127
FXUS63 KDTX 220335
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1135 PM EDT MON JUL 21 2025
KEY MESSAGES
- DRY AND SEASONABLY COOL TUESDAY.
- BECOMING INCREASINGLY HOT AND HUMID WEDNESDAY WITH HEAT INDICES
IN THE LOW 90S.
- THURSDAY WILL BE THE HOTTEST DAY OF THE WEEK WITH HEAT INDICES
POSSIBLY EXCEEDING 100F; SOME STORMS ARE ALSO POSSIBLE, ESPECIALLY
OVERNIGHT.
- WARM AND MUGGY CONDITIONS PERSIST FRIDAY THROUGH MUCH OF THE
WEEKEND WITH ADDITIONAL SHOWER/STORM CHANCES.
AVIATION
SEASONALLY STRONG HIGH PRESSURE WILL REMAINED POSITIONED ACROSS THE
EASTERN GREAT LAKES THROUGH THE TAF PERIOD. OTHER THAN SOME PASSING
MID AND HIGH LEVEL CLOUDS, DRY AIR WILL SUSTAIN MAINLY CLEAR SKIES
BELOW 10K FEET. LIGHT EAST-NORTHEAST WINDS TONIGHT WILL VEER TO THE
SOUTHEAST TUESDAY, WITH A SLIGHT INCREASE IN SPEEDS EXPECTED TUES
AFTERNOON DUE TO DIURNAL MIXING. AVAILABLE LOW LEVEL MOISTURE WILL
BE LEAN, BUT MAY BE ENOUGH TO SUPPORT A FEW MVFR BASED DIURNAL CU
TUESDAY AFTERNOON.
FOR DTW/D21 CONVECTION...NO THUNDERSTORMS WILL OCCUR THROUGH THE TAF
PERIOD.
THRESHOLD PROBABILITIES...
* NONE.
PREV DISCUSSION
ISSUED AT 245 PM EDT MON JUL 21 2025
DISCUSSION...
1022 MB SURFACE HIGH PRESSURE CENTERED OVER ONTARIO DRIFTS EAST,
CROSSING INTO WESTERN QUEBEC THIS EVENING. THIS PRESERVES COOL AND
LIGHT ENE FLOW FOR THE REST OF TODAY AND INTO TONIGHT, ALTHOUGH
WINDS TREND TOWARD CALM, LATE. SPARSE DIURNAL CUMULUS FIELD QUICKLY
DISSOLVES LATE EVENING WITH THE COLLAPSE OF THE MIXED-LAYER, THUS
TEMPERATURES SHOULD EASILY MINIMIZE IN THE 50S. CANNOT RULE OUT SOME
READINGS IN THE UPPER 40S FOR SOME OUTLYING AREAS, MAINLY NORTH OF I-
69.
LONGWAVE RIDGE (WAVELENGTH APPROACHING CONUS WIDTH) AMPLIFIES OVER
CENTRAL NORTH AMERICA, MARKING THE TRANSITION AWAY FROM THERMAL
TROUGHING OVER THE GREAT LAKES. 850 MB TEMPERATURES START TO REBOUND
OFF SEASONABLY COOL SINGLE-DIGITS (CELSIUS). SURFACE FLOW VEERS
SOUTHEASTERLY AS THE SURFACE RIDGE SETTLES EAST OF LAKE ONTARIO. DRY
AGAIN TUESDAY AS COLUMN MOISTURE WILL BE LACKING, BUT EXPECT MORE
DIURNAL CUMULUS. A SHORTWAVE PERTURBATION EMBEDDED WITHIN THE
ANTICYCLONIC JET SUPPORTS HIGH PLAINS/UPPER MIDWEST MCS MAINTENANCE
THROUGH THE NOCTURNAL CYCLE BEFORE DECAYING INTO NORTHERN MICHIGAN
WEDNESDAY MORNING. STATIC STABILITY SHOULD SUFFICE IN KEEPING
UPSTREAM CONVECTION AT-BAY A 596 DAM 500 MB RIDGE BUILDS NORTHEAST,
ALONG THE OHIO RIVER. RETURN FLOW REGIME EVENTUALLY YIELDS HIGHER
DEWPOINTS WEDNESDAY, LIKELY INTO THE UPPER 60S. PAIRED WITH HIGHS
NEAR 90F, HEAT INDICES CLIMB INTO THE LOW 90S. EVEN HIGHER VALUES
ARE POSSIBLE OVER THE TRI-CITIES WHERE DEWPOINTS COULD REACH 70F
GIVEN CLOSER PROXIMITY TO GREATER THETAE ADVECTION, ASSOCIATED WITH
THE MCS REMNANTS.
THURSDAY IS STILL POISED TO BE THE HOTTEST AND MOST HUMID DAY OF THE
WEEK. IN SPITE OF NBM DEWPOINT BIASES (TO THE HIGH SIDE), THE
SYNOPTIC SETUP COULD SUPPORT MID 70S DEWPOINTS ON THURSDAY. DUAL
GULF LLJ FEED (ONE BRANCH OFF THE SOUTHERN TEXAS GULF COAST, AND THE
OTHER OVER FLORIDA) BECOMES INCREASINGLY CONFLUENT OVER THE MID
MISSISSIPPI VALLEY. THIS PORTENDS HEIGHTENED RISK FOR EXTREME HEAT
WHEN COMBINED WITH STRONG DIURNAL HEATING, MARKED BY 850 MB
TEMPERATURES IN THE LOW TO MID 20S (CELSIUS). AS OF NOW, THE
OUTGOING FORECAST MAINTAINS MAX HEAT INDICES BETWEEN 100F AND 105F.
CONFIDENCE IS TOO LOW AT THIS TIME HORIZON IN WIDESPREAD EXTREME
HEAT CRITERIA (+105F), THEREFORE A HEAT ADVISORY WOULD APPEAR MORE
LIKELY. STILL, TOO MANY DAYS OUT TO HOIST ANY HEAT-RELATED HEADLINES
TODAY. ANOTHER COMPLICATING FACTOR FOR THURSDAY'S HEAT WILL BE THE
POTENTIAL FOR CONVECTION. AXIS OF HIGHEST MLCAPE SLIDES THROUGH
EARLY THURSDAY, BUT CAPPING COULD DELAY DIURNAL CONVECTIVE
INITIATION. SHOULD CONVECTION BECOME WIDESPREAD, EXPECT A LOWER
CEILING FOR DAYTIME HIGHS. FRONTAL BOUNDARY DROPS THROUGH THURSDAY
NIGHT INTO FRIDAY MORNING WITH HIGHER CONVECTIVE CHANCES. SLIGHTLY
LESS HOT, BUT STILL HUMID FRIDAY, AND POSSIBLY THROUGH THE WEEKEND
WITH ADDITIONAL OPPORTUNITIES FOR SHOWERS/STORMS.
MARINE...
REGION REMAINS UNDER THE INFLUENCE OF HIGH PRESSURE THROUGH THE
FIRST HALF OF THE WEEK MAINTAINING GENERALLY LIGHT WINDS. HIGH
CENTER SHIFTS FROM NORTHERN ONTARIO TO QUEBEC TONIGHT SHIFTING WINDS
FROM THE NE THIS AFTERNOON TO THE SE BY TUESDAY MORNING. INFLUENCE
OF SAID HIGH WANES INTO WEDNESDAY AS LOW PRESSURE OVER THE NORTHERN
PLAINS LIFTS A WARM FRONT THROUGH THE CENTRAL GREAT LAKES. STORM
CHANCES LOOK TO BE CONFINED TO THE NORTHERN HALF OF THE LAKE HURON
WEDNESDAY-THURSDAY OWING TO CLOSER PROXIMITY TO THE LOW. THESE
CHANCES THEN EXPAND OVER THE REST OF THE REGION THURSDAY NIGHT
THROUGH LATE WEEK AS THE ATTENDANT COLD FRONT SAGS THROUGH THE GREAT
LAKES.
DTX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
AVIATION.....SC
DISCUSSION...KGK
MARINE.......KDK
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