Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 270453 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1153 PM EST WED NOV 26 2014 .AVIATION... //DISCUSSION... A DEEP INVERSION BASED AROUND 4K FT AGL IS EXPECTED TO PERSIST THROUGH THE NIGHT AND INTO EARLY THURS AFTERNOON. THIS WILL SUSTAIN A 3500-4500 FT STRATUS DECK ACROSS SE MI. THERE HAS ALSO BEEN A SECOND CLOUD DECK BASED BETWEEN 2500 FT AND 3000 FT WITH SOME FLURRIES. IN TERMS OF SE MI...THESE LOWER CLOUDS AND FLURRIES HAVE BEEN MORE PREVALENT IN AND AROUND METRO DETROIT WHERE SOME BETTER LOW LEVEL MOISTENING FROM THE EAST HAS OCCURRED THIS AFTERNOON. THE LOW LEVEL FLOW WILL BACK FROM NORTHEAST THIS EVENING TO NORTHWEST OVERNIGHT. SOME ADDED HEAT FLUX OFF LAKE HURON OVERNIGHT MAY BOOST THE INVERSION A LITTLE BIT. THE TREND TOWARD NORTHWEST FLOW MAY ALSO ADD JUST A LITTLE DRYING TO THE LOW LEVELS. THESE FACTORS SUGGEST A TREND TOWARD PREVAILING LOW END MVFR CLOUD BASES /3500-4500 FT/ OVERNIGHT...ALTHOUGH FLUCTUATING CEILINGS COULD STILL BE POSSIBLY THROUGH DAYBREAK THURS. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH TONIGHT AND THURSDAY MORNING. && .PREV DISCUSSION...ISSUED 924 PM EST WED NOV 26 2014 UPDATE... AVAILABLE RADAR DATA OVER LAKE HURON SUGGESTS SOME UPTICK IN SNOW SHOWER ACTIVITY THIS EVENING...AIDED BY LIFT AHEAD OF A WEAK MID LEVEL SHORT WAVE TRACKING INTO THE THUMB REGION. THE 00Z DTX SOUNDING DOES SHOW TEMPS OF -13C AT THE BASE OF INVERSION. SUSPECT CONVECTIVE DEPTHS OVER LAKE HURON TO BE HIGHER. THE NAM AND HRR SUGGEST BUILDING HIGH PRESSURE ACROSS GEORGIAN BAY OVERNIGHT WILL BRIEFLY FORCE THIS CONVERGENCE INTO THE THUMB REGION /POSSIBLY PORT HURON/ PRIOR TO AN OVERALL BACKING OF THE FLOW TO THE NORTHWEST AFTER 09Z. LATEST OBS INDICATE THAT THIS HIGH IS NOT AS STRONG AS THESE SOLUTIONS SUGGEST. THESE FACTORS SUPPORT HOLDING ONTO JUST A CHANCE OF SHSN ACROSS THE LAKE HURON SHORELINE...BUT INCREASING THE CHANCES A BIT FROM THE CURRENT FORECAST. THE DEEP INVERSION WILL HOLD CLOUDS IN PLACE THROUGH THE NIGHT. THIS AND LITTLE TO NO OVERALL THERMAL ADVECTION SUGGESTS NIGHTTIME TEMPS NOT FALLING MUCH FROM CURRENT READINGS. JUST A MINOR UPWARD ADJUSTMENT IN OVERNIGHT LOWS WILL BE MADE. PREV DISCUSSION...ISSUED 351 PM EST WED NOV 26 2014 SHORT TERM...TONIGHT NORTHEAST GRADIENT WRAPPING AROUND THE EAST COAST CYCLONE WILL FUNNEL LIGHT NORTHEASTERLY WINDS INTO ONTARIO THROUGH TONIGHT. LAKE TROUGHING OVER LAKE HURON WILL NUDGE THE FLOW TOWARD A MORE VEERED EASTERLY FETCH AS IT APPROACHES THE SHORELINE OF THE THUMB TONIGHT. INCREASED CONVERGENCE WITHIN THE LAKE-INDUCED TROUGH AND ALONG THE SHORELINE MAY YET SUPPORT A PARTIAL COVERAGE OF SNOW SHOWERS WORKING INLAND. THERMODYNAMIC PROFILES LEAVE A LOT TO BE DESIRED, PARTICULARLY WITH REGARD TO A RESPECTABLE DEPTH OF SATURATION WITHIN THE DENDRITE GROWTH LAYER, SO NOT EXPECTING MORE THAN MINOR ACCUMULATIONS IN HURON AND SANILAC COUNTIES WITH THE MOIST RESIDENT AIRMASS SUPPORTING PATCHES OF FLURRIES ELSEWHERE. STOUT INVERSION EVIDENT ON THIS MORNING`S 12Z DTX SOUNDING AND ONGOING MOIST EASTERLY FETCH THROUGH TODAY YIELD CONTINUED HIGH CONFIDENCE IN LOW CLOUD COVER TONIGHT WHICH WILL CONTAIN OVERNIGHT LOWS TO THE MID/UPPER 20S. LONG TERM...THURSDAY THROUGH TUESDAY FAIRLY UNSTABLE/PROGRESSIVE UPPER LEVEL PATTERN LOOKING TO SET UP ACROSS THE CONUS THIS WEEK AS THE CURRENT TROUGH EXITS EAST BY THE WEEKEND. WITH THE EXIT OF THE AMPLIFIED TROUGH...A MUCH MORE ZONAL FLOW SETUP WILL DEVELOP AS AN UPPER LOW STALLS OFF THE COAST OF CALIFORNIA AND ANOTHER WOBBLES ABOUT ITSELF OVER NORTHERN CANADA. THIS WILL STEER THE FLOW EASTERLY BY NEXT WEEK WITH THE MAIN BAROCLINIC ZONE LINING UP VERY NEAR TO THE AREA. THIS RESULTS IN A LOWER CONFIDENCE FORECAST AS A SLIGHT WOBBLE NORTH OR SOUTH COULD LEAD TO NOTABLE CHANGES IN THE FORECAST. THE CURRENT TROUGH WILL BE DRIFTING EASTWARD ON THANKSGIVING WITH THE UPPER LEVEL TROUGH AXIS TRAVERSING THE AREA IN THE MORNING AND A MID LEVEL TROUGH PASSING OVERHEAD IN THE AFTERNOON. THIS WILL USHER IN A VERY COLD AIRMASS WHICH IS BELOW -22C AT 850MB OVER SOUTH/CENTRAL CANADA BUT WILL BE MODIFIED A BIT TO AROUND -17C BY THE TIME IT REACHES SE MI THURSDAY NIGHT. DURING THE DAY THURSDAY WE WILL HAVE A CHANCE OF LIGHT SNOW SHOWERS DUE TO THE COMBINATION OF THE MID LEVEL TROUGH PASSING AND WESTERLY FLOW AIDING IN A FEW LAKE EFFECT SHOWERS LATER IN THE DAY. DOES NOT LOOK TO MUCH IN THE WAY OF ACCUMULATION WITH THIS SCENARIO AS THE TROUGH PUSHES THE BETTER MOISTURE...A MEAGER 0.25-0.30 PWAT...EARLIER IN THE DAY WITH THE COLDER AIR ALOFT AND BETTER LL LAPSE RATES COMING LATER IN THE DAY. MODEL RH FIELDS SHOW A DRAMATIC DROP OFF IN MOISTURE THROUGHOUT THE COLUMN LATER IN THE DAY AS WELL AS THE SHORTWAVE RIDGE BUILDS INTO LOWER MI. THIS SHOULD SHUT OFF ANY LINGERING SNOW SHOWERS LATER THURSDAY EVENING LEADING TO A DRY OVERNIGHT PERIOD. KEPT ACCUMULATIONS LESS THAN A HALF INCH THROUGH THE DAY. BETTER CHANCE OF SNOWFALL ON FRIDAY AS RIDGING BUILDS EASTWARD THROUGH THE CENTRAL CONUS PUSHES THE ACTIVE JET NORTH INTO THE GREAT LAKES. THIS WILL DIRECT THE LEAD EDGE OF A SHEARING PV ANOMALY INTO SOUTHERN MI COINCIDENT WITH A BAND OF ISENTROPIC ASCENT ON THE ELEVATED WARM FRONT ACROSS CENTRAL MI ON THE NOSE OF A MORE THETA E RICH AIRMASS. MODELS HAVE TRENDED A BIT FURTHER SOUTH WITH THE BEST FGEN/ISENTROPIC ASCENT BAND THUS SLIGHTLY INCREASED THE POP/QPF/SNOW AMOUNTS SOUTHWARD AS WELL. START OF THE SNOW IS IN QUESTION AS MODELS STRUGGLE TO KEEP THE LOW LEVELS SATURATED...EVEN SEVERAL HOURS AFTER THE COLUMN SATURATES ABOVE 800MB. STILL THINK IT LOOKS LIKE A DECENT SETUP FOR SOME LIGHT ACCUMULATIONS AS THE FLOW ALIGNS WITH THE AXIS OF THE FORCING GIVING IT A BETTER RESIDENCE TIME. WITH MODELS IN FAIR AGREEMENT WITH AROUND 0.10 INCHES OF QPF FRI-FRI NIGHT...THINKING A 1-2 INCH SNOWFALL FORECAST SEEMS FAIR. A ZONAL PATTERN WITH MODERATE WARM AIR ADVECTION WILL HOLD THROUGH THE WEEKEND. THIS WILL BOOST TEMPS TO SLIGHTLY ABOVE NORMAL FOR SUNDAY. A MID-LEVEL WAVE WILL THEN DYNAMICALLY FORCE A COLD FRONT ACROSS THE REGION SUNDAY EVENING/NIGHT...WITH MUCH COLDER AIR THEN FILTERING IN. STRONG 1044 MB HIGH PRESSURE SYSTEM WILL USHER IN COLD CANADIAN/ARCTIC AIR EARLY NEXT WEEK. THAT PATTERN WILL HOLD THROUGH THE 7 DAY FORECAST WITH TEMPS TRENDING COLDER THAN NORMAL AND PRECIP CHANCES QUITE LOW. MARINE... WEAK AREA OF HIGH PRESSURE WILL RESULT IN LIGHT EASTERLY WINDS AND LOW WAVE HEIGHTS THROUGH TONIGHT. ON THURSDAY...AN ARCTIC COLD FRONT WILL DROP THROUGH THE GREAT LAKES USHERING IN A COLDER AND MORE UNSTABLE AIRMASS. THIS WILL RESULT IN WINDS INCREASING AS THE BECOME NORTHWESTERLY DURING THE DAY. CURRENT GUIDANCE OFFERS NO CLEARER PICTURE FOR THE POTENTIAL GALE FORCE WINDS OVER CENTRAL LAKE HURON THURSDAY AFTERNOON. WINDS STILL LOOK TO INCREASE RAPIDLY IN THE AFTERNOON BUT DO NOT LOOK TO STAY ELEVATED FOR VERY LONG BEFORE SLOWLY DECREASING THROUGH THE NIGHT AS THE COLD AIR CONTINUES TO ADVECT OVER THE WATERS. WILL HOLD ONTO THE GALE WATCH UNTIL MORE CONFIDENCE CAN BE RESOLVED. FLOW THEN TURNS TO THE SOUTHWEST ON FRIDAY AS A WARM FRONT LIFTS NORTH THROUGH THE AREA. THIS WILL AGAIN INTRODUCE GUSTY WINDS ACROSS THE EASTERN LAKES. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...GALE WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY EVENING FOR LHZ362-363. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....SC UPDATE.......SC SHORT TERM...JVC LONG TERM....DRK/MM MARINE.......DRK YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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