796  
FXUS63 KGRB 131132  
AFDGRB  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREEN BAY WI  
632 AM CDT TUE MAY 13 2025  
 
UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE  
   
KEY MESSAGES
 
 
- ELEVATED FIRE WEATHER CONDITIONS OVER NORTH-CENTRAL WI THIS  
AFTERNOON DUE TO DRY FUELS, LOW HUMIDITY, AND WINDS GUSTING 15  
TO 20 MPH.  
 
- THERE IS A SMALL CHANCE (15-20%) OF SHOWERS AND THUNDERSTORMS  
THIS AFTERNOON, INCREASING TO 30-40% WEDNESDAY AFTERNOON.  
GREATER CHANCES BOTH DAYS WILL BE OVER CENTRAL WI.  
 
- SHOWERS AND STORMS ARE MOST LIKELY (50-80% CHANCE) THURSDAY  
AFTERNOON AND EVENING. STRONG OR SEVERE STORMS ARE POSSIBLE WITH  
THE PASSAGE OF A COLD FRONT. THE PRIMARY HAZARDS WILL BE LARGE  
HAIL AND DAMAGING WINDS.  
 

 
   
DISCUSSION
 
 
ISSUED AT 324 AM CDT TUE MAY 13 2025  
 
PATTERN STARTING TO SHOW SUBTLE SIGNS OF CHANGING AFTER THE  
PROLONGED PERIOD OF DRY WEATHER. UPPER LOW DRIFTING NORTH ACROSS  
THE OHIO VALLEY ALONG WITH WEAK SFC LOW WILL LEAD TO LESS RIDGING  
EXCEPT FOR FAR NORTH CENTRAL WI TODAY. SE FLOW TO THE NORTH OF LOW  
WILL TRANSPORT MORE MOISTURE INTO SOUTHERN AND EASTERN FORECAST  
AREA WHILE THE NORTH REMAINS UNDER THE INFLUENCE OF DRIER LOW-  
LEVELS AND ONE MORE DAY OF LOWER RH VALUES. LIGHT SHOWERS HAVE  
DEVELOPED IN THE STREAM OF INCREASED MOISTURE AND SOME OF THESE  
COULD IMPACT EAST-CENTRAL WI BEFORE DAYBREAK INTO THE MORNING.  
ALSO AS DEWPOINTS IN THE 50S AND EVEN LOWER 60S FLOW OVER THE  
STILL CHILLY LAKE MICHIGAN WATERS (WATER TEMPS OF 39-42F PER THE  
DEPLOYED BUOYS), MARINE ADVECTION FOG MAY EXPAND EARLY THIS  
MORNING. IF THIS OCCURS, THEN FOG WOULD PUSH ONSHORE ALONG LAKE  
MICHIGAN THIS MORNING, BUT DUE TO MIXING ON LAND, PROBABLY WILL  
NOT MAKE TOO MUCH WESTWARD PROGRESS ON THE LAND THE REST OF THE  
DAY. ISOLATED POP-UP SHOWERS/THUNDER COULD OCCUR INLAND ESPECIALLY  
OVER CENTRAL WI THIS AFTERNOON WHERE HIGHEST DEWPOINTS IN THE  
LOWER 50S, SFC BASED CAPE REACHES 500J/KG. CAPE IS SKINNY AND  
THERE IS MINIMAL EFFECTIVE SHEAR, SO JUST LOOKING AT ISOLATED NON-  
SEVERE STORMS, IF THEY OCCUR. TEMPS TODAY WILL BE SIMILAR TO  
YESTERDAY OVER FAR NORTH-CENTRAL WI WITH LESS CLOUD COVER AND  
DEEPER MIXING. OTHERWISE, HIGHS WILL TREND DOWNWARD WITH MID 70S  
TO LOWER 80S, BUT ONLY AROUND 60 NEAR LAKE MICHIGAN.  
 
MOIST, SOUTHEAST FLOW PERSISTS TONIGHT AND THIS LOOKS TO BRING IN  
BETTER CHANCES FOR AREAS OF FOG/STRATUS AS MARINE ADVECTION FOG  
EXPANDS OFF LAKE MICHIGAN. MOS GUIDANCE PICKING UP ON THE FOG AS  
WELL WHICH MAKES SENSE AS CROSSOVER TEMPS ARE FORECAST TO DROP  
BELOW AFTERNOON DEWPOINTS OVER MUCH OF THE AREA. HAVE EXPANDED  
FOG AND LINGERED THIS INTO WEDNESDAY MORNING. ANOTHER ROUND OF  
POP-UP SHOWERS AND STORMS IS EXPECTED FARTHER INLAND FROM LAKE  
STABILIZING FLOW ON WEDNESDAY AFTERNOON AS SFC BASED CAPES  
INCREASE TO 500 TO 750J/KG FROM CENTRAL TO NORTH-CENTRAL WI.  
AGAIN WITH LIMITED EFFECTED SHEAR, NO SEVERE STORMS ARE EXPECTED.  
WITH MORE CLOUDS TO START THE DAY AND LIMITED MIXING, HIGHS ON  
WEDNESDAY WILL COME DOWN ACROSS THE BOARD WITH READINGS IN THE  
70S ALL AREAS, THOUGH STAYING IN THE 50S NEAR THE LAKE MICHIGAN  
SHORE.  
 
AS HAS LOOKED FOR A WHILE, SETUP BECOMES *MUCH* MORE FAVORABLE  
FOR SEVERE WEATHER THURSDAY AFTERNOON INTO THURSDAY EVENING AS  
NEGATIVELY TILTED UPPER TROUGH EMERGES FROM THE NORTHERN PLAINS  
AND LIFTS ACROSS MN AND WI. DECENT DYNAMICS WITH THE SYSTEM GIVEN  
HEIGHT FALLS FROM THE TROUGH ALONG WITH 60+ KT H5 JET NOSING INTO  
WI DURING PEAK HEATING ACTING UPON ROBUST INSTABILITY WITH MLCAPES  
EXCEEDING 2500J/KG (HIGHS BOUNCING BACK UP INTO THE UPPER 70S TO  
LOWER EVEN MID 80S) AND MID-LEVEL LAPSE RATES OVER 7.5C/KM AHEAD  
OF APPROACHING COLD FRONT. LOW-LEVELS FAIRLY VEERED, SO WIND AND  
HAIL ARE THE PRIMARY CONCERNS. KIND OF EARLY TO GET INTO THESE  
DETAILS, BUT GIVEN LENGTH OF HODOGRAPHS AND RELATIVELY LOW WBZERO  
HEIGHTS (UP TO 9KFT) WITH THE DEGREE OF THE INSTABILITY FORECAST,  
IF STORMS REMAIN MORE DISCRETE, HAIL COULD END UP BIGGER THAN THE  
LOWER THRESHOLD FOR SEVERE HAIL (ONE INCH IN DIAMETER). WILL BE  
SOMETHING TO WATCH. SOME POTENTIAL THAT STORMS COULD GROW UPSCALE,  
LEADING TO MORE OF A DAMAGING WIND AND POSSIBLY SPIN UP QLCS  
TORNADO SCENARIO. A LOT OF QUESTIONS TO SORT OUT, BUT SPC DOES NOW  
HAVE ALL BUT FAR NORTHERN WI IN A SLIGHT RISK FOR DAY3/THURSDAY.  
 
ADDITIONAL SHOWERS AND MAYBE THUNDER OCCURS ON FRIDAY AS SECONDARY  
SHORTWAVE SLIDES ACROSS THE AREA. AS MAIN SURFACE LOW CROSSES  
UPPER MICHIGAN AND LAKE SUPERIOR LATE FRIDAY INTO SATURDAY PUSHING  
A SECONDARY COLD FRONT ACROSS THE AREA, SOME SCATTERED SHOWERS  
REMAIN IN THE FORECAST ON SATURDAY, ESPECIALLY OVER NORTHERN WI.  
TEMPS WILL COOL SUBSTANTIALLY WITH HIGHS 60S TO LOWER 70S ON  
FRIDAY, BUT ONLY IN THE 50S TO LOWER 60S ON SATURDAY BEHIND THE  
SECONDARY COLD FRONT. REST OF EXTENDED FEATURES TEMPS STAYING  
AT OR SLIGHTLY BELOW NORMAL. WITH HIGH PRESSURE CLOSE BY AND  
WINDS BECOMING LIGHT, SATURDAY NIGHT AND/OR SUNDAY NIGHT COULD  
SEE PATCHY FROST OVER THE NORTH. NEXT CHANCE OF RAIN RETURNS ON  
TUESDAY.  
 

 
   
AVIATION
 
FOR 12Z TAF ISSUANCE  
ISSUED AT 631 AM CDT TUE MAY 13 2025  
 
MARINE STRATUS AND FOG ON A SOUTHEAST WIND WILL AFFECT THE  
LAKESHORE THIS MORNING (LIFR TO IFR AT MTW), BEFORE CONTRACTING  
BACK OVER THE LAKE THIS AFTERNOON. MVFR STRATUS MAY IMPACT FOX  
VALLEY LOCATIONS (GRB/ATW) AT TIMES THIS MORNING. ELSEWHERE EXPECT  
VFR TO PREVAIL. SLIGHT IMPROVEMENT FOR THIS AFTERNOON FOX VALLEY  
EASTWARD, THEN TONIGHT, EXPECT THE STRATUS AND FOG TO SPREAD OVER  
MOST OF THE AREA. LOWEST CONDITIONS (LIFR AT TIMES) WILL BE NEAR  
THE LAKE AT MTW, BUT OCCASIONAL IFR WILL IMPACT GRB AND ATW. IFR  
CIGS MAY MAKE IT TO CENTRAL AND NORTH-CENTRAL TAF SITES (RHI, AUW  
AND CWA) OVERNIGHT.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 324 AM CDT TUE MAY 13 2025  
 
FIRE WEATHER CONDITIONS WILL BEGIN TO STEP DOWN FROM THE CRITICAL  
CONDITIONS SEEN SUNDAY AND MONDAY AS MOISTURE BEGINS TO INCREASE  
ACROSS THE AREA WITH MORE CLOUDS DURING THE PEAK HEATING OF THE  
DAY, ESPECIALLY CENTRAL AND EAST-CENTRAL WI. CONDITIONS WILL REMAIN  
ELEVATED FOR ONE MORE DAY OVER NORTH-CENTRAL WI THOUGH AS MINIMUM  
RH DROPS TO 25 TO 35 PERCENT AND HIGH TEMPS REACH THE LOWER 80S.  
WINDS WILL BE LIGHTER COMPARED TO SUNDAY AND MONDAY, WITH SUSTAINED  
WINDS UP TO 10 MPH AND GUSTS REMAINING LESS THAN 20 MPH. A SPECIAL  
WEATHER STATEMENT HAS BEEN ISSUED FOR NORTH-CENTRAL WI TO COVER  
THE ELEVATED CONDITIONS.  
 

 
   
GRB WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  
 

 
 

 
 
DISCUSSION.....JLA  
AVIATION.......JLA  
FIRE WEATHER...JLA  
 
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