Area Forecast Discussion

943 FXUS63 KDTX 291447 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 947 AM EST FRI NOV 29 2013 .UPDATE... THE MORNING FOG HAS LIFTED TO A LOW STRATUS DECK OVER LOCATIONS ROUGHLY ALONG AND NORTH OF A HOWELL TO SANDUSKY LINE. THE 12Z DTX SOUNDING HAD TWO INVERSIONS BASED BELOW 925MB. WARM AIR ADVECTION ABOVE 900MB TODAY WILL SUSTAIN A LOW LEVEL INVERSION. THIS ALONG WITH THE LOW SUN ANGLE THIS TIME OF YEAR WILL MEAN THIS STRATUS DECK IS GOING TO TAKE WELL INTO THE AFTERNOON TO MIX OUT...IF IT COMPLETELY MIXES OUT AT ALL. SATELLITE DATA ALSO SUGGESTS THE SHALLOW COLD LAYER IS MAINTAINING A HEALTHY RESPONSE OFF LAKE MI...SUPPORTING A GOOD DEAL OF LAKE CLOUDS. THE LIGHT WESTERLY FLOW MAY ALLOW SOME OF THESE CLOUDS TO FILTER INTO FAR WESTERN PORTIONS OF SE MI THIS AFTERNOON BEFORE THE LOW LEVEL FLOW BACKS TOWARD THE SOUTH. THE EXTENT OF LOW CLOUDS WILL SUPPORT LOWERING FORECAST HIGHS TEMPS A BIT ACROSS THE TRI CITIES/FLINT AND THUMB REGION. MEANWHILE...THE WEAK FLOW LOOKS TO BE PREVENTING THE STRATUS FROM PUSHING SE OF THE IRISH HILLS. THUS MUCH OF METRO DETROIT AND POINTS SOUTH HAVE SEEN FULL MORNING SUN. IN ANTICIPATION OF MORE SUN IN THESE LOCALS...AFTERNOON HIGHS IN THE LOW 30S SEEM REASONABLE. && .AVIATION...ISSUED 550 AM EST FRI NOV 29 2013 //DISCUSSION... AREAS OF LAKE ENHANCED CLOUDS AND FOG WILL DISSIPATE DURING THE MORNING AS HIGH PRESSURE PROGRESSIVELY BUILDS INTO THE REGION. VFR CONDITIONS ARE THEN EXPECTED UNTIL AFTERNOON WHEN DIURNAL MIXING WILL ALLOW A BORDERLINE LOW VFR/HIGH MVFR STRATOCU CLOUD LAYER TO DEVELOP. PLAN TO ABSTAIN FROM SPECIFIC MENTION OF MVFR IN THE 12Z TAF DUE TO LOW CONFIDENCE...OPTING INSTEAD TO MAKE LATER REFINEMENTS BASED ON OBSERVATIONAL TRENDS. BY TONIGHT, LIGHT SOUTHEAST WINDS AROUND THE DEPARTING SURFACE HIGH MAY PICK UP SUFFICIENT MOISTURE FROM LAKE ERIE TO RESULT IN FURTHER DETERIORATION OF CEILINGS BETWEEN 00Z-09Z, PARTICULARLY FURTHER EAST AT KDET, BUT LIKEWISE LOW CONFIDENCE PRECLUDES BEING TOO AGGRESSIVE ATTM. //DTW THRESHOLD THREATS... * MEDIUM CONFIDENCE IN CEILINGS BELOW 5000 FEET

Area Forecast Discussion

 
065 
FXUS63 KDTX 281622
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1122 AM EST THU NOV 28 2013

.UPDATE...
LATE MORNING FORECAST UPDATE WAS TO TWEAK FOR CURRENT TRENDS AND
TO COVER THE POSSIBILITY FOR A POTENTIAL ENHANCEMENT AND EXPANSION BACK
SOUTHWARD OF SNOW DURING THE SECOND HALF OF THE AFTERNOON AND
EARLY EVENING.

CURRENTLY...SNOW HAS TAPERED OFF SOUTH OF A LINE FROM HOWELL TO
DETROIT. THE BACK EDGE SHOULD CONTINUE TO SLOWLY NUDGE
NORTHEASTWARD OVER THE NEXT SEVERAL HOURS...WITH SNOW FILLING IN
OR CONTINUING NORTH OF THE I-69 CORRIDOR AS THE LOW MOVES IN AND
THE SNOW BAND STARTS TO PIVOT. LATEST ROUND OF HI-RES MODELS
(NAM12/RUC13/4KM WRF/HRRR) SHOW ANOTHER ROUND OF LIGHT SNOW
FILLING IN OVER THE SOUTHERN HALF OF THE FORECAST AREA FROM MID-
AFTERNOON INTO THE EVENING. THIS APPEARS TO BE TIED TO THE ARRIVAL
OF A VERY WEAK SURFACE WARM FRONT FROM THE SOUTH SOUTH (NOW OVER
ILLINOIS AND INDIANA) INTERACTING WITH ADDITIONAL MOISTURE THAT
SHOULD BE DRAWN OFF LAKE MICHIGAN. NAM ANALYSIS SHOWS WINDS
TURNING WEST OFF THE SOUTHERN PORTION OF LAKE MICHIGAN AND
SOUTHERN LOWER MICHIGAN AS SURFACE LOW PRESSURE BEGINS TO TRACK
ACROSS THE CENTRAL PART OF THE PENINSULA. WESTERLY TRAJECTORY
COMBINED WITH STEEP LOW-LEVEL LAPSE RATES (ABOUT 9 C/KM FROM
SURFACE TO 700MB) SHOULD PROVIDE SOME ENHANCEMENT OFF THE LAKE.
POPS HAVE THEREFORE BEEN INCREASED AFTER THE EXPECTED BREAK LATE
THIS MORNING/EARLY AFTERNOON...WITH AN ADDITION ACCUMULATION OF LIGHT
SNOW VERY POSSIBLE...UP TO 2 MORE TENTHS. ACTIVITY SHOULD REALLY
BEGIN TO WANE SOUTH OF I-69 AFTER 00Z/7PM AS DRIER AIR WORKS INTO
THE AREA AND STRIPS AWAY ICE NUCLEI...WITH SNOW SHOWERS LINGERING
INTO TRI- CITIES AND ESPECIALLY NORTHERN THUMB UNTIL ABOUT
MIDNIGHT.

&&

.AVIATION...ISSUED 658 AM EST THU NOV 28 2013 

//DISCUSSION...

THE MAIN CONCERN FOR AVIATION INTERESTS WILL BE THE BAND OF SNOW 
THAT WILL EVOLVE IN THE TERMINAL CORRIDOR THROUGH THE DAY. THE 
PATTERN WILL BRING A PERIOD OF IFR VISIBILITY WITH SIMILAR ONSET 
TIMING AT THE BEGINNING OF THE FORECAST BUT DURATION WILL BE SHORTER 
AT DTW COMPARED TO FNT AND MBS. MORNING OBSERVATIONS OVER THE 
MIDWEST ACTUALLY SUPPORT A TREND TO VFR CEILING IN THE DTW AREA 
DURING THE AFTERNOON AS SURFACE LOW PRESSURE MOVES FROM IOWA TO 
ABOUT HTL BY LATE AFTERNOON. THE LOW WILL THEN FILL RAPIDLY AND 
LEAVE A WEAK PRESSURE PATTERN OVER LOWER MICHIGAN TONIGHT RESULTING 
IN QUITE A BIT OF UNCERTAINTY ON CLOUD EVOLUTION THROUGH SUNRISE 
FRIDAY MORNING. FOR NOW, AN OPTIMISTIC VFR SCATTERED TO BROKEN 
CONDITION IS EXPECTED AS WEAK BUT DRY HIGH PRESSURE EVOLVES OVER THE 
MIDWEST.

FOR DTW... ABOUT A HALF INCH OF SNOW ACCUMULATION REMAINS ON TARGET 
AS THE PRIMARY BAND OF SNOW PIVOTS QUICKLY THROUGH THE REGION DURING 
THE MORNING. EXPECT SNOW TO END BY EARLY AFTERNOON WITH IMPROVED 
CEILING CONDITIONS ABOVE 5000 FEET BY MID AFTERNOON.

//DTW THRESHOLD THREATS...  

* HIGH CONFIDENCE IN CEILING BELOW 5000 FT DURING THE MORNING. 

* HIGH CONFIDENCE IN SNOW AS PRECIPITATION TYPE TODAY.

SNOW SQUALL INFORMATION

Issued at 2013-11-28 15:58 UTC by Environment Canada:
Snow squall warning continued for:
   Barrie - Collingwood - Hillsdale, Ont. (044130)
   Goderich - Bluewater - Southern Huron County, Ont. (046330)
Snow squall warning ended for:
   London - Parkhill - Eastern Middlesex County, Ont. (041510)
   Strathroy - Komoka - Western Middlesex County, Ont. (041520)
   Innisfil - New Tecumseth - Angus, Ont. (046510) 

Current details:
Snow squalls weakening today.

Snowsqualls off Lake Huron and Georgian Bay will taper to flurries early this afternoon. Until then local visibilities near zero can be expected.

Motorists should be prepared for hazardous winter driving conditions with near zero visibility in bursts of heavy snow and quickly accumulating snow on untreated roads.

Please refer to your local public forecast for further details.

*SNOW SQUALL WARNING* CONTINUED

Issued at 2013-11-27 23:39 UTC by Environment Canada:
Snow squall warning continued for:

   Watford - Pinery Park - Eastern Lambton County, Ont. (041310)
   London - Parkhill - Eastern Middlesex County, Ont. (041510)
   Strathroy - Komoka - Western Middlesex County, Ont. (041520)
   St. Thomas - Aylmer - Eastern Elgin County, Ont. (041610)
   Rodney - Shedden - Western Elgin County, Ont. (041620)
   Barrie - Collingwood - Hillsdale, Ont. (044130)
   Owen Sound - Blue Mountains - Northern Grey County, Ont. (046220)
   Hanover - Dundalk - Southern Grey County, Ont. (046240)
   Goderich - Bluewater - Southern Huron County, Ont. (046330) 

Current details:
Snow squalls continuing tonight.

Cold Arctic air flowing over Lake Huron and Georgian Bay is generating snow squalls. The snow squalls are expected to continue through the night and start to weaken and drift eastward on Thursday.

Snow squalls coming off Lake Huron are expected to be quite intense and could give 15 to 25 cm to some locales before they weakenThursday morning. The most intense band is coming onshore between Grand Bend and Kettle Point and is penetrating inland to Elgin County. Communities being affected include Parkhill, Komoka, and St Thomas. Current indications suggest that this band will remain nearly stationary tonight. Local accumulations within this band could be more than 30 cm.

Snow squalls off Georgian Bay are expected to be weaker due to the lower water and air temperature contrast and unfavourable wind direction. Local snow accumulations are expected to be in the 10 to 20 cm range by Thursday morning.

Motorists should be prepared for hazardous winter driving con ditions with near zero visibility in bursts of heavy snow and blowing snow and quickly accumulating snow on untreated roads.

Please refer to your local public forecast for further details.

Area Forecast Discussion issued by NWS Detroit/Pontiac

 
870 
FXUS63 KDTX 272335
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
635 PM EST WED NOV 27 2013


.AVIATION...

//DISCUSSION...

RATHER BENIGN CONDITIONS TONIGHT AS NORTHWEST WINDS DIMINISH AND 
GRADUALLY BEGIN TO BACK TO WESTERLY.  OCCASIONAL POCKETS OF VFR LAKE 
STRATUS WILL CONTINUE TO FUNNEL THROUGH AT TIMES...WITH SOME 
INCREASE IN HIGH CLOUD LATE IN ADVANCE OF LOW PRESSURE TRACKING 
THROUGH THE NORTHERN GREAT LAKES.  MAIN FOCUS NOW ON THE THURSDAY 
PERIOD AS A RIBBON OF DEEPER MOISTURE ASSOCIATED WITH THIS SYSTEM 
WORKS ACROSS SE MICHIGAN.  THIS WILL TRANSLATE INTO A PERIOD OF 
LIGHT ACCUMULATING SNOW IN MVFR/IFR AREAWIDE...CENTERED ON THE 
15Z-20Z TIME WINDOW.  ACCUMULATION POTENTIAL RANGING FROM AROUND A 
HALF INCH IN DETROIT...TO AN INCH AND HALF AT MBS.  

//DTW THRESHOLD THREATS...  

* LOW CONFIDENCE IN CEILING INTERMITTENTLY FALLING BELOW 5000 FT 
TONIGHT...HIGH CONFIDENCE IN CEILING BELOW 5000 FT ON THURSDAY. 

* HIGH CONFIDENCE IN SNOW AS PRECIPITATION TYPE ON THURSDAY.

SNOW SQUALL WATCH UPGRADED TO SNOW SQUALL WARNING

Watford - Pinery Park - Eastern Lambton County
1:32 PM EST Wednesday 27 November 2013
Snow squall warning for 
Watford - Pinery Park - Eastern Lambton County upgraded from Snow squall watch

Snow squalls this afternoon and continuing tonight.

A northwesterly flow of fresh cold Arctic air moving into Lake Huron and Georgian Bay has generated multiple lake effect snow bands. These narrow but intense snow bands are expected to intensify through the afternoon as the low level wind directions become more aligned. Snow squalls are expected to continue into this evening and overnight before they start to weaken and drift eastward on Thursday.

Snow squalls coming off Lake Huron are expected to be quite intense and could give 15 to 25 cm to some locales before they weaken Thursday morning. In addition, current indications show a single strong band is likely to form by late afternoon from Central Lake Huron inland to locales between London and Watford to Elgin County. This band could remain quite stationary into this evening and tonight. Local accumulations within this band could be more than 30 cm. There is also potential for this snow squall to shift farther east this evening and tonight to affect the City of London as well.

Snow squalls off Georgian Bay are expected to be weaker due to the lower water and air temperature contrast and unfavourable wind direction. Local snow accumulations are expected to be in the 10 to 20 cm range for this afternoon, this evening and tonight.

Driving conditions will quickly deteriorate as the snow squalls develop. Motorists should be prepared for hazardous winter driving conditions with near zero visibility in bursts of heavy snow and blowing snow and quickly accumulating snow on untreated roads.

Please refer to your local public forecast for further details.