Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 152301
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
601 PM EST MON DEC 15 2014


.AVIATION...

//DISCUSSION...

THETA-E RIDGE WILL PIVOT INTO AREA LATER THIS EVENING INTO THE
OVERNIGHT AND PROVIDE PERIODIC SHOWERS AND A GENERAL INCREASE IN
MOISTURE AS LOW CLOUDS/FOG ALSO RETURN WITH IFR TO OCCASIONAL LIFR
CONDITIONS. THESE CONDITIONS WILL PERSIST INTO TUESDAY MORNING AS
LOW PRESSURE CROSSES THE AREA AND THEN SLOWLY IMPROVE AS THIS LOW
TRACKS TO THE EAST AND NORTHEAST OF THE AREA AND FLOW VEERS FROM
SOUTHEAST TO SOUTHWEST LATE IN THE FORECAST PERIOD.

FOR DTW...A PERIOD OF VFR CONDITIONS CAN BE EXPECTED TO START THE
FORECAST...BUT MVFR CIGS RETURN AFTER 02Z-04Z AND IFR CIGS ARE
LIKELY OVERNIGHT INTO TUESDAY MORNING. VSBYS WILL ALSO FALL BACK
INTO THE 1-3SM RANGE IN -SHRA AND BR...BUT IMPROVE FROM TUESDAY
AFTERNOON INTO THE EVENING AS LOW PRESSURE PASSES EAST OF THE AREA.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET AFTER 02Z-04Z THIS
  EVENING ON THROUGH TUESDAY.

* HIGH CONFIDENCE IN PRECIPITATION TYPE FALLING AS RAIN.

&&

.PREV DISCUSSION...ISSUED 325 PM EST MON DEC 15 2014

SHORT TERM...TONIGHT

MATURE UPPER LEVEL LOW CENTERED OVER NORTHERN MISSOURI/SOUTHERN IOWA
THIS AFTERNOON....AND THE SYSTEM IS UNRAVELING AS IT BEGINS TO
INTERACT WITH NORTHERN STREAM TROUGH DROPPING INTO NORTH DAKOTA.
WELL DEFINED 850-700 MB THETA-E RIDGE WILL BE ARRIVING TOWARD
MIDNIGHT...AND SLOWLY WORKING THROUGH SOUTHEAST MICHIGAN OVERNIGHT
SUPPORTING SHOWERS WITH LOW LEVEL ISENTROPIC ASCENT AND TROWAL
STRUCTURE. CONFIDENCE IS CERTAINTY NOT 100 PERCENT BASED ON
UPSTREAM RADARS REVEALING A BROKEN LINE OF SHOWERS AT THE
MOMENT...COUPLED WITH THE GOOD AMOUNT OF DRY AIR (850-700 MB)
WORKING INTO SOUTHEAST MICHIGAN THROUGH EARLY THIS EVENING...AS
SKIES HAVE CLEARED OUT TOWARD THE OHIO BORDER.

THE 12Z EURO SHOWS 500 MB COLD POOL (-25 C) REACHING FAR SOUTHERN
LAKE MICHIGAN 12Z TUESDAY...WITH GOOD HEIGHT FALLS/500 MB TEMPS DROP
6-12Z TUESDAY OVER THE CWA...WITH MEAN RH (1000-500 MB) BETWEEN 85
AND 95 PERCENT RANGE...AND ENOUGH EVIDENCE TO MAINTAIN THE
INHERITED HIGHER POPS (80S) OVERNIGHT...BUT CONCERNED POPS ARE A
BIT HIGH. WILL HOLD MINS IN THE LOWER 40S...BUT IF CLEARING TREND
CONTINUES NORTH AND HOLDS A BIT PAST SUNSET...A DIP INTO THE UPPER
30S IS POSSIBLE...ESPECIALLY THUMB REGION.

LONG TERM...TUESDAY THROUGH SUNDAY

VERTICALLY STACKED LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL
CONTINUE ITS TREK NORTHEAST TOWARD THE GREAT LAKES. IR/WV SATELLITE
IMAGERY SHOWS A DECENT MOISTURE INFLUX BEING ADDED FROM THE GOM THAT
IS BEING WRAPPED INTO THIS SYSTEM. DESPITE THE SYSTEM CONTAINING
HIGH MOISTURE /OAX AND DVN 12Z RAOBS NEAR .75 PWAT/...THE RADAR
COMPOSITE IS QUITE SPOTTY. EXPECTING LIGHT RAIN FROM THIS EVENT TO
BE ONGOING EARLY TUESDAY AND LIKELY CONTINUE UNTIL NOON AS THE 500
MB TROUGH AXIS SWINGS THROUGH. THE OVERALL WEAKENING OF THE SYSTEM
AND CURRENT DIFFUSE RADAR RETURNS JUSTIFY POPS UNDER 100 AND LOW QPF
AMOUNTS OF .1 TO .2 INCHES.  AFTER 18Z MOST PRECIP WILL BE CONTAINED
IN THE NORTHERN HALF OF THE CWA AS THE NORTHERN FLANK SURFACE TROUGH
PIVOTS THROUGH.

AN INTERESTING INTERACTION ALOFT WILL THEN TAKE PLACE AS A SEPARATE
CLOSED 500 MB LOW FROM NORTHERN MINNESOTA WILL MERGE WITH THE FIRST
SYSTEM. THE TIMING OF THIS WILL BE COINCIDENT WITH THE STRONGEST H85
COLD TEMPERATURE ADVECTION...CAUSING WIND SPEEDS TO RAMP UP INTO THE
20-30 MPH RANGE TUESDAY NIGHT AND PTYPE TO CHANGE TO SNOW. THE
LINGERING QPF AMOUNTS ARE QUITE LOW...SO ACCUMULATING SNOW WILL BE
CONFINED TO A HALF INCH OR LESS IN THE SAGINAW VALLEY TO THUMB
REGION. WITH THE INTRODUCTION OF COLD AIR ALOFT...LAKE MICHIGAN WILL
ACTIVATE AGAIN. THIS SHOULD BRING STREAMING BANDS OF LAKE EFFECT
SNOW OR FLURRIES TO THE WESTERN CWA. NORTHWEST FLOW MAY BACK
SLIGHTLY TO BECOME WNW. THIS CHANGE IN FLOW SUPPORTS A WIDESPREAD
FLURRY MORESO THAN A FUNNELED BAND OF HEAVIER SNOW.

WEATHER CONCERNS MINIMAL FOR THE REMAINDER OF THE FORECAST PERIOD.
ACTIVE SOUTHERN STREAM JET STAYS TO OUR SOUTH WHILE THE REAL COLD
AIR REMAINS LOCKED AT THE POLES. RESULT WILL BE A RATHER PERSISTENT
PATTERN WITH SURFACE HIGH PRESSURE IN PLACE AND TEMPERATURES NEAR
SEASONAL NORMALS. LAST SEVERAL GLOBAL NWP RUNS AND GEFS ENSEMBLES IN
GOOD AGREEMENT OF AMPLIFIED TROUGH OVER THE DESERT SOUTHWEST
DEAMPLIFYING AS IT MOVES EAST WITH ITS ASSOCIATED IMPACTS REMAINING
SOUTH OF THE LOCAL AREA THIS WEEKEND. THIS IS REFLECTED WITH A DRY
FORECAST.

MARINE...

AS AN OCCLUDED SURFACE LOW MOVES INTO THE GREAT LAKES REGION...A
WARM FRONT WILL LIFT NORTH THROUGH LAKE HURON AND USHER IN WARM AND
MOIST AIR. THE SURFACE LOW IS EXPECTED TO WEAKEN AS IT TRACKS ACROSS
THE REGION...BUT THERE WILL STILL BE A DECENT AREA OF COLD AIR
ADVECTION ON THE SOUTHWEST FLANK OF THE LOW. THE TIMING OF THIS
FEATURE WILL HELP INCREASE WIND SPEEDS IN THE TUESDAY NIGHT AND
WEDNESDAY TIME FRAME. MODEL SOUNDINGS SUGGEST THE PEAK WINDS WILL BE
AT THE 925 MB/2000 FT LEVEL. AT THESE HEIGHTS...WINDS COULD REACH UP
TO 35 KT. PEAK MIXING WEDNESDAY AFTERNOON MAY ALLOW FOR BRIEF GUSTS
TO GALES...BUT WIDESPREAD AND PERSISTENT GUSTS AT THAT SPEED ARE NOT
LIKELY. COMMON WIND VECTORS WILL BE 25-30KT FROM THE WEST ON
WEDNESDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....DG
SHORT TERM...SF
LONG TERM....MM/DT
MARINE.......MM


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



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