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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1208 AM EDT SAT OCT 25 2014

.AVIATION...

//DISCUSSION...

SKIES HAVE CLEARED OUT ACROSS THE TAF SITES...WHICH WILL ALLOW FOR 
SOME FOG TO DEVELOP OVERNIGHT...AS SOUTHWEST WINDS ARE VERY LIGHT AT 
THE MOMENT. BEFORE THE FOG IS ABLE TO GET DENSE OR DENSE FOR 
ANY EXTENDED PERIOD...LOOKING AT A RETURN OF MVFR/VFR CLOUDS AND AN 
INCREASE OF SOUTHWEST WINDS AHEAD OF A COLD FRONT BETWEEN 9-12Z. THE 
LOWER CLOUDS WILL THEN LIKELY PREVAIL THROUGH THE MORNING HOURS. 
HOWEVER...A GOOD DEAL OF DRYING WILL OCCUR DURING THE AFTERNOON 
HOURS...AS WESTERLY WINDS ALSO RAMP UP...WITH GUSTS LIKELY REACHING  
AND EXCEEDING 20 KNOTS. ONCE SKIES CLEAR OUT BY LATE IN THE 
DAY...SHOULD SEE MOSTLY CLEAR SKIES PERSIST TONIGHT. HOWEVER...COLD 
NORTHWEST FLOW WILL ATTEMPT TO SEND SOME LAKE INDUCED CLOUDS TOWARD 
THE AREA...MAINLY UP TOWARD MBS. 

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET 10-18Z. 

* LOW CONFIDENCE WIND GUSTS WILL EXCEED CROSSWIND THRESHOLDS 
  THIS AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 340 PM EDT FRI OCT 24 2014 

SHORT TERM... TONIGHT

THE TREND OF VARIABLE CLOUDINESS UNDER A FRAGMENTED STRATO-CU DECK 
CONTINUES TODAY. SOME SHORTWAVE RIDGING AT MID-LEVELS HAS ALLOWED 
FOR SOME SPOTTY CLEARING IN THE CLOUD FIELD...AND THESE WILL BE THE 
AREAS MOST AT RISK FOR FOG DEVELOPMENT TONIGHT. PERSISTENT SURFACE 
TROUGH OVER LAKE MICHIGAN WILL ADD TO THE DEPTH OF A COLD FRONT 
SWEEPING INTO THE STATE TONIGHT. CLOUDINESS WILL RE-STRENGTHEN AHEAD 
OF THIS FRONT TONIGHT AS WARM AIR ADVECTION BRINGS H85 TEMPS UP FROM 
5 TO 10C IN 12 HOURS. EXPECTING A VERY WARM NIGHT IN THE UPPER 40S 
AS THE COLD FRONT DOES NOT QUITE CROSS INTO THE CWA BY 12Z. WENT 
WARMER THAN GUIDANCE FOR MINS...BUT COULD EVEN SEE 2-3 DEGREES 
WARMER IF OVERCAST CONDITIONS PERSIST ALL EVENING.

AS MENTIONED ABOVE...THERE IS A CHANCE FOR PATCHY FOG TONIGHT. THIS 
CHANCE WILL BE MITIGATED BY WINDS AROUND 5KT AND ABUNDANT CLOUD 
COVER. AREAS THAT CLEAR OUT AND RADIATE WILL HOLD THE BEST CHANCE 
FOR DEVELOPING FOG...AND THAT CHANCE APPEARS TO BE NORTH OF I-69 AT 
THIS POINT. MODEL 925MB MOISTURE IS QUITE ROBUST TONIGHT...SO THERE 
IS CERTAINLY POTENTIAL FOR CLOUDY/WARM/FOGLESS CONDITIONS THROUGH 
12Z. DEPTH OF MOISTURE MAY ALSO ADD A NEGLIGIBLE CHANCE FOR
SPRINKLES.

LONG TERM...SATURDAY THROUGH THURSDAY

SATURDAY...SOUTHEASTERN MICHIGAN WILL BECOME INCREASINGLY INFLUENCED 
BY THE ANTICYCLONIC SHEAR ZONE ATTENDENT TO THE RIGHT EXIT REGION 
OF THE +160 KNOT UPPER LEVEL JET MAX INVADING THE GREAT LAKES 
REGION. DYNAMIC TROPOPAUSE MAPS DEPICT THIS WELL WITH A SHARP 
GRADIENT OF POTENTIAL VORTICITY IMPINGING DOWN INTO AND BECOMING 
ESTABLISHED OVER THE NORTHERN 1/3RD OF LAKE HURON. LOW LEVEL THERMAL 
FIELDS AND ISENTROPIC ASCENT FORECAST ANALYSES SHOW A FAVORABLE 
STRUCTURE SUPPORTIVE OF WAA ASCENT FROM ROUGHLY 9-16Z SATURDAY 
MORNING...WITH WARM/MOIST Theta-e WASH. THERE IS A GOOD INITIAL 
SURGE OF LOW LEVEL MOISTURE CAPPED BY VERY STRONG AND ACTIVE 
SUBSIDENCE ALOFT. HOWEVER...THE MOISTURE IS NOISY AND THERE ARE 
INDICATIONS THAT ANY PRECIPITATION POTENTIAL WILL BE DEPENDENT ON A 
DIURNAL HEATING COMPONENT. SATURATION IS GOING TO BE RAZOR THIN IN 
AND AROUND A POTENTIAL THIN UNSTABLE POCKET BETWEEN 925-900MB. THROW 
IN THE MODEL TRYING TO MAINTAIN SOME NOISY AND SPURIOUS CONVECTIVE 
SHREDS...AND WILL INCLUDE A CHANCE OF SPRINKLES SATURDAY MORNING 
BETWEEN 8 AM AND NOON EDT. AT MINIMUM THERE SHOULD AT LEAST BE SOME 
VIRGA ECHOES SHOWING UP ON RADAR. IF ANY PRECIPITATION WERE TO 
MEASURE...LOOKING AT A HUNDREDTH OR TWO MAX. TIME OF YEAR REQUIRES 
ADDITIONAL ATTENTION TO CLOUDS. THERE IS A GOOD TRAPPING OF LOW 
LEVEL MOISTURE BENEATH THE STRONG INVERSION STRUCTURE WITH SOME 
HINTS THAT SATURATION WILL ALSO EXIST WITHIN A FEW HUNDRED METERS OF 
THE STABLE LAYER. HAVE GONE ALONG WITH PERSISTENCE AND THE
INHERITED FORECAST TO GO SLUGGISH WITH THE EXIT OF CLOUDS FOR THE
AFTERNOON. SUSPECT THAT MANY AREAS WILL REMAIN SOCKED IN CLOUDS
UNTIL AS LATE AS 4 PM...WITH A RAPID CLEARING TREND THEREAFTER.
THE COLD FRONT IS FORECASTED TO CLEAR SEMICH BETWEEN 15-21Z FROM
NORTH TO SOUTH. WESTERLY WINDS TOMORROW OF 10-20 MPH WILL HELP THE
MECHANICAL MIXING PROCESS IN WARMING TEMPERATURES INTO THE LOWER
TO MIDDLE 60S...ROUGHLY 5 TO 8 DEGREES ABOVE AVERAGE.

COLD AIR ADVECTION OCCURRING TO THE SOUTHWEST OF THE
ONTARIO/QUEBEC UPPER LEVEL LOW WILL CAUSE 850MB TEMPERATURES TO
FALL FROM 8-9C SATURDAY...DOWN TO 3-5C FOR SUNDAY. THE UPPER LEVEL
RIDGE AXIS WILL REMAIN WELL WEST OF SOUTHEASTERN MICHIGAN DURING
THE DAYLIGHT HOURS WHICH GIVES NO SHOT AT WARM AIR ADVECTION AND
LEAD ISENTROPIC ASCENT MAKING INTO THE AREA. NOT REALLY BAD THOUGH
FOR LATE OCTOBER...PLEASANT FALL CONDITIONS WITH TEMPERATURES
CHECKING IN RIGHT AT AVERAGE.

MODELS SHOWING LOW PRESSURE MOVING NORTH THROUGH WISCONSIN AND 
DRAGGING A COLD FRONT THROUGH SE MI BEGINNING MONDAY. WET WEATHER 
LOOKS LIKELY FOR TUESDAY...WITH COOLER DRIER CONDITIONS DEVELOPING 
BEHIND THE FRONT WEDNESDAY AND THURSDAY. UPPER LEVEL FEATURE WILL 
BRING PRECIPITATION CHANCES BACK INTO THE FORECAST BY FRIDAY. 

MARINE...

STRONG UPPER LEVEL WAVE OF LOW PRESSURE WILL DIVE INTO THE GREAT 
LAKES REGION TONIGHT AND SATURDAY. THE DYNAMIC SYSTEM WILL LEAD TO A 
TIGHT PRESSURE GRADIENT OVER THE NORTHERN GREAT LAKES WITH COLD AIR 
POSSIBLY BUILDING INTO THE NORTHERN 1/3RD OF LAKE HURON. IT IS 
BEHIND THIS DEVELOPING FRONTAL BOUNDARY THAT CONDITIONS WILL BECOME 
QUITE UNSTABLE. UNCERTAINTY EXISTS WITH REGARDS TO EXACTLY HOW FAR 
SOUTH THIS FRONTAL BOUNDARY WILL POSITION ITSELF. A SHIFT IN 
PLACEMENT TO THE NORTH WOULD LEAD TO RELATIVELY MORE SUBDUED 
CONDITIONS. WILL FORGO THE ISSUANCE OF A GALE WATCH THIS FORECAST 
ISSUANCE...BUT DID INCREASE FORECASTED WINDGUSTS SOLIDLY INTO THE 30 
KNOT RANGE. STRENGTH OF THE SYSTEM TO THE NORTHEAST WITH ESTABLISHED 
NORTHWESTERLY GRADIENT FLOW WILL CONTINUE FRESH NORTHWESTERLY WINDS 
THROUGH SUNDAY.

&&

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

&&

$$

AVIATION.....SF
SHORT TERM...MM
LONG TERM....CB/DE
MARINE.......CB


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