665
FXUS63 KGRB 211732
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1232 PM CDT TUE JUL 21 2026
KEY MESSAGES
- COOLER AND LESS HUMID TODAY WITH GUSTY NORTHWEST WINDS REACHING
20 TO 30 MPH. SMALL CRAFT ADVISORIES ARE IN EFFECT THROUGH EARLY
WEDNESDAY MORNING.
- SCATTERED SHOWERS AND AN ISOLATED THUNDERSTORM WILL SPREAD ACROSS
NORTHEAST AND EAST-CENTRAL WISCONSIN LATE THIS MORNING THROUGH
THIS AFTERNOON. NO SEVERE WEATHER IS EXPECTED.
- COMFORTABLE AND QUIET CONDITIONS THROUGH FRIDAY, FOLLOWED BY
INCREASING HEAT, HUMIDITY, AND THUNDERSTORM CHANCES (30 TO 50
PERCENT) OVER THE WEEKEND.
DISCUSSION
ISSUED AT 140 AM CDT TUE JUL 21 2026
THE LATEST SURFACE ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A
PRIMARY COLD FRONT EXITING NORTHEAST WISCONSIN EARLY THIS MORNING,
WHILE A SECONDARY COLD FRONT EXTENDS FROM WESTERN LAKE SUPERIOR
INTO CENTRAL MINNESOTA. UPPER-LEVEL TROUGHING IS SETTLING ACROSS
THE UPPER MIDWEST AND GREAT LAKES WHILE AN AMPLIFIED RIDGE BUILDS
OVER THE INTERMOUNTAIN WEST. THIS PATTERN LEAVES THE REGION UNDER
COOL, CYCLONIC NORTHWEST FLOW ALOFT TODAY INTO MIDWEEK. UPSTREAM,
A BROAD AREA OF STRATOCUMULUS WITH BASES BETWEEN 1500 AND 3500
FEET EXISTS BEHIND THE SECONDARY FRONT, WITH MODERATELY STRONG
COLD AIR ADVECTION DROPPING 850MB TEMPERATURES INTO THE LOWER
TEENS CELSIUS. A HIGH-PRESSURE SYSTEM ACROSS THE CENTRAL PLAINS
WILL GRADUALLY SHIFT EASTWARD TOWARD THE MID-MISSISSIPPI VALLEY
THROUGH WEDNESDAY, EVENTUALLY ANCHORING STABLE AND COMFORTABLE
WEATHER OVER THE WESTERN GREAT LAKES THROUGH THE END OF THE WORK
WEEK.
AS THE SECONDARY COLD FRONT DROPS SOUTHEAST ACROSS NORTHERN
WISCONSIN TODAY, MID-LEVEL HEIGHT FALLS WILL COOL TEMPERATURES
ALOFT INTO THE TENTH PERCENTILE. STRONG DAYTIME HEATING WILL
STEEPEN LOW-LEVEL LAPSE RATES, PRODUCING DIURNAL INSTABILITY IN
THE 300 TO 600 J/KG RANGE ACROSS NORTHEAST AND EAST-CENTRAL
WISCONSIN. SCATTERED SHOWERS CURRENTLY CONFINED TO FAR NORTH-
CENTRAL WISCONSIN WILL EXPAND SOUTHWARD THROUGH LATE MORNING AND
AFTERNOON. AN ISOLATED RUMBLE OF THUNDER CANNOT BE RULED OUT
WITHIN THE STRONGER CONVECTIVE CORES, BUT SEVERE WEATHER IS NOT
EXPECTED DUE TO WEAK INSTABILITY. IN ADDITION, DEEP BOUNDARY-
LAYER MIXING WILL TAP INTO STRONGER WINDS ALOFT, GENERATING GUSTY
NORTHWEST WINDS OF 20 TO 30 MPH ACROSS THE FORECAST AREA THIS
AFTERNOON. THESE WINDS WILL GENERATE HAZARDOUS WAVES IN THE
NEARSHORE WATERS, PROMPTING SMALL CRAFT ADVISORIES ON THE BAY OF
GREEN BAY AND NEARSHORE WATERS OF LAKE MICHIGAN INTO EARLY
WEDNESDAY MORNING. SHOWERS WILL QUICKLY WANE LATE THIS AFTERNOON
AND EVENING WITH LOSS OF HEATING. CLEARING SKIES TONIGHT WILL
CLEAR THE WAY FOR A SUNNY AND COMFORTABLE WEDNESDAY WITH HIGH
TEMPERATURES IN THE MID 70S.
MODELS SHOW MINIMAL POTENTIAL FOR NEAR-SURFACE SMOKE OR
VISIBILITY REDUCTIONS, SO SMOKE HAS BEEN EXCLUDED FROM THE
FORECAST.
FOR THE LONG-TERM PERIOD FROM THURSDAY THROUGH MONDAY, THE WESTERN
GREAT LAKES WILL REMAIN POSITIONED DOWNSTREAM OF THE BROAD RIDGE
BUILDING OVER THE INTERMOUNTAIN WEST, MAINTAINING NORTHWEST FLOW
ALOFT THROUGH FRIDAY. THIS PERSISTENT NORTHWEST FLOW WILL KEEP THE
MAIN RESERVOIR OF DEEP INSTABILITY SUPPRESSED WELL SOUTH OF THE
REGION, ENSURING SEASONABLE TEMPERATURES AND PLEASANT HUMIDITY
LEVELS. HIGHS THROUGH FRIDAY WILL RESIDE IN THE UPPER 70S TO LOW
80S UNDER MOSTLY CLEAR TO PARTLY CLOUDY SKIES. BY SATURDAY AND
SUNDAY, THE UPPER-LEVEL FLOW PATTERN BEGINS TO FLATTEN, ALLOWING
GULF MOISTURE AND AN UNSTABLE AIRMASS TO SURGE NORTHWARD. HIGH
TEMPERATURES WILL CLIMB INTO THE UPPER 80S TO NEAR 90 IN CENTRAL
WISCONSIN ON SUNDAY, ACCOMPANIED BY RISING DEWPOINTS IN THE UPPER
60S. PRECIPITATION CHANCES WILL GRADUALLY INCREASE THIS WEEKEND
(30 TO 50 PERCENT CHANCE) AS SHORTWAVE IMPULSES EMBEDDED WITHIN
THE FLATTENING FLOW INTERACT WITH THE RETURNING INSTABILITY. WHILE
MACHINE LEARNING GUIDANCE INDICATES ONLY A SUBTLE SEVERE WEATHER
THREAT AT THIS TIME, DETAILS ON TIMING AND MESOSCALE ORGANIZATION
WILL NEED TO BE MONITORED IN UPCOMING FORECAST UPDATES.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1232 PM CDT TUE JUL 21 2026
CEILINGS HAVE TRENDED UP THROUGH THE MORNING WITH SCATTERED TO
BROKEN VFR CUMULUS PERSISTING THROUGH THE AFTERNOON. SKIES WILL
GRADUALLY CLEAR THROUGH THE LATE AFTERNOON/EVENING. SCATTERED
SHOWERS WILL CONTINUE THIS AFTERNOON WITH THE THUNDER RISK QUITE
LOW (LESS THAN 15%). GUSTY NORTH TO NORTHWEST WINDS WILL
GRADUALLY SUBSIDE THIS MORNING, REMAINING NORTHERLY INTO
WEDNESDAY.
KOSH
SCATTERED SHOWERS MAY IMPACT KOSH THROUGH AROUND 21Z THIS
AFTERNOON, ALTHOUGH ANY SHOWER WILL BE BRIEF. SHORT-LIVED MVFR
CONDITIONS COULD NOT BE RULED OUT WITH A MORE INTENSE SHOWER,
BUT THE THUNDER POTENTIAL IS VERY LOW. SKIES WILL CLEAR THROUGH
LATE AFTERNOON/EVENING.
THERE IS A LOW CHANCE FOR A FEW GUSTS OVER 30 KTS THIS AFTERNOON
WITH STRONGER DIURNAL MIXING/COLD ADVECTION, BUT THE GUSTINESS
WILL WANE THROUGH THE EVENING.
GRB WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM CDT WEDNESDAY FOR LMZ521-522-
541>543.
DISCUSSION...MPC
AVIATION...JM
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