945
FXUS63 KGRB 202349
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
649 PM CDT WED AUG 20 2025
UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE
KEY MESSAGES
- PATCHY FOG, LOCALLY DENSE, IS EXPECTED LATE TONIGHT THROUGH
THURSDAY MORNING, ESPECIALLY IN CENTRAL AND NORTH-CENTRAL
WISCONSIN.
- DRY CONDITIONS ARE EXPECTED THROUGH FRIDAY MORNING WITH THE NEXT
CHANCE FOR SHOWERS AND THUNDERSTORMS FRIDAY INTO FRIDAY NIGHT.
AN ISOLATED SEVERE STORM IS POSSIBLE.
- TEMPERATURES WILL BE AROUND NORMAL FOR THE REST OF THE WEEK,
WITH THE POTENTIAL FOR WELL BELOW NORMAL TEMPERATURES LATE IN
THE WEEKEND INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 350 PM CDT WED AUG 20 2025
SHORT TERM...TONIGHT AND THURSDAY
THIS EVENING/TONIGHT...THIS AFTERNOON'S SATELLITE AND RADAR IMAGERY
SHOWED MOSTLY CLOUDY SKIES (LOW CLOUDS) AND ISOLATED
SHOWERS/SPRINKLES OCCURRING AT TIMES ACROSS THE REGION. THESE LOW-
LEVEL CLOUDS AND LIGHT PRECIP ARE EXPECTED TO GRADUALLY LESSEN INTO
THIS EVENING AFTER SUNSET AND AS DRY AIR FROM A NEARBY SURFACE HIGH
PRESSURE SLOWLY SHIFTS OVER THE WESTERN GREAT LAKES REGION. WITH
SOME CLEARING EXPECTED OVERNIGHT AND LOW-LEVEL MOISTURE STICKING
AROUND, RADIATION FOG SHOULD DEVELOP. MODELS INDICATE LOCATIONS
NORTH AND WEST OF THE FOX VALLEY WILL SEE THE GREATEST POTENTIAL FOR
FOG AFTER MIDNIGHT THROUGH THURSDAY MORNING (HREF PROBABILITIES FOR
VISIBILITY OF 1 MILE OR LESS AROUND 40-60%). THERE ARE ALSO
INDICATIONS OF LOCALLY DENSE FOG WITH HREF PROBABILITIES FOR
VISIBILITY OF 0.25 MILE OR LESS AROUND 30-50% IN THESE SAME AREAS.
HOWEVER, THE EXTENT OF THE FOG WILL BE DEPENDENT ON HOW MUCH
CLEARING WILL OCCUR. ANY FOG WILL BURN OFF BY MID-MORNING THURSDAY.
THURSDAY...WITH THE SURFACE HIGH PRESSURE SYSTEM PARKED OVER THE
REGION, DRY CONDITIONS AND LIGHT WINDS ARE EXPECTED. WHILE LESS
CLOUD COVER IS ANTICIPATED FOR THURSDAY COMPARED TO TODAY
(WEDNESDAY), SOME FORECAST SOUNDINGS INDICATE AN AFTERNOON CU FIELD
MAY DEVELOP IN SPOTS. THE ADDED SUNSHINE WILL AID IN WARMER
TEMPERATURES COMPARED TO TODAY (WEDNESDAY), WITH HIGHS NEAR NORMAL
IN THE MIDDLE TO UPPER 70S.
LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
TWO MAIN STORIES EMERGING FOR THE LONGER TERM. FIRST IS POTENTIAL
FOR STORMS ON FRIDAY AS STRONG COLD FRONT CROSSES THE REGION.
SECOND IS THE POST FRONTAL FALL-LIKE AIRMASS THAT ARRIVES THIS
WEEKEND BEHIND THE COLD FRONT.
ON FRIDAY, APPROACHING COLD FRONT BRINGS NEXT CHANCE OF SHOWERS
AND STORMS ACROSS THE REGION. INSTABILITY UP TO 1000J/KG AND
EFFECTIVE SHEAR 25+ KTS SHOWN BY LREF MAY SUPPORT AN ISOLATED
STRONG STORM IF FROPA OCCURS DURING MAX HEATING ON FRIDAY AFTERNOON.
OVERALL LOOK OF SOUNDINGS SHOWS TALL, SKINNY CAPES SUGGESTING ANY
SEVERE RISK WOULD BE ISOLATED. CIPS ANALOGS AND MACHINE LEARNING
OUTPUT LEND SUPPORT TO NON-ZERO RISK OF ISOLATED SEVERE STORM.
BEHIND THE FRONT, NEXT WEEKEND INTO EARLY NEXT WEEK STILL LOOKS
FALL-LIKE WITH BELOW NORMAL TEMPERATURES SUNDAY THROUGH TUESDAY.
HIGHS MAY NOT REACH 70, ESPECIALLY SUNDAY AND MONDAY. MONDAY
NIGHT AND/OR TUESDAY NIGHT LOOK CHILLY AS HIGH PRESSURE SETTLES
MORE OVERHEAD. ECMWF EXTREME FORECAST INDEX (EFI) SHOWS SIGNAL
FOR TEMPS WELL BELOW CLIMO. LATEST NBM MIN TEMP FORECASTS ARE
ALREADY SHOWING READINGS AROUND 40 AT FAVORED COLD SPOTS IN
NORTHERN WI MONDAY NIGHT AND TUESDAY NIGHT. NBM 10TH/25TH
PERCENTILE FOR MIN TEMPS ARE AS LOW AS THE LOWER TO MIDDLE 30S,
SO WOULD NOT BE SURPRISED TO SEE FORECAST TEMPS TREND COOLER OVER
TIME.
IN TERMS OF SENSIBLE WEATHER, PLAN ON BREEZY NORTHWEST WINDS WITH
PARTLY TO MOSTLY CLOUDY SKIES THIS WEEKEND INTO EARLY NEXT WEEK.
GREATEST CHANCES FOR SCATTERED SHOWERS WILL BE ON SUNDAY, THOUGH
THERE MAY BE POTENTIAL FOR SHOWERS AND SPRINKLES AT OTHER TIMES
AS STRONGER WAVES DIG ACROSS WITHIN THE MEAN TROUGHING CENTERED
OVER SOUTHERN HUDSON BAY/JAMES BAY. FURTHER INCREASE IN COVERAGE
OF SHOWERS COULD OCCUR DUE TO LAKE EFFECT PROCESSES GIVEN COOL
TEMPS ALOFT (850MB TEMPS DOWN TO +5C) AND WATER TEMPS AROUND 20C
PROVIDING SUFFICIENT DELTA T/S. THIS TASTE OF FALL WILL LAST
THROUGH TUESDAY, BEFORE WARMING TOWARD CLIMO OCCURS MID-LATE NEXT
WEEK.
AVIATION
FOR 00Z TAF ISSUANCE
ISSUED AT 648 PM CDT WED AUG 20 2025
STUBBORN HIGH-END MVFR AND LOW-END VFR CLOUDS REMAINED ACROSS
MOST OF THE AREA LATE THIS AFTERNOON AND SHOULD CONTINUE INTO THE
EVENING. CAN'T RULE OUT A STRAY SPRINKLE OR TWO UNDER THE LOWER
CLOUDS THIS EVENING, BUT NO AVIATION IMPACTS ARE EXPECTED. THE
DIURNAL CLOUDS WILL FADE AFTER SUNSET, WITH THE LARGER AREA OF
CLOUDS EXPECTED TO CONTINUE TO SHRINK THROUGH THE EVENING.
STILL SOME UNCERTAINTY REGARDING FOG DEVELOPMENT TONIGHT AS JUST
HOW FAST CLOUDS CLEAR OUT AND IF/WHERE ANY ADDITIONAL LOW STRATUS
WILL REDEVELOP WILL DETERMINE HOW WIDESPREAD/DENSE THE FOG WILL
BECOME. PROBABILITIES OF A HALF MILE OR LESS VSBY IS HIGHER THAN
LAST NIGHT, BUT REMAINS UNDER 50% (HIGHEST ACROSS NORTH/WEST OF
THE FOX VALLEY). WILL CONTINUE WITH THE TEMPO GROUPS FOR THE
OVERNIGHT AND EARLY MORNING FOG, WITH THE LIFR AT RHI, AND WILL
MONITOR CLOUD TRENDS THROUGH THE EVENING. ANY FOG WILL BURN OFF
AND LIFT THURSDAY MORNING, WITH SOME LINGERING STRATUS AND DAYTIME
CU EXPECTED. WINDS WILL REMAIN LIGHT THROUGH THE TAF PERIOD.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....KRUK/JLA
AVIATION.......BERSCH
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