007
FXUS63 KGRB 201739
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1239 PM CDT MON JUL 20 2026
KEY MESSAGES
- LEVEL 3 OF 5 RISK OF SEVERE STORMS TODAY. DAMAGING WINDS, LARGE
HAIL, AND A FEW TORNADOES ALL POSSIBLE. HIGHEST RISK IS MID
AFTERNOON TO EARLY EVENING (3 TO 8 PM).
- DRIER AND COOLER FOR MID-WEEK.
MESOSCALE
ISSUED AT 1207 PM CDT MON JUL 20 2026
WITH A FAIRLY QUICK DECREASE IN CLOUD COVER THIS MORNING AND
ONGOING WARM, MOIST ADVECTION, WE CAN EXPECT MLCAPE TO BUILD TO
2500-3000 J/KG THIS AFTERNOON, WHILE STRONG DEEP LAYER SHEAR
INCREASES TO 50-60 KT. 995 MB LOW PRESSURE OVER NRN ONTARIO WILL
DEEPEN SLIGHTLY 992 MB AS IT MOVES EWD THIS AFTERNOON. A PRE-
FRONTAL SFC TROUGH EXTENDING SOUTH OF THE LOW AND APPROACHING NW
WI WILL MOVE ACROSS THE NRN HALF OF WI THIS AFTERNOON AND EARLY
EVENING. SFC CONVERGENCE ALONG THIS FEATURE WILL BE MODEST, BUT
AIDED BY A VORTICITY MAXIMUM. ALSO FARTHER TO THE NORTH, THE
MAIN UPPER WAVE OVER SW ONTARIO WILL MOVE OVER NRN LAKE SUPERIOR
FOR LATE AFTERNOON AND DEEPEN SLIGHTLY AS IT MOVES ACROSS ERN
LAKE SUPERIOR THIS EVENING. OVERALL 12HR 500 MB HT. FALLS OF
60-80 METERS ARE EXPECTED ACROSS THE NRN HALF OF WI. WITHOUT
STRONG FORCING, BELIEVE THE CAMS ARE CORRECT WITH DISCRETE
SUPERCELLS AFTER MAINLY 19-20Z INTO THE EARLY EVENING. CANNOT
RULE OUT SOME CONSOLIDATION OF CELLS FARTHER TO THE EAST TOWARD
LAKE MI AND WILL FORECAST 50-70 PERCENT CHANCES FOR SHOWERS AND
STORMS. EFFECTIVE SRH OF 200 M2/S2 IS FORECAST WITH 0-1KM SRH OF
100-150 M2/S2. LCLS AND LFCS WILL BE SUFFICIENTLY FAVORABLE FOR
TORNADOES ALONG WITH THE AFOREMENTIONED LOW LEVEL WIND SHEAR.
DCAPE OF 1200-1600 J/KG WILL BE A LIMITING FACTOR FOR TORNADOES,
AND A STRONGER FACTOR FOR DAMAGING WINDS. OVERALL THOUGH, ALL
HAZARDS, POSSIBLY SIGNIFICANT SEVERE, ARE FORECAST.
DISCUSSION
ISSUED AT 223 AM CDT MON JUL 20 2026
THUNDERSTORM/PRECIP CHANCES:
FORECAST FOR A ROUND OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH THIS EVENING REMAINS ON TRACK. WV IMAGERY SHOWS A POTENT
SHORT-WAVE OVER SOUTHERN MANITOBA THIS MORNING THAT WILL MOVE
SOUTHEAST TOWARD LAKE SUPERIOR THROUGH THE DAY. ACCOMPANYING THE
UPPER WAVE IS A SEASONALLY STRONG JET STREAK (300 MB WINDS NEAR
100KTS). AT THE SURFACE, WINDS VEERING TO THE SOUTHWEST THIS
MORNING WILL BRING A PLUME OF UPPER 60S TO LOW 70S DEW POINTS TO
THE REGION CREATING A HIGHLY UNSTABLE AIRMASS BY EARLY TO MID
AFTERNOON. WITH FAVORABLE THERMODYNAMIC AND KINEMATIC FIELDS HAVE
INCREASING CONFIDENCE IN A HIGHER END SEVERE WEATHER EVENT TAKING
PLACE ACROSS THE REGION THIS AFTERNOON INTO THIS EVENING.
ONE POTENTIAL HINDRANCE TO THIS EVENT REALIZING ITS FULL POTENTIAL
IS A ROUND OF MORNING SHOWERS/STORMS WITHING THE WARM ADVECTION
REGIME. CAMS CONTINUE TO SUGGEST A CLUSTER OR BROKEN LINE OF
SHOWERS/STORMS WILL DEVELOP OVER MN EARLY THIS MORNING AHEAD ALONG AN
INSTABILITY GRADIENT AND TRACK INTO WESTERN WI AROUND SUNRISE. THESE
STORMS WOULD LIKELY BE EXPIATING A DOWNWARD TREND THEY REACH
CENTRAL/NORTHERN WI AS THEY OUT RUN THE BETTER INSTABILITY, BUT
THE REMNANT CLOUD DEBRIS MAY DELAY/MODIFY BUILDING INSTABILITY.
CAMS GENERALLY HAVE THIS ACTIVITY DYING OUT BY 10AM THIS MORNING.
THESE TRENDS WILL BEAR WATCHING AS ANY DIFFERENTIAL HEATING
BOUNDARY/OUTFLOWS MAY SERVE AS INITIATING BOUNDARIES LATER INTO
THE DAY. BY MID MORNING ATTENTION WILL SHIFT TO AN AREA OF RAPIDLY
DESTABILIZING AIR EAST OF THE INCOMING COLD FROM SOUTHERN IA TO
THE WI/UP BORDER. AS THE AFOREMENTIONED UPPER-SHORT WAVE STARTS TO
IMPINGE UPON THIS UNSTABLE AIR EXPECT STORMS TO START INITIATING
ACROSS NORTHWEST AN NORT-CENTRAL WI AROUND 3-4PM (COULD BE AS
EARLY AS 1PM). INITIALLY EXPECT A BROKEN LINE OF SUPER CELLS AS
0-6 SHEAR VECTORS ARE ANGLED ABOUT 30 DEGREES OFF THE COLD FRONT
WHICH SHOULD HELP TO KEEP CELLS DISCRETE INITIALLY. THINK THESE
INITIAL CELLS WILL POSE THE GREATEST STRONG TORNADO (EF2+) AND
LARGE HAIL (2+ INCH) THREAT AS THE DEEP SHEAR WILL PROMOTE WELL
ORGANIZED AND PERSISTENT UPDRAFTS, ESPECIALLY ANY STORMS THAT
DEVIATE TO THE RIGHT OF THE MEAN WIND. WITH TIME AND EASTWARD
EXTENT FORCING ALONG THE FRONT AND INCREASE STORM COVERAGE SHOULD
LEAD TO COLD POOL AGGREGATION AND THE DEVELOPMENT OF ONE OR MOVE
BOWING SEGMENTS THAT WILL POSE A DAMAGING (70+ MPH) WIND THREAT AS
WELL AS BRIEF SPIN UP TORNADOS. THE SEVERE WEATHER THREAT IS
EXPECTED TO PERSIST ALL THE WAY TO THE LAKESHORE WITH STORMS
EXITING THE REGION AROUND 8-10PM TONIGHT.
IN ADDITION TO THE SEVERE THREAT HIGH RAIN RATES ARE EXPECTED WITH
THESE STORMS, HOWEVER, THE SCATTERED NATURE OF THE STORMS AND
PROGRESSIVE MOVEMENT LIKELY WILL LIMIT WIDESPREAD HIGHER RAIN
AMOUNTS, BUT LOCALIZED 2 INCH AMOUNTS COULD OCCUR. URBAN AREAS OR
POOR DRAINAGE AREAS WILL BE SUSCEPTIBLE TO HIGHER RAIN RATES AND
LOCALIZED FLOODING.
BEHIND THE FRONT TUESDAY SCATTERED DIURNALLY DIVER SHOWERS MAY
POP-UP ACROSS NORTHERN WI WITH NORTHWEST WINDS OVER LAKE
SUPERIOR. FORECAST SOUNDING SHOW THIS SHOULD BE VERY SHALLOW
CONVECTION SO DON'T EXPECT MUCH IF ANY LIGHTNING WITH THESE
SHOWERS. BEYOND TUESDAY A BUILDING RIDGE SHOULD KEEP THE MIDDLE OF
THE WEEK DRY WITH A POSSIBLE RETURN IN SHOWERS/STORMS LATE IN THE
WEEK INTO NEXT WEEKEND, BUT PREDICTABILITY IS LOW.
SMOKE TRENDS:
SURFACE OBS IN CENTRAL WI ARE SHOWING SLOWING DECREASING VISIBILITY
EARLY THIS MORNING WITH SMOKE TRAPPED UNDER AN INVERSION. THESE
TRENDS SHOULD REVERSE BY MID-MORNING AS THE BOUNDARY LAYER STARTS TO
MIX. INCREASE SOUTHWESTERLY SURFACE WINDS TODAY SHOULD ALSO GREATLY
HELP WITH CLEARING SURFACE SMOKE FROM WEST TO EAST. HRRR/RRFS DO
SHOW ANOTHER POSSIBLE PLUMB OF SMOKE PUSHING INTO THE REGION TUESDAY
AND WEDNESDAY AS WINDS TURN NORTHWESTERLY, HOWEVER, THERE IS A HIGH
DEGREE OF UNCERTAINTY WITH HOW DENSE SMOKE MAY BE.
TEMP TRENDS:
TODAY WILL BE THE WARMEST DAY OF THE WEEK WITH HIGHS IN THE MIDDLE
TO UPPER 80S. COOLER TEMPERATURES ARRIVE BEHIND THE COLD FRONT AND
LINGER THROUGH MUCH OF THE WEEK.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1240 PM CDT MON JUL 20 2026
SKIES HAVE BEEN CLEARING EARLY THIS AFTERNOON WITH GUSTY
SOUTHWESTERLY WINDS DEVELOPING. EXPECT SCATTERED TO NUMEROUS
STORMS TO FORM AHEAD OF A COLD FRONT, PEAKING BETWEEN 21Z AND
03, POTENTIALLY RESULTING IN BRIEF IFR PERIODS. BEHIND THE
FRONT, WINDS WILL GRADUALLY BECOME NORTHWESTERLY WITH SOME GUSTS
EXCEEDING 20 KTS BY TUESDAY MORNING. A PERIOD OF MVFR STRATUS
MAY OCCUR BEHIND THE FRONT TUESDAY MORNING, WITH THE HIGHEST
CHANCES ACROSS CENTRAL INTO NORTH-CENTRAL WISCONSIN (60-90%).
THE HRRR SMOKE MODEL SUGGESTS SOME WILDFIRE SMOKE MAY ADVECT
SOUTH BEHIND THE FRONT OVERNIGHT, BUT CONFIDENCE IN REDUCED
VISIBILITY IS LOW AT THIS TIME.
KOSH
EXPECT MVFR VISIBILITY RESTRICTIONS TO IMPROVE THIS AFTERNOON
WITH GUSTY SOUTHWEST FLOW DEVELOPING. ATTEMPTED TO PROVIDE SOME
TIMING DETAIL WITH THE GREATEST THREAT FOR STORMS BETWEEN 00Z
AND 02Z. AS CONFIDENCE INCREASES, WILL INCLUDE ADDITIONAL
TIMING/WEATHER DETAILS IN THE TAF. THERE'S A 20-40% CHANCE FOR A
PERIOD OF MVFR CEILINGS AT KOSH BEHIND THE COLD FRONT,
ESPECIALLY AFTER 12Z TUESDAY.
MARINE
ISSUED AT 223 AM CDT MON JUL 20 2026
SOUTH TO SOUTHWEST WINDS WILL INCREASE THIS MORNING, WITH GUSTS TO
30 KTS LIKELY THIS AFTERNOON. WAVES ON LAKE MICHIGAN WILL BUILD TO 4-
7 FT, AND TO 2-4 FT ON THE BAY. SMALL CRAFT AND BEACH HAZARD
STATEMENTS ARE IN EFFECT TODAY.
GRB WATCHES/WARNINGS/ADVISORIES
WI...BEACH HAZARDS STATEMENT THROUGH TUESDAY MORNING FOR WIZ022-040-
050.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM CDT TUESDAY FOR LMZ521-522.
SMALL CRAFT ADVISORY UNTIL 7 AM CDT TUESDAY FOR LMZ541>543.
MESOSCALE...
DISCUSSION...GK
AVIATION...JM
MARINE...GK
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