Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 031110 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 610 AM EST TUE MAR 3 2015 .AVIATION... SNOW WILL OVERSPREAD THE TERMINALS BETWEEN 12Z AND 14Z BECOMING STEADY IN THE 14Z-16Z TIME FRAME. PRECIPITATION WILL THEN BEGIN TO CHANGE TO FZRA FOR THE I-94 TERMINALS BY 17Z-18Z AND A MIX OF FZRA AND PL FURTHER NORTH INTO PTK/FNT BY 19Z-20Z. KMBS SHOULD REMAIN MAINLY SNOW. VFR CONDITIONS WILL BECOME MVFR AND THEN IFR AS THIS MOISTURE INCREASES TODAY. AS MID LEVEL MOISTURE STRIPS AWAY TO THE EAST THIS AFTERNOON...A PERIOD OF DZ/FZDZ WILL FOLLOW THE STEADIER PRECIPITATION WITH THIS THEN ENDING BY 01Z OR SO. BY THAT TIME A DRIER WEST/NORTHWEST FLOW IN THE WAKE OF THIS SYSTEM WILL BRING A GRADUAL IMPROVEMENT IN CONDITIONS WITH MVFR/LOWER VFR CIGS EXPECTED TONIGHT. FOR DTW...ONSET OF ACCUMULATING SNOWFALL STILL EXPECTED 13Z-15Z. BURST OF MODERATE SNOW IN IFR INITIALLY MAY RESULT IN A QUICK INCH OF ACCUMULATION LATE THIS MORNING. A TRANSITION TOWARD A PERIOD OF FZRA/IP CENTERED ON 17Z-19Z...THEN RA/DZ FROM MID AFTERNOON INTO THE EARLY EVENING. //DTW THRESHOLD PROBABILITIES... * HIGH IN CEILINGS BELOW 5000 FT 06Z TONIGHT...LOWER CONFIDENCE THEREAFTER. * LOW IN VISIBILITY AOB 1/2 MILE IN FOG MID AFTERNOON INTO THE EVENING. * HIGH IN SNOW AS DOMINANT PTYPE THROUGH 17Z...THEN TRANSITIONING TO FZRA/IP 17Z-19Z...AND RA/DZ AFTER 19Z-21Z. && .PREV DISCUSSION...ISSUED 320 PM EST MON MAR 2 2015 SHORT TERM...TONIGHT HIGH CLOUDS EMBEDDED WITHIN THE STRENGTHENING UPPER WIND FIELD ARE ADVECTING ACROSS THE UPSTREAM LOW AMPLITUDE SHORTWAVE RIDGE AXIS AND ARE RACING EAST ACROSS THE UPPER MIDWEST. THESE CLOUDS WILL PROVIDE THE ONLY INHIBITION TO RADIATING FOR THE FIRST HALF OF THE NIGHT AS SURFACE HIGH PRESSURE SLOWLY DEPARTS FROM THE REGION AND MAINTAINS A LIGHT GRADIENT THROUGH 06Z. DURING THIS TIME, DECENT RADIATING CONDITIONS SHOULD ALLOW TEMPERATURES TO FALL INTO THE TEENS AREAWIDE. INCREASING SE FLOW AND THICKENING CLOUD COVER WILL BOUNCE SURFACE TEMPS BACK UP TOWARD 20 DEGREES BY SUNRISE. LONG TERM...TUESDAY THROUGH SUNDAY MAIN FOUCS IS ON THE MIXED PRECIPITATION EVENT EXPECTED TUESDAY. IN SUMMARY...WINTER WEATHER ADVISORY IS IN EFFECT BEGINNING 13Z. 1-2 INCHES OF SNOW/SLEET FOR I-94 COUNTIES AND SOUTH...WITH 2-4 INCHES NORTH. ADDITIONALLY...UP TO 0.1 INCH ICE IS POSSIBLE FROM THE I-69 CORRDIOR SOUTHWARD. BRUNT OF THE EVENT IS EXPECTED BETWEEN 15-21Z. GOOD INTERMODEL AND RUN-TO-RUN CONSISTENCY WITH THE GENERAL EVOLUTION OF THE LARGE SCALE PATTERN AND TIMING OF LOCAL IMPACTS. SHORTWAVE ENERGY WILL EJECT FROM THE SOUTHERN CA UPPER LOW AND ZIP ACROSS THE PLAINS INTO THE GREAT LAKES TUESDAY. NO REAL PHASING BETWEEN THIS ENERGY AND THE NORTHERN STREAM TROUGH DROPPING OUT OF THE PRAIRIE PROVINCES...SO EXPECTING THIS EVENT TO BE A RELATIVELY QUICK-HITTER. MOISTURE TRANSPORT IS EXPECTED TO BE EXCELLENT BETWEEN THE DEPARTING SURFACE HIGH AND A BROAD AREA OF SURFACE LOW PRESSURE ATTENDANT TO THE LARGE-SCALE UPPER TROUGH...WITH NAM PROGS SHOWING PWAT NEAR 1 INCH ALONG THE OHIO BORDER FOR A BRIEF PERIOD AROUND 21Z...AND CROSS SECTIONS SHOWING H85-H7 SPECIFIC HUMIDITY OF 4-6 G/KG FROM 15-24Z. MAIN FORCING MECHANISM WILL BE ISENTROPIC LIFT ALONG THE LOW/MID TROPOSPHERIC TEMPERATURE GRADIENT. DESPITE MODEL AGREEMENT WITH THE LARGE SCALE FEATURES AND EVOLUTION...CONSIDERABLE UNCERTAINTLY REMAINS WITH RESPECT TO THERMAL FIELDS AND RESULTING P TYPE. GENERAL PROGRESSION WILL BE SNOW/SLEET TO FREEZING RAIN/RAIN. MODEL SOUNDINGS INDICATE A CONSIDERABLE DRY LAYER BETWEEN H9 AND H7 MUST BE OVERCOME...SO LIFT WILL INITIALLY GO TO SATURATING THE COLUMN. THE GOOD MOISTURE TRANSPORT WILL BE ABLE TO OVERCOME THE DRY LAYER THOUGH WITH PRECIP BREAKING OUT ROUGHLY 13-15Z AND QUICKLY SPREADING ACROSS THE REGION. PRECIP SHOULD BE SNOW INITIALLY BEFORE THE WARM NOSE CENTERED AROUND H8 POKES IN FROM SOUTH TO NORTH. THIS WILL CAUSE PRECIP TO MIX WITH AND CHANGE TO SLEET AND FREEZING RAIN. SURFACE TEMPS ARE A TOUGH CALL...WITH WAA BEING OFFSET BY WET BULBING. THERE DOES EXIST A BRIEF WINDOW FOR FREEZING RAIN ALONG/SOUTH OF I-69 ROUGHLY 17-21Z AS CURRENT FORECAST CALLS FOR SURFACE TEMPS TO REMAIN AOB FREEZING UNTIL 18-21Z. HOWEVER...THIS DOES NOT APPEAR TO BE A CLASSIC SETUP FOR A GOOD ICING EVENT GIVEN THE STRONG WAA /LACK OF LOW-LEVEL COLD AIR RESUPPLY/ AND MARGINAL MAGNITUDE OF THE WARM NOSE. BACK ROADS WILL LIKELY SEE GREATER IMPACTS THOUGH GIVEN FROZEN GROUND AND MAY SEE LIQUID FREEZING ON SURFACES EVEN IF AIR TEMPS ARE ABOVE FREEZING. MODERATE/LOCALLY HEAVY PRECIP IS POSSIBLE 15-21Z GIVEN THE MOISTURE QUALITY AND REDUCED STATIC STABILITY ABOVE THE LOW-LEVEL TEMPERATURE GRADIENT AS INDICATED BY CROSS SECTIONS...POSSIBLY LEADING TO A MORE CONVECTIVE/SHOWERY LOOKING PRECIP SHIELD. MODEL QPF CONSENSUS IS NOT GREAT WITH ECMWF SPITTING OUT A BROAD 0.25 AROSS THE AREA WHILE NAM APPEARS TO BE MORE AGRESSIVE WITH THE DRY SLOT DRYING THINGS OUT OVER THE NORTH AND SHOWING ENHANCED CONVECTION TO THE SOUTH OF THE DRY SLOT LEADING TO LOCALLY UP TO 0.50". OPTED FOR A COMPROMISE WITH 0.25" ACROSS THE NORTH TO 0.35" ACROSS THE SOUTH...THOUGH GIVEN CONVECTIVE NATURE OF PRECIP IT WILL LIKELY NOT END UP BEING A SMOOTH DISTRIBUTION. A COMBINATION OF THE DRY SLOT ARRIVAL AND MAIN MOISTURE AXIS PEELING OFF TO THE EAST WILL CAUSE PRECIP TO COME TO AN END 21-00Z. SOME POTENTIAL FOR DZ/FZDZ AS THIS OCCURS. CAA ENSUES AFTER 00Z AS WINDS VEER WESTERLY...WITH LOWS IN THE LOW/MID 20S BY 12Z WED. LONG WAVE TROUGH AMPLIFICATION ACROSS THE WRN GREAT LAKES ON WEDNESDAY WILL USHER IN ANOTHER ROUND OF ARCTIC AIR TO THE REGION /850MB TEMPS ARE FORECAST TO DROP TO -22C BY 06Z THURS/. THIS WILL RESULT IN WED HIGH TEMPS OCCURRING IN THE MORNING AND SLOWLY FALLING DURING THE AFTERNOON AND EVENING. A STRONG BAROCLINIC ZONE ACROSS THE ERN US AND LONG WAVE TROUGH AMPLIFICATION WILL INTENSIFY THE UPPER JET STREAK OVER THE GREAT LAKES /190+ KTS/ ON WEDNESDAY. WHILE THE FRONTAL DYNAMICS AND DEEP MOISTURE WILL RESIDE WELL SOUTH OF THE STATE...A FAIR AMOUNT OF MID/HIGH LEVEL CLOUDS ARE LIKELY TO RESIDE OVER SE MI. THIS ALONG WITH SOME LOW LEVEL MOISTURE ALONG A SECONDARY SFC TROUGH POSITIONED ACROSS THE NRN GREAT LAKES MAY SUSTAIN A GOOD DEAL OF CLOUDS WELL INTO WED NIGHT...SUPPORTING A CONSERVATIVE APPROACH TO WED NIGHT MINS /AROUND ZERO/. THURS WILL BE THE COLDEST DAY OF THE FORECAST PERIOD AS HIGHS MAY STRUGGLE TO REACH 20 WITH A DEEP POOL OF ARCTIC AIR OVER LOWER MI. SURFACE HIGH PRESSURE WILL THEN SLIDE INTO THE MID ATLANTIC ON FRIDAY AS MID LEVEL HEIGHTS REBOUND ACROSS THE GREAT LAKES REGION. WITH THE DEPARTURE OF THE DEEP COLD POOL TO THE EAST AND STRENGTHENING SOUTHERLY FLOW...A MODEST WARMING TREND WILL OCCUR FRI INTO SATURDAY. THE OVERALL LONG WAVE PATTERN THIS WEEKEND INTO EARLY NEXT WEEK WILL CONTINUE TO FEATURE A LONG WAVE RIDGE OVER THE WEST COAST AND TROUGH ACROSS THE GREAT LAKES/ERN CANADA. THE WAVELENGTH WILL JUST NOT BE AS AMPLIFIED AS THE LAST MONTH. THIS AND SEVERAL SHORTER WAVELENGTH PERTURBATIONS ROTATING INTO THE NRN GREAT LAKES WILL HOLD TEMPS A LITTLE COLDER THAN EARLY MARCH MEANS DURING THE LATER HALF OF THE FORECAST PERIOD. MARINE... THE DEPARTURE OF HIGH PRESSURE TO THE EAST AND APPROACH OF A LOW PRESSURE SYSTEM WILL CAUSE SOUTHERLY WINDS TO DEVELOP TONIGHT. THE SURFACE LOW IS FORECAST TO TRACK ACROSS THE STRAITS ON TUESDAY. SOUTHERLY WINDS WILL INCREASE AS THIS LOW APPROACHES. WINDS WILL THEN VEER TO THE WEST TUES NIGHT AS THE LOW DEPARTS TO THE EAST. THERE WILL BE AN INCREASE IN THE WESTERLY WINDS ON WED AS ANOTHER SURGE OF ARCTIC AIR OVERSPREADS THE LAKES. THERE IS A POTENTIAL FOR GUSTS TO APPROACH GALE FORCE OVER FAR NORTHERN LAKE HURON ON WEDNESDAY. THE CHANCES FOR ANY GALE FORCE GUSTS TO EXCEED TWO HOURS IN DURATION DOES NOT APPEAR HIGH ENOUGH TO JUSTIFY A GALE WATCH ATTM. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MIZ047>049- 053>055-060>063-068>070. WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR MIZ075- 076-082-083. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....DG SHORT TERM...JVC LONG TERM....DT/SC MARINE.......SC YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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