUT OFFSHORE FLOW WILL KEEP WAVE HEIGHTS DOWN SOMEWHAT ALONG
WITH SOME ICE COVER SHOWING UP IN INNER SAGINAW BAY. WINDS WILL
DECREASE BELOW CRITERIA THIS AFTERNOON BUT WILL STAY ELEVATED
THROUGH TONIGHT AS THEY VEER TO THE NORTHWEST. ALTHOUGH WINDS WILL
FALL BELOW CRITERIA...THE CONTINUED FETCH OFF LAKE HURON WITH THE
NORTHWEST WINDS WILL MAINTAIN HIGHER WAVES THROUGH TONIGHT ACROSS
OUTER SAGINAW BAY AND LAKE HURON FROM PORT AUSTIN TO HARBOR BEACH.
WINDS AND WAVES WILL CONTINUE TO SLOWLY CALM AS HIGH PRESSURE
BUILDS IN ACROSS THE CENTRAL GREAT LAKES THURSDAY AND FRIDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LHZ422-442-
     443.

     SMALL CRAFT ADVISORY UNTIL 4 AM EST THURSDAY FOR LHZ421-441.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LEZ444.

&&

$$

AVIATION.....HLO
SHORT TERM...BT
LONG TERM....KURIMSKI
MARINE.......KURIMSKI


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



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