Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220212
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
912 PM EST SUN DEC 21 2014

.UPDATE...

STRATOCU HAS BEEN HANGING ON THIS EVENING...BUT SHOULD SCATTER OUT
WITHIN A COUPLE OF HOURS ON EITHER SIDE OF MIDNIGHT. THEN THE WILL
BE LEFT WITH SCATTERED TO BKN...AND SOMETIMES THIN...CIRRUS FOR
THE NIGHT. THAT SHOULD BE ENOUGH TO ALLOW SOME PATCHY FOG TO
DEVELOP WITH THE MOIST SOUTHEAST FLOW OFF OF THE GREAT LAKES.
TEMPS ARE ON TARGET WITH LOWS MID TO UPPER 20S WHICH IS NOT MUCH
OF A FALL FROM CURRENT TEMPS. ENOUGH GRADIENT AND CLOUDS TO KEEP
THEM FROM FALLING TOO MUCH.

&&

.AVIATION...ISSUED 620 PM EST SUN DEC 21 2014

CEILINGS AROUND 5K TO 6K FEET WILL CONTINUE THROUGH THE EVENING
HOURS. SOME BREAKS NOTED IN SW LOWER MI AND INDIANA AND THAT SHOULD
SPREAD INTO SOUTHEAST MI IN THE LATE EVENING. THERE IS ALSO SOME
MOISTURE AROUND 2000 FEET ACROSS NRN OH AND ONTARIO. WITH THE ESE
FLOW...THIS MAY BRING A FEW HOURS OF MVFR CIGS TO THE DETROIT AREA
TAFS BETWEEN 00Z AND 06Z. WITH THE DECREASE IN LOWER LEVEL MOISTURE
AFTER 06Z...EXPECT SOME MVFR FOG TO DEVELOP.  THIS REALLY SHOULD NOT
BE TOO DIFFICULT GIVEN THAT VISIBILITIES ARE ALREADY HOVERING AROUND
7 MILES.

FOR MONDAY AFTER THE MORNING FOG DISSIPATES EXPECT JUST CI UNTIL
AFTER 20Z WHEN LOW LEVEL MOISTURE INCREASES AHEAD OF THE NEXT
SYSTEM.

FOR DTW...CEILING ABOVE 5000 FEET WILL CONTINUE THROUGH THE EVENING.
THERE IS AN AREA OF MOISTURE AROUND 2000 FEET THAT MAY LEAD TO SOME
BKN CONDITIONS DURING THE EVENING. AFTER 06Z THIS LOW LEVEL MOISTURE
LEAVES AND MVFR VISIBILITIES DEVELOP WITH FOG. WINDS WILL BECOME
MORE EASTERLY THROUGH THE NIGHT AND DAY ON MONDAY. THOSE EASTERLY
WINDS WILL INCREASE ABOVE 7 KTS ON MONDAY.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CEILINGS BELOW 5000 FEET THROUGH 06Z TONIGHT.

* MODERATE CONFIDENCE IN CEILINGS AOA 5000 FEET AFTER 06Z TONIGHT.

* MODERATE CONFIDENCE IN MVFR VISIBILITY BETWEEN 06Z AND 15Z.

&&

.PREV DISCUSSION...ISSUED 332 PM EST SUN DEC 21 2014

SHORT TERM...THROUGH TONIGHT

AMOUNT OF CLOUD COVER AND FOG POTENTIAL APPEAR TO BE THE MAIN
CONCERNS FOR THIS EVENING AND TONIGHT AS WESTERN EXTENT OF THE SFC
RIDGE HOLD OVER THE AREA. THE UPPER LEVEL FLOW WILL BE PIVOTING OVER
THE AREA TONIGHT...BECOMING MORE SOUTH TO NORTH...AS THE LONGWAVE
TROUGH DEEPENS OVER THE CENTRAL PLAINS. A SHORTWAVE RIDGE WILL SLIDE
OVER THE AREA TONIGHT AHEAD AN ELEVATED WARM FRONT WHICH WILL LOSE
STRUCTURE AS IT PASSES TONIGHT. IT WILL CAUSE THE WINDS TO VEER MORE
SOUTHWESTERLY FROM THE SFC TO 400MB...ALLOWING WARMER AIR TO ADVECT
INTO THE REGION.

THE CLOUD/FOG FORECAST WILL BE A BIT CHALLENGING TONIGHT. EXPANSIVE
AREA LOW DEWPOINTS IN THE 20S ACROSS OH/IN IS TAKING ITS TOLL ON LOW
CLOUDS OVER THAT AREA AS ONLY CIRRUS DEBRIS IS SHOWING UP ON VISIBLE
SATELLITE THIS AFTERNOON. THIS DRY AIR WILL CONTINUE TO LIFT INTO SE
MI TONIGHT...AS IT HAS BEEN THIS AFTERNOON...WHICH WILL ATTEMPT TO
SCOUR OUT THE 5-6KFT CLOUD DECK CURRENTLY PRESENT ACROSS LOWER MI.
MODELS CONTINUE TO HOLD ONTO SFC MOISTURE WHICH IS REPRESENTED BY A
LOW STRATUS DECK IN THE SOUNDINGS BUT THINK THIS MOIST LAYER IS
BEING OVERDONE. EXPECT THE DRY AIR TO ERODE THE CLOUDS FROM SE TO NW
THROUGH THE NIGHT WITH THE SAGINAW VALLEY BEING A BIT OF A STICKING
POINT AS IT WILL BE VERY CLOSE TO THE RIBBON OF MOISTURE AND
ISENTROPIC ASCENT AHEAD OF THE DEVELOPING LOW OVER NORTHERN PLAINS.
SO HELD ONTO CLOUDS A BIT LONGER FOR THE SAGINAW VALLEY...BUT THEY
COULD VERY WELL STAY CLOUDY ALL NIGHT. WITH MOST OF THE CLOUDS
SCOURING OUT...TEMPS SHOULD FALL INTO THE MID/UPPER 20S. EXPECT
ANOTHER ROUND OF PATCHY FOG TO DEVELOP TOWARD MORNING...ESPECIALLY
FOR OUR EASTERN COUNTIES THAT MAY EXPERIENCE TEMPS FALLING OFF
EARLIER DUE TO CURRENT LACK OF CLOUDS.

LONG TERM...MONDAY THROUGH NEXT SUNDAY

AVAILABLE UPPER AIR OBS FROM THIS MORNING SHOWED A 170KT UPPER JET
NOSING INTO THE PACIFIC NORTHWEST...WHILE THE RECENT WATER VAPOR
IMAGERY OVER THE NORTH PACIFIC SUGGESTS ONGOING AMPLIFICATION IN THE
LONG WAVE PATTERN. THE NET RESULT OF THIS WILL BE DOWNSTREAM
AMPLIFICATION IN THE LONG WAVE TROUGH MON INTO MON NIGHT. THE TREND
IN THE RECENT MODEL SUITE HAVE BEEN TOWARD A LITTLE FASTER EVOLUTION
INTO A CUT OFF MID LEVEL CIRCULATION OVER THE CENTRAL PLAINS...WITH
THE DEEP MOISTURE PLUME AND ISENTROPIC ASCENT WITHIN THE WARM
CONVEYOR NOT FORECAST TO ARRIVE INTO SE MI UNTIL MON NIGHT INTO TUES
MORNING. SO PRECIP WILL BE REMOVED THROUGH MON AFTERNOON.

THE DEGREE OF MOISTURE ADVECTION /PWATS EXCEEDING 0.8 INCH/ WITHIN
THE DEEP THETA E RIDGE WILL CONTINUE TO WARRANT HIGH PROBABILITIES
OF RAIN MON NIGHT INTO AT LEAST EARLY TUES. LOW LEVEL DRY AIR AND
SUBSEQUENT LOW WET BULB ZERO HEIGHTS PRIOR TO THE ARRIVAL OF RAIN
DOES RAISE SOME CONCERNS OF A BRIEF INTERVAL OF LIGHT FREEZING RAIN
MON NIGHT. MODEL SOUNDINGS SUGGEST THAT A RAPID RISE IN SFC
DEWPOINTS ABOVE FREEZING WILL OCCUR WITH THE ONSET OF RAIN...
SUPPORTIVE OF MAINTAINING ALL RAIN IN THE FCST ATTM. THE MAIN RIBBON
OF ISENTROPIC ASCENT WILL LIFT NE OF THE REGION TUES AFTERNOON. WITH
SFC DEWPOINTS EXPECTED TO BE IN THE 40S AND AMPLE DEEP LAYER
MOISTURE OVERHEAD...LIGHT RAIN/DRIZZLE AND FOG SHOULD BE WIDESPREAD
INTO AT LEAST EARLY CHRISTMAS EVE.

THE TRACK AND INTENSITY OF A SECONDARY LOW PRESSURE SYSTEM
ORIGINATING FROM THE GULF COASTAL REGION AND ITS POTENTIAL IMPACT
ON SE MI CHRISTMAS EVE AND CHRISTMAS DAY HAS CARRIED A GOOD DEAL OF
UNCERTAINTY THE LAST SEVERAL FORECAST CYCLES. WHILE THE 12Z MODEL
SUITE /NAMELY THE GFS...CANADIAN AND ECMWF/ HAVE CONVERGED TOWARD A
CLOSER SOLUTION...A GOOD DEAL OF SPREAD AMONG ENSEMBLE MEMBERS AND
THE EARLY STAGE IN THE FORECAST CYCLE SUGGESTS ADDITIONAL
FLUCTUATIONS IN MODEL SOLUTIONS ARE PROBABLE. THE INTENSE UPPER JET
WILL LEAD TO AMPLIFICATION IN THE BASE OF THE LONG WAVE TROUGH OVER
THE SOUTHERN PLAINS TUES...THUS FORCING THE CNTL PLAINS UPPER LOW
INTO THE UP/LAKE SUPERIOR TUES NIGHT. MODEL SOLUTIONS SUGGEST SOME
PHASING OF UPPER JET ENERGY WITH THE SOUTHERN STREAM WILL RAPIDLY
INTENSIFY UPPER LEVEL DIVERGENCE ACROSS THE OHIO VALLEY/ERN GREAT
LAKES CHRISTMAS EVE. THE UPPER TROUGH IN TURN IS FORECAST TO
DEVELOP A NEGATIVE TILT AS IT LIFTS TO THE NORTH AND ACROSS LOWER MI
WED NIGHT. THE RESULT WILL BE A RAPIDLY DEEPENING SFC LOW FORECAST
TO LIFT FROM THE GULF COASTAL REGION TUES ACROSS THE ERN GREAT LAKES
OR LOWER MI WED AFTN/EVENING. THE ECMWF /WHICH HAD TRENDED MUCH
WEAKER THE LAST MODEL RUN/ NOW FCSTS THE LOW TO DEEPEN TO 977MB AS
IT LIFTS NE OF DETROIT WED EVENING /SIMILAR TO THE GFS AND CANADIAN/.

ADDITIONAL LOW LEVEL WARM AIR ADVECTION PRECEDING THE SFC LOW WILL
SUPPORT ALL RAIN WED INTO WED EVENING. THERE IS THE POTENTIAL FOR
SOME FAIRLY GOOD RAINFALL RATES CONSIDERING THE DYNAMICS. COLDER AIR
WILL ADVANCE INTO SE MI WITH THE DEPARTURE OF THE SFC LOW CHRISTMAS
EVE NIGHT. THE GFS AND ECMWF HOLD ONTO ENOUGH RESIDUAL MID LEVEL
FORCING IN THIS COLDER AIR TO SUPPORT A CHANCE OF SOME MINOR SNOW
ACCUMS OVER PORTIONS OF THE AREA ON THE BACK EDGE OF THE DEEPER
MOISTURE. THE MAIN CONCERN WITH THIS SYSTEM HOWEVER WILL BE THE
WINDS IN LIGHT OF THE EXPECTED RATE OF DEEPENING AS IT TRAVERSES THE
REGION. THE STRONGEST WINDS WILL BE WITHIN THE LOW LEVEL COLD AIR
ADVECTION CHRISTMAS EVE NIGHT INTO CHRISTMAS MORNING. MODEL
SOUNDINGS SUGGEST WIND GUSTS UP TO OR IN EXCESS OF 40 MPH ARE
POSSIBLE. THE GRADIENT AND THUS WIND SPEEDS WILL DIMINISH BY
CHRISTMAS AFTERNOON. THE FCST PROGRESSIVE NATURE OF THE FLOW
SUGGESTS THAT WARM AIR ADVECTION BY CHRISTMAS AFTERNOON WILL LEAD TO
AFTERNOON HIGHS WELL INTO THE 30S.

MARINE...

A DEVELOPING LOW PRESSURE SYSTEM OVER THE PLAINS TONIGHT INTO MONDAY
WILL SUPPORT INCREASING S-SE WINDS ACROSS LAKE HURON. THE LOW WILL
ONLY SLOWLY ROTATE INTO THE WESTERN GREAT LAKES MON NIGHT INTO
TUESDAY. PERSISTENT LOW LEVEL WARM AIR ADVECTION WILL INCREASE OVER
LAKE STABILITY AND THUS SUPPRESS PEAK WIND FROM EXCEEDING 25 KNOTS.
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 WINDS AND WAVES
TUES INTO TUES NIGHT. A SECONDARY SURFACE LOW IS FORECAST TO RAPIDLY
DEEPEN AS IT MOVES FROM THE DEEP SOUTH TUES NIGHT INTO THE ERN GREAT
LAKES WEDNESDAY. THIS SYSTEM WILL CONTINUE TO STRENGTHEN AS IT LIFTS
NORTHEAST OF THE REGION WED NIGHT. COLD AIR ADVECTION IN THE WAKE OF
THIS SYSTEM WILL POSE THE RISK OF GALE FORCE WINDS OVER THE LAKES
WED NIGHT INTO THURS MORNING. ENOUGH UNCERTAINTY IN THE STRENGTH AND
TRACK OF THIS SYSTEM REMAINS AT THIS EARLY STAGE IN THE FORECAST TO
HOLD OFF ON THE ISSUANCE OF A GALE WATCH.

&&

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

$$

UPDATE.......RBP
AVIATION.....RBP
SHORT TERM...DRK
LONG TERM....SC
MARINE.......SC


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