973
FXUS63 KGRB 170744
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
244 AM CDT WED SEP 17 2025
FORECAST DISCUSSION FOR ROUTINE MORNING FORECAST ISSUANCE
KEY MESSAGES
- ISOLATED STRONG STORMS COULD PRODUCE GUSTY WINDS IN EXCESS OF 40
MPH AND SMALL HAIL OVER NORTHERN WISCONSIN LATE THIS AFTERNOON
AND EARLY THIS EVENING.
- ADDITIONAL SCATTERED SHOWERS AND STORMS ARE POSSIBLE AT TIMES
THURSDAY THROUGH MONDAY. THE RISK OF SEVERE WEATHER IS LOW.
- TEMPERATURES ABOUT 10 TO 15 DEGREES ABOVE NORMAL TODAY, BEFORE
RETURNING TO NEAR NORMAL FROM FRIDAY INTO THE WEEKEND.
- CONDITIONS HAZARDOUS TO SMALL CRAFT WILL BE POSSIBLE ON LAKE
MICHIGAN SOUTH OF TWO RIVERS ON FRIDAY NIGHT AND SATURDAY
MORNING. THERE WILL ALSO BE AN INCREASED RISK OF RIP CURRENTS ON
LAKE MICHIGAN BEACHES ALONG THIS SECTION OF SHORELINE.
DISCUSSION
ISSUED AT 241 AM CDT WED SEP 17 2025
SHORT TERM...TODAY...TONIGHT...AND THURSDAY
THE LATEST RAP ANALYSIS AND SATELLITE/RADAR IMAGERY EARLY THIS
MORNING REVEAL A SHALLOW COLD FRONT EXTENDING FROM SOUTHWEST
MINNESOTA TO WESTERN LAKE SUPERIOR. WHILE CLUSTERS OF STORMS ARE
ACTIVE OVER THE CENTRAL PLAINS (NEBRASKA TO IOWA), AREAS FURTHER
NORTH ALONG THE FRONT ACROSS THE NORTHWEST HALF OF WISCONSIN ARE
EXPERIENCING MOSTLY CLEAR SKIES. FOG HAS BEEN RELATIVELY LIMITED
SO FAR THIS MORNING, PRIMARILY CONFINED TO NORTH-CENTRAL WISCONSIN
WHERE DEWPOINTS ARE IN THE LOW TO MID 60S. HOWEVER, THERE REMAINS
A POSSIBILITY FOR PATCHY DENSE FOG DEVELOPMENT IN THIS AREA AND
ELSEWHERE ACROSS NORTHEAST WISCONSIN WHERE DEWPOINT DEPRESSIONS
ARE AT OR NEAR 0 DEGREES (E.G., OCONTO, MANITOWOC). VISIBILITIES
WILL CONTINUE TO BE MONITORED. AS THE FRONT GRADUALLY SAGS INTO
NORTHERN WISCONSIN, THE PRIMARY FORECAST CONCERNS CENTER AROUND
THE POTENTIAL FOR THUNDERSTORMS.
THE COLD FRONT IS EXPECTED TO SLOWLY DROP SOUTHWARD, REACHING
NORTH-CENTRAL AND FAR NORTHEAST WISCONSIN THIS AFTERNOON. BETWEEN
THE PRESENCE OF A CAPPING LAYER AND WEAK CONVERGENCE ALONG THE
BOUNDARY THIS MORNING, MINIMAL SHOWER ACTIVITY IS ANTICIPATED.
CONVECTIVE TEMPERATURES ARE IN THE LOWER 80S, WHICH ARE FORECAST
TO BE BREACHED EARLY THIS AFTERNOON, LEADING TO THE BUILD-UP OF
CONVECTIVE CLOUDS ALONG THE FRONT. MOST CONVECTIVE ALLOWING MODELS
(CAMS) SUGGEST THUNDERSTORM DEVELOPMENT WILL HOLD OFF UNTIL 4-6
PM AS MOISTURE CONVERGENCE INCREASES.
ANALYSIS OF THE INGREDIENTS FOR THUNDERSTORM DEVELOPMENT SHOWS
SURFACE-BASED INSTABILITY BETWEEN 1700-2200 J/KG. PRECIPITABLE
WATER VALUES ARE AROUND 90% OF NORMAL, AND DOWNDRAFT CAPE IS
APPROXIMATELY 1000 J/KG. WHILE ORGANIZED SEVERE WEATHER IS NOT
EXPECTED, THESE INGREDIENTS FAVOR THE DEVELOPMENT OF PULSE STORMS
THAT COULD BRIEFLY BECOME STRONG, PRODUCING WIND GUSTS IN EXCESS
OF 40 MPH AND SMALL HAIL. THE SLOW MOTION OF THESE STORMS COULD
RESULT IN LOCALLY HEAVY RAINFALL EXCEEDING 1 INCH; HOWEVER, THE
THREAT OF FLASH FLOODING IS CONSIDERED LOW.
THUNDERSTORMS WILL GRADUALLY SINK SOUTHWARD THIS EVENING AND
WEAKEN WITH THE LOSS OF DAYTIME INSTABILITY. THE COLD FRONT IS
FORECAST TO STALL FROM WEST-CENTRAL WISCONSIN TO SOUTHEAST
WISCONSIN OVERNIGHT THROUGH THURSDAY. WEAK FLOW ALOFT AND OVER THE
BOUNDARY COULD LEAD TO ISOLATED SHOWERS AT TIMES FROM LATE
TONIGHT INTO THURSDAY. AN ISOLATED STORM REMAINS POSSIBLE OVER
CENTRAL WISCONSIN ON THURSDAY, CLOSER TO THE AREA OF INSTABILITY,
BUT SEVERE WEATHER IS NOT ANTICIPATED.
ANOTHER SEASONABLY WARM DAY IS EXPECTED THIS AFTERNOON WITH HIGHS
IN THE LOWER TO MIDDLE 80S. WITH WINDS VEERING TO THE NORTHEAST
OR EAST ON THURSDAY, COOLER TEMPERATURES IN THE 70S ARE EXPECTED
FOR MOST LOCATIONS.
LONG TERM...THURSDAY NIGHT THROUGH TUESDAY
THE LARGE-SCALE PATTERN THROUGH THE MEDIUM-RANGE PERIOD WILL
CONTINUE TO BE CHARACTERIZED BY TROUGHING OVER THE NORTHERN
PLAINS/UPPER MIDWEST. THIS TROUGHING IS EXPECTED TO BRING
SCATTERED SHOWERS AND THUNDERSTORMS TO THE REGION AT TIMES THIS
WEEKEND. MORE POTENT TROUGHING IS THEN FORECAST TO ENTER THE
PACIFIC NORTHWEST SATURDAY NIGHT AND REACH THE MIDWEST OR GREAT
LAKES BY MONDAY NIGHT OR TUESDAY. DURING MOST OF THIS PERIOD, THE
FOCUS FOR THIS PART OF THE FORECAST WILL BE ON THE POTENTIAL FOR
THUNDERSTORMS.
THE COLD FRONT WILL STALL FROM WEST-CENTRAL WISCONSIN TO SOUTHERN
WISCONSIN ON THURSDAY NIGHT. WITH LINGERING INSTABILITY, A SMALL
CHANCE OF SHOWERS WILL CONTINUE.
LOOKING AHEAD, THE TROUGHING PATTERN OVER THE UPPER MIDWEST IS
EXPECTED TO PERSIST, MAINTAINING A CHANCE OF SCATTERED SHOWERS AND
THUNDERSTORMS THROUGH THE WEEKEND. AS THE MORE POTENT TROUGHING
SYSTEM APPROACHES FROM THE PACIFIC NORTHWEST EARLY NEXT WEEK, IT
IS LIKELY TO BRING A MORE SIGNIFICANT CHANCE OF WIDESPREAD SHOWERS
AND THUNDERSTORMS TO NORTH-CENTRAL AND NORTHEAST WISCONSIN BY
MONDAY NIGHT OR TUESDAY. MODEL SPREAD IS RATHER LARGE WITH THIS
SYSTEM, LEADING TO LOW PREDICTABILITY IN THE FORECAST DETAILS FOR
THE LATTER PART OF THE LONG-TERM PERIOD. TEMPERATURES ARE
EXPECTED TO REMAIN NEAR OR SLIGHTLY ABOVE SEASONAL AVERAGES
DURING THIS TIME, PARTICULARLY FOLLOWING THE PASSAGE OF THE MORE
SIGNIFICANT TROUGH.
MARINE...FRIDAY NIGHT AND SATURDAY
WINDS ARE EXPECTED TO VEER TO THE SOUTHEAST AND GUST UP TO 20 KTS
ON LAKE MICHIGAN SOUTH OF TWO RIVERS. BOTH WINDS AND WAVES ARE
MARGINAL FOR SMALL CRAFT ADVISORIES AND BEACH HAZARD STATEMENTS.
TRENDS WILL CONTINUE TO BE MONITORED FOR MARINE AND BEACH
HEADLINES IN THE UPCOMING FORECASTS.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 1039 PM CDT TUE SEP 16 2025
PRIMARY CONCERN OVERNIGHT WILL BE FOG POTENTIAL. GROUND FOG IS
LIKELY FROM CENTRAL TO NORTH-CENTRAL WI, AND ALSO NEAR THE
LAKESHORE. GREATEST RISK OF IFR OR LOWER CONDITIONS WILL BE AT MTW
WHERE IT IS NEARLY SATURATED ALREADY AND ADDITIONAL COOLING IS
EXPECTED WITH LIGHT WINDS. ALSO HAVE A MENTION FOR LOWER
CONDITIONS AT RHI, THOUGH THICKER MID AND HIGH CLOUDS OVERNIGHT
MAY DAMPEN THE POTENTIAL. ALSO, KEPT MENTION OF MVFR GROUND FOG
AT AUW/CWA, BUT THIS IS LOOKING LESS LIKELY, AGAIN DUE TO THE
CLOUDS. FINALLY, AT GRB/ATW, GIVEN THE MIXING THAT OCCURRED
TUESDAY AFTERNOON, EXPECT MINIMAL FOG TO OCCUR.
ONCE ANY FOG BURNS OFF AFTER 12Z-13Z WEDNESDAY, THE MAIN FOCUS
WILL TURN TO SCATTERED SHOWERS AND STORMS EXPECTED TO DEVELOP
AFTER 19Z-21Z AS A COLD FRONT SETTLES OVER NORTHWEST WI AND
INSTABILITY BUILDS AHEAD OF IT. GREATEST POTENTIAL FOR STORMS WILL
BE OVER NORTH-CENTRAL WI, BUT COVERAGE DOES NOT LOOK EXTENSIVE
ENOUGH TO CARRY ANYTHING MORE THAN PROB30 MENTIONS FOR RHI, AUW
AND CWA. STRONGEST STORMS WILL PRODUCE SMALL HAIL, GUSTY WINDS AND
HEAVY RAIN, ALONG WITH BRIEF MVFR VSBY.
ONCE THE SHOWERS AND STORMS DIMINISH ON WEDNESDAY EVENING, EXPECT
THE COLD FRONT TO DROP ACROSS THE AREA. THERE MAY BE LOW CLOUDS
LATE WEDNESDAY NIGHT OVER THE NORTH BEHIND THE FRONT, INCLUDING
AT RHI.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....MPC
AVIATION.......JLA
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