Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 301947 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 347 PM EDT WED JUL 30 2014 .SHORT TERM...THIS EVENING AND TONIGHT THE DOMINANT WEATHER FEATURE FOR THE REGION REMAINS THE LONGWAVE UPPER LEVEL TROUGH AND CLOSED MIDLEVEL LOW PRESSURE SYSTEM THAT IS CENTERED OVER JAMES BAY. LOWER MICHIGAN IS SITUATED WITHIN THE BROAD CYCLONIC FLOW AT THE PERIPHERY...A LOCATION THAT HAS BEEN AT THE MERCY OF EPISODIC SHORTWAVES AND VARYING LOW TO MIDLEVEL SATURATION PINWHEELING AROUND THE LOW. TWO SEPARATE MIDLEVEL TROUGH AXES ARE PROVIDING SOME FOCUS AND GENERAL ORGANIZATION TO THE PRECIPITATION IN THE GREAT LAKES REGION THIS AFTERNOON. THE FIRST TROUGH AXIS IS QUICKLY CENTERING INTO PORTIONS OF LAKE ERIE AND OHIO. RADAR AND LIGHTNING OBSERVATIONS SHOW THE VAST MAJORITY OF THE THUNDERSTORM ACTIVITY IS OCCURRING AHEAD OF THIS AXIS...WITHIN A RIBBON OF MUCH DEEPER MOISTURE. THE SECOND OF THE TWO TROUGH AXES WILL SOON ENTER THE NORTHERN REACHES OF FAR NORTHWESTERN LAKE SUPERIOR. SATELLITE ALONG WITH VARIOUS OBSERVATIONAL DATASETS HAVE CONSISTENTLY SHOWN A STRONG SHORTWAVE TIED TO THIS -DIV ZONE ALONG WITH A GOOD SURGE OF ATLANTIC WRAPAROUND MOISTURE. SHOWER AND ISOLATED THUNDERSTORMS HAVE BLOSSOMED WITHIN THE OVERLAP OF THESE INGREDIENTS OVER PORTIONS OF ONTARIO AND LAKE SUPERIOR. ACROSS SOUTHEASTERN MICHIGAN MUCH OF THE ACTIVITY THIS AFTERNOON HAS REMAINED FOCUSED ALONG THE I69 CORRIDOR...ROUGHLY LANSING TO PORT HURON. THIS FOCUS IS ALONG A 700MB THETA E GRADIENT...A BOUNDARY THAT WAS TIED TO THE SHORTWAVE NOW ENTERING WESTERN LAKE ERIE. THIS BOUNDARY WILL SETTLE STEADILY SOUTHWARD THROUGH 00Z CARRYING A CONTINUED POTENTIAL FOR SCATTERED SHOWERS. A SECONDARY LOCATION TO WATCH FOR WILL BE ALONG THE LAKE HURON SHORELINE 23-02Z AS SOME ENHANCED MOISTURE WILL SWING DOWN FROM NORTHEASTERN LOWER MICHIGAN. MARGINAL CONVECTIVE INSTABILITY AND THE OVERALL LOW THETA E CONTENT OF THE OVERHEAD AIRMASS LIMITS THE THUNDER AND LIGHTNING POTENTIAL. CONVECTIVE DEPTHS WILL INCREASE THIS AFTERNOON BUT NOT EXPECTING SIMILAR ACTIVITY TO YESTERDAY. FOR TONIGHT...NWP ADVERTISES A CONTRACTION OF THE CLOSED LOW DUE TO AN IMPRESSIVE LATE JULY INNER JET CORE DIGGING STRAIGHT SOUTHWARD. THIS UPPER LEVEL JET AXIS NOW OVER LAKE SUPERIOR WILL SWING RAPIDLY TO WESTERN PA/NY BY 12Z THURSDAY. THIS STRONG ACCELERATION COMPONENT WILL MAKE IT DIFFICULT TO KEEP ORGANIZED FORCING IN ANY ONE LOCATION FOR ANY LENGTH OF TIME. FOR THIS REASON...CUT BACK ON THE POPS DISTRIBUTION RATHER AGGRESSIVELY DESPITE SOME ELEVATED CONVECTIVE INSTABILITY PERSISTING WITHIN THE COLUMN. SOME CONVECTION ALLOWING MODELS SUGGEST THAT SOME RAGGED SHOWERS MAY BE ADVECTED WITHIN THE CYCLONIC FLOW TO THE SAGINAW BAY REGION SOMETIME/AROUND 10-12Z TOMORROW MORNING. && .LONG TERM...THURSDAY THROUGH NEXT WEDNESDAY MID LEVEL HEIGHTS WILL BE ON THE RISE ACROSS LOWER MI BY THURSDAY MORNING AS SHORT WAVE ENERGY DEPARTS TOWARD UPSTATE NEW YORK AND DRAGS THE CORE OF EXTREMELY COLD AIR ALOFT /500MB TEMPS DOWN TO -20C/ EAST OF THE REGION. THE ANOMALOUSLY DEEP UPPER LOW WILL HOWEVER REMAIN JUST SOUTH OF JAMES BAY THROUGH THE DAY THURSDAY AND WILL DRIVE A SURFACE TROUGH INTO THE NORTHERN GREAT LAKES. SW FLOW IN ADVANCE OF THIS TROUGH WILL LEAD TO SOME MOISTURE ADVECTION THROUGH THE DAY...PROVING AN OPPORTUNITY FOR WEAK DAYTIME DESTABILIZATION. THE HIGHEST INSTABILITY SHOULD BE OVER THE SAGINAW VALLEY AND THUMB REGION GIVEN THE CLOSER PROXIMITY TO THE MOISTURE PLUME. FARTHER SOUTH...LOWER SFC DEWPOINTS AND BUILDING MID LEVEL HEIGHTS WILL BE A LARGE LIMITING FACTOR FOR AFTERNOON CONVECTION...SUPPORTING JUST A SLIGHT CHANCE OF LATE DAY SHOWERS/THUNDERSTORMS. A PLUME OF STEEPER MID LEVEL LAPSE RATES IS FORECAST TO EXPAND INTO LOWER MI THURS NIGHT UNDER MID LEVEL W-SW FLOW...WHILE SUBTLE MOISTURE ADVECTION PERSISTS IN THE LOW LEVELS. THIS SUGGESTS A SLIGHT CHANCE OF SOME CONVECTION DURING THE NIGHT...WITH SLIGHTLY HIGHER CHANCES CLOSER TO THE REMNANT LOW LEVEL CONVERGENCE AXIS EXPECTED TO BE RESIDING OVER CENTRAL LOWER MI. THE UPPER LOW WILL BE DRIVEN INTO EASTERN CANADA FRIDAY INTO SATURDAY. THERE IS GOOD AGREEMENT AMONG THE MODEL SUITE THAT SHORT WAVE ENERGY ROTATING AROUND THE BACK SIDE OF THIS TROUGH WILL UNDERGO SOME AMPLIFICATION AS IT TRACKS FROM THE UPPER MS VALLEY THURS INTO THE GREAT LAKES AND OHIO VALLEY FRI INTO SATURDAY. SUBTLE COOLING ALOFT AND FAIRLY GOOD LOW LEVEL MOISTURE QUALITY WILL LEAD TO MODEST DAYTIME DESTABILIZATION BOTH FRI AND SAT....SUPPORTIVE OF THE CURRENT CHANCE OF SHOWERS/THUNDERSTORMS. MOST LIKELY TIMING BOTH DAYS WILL BE LATE AFTERNOON AND EVENING. LOW LEVEL WARM AIR ADVECTION ON THURS WILL BOOST TEMPS BACK CLOSER TOWARD TYPICAL MID SUMMER TEMPERATURES. LITTLE OVERALL CHANGE IN THE THERMAL PROFILE AND EXPECTED MIXING HEIGHTS WILL SUSTAIN THESE NEAR NORMAL TEMPS INTO THE WEEKEND. WEATHER PATTERN SHOWS LITTLE CHANGE WITH A GENERAL RIDGE WEST/TROUGH EAST SET UP...PRECLUDING ANY BIG WARM-UPS. UPPER TROUGH AXIS/COLD POOL WILL CONTINUE...SO DIURNALLY ENHANCED SHOWERS AND THUNDERSTORMS WILL BE A POSSIBILITY THROUGH MUCH OF NEXT WEEK. TEMPERATURES ARE EXPECTED TO REMAIN NEAR TO SLIGHTLY BELOW NORMAL. && .MARINE... WINDS WILL REMAIN LIGHT THROUGH THE NIGHT AS A WEAK PRESSURE GRADIENT RESIDES OVER THE AREA. THE SURFACE TROUGH WILL PUSH SOUTH ACROSS THE NORTHERN GREAT LAKES ON THURSDAY. THIS WILL INVOKE SLIGHTLY STRONGER SOUTHWEST WINDS ON THE LAKES. THE GRADIENT WILL THEN RELAX AGAIN BY FRIDAY...WITH LIGHT WINDS PREVAILING THROUGH THE WEEKEND. THE BETTER CHANCES FOR THUNDERSTORMS DURING THE PERIOD WILL BE CLOSER TO THE SHORELINES. && .AVIATION...ISSUED 154 PM EDT WED JUL 30 2014 //DISCUSSION... A CORRIDOR OF ENHANCED MIDLEVEL MOISTURE OVER THE SOUTHERN HALF OF THE CWA WILL ALLOW FOR SHOWER AND THUNDERSTORM DEVELOPMENT THIS AFTERNOON. MODELS REMAIN AGGRESSIVE WITH THE AMOUNT OF SUBSIDENCE THAT WILL ARRIVE AFTER 21Z. WILL CONTINUE TO HONOR THIS OUTPUT AND FORECAST THE BEST TIME PERIOD FOR SHOWERS AND POSSIBLE THUNDER BETWEEN 18-22Z. THE WEATHER PATTERN THIS EVENING WILL BE INFLUENCED BY LARGE SCALE SUBSIDENCE...WHICH WILL CARRY WELL INTO THE NOCTURNAL HEATING MINIMUM. FROM THIS VANTAGE POINT...THIS LIMITS THE POTENTIAL FOR ADDITIONAL SHOWER DEVELOPMENT LATE TONIGHT AND INCREASES THE UNCERTAINTY IN COVERAGE AND LOCATION. WILL REFRAIN FROM INTRODUCING PRECIPITATION FOR TONIGHT WITH THIS TAF CYCLE. FOR DTW... THE MOST FAVORABLE TIME PERIOD FOR SHOWERS TO IMPACT THE TERMINAL IS 18-22Z. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILING BELOW 5000 FEET THIS AFTERNOON. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ SHORT TERM...CB LONG TERM....SC/DE MARINE.......SC AVIATION.....CB YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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