Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 261714 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 114 PM EDT THU MAR 26 2015 .AVIATION...
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SOLID VFR STRATOCU DECK OVERHEAD WILL PERSIST THROUGH THE AFTERNOON AS COLD AIR POURS INTO THE REGION...POSSIBLY BREIFLY MVFR OVER DETROIT METRO TERMINALS EARLY THIS AFTERNOON WHERE LOW LEVEL MOISTURE HAS BEEN SLOWER TO EXIT. HIGHEST POTENTIAL FOR CIGS TO LOWER INTO MVFR RANGE AFTER SUNSET FROM PTK NORTHWARD...LESS CERTAINTY FOR THE METRO DETROIT TERMINALS. LIGHT SNOW SHOWERS ARE POSSIBLE ALONG/BEHIND A FRONTAL BOUNDARY TOMORROW MORNING/AFTERNOON...REFRAINED FROM INCLUSION IN THE TAFS FOR THIS PERIOD UNTIL CONFIDENCE INCREASES. FOR DTW...SOME OPPORTUNITY FOR CIGS AOB 5KFT TO SCATTER OUT LATER THIS AFTERNOON INTO THE EARLY OVERNIGHT HOURS. SOME LIGHT SNOW SHOWERS ARE POSSIBLE TOMORROW ALONG/BEHIND A COLD FRONT AFTER AROUND 15Z TOMORROW. //DTW THRESHOLD PROBABILITIES... * MEDIUM IN CEILINGS BELOW 5000 FT THROUGH THE TAF PERIOD.
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&& .PREV DISCUSSION...
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ISSUED 919 AM EDT THU MAR 26 2015 UPDATE... QUICK UPDATE TO ADD SNOW TO THE GRIDS FOR LENAWEE/MONROE COUNTIES. BETTER RATES HAVE LED TO SNOW BEING THE PREDOMINANT P-TYPE THERE...WHILE TO THE NORTH THE WARMER BOUNDARY LAYER/LACK OF BETTER WET BULBING HAS KEPT PRECIP LIGHT RAIN. EVEN WHERE SNOWFALL IS OCCURRING...ONLY LIGHT ACCUMULATIONS CONFINED TO GRASSY SURFACES ARE EXPECTED WITH SFC TEMPS/DEWPOINTS AOA FREEZING. ONLY HAZARD WILL BE VISIBILITIES DROPPING TO 1 MILE OR LESS. OTHERWISE...PRECIP SHIELD STILL ON TRACK TO EXIT BY 15Z. PREV DISCUSSION...ISSUED 326 AM EDT THU MAR 26 2015 SHORT TERM...TODAY AND TONIGHT THE DYNAMIC RESPONSE ALONG A DEEP LAYER FRONTAL BOUNDARY EXTENDING FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY IS BEING DRIVEN BY UPPER LEVEL DIVERGENCE WITHIN THE ENTRANCE REGION OF A STRENGTHENING UPPER JET MAX. THE REGIONAL RADAR LOOP HAS BEEN SHOWING THE ENTIRE AREA OF RAIN LIFTING NORTHEASTWARD ACROSS IL/IN. THIS IS OCCURRING AS THE UPPER JET MAX STRENGTHENS AND LIFTS NORTHWARD...PULLING THE ELEVATED FRONT FARTHER TO THE NORTH AND EAST. SATELLITE/RADAR COMPOSITE ALSO SHOWS A MID LEVEL SHORT WAVE IMPULSE OVER SOUTH CENTRAL ILLINOIS. THIS FEATURE WILL CONTINUE ON A NORTHEASTWARD TRACK INTO OHIO THIS MORNING...FURTHER AIDING THE NORTHEAST EXPANSION OF THE PRECIP SHIELD. THE MID LEVEL FRONTAL FORCING /700-600MB LAYER/ IS DRIVING THE EXPANDING REGION OF RAIN ACROSS NRN INDIANA. THIS MID LEVEL ASCENT WILL TRACK ACROSS FAR SE MI DURING THE 09Z TO 15Z TIME FRAME...WITH THE PEAK FORCING EXPECTED AROUND 12Z. THERE IS A REGION OF SUBSTANTIAL MID LEVEL DRY AIR WITHIN THE DESCENDING BRANCH OF THE ELEVATED FRONTAL CIRCULATION. THIS HAS AND WILL CONTINUE TO SUPPORT A SHARP CUT OFF TO THE PRECIP ON ITS NORTHERN EDGE. VARIOUS HIRES MODEL SOLUTIONS /INCLUDING THE HRR...4KM WRF...NAM12 AND RAP/ SUGGEST THAT LOCALS GENERALLY ALONG AND SOUTH OF AN ANN ARBOR TO PORT HURON LINE WILL SEE THE WIDESPREAD PRECIP...WITH CHANCES DROPPING OFF RAPIDLY TO THE NORTH. WITH A DEEPER DRY LAYER ACROSS SE MI...THERE WILL BE A GOOD DEGREE OF WET BULB COOLING AS THE PRECIP EXPANDS INTO THE FORECAST AREA. NAM MODEL SOUNDINGS ACTUALLY SUGGEST THE PRECIP WILL BE ALL SNOW BY 12Z. BASED ON SFC OBS...THE NAM SEEMS A LITTLE TOO COOL IN THE BOUNDARY LAYER. THERE IS ALSO CONCERN THE NAM MAY BE TOO STRONG WITH THE ASCENT. LEANING TOWARD THE RAP THERMAL PROFILES...A MIX OF RAIN AND SNOW WILL BE CARRIED WITH NO ACCUMULATIONS. THIS OF COURSE WILL BE MONITORED CLOSELY THIS MORNING. WEAK LOW LEVEL COLD AIR ADVECTION TODAY WILL BE OFFSET A BIT BY DIURNAL HEATING. THERE IS A CONSIDERABLE AMOUNT OF STRATUS ACROSS THE REGION...NOT TO MENTION THE MID/HIGH CLOUDS ASSOCIATED WITH THE MID LEVEL FGEN. THESE FACTORS WILL LIMIT DAYTIME MIXING DEPTHS AND SUPPORT GUIDANCE MAX TEMPS OF LOW-MID 40S. A SURFACE COLD FRONT NOW DRAPED ACROSS LAKE SUPERIOR WILL PUSH SOUTH ACROSS LAKE HURON THIS EVENING AND INTO SE MI OVERNIGHT AS HIGH PRESSURE EXPANDS INTO UPPER MI. THIS ALONG WITH A DEEPENING LONG WAVE TROUGH OVER THE GREAT LAKES WILL LEAD TO AN INFLUX OF ARCTIC AIR INTO THE FORECAST AREA. STEEPENING LOW LEVEL LAPSE RATES ALONG THE SFC FRONT AND LINGERING LOW LEVEL MOISTURE WILL PROVIDE A CHANCE OF SOME SNOW SHOWERS OVERNIGHT. THE HIGHEST CHANCES WILL BE ACROSS THE THUMB REGION WHERE LOW LEVEL DELTA THETA E ACTUALLY SUGGEST THE AIRMASS WILL BE COLD ENOUGH TO GENERATE SOME WEAK MOISTURE FLUX OFF THE OPEN WATERS OF LAKE HURON...PERHAPS ENOUGH TO SUPPORT A DUSTING OF SNOW ACCUMS. LONG TERM...FRIDAY THROUGH WEDNESDAY DEEPLY AMPLIFIED LONGWAVE PATTERN SETTING UP ACROSS THE CONUS WITH A WEST COAST RIDGE AND EAST COAST TROUGH TO HEAD INTO THE WEEKEND. BY SATURDAY MORNING THE 850MB 0C ISOTHERM WILL HAVE MADE IT ALL THE WAY TO THE FLORIDA PANHANDLE. OVER SOUTHERN MI WE WILL BE LOOKING AT 500/850MB TEMPS AROUND -35/-15C RESPECTIVELY FRIDAY THROUGH FRIDAY NIGHT AS THE COLD POOL SINKS THROUGH THE REGION BEHIND AN ARCTIC FRONT THAT MORNING. THIS SHOULD RESULT IN HIGHS FRIDAY ONLY AROUND 30 AND LOWS OVERNIGHT IN THE LOW TEENS. THE OTHER ISSUE FOR FRIDAY WILL BE THE POTENTIAL FOR SOME LIGHT SNOW SHOWERS. AS THE COLD POOL AND MID LEVEL TROUGH AXIS PASSES OVER...LAPSE RATES WILL STEEPEN AS WITH MOISTURE TRAPPED IN THE LOWEST 7KT OF THE COLUMN. SHOULD BE ENOUGH MOISTURE AND BROAD LIFT TO IGNITE AN AREA OF SHOWERS THROUGH THE FRONT PART OF THE DAY. AS THE TROUGH PUSHES EAST...THE SHOWERS WILL CEASE EXCEPT POSSIBLY OVER EASTERN THUMB WHICH COULD GET SOME LAKE ENHANCED SNOW SHOWERS. WITH THE UPTICK IN NORTHERLY WINDS BRINGING A SURGE OF COLD AIR OVER THE LAKE...NOW WITH A GOOD DEAL OF OPEN WATER...MODELS ARE HINTING AT A CONVERGENCE BAND SETTING UP FOR A FEW HOURS BEFORE WINDS BACK TO NW AND DRY AIR PUTS AN END TO IT. NOTHING OVERLY IMPRESSIVE AT THIS TIME SO KEEPING ACCUMS TO A FEW TENTHS. SOMETHING TO WATCH AS HIRES MODELS START COVERING THAT TIMEFRAME. SFC HIGH PRESSURE STARTS BUILDING OVER THE REGION FRIDAY NIGHT...CENTERING ITSELF OVER LOWER MI ON SATURDAY. NOT MUCH RECOVERY TEMPERATURE WISE AS COLD DOME IS STILL LOCKED OVERHEAD. BUT A REDUCTION IN CLOUD COVER WILL ALLOW SOME ADDITIONAL HEATING INTO THE MID 30S. SATURDAY NIGHT WILL FEATURE A STRONG SHORTWAVE SURGING EASTWARD ALONG THE US/CANADA BORDER WHICH WILL BREAK DOWN THE STEEP RIDGE OVER THE WEST COAST. THIS WILL LEAD TO A MORE PROGRESSIVE PATTERN FIRST SWEEPING A RIDGE ACROSS THE AREA ON SUNDAY...FOLLOWED QUICKLY BY THE COLD FRONT EXTENDING SOUTH FROM THE RESULTANT LOW. WITH TEMPERATURES IN THE LOW/MID 30S OVER NIGHT...THIS COULD RESULT IN RAIN...SNOW...OR A MIX DEPENDING ON THE TIMING OF THE FRONT. THE PROGRESSIVE PATTERN CONTINUES FOR THE FRONT HALF OF THE COMING WORK WEEK WITH A SERIES OF CLIPPERS EMBEDDED IN THE NW FLOW TRACKING NEAR THE AREA. THIS WILL BE SOMETHING TO WATCH IN THE COMING DAYS. THE FLATTER FLOW WILL ALLOW THE WARM AIR TO LIFT FURTHER NORTH WHICH WILL RESULT IN TEMPERATURES CLOSER TO NORMAL FOR LATE MARCH/EARLY APRIL. MARINE... WESTERLY WINDS WILL BRIEFLY RELAX TODAY AS A FRONTAL BOUNDARY BECOMES DRAPED THROUGH THE CENTRAL GREAT LAKES. WINDS WILL AGAIN BECOME EXCITED OUT OF THE NORTH BEHIND THE FRONT TONIGHT THROUGH FRIDAY. COLD AIR WILL REDUCE THE STABILITY OVER THE LAKE ALLOWING FOR GUSTS OF 25 TO 30 KNOTS. IN ADDITION...THE FRONT AND INITIAL COLD BURST BEHIND IT WILL PRODUCE SOME LIGHT SNOW SHOWERS TONIGHT AND FRIDAY. THE SOUTHWARD MOVING FRONT WILL CLEAR THE REMAINDER OF THE WATERS DURING THE DAY ON FRIDAY. WINDS WILL THEN DIMINISH LATE FRIDAY NIGHT INTO SATURDAY AS HIGH PRESSURE BUILDS INTO THE REGION.
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&& .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....DT UPDATE.......DT SHORT TERM...SC 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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