662
FXUS63 KGRB 160340
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1040 PM CDT FRI AUG 15 2025
UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE
KEY MESSAGES
- THE FIRST OF SEVERAL WEEKEND ROUNDS OF THUNDERSTORMS IS EXPECTED
TO IMPACT MAINLY THE SOUTHERN PART OF THE FORECAST AREA
OVERNIGHT. STORMS MAY PRODUCE GUSTY WINDS AND BRIEF TORRENTIAL
RAINFALL.
- THERE IS HIGHER POTENTIAL FOR HEAVY RAIN AND THUNDERSTORMS AREA
WIDE FROM LATE SATURDAY MORNING THROUGH MUCH OF THE DAY. SEVERE
STORMS AND LOCALIZED FLOODING REMAIN POSSIBLE.
- WITH HIGH RAINFALL RATES LIKELY IN ANY STORMS, THE RISK FOR
FLOODING MAY INCREASE IF REPEATED ROUNDS OF STORMS IMPACT THE
SAME AREAS. PROBABILITIES FOR AT LEAST 2 INCHES OF RAIN ARE 20
TO 60% FROM NOW THROUGH MONDAY MORNING.
DISCUSSION
ISSUED AT 356 PM CDT FRI AUG 15 2025
WHILE TIMING/LOCATION DETAILS OF RAIN AND THUNDERSTORMS OVER THE
NEXT THREE AND A HALF DAYS REMAIN DIFFICULT TO GET TOO SPECIFIC,
THE OVERALL WEATHER SETUP HAS REMAINED LARGELY THE SAME. LARGE-
SCALE, UPPER LEVEL FORCING IS LIMITED, BUT A SURFACE COLD FRONT
APPROACHES FROM THE NORTHWEST THIS EVENING, THEN SLOWLY SAGS
SOUTH ACROSS WI ON SATURDAY, REACHING SOUTHERN WI ON SUNDAY. THE
PLACEMENT OF THIS FRONT, ALONG WITH A MOIST AND UNSTABLE AIRMASS,
WILL ALLOW FOR MULTIPLE ROUNDS OF RAIN AND THUNDERSTORMS ACROSS
THE UPPER MISSISSIPPI RIVER VALLEY/WESTERN GREAT LAKES FROM THIS
EVENING THROUGH MONDAY.
HEAVY RAIN/FLOODING...PWATS WILL BE FAIRLY STEADY AROUND 1.6 TO
2.1 INCHES THROUGHOUT THE NEXT THREE DAYS, WHICH IS IN THE 90%+
PERCENTILE OF CLIMATOLOGY. THEREFORE, ANY STORMS WHICH DO COME
THROUGH WILL HAVE THE POTENTIAL FOR HIGH RAINFALL RATES OF 1"/HR
OR GREATER, WHICH COULD LEAD TO LOCALIZED FLOODING, ESPECIALLY IN
URBAN OR POOR DRAINAGE AREAS. ADDITIONALLY, DUE TO THE MULTIPLE
ROUNDS OF RAIN EXPECTED, ANY LOCATIONS WHICH RECEIVE REPEATED
HEAVY RAINS COULD SEE STEADY RISES IN RIVERS/CREEKS AND LOCALIZED
FLOODING. THE MOST LIKELY 72-HOUR RAINFALL TOTALS FROM TODAY
THROUGH 7AM MONDAY RANGE FROM 0.5 TO 2.0", BUT THERE IS CERTAINLY
POTENTIAL FOR HIGHER AMOUNTS IN LOCALIZED AREAS. THE PROBABILITY
FOR AT LEAST 1 INCH OF RAIN RANGES FROM 50-90%, HIGHEST ACROSS
CENTRAL WI. THE PROBABILITY FOR AT LEAST 3 INCHES OF RAIN RANGES
FROM 10-35% IN CENTRAL WI, AND IS VERY LOW ELSEWHERE. HYDRO
MONITORING WILL BE NEEDED DURING AND AFTER EACH ROUND OF PRECIP.
THUNDERSTORMS TONIGHT...MODELS ARE LESS AGGRESSIVE OVER NORTHEAST
WI THAN PREVIOUS FORECASTS HAVE INDICATED. THERE IS CURRENTLY ONE
AREA OF CONVECTION ACROSS NORTHERN IOWA, BUT THIS LOOKS TO TREND
DUE EAST, AND EVENTUALLY WEAKEN, LIKELY MISSING THE GRB FORECAST
AREA. THERE IS ANOTHER AREA OF SHOWERS/STORMS TO THE WEST AND
NORTHWEST ASSOCIATED WITH A SHORTWAVE AND NEAR THE SFC COLD FRONT.
THIS IS THE AREA WHICH NEEDS WATCHING THIS EVENING. CAMS ARE ALL
OVER THE PLACE, BUT GENERALLY FAVOR MORE SCATTERED CELLULAR OR
SMALL CLUSTERS OF STORMS (AS SUPPOSED TO A LARGE COMPLEX) THIS
EVENING. THIS DEVELOPMENT IS MOST LIKELY ACROSS C/NC WI THIS
EVENING (~00-06Z), WITH SOME WEAKENING BY THE TIME IT REACHES THE
FOX VALLEY/LAKESHORE. SEVERE STORMS ARE POSSIBLE AND MUCH OF THE
AREA REMAINS IN A SLIGHT RISK OF SEVERE STORMS TONIGHT. DAMAGING
WINDS ARE THE MAIN CONCERN, AS FREEZING LEVELS ARE SOMEWHAT HIGH
FOR LARGE HAIL, BUT CANNOT RULE OUT SOME HAIL AROUND 1".
THUNDERSTORMS SATURDAY...OF INCREASED INTEREST IS THE POTENTIAL
FOR A THUNDERSTORM COMPLEX ON SATURDAY, ESPECIALLY IF STORMS
TONIGHT ARE LESS ABUNDANT. CAMS AND MACHINE LEARNED HAS INCREASED
POTENTIAL FOR A COMPLEX DEVELOPING AROUND EASTERN MN/WESTERN WI
SATURDAY MORNING, AND THEN TRACKING EAST ACROSS THE GRB FORECAST
AREA. THE MAIN LINE LOOKS TO TRACK THROUGH IN THE ~14-20Z TIME
FRAME, BUT ADDITIONAL, SCATTERED DEVELOPMENT IS ALSO POSSIBLE
BEHIND THIS COMPLEX. SEVERE STORMS AREA POSSIBLE, WITH DAMAGING
WINDS, HAIL, AND HEAVY RAIN/LOCALIZED FLOODING.
REST OF THE FORECAST...AFTER SATURDAY EVENING, THERE ARE
INDICATIONS OF A BREAK FROM THE PRECIP, WITH MUCH OF SUNDAY
POTENTIALLY ENDING UP DRY AS THE FRONT MOVES SOUTH OF THE AREA.
THEN, ANOTHER ROUND OF RAIN AND THUNDERSTORMS IS POSSIBLE ON
MONDAY AS A LOW APPROACHES AND THIS FRONT MOVES A BIT FARTHER
NORTH. ONCE AGAIN, DETAILS THIS FAR OUT REMAIN DIFFICULT TO
DETERMINE. HIGH PRESSURE STARTS TO BUILD IN LATE TUE AND
WEDNESDAY, WITH QUIETER WEATHER ANTICIPATED FOR THE MIDDLE OF NEXT
WEEK.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 1025 PM CDT FRI AUG 15 2025
THUNDERSTORMS CHANCES ARE THE MAIN AVIATION THREAT, WITH A
SECONDARY CONCERN FOR LOW CLOUDS ACROSS NC WI SATURDAY MORNING,
AND REGIONWIDE SATURDAY NIGHT.
SHOWERS AND A FEW THUNDERSTORMS WITH GUSTY WINDS AND BRIEF
TORRENTIAL RAINFALL WERE IMPACTING THE SOUTHERN PART OF THE
FORECAST AREA LATE THIS EVENING. MOST OF THE REMAINING OVERNIGHT
ACTIVITY SHOULD STAY SOUTH OF THE FORECAST AREA, BUT ANY
LINGERING CONVECTION SHOULD FADE AS THE LLJ VEERS FROM SOUTHWEST
TO WEST AND WEAKENS LATE TONIGHT. THE EXCEPTION MAY BE OVER NORTH
CENTRAL WI, WHERE A WEAK COLD FRONT MAY BRING A SMALL CHANCE OF
SHOWERS OR AN ISOLATED STORM TOWARD DAYBREAK. SOME LOW CLOUDS MAY
ALSO ACCOMPANY THE COLD FRONT IN NC WI SATURDAY MORNING.
THERE IS INCREASING SUPPORT FOR A LINEAR MCS TO MOVE THROUGH THE
FORECAST AREA BETWEEN 16Z-20Z/SATURDAY, SO WILL ADD IN TEMPO
GROUPS FOR STORMS WITH GUSTY WINDS AND HEAVY RAINFALL WITH THIS
NEW SET OF TAFS. CONFIDENCE IS LOW ON WHAT HAPPENS AFTER THE LINE
MOVES THROUGH, THOUGH WOULD THINK THE OUTFLOW WOULD TEND TO PUSH
ANY FRONTAL BOUNDARY (AND VERY MOIST AND UNSTABLE AIR) SOUTH OF
THE REGION, AND FOCUS SATURDAY NIGHT'S CONVECTION OVER SOUTHERN
WI. DEVELOPING NE WINDS COULD PULL LOW CLOUDS SOUTH ACROSS THE
REGION DURING SATURDAY EVENING.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....KLJ
AVIATION.......KIECKBUSCH
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