446  
FXUS63 KDTX 251738  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
138 PM EDT TUE SEP 25 2018  
 
   
AVIATION
 
 
FOCUS FOR THE FORECAST IS ON CONVECTIVE TRENDS THROUGH THE FIRST 12  
OR SO HOURS AHEAD OF A COLD FRONT THAT WILL SWEEP THROUGH EARLY  
WEDNESDAY MORNING. THERE IS A CHANCE OF SHOWERS AND/OR THUNDERSTORMS  
THROUGHOUT THIS PERIOD ALTHOUGH THERE ARE A FEW SMALLER WINDOWS TO  
KEEP AN EYE ON. FIRST WILL BE THIS AFTERNOON AROUND 21-24Z AS AN  
AREA OF ELEVATED CONVECTION LIFTS INTO THE AREA OUT OF INDIANA. THIS  
ACTIVITY SHOULD WEAKEN AS IT LIFTS NORTH THROUGH THE AREA. NEXT WILL  
BE GENERALLY IN THE 00-06Z WINDOW INSTABILITY PEAKS AND STORMS  
INITIATE AHEAD OF THE FRONT. THESE WOULD LIKELY BE THE STRONGEST  
STORMS IN THE FORECAST. THE FINAL OPPORTUNITY WILL COME WHEN THE  
FRONT ITSELF SWEEPS THROUGH THE AREA ENDING AROUND 10-12Z. EARLY  
STORMS COULD IMPACT POTENTIAL FOR LATTER STORMS SO AMENDMENTS WILL  
BE MADE AS NEEDED. WINDS WILL BE OUT OF THE SOUTHWEST INTO THE  
OVERNIGHT BEFORE FLIPPING TO NORTHWEST BEHIND THE DEPARTING COLD  
FRONT.  
 
FOR DTW...TIMING AND COVERAGE OF CONVECTION AS SHOWERS AND STORMS  
COULD POP UP AT ANY POINT THROUGH ABOUT 06Z. BEST CHANCES OF STORMS  
IMPACTING THE TERMINAL WILL BE THIS AFTERNOON AS A CLUSTER OF  
ELEVATED STORMS LIFTS NORTH OUT OF INDIANA, AND AGAIN TONIGHT AS A  
COLD FRONT SWEEPS THROUGH. IN BETWEEN THERE WILL LIKELY BE STORMS  
POPPING UP AS INSTABILITY CLIMBS, BUT COVERAGE WILL BE HARDER TO  
PIN POINT.  
   
DTW THRESHOLD PROBABILITIES
 
 
 
* HIGH FOR CEILING AOB 5000 FT TODAY AND TONIGHT.  
 
* MODERATE CONFIDENCE THAT THUNDERSTORMS WILL OCCUR THROUGH THE  
EVENING BUT LOW CONFIDENCE ON TIMING/COVERAGE.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 310 AM EDT TUE SEP 25 2018  
 
DISCUSSION...  
 
ROBUST UPPER LEVEL TROUGH AXIS/500 MB HEIGHT FALL CENTER TRACKING  
OUT THE CENTRAL PLAINS TODAY, AND MOVING THROUGH THE CENTRAL GREAT  
LAKES ON WEDNESDAY.  
 
LOW CLOUDS CAME IN FAST AND AGGRESSIVE YESTERDAY, AND FAVOR THE  
CLOUDS HOLDING STRONG THROUGH THE DAY, AS LOW CLOUDS ARE EVIDENT UP  
AND DOWN THE MISSISSIPPI RIVER VALLEY. THUS, MAX TEMPS ARE EXPECTED  
TO HOLD IN THE MID/UPPER 70S. MOIST ISENTROPIC ASCENT DURING THE  
DAY, COUPLED WITH LOW INSTABILITY WILL LIKELY BE SUFFICIENT TO  
SUSTAIN SCATTERED-NUMEROUS SHOWERS AND POSSIBLE THUNDERSTORMS. THE  
TRENDS TONIGHT FAVOR A SLOWER PASSAGE OF THE COLD FRONT AFTER  
MIDNIGHT. DESPITE THIS, 00Z NAM STILL ADVERTISING SBCAPES IN EXCESS  
OF 1000 J/KG AS SURFACE DEW PTS OF 68 TO 70 DEGREES LOOK TO ADVECT  
IN. STRONG DYNAMICS/WIND FIELDS TONIGHT (0-6 KM BULK SHEAR OF 50+  
KNOTS/40 KNOTS AT BOTH 700/850 MB) WILL CONTINUE TO SUPPORT CHANCE  
OF SEVERE STORMS/WIND POTENTIAL (60 MPH). STILL WILL HAVE TO BE  
LEARY OF INCREASING 0-1 KM BULK SHEAR DURING THE EVENING, RAMPING UP  
ABOVE 30 KNOTS BY MIDNIGHT, AND TORNADIC DEVELOPMENT CAN NOT BE  
RULED OUT, AS SPC HAS MUCH OF SOUTHEAST MICHIGAN IN 2 PERCENT RISK,  
WITH A 5 PERCENT RISK SOUTH OF ANN ARBOR-DETROIT. MID LEVEL LAPSE  
RATES LOOK TO BE WEAK, 6 C/KM OR LESS FROM 700-500 MB, AND MAY PROVE  
TO BE THE SAVING GRACE TO KEEP ACTIVITY MUTED OR CERTAINLY LIMITED  
IN COVERAGE, AS SUGGESTED BY VARIOUS HIRES SOLUTIONS. NONE-THE-LESS,  
A SLIGHT CHANCE OF SEVERE STORMS REMAINS VALID FOR LATE TODAY  
THROUGH MUCH OF TONIGHT.  
 
AGGRESSIVE DRYING/SUBSIDENCE TAKING PLACE BETWEEN 9-12Z WEDNESDAY, AS PW  
VALUES CRASH TO JUST UNDER 0.5 INCHES. 850 MB TEMPS LOWERING TO 3 TO  
5 C SUPPORTS HOLDING MAXES IN THE 60S.  
 
RIDGE OF HIGH PRESSURE SLIDING THROUGH SOUTHEAST MICHIGAN WEDNESDAY  
NIGHT, PROVIDING FAVORABLE RADIATING NIGHT, AND LOOKING AT LOWS IN  
40S, WITH UPPER 30S POSSIBLE IF WINDS DECOUPLE, MOST LIKELY NEAR  
OHIO BORDER, WHERE THERE IS ALSO FOG POTENTIAL.  
 
VERY DRY AIRMASS/850-700 MB THETA-E MINIMUM HANGS AROUND MOST OF  
THURSDAY BEFORE NARROW MOISTURE AXIS WITH NEXT COLD FRONT ARRIVES  
LATE IN THE DAY. LARGE SCALE UPPER LEVEL TROUGH ENCOMPASSING NORTHERN  
CONUS LATE IN THE WORK WEEK, SETTINGS US OF FOR A SEASONABLY COOL  
WEEKEND, AS 850 MB TEMPS DROP AT OR BELOW ZERO (PER 00Z EURO).  
SURFACE HIGH PRESSURE (1030 MB) OVER THE WEEKEND HAS TRENDED STRONGER  
FOR THE WEEKEND, WHICH FAVORS DRY WEATHER BEFORE NEXT LOW PRESSURE  
COMES OUT OF THE PLAINS, WITH GOOD OVER RUNNING SET UP FOR MONDAY.  
ALTHOUGH THE GOOD MID LEVEL FGEN/SHOWERS COULD END UP BEING DISPLACED  
NORTH OVER NORTHERN LOWER MICHIGAN.  
 
MARINE...  
 
A MODERATE EARLY DAY SOUTHEASTERLY WIND WILL GRADUALLY EASE WHILE  
TURNING SOUTHERLY THROUGH THE DAY. SMALL CRAFT CONDITIONS CONTINUE  
THIS MORNING BEFORE THE DECREASING WIND SPEED PROMPTS A  
CORRESPONDING REDUCTION IN WAVE ACTION THIS AFTERNOON. A COLD FRONT  
WILL TRACK THROUGH THE REGION TONIGHT. A MILD AND MOIST PRE-FRONTAL  
ENVIRONMENT WILL BRING THE CHANCE FOR THUNDERSTORMS DURING THE  
EVENING HOURS. WINDS THEN TURN NORTHWESTERLY AND STRENGTHEN WITH THE  
FRONTAL PASSAGE WEDNESDAY MORNING. STRONGEST WINDS NOTED ACROSS  
NORTHERN SECTIONS OF LAKE HURON, WHERE A BRIEF PERIOD OF GUSTS TO  
NEAR GALES WILL BE POSSIBLE. NORTHWEST WINDS DIMINISH LATE WEDNESDAY  
AND WEDNESDAY NIGHT AS HIGH PRESSURE BUILDS INTO THE REGION. WINDS  
BECOME SOUTHWESTERLY AND STRENGTHEN AGAIN THURSDAY IN ADVANCE OF THE  
NEXT COLD FRONT.  
 
HYDROLOGY...  
 
SCATTERED-NUMEROUS SHOWERS CONTINUE THIS MORNING WITHIN A VERY MOIST  
ENVIRONMENT. THE CHANCE FOR ADDITIONAL SHOWERS, ALONG WITH ISOLATED  
THUNDERSTORMS, WILL EXIST THIS AFTERNOON INTO TONIGHT. RAINFALL  
TOTALS WILL AVERAGE AROUND ONE QUARTER OF AN INCH, ALTHOUGH ANY  
THUNDERSTORM ACTIVITY COULD BRING VERY LOCALIZED HIGHER AMOUNTS. A  
COLD FRONT WILL THEN SWEEP THROUGH THE REGION OVERNIGHT, BRINGING  
DRIER CONDITIONS FOR THE LATE WEEK PERIOD. NO FLOODING IS EXPECTED  
THROUGH THE UPCOMING WEEK.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...NONE.  
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
AVIATION.....DRK  
DISCUSSION...SF  
MARINE.......MR  
HYDROLOGY....MR  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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