847
FXUS63 KGRB 151800
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
100 PM CDT FRI AUG 15 2025
UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE
KEY MESSAGES
- A FEW SPOTTY SHOWERS ARE POSSIBLE THIS MORNING, BUT DRY
CONDITIONS ARE FORECAST FOR MOST LOCATIONS THROUGH THIS
AFTERNOON.
- MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED FROM
THIS EVENING THROUGH MONDAY NIGHT. THERE IS A LEVEL 2 OF 5 RISK
FOR SEVERE STORMS TONIGHT, BUT CONFIDENCE IS STILL LOW WITH
REGARD TO TIMING/PLACEMENT. THERE IS ALSO A LEVEL 1 OF 5 RISK
FOR SEVERE STORMS ACROSS THE ENTIRE AREA ON SATURDAY.
- 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 30
TO 70% THROUGH THROUGH EARLY SUNDAY EVENING.
DISCUSSION
ISSUED AT 259 AM CDT FRI AUG 15 2025
SHORT TERM...TODAY...TONIGHT...AND SATURDAY
THE LATEST RAP ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A SURFACE
RIDGE AXIS MOVING EAST ACROSS THE EASTERN GREAT LAKES EARLY THIS
MORNING, LEADING TO GENERALLY QUIET CONDITIONS ACROSS MUCH OF THE
FORECAST AREA. MEANWHILE, MULTIPLE CORRIDORS OF WARM ADVECTION ARE
OCCURRING SPURRED ON BY SHORTWAVE ENERGY ACROSS THE NORTHERN
MISSISSIPPI VALLEY AND WESTERN GREAT LAKES. THIS IS LEADING TO LIGHT
SHOWERS DEVELOPING OVER SOUTHWEST WISCONSIN AND FAR NORTHERN
WISCONSIN, IN CLOSER PROXIMITY TO THESE SHORTWAVE IMPULSES. OTHER
AREAS OF THUNDERSTORMS ARE CURRENTLY OCCURRING OVER WESTERN SOUTH
DAKOTA AND NEBRASKA WHERE SEVERAL EMBEDDED SHORTWAVES ARE MOVING IN
THE MEAN WESTERLY FLOW. THIS ACTIVITY IS AHEAD OF A COLD FRONT
CURRENTLY MOVING SOUTHEAST OVER NORTHERN MINNESOTA. AS THIS COLD
FRONT MOVES INTO NORTHWEST WISCONSIN TONIGHT AND CENTRAL WISCONSIN
ON SATURDAY, THE PRIMARY FOCUS OF THIS FORECAST REVOLVES AROUND THE
POTENTIAL FOR SEVERE STORMS AND HEAVY RAINFALL.
THUNDERSTORMS: THE FORECAST FOR TONIGHT AND SATURDAY IS PARTICULARLY
CHALLENGING. WHILE SHORTWAVE ENERGY TRAVERSING THE REGION WILL MOSTLY
BE EAST OF THE AREA BY 7 AM THIS MORNING, WARM ADVECTION WILL
CONTINUE FOR MUCH OF THE DAY, USHERING IN AN INCREASINGLY UNSTABLE
AIRMASS. FORECAST SOUNDINGS SHOW A CAPPED ATMOSPHERE FOR MUCH OF
THE DAY, WHICH SHOULD LEAD TO QUIET CONDITIONS CONTINUING THROUGH
THE AFTERNOON. FOCUS THEN TURNS TO THE COLD FRONT AS IT
APPROACHES NORTHWEST WISCONSIN BY LATE THIS AFTERNOON OR EARLY
THIS EVENING. FORECAST SOUNDINGS AT HAYWARD INDICATE THE CAP
ERODING BY PEAK HEATING, WITH ROBUST INSTABILITY OF 2000-3000 J/KG
DEVELOPING BY LATE AFTERNOON. WITH THE HELP OF SHORTWAVE ENERGY
ARRIVING FROM WESTERN SOUTH DAKOTA, THIS SHOULD SET THE STAGE FOR
DEEP CONVECTION INITIATING, WHICH IS WELL SUPPORTED BY HREF
PAINTBALL IMAGERY. DEEP LAYER SHEAR WILL BE FAVORABLE FOR
ORGANIZED UPDRAFTS AS STORMS TRACK TOWARDS NORTH-CENTRAL WISCONSIN
IN THE EVENING. BY THE TIME THESE STORMS ARRIVE, THEY WILL HAVE
THE POTENTIAL FOR LARGE HAIL AND DAMAGING WINDS. STORMS SHOULD
WEAKEN THROUGH THE EVENING WITH SOUTHEAST EXTENT, THOUGH THE EXACT
TIMING OF THIS WEAKENING IS UNCERTAIN. ADDITIONAL THUNDERSTORM
ACTIVITY WILL BE POSSIBLE ALONG THE FRONT THROUGH THE NIGHT AS
MOST UNSTABLE CAPE NEAR 1000 J/KG SHOULD PERSIST, BUT COVERAGE AND
INTENSITY ARE NOT CLEAR GIVEN THE RISING MID-LEVEL HEIGHTS AND
TEMPERATURES ACROSS THE REGION.
CONVECTIVE DETAILS ON SATURDAY ARE ALSO MURKY AND DEPEND TO SOME
DEGREE ON HOW THUNDERSTORMS EVOLVE TONIGHT. LARGE-SCALE ASCENT WILL
REMAIN WEAK, BUT A LARGE RESERVOIR OF INSTABILITY (1000-2000 J/KG)
WILL EXIST SOUTH OF THE EFFECTIVE COLD FRONT. THERE ARE SOME
INDICATIONS THAT ONGOING NOCTURNAL CONVECTION COULD SUSTAIN ITSELF
INTO THE REGION ON SATURDAY MORNING ON THE NOSE OF A WEAK LOW-LEVEL
JET. THERE IS CONCERN THAT THE PERSISTENT LOW-LEVEL JET IMPINGING ON
THE BOUNDARY COULD LEAD TO SEVERAL ROUNDS OF STORMS THROUGH THE
DAY. STRONG TO SEVERE STORMS ARE POSSIBLE IF THE ATMOSPHERE CAN
RECHARGE AFTER THE OVERNIGHT CONVECTION, GIVEN THE INSTABILITY,
DEEP LAYER SHEAR OF 25-30 KNOTS, AND STEEP MID-LEVEL LAPSE RATES
OF 7-7.5 C/KM ABOVE THE FRONTAL ZONE.
FLOODING: WITH PRECIPITABLE WATER VALUES IN THE 97.5 TO 99
PERCENTILES AND THE POTENTIAL FOR MULTIPLE ROUNDS OF STORMS, SIGNALS
FOR 2+ INCHES OF RAIN PERSIST BY 7 PM SATURDAY (20-30% CHANCE) FOR
PARTS OF THE AREA, PARTICULARLY OVER CENTRAL AND EAST-CENTRAL
WISCONSIN. LOCAL AMOUNTS IN EXCESS OF 3 INCHES APPEAR POSSIBLE BASED
ON THE HREF LOCALIZED PROBABILITY-MATCHED MEAN. CONVECTIVE RAINFALL
RATES ALONE MAY BE SUFFICIENT TO CAUSE FLOOD CONCERNS EVEN OVER
SHORTER TIME SCALES, GIVEN THE SATURATED ENVIRONMENTAL CONDITIONS AND
HIGH MOISTURE CONTENT.
LONG TERM...SATURDAY NIGHT THROUGH THURSDAY
THE ENSEMBLE MEANS CONTINUE TO ADVERTISE THAT SUB-TROPICAL
RIDGING ACROSS THE GREAT LAKES WILL RETROGRADE EARLY NEXT WEEK,
THEREBY BRINGING THE REGION INTO NORTHWEST FLOW ALOFT BY TUESDAY-
WEDNESDAY. THIS SHIFT IN THE PATTERN WILL LEAD TO QUIETER LATE
SUMMER WEATHER RETURNING TO THE REGION. UNTIL THEN, THE PRIMARY
FOCUS OF THE FORECAST REVOLVES AROUND THE POTENTIAL FOR REPEATED
ROUNDS OF THUNDERSTORMS AS WELL AS HEAVY RAINFALL ALONG A SLOW-
MOVING COLD FRONT FROM SATURDAY NIGHT THROUGH MONDAY.
THUNDERSTORMS AND FLOODING POTENTIAL: WHILE CONVECTIVE DETAILS IN
PRIOR PERIODS LIMIT CONFIDENCE IN THE EXACT EFFECTIVE FRONTAL
POSITIONS, ENSEMBLE GUIDANCE SUGGESTS THAT THE WAVY COLD FRONT
WILL BE IN THE VICINITY OF CENTRAL AND EAST-CENTRAL WISCONSIN AT
THE START OF SATURDAY EVENING. ASSUMING THIS SCENARIO IS REMOTELY
ACCURATE, THERE IS POTENTIAL FOR ADDITIONAL MESOSCALE CONVECTIVE
SYSTEM (MCS) ACTIVITY ON SATURDAY NIGHT AND SUNDAY AS A MODEST
LOW-LEVEL JET IMPINGES ON THE BOUNDARY. A LARGE RESERVOIR OF
INSTABILITY OF 1000-2000 J/KG WILL BE GRADUALLY SHIFTING SOUTH,
BUT PRECIPITABLE WATER VALUES OF 160-170% OF NORMAL (97.5-99
PERCENTILE) AND LARGE WARM CLOUD DEPTHS ARE FORECAST ACROSS THE
REGION. THE HIGHEST PROBABILITIES OF RAINFALL IN EXCESS OF 1 INCH
CONTINUE TO RESIDE OVER CENTRAL AND EAST-CENTRAL WISCONSIN, WHERE
THERE IS A 50-70% CHANCE FROM 00Z SUNDAY TO 00Z MONDAY. THIS AREA
COINCIDES WITH A SLIGHT RISK OF EXCESSIVE RAINFALL AS HIGHLIGHTED
BY THE WEATHER PREDICTION CENTER (WPC). ADDITIONAL SHORTWAVE
ENERGY COULD TRAVERSE THE REGION ON MONDAY, PROLONGING THE
POTENTIAL FOR EXCESSIVE RAINFALL. GIVEN MULTIPLE DAYS (FRIDAY
NIGHT THROUGH POTENTIALLY MONDAY NIGHT) CONDITIONALLY FAVORABLE
FOR HEAVY RAINFALL, A FLOOD THREAT COULD INCREASE IF THUNDERSTORMS
FOCUS ALONG THE SAME CORRIDORS REPEATEDLY DURING THIS TIME.
CONCERN IS HIGHEST OVER CENTRAL AND EAST-CENTRAL WISCONSIN WHERE
THERE IS A 20-50% CHANCE OF GREATER THAN 3 INCHES OF RAIN THROUGH
7 PM SUNDAY. THIS AREA COINCIDES WITH THE MOST PRONE AREAS FOR
FLOODING ACROSS NORTH-CENTRAL AND EAST-CENTRAL WISCONSIN.
QUIET CONDITIONS TUESDAY-WEDNESDAY: AS THE SUB-TROPICAL RIDGE
RETROGRADES AND THE REGION TRANSITIONS INTO NORTHWEST FLOW ALOFT
BY TUESDAY AND WEDNESDAY, A MUCH QUIETER LATE SUMMER WEATHER
PATTERN IS EXPECTED TO RETURN. THIS WILL LIKELY BRING A PERIOD OF
MORE STABLE CONDITIONS WITH REDUCED CHANCES OF THUNDERSTORMS AND
LIGHTER RAINFALL. TEMPERATURES SHOULD REMAIN SEASONABLE THROUGH
NEXT THURSDAY.
AVIATION
FOR 18Z TAF ISSUANCE
ISSUED AT 100 PM CDT FRI AUG 15 2025
ONE OR TWO ROUNDS OF THUNDERSTORMS ARE EXPECTED OVER THE NEXT 24
HOURS WHICH COULD IMPACT SOME OR ALL OF THE NORTHEAST WI TAF
SITES; HOWEVER, DETERMINING THE EXACT TIMING IS CHALLENGING. OF
MEDIUM POTENTIAL, IS FOR AN AREA OF THUNDERSTORMS TO APPROACHING
CENTRAL WI AROUND OR JUST AFTER 00Z, AND THEN CONTINUE EAST. IF
THIS ROUND MATERIALIZES CHANCES LESSEN BY THE TIME IT REACHES THE
FOX VALLEY/LAKE SHORE AREA. OF HIGHER POTENTIAL IS FOR A ROUND OF
STORMS TO APPROACH CENTRAL WI MID-LATE MORNING SATURDAY, AND THEN
TRACK EAST. USED PROB30 GROUPS TO HIGHLIGHT THE MOST LIKELY TIMING
WINDOW AT EACH TAF SITE. IF/WHEN STORMS DO MOVE THROUGH, DROPS TO
LOWER VSBYS, CIGS, AND STRONG WINDS GUSTS ARE LIKELY.
OUTSIDE OF ANY THUNDERSTORMS, VFR CONDITIONS WILL PREVAIL. THE
ONLY EXCEPTION MAY BE A LITTLE BIT OF FOG IN C-NC WI LATE TONIGHT.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....MPC
AVIATION.......KLJ
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page