535  
FXUS63 KGRB 151810  
AFDGRB  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREEN BAY WI  
ISSUED BY NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI  
110 PM CDT THU MAY 15 2025  
   
KEY MESSAGES  
 
- MARINE DENSE FOG ADVISORY FOR THE NEARSHORE AREAS OF LAKE  
MICHIGAN THROUGH THE EARLY EVENING. A SMALL CRAFT ADVISORY  
 
- A BROKEN LINE OF STRONG THUNDERSTORMS WILL CROSS NORTHERN WI  
BETWEEN 4 AND 9 PM TODAY. SOME SEVERE STORMS ARE LIKELY WITH  
THE PASSAGE OF A COLD FRONT. ALL HAZARDS POSSIBLE OVER CENTRAL  
WI AND LARGE HAIL POSSIBLE OVER EASTERN WI.  
 
- ANOTHER PERIOD OF SHOWERS AND WEAK STORMS EXPECTED FRIDAY WITH  
SOME POTENTIAL FOR GUSTY WINDS WITH SOME OF THESE  
SHOWERS/STORMS.  
 
 
   
DISCUSSION  
 
ISSUED AT 1115 AM CDT THU MAY 15 2025  
 
MORNING UPDATE:  
 
FOG HAS LARGELY LIFTED/MIXED THIS MORNING ALONG THE LAKESHORE  
WITH POCKETS ABOVE DENSE FOG CRITERIA REMAINING OVER KEWAUNEE,  
MANITOWOC, AND DOOR COUNTIES. THIS FOG SHOULD CONTINUE TO MIX  
AND PEEL BACK TO LAKE MICHIGAN INTO THE AFTERNOON.  
 
AT THIS TIME, WE ARE KEEPING AN EYE ON SURFACE OBSERVATIONS AND  
SATELLITE AHEAD OF TODAY'S EXPECTED SEVERE WEATHER. AN ARC OF  
STRATOCU IS CURRENTLY VISIBILE FROM JANESVILLE IN SOUTHERN WI,  
TO MINNEAPOLIS, ROUGHLY MARKING THE ADVENT OF THE WARM FRONT AND  
WARM SECTOR INTO WI. THIS FRONT SHOULD LIFT NORTH WITH TIME AND  
SOMEWHAT STALL FROM OSHKOSH UP THROUGH THE ATHENS, WAUSAU, AND  
MERRILL AREA EARLY THIS AFTERNOON. SEVERE STORM DEVELOPMENT IS  
THEN STILL ON TRACK TO BEGIN OVER CENTRAL WI AROUND 4PM AND EXIT  
NORTHEAST BY 9PM.  
 
THIS AFTERNOON THROUGH FRIDAY NIGHT:  
 
CONCERN WILL THEN TURN TO THE AFTERNOON AND EVENING WITH THE  
POTENTIAL FOR A SIGNIFICANT SEVERE WEATHER EVENT ACROSS THE CWA.  
THE EML COMING INTO THE REGION THIS MORNING, ORIGINALLY  
PRESENTED THE AREA WITH THE CONCERN THAT CAPPING MIGHT BE STRONG  
ENOUGH TO POTENTIALLY PREVENT CONVECTION IN PARTS OF THE  
REGION. HOWEVER, MODELS, ESPECIALLY CAMS, HAVE LARGELY PUT THIS  
POTENTIAL TO BED WITH THE FORCING FROM THE UPPER LOW AND SURFACE  
FRONT LIKELY HELPING OVERCOME THE CAP AND ALLOW FOR WIDESPREAD  
CONVECTION TO DEVELOP IN THE WESTERN FRINGES OF THE CWA BY THE  
MID TO LATE AFTERNOON. SEVERE STORMS HAVE BECOME INCREASINGLY  
LIKELY WITH THIS EVENT AS THE POTENTIAL LIMITING FACTORS HAVE  
BEEN MITIGATED WITH THE LATEST MODEL GUIDANCE.  
 
THIS EVENT CONTINUES TO FEATURE VERY HIGH INSTABILITY IN THE  
RANGE OF 2000-3000 J/KG OF MLCAPE. AS STORMS DEVELOP AND PUSH  
EAST INSTABILITY WILL DECREASE SOMEWHAT BUT REMAIN IN THE  
1000-2000 J/KG RANGE. THIS IS LARGELY DUE TO THE MIDLEVEL LAPSE  
RATES AROUND 7.5-8.0 C/KM. DEEP LAYER SHEAR WILL INCREASE INTO  
THE EARLY AFTERNOON BEFORE STEADILY DECREASING INTO THE LATE  
AFTERNOON AND EARLY EVENING BUT WILL STILL BE PLENTY, HANGING IN  
THE 40-50 KT RANGE AHEAD OF EXPECTED CONVECTION. 0-3KM SRH WILL  
BE IN THE 200-300 MS/S2 RANGE WITH THE 0-1KM SRH 50-100 M2/S2  
INITIALLY BUT WILL GRADUALLY INCREASE AS STORMS PUSH EAST. THE  
SUPERCELL COMPOSITE WILL BE IN THE 10-15 RANGE IN THE SOUTHERN  
HALF OF THE CWA WITH DECREASING VALUES FURTHER NORTH WHERE THE  
BETTER LIKELIHOOD FOR STORMS BECOMING MORE LINEAR EXISTS. THE  
HREF STP SHOWS VALUES IN THE 2-4 RANGE WHICH IS SUGGESTIVE OF  
SOME HIGHER END TORNADIC POTENTIAL. THERE ARE A FEW LIMITING  
FACTORS THAT MAY LIMIT SOME OF THE HIGHER END SEVERE POTENTIAL.  
THE FIRST IS THAT WHILE CAMS INDICATE THE MODE MAY LARGELY BE  
DISCRETE THERE WILL BE CONCERNS FOR THE PROXIMITY OF STORMS TO  
BE CLOSE SO AS TO CAUSE STORM TO STORM INTERACTIONS THAT MAY  
INGEST RAIN-COOLED AIR FROM EACH OTHER AND THUS HELP WEAKEN  
STORMS OVERALL CUTTING OFF THE INGEST OF MORE WARM MOIST AIR  
AHEAD. THIS IS SOME WAYS COULD HELP THE COOL TEMPERATURES A BIT  
AND LOWER LCLS AS LCLS WILL LIKELY BE FAIRLY HIGH AROUND  
1000-1500M WHICH WOULD MAKE TORNADOES A BIT MORE DIFFICULT. ALL  
HAZARDS WILL BE POSSIBLE WITH THIS EVENT AS VERY LARGE HAIL,  
TORNADOES (POTENTIALLY STRONG) AND DAMAGING WINDS (DCAPE > 1000  
J/KG). THE HIGHER END TORNADO RISK DOES APPEAR MORE LIMITED  
TOWARD SOUTHERN PORTIONS OF THE CWA  
 
THE TIMING FOR THIS EVENT IS THE MID TO LATE AFTERNOON IN THE  
FAR SOUTHEASTERN PARTS OF THE CWA AND PUSH OUT OF THE CWA BY THE  
MID EVENING HOURS. THE PRIME AREA OF CONCERN SEEMS TO LINE UP  
PRIMARILY IN THE SOUTHWESTERN PARTS OF THE CWA WITH THE  
STRONGEST STORMS LIKELY FROM AROUND MARATHON COUNTY DOWN TO  
WAUSHARA AND WINNEBAGO COUNTIES. AS STORMS PUSH EAST OF THERE  
THEY COULD BEGIN TO INTERACT WITH THE LAKE BREEZE BOUNDARY.  
WHILE INITIALLY THIS COULD ADD SOME ENHANCED STRETCHING  
POTENTIAL STORMS WILL BECOME ELEVATED AS THEY OVERRUN THE  
BOUNDARY. THIS WOULD LESSEN THE TORNADO AND WIND RISK THOUGH THE  
HAIL RISK MAY REMAIN. INTO THE EVENING STORMS WILL GRADUALLY  
WEAKEN AS THEY LOSE INSTABILITY AS WE LOSE OUR DIURNAL HEATING  
BUT THERE WILL BE SEVERE RISKS CONTINUING THROUGHOUT THE CWA  
UNTIL STORMS EXIT BY THE LATE EVENING HOURS. QUIETER CONDITIONS  
ARE EXPECTED THURSDAY NIGHT.  
 
THE CLOSED UPPER LOW AND ASSOCIATED WEAKENING SURFACE LOW WILL TRACK  
THROUGH CENTRAL AND NORTHERN MN DURING THE DAY FRIDAY. SOME  
SHORTWAVE ENERGY IS EXPECTED TO SLIDE ACROSS THE EASTERN HALF  
OF WI FRIDAY OUT AHEAD OF THAT UPPER LOW. IN ADDITION, THE LOW  
LEVEL JET WILL ALSO BE STREAMING ACROSS THE REGION AND THERE  
MAY BE SOME UPPER DIVERGENCE PRESENT FROM THE LEFT EXIT REGION  
OF AN UPPER LEVEL JET TO THE SOUTH.  
 
THE MAIN CONCERN WITH THIS WILL BE THE VERY STRONG WINDS AVAILABLE  
TO MIX DOWN TO THE SURFACE DURING THE DAY FRIDAY. GUSTS FROM 30  
TO AS HIGH AS 45 MPH ARE LOOKING LIKELY FOR THE EARLY AFTERNOON  
HOURS IN THE FOX VALLEY. A WIND ADVISORY MAY BE NEEDED FOR THIS  
REGION. IN ADDITION, A FEW THUNDERSTORMS ARE POSSIBLE FRIDAY  
AFTERNOON. CONTINUED GUSTY WINDS AND A FEW SHOWERS ARE POSSIBLE  
OVER THE REST OF THE AREA FRIDAY EVENING. THERE IS SOME CONCERN  
WITH THESE SHOWERS AND WEAK STORMS TO MIX DOWN SOME STRONGER  
WINDS ALOFT. WITH THE GUSTY WINDS ALOFT SOME MODELS ARE  
INDICATING THAT WINDS FROM SOME OF THESE WEAK STORMS/SHOWERS  
COULD BE BORDERLINE SEVERE WITH SOUNDINGS SUGGESTIVE OF THIS  
POTENTIAL AS WELL GIVEN UNSTABLE CONDITIONS TO 700MB AND EVEN  
AREAS WHERE DCAPE > 1000 J/KG.  
 
SATURDAY THROUGH TUESDAY:  
 
THE CLOSED LOW WILL CONTINUE EAST ACROSS THE GREAT LAKES REGION  
SATURDAY. THE ASSOCIATED OCCLUDED AND WEAKENING SURFACE LOW PRESSURE  
SYSTEM IS EXPECTED TO MOVE NORTHEAST FROM NORTHEASTERN WI AND THE UP  
OF MICHIGAN TO QUEBEC AND ONTARIO CANADA. WHAT REMAINS OF THE  
CYCLONIC FLOW SHOULD BE ABLE TO PROVIDE ENOUGH LIFT TO GENERATE SOME  
SHOWERS ACROSS THE FORECAST AREA. RAIN SHOWERS ARE LIKELY TO BE  
DIURNALLY DRIVEN WITH COVERAGE INCREASE A BIT DURING THE AFTERNOON  
VS THE MORNING AND EVENING HOURS. REGARDLESS OF THIS COVERAGE IS  
EXPECTED TO BE SCATTERED TO ISOLATED. AS WINDS BECOME NORTHERLY, DRY  
AIR WILL ALSO MOVE IN ACROSS NORTHERN AND CENTRAL WISCONSIN. POPS  
WILL BE AROUND 20 TO 40% ACROSS THE FORECAST AREA SATURDAY. BY  
SATURDAY NIGHT, POPS DROP OFF QUICKLY AS DRY AIR MOVES IN AND THE  
CYCLONIC FLOW MOVES OFF TO THE NORTHEAST.  
 
BY SUNDAY, AN UPPER LEVEL RIDGE AND HIGH PRESSURE BEGIN TO MOVE INTO  
WISCONSIN. WITH THE CENTER OF THE HIGH PASSING TO OUR NORTH ACROSS  
MANITOBA AND QUEBEC CANADA, A COMPONENT TO THE NORTHERLY WINDS  
ARE EXPECTED TO STAY IN PLACE THROUGH MONDAY. NORTH TO NORTHEAST  
WINDS WILL USHER IN SOME CAA LEADING TO A COOLING TREND WITH  
HIGHS IN THE MID 50S TO MID 60S AND OVERNIGHT LOWS IN THE LOW  
30S TO MID 40S. SUNDAY NIGHT LOOKS TO BE THE COLDEST WITH  
TEMPERATURES NEAR 30 ACROSS NORTH CENTRAL WISCONSIN. THIS WILL  
BE THE AREA TO KEEP AN EYE ON FOR AN FROST POTENTIAL. QUIET  
WEATHER WILL CONTINUE MONDAY.  
 
THE NEXT CHANCE FOR RAIN AND STORMS WILL BE LATE MONDAY NIGHT INTO  
TUESDAY AS ANOTHER TROUGH APPROACHES THE STATE FROM THE PLAINS.  
WINDS SHOULD SHIFT TO SOUTHEASTERLY AHEAD OF THIS APPROACHING TROUGH  
LEADING TO SOME WARMER TEMPERATURES AND WAA FOR TUESDAY. THE SHOWERS  
AND STORM POTENTIALLY IS LIKELY TO EXTEND INTO THE OVERNIGHT  
HOURS TUESDAY WITH SOME BROAD LIFT ACROSS THE REGION. ITS LIKELY  
THAT THE POPS OF 50-80% ARE LIKELY TO TIGHTEN UP IN TIME AS WE  
GET CLOSER TO EARLY NEXT WEEK.  
 
 
   
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/  
 
ISSUED AT 100 PM CDT THU MAY 15 2025  
 
CURRENT CONDITIONS ARE LARGELY VFR ACROSS THE CWA WITH SCT TO  
CLR CONDITIONS MOST EVERYWHERE SAVE FOR AREAS FROM KOSH TO KCWA  
WHERE BKN040 IS LARGELY PRESENT. THROUGH TODAY, VFR CLOUDS  
SHOULD INCREASE AS A WARMER MORE MOIST AIRMASS LIFTS NORTHWARD.  
THUNDERSTORMS ARE EXPECTED TO FORM ALONG A COLD FRONT AND LIFT  
NORTHEAST, MAINLY FROM 21Z TO 03Z THIS EVENING. THESE STORMS  
WILL FEATURE GUSTY WINDS, AND LARGE HAIL. FOLLOWING STORMS,  
SKIES ARE EXPECTED TO REMAIN CLEAR OVERNIGHT AS A DRY SLOT MOVES  
IN, WITH MOSTLY CLEAR WINDS.  
 
VFR CEILINGS RETURN TOMORROW AFTERNOON WITH SFC WIND GUSTS  
BECOMING STRONG OUT OF THE SOUTHWEST TO 35 KNOTS IN SPOTS. THERE  
MAY BE ADDITIONAL SCATTERED THUNDERSTORM DEVELOPMENT IN THE  
AFTERNOON WITH GUSTY WINDS BEING THE PRIMARY THREAT.  
 
 
   
MARINE  
 
ISSUED AT 330 AM CDT WED MAY 15 2025  
 
GIVEN THAT THE ENVIRONMENT WILL CONTINUE TO REMAIN FAVORABLE  
(MOIST AIR OVER THE COOL OPEN WATERS) FOR DENSE FOG UNTIL THIS  
PATTERN BREAKS, THE MARINE DENSE FOG ADVISORY IS IN EFFECT UNTIL  
7PM TODAY. WE MAY BE ABLE TO EXPIRE THAT A LITTLE EARLIER ON  
THURSDAY AS SOUTHEAST WINDS KICK IN, SO THERE IS UNCERTAINTY IN  
THE END TIME. THIS INCLUDES THE BAY AREA, ALTHOUGH WE MAY SEE  
LESS FOGGY CONDITIONS DURING THE DAYLIGHT HOURS THERE.  
 
CRONCE  
 
 
   
GRB WATCHES/WARNINGS/ADVISORIES  
 
WI...NONE.  
MARINE...DENSE FOG ADVISORY UNTIL 7 PM CDT THIS EVENING FOR LMZ521-522-  
541>543.  
SMALL CRAFT ADVISORY UNTIL 1 AM CDT FRIDAY FOR LMZ522.  
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 PM CDT  
THIS EVENING FOR LMZ542-543.  
 
 
 
 
 
DISCUSSION...  
AVIATION...  
MARINE...  
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