648
FXUS63 KGRB 032320
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
620 PM CDT WED SEP 3 2025
UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE
KEY MESSAGES
- TEMPERATURES WILL BE UNSEASONABLY COOL THROUGH THE WEEKEND.
FROST MAY FORM TONIGHT ACROSS CENTRAL INTO NORTHERN WISCONSIN
WHERE SKIES CLEAR, WITH 40 TO 70 PERCENT CHANCES FOR
TEMPERATURES BELOW 37F.
- MORE SHOWERS WILL IMPACT THE REGION THURSDAY NIGHT INTO EARLY
FRIDAY WITH A SMALL (20%) CHANCE FOR A THUNDERSTORM. WINDS MAY
GUST NEAR 40 MPH EARLY FRIDAY, ESPECIALLY ACROSS EAST-CENTRAL
WISCONSIN.
- TEMPERATURES WILL SLOWLY MODERATE INTO NEXT WEEK WITH LITTLE
SIGNAL FOR ADDITIONAL IMPACTFUL PRECIPITATION.
DISCUSSION
ISSUED AT 257 PM CDT WED SEP 3 2025
TONIGHT-FRIDAY: UNSEASONABLY COOL, MORE SHOWERS/GUSTY WINDS THURSDAY
NIGHT INTO FRIDAY
THE COLD FRONT HAS CLEARED THE AREA WITH NORTHWEST WINDS IN ITS WAKE
AND FAIRLY STRONG LOW-LEVEL COLD ADVECTION. DEEP NORTHWESTERLY FLOW
WILL CONTINUE TO BECOME ESTABLISHED OVERNIGHT AS A TROUGH DEEPENS
ACROSS THE GREAT LAKES. FOR TONIGHT, CLOUDS LIKELY WILL IMPACT
TEMPS, WITH THE MOST LIKELY AREA FOR MORE CLOUDS/SHOWERS TO PERSIST
ARE ACROSS FAR NORTHERN WISCONSIN DOWNSTREAM FROM LAKE SUPERIOR.
MEANWHILE, THE NBM SHOWS MEDIUM TO HIGH PROBABILITIES (40-80%) FOR
LOW TEMPS DOWN TO AT LEAST 35 DEGREES AND SMALLER (20-50%)
PROBABILITIES FOR NEAR FREEZING TEMPS ACROSS FAR NORTH-CENTRAL
WISCONSIN. IN ADDITION TO ANY CLOUDS, RAP SOUNDINGS SHOW ONLY A
WEAK INVERSION WITH STRONGER FLOW ALOFT, SO WINDS MAY STRUGGLE
TO DECOUPLE. DUE TO EARLY SEASON TIMEFRAME, THOUGH, COORDINATED
WITH SURROUNDING OFFICES FOR A FROST ADVISORY ACROSS CENTRAL
WISCONSIN WHERE CONFIDENCE IS HIGHEST FOR CLEARING SKIES ALONG
WITH THE COOLER TEMPS. THESE TRENDS WILL NEED TO BE MONITORED
THIS EVENING, THOUGH.
THE COOL AIR WILL REMAIN ANCHORED OVER THE AREA THROUGH THE
WEEKEND WITH NAEFS 850 MB TEMPS BELOW THE 1ST PERCENTILE, AND
EVEN NEAR MIN VALUES IN SPOTS, RELATIVE TO CLIMATOLOGY. RECORD
LOW MAX TEMPS ARE STILL ON THE TABLE FOR SOME LOCATIONS OVER THE
NEXT FEW DAYS.
A PRONOUNCED EMBEDDED SHORTWAVE WILL SLIDE SOUTHEAST THROUGH THE
BASE OF THE TROUGH THURSDAY NIGHT, WHICH SHOULD BRING WIDESPREAD
SHOWERS TO THE AREA. INSTABILITY LOOKS QUITE WEAK, BUT ISOLATED
THUNDER COULD NOT BE RULED OUT. THIS SYSTEM SHOULD BE A QUICK HITTER
WITH A FEW LINGERING SHOWERS ON FRIDAY. HOWEVER, STRONG COLD
ADVECTION AND A TIGHTENING PRESSURE GRADIENT SHOULD LEAD TO GUSTY
WINDS ON FRIDAY. THE EPS SHOWS A ROBUST SIGNAL FOR GUSTS NEAR/ABOVE
40 MPH, ESPECIALLY ACROSS EAST-CENTRAL WISCONSIN, WHILE THE 90TH
PERCENTILE NBM VALUES ALSO EXCEED 40 MPH IN SOME AREAS, ESPECIALLY
NEAR THE LAKE MICHIGAN SHORELINE.
SATURDAY-WEDNESDAY: GRADUALLY WARMING UP, MAINLY DRY
THE DEEP MID-LEVEL TROUGH CENTERED ACROSS THE GREAT LAKES WILL
SLOWLY PASS EASTWARD AS MID-LEVEL RIDGING BUILDS EASTWARD INTO THE
MIDDLE OF NEXT WEEK. THIS WILL RESULT IN A SLOW MODERATING TREND IN
TEMPS AS DRY CANADIAN SURFACE HIGH PRESSURE SLOWLY WORKS ACROSS THE
MIDWEST, WITH RETURN SOUTHERLY FLOW EVENTUALLY SETTING UP BY EARLY
TO MID WEEK.
WITH THE DRY AIRMASS AND SURFACE HIGH OVER THE AREA, PATCHY FROST
WILL BE POSSIBLE DURING THE EARLY MORNING HOURS THROUGH MONDAY
BEFORE WARMER AIR RETURNS.
RAIN CHANCES OVERALL LOOK LOOK DURING THIS TIME, WITH LOW END (20-
30%) CHANCES SATURDAY WITHIN THE CYCLONIC MID-LEVEL FLOW AS A
SHORTWAVE TROUGH ROTATES THROUGH THE BROADER TROUGH. ADDITIONAL
SMALL RAIN CHANCES EXIST EARLY NEXT WEEK WITH ANY WEAK WAVES AS THE
PATTERN TRANSITIONS TO LARGER SCALE RIDGING.
AVIATION
FOR 00Z TAF ISSUANCE
ISSUED AT 619 PM CDT WED SEP 3 2025
BENEATH AN UPPER LOW, CEILINGS ARE PRIMARILY VFR, WITH THE
EXCEPTION OF MVFR CONDITIONS EXTENDING FROM RHI TO THE U.P.
BORDER. SCATTERED SHOWERS ARE TRACKING SOUTHEAST, AIDED BY A
COMPACT SHORTWAVE. THESE SHOWERS ARE EXPECTED TO GRADUALLY
DISSIPATE THIS EVENING AS DAYTIME INSTABILITY WANES. HOWEVER, THE
CLEARING TREND WILL LIKELY BE DELAYED UNTIL THIS WAVE EXITS LATE
THIS EVENING.
WITH A NORTHWEST FLOW, MVFR CEILINGS COULD PERSIST OVER NORTH-
CENTRAL WISCONSIN THROUGH THE EVENING. A SUBTLE BACKING OF WIND
TRAJECTORIES SHOULD SUPPORT RISING CEILINGS OVERNIGHT. SHALLOW
FAIR-WEATHER CLOUDS, AROUND 4-5 KFT, ARE LIKELY TO REDEVELOP WITH
THE HEAT OF THE DAY AROUND 15-16Z AND PERSIST THROUGH THE
AFTERNOON.
WINDS WILL SUBSIDE THIS EVENING, WITH SOME DIURNAL INCREASE ON
THURSDAY AS MIXING COMMENCES IN THE 15-16Z TIMEFRAME.
MARINE
ISSUED AT 257 PM CDT WED SEP 3 2025
GUSTY POST-FRONTAL WINDS WILL PERSIST THIS AFTERNOON WITH WINDS
DECREASING OVERNIGHT. A REINFORCING COLD FRONT WILL MOVE THROUGH
THURSDAY NIGHT INTO FRIDAY WITH SOME POTENTIAL FOR GALES FOR THE
NEARSHORE WATERS OF NORTHERN LAKE MICHIGAN LATE THURSDAY NIGHT
INTO FRIDAY MORNING. THE NBM SHOWS HIGHER END (90TH PERCENTILE)
WIND GUST VALUES NEARING 40 KTS FOR A RELATIVELY SHORT TIME, SO
A PERIOD OF GALE FORCE GUSTS ARE POSSIBLE. WATERSPOUTS COULD NOT
BE RULED OUT WITH DEEPER EQUILIBRIUM LEVELS AND SOME INSTABILITY
AS THE COLD AIR MOVES OVER WARM WATERS.
GRB WATCHES/WARNINGS/ADVISORIES
FROST ADVISORY FROM 2 AM TO 8 AM CDT THURSDAY FOR WIZ018-019-030.
DISCUSSION.....JM
AVIATION.......MPC
MARINE.........JM
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