Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241940
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 1242 PM EDT FRI OCT 24 2014

//DISCUSSION...

VISIBLE SATELLITE AND SURFACE OBS PAINT A PICTURE OF BROKEN STRATO-
CU STEADILY MOVING TOWARD THE TAF CORRIDOR THIS AFTERNOON.
WEAKENING MID-LEVEL TROUGH WILL CONTINUE TO FRACTURE AS IT CROSSES
THE AREA TODAY. THIS WILL ALLOW FOR BROKEN CIGS TO HOVER IN THE
3-5KFT RANGE BEFORE SUBSTANTIAL CLEARING THIS EVENING DEADENS THE
THREAT FOR MVFR CONDITIONS. STRONGER THREAT FOR STRATUS AND BR TO
REACH MVFR LEVELS EARLY SATURDAY THROUGH 18Z.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE ON CEILINGS BELOW 5000 FEET THIS AFTERNOON.
  HIGH CONFIDENCE SATURDAY.

&&

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

&&

$$

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


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



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