529
FXUS63 KGRB 152018
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
318 PM CDT MON SEP 15 2025
FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE
KEY MESSAGES
- PATCHY DENSE FOG LATE TONIGHT INTO EARLY TUESDAY MORNING MAY
IMPACT TRAVEL ACROSS FAR NORTHEAST AND EAST-CENTRAL WI.
- ISOLATED SHOWERS AND STORMS CENTRAL TO NORTH-CENTRAL WISCONSIN
THROUGH TUESDAY.
- CHANCES FOR SHOWERS AND THUNDERSTORMS WEDNESDAY INTO THURSDAY AS
COLD FRONT CROSSES THE REGION. ADDITIONAL SCATTERED SHOWERS AND
ISOLATED STORMS AT TIMES FRIDAY THROUGH MONDAY. NO SEVERE STORMS
EXPECTED.
- TEMPERATURES ABOUT 10 TO 15 DEGREES ABOVE NORMAL THROUGH MID-
WEEK, WITH A RETURN TO NEAR NORMAL CONDITIONS EXPECTED FROM
FRIDAY INTO THE WEEKEND.
DISCUSSION
ISSUED AT 317 PM CDT MON SEP 15 2025
NEAR TERM THROUGH TUESDAY...HIGH PRESSURE CENTERED OVER EASTERN
CANADA CONTINUES TO LEAD TO DRY CONDITIONS WITH NIGHTTIME FOG.
PATTERN BEGINNING TO BREAK DOWN THOUGH. FORCING WITH NEGATIVE
TILTED TROUGH LIFTING NORTH ACROSS MN INTERACTING WITH INSTABILITY
GRADIENT OVER THE UPPER MISSISSIPPI RIVER VALLEY HAS RESULTED IN
CLUSTERS OF SHOWERS AND STORMS OVER WESTERN WI, THAT ARE MOVING
SOUTH TO NORTH. HAVE ADDED SMALL CHANCE POPS AND SPRINKLES THROUGH
TUESDAY OVER OUR FAR WESTERN ZONES THAT WILL BE IN THE PROXIMITY
OF RIGHT ENTRANCE REGION OF MID-LEVEL JET AND CLOSER TO SOUTHERLY
WEAK LOW-LEVEL JET AND GRADIENT OF INSTABILITY. FARTHER EAST IT
SHOULD STAY DRY THROUGH TUESDAY. FOG AGAIN TONIGHT AS THAT PART OF
THE PATTERN PERSISTS. ONCE AGAIN GREATEST SIGNAL FOR LOWER VSBY
IS SHOWING UP OVER FAR NORTHEAST WI TO NORTHERN EDGE OF THE FOX
VALLEY AND ON EAST TO THE LAKESHORE. FOG COVERAGE NOT EXPECTED TO
JUSTIFY AN ADVISORY, BUT WILL KEEP THE MENTION IN HWO. LATE SEASON
WARMTH PERSISTS. BASED ON 850MB TEMPS STARTING DAY 15-16C, EXPECT
HIGHS ON TUESDAY TO REACH THE MID 80S OVER MUCH OF CENTRAL AND
NORTHEAST WI. SOUTHEAST WINDS WILL KEEP THE LAKESHORE AS COOL AS
THE MID TO UPPER 70S. YET, EVEN THESE COOLER VALUES ARE ABOVE
CLIMO FOR MID SEPTEMBER. NORMAL HIGH FOR 9/16 AT GRB IS DOWN TO 72
AND HAS NOW SLIPPED TO 70 AT RHI.
PRECIPITATION TRENDS BEYOND TUESDAY...LARGE RIDGE OVER THE GREAT
LAKES SHIFTS EAST WHILE DAMPENING, THEN TRIES TO RE-EMERGE BRIEFLY
WEDNESDAY INTO THURSDAY AS TROUGHING OCCURS OVER THE PLAINS. AT
THE SAME TIME, COLD FRONT WILL DROP ACROSS THE UPPER GREAT LAKES
LATE WEDNESDAY AND CONTINUE CROSSING THE GREAT LAKES ON THURSDAY.
AS THE FRONT ARRIVES FROM THE NORTH ON WEDNESDAY, LARGER AREA OF
SCATTERED SHOWERS AND STORMS WILL IMPACT ESPECIALLY CENTRAL AND
NORTH-CENTRAL, FAR NORTHEAST WI DURING PEAK HEATING ON WEDNESDAY.
MEAN MLCAPES ARE FORECAST ABOVE 1500J/KG, BUT AS IT HAS LOOKED
LIKE FOR A WHILE NOW, WIND FIELDS ALOFT AND RESULTING EFFECTIVE
SHEAR IS WEAK, THUS ORGANIZED SEVERE WEATHER RISK ON WEDNESDAY IS
ON LOWER SIDE. HOWEVER, ISOLATED STRONG TO SEVERE STORM NOT OUT
OF QUESTION GIVEN THE INSTABILITY AND THE FRONT ARRIVING DURING
PEAK HEATING, ESPECIALLY IF CLOUDS ARE AT A MINIMUM BEFORE THE
FRONT ARRIVES. NSSL MACHINE LEARNING GUIDANCE HINTS AT AT LEAST A
SMALL POTENTIAL FOR SEVERE STORMS.
SHOWER CHANCES DECREASE SOME WITH LOSS OF INSTABILITY ON WEDNESDAY
NIGHT ESPECIALLY AS MAIN LOW-LEVEL FORCING SHIFTS MORE EAST. ON
THURSDAY, CHANCES FOR SHOWERS AND STORMS INCREASE AGAIN DURING THE
AFTERNOON AS INSTABILITY BUILDS DURING THE AFTERNOON. MLCAPES NOT
AS ELEVATED AS WEDNESDAY AFTERNOON. JOINT PROBABILITY OF SHEAR
OVER 20 KTS AND CAPE OVER 500J/KG HAVE INCREASED OVER LAST COUPLE
DAYS, BUT ARE MAINLY FOCUSING OVER IA INTO SOUTHERN MN CLOSER TO
THE LOW-LEVEL JET AXIS NEAR THE PLAINS SFC LOW.
MOVING INTO FRIDAY AND THE WEEKEND, THERE REMAINS UNCERTAINTY ON
FRIDAY AS IT IS NOT CERTAIN HOW FAR EAST THE PLAINS SFC LOW WILL
PROGRESS. THERE LIKELY WILL BE A GRADIENT FROM SOUTHWEST TO
NORTHEAST ACROSS OUR AREA IN WHERE GREATEST COVERAGE OF SHOWERS
WILL BE. AS THE PLAINS TROUGH CROSSES THE WESTERN GREAT LAKES FOR
THE WEEKEND, CHANCES FOR SCATTERED SHOWERS AND AT LEAST ISOLATED
STORMS (MLCAPES LESS THAN 500J/KG) INCREASE. CHANCES FOR SHOWERS
CONTINUE ON MONDAY AS ANOTHER WARM FRONT LIFTS TOWARD THE REGION.
OVERALL, COMPARED TO THE REGIME WE HAVE BEEN IN RECENTLY, EXPECT A
MORE UNSETTLED AND ACTIVE WEATHER PATTERN BEGINNING LATER THIS
WEEK.
TEMPERATURE AND WIND TRENDS BEYOND TUESDAY...WEDNESDAY WILL FEATURE
WELL ABOVE NORMAL TEMPS AGAIN, WITH GREATEST POTENTIAL FOR HIGHS
IN THE MID 80S FAR NORTHEAST WI TO THE FOX VALLEY AND THE LAKESHORE.
TEMPS TREND DOWNWARD ON THURSDAY AS THE FRONT CROSSES, THEN BOTTOM
OUT IN THE 60S NORTH AND NEAR THE LAKESHORE, TO THE LOWER 70S
ELSEWHERE, BEHIND THE FRONT FRIDAY INTO THE WEEKEND. COULD SEE
TEMPS ENDING UP LOWER ON FRIDAY THAN FORECAST GIVEN WHAT WILL BE
GUSTY EASTERLY WINDS OFF OF LAKE MICHIGAN, ESPECIALLY IF THERE ARE
MORE CLOUDS AND SHOWERS AROUND. THESE GUSTY WINDS WILL LINGER INTO
SATURDAY, BEFORE BECOMING LIGHTER FROM THE SOUTH SUNDAY INTO MONDAY.
AVIATION
FOR 18Z TAF ISSUANCE
ISSUED AT 1243 PM CDT MON SEP 15 2025
MORNING FOG HAS BURNED OFF. SCATTERED HIGH CLOUDS MAY IMPACT THE
AREA AS ISOLATED SHOWERS AND STORMS DEVELOP OVER WESTERN WI. AT
THIS TIME, MOVEMENT ON THE SHOWERS AND STORMS IS TO THE NORTH
VERSUS TO THE EAST SO HAVE NOT INCLUDED THEM AT CWA/AUW. HOWEVER,
THOSE FLYING TO THE WEST INTO WESTERN WI WILL NEED TO CONSIDER
THIS CONVECTION IN THEIR PLANS. LIKE YESTERDAY, MINIMAL CU IS
EXPECTED TO FORM THIS AFTERNOON.
AREAS OF FOG ARE EXPECTED AGAIN TONIGHT, ESPECIALLY FROM FAR
NORTHEAST WI TO THE LAKESHORE. GRB AND MTW ARE THE PRIMARY TAF
SITES THAT WILL BE IMPACTED WITH IFR OR LOWER CONDITIONS. SIMILAR
TO TODAY, EXPECT THE FOG TO DIMINISH AFTER 12Z ON TUESDAY, WITH
THE THICKER AREAS OF FOG NOT ABATING UNTIL AFTER 14Z.
SOUTHERLY WINDS MAY GUST OVER 15 KTS AT GRB AND ATW THIS AFTERNOON.
WINDS WILL BE LIGHT EAST-SOUTHEAST TONIGHT THEN BECOME SOUTHERLY
AGAIN 5 TO 10 KTS ON TUESDAY.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....JLA
AVIATION.......JLA
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