Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 300453 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1153 PM EST THU JAN 29 2015 .AVIATION... SHALLOW COLD AIR ADVECTION UNDER A DEEP LOW LEVEL INVERSION WILL SUSTAIN MVFR CIGS AND GUSTY WINDS...POSSIBLY GUSTING TO 30 KNOTS AT TIMES...OVERNIGHT. HIGH PRESSURE BUILDING IN ACROSS TEH WESTERN GREAT LAKES ON FRIDAY WILL CLEAR OUT THE CEILINGS FRIDAY MORNING...WITH LIGHTER WINDS EXPECTED BY THE AFTERNOON AS THE PRESSURE GRADIENT LOOSENS. FOR DTW...CIGS AROUND 3000 FT ARE EXPECTED THROUGH FRIDAY MORNING WHEN HIGH PRESSURE BRINGS DRIER AIR IN OVER THE CENTRAL GREAT LAKES. //DTW THRESHOLD PROBABILITIES... * HIGH IN CIGS BELOW 5000 FT OVERNIGHT. * MEDIUM IN WIND GUSTS EXCEEDING CROSS WIND THRESHOLDS OVERNIGHT. && .PREV DISCUSSION...ISSUED 806 PM EST THU JAN 29 2015 UPDATE... LARGE SCALE SUBSIDENCE BEHIND A DEPARTING COLD FRONT HAS BROUGHT AN END TO THE SNOW SHOWERS ACROSS SOUTHEAST MICHIGAN EARLY THIS EVENING...WITH ONLY SOME LIGHT SNOW SHOWERS OR FLURRIES EXPECTED THE REST OF THE NIGHT WITH NO ADDITIONAL ACCUMULATIONS. SNOWFALL ACCUMULATIONS THIS AFTERNOON AND EARLY THIS EVENING CAME IN AT ABOUT 1 TO 1.5 INCHES FROM DETROIT NORTHWARD. WHILE THE FRONT HAS BROUGHT AN END TO THE SNOW...IT HAS BROUGHT A MARKED INCREASE IN WIND SPEEDS WITH NORTHWESTERLY WINDS GUSTING TO 20 TO 30 MPH. A SECONDARY COLD FRONT WILL SEND TEMPERATURES PLUMMETING LATER TONIGHT AS WIND SPEEDS INCREASE FURTHER TO AROUND 30 MPH. THE COMBINATION OF COLD AND WIND WILL SEND WIND CHILLS DOWN BELOW ZERO LATE TONIGHT. PREV DISCUSSION...ISSUED 254 PM EST THU JAN 29 2015 SHORT TERM...LATE THIS AFTERNOON AND TONIGHT THE BACK EDGE OF THE PRECIPITATION SHIELD WILL CONTINUE ON AN EASTWARD TRACK LATE THIS AFTERNOON...ADVANCING ACROSS SE MI OVER THE NEXT TWO TO THREE HOURS. SOME LINGERING MID LEVEL DEFORMATION ASSOCIATED WITH THE SHORT WAVE NOW OVER OHIO AND BRIEF MID LEVEL FGEN PRECEDING A MID LEVEL TROUGH NOW WORKING INTO LAKE MI HAVE BEEN THE PRIMARY FORCING MECHANISMS DRIVING THIS PRECIP. THERE HAS BEEN JUST ENOUGH LOW LEVEL COOLING TO SUPPORT A COMPLETE CHANGE OVER TO SNOW IN MOST LOCALS. STEEP MID LEVEL LAPSE RATES WILL CONTINUE TO SUPPORT SOME BRIEF BURSTS OF HEAVY SNOW. GIVEN THE SHORT DURATION AND WITH SFC TEMPS IN THE 30S OVER MOST OF THE FORECAST AREA...ADDITIONAL SNOW ACCUMS PRIOR TO THE END OF THE PRECIP SHOULD REMAIN A HALF INCH OR LESS. LARGE SCALE SUBSIDENCE WITHIN THE DESCENDING BRANCH OF THE MID LEVEL FRONTAL CIRCULATION WILL OVERSPREAD SE MI EARLY THIS EVENING. THIS WILL SUSTAIN A DEEP LOW LEVEL INVERSION...HOLDING AMPLE LOW CLOUDS OVER THE REGION. A POTENT NORTHERN STREAM MID LEVEL TROUGH HAS BEEN TRACKING ACROSS NRN ONTARIO THIS AFTERNOON. THIS WAVE WILL CONTINUE TO ADVANCE TO THE SOUTHEAST TONIGHT...MOVING ACROSS SE MI DURING THE FIRST HALF OF THE OVERNIGHT PERIOD. THIS WILL DRIVE AN ARCTIC COLD FRONT ACROSS THE FORECAST AREA DURING THE 03Z TO 06Z TIME FRAME. PRIOR TO THE ARRIVAL OF THIS FRONT...LIMITED COLD AIR ADVECTION WILL HOLD TEMPS IN THE LOW 30S EARLY THIS EVENING. 925MB TEMPS ARE THEN FORECAST TO PLUNGE TO -18C BY DAYBREAK FRI IN THE WAKE OF THE COLD FRONT. THIS WILL CAUSE SFC TEMPS TO DROP TOWARD THE LOW TEENS/UPPER SINGLE DIGITS. THE COLD AIR WILL BE DRIVEN INTO THE AREA VIA STRONG W-NW WINDS. WHILE THE SFC ISSALOBARIC COMPONENT WILL BE RATHER WEAK...A PUSH OF GOOD SYSTEM RELATIVE ISENTROPIC DESCENT TRAILING THE MID LEVEL WAVE AND STEEPENING LOW LEVEL LAPSE RATES WILL BRING SOME STRONGER WIND GUSTS TO THE SFC. RECENT MODEL SOUNDINGS WOULD SUPPORT A FEW GUSTS TOPPING 30 MPH OVERNIGHT. WIND CHILLS WILL IN TURN BE DRIVEN DOWN TO THE SINGLE DIGITS AND SUB ZERO READINGS BY EARLY FRI MORNING. ALTHOUGH THERE WILL BE GOOD LARGE SCALE ASCENT LATE THIS EVENING PRECEDING THE MID LEVEL WAVE...THE LACK OF MOISTURE ABOVE THE INVERSION WILL LIMIT SNOWFALL POTENTIAL. LAKE CONTRIBUTION INTO SE MI WILL ALSO BE LIMITED BY THE MEAN NW WIND TRAJECTORIES. THUS JUST SOME FLURRIES OR LIGHT SNOW SHOWERS LOOK POSSIBLE /MAINLY ALONG THE LEAD PUSH OF LOW LEVEL ASCENT ALONG THE ARCTIC FRONT/. LONG TERM... HEALTHY SHOT OF ARCTIC AIR IN PLACE TO START THE DAY ON FRIDAY...WITH 925 MB TEMPS ADVERTISED TO BE IN THE NEGATIVE UPPER TEENS. THE LOW LEVEL COLD ADVECTION WILL BE EXHAUSTED DURING THE DAY...AS FLOW WEAKENS AND UPPER LEVEL RIDGE BUILDS OVER THE WESTERN GREAT LAKES LATE IN THE DAY. NAM SOUNDINGS INDICATING SUPERSATURATION WITH RESPECT TO ICE BETWEEN 1000-2000 FOOT LAYER...ENOUGH FOR MENTION OF A FLURRY OR TWO. HOWEVER...FLOW WILL BE NORTHWEST-NORTH...UNFAVORABLE FOR ANY LAKE FEED (EXCEPT FOR EASTERN THUMB SHORELINE WHERE MAIN LAKE BAND WILL HAVE TO BE WATCHED)...WITH DOWN SLOPING COMPONENT INTO MUCH OF SOUTHEAST MICHIGAN. WILL THUS ALLOW FOR GOOD SHARE OF SUNSHINE...ALLOWING MAXES TO REACH INTO THE MID TEENS TO AROUND 20 DEGREES...WHICH IS STILL OVER 10 DEGREES BELOW NORMAL. SEVERAL KEY FEATURES TO FOCUS ON FOR THE WEEKEND FORECAST. THE FIRST ONE BEING THE INTENSE CYCLONE OFF THE NEW ENGLAND COAST FRIDAY NIGHT. THIS SYSTEM IS SLOW TO EXIT...AND THUS BECOMES MERGED WITH NEXT STRONG UPPER LEVEL TROUGH SWINGING THROUGH ONTARIO ON SATURDAY. THE FAILURE OF THIS SYSTEM TO CLEAR EASTERN CANADA IN TIMELY MANNER LIKELY CONTRIBUTING TO SUPPRESSING/DELAYING THE AMPLIFICATION OF THE SYSTEM COMING OUT OF THE CENTRAL/SOUTHERN PLAINS FOR THE SECOND HALF OF THE WEEKEND. THAT SYSTEM IS RELYING ON THE INTERACTION OF AT LEAST TWO UPPER WAVES...ONE ZIPPING OUT OUT OF THE GULF OF ALASKA AND THE OTHER BEING THE UPPER LEVEL LOW OFF THE COAST OF BAJA CALIFORNIA. THAT SOUTHERN SYSTEM IS AWFUL FAR TO THE SOUTH AND OFFSHORE...WITH ONLY A PIECE OF ENERGY EXPECTED TO BREAK OFF AND INTERACT WITH NORTHERN STREAM WAVE. AS SUCH...MODEL CONSENSUS (GFS/NAM) IS FOR UPPER LEVEL WESTERN CONFLUENT FLOW AND HIGH PRESSURE BUILDING UNDERNEATH TO WIN OUT OVER MUCH OF GREAT LAKES REGION ON SUNDAY...AS EVEN 12Z CANADIAN HAS ABANDONED SHIP FROM ITS 00Z RUN. STILL...UNTIL THE WAVE OVER THE GULF OF ALASKA FULLY COMES ONSHORE AND MAGNITUDE IS RESOLVED...WILL NOT RULE OUT LIGHT ACCUMULATING SNOW ALL TOGETHER FOR SUNDAY JUST YET...SEE 12Z EURO/NAVGEM...BUT CHANCES ARE CERTAINLY HIGHEST TOWARD THE OHIO BORDER WHERE WILL CARRY A 50 POP. A NORTHEAST COMPONENT OFF LAKE HURON MAY ALSO BE SUFFICIENT TO GENERATE SOME LAKE EFFECT SNOW SHOWERS...BUT OVERALL DRY AIRMASS (SURFACE DEW PTS OF -20 TO -30 F NEAR GEORGIAN BAY) AND LOW INVERSION HEIGHTS WILL BE TOUGH TO OVERCOME. THE LOW WILL BE IN THE PROCESS OF LIFTING OFF TO THE NORTHEAST TOWARDS THE EAST COAST OVERNIGHT SUNDAY INTO EARLY MONDAY. THINGS SETTLE DOWN ON MONDAY AS HIGH PRESSURE BUILDS IN...HOWEVER LOOKING AT TEMPS ONLY TOPPING OFF IN THE TEENS FOR HIGHS ON MONDAY. THE NEXT ACTIVE PERIOD RETURNS TO THE AREA IN THE TUESDAY/WEDNESDAY TIMEFRAME AS ANOTHER POTENTIAL CLIPPER MOVES IN. MARINE... LOW PRESSURE EXITING THE CENTRAL GREAT LAKES THIS AFTERNOON...WITH QUICK RAMP UP TO NORTHWEST GALES EXPECTED BY EARLY THIS EVENING AS AIRTIC AIRMASS STREAMS INTO THE AREA. CONFIDENCE IS HIGH IN GALES FOR MAJORITY OF LAKE HURON WITH LAKE INDUCED TROUGHING ENHANCING THE FLOW...ALONG WITH WINDS BECOMING NORTHWEST-NORTH INCREASING THE FETCH. LARGE AREA OF HIGH PRESSURE WILL SLOWLY BUILD EAST INTO THE ENTIRE GREAT LAKES REGION ON FRIDAY...ALLOWING WINDS TO BECOME LIGHT LATE IN THE DAY INTO FRIDAY NIGHT. A WEAK LOW WILL TRACK ACROSS THE NORTHERN GREAT LAKES ON SATURDAY...LEADING TO MODERATE SOUTHWEST FLOW OVER CENTRAL LAKE HURON AHEAD OF IT. WINDS WILL THEN SWING AROUND TO THE NORTHWEST AND VEER AROUND TO THE NORTHEAST AS WE HEAD INTO SUNDAY. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...HEAVY FREEZING SPRAY WARNING UNTIL 7 PM EST FRIDAY FOR LHZ362-363- 441-462>464. GALE WARNING UNTIL 10 AM EST FRIDAY FOR LHZ362-363-421-441>443- 462>464. HEAVY FREEZING SPRAY WARNING UNTIL 4 AM EST FRIDAY FOR LHZ361. GALE WARNING UNTIL 4 AM EST FRIDAY FOR LHZ361. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI UPDATE.......KURIMSKI SHORT TERM...SC LONG TERM....SF/SS MARINE.......SF YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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