Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271810
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
110 PM EST SAT DEC 27 2014


.AVIATION...

A DIFFICULT 18Z TAF FORECAST WITH LOW CLOUD IFR CIGS...WELL MIXED
SOUTHWESTERLY FLOW...AND PRECIPITATION CHANCES THIS AFTERNOON.
EASIEST ITEM TO ADDRESS IS WELL MIXED BOUNDARY LAYER
SOUTHWESTERLIES IN THE 15 TO 25 KNOT RANGE. THESE WINDS ARE
EXPECTED TO PERSIST UNTIL WINDS CHANGE DIRECTION POST COLD FRONT
TO 260. HAVE SEEN ALL AREAS SOCK IN WITH IFR CIGS BEHIND THE
EARLIER PRECIPATIATION. THESE CLOUDS HAVE FILLED WITHIN THE LOW
LEVEL MOISTURE RIDGE THAT IS DIRECTLY OVER SOUTHEASTERN MICHIGAN.
THE DURATION OF THESE LOW CIGS IS MOST UNCERTAIN ASPECT WHEN
CONSIDERING THE WELL MIXED SOUTHWESTERLIES. BEGAN TAF PERIOD IN
IFR...THEN ALLOWED CIGS TO LIFT INTO THE 1000-1500 FT AGL RANGE.
PRECIPITATION POTENTIAL FOR THE AFTERNOON IS IN QUESTION WITH
UPSTREAM RADAR IMAGERY. SURFACE REPORTS IN THE CHICAGOLAND AREA
HAVE BEEN DRY OR DRIZZLE...WHILE RADAR MOSAIC HAS FILLED IN
ROBUSTLY FROM WEST CENTRAL LOWER MICHIGAN AND POINTS NORTHWARD.
WILL NEED TO MONITOR TRENDS AT KMBS...BUT THE MID TO UPPER LEVEL
RIDGE IS EXPECTED TO KEEP CONDITIONS DRY FOR MUCH OF THE AREA
THROUGHOUT THE AFTERNOON.

FOR DTW...LITTLE ADDITIONAL INFORMATION TO PROVIDE. PRECIPITATION
POTENTIAL REMAINS LOW THIS AFTERNOON...INCREASING CONSIDERABLY
BETWEEN 01-05Z FOR THE TERMINAL SOUTHWARD. HIGH UNCERTAINTY EXISTS
WITH REGARDS TO TIMING OF IFR TO MVFR CIG TRANSITION. 200 SURFACE
WIND OF 15 TO 20 KNOTS WILL CONTINUE TO APPROXIMATELY 03Z WHEN
WIND DIRECTION VEERS 270.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING BELOW 5000 FEET THROUGH TONIGHT.

&&

.PREV DISCUSSION...ISSUED 1057 AM EST SAT DEC 27 2014

UPDATE...

THE WIDESPREAD AREAL COVERAGE OF SHOWERS THAT IMPACTED
SOUTHEASTERN MICHIGAN THIS MORNING SOUTH OF INTERSTATE 69 WAS
FORCED AHEAD AND ALONG A RIBBON/RIDGE OF RICHER 850-700 MB
EQUIVALENT POTENTIAL TEMPERATURE. THESE SHOWERS WILL PUSH EAST OF
THE RIVERS MOMENTARILY. WITH THE LOSS OF THE THETA E GRAIDENT AND WARM
AIR ADVECTION...THE POTENTIAL FOR MEASURABLE PRECIPIATION NOW
WANES FOR MUCH OF TODAY ESPECIALLY WHEN ONE CONSIDERS THE MID TO
UPPER LEVEL RIDGING THAT WILL OVERLAP THE AREA. DID HOLD FIRM TO
THE INHERITED LOW CHANCE POP TO ACCOUNT FOR RICH BOUNDARY LAYER
MOISTURE AND DRIZZLE POTENTIAL. THE MAIN FEATURE TO CONTEND WITH
MOVING FORWARD WILL BE THE COLD FRONT THAT WILL SWEEP ACROSS
BETWEEN 21-06Z. MODELS STILL ADVERTISE THAT POSITIVE D(MAG)/DT OF
MAIN UPPER LEVEL JET BRANCH WILL DRAW MOISTURE NORTHWARD AGAIN IN
A REGION OF RIGHT ENTRANCE REGION DYNAMICS AHEAD OF THE
APPROACHING COLD FRONT AFTER 00Z TONIGHT. THIS IS EXPECTED TO
OCCUR MAINLY ACROSS OHIO...BUT SHOULD IMPACT DETROIT AND DOWNRIVER
PRIMARILY BETWEEN 01-06Z TONIGHT (INCREASED POPS TO LIKELY FOR
THIS SLIVER).

PREV DISCUSSION...ISSUED 342 AM EST SAT DEC 27 2014

SHORT TERM...TODAY AND TONIGHT

A SURFACE LOW IS COMING TOGETHER OVER EASTERN IOWA EARLY THIS
MORNING ALONG A STATIONARY FRONT EXTENDING FROM LAKE SUPERIOR DOWN
TO CENTRAL TEXAS. THE LOW IS FORECAST TO STRENGTHEN AS IT TRACKS
TOWARD THE SOO 18Z THIS AFTERNOON...THEN INTO QUEBEC TONIGHT. THE
FRONT IS ALIGNED ALONG THE UPPER LEVEL JET WHICH IS LEADING TO A
GOOD DEAL OF SHEARING FOR THE SYSTEM TO ENDURE...YET MODELS STILL
SHOW THE STRENGTHENING OF A CLOSED LOW DOWN TO 1004MB DUE TO A
POTENT 150+ KNOT JET OVERHEAD. A SURGE OF MOISTURE...WHICH LINES UP
WITH THE 850-700MB THETA E FIELD...IN THE WARM SECTOR IS HEADING
TOWARD LOWER MI AND HAS A GOOD CHANCE TO CLIP THE METRO DETROIT AREA
AROUND SUNRISE. MODEL DATA SHOWS A RELATIVE MOISTURE MINIMUM HEADING
NW TOWARD THE LOW PRESSURE CENTER WHICH CURRENTLY IS SUPPORTED BY
SCATTERED SHOWERS ON REGIONAL RADAR MOSAIC. SO INCREASED CHANCE POPS
A BIT ACROSS THE SOUTH FOR THE MORNING HOURS TO ACCOUNT FOR RADAR
TRENDS. WITH THE INFLUX OF LL MOISTURE THROUGH THE DAY WE WILL CARRY
A CHANCE OF LIGHT SHOWERS INTO THE AFTERNOON HOURS...EVEN THOUGH
MODELS AREA ADVERTISING A LULL IN THE ACTION BETWEEN THIS PREFRONTAL
RIBBON OF MOISTURE AND THE APPROACHING FRONT TO THE WEST.

A COLD FRONT WILL GET PULLED THROUGH SE MI THIS EVENING AROUND 00-
03Z. THERE IS A SECONDARY UPTICK IN MOISTURE RIGHT ALONG THE FRONT
AND THIS MOISTURE POOLING WILL ACCOUNT FOR HIGHER CHANCE POPS AGAIN
BETWEEN ABOUT 21Z-03Z THIS EVENING. DO NOT SEE ENOUGH EVIDENCE FOR A
WIDE SPREAD SWATH OF SHOWERS WORKING THROUGH THE AREA TO WARRANT
INCREASING TO LIKELY POPS AT THIS TIME. COOL AND DRY AIR WILL FILL
IN QUICKLY BEHIND THE FRONT RESULTING IN A SHARP CUTOFF TO THE
SHOWERS TONIGHT. ALL THE PRECIP AHEAD OF THE FRONT WILL FALL AS
LIQUID AS TEMPERATURES MAKE A RUN AT 50 DEGREES. A WEAK LAKE EFFECT
SIGNATURE SHOWS UP POST FRONTAL BUT WILL HOLD OFF ON ADDING ANY SNOW
OR DRIZZLE TO THE FORECAST AT THIS POINT AS CONFIDENCE IS LOW IT
WOULD SURVIVE THE TRACK ACROSS THE STATE. SOUNDINGS SHOW MOISTURE
DEPTHS UNDER 3000FT WITH A WEALTH OF DRY AIR ALOFT FROM MID LEVEL
CONFLUENT FLOW.

LAST THING OF NOTE WILL BE THE WINDS. DEPP LAYER OF SW FLOW WITH A
STRONG PREFRONTAL LL JET AROUND 60 KNOTS WILL RESULT IN GUSTY WINDS
THIS AFTERNOON. STRONGEST WINDS WILL OCCUR THROUGH CENTRAL MI WITH
GUSTS TO 25 KNOTS POSSIBLE...TAPER OFF TOWARD THE OHIO BORDER. WINDS
WILL TURN WESTERLY BEHIND THE FRONT WITH A BRIEF BURST RIGHT BEHIND
THE FRONT BUT EXPECT WINDS TO RELAX THROUGH THE OVERNIGHT.

LONG TERM... SUNDAY THROUGH FRIDAY

MID LEVEL PATTERN WILL EASE INTO A WEAKLY CONFLUENT ZONAL
CONFIGURATION FOR THE LATTER HALF OF THE WEEKEND.  THIS WILL PRESENT
A PERIOD OF BENIGN CONDITIONS AS WEAK SURFACE RIDGING EDGES IN
BEHIND THE DEPARTING TRAILING SHEAR AXIS.  RECENT MODEL SOUNDING
DATA AND RH FIELDS SUGGEST SOME LINGERING CLOUDINESS DURING THE
FIRST HALF OF THE DAY /PARTIAL COVERAGE/ WITH SOME DIURNAL
ENHANCEMENT.  LOW LEVEL FLOW THEN VEERS TO NORTHWESTERLY LATE SUNDAY
IN RESPONSE TO CHANGES IN THE PRESSURE FIELD FROM THE SOUTHWEST.
THIS WILL PROVIDE SOME RENEWED DRY AIR ADVECTION AND FAVOR A
CLEARING SKY INTO THE EVENING PERIOD.  COOLER AIRMASS IN PLACE
RELATIVE TO TODAY...BUT STILL A TOUCH ABOVE NORMAL FOR LATE
DECEMBER.  HIGHS SUNDAY RANGING FROM MID 30S NORTH TO UPPER 30S
SOUTH.

A STEADY INTRUSION OF ARCTIC AIR REMAINS ON TARGET FOR EARLY NEXT
WEEK...PROMPTED BY THE SOUTHWARD EXPANSION OF THE MAIN HEIGHTS FALLS
WORKING THROUGH THE MEAN CENTRAL CANADIAN HIGH AMPLITUDE UPPER
TROUGH.  THIS PROCESS WILL INITIATE WITH A SHALLOW LOOKING SURFACE
FRONTAL PASSAGE LATE SUNDAY NIGHT INTO MONDAY.  00Z NAM PRESENTS
SOME HINTS FOR THE TRAILING ELEVATED FRONTAL ZONE TO PERHAPS BECOME
ACTIVE ENOUGH TO GENERATE A FEW SNOWFLAKES BY MONDAY NIGHT.
DISORGANIZED APPEARANCE OF THE FRONTAL STRUCTURE AND ATTENDANT
FORCING...AS WELL AS A LACK OF GREATER MOISTURE QUALITY WILL LIMIT
THE POTENTIAL.  TEMPERATURES TRENDING DOWNWARD THROUGH AT LEAST
MIDWEEK AS THE ARCTIC AIR TAKES A FIRM HOLD.  850 MB TEMPERATURES OF
-16 TO -18C TUESDAY AND WEDNESDAY...GOOD FOR DAYTIME HIGHS IN THE
20S EACH DAY.

MARINE...

MODERATE SOUTHERLY WINDS TODAY WILL STRENGTHEN INTO THE EARLY
EVENING AS A LOW PRESSURE SYSTEM LIFTS THROUGH THE STRAITS.  THIS
WILL RESULT IN A BRIEF PERIOD OF GUSTS TO 30 KNOTS ACROSS CENTRAL
LAKE HURON.  WINDS SHIFT TO NORTHWESTERLY IN THE WAKE OF THIS SYSTEM
TONIGHT.  A PERIOD OF STRONGER WINDS WILL FAVOR NORTHERN PORTIONS OF
LAKE HURON.  THIS WILL BRING THE POTENTIAL FOR A BRIEF PERIOD OF
MARGINAL GUSTS TO GALES.  CONFIDENCE IN BOTH OCCURRANCE AND DURATION
STILL REMAIN ON THE LOWER SIDE...SUPPORTING A CONTINUATION OF THE
GALE WATCH ACROSS THIS CORRIDOR.  WINDS AND WAVES WILL THEN
GRADUALLY SUBSIDE SUNDAY INTO SUNDAY NIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...GALE WATCH FROM 7 PM EST THIS EVENING THROUGH LATE TONIGHT FOR
     LHZ361-362.

     SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 4 AM EST SUNDAY
     FOR LHZ421-441.

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

$$

AVIATION.....CB
UPDATE.......CB
SHORT TERM...DRK
LONG TERM....MR
MARINE.......MR


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


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