888
FXUS63 KDTX 160825
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
425 AM EDT SAT AUG 16 2025
KEY MESSAGES
- ISOLATED STRONG TO SEVERE THUNDERSTORMS POSSIBLE LATE THIS
AFTERNOON AND EVENING, WITH DAMAGING WIND GUSTS TO 60 MPH AS THE
MAIN THREAT.
- WARM AND HUMID TODAY WITH HEAT INDICES IN THE MID 90S.
- ADDITIONAL SHOWER AND THUNDERSTORM CHANCES EXIST TONIGHT AND AGAIN
MONDAY-TUESDAY. LOCALLY HEAVY RAINFALL IS POSSIBLE.
- COOLER AND DRIER CONDITIONS EXPECTED WEDNESDAY THROUGH FRIDAY.
DISCUSSION
AN ACTIVE MORNING ACROSS THE CENTRAL PART OF CONUS AS AREAS OF
CONVECTION HAVE DEVELOPED IN RESPONSE TO LOW LEVEL JET FORCING
IMPINGING UPON THE THETA-E RIDGE AXIS. COMPLEX OVER WI/MN/IA HAS
LOST MOST OF ITS CONVECTIVE VIGOR, WITH A MARKED DECREASE IN
LIGHTNING ACTIVITY OVER THE PAST SEVERAL HOURS. IMPACTS OF THIS
FEATURE WILL HOWEVER STILL BE FELT THROUGHOUT THE DAY, WITH HIGHEST
CONFIDENCE IN THE ADDED PRESENCE OF CLOUD COVER ALOFT THAT HAS
ALREADY STARTED SPILLING INTO SE MICHIGAN. HIGH TEMPERATURES TODAY
WILL MAKE A RUN AT 90 DEGREES, BUT COULD BE DAMPENED A COUPLE OF
DEGREES WHERE THICKER PATCHES OF CLOUD COVER DEVELOP. LOWER
CONFIDENCE ITEM IS IF OUTFLOW FROM THIS FEATURE WILL TRIGGER ANY
ADDITIONAL CONVECTION AS IT TRACKS OVERHEAD. GIVEN CURRENT
PROPAGATION AND LOCATION OF THE INSTABILITY GRADIENT, THINKING ANY
REDEVELOPMENT THIS MORNING WOULD OCCUR WEST OF THE CWA.
A MUCH MORE INTENSE CONVECTIVE EPISODE IS OCCURRING FURTHER UPSTREAM
OVER SOUTH DAKOTA, WHERE AN MCS HAS DEVELOPED OVERNIGHT AND IS NOW
TRACKING INTO A RESERVOIR OF 4000-5000 J/KG OF MUCAPE. THIS SYSTEM
HAS GENERATED SHORTWAVE PERTURBATIONS IN THE MODEL GUIDANCE FOR
SEVERAL DAYS NOW, AND WILL BE THE MOST WELL-DEFINED SOURCE OF
CONVECTIVE POTENTIAL AS IT MOVES INTO THE GREAT LAKES REGION LATE
THIS AFTERNOON-EVENING (ROUGHLY 4PM-11PM). THE FIRST POINT OF
UNCERTAINTY IS HOW WELL THE MCS WILL HOLD TOGETHER AS IT MOVES INTO
EASTERN MN/WI WHERE CONVECTION (ALBEIT WEAK) HAS BEEN OCCURRING FOR
MOST OF THE NIGHT. THIS WILL OCCUR ON THE EARLY SIDE OF THE DIURNAL
CYCLE, AND MAY NOT PROVIDE ENOUGH TIME FOR INSTABILITY TO REBOUND.
IN THIS CASE THE MCS WILL EITHER FALL APART, OR DIVE SOUTH TOWARD
THE MORE FAVORABLE INSTABILITY. EITHER WAY, THE LATEST HI-RES RUNS
(06Z HRRR/NAM NEST) SHOW SOME INTERFERENCE WITH THE CAPE MINIMUM
OVER WISCONSIN. THE REMNANT FORCING/CONVECTION THEN ARRIVES TO SE
MICHIGAN LATE AFTERNOON-EARLY EVENING, WHICH ALIGNS WELL WITH THE
PEAK HEATING CYCLE, AND TRIGGERS REDEVELOPMENT INTO A BROKEN
LINEAR/MULTICELLULAR MODE. THE MAIN POINT HERE IS THAT EVEN IF THE
LINE LOOKS LIKE IT FALLS APART UPSTREAM, IT MAY REDEVELOP WITH TIME
AND WILL STILL POSE A THREAT TO SE MICHIGAN LATER TODAY. SWODY1
MARGINAL RISK CONTINUES TO HIGHLIGHT AN ISOLATED DAMAGING WIND
THREAT FOR SE MICHIGAN, SUPPORTED BY LINEAR STORM MODE AND DRY AIR
THAT WILL ENHANCE DOWNDRAFT STRENGTH. SEVERAL ADDITIONAL ROUNDS OF
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVERNIGHT AS OUTFLOW
INTERACTS WITH MOISTURE CONVERGENCE AHEAD OF THE COLD FRONT THAT
DROPS THROUGH THE AREA ON SUNDAY.
OUTFLOW FROM TONIGHT'S CONVECTION ACTS TO CLEAR INSTABILITY TOWARD
THE STATE LINE SUNDAY MORNING, EVEN WITH THE SYNOPTIC COLD FRONT
LAGGING BEHIND. THE FRONT ITSELF SINKS THROUGH THE AREA SUNDAY
MORNING, AND MAY TRIGGER LOW COVERAGE SHOWERS IN ITS WAKE GIVEN
REMNANT BOUNDARY LAYER MOISTURE AND SHALLOW, WEAK INSTABILITY.
FORECAST SOUNDINGS BECOME INCREASINGLY CAPPED AND STATICALLY STABLE
THROUGHOUT THE DAY TO PREVENT ANY DEEPER CONVECTION FROM FORMING.
THE FRONTAL BOUNDARY IS NOTED IN SOUNDINGS BY A DISTINCT BACKING
PATTERN IN THE LOWEST 1 KM OR SO, WITH MUCH COOLER TEMPERATURES IN
STORE FOR SUNDAY ESPECIALLY FOR THE NORTH HALF OF THE CWA (MID TO
UPPER 70S). BREEZY CONDITIONS, ESPECIALLY TOWARD THE THUMB, AND LAKE
ENHANCED CLOUD COVER MAY ACCOMPANY THE COLD ADVECTIVE PATTERN.
EASTERLY FLOW WILL BE IN PLACE TO START THE DAY MONDAY, BUT
REORGANIZES OUT OF THE SOUTHWEST IN THE AFTERNOON AS THE GOVERNING
RIDGE AXIS SLIDES OVERHEAD. THIS DRAWS THE FRONT BACK NORTH THROUGH
THE AREA AS A WARM FRONT, WHICH REESTABLISHES MOIST AND UNSTABLE
CONDITIONS. DAYTIME HIGHS ON MONDAY ONLY IN THE LOW TO MID 80S
REFLECT THE AFTERNOON ARRIVAL OF THE WARM FRONT, BUT SHOULD BE
ENOUGH IN COMBINATION WITH UPPER 60S-LOW 70S DEWPOINTS TO GENERATE
WEAK SURFACE-BASED INSTABILITY DURING PEAK HEATING. INITIAL FORCING
WILL BE DRIVEN BY BACKGROUND ISENTROPIC ASCENT AND PERHAPS A
CONVECTIVE PERTURBATION ALOFT, BUT WILL TRANSITION TO BROADER
SYNOPTIC FORCING MONDAY NIGHT-TUESDAY AS LOW PRESSURE SLIDES ALONG
THE EXISTING BAROCLINIC ZONE AND INTO SE MICHIGAN. MEAN ENSEMBLE
PWAT OF ~1.7-1.8" AND MUCAPE VALUES RISING ABOVE 1000 J/KG BOTH
CHARACTERIZE THE HIGH MOISTURE ENVIRONMENT THAT WILL BE IN PLACE
MONDAY-TUESDAY. HEAVY RAIN WITH MULTIPLE PERIODS OF THIS RAINFALL
WILL BE POSSIBLE EARLY NEXT WEEK, WITH WPC ERO DESIGNATING A
MARGINAL RISK FOR BOTH DAYS.
THE LOW EVENTUALLY DRAGS A COLD FRONT THROUGH LOWER MICHIGAN
TUESDAY, FOLLOWED BY COLD ADVECTION AND HIGH PRESSURE FOR THE REST
OF THE WEEK. A DRY AND MILD PATTERN THUS EMERGES FOR THE BACK HALF
OF THE WORK WEEK, WITH DAYTIME HIGHS EXPECTED TO BE IN THE MID 70S
TO LOW 80S.
MARINE
CONTINUED LOW LEVEL WARMING TODAY AHEAD OF A COLD FRONT SHOULD CAP
SOUTHERLY WIND SPEEDS IN THE 15 TO 20 KNOT RANGE. NUMEROUS SHOWERS
AND THUNDERSTORMS DEVELOPING BY THIS EVENING AS THE COLD FRONT
ENTERS THE REGION. ALTHOUGH THE FRONT QUICKLY DROPS SOUTH OF THE
STATE SUNDAY MORNING, STILL A LINGERING CHANCE OF SHOWERS AND
THUNDERSTORMS FOR GOOD PORTION OF THE DAY. STRONG HIGH PRESSURE
BUILDING OVER NORTHWEST ONTARIO AND SOLID COLD ADVECTION (850 MB
TEMPS LOWERING INTO LOWER TEENS) OVER LAKE HURON ON SUNDAY WILL
ALLOW NORTHEAST WINDS TO REACH 20-25 KNOTS, WITH STILL THE POTENTIAL
FOR WINDS TO BRIEFLY GUST TO AROUND 30 KNOTS. EVEN IF WINDS COME UP
A BIT SHORT, THE PROLONG NORTHEAST WINDS WILL ALLOW WAVES TO BUILD
IN EXCESS OF 4 FEET ACROSS THE NEARSHORE WATERS OF LAKE HURON, AS
EASTERLY WINDS PERSIST INTO EARLY NEXT WEEK WITH ANOTHER STRONG HIGH
PRESSURE SYSTEM DEVELOPING OVER EASTERN CANADA.
HYDROLOGY
A BROKEN LINE OF SHOWERS AND THUNDERSTORMS IS EXPECTED LATE THIS
AFTERNOON-EVENING FOLLOWED BY ADDITIONAL ROUNDS OF RAINFALL THROUGH
EARLY SUNDAY MORNING. HIGH MOISTURE CONTENT MAY PRODUCE LOCALLY
HEAVY RAINFALL RATES IN EXCESS OF 1"/HR UNDER THE STRONGEST STORMS.
BASIN AVERAGE RAINFALL AMOUNTS OF 0.25" TO 0.50" WILL BE POSSIBLE,
WITH LOCALLY HIGHER AMOUNTS IN EXCESS OF ONE INCH IF MULTIPLE STORMS
IMPACT THE SAME AREA. LOCALIZED FLOODING OF URBAN, LOW-LYING AND
POOR DRAINAGE AREAS WILL BE POSSIBLE.
PREV DISCUSSION
ISSUED AT 1217 AM EDT SAT AUG 16 2025
AVIATION...
VFR DURING THE LATE NIGHT AND EARLY MORNING WITH CALM TO LIGHT SOUTH
WIND WHILE A CANOPY OF HIGH CLOUDS WASHES IN AS DEBRIS FROM UPPER
MIDWEST CONVECTION. THE FORCING RESPONSIBLE FOR THIS ACTIVITY WILL
SLOWLY MARCH EAST INTO THE CENTRAL GREAT LAKES LATER TODAY.
INCREASING BOUNDARY LAYER MOISTURE AND ACCOMPANYING INSTABILITY
SUPPORTS GREATER CUMULUS COVERAGE AND EVENTUALLY SHOWER AND
THUNDERSTORM DEVELOPMENT AND/OR MAINTENANCE OF ONGOING ACTIVITY
FARTHER UPSTREAM OVER THE CORNBELT. TIMING IS A BIT TENUOUS, OUTSIDE
THE GREATER CERTAINTY OF INSTABILITY INCREASING IN DEPTH AND QUALITY
DURING THE MID-LATE AFTERNOON HOURS. AS SUCH WILL ADVERTISE
CONVECTIVE CHANCES INCREASING FROM SOUTH TO NORTH ALONG THE SE MI
TERMINAL CORRIDOR AFTER 20Z THIS AFTERNOON. PLENTY OF OPPORTUNITY
FOR FORECAST REFINEMENT AS MUCH OF THE FORECAST HINGES ON EVOLUTION
OF THE 3-4 CONVECTIVE COMPLEXES UPSTREAM.
FOR DTW/D21 CONVECTION... CURRENT TIMING ESTIMATES SUPPORT A GOOD
CHANCE FOR THUNDERSTORMS AFTER 22Z THIS AFTERNOON ACROSS THE
NORTHERN PORTIONS OF THE D21 AIRSPACE WITH CHANCES INCREASING AFTER
00Z SUNDAY ACROSS THE CENTRAL AND SOUTHERN PORTIONS.
THRESHOLD PROBABILITIES...
* MEDIUM FOR CEILING AT OR BELOW 5 KFT SATURDAY AFTERNOON.
* MEDIUM FOR THUNDERSTORMS SATURDAY EVENING - MAINLY AFTER 00Z.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
DISCUSSION...MV
MARINE.......SF
HYDROLOGY....MV
AVIATION.....MANN
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