Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 301720 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 120 PM EDT THU OCT 30 2014 .AVIATION...
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//DISCUSSION... FAIRLY SOLID VFR STRATOCU DECK IN PLACE OVER MUCH OF LOWER MI SHOULD PERSIST INTO THE EVENING. OTHERWISE BENIGN CONDITIONS EXPECTED THE REST OF THE DAY INTO THE EARLY OVERNIGHT HOURS. ATTENTION THEN TURNS TO A STRONG SYSTEM DROPPING SOUTHWARD OUT OF SOUTHERN CANADA. THIS SYSTEM WILL DRAG A STRONG FRONT THROUGH THE REGION ON FRIDAY WITH PERIODS OF RAIN DEVELOPING. THE HEAVIER PRECIPITATION WILL OCCUR BEHIND THE FRONT...THOUGH SOME LIGHER PRECIPITATION WILL BEGIN LATE TONIGHT...SPREADING SOUTHEASTWARD THROUGH THE TERMINAL CORRIDOR. BANDS OF HEAVIER RAIN ARE POSSIBLE DURING THE DAY FRIDAY...AGAIN SPREADING SOUTHEASTWARD. THE RAIN MAY MIX WITH/TURN TO SNOW FRIDAY TOWARD THE END OF THE TAF PERIOD AS COLDER AIR WRAPS IN. THE STRONGER WINDS SHOULD HOLD OFF UNTIL AFTER THE 24 HOUR TAF PERIOD...BUT IFR CIGS/VIS ARE POSSIBLE FRIDAY. PREFER TO LEAVE IFR AND SNOW MENTION OUT OF THE TAFS FOR THIS ISSUANCE AND REFINE IN SUBSEQUENT FORECASTS. FOR DTW...SUB-5KFT DECK IN PLACE THIS AFTERNOON. SOME UNCERTAINTY WITH WHETHER BASES WILL LIFT AND/OR CIGS WILL SCATTER FOR A PERIOD LATE THIS EVENING AS INCREASING ASCENT ACTS TO RAISE THE INVERSION. THIS SCENARIO IS SUPPORTED BY SOME CLEARING OVER LAKE MI/INDIANA...HOWEVER WILL SIDE WITH FORECAST SOUNDINGS WHICH DEPICT CLOUD BASES REMAINING STEADY. ANY MEANINGFUL PRECIPITATION LOOKS TO HOLD OFF UNTIL FRIDAY MORNING AS THE UPPER SYSTEM AND COLD FRONT NEAR. BANDS OF HEAVIER RAIN ARE POSSIBLE DURING THE AFTERNOON AND EVENING WITH IFR RESTRICTIONS POSSIBLE. THE RAIN WILL TEND TO MIX WITH SNOW TOWARD FRIDAY EVENING AS WINDS TURN NORTHERLY AND BECOME QUITE GUSTY. LITTLE TO NO ACCUMULATION IS EXPECTED. WILL ADD MORE DETAIL WITH SUBSEQUENT FORECASTS. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS BELOW 5KFT THROUGH THIS EVENING...MEDIUM CONFIDENCE OVERNIGHT...HIGH CONFIDENCE FRIDAY. * MEDIUM CONFIDENCE IN SNOW MIXING WITH RAIN FRIDAY EVENING.
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&& .PREV DISCUSSION...ISSUED 335 AM EDT THU OCT 30 2014 SHORT TERM...TODAY AND TONIGHT SHORTWAVE RIDGING WILL TRACK EAST THROUGH THE CENTRAL GREAT LAKES THIS MORNING...KEEPING WINDS CALM AND CONDITIONS RELATIVELY DRY DURING THE DAYTIME HOURS. DESPITE MORNING SUNSHINE...CLOUDS WILL INCREASE THROUGH THE DAY AS MOISTURE ADVECTS IN FROM THE WEST AHEAD OF A DEVELOPING LOW PRESSURE SYSTEM DIVING SOUTH FROM CANADA TOWARDS THE NORTHWESTERN GREAT LAKES THIS AFTERNOON. GIVEN THE MID AND UPPER LEVEL WAVE WILL STILL BE FAR TO THE NORTHWEST...RAIN WITH THIS SYSTEM IS NOT EXPECTED TO AFFECT THE AREA TODAY. WITH COLD AIR STILL IN PLACE AND INCREASING CLOUDS...HIGHS WILL GENERALLY BE AROUND 50 DEGREES...WITH SOME MID 40S POSSIBLE OVER THE NORTHERN THUMB REGION. THE POSITIVELY TILTED MID LEVEL TROUGH OVER THE NORTHWESTERN GREAT LAKES WILL DIVE SOUTH OVER LAKE MICHIGAN TONIGHT AS THE SURFACE LOW TRACKS FROM THE SOO TO CENTRAL LAKE HURON. THIS WILL DRAG A SURFACE COLD FRONT THROUGH THE MIDDLE OF THE CWA LATE TONIGHT...BRINGING A RENEWED CHANCE FOR RAIN TO THE AREA. THE REAL COLD AIR WITH THIS FRONT WILL HOLD OFF A BIT...WITH ALL LIQUID PRECIPITATION EXPECTED THROUGH THE OVERNIGHT HOURS AS SOUNDINGS SHOW A FAIRLY WARM BOUNDARY LAYER THROUGH 12Z FRIDAY. THEREFORE WILL KEEP OUT MENTION OF SNOW MIXING IN WITH THE RAIN THROUGH THE OVERNIGHT HOURS. ALTHOUGH THE SURFACE FRONT WILL MAKE IT OVER THE WESTERN CWA LATE TONIGHT...THE MAIN MID AND UPPER LEVEL DYNAMICS WILL LAG BEHIND THE FRONT A BIT...AS EVIDENCED BY THE ABUNDANT AMOUNT OF POST FRONTAL PRECIPITATION. GIVEN THESE FACTORS WILL CONTINUE WITH THE HIGH LIKELY POPS ACROSS THE WEST TONIGHT AND NOT RAISE POPS TO CATEGORICAL WITH THIS ISSUANCE. THE ABUNDANT CLOUD COVER AND RAIN SHOWERS WILL KEEP THE DIURNAL RANGE TO A MINIMUM WITH LOWS AROUND 40 DEGREES TONIGHT GIVEN THE LAG OF COLD AIR BEHIND THE SURFACE COLD FRONT. LONG TERM... LATEST WATER VAPOR IMAGERY SHOWS CENTER OF UPPER LEVEL CIRCULATION/ PV ANOMALY OVER NORTHERN MANITOBA...ADVANCING SOUTHEAST. UNFORTUNATELY...THE 00Z MODELS (GFS/NAM/CANADIAN/EURO) STILL ARE NOT IN GOOD AGREEMENT WITH THE TRACK AND CLOSING OFF OF THE 500 MB LOW. NAM/GFS ARE CLOSING THE 500 MB OFF FASTER AND ARE FARTHER EAST...OVER WESTERN HALF OF LOWER MICHIGAN...WHILE EURO REMAINS OPEN A BIT LONGER AND IS MUCH FARTHER WEST...WITH THE CANADIAN BEING THE FARTHER EAST...TRACKING IN BETWEEN THE CENTRAL/EASTERN GREAT LAKES. REGARDLESS OF THE SOLUTION...A VERY TIGHT LOW LEVEL (925-850 MB) BAROCLINIC ZONE OVER SOUTHEAST MICHIGAN SETTING UP...WITH THE INCREASING NORTHEAST FLOW OFF THE WARM WATERS (LOWER 50S) OF LAKE HURON FURTHERING STRENGTHENING OR AT THE VERY LEAST MAINTAINING FRONTAL ZONE INTO FRIDAY NIGHT. SKEWING THE FORECAST A BIT TOWARD THE NAM...WHICH HOPEFULLY CAN FACTOR IN THE MESOSCALE INFLUENCE OF LAKE HURON A BIT BETTER...IT CONTINUES TO LOOK LIKE PREDOMINATELY RAIN/NON-ACCUMULATING WET SNOW THROUGH THE DAY ON FRIDAY...AS NAM MAINTAINS SURFACE DEW PTS COMFORTABLY ABOVE FREEZING THROUGH 21Z...WITH SIGNIFICANT DRYING THEN ATTEMPTING TO MAKE INROADS TOWARD THE U.S. 23 CORRIDOR. EXPECTING PRECIPITATION TO CONTINUE EAST OF U.S. 23 THROUGH FRIDAY NIGHT AS 850-700 MB MOISTURE/THETA-E RIDGE SEEN ARCHING BACK FRIDAY EVENING WITH CONTINUED LAKE HURON ENHANCEMENT TAKING PLACE BASED ON 850 MB TEMPS OF -5 TO -10 C. THE STRONG INFLUENCE/FLOW OFF LAKE HURON LOOKS TO BE THE OVERRIDING FACTOR IN THE EQUATION KEEPING SURFACE/NEAR SURFACE LAYER JUST WARM ENOUGH TO PREVENT MUCH IN THE WAY OF SNOW ACCUMULATION AS BOTH GFS/NAM INDICATING 925 MB TEMPS REMAINING ABOVE -3 C EAST OF U.S 23...WITH SURFACE DEW PTS STILL HOVERING AT OR ABOVE FREEZING. ALONG AND WEST OF U.S. 23...DRY AIR WILL PROBABLY WIN OUT...ESPECIALLY IF ONE IS TO BELIEVE THE EURO...BUT IF ANY PRECIPITATION DOES MAKE IT THIS FAR WEST...LIGHT SNOW ACCUMULATIONS WILL BE POSSIBLE. NORTHERLY WINDS WILL BE STRONG FRIDAY AFTERNOON/EVENING...BUT THERE IS LITTLE IN THE WAY OF DOWNWARD MOMENTUM (PREDOMINATELY CONTINUED POSITIVE LOW LEVEL ASCENT)...AND PRECIPITATION DRAG ISSUES TO CONTEND WITH. RISE/FALL COUPLET WORKING THROUGH IS ALSO NOTHING SPECIAL 10-12 MB...AND THUS EXPECTING GUSTS TO TOP OUT IN THE 35 TO 40 MPH RANGE...THE EXCEPTION WOULD BE RIGHT NEAR THE LAKE HURON LAKESHORE WHERE HIGHER GUSTS ARE POSSIBLE. AMPLIFIED UPPER LEVEL RIDGE WILL GRADUALLY BUILD INTO THE GREAT LAKES REGION OVER THE WEEKEND....SHUTTING OFF THE LAKE EFFECT AND ALLOWING TEMPERATURES TO ATTEMPT TO MODERATE. THE PROBLEM IS SURFACE HIGH BUILD IN WILL ALLOW FOR SURFACE TEMPERATURES TO CRATER (20S) SATURDAY NIGHT AS SKIES ARE EXPECTED TO BE MOSTLY CLEAR...AND BOUNDARY LAYER MIXING ON SUNDAY WILL BE LIMITED...AS SUN ANGLE/OVERALL INSOLATION DECLINES AS WE HEAD INTO NOVEMBER. 925 MB FORECASTED (EURO)TEMPS TO CLIMB TO SLIGHTLY POSITIVE...SUPPORTIVE OF MID 40S FOR HIGHS. MARINE... A RIDGE OF HIGH PRESSURE WILL MAINTAIN FAIRLY LIGHT WINDS AND LOW WAVES TODAY. A STRONG LOW PRESSURE SYSTEM AND ARCTIC FRONT REMAINS ON TRACK TO SWING INTO THE CENTRAL GREAT LAKES LATE TONIGHT. NORTHERLY WINDS WILL BECOME STRONG BEHIND THE FRONT FRIDAY AND FRIDAY NIGHT...WITH GUSTS LIKELY REACHING GALE FORCE OVER MUCH OF LAKE HURON. THE STRONG PERSISTENT NORTHERLY WINDS WILL ALLOW WAVE HEIGHTS TO BUILD IN EXCESS OF 10 FEET OVER SOUTHERN LAKE HURON. WINDS WILL GRADUALLY DIMINISH ON SATURDAY AS THE LOW MOVES EAST AND HIGH PRESSURE BUILDS INTO THE AREA. HOWEVER...THE WAVES WILL BE SLOWER TO DECREASE...AND WILL LIKELY NOT DROP BELOW 4 FEET UNTIL SATURDAY NIGHT. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...GALE WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING FOR LHZ362- 363-421-422-441-462. GALE WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY MORNING FOR LHZ442-443-463-464. GALE WATCH FROM FRIDAY MORNING THROUGH FRIDAY AFTERNOON FOR LHZ361. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....DT SHORT TERM...KURIMSKI LONG TERM....SF MARINE.......SF YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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