FXUS63 KDTX 181101 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 701 AM EDT THU MAR 18 2010 .AVIATION... THE CONTINUED PRESENCE OF VERY DRY AIR WILL MAINTAIN VFR CONDITIONS WITH JUST SOME PASSING CIRRUS AT TIMES THROUGH TONIGHT. THE COMBINATION OF A TIGHTENING PRESSURE GRADIENT AND DEEP MIXING WILL ALLOW WEST-SOUTHWEST WINDS TO INCREASE INTO THE AFTERNOON. THIS WILL LEAD TO GUSTS OF 20 TO 25 KNOTS...HIGHEST ACROSS THE NORTHERN SITES. THE GUSTINESS WILL DIMINISH AFTER SUNSET AS MIXING CEASES. && .PREV DISCUSSION...ISSUED 331 AM EDT THU MAR 18 2010 SHORT TERM...TODAY EXTENDED STRETCH OF WARM AND TRANQUIL CONDITIONS WILL CONTINUE TODAY WITH THE REGION REMAINING WITHIN WEAK MID LEVEL RIDGING AND INCREASING SOUTHWEST LOW LEVEL FLOW. THIS SETUP WILL ALLOW FOR SLIGHT WARM AIR ADVECTION WHILE MAINTAINING A DEEP MIXED LAYER UNDER FULL INSOLATION. 925/850 MB TEMPERATURES AND LOW LEVEL THICKNESSES NUDGE UPWARD SLIGHTLY TODAY. GIVEN A MIXED LAYER THROUGH AT LEAST 800 MB /SIMILAR TO THE LAST TWO DAYS/...THIS WILL TRANSLATE INTO HIGHS AGAIN WELL INTO THE LOW-MID 60S...OR AROUND 20 DEGREES ABOVE THE SEASONAL NORM FOR MID MARCH. SOME HIGHER CLOUDINESS WILL FILTER OVER THE RIDGE AXIS AND INTO THE AREA THIS AFTERNOON...BUT WILL DO LITTLE TO DETER TEMPERATURES FROM REACHING THESE SEASONABLY WARM READINGS. LONG TERM...TONIGHT THROUGH NEXT WEDNESDAY PER MODEL TRENDS...MADE A SIGNIFICANT SOUTHERN ADJUSTMENT TO THE GOING FORECAST IN REGARDS TO THE MAIN STORM SYSTEM SET TO IMPACT THE REGION THIS WEEKEND. WITH THE RAOBS SAMPLING MORE OF THE MAIN ENERGY ACROSS THE CANADIAN ROCKIES...MODELS HAVE MADE A SIGNIFICANT ADJUSTMENT TO THE SOUTH WITH THE TRACK OF THIS WEEKENDS LOW PRESSURE SYSTEM. THE 17.12Z ECMWF WAS FIRST ONBOARD WITH SOME SUBTLE SECONDARY CYCLOGENESIS OVER THE WESTERN CAROLINAS SUNDAY NIGHT...AND NOW THE 18.00Z GFS IS IN VERY GOOD AGREEMENT. THE MOST IMPORTANT CHANGES BETWEEN THE PREVIOUS AND CURRENT RUNS IS THE DOMINANT PV ANOMALY IS SOME 6-8 HRS SLOWER AS IT DIGS DOWN NEAR ARKLATEX AND ALSO STRONG CONVECTION ACROSS THE FAR SOUTH SUNDAY SHOULD PULL LARGE SCALE HEIGHT FALLS AND COPIOUS MOISTURE STRAIGHT EASTWARD. THUS...MUCH SLOWER NEGATIVE TILTING OF THE UPPER LEVELS IS EXPECTED UNTIL IT REACHES THE SOUTHEASTERN UNITED STATES. WHAT THIS MEANS FOR SOUTHEASTERN MICHIGAN IS THAT LESS TOTAL PRECIPITATION WOULD FALL. ANOTHER MILD DAY FOR FRIDAY DESPITE INCREASING MID TO UPPER LEVEL MOISTURE. LOW TO MIDLEVEL TEMPERATURES ARE EXPECTED TO BE A TOUCH COOLER DUE TO VERY WEAK CAA...BUT 850MB TEMPERATURES OF 2-3C SUGGESTS THAT HIGHS SHOULD BE ABLE TO PUSH 60 DEGREES. PASSING SURFACE LOW PRESSURE NORTH OF LAKE SUPERIOR WILL START THE ENGINES ON AN INCREASED NORTHERLY FLOW ACROSS THE NORTHERN LAKES AND PUSH A COLD FRONT/MAIN BAROCLINIC ZONE INTO CENTRAL LOWER MICHIGAN FRIDAY NIGHT. WONDERFUL UPPER LEVEL JET SUPPORT WILL OCCUR ACROSS LOWER MICHIGAN UNDER RIGHT ENTRANCE REGION...FORCING INCREASED FRONTAL DYNAMICS. THE THERMAL GRADIENT...ALREADY HEALTHY TO BEGIN WITH...WILL UNDERGO TIGHTENING AS IT SLIDES SOUTHWARD...HERALDING VERY STRONG FGEN LATE FRIDAY NIGHT AND SATURDAY. THE SOUTHERN ADJUSTMENT IN THE MODELS AND THE STRENGTH OF THE NORTHERLY WIND FIELD ALLOWS THE QUASI-STATIONARY FRONT TO DIP MORE INTO THE NORTHERN CWA ON SATURDAY. THERMAL PROGS AND THICKNESS VALUES SUPPORT AT LEAST A MIX OF SNOW AND RAIN FOR THE TRI CITIES. GIVEN MUCH OF THIS PRECIPITATION WILL FALL DURING A LATE MARCH DAY...HAVE TO BELIEVE THAT MUCH OF SNOW WOULD MELT AT CONTACT. THEREFORE...EXPECTING ONLY AN INCH OF SNOW POSSIBLE FOR THE TRI CITIES SATURDAY. THEN...THE CWA REMAINS WITHIN A ZONE OF WEAK LARGE SCALE ASCENT. TOTAL COLUMN SATURATION WILL FLUCTUATE THROUGHOUT THIS TIME DEPENDENT ON OVERALL FORCING. THEREFORE...THE TIME PERIOD OF SATURDAY NIGHT THROUGH SUNDAY IS EXPECTED TO TRANSITION TO A HIGH POP/VERY LOW QPF EVENT. DID DIP THE SNOW/RAIN LINE SOUTHWARD SATURDAY NIGHT...BEFORE LIFTING IT NORTH AGAIN SUNDAY AS ANOTHER ROUND OF RIGHT ENTRANCE REGION DYNAMICS OVERSPREADS THE STATE. SOME QUESTION AS TO EXACTLY WHERE THAT THIN BAND OF ENHANCED PRECIPITATION WILL FALL BUT NOT EXPECTING MUCH MORE THAN A TENTH OR TWO OF QPF. STRONG SUBSIDENCE AND BUILDING SURFACE HIGH PRESSURE WILL LEAVE PRECIPITATION FREE CONDITIONS FOR MONDAY. TEMPERATURES WILL BE COLD...HOWEVER...WITH ONLY EXPECTING HIGHS TO MANAGE THE UPPER 30S. MARINE... SOUTHWEST WINDS WILL INCREASE SLIGHTLY TODAY AS THE PRESSURE GRADIENT TIGHTENS IN RESPONSE TO A LOW PRESSURE SYSTEM TRACKING ACROSS SOUTHERN ONTARIO. THIS COMBINED WITH DEEP MIXING WILL BRING GUSTS OF 15-20 KNOTS DURING THE AFTERNOON. SIMILAR CONDITIONS IN PLACE ON FRIDAY IN ADVANCE OF A WEAK COLD FRONT. THIS FRONTAL PASSAGE WILL BRING A WIND SHIFT TO THE NORTH FOR THE WEEKEND. A LOW PRESSURE SYSTEM LIFTING NORTHEAST ALONG THE BOUNDARY WILL BRING THE CHANCE OF RAIN AND SNOW TO THE REGION DURING THE WEEKEND. NORTHWEST WINDS WILL STRENGTHEN IN THE WAKE OF THIS SYSTEM SUNDAY NIGHT AND MONDAY. THE POTENTIAL EXISTS FOR GUSTS TO REACH SMALL CRAFT CONDITIONS ALONG THE NEARSHORE WATERS AND UP TO 30 KNOTS OVER THE LAKE HURON OPEN WATERS. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....MR SHORT TERM...MR LONG TERM....CB MARINE.......MR YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).