000 FXUS63 KDTX 100451 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1151 PM EST THU FEB 9 2012 .AVIATION... //DISCUSSION... HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THROUGH THE MORNING HOURS AS A COLD FRONT APPROACHES FROM THE NORTH ALONG WITH A WAVE FROM THE GULF COAST. IMPACTS FROM THE COLD FRONT WILL NOT ARRIVE UNTIL THE AFTERNOON HOURS...WITH SNOWFALL EXPECTED TO ARRIVE AT KMBS AROUND 18Z FRIDAY...THEN TO THE METRO AIRPORTS AROUND 22Z. THE SNOW WILL REDUCE CIGS TO MVFR WITH IFR VSBYS EXPECTED IN THE SNOW SHOWERS. SOUTHWEST WINDS WILL TURN TO THE NORTHWEST BEHIND THE FRONT AND GUST TO 20 TO 25 KNOTS. THE SNOW SHOULD WIND DOWN FROM NORTH TO SOUTH DURING THE OVERNIGHT HOURS...WITH LIGHT SNOW SHOWERS AND FLURRIES LINGERING THROUGH MUCH OF THE NIGHT. FOR DTW...VFR CONDITIONS AND MODEST SOUTHWEST WIND WILL PRECEDE THE COLD FRONT WHICH IS NOT EXPECTED TO ARRIVE AT DTW UNTIL ABOUT 22Z. THE FRONT IS EXPECTED TO BRING AN INCH OR TWO OF SNOW ACCUMULATION TO THE AREA. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILING BELOW 5000 FEET AFTER 22Z. * HIGH CONFIDENCE IN SNOW AS PRECIPITATION TYPE AFTER 22Z. && .PREV DISCUSSION...ISSUED 405 PM EST THU FEB 9 2012 SHORT TERM... TONIGHT SOUTHWEST WIND GUSTING TO 25 MPH WILL SETTLE DOWN TO A GRADIENT WIND IN THE 5 TO 10 MPH RANGE BY SUNSET. THIS WILL BE ENOUGH TO PREVENT A BIG DROP IN TEMPERATURE DURING THE EVENING THAT WOULD OTHERWISE BE EXPECTED UNDER CLEAR SKY. THE CONCERN IS WITH HOW THE SOUTHWEST FLOW STRUGGLED TO LIFT TEMPS MUCH IN THE FIRST PLACE DURING THE AFTERNOON AS READINGS STRUGGLE TO REACH THE 40 DEGREE MARK AT PRESS TIME. THIS UNDERACHIEVEMENT SUPPORTS MIN TEMPS IN THE MID 20S MOST LOCATIONS BEFORE CLOUDS INCREASE IN COVERAGE AND THICKNESS LATER IN THE NIGHT. A LOOK AT AFTERNOON SATELLITE IMAGERY INDICATES THE FIRST CLOUDS TO ARRIVE IN OUR AREA WILL BE FROM THE MID MISSISSIPPI VALLEY AND POSSIBLY FROM THE CLOUD MASS OVER THE OHIO VALLEY. LOW LEVEL WIND FIELDS FROM THE 12Z MODEL RUNS INDICATE ENOUGH OF A WESTERLY COMPONENT TO CARRY THE CLOUDS IN MORE FROM THAT DIRECTION THAN FROM THE SOUTH. THE OHIO VALLEY CLOUDS COULD BRUSH THROUGH THE BORDER REGION BEFORE HIGH CLOUDS START TO THICKEN AFTER MIDNIGHT, AND LOW CLOUDS FILL IN FROM THE WEST ALONG AND AHEAD OF THE COLD FRONT. LONG TERM...FRIDAY THROUGH WEDNESDAY THE MAIN ITEM OF CONCERN IS THE POTENTIAL FOR LIGHT SNOW ACCUMULATION FRIDAY INTO FRIDAY NIGHT. WEAK MID LEVEL ISENTROPIC ASCENT WILL FILL IN BEHIND THE OPEN WAVE PASSING TO OUR SOUTH TONIGHT WITH RIGHT ENTRANCE JET SUPPORT PROVIDING A BOOST THROUGH THE MORNING HOURS. WITH PLENTY OF DRY AIR IN PLACE, WEAK ASCENT WILL DO NOTHING MORE THAN SERVE TO GRADUALLY SATURATE THE COLUMN IN THE PRE-FRONTAL ENVIRONMENT. THE DURATION OF THE WEAKLY ASCENDING SOUTHWESTERLY FLOW COULD BE SUFFICIENTLY LONG OVER SOUTHEASTERN PORTIONS OF THE CWA FOR A LITTLE LIGHT PRECIP TO DEVELOP AS EARLY AS 18Z. OTHERWISE THE BULK OF THE FORCING AND SUBSEQUENT SNOWFALL WILL INITIALLY OCCUR ALONG THE FRONT ITSELF. MODEL CROSS-SECTIONS CONTINUE TO INDICATE A 2-3 HOUR PERIOD OF STRONG SFC-850MB FGEN THAT WILL BE BRIEFLY AUGMENTED BY VERY STRONG CONVERGENCE ALONG THE LEADING EDGE OF THE FRONTAL BOUNDARY. THIS WILL SUPPORT A QUICK RAMP UP TO HIGHER INTENSITY SNOW AS A NARROW BUT POTENTIALLY INTENSE BAND OF SNOW WILL ACCOMPANY THE FRONTAL PASSAGE. MODEST JET SUPPORT WILL ACCOMPANY THE FRONT FOR MUCH OF THE DAY BEFORE MUCH STRONGER MID AND UPPER SUPPORT ARRIVE IN THE EVENING. HERE, THE 12Z GFS HAS TRENDED STRONGLY TOWARD THE SLOWER AND DEEPER ECMWF SOLUTIONS OF THE THE LAST SEVERAL MODEL CYCLES. THESE SOLUTIONS FEATURE A SLIGHTLY STRONGER WAVE COMING OUT OF SK AS WELL AS TODAY'S COLORADO SHORTWAVE ENERGY LIFTING NORTHWARD AHEAD OF THE TROUGH. THE FORECAST THEREFORE REFLECTS THIS SCENARIO, WITH STRONGER UPPER LEVEL SUPPORT DEVELOPING BETWEEN 21Z-03Z RESULTING IN ENHANCED BAROCLINICITY AND A STRONGER DEFORMATION RESPONSE THAT WILL LAST WELL INTO FRIDAY EVENING. THE NAM/GEM HAVE SHOWN SIMILAR ADJUSTMENTS BUT OF A NOTICEABLY LESSER MAGNITUDE. HOWEVER, THE RUN OF EXCELLENT CONTINUITY BY THE ECMWF COUPLED WITH TODAY'S ADJUSTMENT BY THE GFS, GIVE HIGH CONFIDENCE FOR TRENDING THE FORECAST IN THIS DIRECTION. THE RESULT IS THAT THE 2 TO 2.5" UPPER END POTENTIAL NOTED IN OVERNIGHT DISCUSSION IS A MORE PLAUSIBLE SCENARIO THAN IT WAS 12 TO 24 HOURS AGO. THE GFS ACTUALLY ALLOWS THE SYSTEM TO EVOLVE QUICKLY ENOUGH SO THAT SOUTHEASTERN AREAS, INCLUDING METRO DETROIT, BASICALLY SEE 2X THE QPF OF AREAS TO THE NORTHWEST. WHILE CONFIDENCE IN THAT LEVEL OF DETAIL IS NOT THERE YET, THE GFS/ECMWF ARE IN STILL EXCELLENT AGREEMENT AS FAR AS THE SPATIAL/TEMPORAL EVOLUTION WITH A BLEND OF THESE TWO MODELS PROVIDING A DESIRABLE QPF TEMPLATE. AREA BUFKIT SOUNDINGS INDICATE THE DGZ WILL BE FAVORABLY LOCATED AT THE TOP OF THE MIXED LAYER THROUGH THE EARLY STAGES OF THE EVENT BEFORE BECOMING CONSIDERABLY DEEPER, AS DEEP AS 200MB IN VERTICAL EXTENT, AS COLD AIR FILLS IN AND DEFORMATION BEGINS TO RAMP UP. AT THIS POINT, AVERAGE SNOW RATIOS ARE EXPECTED TO BE IN THE NEIGHBORHOOD OF 16:1. THUS...THE PREFERRED GUIDANCE SUGGEST TOTAL SNOW ACCUMULATIONS OF AROUND 2 INCHES FROM I-69 SOUTHWARD. WITH TIME FOR TWO MORE MODEL RUNS BEFORE THE EVENT, PREFERRED TO STAY CONSERVATIVE ACROSS THE SOUTHEASTERN PORTION OF THE CWA, INCLUDING DETROIT. HOWEVER, A SWATH OF 2-3" WOULD NOT BE OUT OF THE QUESTION IF NOTHING CHANGES. THERE IS A BIT OF HESITATION IN ALLOWING DEFORMATION TO HANG AROUND ALL THE WAY INTO SATURDAY MORNING PER THE LOWER RESOLUTION GUIDANCE. GIVEN THE STRENGTH OF THE FRONT AND FORWARD MOMENTUM OF THE AIRMASS ITSELF, NOT TO MENTION THE SHARP INTRUSION OF DRY AIR PUNCHING IN BEHIND IT, THE PREFERENCE IS TOWARD A SLIGHTLY FASTER OVERALL EVOLUTION WITH SNOW TAPERING OFF BY 06Z. THE FRONT IS FORECAST TO PASS THROUGH THE TRI-CITIES AROUND NOON FOLLOWED BY DETROIT METRO AROUND 21Z. SOUTHERN AREAS COULD POTENTIALLY SEE A FEW RAIN DROPS TO START OFF GIVEN THE WARM SURFACE TEMPS...BUT IT HARDLY SEEMS WORTH A MENTION WITH THE POTENTIAL FOR LIQUID PRECIP EXTREMELY LIMITED BY DIABATIC COOLING AND STRONG FORCED ASCENT THROUGH THE LOWER TROPOSPHERE. HIGH TEMPERATURES WILL RANGE IN THE 30S AHEAD OF THE FRONT WITH TEMPERATURES QUICKLY FALLING OFF IN ITS WAKE, ULTIMATELY BOTTOMING OUT IN THE LOW TEENS ON FRIDAY NIGHT. SOME LAKE EFFECT WILL BE POSSIBLE FOR THE EASTERN THUMB LATE FRIDAY NIGHT, BUT THE POTENTIAL FOR ORGANIZED LES AND NOTEWORTHY ACCUMS WILL BE LIMITED BY A SHORT-LIVED NORTHERLY FETCH. CONTINENTAL ARCTIC AIRMASS WILL SETTLE OVER THE STATE FOR SATURDAY WITH HIGHS REACHING 20 DEGREES AND WIND CHILLS IN THE SINGLE DIGITS BELOW ZERO EARLY...INCREASING TO ABOVE ZERO IN THE AFTERNOON. TEMPERATURES WILL SLOWLY MODERATE INTO NEXT WEEK WITH A ROUND OF LIGHT SNOW POSSIBLE ON MONDAY AS A TROUGH SHIFTS THROUGH THE GREAT LAKES. MARINE... SOUTHWEST FLOW OVER ALL MARINE AREAS TONIGHT WILL MAINTAIN MARINE CONDITIONS WORTHY OF ADVISORIES TO SMALL CRAFT ON OUTER SAGINAW BAY AND AROUND THE THUMB. THESE WINDS WILL BE AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH THE REGION DURING FRIDAY. GUSTS TO 30 KNOTS WILL ALSO BE COMMON AS THE WIND TURNS TOWARD THE NORTH BEHIND THE FRONT THROUGH FRIDAY NIGHT. STRONG HIGH PRESSURE WILL THEN SETTLE OVER THE PLAINS AND MIDWEST DURING SATURDAY AS ANOTHER SURGE OF ARCTIC AIR MOVES OVER THE GREAT LAKES. THE STEEP PRESSURE GRADIENT WILL MAINTAIN GREATER POTENTIAL FOR NORTHWEST GALES OVER THE LAKE HURON OPEN WATERS THROUGH SATURDAY NIGHT BEFORE A MODERATING TREND BEGINS SUNDAY. A GALE WATCH IS IN EFFECT FOR THE LAKE HURON OPEN WATERS SATURDAY THROUGH SATURDAY NIGHT WITH SMALL CRAFT ADVISORIES FOR THE SOUTHERN NEARSHORE WATERS THROUGHOUT THE WEEKEND. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON... SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON INCLUDING OUTER SAGINAW BAY...UNTIL 7 AM SUNDAY. SMALL CRAFT ADVISORY...INNER SAGINAW BAY...UNTIL 5 AM FRIDAY. GALE WATCH...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...FROM 7 AM SATURDAY TO 7 AM SUNDAY. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI SHORT TERM...BT LONG TERM....JVC MARINE.......BT YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).