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
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