Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 010358 CCA AFDDTX AREA FORECAST DISCUSSION...CORRECTED TYPO NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1155 PM EDT TUE SEP 30 2014 .AVIATION... //DISCUSSION... IFR CIGS CONTINUE TO SPREAD SOUTHWARD THROUGH THE CWA WITHIN MOIST CYCLONIC FLOW ON WEST SIDE OF LOW PRESSURE. CIGS/VSBYS ARE EXPECTED TO EDGE DOWN THROUGH THE NIGHT WITH IFR/LIFR COMMON BY DAWN AS LOW LEVEL MOISTURE REMAINS TRAPPED UNDER LOWERING INVERSION. CONDITIONS WILL THEN GRADUALLY IMPROVE ON WEDNESDAY AS THE AFOREMENTIONED LOW SHIFTS TO THE EAST/SOUTHEAST. FOR DTW...EXPECT CIGS TO LOWER BELOW 1000 FEET BETWEEN 06Z-08Z WITH AREAS OF FOG POSSIBLE AFTER 08Z. THIS WILL LINGER THROUGH 14Z OR SO...BEFORE GRADUAL IMPROVEMENT IN CIGS/VSBYS ENSUES FOR THE REST OF THE FORECAST PERIOD. //DTW THRESHOLD THREATS... * HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET THROUGH WEDNESDAY MORNING...WITH MEDIUM CONFIDENCE FOR WEDNESDAY AFTERNOON/EVENING. && .PREV DISCUSSION...ISSUED 354 PM EDT TUE SEP 30 2014 SHORT TERM...TONIGHT CURRENT MODEL RUNS ARE STILL SHOWING SURFACE RIDGING TO BUILD ACROSS THE REGION TONIGHT HELPING TO PUT AN END TO ANY LINGERING DRIZZLE AND RAIN SHOWERS BY EARLY EVENING. ORIGINAL THINKING WAS FOR CLOUDS TO ALSO DIMINISH SLIGHTLY...HOWEVER...WITH ABUNDANT MOISTURE AROUND FROM RAIN AND DRIZZLE THROUGHOUT THE DAY...CONFIDENCE IS HIGH IN CLOUD COVER REMAINING OVERCAST TONIGHT. THIS LOW LEVEL MOISTURE COMBINED WITH SOME WEAK WARM AIR ADVECTION WILL RESULT IN A HIGHER PROBABILITY OF LOW STRATUS AND EVEN SOME FOG DEVELOPMENT ESPECIALLY IN LOW LYING AREAS. ONLY MAJOR CONCERN TO WATCH OUT FOR DURING THE NEXT FORECAST SHIFT IS THE UNCERTAINTY ABOUT HOW DENSE THE FOG WILL BE OVERNIGHT. OVERCAST SKIES OVERNIGHT WILL RESULT IN TEMPERATURES TO ONLY DROP A FEW DEGREES FROM TUESDAYS HIGH TEMPS INTO THE UPPER 40S AND LOW 50S ACROSS SOUTHEAST MICHIGAN. LONG TERM...WEDNESDAY THROUGH MONDAY LONGWAVE PATTERN TO UNDERGO SOME BIG CHANGES THROUGH THE REST OF THE WEEK LEADING TO A VERY COOL WEEKEND AS A DEEP TROUGH OVERTAKES THE REGION. THE MIDWEEK TIME FRAME WILL BE THE TRANSITION PERIOD FOR THE PATTERN AS THE FIRST STRONG WAVE COMES ASHORE THE NW CONUS. THIS WILL CARVE OUT A TROUGH OVER THE MOUNTAIN WEST WHICH WILL ABSORB A CUTOFF LOW AS IT MOVES FURTHER EAST. NARROW RIDGE AXIS IN ADVANCE OF THE TROUGH WILL PASS OVER THE GREAT LAKES WEDNESDAY. MEANWHILE AT THE SFC...SOUTHERN PERIPHERY OF HIGH PRESSURE OVER ONTARIO/QUEBEC REMAINS IN CONTROL AT THE SFC BUT WILL DRIFT EAST LOOSENING ITS GRIP. COOL EASTERLY FLOW WILL BE REPLACED WITH WARMER AND MOISTER SOUTH/SOUTHWEST FLOW AS THE DEEPENING TROUGH REACHES THE PLAINS STATES. PATTERN STALLS OVER THE UPPER MISSISSIPPI VALLEY AS A STRONG WAVE DIVES THROUGH THE TROUGH CHANGING IT FROM A POSITIVE TO NEUTRAL TILT. AS THE WAVE LIFTS NE OUT OF THE TROUGH...CYCLOGENESIS WILL ENSUE ALONG A COLD FRONT EXTENDING FROM ONTARIO DOWN INTO OKLAHOMA. THIS SFC LOW WILL UNDERGO RAPID INTENSIFICATION...DEEPENING FROM 1004MB 18Z THURSDAY DOWN TO 988MB 12Z FRIDAY WHICH IS NEARLY 1 MB/HR. BUT THIS SFC LOW WILL HAVE LITTLE FORWARD PROPAGATION DUE TO THE UPPER LEVEL TROUGH STALLING. NOW FOR WHAT THIS MEANS FOR SE MI WEDNESDAY AND THURSDAY. WEDNESDAY WILL START OFF VERY CLOUDY AS MODEL CONSENSUS KEEPS A VERY MOISTURE LADEN BL UNDER A STRONG BUT WEAKENING INVERSION. INCREASING HEIGHTS WITH RIDGE AXIS OVERHEAD WILL PROMOTE SOME WARMING ALONG WITH THE MORE FAVORABLE WIND DIRECTION. EAST WINDS WILL VEER AROUND SOUTH LATE IN THE DAY BECOMING SOUTHWEST OVERNIGHT. CURRENT THINKING KEEPS TEMPS IN THE MID 60S. WILL BE SOME ADDITIONAL POTENTIAL FOR TEMPS TO JUMP A DEGREE OR TWO WITH WARMER AIR ALOFT BUT MODEL SOUNDINGS SHOW MIXING DEPTHS STRUGGLING TO TAP INTO THAT AIR. THERE WILL LIKELY BE A SHARP GRADIENT IN PRECIPITATION ON THURSDAY AS A PREFRONTAL LINE OF SHOWERS APPROACHES SE MI. THE RIDGE WILL HOLD IT TO THE WEST FOR MOST OF THE DAY WITH ONLY OUR WESTERN COUNTIES HAVING A CHANCE FOR ANY SHOWERS. THE STRONGEST OF THE SHORTWAVES THUS FAR WILL SURGE THROUGH THE TROUGH FORCING THE COLD FRONT THROUGH LOWER MI LATE THURSDAY NIGHT INTO FRIDAY. GOOD SW FLOW AHEAD OF THE FRONT WILL RAMP UP WAA WITH TEMPS IN THE MID 70S WHICH WILL DROP OFF SIGNIFICANTLY POST FRONTAL AS WE EXPERIENCED TODAY FROM THE MOST RECENT COLD FRONT. DEEPENING LOW PRESSURE AND ASSOCIATED COLD FRONT WILL CROSS THROUGH THE STATE ON FRIDAY. THIS FEATURE WILL SPREAD RAIN...BRISK WINDS...AND A SHARP TEMPERATURE DROP TO THE AREA. EXPECT LOW STRATUS...DRIZZLE...AND MUCH COOLER TEMPERATURES FOR THE WEEKEND IN THE POST FRONTAL/UPPER TROUGH PATTERN. TEMPS WILL BE HOVERING AROUND 10 DEGREES BELOW NORMAL FOR THE WEEKEND INTO EARLY NEXT WEEK. MARINE... A TIGHT NORTHERLY GRADIENT REMAINS OVER CENTRAL LAKE HURON KEEPING WIND SPEEDS UP LONGER INTO THE AFTERNOON. THESE WINDS WILL CONTINUE TO BUILD WAVES UP TO SMALL CRAFT CRITERIA ALONG THE LAKE HURON SHORELINE OF THE THUMB. SMALL CRAFT ADVISORIES WILL CONTINUE THROUGH THIS EVENING TO ACCOUNT FOR THAT. WINDS WILL DIMINISH TONIGHT AS HIGH PRESSURE LESSENS THE GRADIENT OVER THE LAKES BUT THE PERSISTENT NORTHEAST FLOW WILL KEEP SOME ELEVATED WAVES HEIGHTS INTO THE OVERNIGHT HOURS. LIGHT WINDS AND LOW WAVES WILL PERSIST WEDNESDAY INTO THURSDAY. HOWEVER...SOUTHERLY WINDS DEVELOPING AHEAD OF A COLD FRONT LATE THURSDAY COULD RESULT IN WINDS UP TO 30 KNOTS OVER THE OPEN WATERS OF LAKE HURON THURSDAY NIGHT. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON... SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 4 AM WEDNESDAY. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....DG SHORT TERM...RK LONG TERM....DRK/MM MARINE.......DRK YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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