Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 201127 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 727 AM EDT WED AUG 20 2014 .AVIATION... //DISCUSSION... SOME MORNING FOG WILL PLAGUE THE TAF SITES EARLY THIS MORNING...WITH THE LOWEST CONDITIONS OF LIFR OVER MBS...WITH ONLY MVFR OVER THE METRO AIRPORTS. THIS FOG IS EXPECTED TO LIFT LATER THIS MORNING WITH THE ONSET OF DAYTIME HEATING. SHOWERS AND THUNDERSTORMS ARE AGAIN EXPECTED THIS AFTERNOON AND EARLY THIS EVENING UNDERNEATH A MID LEVEL LOW PRESSURE SYSTEM WITH INSTABILITY FROM DAYTIME HEATING. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILING AOB 5000 FT THIS MORNING. * MEDIUM CONFIDENCE IN THUNDERSTORM COVERAGE AND TIMING. && .PREV DISCUSSION...ISSUED 357 AM EDT WED AUG 20 2014 SHORT TERM...TODAY AND TONIGHT SHOWERS AND THUNDERSTORMS HAVE TRACKED EAST AS A COLD FRONT HAS SWEPT THROUGH THE CENTRAL GREAT LAKES. HOWEVER THIS COLD FRONT WILL NOT BRING MUCH RELIEF WITH REGARDS TO MOISTURE AS DEW POINTS ARE STILL IN THE LOWER TO MIDDLE 60S. THE LACK OF DRY AIR BEHIND THE FRONT AND FAIRLY CALM WINDS BRINGS WITH IT THE POTENTIAL FOR FOG ACROSS THE AREA. LINGERING CLOUDS SHOULD DELAY THE ONSET OF FOG FORMATION...WITH AREAS TO THE EAST PROBABLY NOT GOING DOWN UNTIL AROUND SUNRISE. ALTHOUGH THERE ARE EXPECTED TO BE AREAS OF DENSE FOG THIS MORNING...IT IS NOT EXPECTED TO BE WIDESPREAD ENOUGH TO WARRANT A DENSE FOG ADVISORY AT THIS POINT. HOWEVER IF VISIBILITIES DROP SIGNIFICANTLY WILL ISSUE THE APPROPRIATE HEADLINES AS NEEDED. THE LINGERING MOISTURE MAY STILL SPARK OFF SOME LIGHT SHOWER ACTIVITY EARLY THIS MORNING AS A RIBBON OF HIGH LOW LEVEL THETA-E AIR REMAINS OVER SOUTHEAST MICHIGAN. DAYTIME HEATING WILL ONCE AGAIN CAUSE AN UNSTABLE ATMOSPHERE AS IT COMBINES WITH A STILL MOIST BOUNDARY LAYER TO PRODUCE MUCAPES OF 1500 TO 2000 J/KG. THIS SHOULD ONCE AGAIN SPARK OFF THUNDERSTORMS ACROSS THE AREA AS THE MID LEVEL LOW PRESSURE SYSTEM TRACKS THROUGH THE SOO TODAY. HOWEVER UNLIKE YESTERDAY 0-6KM BULK SHEAR VALUES WILL BE MUCH WEAKER AT AROUND 20 KNOTS...MAKING THE THREAT FOR SEVERE WEATHER MUCH LOWER. STORMS TODAY MAY PRODUCE WIND GUSTS UP OF 40 TO 50 MPH WITH HAIL AROUND ONE HALF OF AN INCH UP TO DIME SIZE WITH THE STRONGEST STORMS. ALTHOUGH THE MID LEVEL LOW WILL REMAIN OVER LAKE HURON OVERNIGHT...RAIN CHANCES WILL DROP OFF WITH THE LOSS OF DAYTIME HEATING. RAIN SHOULD BE CONFINED TO THE AREAS NEAR THE LOW WHICH WILL BE THE THUMB REGION...WITH CHANCES CREEPING IN ACROSS THE EXTREME SOUTHERN CWA LATE TONIGHT AS A QUICK MOVING SHORTWAVE TRACKS THROUGH THE SOUTHERN GREAT LAKES. LONG TERM... A LONGWAVE AMPLIFIED RIDGE AXIS WILL BUILD AGGRESSIVELY INTO NORTHEASTERN NORTH AMERICA DURING THE NEXT 48 HOURS. IT GOES WITHOUT SAYING...BUT AN EXTREMELY ATYPICAL EVENT FOR THIS SUMMER. WHAT THIS WILL DO IS ESSENTIALLY THROW A CURVE BALL TO THE LOCAL WEATHER PATTERN...LIKELY BRINGING IN THE LARGEST RUN OF SUMMER WARMTH THIS REGION HAS SEEN ALL SEASON LONG. BEFORE THIS CAN REALLY BECOME ESTABLISHED DURING THE LATTER HALF OF THE WEEKEND...SOUTHEASTERN MICHIGAN WILL HAVE TO CONTEND WITH AN INTERNAL RIDGE STRUCTURE AND SECONDARY JET CORE. IT IS THIS SECONDARY JET OVERHEAD THAT WILL DIRECT SHORTWAVE ENERGY AND POTENTIAL RIDGE RIDER TYPE MCS INTO THE AREA LIKELY ANYTIME THROUGH SATURDAY. AN ACTIVE PERIOD IS IN STORE THROUGH THE END OF THE WEEK. THURSDAY...A LOWER GEOPOTENTIAL HEIGHT ANOMALY WILL BUILD OFF OF LAKE HURON AND INTO THE NORTHEASTERN UNITED STATES DURING THE DAY ON FRIDAY. IT IS THE COMBINATION OF THIS ACTION AND AN UPPER LEVEL JET CORE CRESTING THE RIDGE AXIS OVER THE PLAINS/NORTHERN MISSISSIPPI RIVER VALLEY THAT THAT WILL FREEZE THE HEIGHT PATTERN OVER LOWER MICHIGAN. QUITE THE GRADIENT IN TEMPERATURES IS EXPECTED WITH A STATIONARY FRONTAL BOUNDARY DRAPED FROM PORTIONS OF OHIO NORTHWESTWARD TO CENTRAL LOWER MICHIGAN NW TO PORTIONS OF THE U.P. THE FRONTAL BOUNDARY IS NOT EXPECTED TO MOVE MUCH KEEPING THE HEAT TO THE SOUTHWEST. MODELS KEEP THE BULK OF THE CWA DRY...ALTHOUGH THE FRONTAL BOUNDARY WILL BRING THE POTETNIAL FOR SHOWERS AND THUNDERSTORMS PARTICULALRY SOUTH AND WEST OF M 59. TEMPERATURE SHOULD TICK ABOVE THE 80 DEGREE MARK FOR MANY AREAS. THE AFORMENTIONED 300MB JETLET IS FORECASTED TO CREST THE RIDGE THURSDAY EVENING AND SLIDE DIRECTLY INTO SOUTHEASTERN MICHIGAN THURSDAY NIGHT/FRIDAY MORNING. MODELS ARE EXTREMELY NOISY...BUT OVERALL THERE IS A VERY GOOD SIGNAL THAT AN MCS COULD BUILD ACROSS THE NORTHERN MISSSIPPI RIVER VALLEY THURSDAY AND RELEASE TOWARDS THE AREA THURSDAY NIGHT. ALOT OF TIME TO FIGURE THIS OUT...BUT DEGREE OF INSTABILITY IMMEDIATELY TO THE SOUTH DUE TO STRONG LAPSE RATES ALOFT COULD LEAD TO SEVERE WEATHER RISK FRIDAY MORNING. ONE THING TO MONIOR IS THE MCS WILL LIKELY ORGANIZED/INTENSIFY IN AN AREA OF STRONG LEFT EXIT REGION DYNAMICS. THE OVERALL SYSTEM IS THEN SHOWN TO OUTRUN THE UPPER LEVEL JET SUPPORT BY DIVING TO THE SOUTH. FRIDAY...FRIDAY IS A DIFFICULT FORECAST PERIOD. WILL LIKELY NEED TO COMBAT SUBSIDENCE AND MIDLEVEL LATENT HEATING LEFTOVER FROM THE MCS IMPACTING THE REGION. UPPER LEVEL JET CORE WILL MAINTAIN ENOUGH INTEGRITY TO BRING PESKY SHORTWAVE ENERGY INTO PLAY. MODELS SUPPORT ADVECTING HIGH THETA E INTO THE STATE ENOUGH FOR WHAT COULD END UP TO BE A VERY HIGH CAPE SETUP. MARINE... A WEAK AREA OF LOW PRESSURE WILL SLIDE ACROSS LOWER MICHIGAN TODAY BRINGING A WEAK SOUTHEASTERLY WIND TO MANY AREAS. A SECOND WEAK AREA OF LOW PRESSURE WILL PUSH INTO THE NORTHERN GREAT LAKES ON FRIDAY...MAINTAINING A RATHER SIZABLE SURFACE TROUGH STRUCTURE OVER THE GREAT LAKES REGION. OUTSIDE OF CONTINUAL SHOWER AND THUNDERSTORM CHANCES...AN EXTENDED STRETCH OF MARINE WEATHER IS ANTICIPATED. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI SHORT TERM...KURIMSKI LONG TERM....CB MARINE.......CB YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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