Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 242301 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 701 PM EDT FRI OCT 24 2014 .AVIATION...
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//DISCUSSION... LINGERING MOISTURE FROM A WEAKENING TROUGH RESULTED IN A STRATO CU FIELD WHICH SHOULD RESIDE OVER THE TERMINALS FOR AT LEAST THE NEXT 2 TO 3 HOURS. THERE HAS APPARENTLY BEEN ENOUGH DAYTIME HEATING TO LIFT BASES INTO MVFR FOR MOST OF THE AREA. WEAK SURFACE RIDGING BUILDING IN FROM THE WEST IS EXPECTED TO SCOUR OUT THESE CLOUDS BY LATE EVENING. THIS WILL OPEN THE DOOR FOR POTENTIAL FOG AND OR/LOW STRATUS WITH SUBTLE LOW LEVEL MOISTURE ADVECTION FROM THE WEST. THE CURRENT FORECAST THOUGHTS REMAIN THAT FOG WILL BE MORE PROBABLE. HOWEVER...TRENDS WITH THE LOW STRATUS NOW COVERING W-CNTL LOWER MI WILL CONTINUE TO BE MONITORED AS THEY MAY SLIDE INTO MBS OVERNIGHT. ANOTHER INFLUX OF LOW LEVEL MOISTURE ALONG ANOTHER SFC TROUGH WILL BRING MORE WIDESPREAD LOW CLOUDS /MVFR OR POSSIBLE IFR/ BACK TO THE REGION BY DAYBREAK SAT. FOR DTW...GIVEN THE LIGHT WIND WHICH IS EXPECTED TO HOLD THROUGH THE NIGHT AND SOME POSSIBLE HIGH CLOUDS...RESTRICTIONS IN VSBY DUE TO FOG LATE TONIGHT WILL BE KEPT IN THE MVFR CATEGORY ATTM. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THIS EVENING...LOW CONFIDENCE OVERNIGHT AND MEDIUM CONFIDENCE SATURDAY MORNING. * LOW CONFIDENCE WIND GUSTS WILL EXCEED CROSSWIND THRESHOLDS SATURDAY AFTERNOON.
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&& .PREV DISCUSSION...
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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.
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&& .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....SC SHORT TERM...MM LONG TERM....CB/DE MARINE.......CB YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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