976
FXUS63 KGRB 261111
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
611 AM CDT SUN JUL 26 2026
UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE
UPDATE
ISSUED AT 423 AM CDT SUN JUL 26 2026
DENSE FOG HAS BECOME MORE WIDESPREAD OVER NORTH-CENTRAL WI PER
WEBCAMS AND OBSERVATIONS EARLY THIS MORNING, SO DECIDED TO ISSUE A
DENSE FOG ADVISORY UNTIL 8 AM.
KEY MESSAGES
- HEAT INDICES APPROACHING 100 DEGREES ACROSS CENTRAL WISCONSIN
THIS AFTERNOON, WHERE A HEAT ADVISORY IS IN EFFECT FOR WOOD,
PORTAGE, WAUPACA, AND WAUSHARA COUNTIES.
- STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE MID TO LATE THIS
AFTERNOON THROUGH LATE THIS EVENING, AND AGAIN ON MONDAY
AFTERNOON AND EVENING. DAMAGING WINDS AND LARGE HAIL WILL BE THE
PRIMARY HAZARDS.
- A COLD FRONT PASSING THROUGH THE REGION WILL BRING A SHIFT TO
NORTHERLY WINDS AND RELIEF FROM THE HIGH HUMIDITY FOR TUESDAY
THROUGH MID-WEEK, WITH LOWER THUNDERSTORM CHANCES UNTIL LATE IN
THE WORK WEEK.
DISCUSSION
ISSUED AT 226 AM CDT SUN JUL 26 2026
THE LATEST RAP ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A POTENT
SUB-TROPICAL RIDGE CENTERED OVER THE INTERMOUNTAIN WEST AND
CENTRAL GREAT PLAINS EARLY THIS MORNING. THE LEADING EDGE OF A
VERY WARM AND MUGGY AIRMASS STRETCHES ALONG A WARM FRONT EXTENDING
FROM CENTRAL MINNESOTA TO SOUTHWEST WISCONSIN. THE ACTIVE RING OF
FIRE CONVECTIVE PATTERN AROUND THE RIDGE HAS MAINTAINED
THUNDERSTORM CLUSTERS FROM MONTANA DOWN INTO IOWA AND MINNESOTA
OVERNIGHT. ACROSS NORTH-CENTRAL AND NORTHEAST WISCONSIN, LOW
STRATUS HAS BEEN GRADUALLY ERODING FROM WEST TO EAST EARLY THIS
MORNING, PROMOTING AREAS OF LOCALLY DENSE GROUND FOG ACROSS NORTH-
CENTRAL WISCONSIN. WILL BE MONITORING TRENDS FOR A DENSE FOG
ADVISORY. THE CLEARING TREND SHOULD CONTINUE THROUGH DAWN BEFORE
CLOUD DEBRIS FROM MINNESOTA STORMS DRIFTS OVERHEAD. ELEVATED
MOISTURE CONVERGENCE TRANSLATING EASTWARD MAY DRIVE A FEW DYING
SHOWERS INTO CENTRAL WISCONSIN EARLY, BUT MOST ACTIVITY SHOULD
FIZZLE OR STAY SOUTHWEST OF THE FORECAST AREA.
HEAT AND HUMIDITY TODAY THROUGH MONDAY...
AS THE WARM FRONT LIFTS NORTHEAST ACROSS THE REGION TODAY, HOT
AND MUGGY CONDITIONS WILL OVERSPREAD NORTH-CENTRAL AND NORTHEAST
WISCONSIN. MODEL TIME-HEIGHT CROSS SECTIONS SHOW LOW-LEVEL CLOUDS
DISSIPATING BY MID-MORNING, ALLOWING STRONG DIURNAL HEATING TO
BOOST TEMPERATURES INTO THE UPPER 80S AND LOWER 90S FROM THE FOX
VALLEY AND BAYSHORE WESTWARD. LAKE MICHIGAN SHORELINE AREAS WILL
REMAIN COOLER IN THE LOW TO MIDDLE 80S DUE TO LAKE INFLUENCE.
COMBINED WITH DEWPOINTS SURGING INTO THE LOWER 70S, HEAT INDEX
VALUES WILL REACH NEAR 100 DEGREES THIS AFTERNOON ACROSS PARTS OF
CENTRAL WISCONSIN. A HEAT ADVISORY HAS BEEN ISSUED FOR WOOD,
PORTAGE, WAUPACA, AND WAUSHARA COUNTIES. WILDFIRE SMOKE ALOFT MAY
LIMIT SURFACE INSOLATION SLIGHTLY, BUT EVEN ACCOUNTING FOR A MINOR
TEMPERATURE REDUCTION, HEAT INDICES NEAR 100 DEGREES REMAIN
LIKELY. TEMPERATURES ON MONDAY WILL BE SLIGHTLY COOLER, BUT HEAT
INDICES WILL STILL APPROACH THE MIDDLE 90S.
SEVERE THUNDERSTORM POTENTIAL TONIGHT AND MONDAY...
WHILE WARMED TEMPERATURES ALOFT WILL KEEP THE FORECAST AREA
CAPPED AND LARGELY DRY THROUGH LATE AFTERNOON, THE COMBINATION OF
INTENSE HEATING, THE ADVANCING WARM FRONT, AND A WEAK SHORTWAVE
IMPULSE IS EXPECTED TO TRIGGER EXPLOSIVE CONVECTIVE DEVELOPMENT
OVER NORTHERN MINNESOTA LATE THIS AFTERNOON. STORMS ARE FORECAST
TO GROW UPSCALE INTO ONE OR MORE CONVECTIVE CLUSTERS THAT WILL
RACE SOUTHEAST INTO NORTH- CENTRAL WISCONSIN DURING THE EVENING
AND OVERNIGHT HOURS. DAMAGING WIND GUSTS WILL BE THE PRIMARY
THREAT WITH THESE CLUSTERS, THOUGH ISOLATED LARGE HAIL WILL BE
POSSIBLE WHEN STORMS FIRST ARRIVE INTO NORTHERN WI. STORMS WILL
WEAKEN OVERNIGHT AS THEY MOVE EAST, BUT WARM ADVECTION COULD KEEP
LINGERING ELEVATED SHOWERS AND NON- SEVERE STORMS IN PLACE INTO
MONDAY MORNING.
ON MONDAY, ANOTHER SHORTWAVE TROUGH AND COLD FRONT WILL TRAVERSE
THE WESTERN GREAT LAKES. MODEL GUIDANCE INDICATES FAVORABLE SEVERE
PARAMETERS WITH 2000-3000 J/KG OF ML CAPE AND 40+ KNOTS OF DEEP
LAYER SHEAR. CONVECTIVE EVOLUTION ON MONDAY CARRIES MODERATE
UNCERTAINTY DUE TO POTENTIAL CLOUD COVER AND MORNING RAIN DEBRIS,
BUT WHERE SUFFICIENT SURFACE HEATING OCCURS, ORGANIZED STORMS
CAPABLE OF LARGE HAIL AND DAMAGING WINDS COULD DEVELOP ALONG THE
FRONT.
LONG TERM...TUESDAY THROUGH SATURDAY
WINDS WILL SHIFT TO THE NORTH ON TUESDAY IN THE WAKE OF THE COLD
FRONT, BRINGING AN END TO THE OPPRESSIVE HUMIDITY EVEN AS DAYTIME
HIGHS REMAIN SLIGHTLY ABOVE NORMAL IN THE 80S. SURFACE HIGH
PRESSURE WILL BUILD INTO THE UPPER GREAT LAKES ON TUESDAY AND
PERSIST THROUGH THURSDAY, YIELDING AN EXTENDED STRETCH OF DRY,
PLEASANT WEATHER WITH SEASONABLE TEMPERATURES. THE NEXT SHORTWAVE
TROUGH AND ASSOCIATED FRONTAL BOUNDARY ARE SCHEDULED TO ARRIVE
LATE THURSDAY NIGHT INTO FRIDAY, BRINGING THE NEXT WIDESPREAD
CHANCE FOR SHOWERS AND THUNDERSTORMS TO NORTH-CENTRAL AND
NORTHEAST WISCONSIN. NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES
ARE FORECAST FOR NEXT WEEKEND.
AVIATION
FOR 12Z TAF ISSUANCE
ISSUED AT 611 AM CDT SUN JUL 26 2026
LOCALLY DENSE FOG PRODUCING VLIFR CONDITIONS ACROSS NORTH-CENTRAL
WISCONSIN WILL LIFT BETWEEN 13Z AND 14Z. SCATTERED CLOUD BASES
BETWEEN 2000 AND 5000 FEET OVER CENTRAL AND EAST-CENTRAL WISCONSIN
WILL DISSIPATE BY LATE MORNING. THEREAFTER, STRONG CAPPING WILL
ALLOW VFR CONDITIONS TO PREVAIL THROUGH EARLY EVENING.
CLUSTERS OF SEVERE THUNDERSTORMS ARE FORECAST TO DIVE SOUTHEAST
ACROSS THE REGION THIS EVENING, BRINGING STRONG SURFACE WIND GUSTS
OVER 40 KNOTS, LIFR VISIBILITIES, AND IFR CEILINGS IN THE
STRONGEST ACTIVITY. LOW FORECAST CONFIDENCE EXISTS REGARDING
CONVECTIVE EVOLUTION. THEREFORE, BROAD 4-HOUR TEMPO GROUPS ARE
INCLUDED AT ALL TERMINALS, INCLUDING KGRB, KATW, KMTW, KAUW, KCWA,
AND KRHI.
LINGERING SHOWERS REMAIN POSSIBLE OVERNIGHT WITH PATCHY GROUND FOG
DEVELOPING LATE TONIGHT BEHIND THE EXITING CONVECTION. LOWER
VISIBILITIES WILL LIKELY NEED TO BE ADDED WHEN THUNDERSTORM
EVOLUTION BECOMES MORE CERTAIN.
KOSH
BROKEN MVFR CEILINGS CONTINUE TO LINGER EARLY THIS MORNING. TIME
HEIGHT CROSS SECTIONS INDICATE THESE CLOUDS WILL BE MIXING OUT BY
LATE MORNING (15-17Z). THEREAFTER, STRONG CAPPING WILL ALLOW VFR
CONDITIONS TO PREVAIL THROUGH EARLY EVENING.
THE CHANCE OF THUNDERSTORMS WILL INCREASE THIS EVENING WHEN
CLUSTERS OF STORMS PASS ACROSS THE REGION. CONFIDENCE HAS
INCREASED ENOUGH TO ADD A TEMPO GROUP IN THIS FORECAST ISSUANCE.
THE TIMING WILL NEED TO GET NARROWED DOWN WHEN THUNDERSTORM
EVOLUTION BECOMES MORE CERTAIN.
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING STRONG SURFACE WIND
GUSTS OVER 40 KNOTS, LIFR VISIBILITIES, AND IFR CEILINGS IN THE
STRONGEST ACTIVITY.
GRB WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 8 AM CDT THIS MORNING FOR WIZ005-010-
011-018-019.
HEAT ADVISORY FROM NOON TODAY TO 9 PM CDT THIS EVENING FOR
WIZ035>037-045.
UPDATE.........MPC
DISCUSSION.....MPC
AVIATION.......MPC
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