Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 200413 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1213 AM EDT MON OCT 20 2014 .AVIATION...
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//DISCUSSION... VFR SKIES WILL CONTINUE TO STEADILY LOWER OVERNIGHT AS A COLD FRONT MAKES ITS WAY TOWARDS THE AREA FROM THE WEST. LOW VFR/MVFR CEILINGS ARE ANTICIPATED BY MONDAY MORNING WITH THE STRENGTHENING SOUTHWEST FLOW...WITH LIGHT SHOWERS DEVELOPING DURING THE DAYTIME HOURS. THESE SHOWERS ARE EXPECTED TO LAST THROUGH MONDAY AFTERNOON AS THE COLD FRONT SWEEPS THROUGH THE AREA WITH LIGHT SHOWERS MONDAY EVENING BEHIND THE COLD FRONT. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS DROPPING BELOW 5000 FEET TOWARD SUNRISE MONDAY AND CONTINUING THROUGH MONDAY NIGHT.
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&& .PREV DISCUSSION...ISSUED 338 PM EDT SUN OCT 19 2014 SHORT TERM...TONIGHT 12Z DTX SOUNDING REVEALED A VERY DRY AIRMASS IN PLACE...AND MUCH OF THE ISENTROPIC ASSENT (295 K) TONIGHT WILL BE USED UP JUST TO SATURATE THE ATMOSPHERE. THE 12Z NAM STILL SHOWING 295 K CONDENSATION PRESSURE DEFICITS ABOVE 10 MB THROUGH 12Z MONDAY...WHICH DOES NOT GIVE ONE A WHOLE LOT OF CONFIDENCE IN SHOWERS DEVELOPING. HOWEVER...THE UPPER WAVE/ENERGY IS CARVING THROUGH THE UPPER MISSISSIPPI RIVER VALLEY THIS AFTERNOON...AND THE RESPONSE DOWN LOW/RADAR ACTIVITY IS ON THE UPTICK. WITH THE SYSTEM CONTINUING TO DIG SOUTHEAST AND FURTHER MOISTURE TRANSPORT TAKING PLACE...HIGHER CHANCE POPS ACROSS THE NORTH HALF OF THE CWA...CLOSE TO THE PARENT SURFACE LOW...SEEMS APPROPRIATE. LOW LEVEL WARM ADVECTION THROUGH THE NIGHT (925 MB TEMPS RISING TO 7 C) COUPLED WITH INCREASING/THICKENING CLOUDS AND MODEST SOUTHWEST WINDS EXPECTED TO HOLD MINS IN THE LOW TO MID 40S...IN LINE WITH LATEST GUIDANCE. TEMPERATURES WILL PROBABLY BOTTOM OUT THIS EVENING AND THEN HOLD OR ACTUALLY RISE SLIGHTLY OVERNIGHT. LONG TERM... MONDAY THROUGH NEXT WEEKEND THE SYSTEM MOVING OUT OF CENTRAL CANADA TODAY AND INTO THE NORTHERN GREAT LAKES TONIGHT WILL BE POSITIONED ON GOOD MODEL AGREEMENT ABOUT OVER THE STRAITS TO START THE DAY MONDAY. SE MICHIGAN WILL BE SUBJECTED TO MILD SOUTHWEST LOW LEVEL FLOW AND THE MODEST RAIN PATTERN ASSOCIATED WITH REMAINING WARM ADVECTION THROUGH THE MORNING. THE BEST RAIN POTENTIAL WILL DEVELOP DURING THE AFTERNOON AS FORCING TRANSITIONS TO UPPER WAVE DYNAMICS AND INTERACTION OF THE MOISTURE AXIS WITH THE COLD FRONT. THE LOW LEVEL THETA-E RIDGE WILL BUILD FULLY OVERHEAD BY 18Z AND CONSIST OF SURFACE DEWPOINT RISING TO ABOUT 50 F AND 850 MB DEWPOINT NEAR 5 C. SURFACE BASED INSTABILITY DEVELOPS MORE CONVINCINGLY OVER OHIO AND ONTARIO IN THE NAM OUTPUT BUT ELEVATED INSTABILITY WILL BE ADEQUATE TO MAINTAIN THE ISOLATED MENTION OF THUNDER ADVERTISED IN THE FORECAST OVER THE LAST FEW FORECAST CYCLES. LAPSE RATES IN THE 700-500 MB LAYER ARE SHOWN IN MODEL DATA TO STEEPEN NEAR 7.5 C/KM AS THE UPPER LEVEL COLD POOL ADVECTS INTO THE REGION WITH 500 MB TEMPS APPROACHING -23 C. MODEL THETA-E CROSS SECTIONS ALSO INDICATE ELEVATED INSTABILITY COMMENSURATE WITH 850 MB LI AROUND -1 C WHICH...WHEN COMBINED WITH DCVA FROM THE UPPER WAVE AND FRONTAL CONVERGENCE...WILL RESULT IN NUMEROUS SHOWERS ALONG WITH THE ISOLATED STORM POSSIBILITY. AFTER A PAUSE IMMEDIATELY POST FRONT...EXPECT SOME MOISTURE TO WRAP AROUND THE WAVE AND LINGER OVER SE MICHIGAN DURING MONDAY EVENING... BUT ESPECIALLY OVERNIGHT. THIS IS WHEN STRONG CYCLONIC FLOW WILL DEVELOP A NORTHEAST COMPONENT AND WRING OUT ADDED MOISTURE FROM LAKE HURON. MODEL SOUNDINGS AND PLAN VIEW TEMPERATURE FIELDS INDICATE SATURATION THROUGHOUT THE LOW LEVEL THERMAL TROUGH WHICH POINTS TO DEVELOPING LAKE INSTABILITY HAVING POTENTIAL FOR DEEP INLAND PROGRESS AND FOR SHOWERS TO HAVE ENOUGH LONGEVITY TO CARRY WELL INTO TUESDAY MORNING. COLD ADVECTION WILL THEN CONTINUE THROUGH TUESDAY INTO TUESDAY NIGHT BUT WILL BECOME PROHIBITIVELY DRY FOR PRECIPITATION AS LOW LEVEL FLOW RELAXES AND THE INFLUENCE OF HIGH PRESSURE TAKES OVER. THE PACE OF THIS TRANSITION LOOKS SOLID IN THE LARGER SCALE MODEL PRESSURE AND LAYER MOISTURE FIELDS ACROSS SOLUTIONS...BUT THE PACE OF BOUNDARY LAYER DRYING SUGGESTS A SLOWER CLEARING TREND TOWARD WEDNESDAY MORNING. WEDNESDAY AND BEYOND WILL FEATURE A TRANSITION TO UPPER RIDGING BUILDING INTO THE GREAT LAKES REGION IN THE WAKE OF THE UPPER LOW MOVING TOWARD THE MID-ATLANTIC COAST. WEDNESDAY WILL STILL FEATURE COOL TEMPERATURES WITH LOW LEVEL FLOW REMAINING NORTHERLY THROUGH MOST OF THE DAY AS IT WILL TAKE A WHILE FOR THE THERMAL TROUGH TO DEPART AND SURFACE HIGH TO BUILD IN. CALLED FOR A SLOWER BURNOFF OF CLOUDS AND HIGHS IN THE LOW 50S. AFTER A CHILLY WEDNESDAY NIGHT...A NICE WARMING TREND AND PLEASANT FALL WEATHER IS IN STORE THURSDAY INTO THE WEEKEND WITH HIGHS LIKELY REACHING BACK INTO THE 60S BY FRIDAY. ONE THING TO WATCH WILL BE THE SHORTWAVE TROUGH APPROACHING THE REGION FROM THE PLAINS THURSDAY NIGHT...BUT MODEL CONSENSUS SUPPORTS THIS WAVE SHEARING OUT WITH MINIMAL IMPACT TO WEATHER LOCALLY SAVE FOR PERHAPS AN INCREASE IN MIDLEVEL CLOUDS. MARINE... SOUTHWEST WIND WILL STEADILY INCREASE DURING THE NIGHT AS THE NEXT LOW PRESSURE SYSTEM MOVES FROM NORTHWEST ONTARIO TO THE STRAITS BY MONDAY MORNING. THE LOW AND ASSOCIATED COLD FRONT WILL PASS ACROSS LAKE HURON AND LOWER MICHIGAN DURING THE DAY WITH A PATTERN OF SHOWERS LASTING THROUGH MONDAY NIGHT. WINDS WILL THEN VEER TO NORTHEAST AS THE LOW PRESSURE SYSTEM CONTINUES TO MOVE TOWARD THE ATLANTIC COAST AND AS HIGH PRESSURE BUILDS ACROSS NORTHERN ONTARIO. THE COMBINATION OF A STRONGER GRADIENT AND ONSHORE FLOW WILL BRING A PERIOD OF GUSTY WIND AND BUILDING WAVES THROUGHOUT CENTRAL AND SOUTHERN LAKE HURON THROUGH TUESDAY. THE POTENTIAL FOR GUSTS AROUND 30 KNOTS LOOKS SOLID WITH A LOWER PROBABILITY FOR BRIEF GUSTS TO GALES EARLY TUESDAY. THE COLDER AIR OVER THE WARM LAKE WATER WILL YIELD STRONG INSTABILITY BUT MAY ALSO LIMIT THE POTENTIAL FOR GALE FORCE GUSTS BY ALTERING THE PRESSURE FIELD AND LIMITING THE GRADIENT FLOW. NO GALE HEADLINES ARE PLANNED AT THIS TIME BUT SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED TUESDAY INTO TUESDAY NIGHT. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI SHORT TERM...SF LONG TERM....BT/DT MARINE.......BT YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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