739
FXUS63 KDTX 212312
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
712 PM EDT TUE JUL 21 2026
KEY MESSAGES
- THERE REMAINS AN ISOLATED RISK FOR STRONG THUNDERSTORMS EARLY THIS
EVENING WITH THE PASSAGE OF A COLD FRONT.
- DRY CONDITIONS WITH TEMPERATURES DIPPING BELOW AVERAGE DURING THE
MID TO LATE WEEK PERIOD.
- NEXT CHANCE OF PRECIPITATION SATURDAY NIGHT INTO SUNDAY.
AVIATION
THE PRIMARY COLD FRONT, CROSSING THE I-69 CORRIDOR AT FORECAST
ISSUANCE, MOVES QUICKLY THROUGH THE REST OF SE MI THIS EVENING.
CONVECTION CONSISTS OF A FEW STRUGGLING SHOWERS OUT AHEAD OF THE
FRONT WITH A BROKEN LINE OF SHOWERS ALONG THE FRONT ITSELF. SURFACE
BASED CAPE OF 1000-1500 J/KG GENERALLY SOUTH OF I-69 STILL REQUIRES
MONITORING FOR AN ISOLATED STRONGER STORM ALONG LINGERING OUTFLOWS
AND BEFORE THE FRONT EXITS INTO ONTARIO AND OHIO BEFORE MIDNIGHT.
DRY WEATHER POST FRONT TURNS THE FORECAST TOWARD CLOUD TRENDS FOR
THE LATE NIGHT AND WEDNESDAY MORNING. EARLY EVENING OBSERVATIONS
SHOW SCATTERED TO BROKEN MVFR COVERAGE IMMEDIATELY POST FRONT WHERE
STRONG COLD AND DRY AIR ADVECTION MAINTAINS A WELL MIXED BOUNDARY
LAYER. MVFR CEILING SOLIDIFIES FARTHER NORTH IN NORTHERN LOWER AND
THE U.P. WHICH HAS A CHANCE TO MAKE DOWNSLOPE INTO THE SAGINAW
VALLEY AFTER MIDNIGHT AND THEN DOWN TOWARD PTK BEFORE SUNRISE.
DAYTIME HEATING AND COOLER/DRY NW FLOW GUSTING NEAR 20 KNOTS THEN
QUICKLY MIX OUT REMAINING CLOUDS BY AFTERNOON LEAVING
SCATTERED/SHALLOW CUMULUS UNTIL EVENING.
D21/DTW CONVECTION... THE EVENING TIME WINDOW FOR THUNDERSTORMS
CLOSES AS THE PRIMARY COLD FRONT EXITS THE DTW AREA FROM 02Z-03Z.
THUNDERSTORMS ARE THEN NOT IN THE FORECAST FOR THE REST OF TONIGHT
AND WEDNESDAY.
DTW THRESHOLD PROBABILITIES
* LOW FOR THUNDERSTORMS THIS EVENING.
* LOW FOR CEILING 5000 FT OR LESS LATE TONIGHT AND WEDNESDAY
MORNING.
PREV DISCUSSION
ISSUED AT 330 PM EDT TUE JUL 21 2026
DISCUSSION...
SURFACE COLD FRONT BEGINS THE PROCESS OF DROPPING THROUGH THE REGION
THIS EVENING MAINTAINING SCATTERED CONVECTION ACROSS THE NORTH FOR
THE EARLY EVENING BEFORE SHIFTING SOUTH FOR THE LATTER HALF.
AVAILABLE INSTABILITY DECREASES THROUGH THE REST OF THE DAY (MLCAPE
FALLING FROM ~2000 J/KG TOWARDS 1400 J/KG) RESULTING IN LESSENING
COVERAGE AS THE EVENING PROGRESSES. COVERAGE IS EXPECTED TO BE MORE
ISOLATED TO WIDELY SCATTERED IN NATURE ONCE THE FRONT REACHES THE
SOUTHERN HALF OF THE AREA LATE EVENING- PARTLY FROM ARRIVAL LATE IN
THE DIURNAL WINDOW AND PARTLY FROM DRIER AIR IN PLACE (DEWPOINTS IN
THE LOWER 60S VS THE NORTHERN UPPER 60S). ANY STRONG TO SEVERE STORM
CHANCE REMAINS ISOLATED AT BEST AS MLCAPE FALLS SUB 1500 J/KG WITH
SHEAR VALUES HOLDING AROUND 25-30KTS.
FRONTAL PASSAGE USHERS IN A MARKEDLY COOLER AIRMASS AS 850MB TEMPS
FALL FROM MID TEENS TO MID SINGLE DIGITS (C) OVERNIGHT DROPPING LOWS
TOWARD THE LOWER 50S. UPPER TROUGHING AND ASSOCIATED THERMAL
TROUGHING SETTLES ACROSS THE GREAT LAKES FOR THE MIDWEEK PERIOD
LEADING TO SEASONABLY COOL TEMPERATURES. COOLEST DAY OF THE WEEK IS
WEDNESDAY WHERE HIGHS ONLY REACH THE LOWER 70S WITH OVERNIGHT LOWS
AROUND 50, SOME 10-15 DEGREES BELOW NORMAL FOR LATE JULY. TROUGH
AXIS SHIFTS EAST OVER SOUTHERN ONTARIO BY THURSDAY ALLOWING FOR
SLIGHT WARMING (850MB IN THE UPPER SINGLE DIGITS C) SUPPORTING HIGH
TEMPS CLOSER TO THE MID/UPPER 70S.
WARM ADVECTION EVENTUALLY REDEVELOPS FRIDAY AS QUASI-ZONAL MID-UPPER
FLOW EXPANDS ACROSS THE GREAT LAKES ALLOWING HIGHS TO RETURN AROUND
80. BUILDING UPPER RIDGING OVER THE CENTRAL CONUS THIS WEEKEND
DRIVES A WEAK PERIPHERY SHORTWAVE INTO THE GREAT LAKES LATE SATURDAY
NIGHT-SUNDAY OFFERING THE AREA'S NEXT SHOT SEEING SOME SCATTERED
RAIN. UPPER 80S ALSO LOOK TO MAKE A RETURN LATE WEEKEND/EARLY NEXT
WEEK AS UPPER RIDGING BUILDS EAST INTO THE CENTRAL GREAT LAKES.
MARINE...
UPPER LEVEL DISTURBANCE TRACKING ACROSS NORTHERN MICHIGAN HAS LED TO
NUMEROUS THUNDERSTORMS ACROSS LAKE HURON AND SAGINAW BAY. A FEW OF
THESE STORMS HAVE EXHIBITED STRONG TO SEVERE POTENTIAL, WITH
DAMAGING WINDS OF 35 TO 50 KNOTS AND FREQUENT LIGHTNING THE MAIN
CONCERNS THROUGH EARLY EVENING. A COLD FRONT TRACKING THROUGH THIS
EVENING THEN CLEARS OUT REMAINING INSTABILITY TO BRING DECREASING
THUNDERSTORM COVERAGE, WHILE ALSO SHIFTING WINDS TO THE NORTHWEST. A
QUICK POP IN WIND GUSTS TOWARD GALE FORCE ARRIVES THIS EVENING,
CENTERED AROUND 00Z (8PM LOCAL) JUST ALONG/BEHIND THE FRONTAL
PASSAGE. STILL THINKING THE DURATION OF GALES WILL BE SHORT ENOUGH
TO FALL BELOW WARNING CRITERIA, BUT WILL MONITOR OBSERVATIONS
CLOSELY FOR A SHORT-FUSED PRODUCT. STRONG COLD ADVECTION WILL
CONTINUE THROUGH WEDNESDAY, MAINTAINING BREEZY NORTHWEST FLOW
THROUGH THE DAY AND KEEPING SMALL CRAFT ADVISORIES IN EFFECT. BEACH
HAZARDS STATEMENTS ARE ALSO LIKELY AGAIN WEDNESDAY. HIGH PRESSURE
THEN FILLS IN FOR THE LATTER HALF OF THE WEEK, RESULTING IN A
QUIETER PATTERN FOR THE GREAT LAKES.
DTX WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT THROUGH WEDNESDAY EVENING FOR MIZ049.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EDT WEDNESDAY FOR LHZ421-441>443.
SMALL CRAFT ADVISORY UNTIL 4 PM EDT WEDNESDAY FOR LHZ422.
LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LCZ460.
MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LEZ444.
AVIATION.....BT
DISCUSSION...KDK
MARINE.......MV
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page