Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 010450 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1150 PM EST SAT JAN 31 2015 .AVIATION... MVFR CIGS CONTINUE TO SLOWLY ADVECT SOUTHWARD THIS EVENING AS LOW LEVEL MOISTURE SINKS SOUTH AND SNOWFALL ADVECTS NORTH. UPSTREAM RADAR OBSERVATIONS SHOW A SHIELD OF LIGHT SNOW LIFTING NORTHEAST FROM SOUTHWESTERN MICHIGAN EARLY SUNDAY MORNING...THE BEGINNING OF A LONG DURATION WINTER STORM SYSTEM EXPECTED TO LAST THROUGH SUNDAY NIGHT. WELL ORGANIZED DYNAMICS AT THE START SUGGESTS IFR VSBYS IN SNOW AT THE START. LIFR CONDITIONS ARE EXPECTED DURING THE LATE AFTERNOON AND EVENING HOURS DURING THE HEIGHT OF THE EVENT. SEVERAL INCHES OF ACCUMULATING SNOW ARE EXPECTED WITH HIGHEST TOTALS AT THE METRO TAF SITES. AT DTW...TIMING OF LIGHT SNOW AT DTW IS BETWEEN 6Z AND 8Z. SNOWFALL RATES OF A QUARTER INCH TO A THIRD OF AN INCH PER HOUR IS EXPECTED AT ONSET. //DTW THRESHOLD PROBABILITIES... * HIGH CONFIDENCE IN CIGS BELOW 5000 FT THROUGH THE TAF PERIOD. * HIGH CONFIDENCE IN PRECIPITATION TYPE OF SNOW. && .PREV DISCUSSION...ISSUED 350 PM EST SAT JAN 31 2015 SHORT TERM... STORM TERM TONIGHT THROUGH SUNDAY NIGHT WATCH HEADLINES WILL BE UPGRADED TO A WARNING WITH THE AFTERNOON FORECAST PACKAGE AND AN ADVISORY WILL BE ISSUED FOR THE I-69 CORRIDOR ALL BEGINNING 06Z TONIGHT AND ENDING 12Z MONDAY. THE EXPIRATION IS EXTENDED OVER THE WATCH VALID TIME TO ENCOMPASS A SLIGHTLY SLOWER SYSTEM DEPARTURE. THE ADDITION OF THE M-59 CORRIDOR TO THE WARNING IS BASED ON THE EXPECTATION OF SNOWFALL TOTALS REACHING OR EXCEEDING 6 INCHES IN THE 9 TO 12 HOUR PERIOD FROM ABOUT 21Z SUNDAY TO 09Z MONDAY MORNING...BUT ALSO WITH A HIGH LIKELIHOOD THAT EVENT TOTALS WILL REACH 8 INCHES ALONG THE I-96/696 CORRIDOR. TOTALS WILL EASILY EXCEED 8 INCHES FOR THE 24-30 HOUR EVENT FROM ANN ARBOR TO DETROIT AND SOUTH TO THE OHIO BORDER. THE HIGHEST POTENTIAL FOR DOUBLE DIGIT ACCUMULATION REMAINS ALONG AND SOUTH OF THE I-94 CORRIDOR WHERE ONSET WILL BEGIN FIRST TONIGHT SHORTLY AFTER MIDNIGHT AND END CLOSER TO SUNRISE MONDAY. TODAY AT LEAST TURNED OUT NICE WITH SOME SUNSHINE HELPING LIFT AFTERNOON TEMPS INTO THE LOWER HALF OF THE 30S. THE MILD SOUTHWEST WIND IS OCCURRING AHEAD OF A COLD FRONT THAT WILL SWEEP THE REST OF THE WAY THROUGH LOWER MICHIGAN DURING THE EVENING WILL LITTLE CONSEQUENCE OTHER THAN MOVING SOUTH OF THE OHIO BORDER TO AWAIT THE PLAINS LOW PRESSURE SYSTEM. SATELLITE IMAGERY INDICATES THE UPPER LEVEL FEATURES FACTORING INTO THE PLAINS SYSTEM ARE DEVELOPING ACCORDING TO MODEL PLAN. A DISTINCTIVE PIECE OF THE SW U.S. CLOSED LOW IS BREAKING OUT OF THE CIRCULATION AND INTO THE PLAINS WHERE SURFACE PRESSURE FALLS ALREADY HAVE A WELL-DEFINED PLUME OF MOISTURE TRANSPORT UNDERWAY. THIS WILL CONTINUE TO EVOLVE THROUGH THE LOW LEVEL BAROCLINIC ZONE ASSOCIATED WITH THE COLD FRONT AND WITHIN THE BROAD ENTRANCE REGION OF THE UPPER JET IN THE NORTHERN STREAM THAT IS POSITIONED FROM THE UPPER MIDWEST TO MID APPALACHIANS. THAT LEAVES THE NORTHERN STREAM SHORT WAVE SHOWN MOVING THROUGH THE CENTRAL ROCKIES TO CLOSE THE GAP ENOUGH TO PHASE/MERGE WITH THE LEAD WAVE AND ACCELERATE CYCLOGENESIS THROUGH THE MID MISSISSIPPI VALLEY TONIGHT AND ALLOW THE SPREAD OF STRONG ISENTROPIC ASCENT AND MOISTURE TRANSPORT TO CARRY SNOW INTO SE MICHIGAN AFTER MIDNIGHT. THE SYSTEM IS ON PACE TO BRING IN AN INCH OR TWO OF ACCUMULATION UP TO THE I-96 CORRIDOR BY SUNRISE SUNDAY AND THEN RAMPING UP FROM THERE DURING THE REST OF THE MORNING. MOISTURE TRANSPORT/THETA-E ADVECTION CONSTITUTING THE FIRST PHASE OF THE EVENT WILL STRENGTHEN DURING THE MORNING THROUGH ABOUT MID AFTERNOON BEFORE TRANSITIONING TO A DEFORMATION PHASE FROM MID AFTERNOON THROUGH THE OVERNIGHT. MID LEVEL WARM FRONTOGENESIS WILL OCCUR DURING THE DAY WITHIN A MODEST STABILITY PROFILE SUITABLE FOR MAINTENANCE OF A BROAD AND UNIFORM AREA OF MODERATE SNOW. THE POTENTIAL FOR GREATER MESOSCALE FORCING THEN BUILDS DURING LATE AFTERNOON AND THROUGH SUNDAY EVENING AS FORCING TRANSITIONS INTO THE DEFORMATION PHASE. THE GFS IS PARTICULARLY AGGRESSIVE WITH THE STRUCTURE OF THE TROWAL AXIS AND BORDERLINE CONVECTIVE INSTABILITY WITHIN IT THROUGH THE 700-500 MB LAYER BASED ON THETA-E CROSS SECTIONS. THIS IS WHERE THE POTENTIAL FOR OVERACHIEVEMENT WILL BE GREATEST BUT ALSO WERE THE STRENGTH...LOCATION...AND DURATION OF THE FEATURE WILL BE MOST SENSITIVE IN THE FORECAST. THE PRODUCTION OF THE TROWAL WILL ALSO BE SUBJECT TO ANY CHANGES IN THE OVERALL SYSTEM EVOLUTION ARISING FROM THE LATENT HEAT CONTRIBUTION OF THE LARGE MASS OF CONVECTION EXPECTED IN THE WARM SECTOR OVER THE TENNESSEE VALLEY. THESE ARE FORECAST REFINEMENTS THAT MAY NEED TO WAIT UNTIL NEAR REAL-TIME BUT THE POTENTIAL FOR WHICH ARE WORKED INTO THE FORECAST THIS CYCLE BY INCREASING ACCUMULATION IN THE M-59 TO I-69 CORRIDOR WHILE MOSTLY HOLDING THE LINE TO THE SOUTH. SHOULD THE TROWAL REALIZE FULL POTENTIAL WITH AN INFLECTION NEAR THE OHIO BORDER...THEN AMOUNTS THERE MAY HAVE TO BE RAISED FARTHER INTO DOUBLE DIGIT TERRITORY BY SUNRISE MONDAY. DEEP DRY AIR IN THE LOW LEVELS WILL MAINTAIN A SHARP NORTH GRADIENT IN ACCUMULATION INTO THE TRI CITIES AND NORTHERN THUMB THROUGHOUT THE EVENT. LITTLE TO NO LAKE ENHANCEMENT IS PROJECTED AS PLAN VIEW RH FIELDS AROUND 850 MB INDICATE VALUES NEAR 20 PERCENT OVER THE CENTRAL AND NORTH SECTIONS OF THE LAKE. MODEL SOUNDINGS SHOW THE COLD BUT DRY AIR FORCING CONVECTIVE DEPTH AS LOW AS 950 MB/1500 FT AT THE SOUTH BUOY LOCATION THROUGH THE EVENT. THIS MAY FORCE WEATHER CONCERNS DOWN TO WIND CHILL IN THE 10 TO 20 BELOW RANGE...WHICH WILL CONTINUE TO BE MENTIONED IN THE WINTER WEATHER HEADLINES. A WIND CHILL ADVISORY MAY BE ADDED LATER FOR THE TRI CITIES AND THUMB SUNDAY NIGHT WHERE SNOW AMOUNTS WILL BE UNDER HEADLINE CRITERIA IF WIND CHILL PROJECTIONS HOLD HEADING INTO SUNDAY NIGHT. LONG TERM... MONDAY THROUGH FRIDAY FAIRLY QUIET WEATHER PATTERN SETTING UP IN THE WAKE OF THE APPROACHING WINTER STORM LATE TONIGHT THROUGH SUNDAY NIGHT. UPPER LEVEL RIDGING WILL HOLD OVER THE WEST COAST WHILE A TRAIN A WAVES ROUNDING THE RIDGE ACTS TO REINFORCE TROUGHING OVER THE NORTHERN AND EASTERN CONUS. THIS WILL RESULT IN NORTHWESTERLY FLOW FOR THE BULK OF THE PERIOD FOR LOWER MI. THE MAIN BAROCLINIC ZONE WILL MEANDER VERY CLOSE TO SE MI MUCH OF THE PERIOD AS THESE WAVES TRACK IN THE VICINITY OF THE GREAT LAKES BRINGING A COUPLE ARCTIC FRONTS THROUGH THE REGION. THE FIRST AND ONLY REAL SHOT SHOT AT PRECIP IN THE EXTENDED PERIOD WILL COME LATE TUESDAY AND INTO WEDNESDAY AS A CLIPPER DIVES THROUGH THE REGION. THE CLIPPER WILL RESIDE ON THE NOSE OF AN INCREASING JET STREAK AND THE NEXT LOBE OF PV AND TROUGH OF LOW PRESSURE ROTATING AROUND THE LARGE UPPER LOW OVER NORTHERN CANADA. THE ECMWF AND GFS CONTINUE TO DISAGREE IN OVERALL STRUCTURE...THUS STRENGTH...OF THE CLIPPER AS IT TRACKS THROUGH SOUTHERN MI. THE ECMWF HAS A MUCH CLEANER LOOKING UPPER LEVEL JET STREAK STRENGTHENING SOMEWHAT AS IT PASSES...WHEREAS THE GFS HAS A MORE UNORGANIZED JET COMING TOGETHER BETTER JUST DOWNSTREAM OF US. AT THIS POINT WILL KEEP SNOW ACCUMS IN THE GENERAL 1-3 INCH RANGE AND MAKE A SLIGHT ADJUSTMENT SOUTHWARD TO ACCOUNT FOR STRENGTH OF THE CLIPPER/LOW VS STRENGTH OF FRONTAL FORCING DRAPED ACROSS LOWER MI. AN ARCTIC FRONT WILL SURGE THROUGH THE GREAT LAKES BEHIND THIS CLIPPER BRING VERY COLD TEMPERATURES BACK TO THE REGION. 850MB/500MB TEMPS WILL DROP TO NEAR -25C/-40C RESPECTIVELY BY WEDNESDAY NIGHT WITH A SLOW RECOVERY THROUGH THURSDAY THURSDAY NIGHT. RIDGING OVER THE CENTRAL PLAINS AND MID MISSISSIPPI VALLEY WILL THEN GET FOLDER OVER THROUGH THE SOUTHERN GREAT LAKES PROVIDING SOME THERMAL RELIEF. LOOK FOR TEMPERATURES TO STRUGGLE TO GET OUT OF THE TEENS THURSDAY AND FRIDAY BEFORE APPROACHING 30 AGAIN BY SATURDAY. MARINE... AN ARCTIC FRONT STRETCHING ACROSS THE CENTRAL GREAT LAKES WILL SLOWLY SETTLE SOUTHWARD OVER THE SOUTHERN GREAT LAKES TONIGHT. WINDS WILL SHIFT FROM SOUTHEASTERLY THROUGH NORTHWEST TONIGHT...SETTLING ON NORTHEASTERLY BY EARLY SUNDAY. THE UNSTABLE AIRMASS WILL RESULT IN INCREASING WIND SPEEDS TONIGHT WHICH WILL REMAIN ELEVATED THROUGH SUNDAY NIGHT. PEAK WIND GUSTS LOOK TO TOP OUT AROUND 30 KNOTS WITH A STRAY GUST TO GALE FORCE POSSIBLE BUT LIMITED IN OCCURRENCE AND MAINLY ACROSS CENTRAL LAKE HURON AND INTO SAGINAW BAY. HIGH PRESSURE WILL BUILD BACK INTO THE REGION ON MONDAY ALLOWING WINDS TO RELAX. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR MIZ068>070-075-076- 082-083. WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR MIZ060>063. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI SHORT TERM...BT LONG TERM....DRK MARINE.......DRK YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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