Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 291957 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 357 PM EDT SAT AUG 29 2015 .SHORT TERM... AFTERNOON AND TONIGHT SCATTERED TO NUMEROUS COVERAGE OF SHOWERS WILL CONTINUE DURING THE AFTERNOON AND EVENING. THIS WILL BE THE RESULT OF A WELL ORGANIZED LARGE SCALE PATTERN SUPPLYING MODERATE FORCING IN A MOIST BUT WEAKLY UNSTABLE ENVIRONMENT. IR AND WV SATELLITE IMAGERY CONTINUE TO SHOW A GOOD COMBINATION OF SUPPORT FROM THE RIGHT ENTRANCE REGION OF THE UPPER JET AND DOWNSTREAM OF THE TROUGH AXIS...INCLUDING AN INFUSION OF DCVA MOVING THROUGH THE TROUGH FROM IOWA/ILLINOIS/WISCONSIN. THESE LARGE SCALE FEATURES WILL CONTINUE TO DRIVE LOW TO MID LEVEL MOISTURE TRANSPORT/ISENTROPIC LIFT WITHIN THE SURFACE TO 850 MB ZONE OF THE WARM FRONT. MID AFTERNOON RADAR TRENDS DEPICT A CHANCE POP SCENARIO REFLECTED IN THE FORECAST TOWARD EARLY EVENING. AN INCREASE IN COVERAGE OF SHOWERS IS THEN EXPECTED FOR THE BULK OF THE EVENING AS THE UPSTREAM VORTICITY MAX MOVES THROUGH THE TROUGH AXIS...MORE DUE TO THE EXTRA FORCING THAN ANY ADDED INSTABILITY. THE CLOUDS... PRE-EXISTING SHOWERS...AND MEAGER MID LEVEL LAPSE RATES WILL ENSURE EVEN MUCAPE STAYS NEAR OR EVEN UNDER 500 J/KG. THE FORECAST DOES CARRY AN ISOLATED THUNDERSTORM FOR ANY ELEVATED ACTIVITY THAT REMAINS POSSIBLE WITHIN THE SURFACE TO 850 MB FRONTAL ZONE BEFORE THE UPPER TROUGH AXIS SLIDES EASTWARD AFTER MIDNIGHT AND SHOWER CHANCES DIMINISH. THE REMAINS OF THE SURFACE WARM FRONT JUST SOUTH OF THE INDIANA/OHIO BORDER DURING THE EVENING WILL DRIFT NORTHWARD OVERNIGHT. THE FRONT WILL WEAKEN WITH TIME BUT STILL BE ABLE TO TAP BOUNDARY LAYER MOISTURE SUPPLYING LOW STRATUS OVER MUCH OF SOUTHERN WISCONSIN/IOWA AND NORTHERN ILLINOIS. EXPECT AREAS OF FOG WILL ALSO BE LIKELY BY SUNRISE AS MIN TEMPS SETTLE MOSTLY INTO THE LOWER 60S MATCHING MID AFTERNOON OBSERVED DEWPOINT ACROSS THE AREA. && .LONG TERM...SUNDAY THROUGH FRIDAY A WEAKNESS IN THE UPPER LEVEL HEIGHT FIELD OR SUBTLE TROUGH AXIS WILL GRADUALLY EASE EASTWARD OUT OF LOWER MICHIGAN DURING THE FIRST HALF OF THE DAY ON SUNDAY. THE ABSOLUTE VORTICITY MAXIMUM IS PROGGED TO BE DIRECTLY OVER PORTIONS OF THE FAR EASTERN CWA AT 12Z WITH DECREASING DIFFERENTIAL CYCLONIC VORTICITY ADVECTION THEN SET FOR THE DAYLIGHT HOURS. THE KINEMATIC FIELD OVERHEAD WILL BE WEAK...WITH LITTLE TO NO TANGIBLE ADVECTION. AS A RESULT...LOOKING AT A WEAK THETA E DISCONTINUITY OR FRONTAL BOUNDARY TO REMAIN PARKED OVER THE CENTRAL TO NORTHERN PORTIONS OF THE CWA. THE THETA E RIDGE AXIS IS FORECASTED TO BECOME SHEARED EASTWARD DURING THE AFTERNOON WITH DEAMPLIFICATION OF THE FEATURE. THE SUM OF THE PARTS POINTS TO SOME VERY WEAK FORCING FOR ASCENT OCCURRING IN THE LOW LEVELS ALONG THIS BOUNDARY WITH A LACK OF FAVORABLE SYNOPTIC SCALE FORCING FOR ASCENT ALOFT. MODELED THERMODYNAMICS ARE VERY MARGINAL WITH INSTABILITY OF A FEW HUNDRED J/KG POSSIBLE BY THE AFTERNOON HOURS. CAMS AND DETERMINISTIC OFFER A SOLUTION THAT ANY WARM AIR ADVECTION/MOISTURE ADVECTION PRECIPITATION WILL BE SOUTH AND EAST OF THE CWA AT 12Z. THIS LIMITS THE PRECIPITATION POTENTIAL TOMORROW TO A ISO-SCT SHOWER DEVELOPMENT THAT MAY GENERATE ALONG THE AFOREMENTIONED WEAK THETA E DISCONTINUITY. REMOVED PRECIPITATION MENTION DURING THE MORNING AND WANTED TO COMMUNICATE THE POTENTIAL FOR THE AFTERNOON. WILL MAINTAIN A MENTION OF THUNDER GIVEN A SLIGHTLY UNSTABLE COLUMN AND MOISTURE....BUT NO STRONG WEATHER IS ANTICIPATED. GIVEN HEART OF THETA E RIDGE OVERHEAD...LOOKING AT HIGHS TOPPING OUT AROUND 80 DEGREES WITH SOME PEAKS OF SUNSHINE DEVELOPING AS THE DAY PROGRESSES. AN EXPANDING AND EASTWARD PROGRESSING UPPER LEVEL RIDGE AXIS WILL THEN ALLOW HEIGHTS TO INCREMENT UPWARD OVER SOUTHEASTERN MICHIGAN FOR THE BEGINNING OF THIS WEEK. A STRONG UPPER LEVEL RIDGE IS FORECASTED WITH 500 MB HEIGHTS OF 590 DAM BY MONDAY EVENING. IT IS APPEARING WITH MORE AND MORE LIKELIHOOD THAT AN EXTENDED RUN OF ABOVE NORMAL TEMPERATURES WILL BEGIN MONDAY WITH DAYTIME HIGHS RISING EASILY INTO THE MID TO UPPER 80S. .EXTENDED...ABOVE NORMAL TEMPERATURES WILL BE COMING BACK TO THE AREA NEXT WEEK AS BROAD UPPER LEVEL RIDGING TAKES HOLD. MAINLY DRY CONDITIONS ARE EXPECTED DURING THIS TIME EXCEPT ON WEDNESDAY AS MODELS ARE ADVERTISING A WEAK WAVE MOVE THROUGH. && .MARINE... BENIGN MARINE WEATHER WILL CONTINUE ACROSS THE GREAT LAKES REGION THROUGH MUCH OF THE UPCOMING WEEK. A STRONG RIDGE OF UPPER LEVEL HIGH PRESSURE WILL MAINTAIN LIGHT FLOW AND A GENERAL SOUTHWEST WIND DIRECTION. && .AVIATION...ISSUED 147 PM EDT SAT AUG 29 2015 SHOWERS WILL BE A HINDRANCE TO AVIATION OPERATIONS FOR THE AFTERNOON THROUGH THE EVENING. THE PATTERN WILL HAVE LOW END VFR CEILING AND VISIBILITY WITH JUST A FEW POCKETS OF MVFR VISIBILITY RESTRICTION IN A HEAVIER SHOWER. THUNDERSTORM POTENTIAL...IF ANY...REMAINS TOO LOW TO INCLUDE IN THE TERMINAL FORECASTS. MVFR CEILING AND VISIBILITY WILL THEN BECOME MORE WIDESPREAD OVERNIGHT THROUGH SUNDAY MORNING AS THE SURFACE WARM FRONT DRIFTS NORTH OF THE INDIANA/OHIO BORDER. A PERIOD OF IFR SHOULD ALSO BE EXPECTED AROUND SUNRISE BOTH IN TERMS OF FOG AND STRATUS AT ALL TERMINALS. FOR DTW... THUNDERSTORM POTENTIAL REMAINS LOW DURING THE AFTERNOON AND EVENING. CEILING BELOW 5000 FT WILL BE INCONSISTENT EVEN WITHIN SHOWERS DURING THE AFTERNOON AND THEN FILL IN MORE SOLIDLY DURING THE EVENING. A STEADY TREND INTO MVFR OVERNIGHT AND INTO IFR TOWARD SUNRISE IS LIKELY AS A WARM FRONT MOVES INTO THE REGION. //DTW THRESHOLD PROBABILITIES... * MEDIUM FOR CEILING 5000 FT OR LESS DURING AFTERNOON AND EVENING... HIGH OVERNIGHT THROUGH SUNDAY MORNING. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MICHIGAN WATERS OF LAKE ERIE...NONE. && $$ SHORT TERM...BT LONG TERM....CB/SS MARINE.......CB AVIATION.....BT YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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