Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221747
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1247 PM EST MON DEC 22 2014


.AVIATION...

SEVERAL WAVES OF MOISTURE WILL BE LIFTED INTO THE REGION FROM A LOW
PRESSURE SYSTEM OVER THE NORTHERN PLAINS. THIS MOISTURE WILL SLOWLY
REPLACE DRY AIR...AND SUNNY SKIES...OVER THE REGION THROUGH THE
EVENING HOURS. DEEPER PLUME OF MOISTURE WILL LIFT NORTH TONIGHT
WHICH WILL INTRODUCE MVFR/IFR CIGS AND VSBYS AS RAIN SHOWERS SPREAD
ACROSS THE STATE. STILL LOOKS LIKE CONDITIONS WILL DETERIORATE TO
MVFR BETWEEN 04-08Z WITH IFR POSSIBLE AROUND 10-14Z. ONE ADDITIONAL
CONCERN FOR MBS...AND POSSIBLY FNT...IS THAT SUB FREEZING
TEMPERATURES AT THE SFC MAY LEAD TO A COUPLE HOURS OF LIGHT FREEZING
DRIZZLE AT THE ONSET BEFORE RAINFALL RATES INCREASE AND TEMPERATURES
RISE SLIGHTLY. BEST CHANCE FOR THIS WOULD BE BETWEEN 03-06Z.
CONFIDENCE IS LOW AT THE MOMENT SO WILL LEAVE OUT OF THE TAFS.

FOR DTW...CEILINGS AROUND 4000FT WILL LIFT NORTH OVER THE TERMINAL
THIS EVENING AS DEEPER PLUME OF MOISTURE LIFTS INTO THE REGION. MVFR
RAIN SHOWERS WILL BEGIN AROUND 06-08Z WITH IFR CIGS/VSBYS POSSIBLE
BETWEEN 11-14Z. FLOW WILL BE OUT OF THE E/SE AS THE SFC WARM FRONT
REMAINS TO OUR SOUTH.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS ABOVE 5000 FEET THROUGH 21Z TODAY.

* HIGH IN CEILINGS AOB 5000 FEET AFTER 00Z TONIGHT.

&&

.PREV DISCUSSION...ISSUED 1011 AM EST MON DEC 22 2014

UPDATE...
UPDATE MAINLY FOR SKY COVER AS MOSTLY SUNNY SKIES ARE PREVAILING
WITH ONLY A THIN LAYER OF CIRRUS FOR MOST LOCATIONS. THE DENSE CLOUD
SHIELD NOW ENTERING SW LOWER SHOWS THE NOSE OF THE INITIAL MOISTURE
GRADIENT THAT WILL MOVE NORTHWARD THROUGH THE AREA TODAY. DEEP
LAYER OF DRY AIR WILL PREVENT ANY PRECIPITATION FROM THIS MOISTURE
SURGE BUT WILL REINTRODUCE CLOUDS THIS AFTERNOON. DEEPER MOISTURE
LOOKS TO HOLD OFF TIL LATER THIS EVENING/TONIGHT WHICH WILL
PROVIDE THE SATURATION NEEDED FOR RAIN TO BEGIN.

PREV DISCUSSION...ISSUED 348 AM EST MON DEC 22 2014

SHORT TERM...TODAY THROUGH TONIGHT

AMPLIFYING UPPER TROUGH OVER THE PLAINS/MIDWEST WILL LEAD TO AN EVER
INCREASING DEGREE OF MOISTURE OVER THE AREA LATE TODAY INTO TONIGHT
AS BROAD SOUTHWEST FLOW REGIME BECOMES ESTABLISHED IN ADVANCE OF
THIS SYSTEM. INITIAL THETA-E SURGE WILL WORK INTO THE AREA IN THE
03Z-06Z TIME FRAME THIS EVENING AND EXPAND TO ENCOMPASS THE ENTIRE
CWA OVERNIGHT.

HAVE ADJUSTED THE RAIN FORECAST TO INCLUDE MORE DEFINITION AS RAIN
CHANCES WILL INCREASE STEADILY FROM SOUTHWEST TO NORTHEAST ACROSS
LOWER MICHIGAN DURING THE EVENING AND THEN CONTINUE OVERNIGHT FOR
MUCH OF THE AREA AS HIGHER THETA-E AIR GRADUALLY DISLODGES ALREADY
MODIFIED POLAR AIRMASS IN PLACE. ESSENTIALLY...PRECIPITATION CHANCES
WERE LOWER FOR THE EVENING HOURS...PARTICULARLY FROM THE NORTHEAST
HALF OF THE CWA INTO LAKE HURON AND INCREASE SLIGHTLY OVERNIGHT TO
ACCOUNT FOR LIKELY TO CATEGORICAL RAIN CHANCES AREA-WIDE IN THE 06Z
TO 12Z PERIOD.

HIGHS TODAY WILL CLIMB INTO THE MID/UPPER 30S AS EXTENSIVE CLOUD
COVER WILL OFFSET WARM AIR ADVECTION PATTERN. EAST TO SOUTHEAST
SURFACE FLOW WILL ALSO LIMIT WARMING TODAY INTO PARTS OF THIS
EVENING. WITH HIGHS REMAINING IN THE 30S IN MOST LOCATIONS...LOW
TEMPERATURES WILL MOST LIKELY FALL BACK TO NEAR FREEZING IN SOME
LOCATIONS...AT LEAST OVER THE THUMB...THIS EVENING BEFORE STEADY TO
RISING TEMPERATURES ENSUE OVERNIGHT. ONLY MINOR ADJUSTMENTS TO THE
FORECAST WERE MADE IN THIS REGARD.

LONG TERM...

ENERGETIC FLOW DIVING SOUTHEAST FROM THE GULF OF ALASKA...THROUGH
THE ROCKIES...AND INTO THE SOUTHERN PLAINS THIS MORNING. THE SUPPLY
OF UPPER LEVEL PV IS PLENTIFUL...WITH THE FLOW QUICKLY BUCKLING AND
LEADING TO CLOSED 500 MB LOW OVER THE CENTRAL CONUS TONIGHT. NO
SIGNIFICANT INITIALIZATIONS ERRORS NOTED TO LATCH ONTO. STILL ISSUES
WITH THE AMOUNT OF ENERGY AND TIMING OF 500 MB COLD POOL WORKING
THROUGH THE BACKSIDE OF THE LONGWAVE TROUGH INTO TEXAS ON
TUESDAY...WITH DIFFERENCES ON THE STRENGTH AND PLACEMENT OF THE
SECONDARILY LOW PRESSURE SYSTEM SPINNING UP BETWEEN 00Z
NAM/GFS/CANADIAN AND EURO. LEAD SHEARING OUT/ELONGATED UPPER WAVE
WORKING THROUGH THE WESTERN GREAT LAKES WILL LAY THE TRACKS SO TO
SPEAK. THE TRACKS ARE ALREADY DISPLACED BY TUESDAY EVENING...AS THE
NAM AND CANADIAN AVERAGE 850-700 MB TEMPERATURE DIVERGES BY A
SIGNIFICANT 4 DEGREES OVER SOUTHEAST MICHIGAN. WITH NOT A WHOLE LOT
OF COLD AIR TO WORK WITH...PACIFIC ORIGIN OF THE AIRMASS OVER
WESTERN CANADA...WILL LEAN TOWARD THE MILDER SOLUTION...WHICH
MAINTAINS THE BAROCLINIC ZONE CLOSE BY...ENOUGH FOR THE DEVELOPING
WESTERN GULF COAST LOW TO HEAD TOWARD THE CENTRAL/EASTERN GREAT
LAKES ON WEDNESDAY. THE PROBLEM IS...EVEN WITH A FAVORABLE SURFACE
LOW TRACK JUST TO OUR SOUTH AND EAST...THE LACK OF COLD
AIR/CONNECTION WITH THE POLAR STREAM... AND MILD/MOIST AIR PICKED UP
FROM THE GULF OF MEXICO WILL LIKELY SUPPORT MOSTLY A RAIN EVENT.
CONFIDENCE IS AVERAGE AT BEST HOWEVER. NO SNOW COVER ON THE GROUND
HELPS ONE LEAN TOWARD THIS DIRECTION...AS THE DAYTIME TIMING IS ALSO
A SLIGHT NEGATIVE AS WELL. SO...WILL HOLD ONTO THE CATEGORICAL RAIN
FORECAST ON WEDNESDAY...DESPITE THE DRY FORECAST OUT OF THE NAM. THE
STRENGTH OF THE LOW STILL REMAINS A BIT UNCERTAIN...BUT EVEN IF A
DEEPER LOW MATERIALIZES (SEE EURO/CANADIAN)...NOT SURE WE WILL SEE
WIND ADVISORY CRITERIA (DESPITE GOOD 23 MB RISE/FALL PRESSURE
COUPLET) AS THERE SHOULD BE PRECIPITATION DRAG ISSUES AND NO GOOD
DOWNWARD DESCENT...AS A PERIOD OF SNOW APPEARS LIKELY AS
PRECIPITATION SHUTS OFF WEDNESDAY EVENING/NIGHT. THE 00Z EURO IS
REALLY TOWING THE RAIN/SNOW LINE...WITH THE POSSIBILITY OF SEVERAL
INCHES OF SNOW ACCUMULATION WITH THE DEFORMATION WEDNESDAY
EVENING/NIGHT. HOWEVER...SURFACE DEW PTS ARE STILL ADVERTISED TO BE
33+ DEGREES THROUGH 6Z THURSDAY...WITH 1000-850 MB THICKNESSES IN
THE 1295-1300 M RANGE. SO...NOT EXACTLY SURE WHEN ACCUMULATION WILL
BEGIN TO TAKE PLACE. AT THIS POINT...WILL THE HIGHLIGHT THE
POTENTIAL OF 1 TO 3 INCHES BEFORE PRECIPITATION TAPERS OFF...THUS
KEEPING THE HOPES OF A WHITE CHRISTMAS ALIVE AND WELL.

MARINE...

A DEVELOPING LOW PRESSURE SYSTEM OVER THE PLAINS TODAY WILL SUPPORT
INCREASING S-SE WINDS ACROSS LAKE HURON. THE LOW WILL SLOWLY ROTATE
INTO THE WESTERN GREAT LAKES TONIGHT INTO TUESDAY. PERSISTENT LOW
LEVEL WARM AIR ADVECTION WILL INCREASE OVER LAKE STABILITY AND THUS
SUPPRESS PEAK WINDS FROM EXCEEDING 25 KNOTS. HOWEVER...WAVES WILL
STILL LIKELY REACH AROUND 4 FEET ACROSS NEARSHORE WATERS OF NORTHERN
THUMB REGION...AND HAVE ISSUED SMALL CRAFT ADVISORIES. THE SURFACE
LOW WILL ACTUALLY WEAKEN AS IT LIFTS INTO THE NORTHERN GREAT LAKES
ON TUESDAY. A SUBSEQUENT WEAKENING IN THE GRADIENT OVER LAKE HURON
WILL LEAD TO A DIMINISHING TREND IN THE WIND AND WAVES TUESDAY INTO
TUESDAY NIGHT. A SECONDARY SURFACE LOW IS FORECAST TO RAPIDLY DEEPEN
AS IT MOVES FROM THE DEEP SOUTH TUESDAY NIGHT AND IN BETWEEN THE
CENTRAL AND EASTERN GREAT LAKES WEDNESDAY. THIS SYSTEM WILL CONTINUE
TO STRENGTHEN AS IT LIFTS NORTHEAST OF THE REGION WEDNESDAY NIGHT.
COLD AIR ADVECTION IN THE WAKE OF THIS SYSTEM WILL POSE THE RISK OF
GALE FORCE WINDS OVER THE LAKES WEDNESDAY NIGHT INTO THURSDAY
MORNING. ENOUGH UNCERTAINTY IN THE STRENGTH AND TRACK OF THIS SYSTEM
REMAINS AT THIS STAGE IN THE FORECAST TO HOLD OFF ON THE ISSUANCE OF
A GALE WATCH.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST TUESDAY FOR
     LHZ421-441-442.

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

$$

AVIATION.....DRK
UPDATE.......DRK
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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