257
FXUS63 KGRB 160006
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
706 PM CDT FRI AUG 15 2025
UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE
KEY MESSAGES
- THE FIRST OF SEVERAL WEEKEND ROUNDS OF THUNDERSTORMS IS EXPECTED
TO IMPACT MAINLY THE SOUTHWEST PART OF THE FORECAST AREA THIS
EVENING AND OVERNIGHT. SEVERE STORMS ARE POSSIBLE WITH DAMAGING
WINDS, HAIL, AND HEAVY RAIN.
- 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 00Z TAF ISSUANCE
ISSUED AT 652 PM CDT FRI AUG 15 2025
THUNDERSTORMS CHANCES ARE THE MAIN AVIATION THREAT, WITH A
SECONDARY CONCERN FOR LOW CLOUDS ACROSS NC WI LATE TONIGHT INTO
SATURDAY MORNING.
MCS'S ASSOCIATED WITH MCV'S WERE SPLITTING NORTH AND SOUTH OF THE
FORECAST AREA EARLY THIS EVENING, BUT A THIRD AREA OVER EC MN AND
WC WI MAY IMPACT OUR SOUTHWEST COUNTIES LATER THIS EVENING AND
OVERNIGHT. THE THIRD AREA OF CONVECTION WAS FOCUSED NORTH OF A
WARM FRONT, WHERE A DEVELOPING LLJ WAS GENERATING STRONG MOISTURE
CONVERGENCE IN A VERY UNSTABLE AIR MASS. WHILE THERE HAS BEEN A
SOUTHEAST PUSH OF THE MOST INTENSE CONVECTION, SOME OF THIS
ACTIVITY SHOULD BUILD INTO CENTRAL WI, AND POSSIBLY THE SOUTHERN
FOX VALLEY, LATER TONIGHT AS THE LLJ SHIFTS EAST. THINK MOST OF
THIS THUNDERSTORM ACTIVITY WILL FADE AS THE LLJ VEERS FROM
SOUTHWEST TO WEST AND WEAKENS LATE TONIGHT. HAVE ADDED PROB30 FOR
THUNDERSTORMS AT ALL BUT RHI.
SOME LOW CLOUDS MAY ACCOMPANY THE ARRIVAL OF A WEAK COLD FRONT
IN NC WI LATE TONIGHT INTO EARLY SATURDAY, AND THESE MAY PERSIST
UNTIL ABOUT MIDDAY BEFORE ERODING OR LIFTING TO VFR.
THERE IS SUPPORT AMONG A FEW MODELS FOR A LINEAR MCS TO MOVE
THROUGH THE FORECAST AREA BETWEEN 15Z-19Z/SATURDAY, BUT THIS IS
FAR FROM A CONSENSUS FORECAST. CONFIDENCE IS LOW IN THIS SCENARIO,
BUT GIVEN THE POTENTIAL IMPACTS (STRONG WINDS), HAVE ADDED PROB30
FOR STORMS DURING THE MOST LIKELY 2-HOUR TIME FRAME AT EACH TAF
SITE.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....KLJ
AVIATION.......KIECKBUSCH
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