122  
FXUS63 KGRB 140155  
AFDGRB  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREEN BAY WI  
ISSUED BY NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI  
855 PM CDT TUE MAY 13 2025  
   
KEY MESSAGES  
 
- AREAS OF DENSE FOG ALONG THE LAKESHORE THIS EVENING MAY  
AFFECT EASTERN COUNTIES OVERNIGHT. MARINE DENSE FOG ADVISORY  
FOR NEARSHORE AREAS SOUTH OF STURGEON BAY.  
 
- THERE IS A CHANCE (30-40%) WEDNESDAY AFTERNOON FOR CENTRAL  
WI.  
 
- SHOWERS AND STORMS ARE MOST LIKELY (50-80% CHANCE) THURSDAY  
AFTERNOON AND EVENING. SEVERE STORMS ARE POSSIBLE WITH THE  
PASSAGE OF A COLD FRONT WITH ALL HAZARDS POSSIBLE.  
 
 
   
DISCUSSION  
 
ISSUED AT 856 PM CDT TUE MAY 13 2025  
 
DENSE FOG OF 1/4 MILE VISIBILITY OR LESS IS SLOWLY SPREADING  
INLAND FROM LAKE MICHIGAN IN KEWAUNEE AND MANITOWOC COUNTIES. A  
DENSE FOG ADVISORY IS IN EFFECT FOR THESE COUNTIES THROUGH 10 AM  
CDT WEDNESDAY. THIS FOG BANK MAY CONTINUE INLAND INTO THE FOX  
VALLEY TONIGHT, BUT CONFIDENCE IS LOWER FOR WIDESPREAD DENSE FOG  
IN THIS REGION DUE TO ADVECTIVE WINDS WEAKENING AND WARMER  
TEMPERATURES PERSISTING IN THE VALLEY ITSELF. AS MID-LEVEL  
CLOUDS CLEAR LATE TONIGHT INTO EARLY WEDNESDAY MORNING,  
TEMPERATURES WILL FALL TO NEAR DEWPOINT TEMPERATURES AND AREAS  
OF FOG, LOCALLY DENSE (1/4 TO 1/2 MILE VISIBILITY), WILL  
DEVELOP ACROSS MUCH OF EASTERN WISCONSIN, WITH PATCHY FOG AT 1  
TO 3 MILE VISIBILITY ACROSS CENTRAL WISCONSIN. IF TEMPERATURES  
COOL QUICKLY ENOUGH TONIGHT, DENSE FOG ADVISORIES MAY ALSO BE  
NEEDED IN THE FOX VALLEY AND DOOR COUNTY LATE TONIGHT INTO  
WEDNESDAY MORNING.  
 
PREVIOUS DISCUSSION  
 
A CLOSED UPPER LOW SPINNING OVER THE UPPER GREAT LAKES REGION  
WILL CONTINUE TO BRING MOIST, SOUTHEAST FLOW INTO EASTERN WI  
THROUGH WEDNESDAY NIGHT. DEWPOINTS HAVE INCREASED INTO THE LOWER  
60S EAST TO THE MID 50S CENTRAL AND CLOUDS ARE WIDESPREAD.  
THERE ARE A FEW LIGHT SHOWERS OUT THERE WEST OF THE FOX VALLEY.  
MARINE FOG IS LOOMING OVER THE OPEN WATERS OF LAKE MICHIGAN, AND  
THE LIGHT EASTERLY BREEZE TONIGHT AND ABUNDANT LOW LEVEL  
MOISTURE IS EXPECTED TO HELP USHER THAT FOG INLAND OVERNIGHT.  
THE LAKESHORE CITIES AND TOWNS MAY SEE FOG AS EARLY AS 9PM, BUT  
IT SHOULD TAKE A LITTLE LONGER FOR IT TO OVERSPREAD THE REST OF  
THE FOX VALLEY, PROBABLY AFTER MIDNIGHT. FOR AREAS WEST OF THE  
FOX VALLEY, FOG SHOULD BE MORE PATCHY AND LESS DENSE. A DENSE  
FOG ADVISORY MAY BE NEEDED TONIGHT FOR EASTERN AREAS.  
 
ANOTHER ROUND OF POP-UP SHOWERS AND STORMS IS EXPECTED FARTHER  
INLAND FROM THE LAKE STABILIZING FLOW ON WEDNESDAY AFTERNOON AS  
SFC BASED CAPE INCREASES TO 500 TO 750 J/KG FROM CENTRAL TO  
NORTH- CENTRAL WI. AGAIN WITH LIMITED EFFECTIVE 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  
LOWER 60S NEAR THE LAKE MICHIGAN SHORE.  
 
MRC  
 
THURSDAY THROUGH TUESDAY:  
 
THE MAIN FOCUS FOR THURSDAY REMAINS ON THE POTENTIAL FOR SEVERE  
THUNDERSTORMS ACROSS MOST OF WISCONSIN. QUESTIONS REMAIN ABOUT STORM  
COVERAGE AND MODE, ESPECIALLY ACROSS THE SOUTHERN PORTION OF THE  
STATE.  
 
A STRONGLY CAPPED ELEVATED MIXED LAYER WILL BE BUILDING INTO  
WISCONSIN STARTING THURSDAY MORNING, AS A WARM FRONT SURGES NORTH  
ACROSS THE REGION. THIS EML WILL FEATURE STEEP MID LEVEL LAPSE RATES  
ON THE ORDER OF 7.5-8 DEG C/KM, ATOP AN INVERSION CENTERED BETWEEN  
850 AND 750 MB. A FEW SHOWERS OR PERHAPS A THUNDERSTORM OR TWO MAY  
BE ONGOING ALONG THE LEADING EDGE OF THE EML EARLY THURSDAY, MAINLY  
ACROSS THE NORTHERN PORTIONS OF THE STATE, BUT FOR THE MOST PART THE  
STRONG CAP SHOULD LIMIT SHOWER/THUNDERSTORM ACTIVITY THROUGH AT  
LEAST EARLY AFTERNOON. AT THE SURFACE, SOUTH TO SOUTHEAST FLOW WILL  
SUPPORT WARMING TEMPERATURES AWAY FROM LAKE MICHIGAN, WITH MID TO  
UPPER 80S POSSIBLE OVER SOUTH CENTRAL WISCONSIN, AND UPPER 70S TO  
LOW 80S OVER THE CENTRAL AND NORTHERN PORTIONS OF THE STATE. THE  
SOUTHEAST FLOW WILL RESULT IN A GRADIENT WITH TEMPERATURES  
STRETCHING FROM RACINE AND MILWAUKEE NORTHWESTWARD TOWARD GREEN BAY,  
WITH PROGRESSIVELY COOLER READINGS EAST OF THIS LINE (I.E., TOWARD  
THE LAKE), WITH LOCATIONS RIGHT ALONG THE LAKESHORE LIKELY REMAINING  
IN THE 60S.  
 
SURFACE MOISTURE WILL ALSO INCREASE THROUGH THE DAY, WITH DEWPOINTS  
EXPECTED TO RISE INTO THE UPPER 50S TO MID 60S, HIGHEST WITH  
SOUTHWARD EXTENT. THIS IS EXPECTED TO RESULT IN A LARGE REGION OF  
2000+ J/KG OF MLCAPE ACROSS MUCH OF THE STATE BY EARLY AFTERNOON.  
 
A SHORTWAVE ASSOCIATED WITH THE UPPER LOW CENTERED OVER SOUTH DAKOTA  
WILL SURGE EASTWARD TOWARD THE REGION DURING THE AFTERNOON HOURS,  
ALONG WITH A COLD FRONT AT THE SURFACE, WITH THE FRONT CURRENTLY  
EXPECTED TO REACH THE MISSISSIPPI RIVER BETWEEN 1 AND 4 PM. AT THE  
SAME TIME, INCREASINGLY FAST FLOW AT 500 AND 300 MB WILL BE  
OVERSPREADING THE AREA FROM THE WEST, RESULTING IN 30-50 KT OF DEEP  
LAYER SHEAR ACROSS THE REGION.  
 
MID LEVEL DRY AIR REMAINS THE GREATEST WRINKLE IN THE FORECAST FOR  
THURSDAY. WHILE MOST MODEL GUIDANCE SUGGESTS QUITE A BIT OF DRY AIR,  
ESPECIALLY IN THE 700-500 MB LAYER, THERE ARE DIFFERENCES AMONG THE  
VARIOUS MODELS. ULTIMATELY THIS WILL BOIL DOWN TO IF AND WHERE THE  
COMBINATION OF LARGE SCALE LIFT AND A WARM AND MOIST LOW LEVEL  
AIRMASS IS SUFFICIENT TO OVERCOME THE DRY AIR.  
 
WITH ALL OF THAT SAID, IF/WHERE CONVECTION IS INDEED ABLE TO  
OVERCOME THE DRY MID LEVELS, CONVECTIVE INITIATION IS EXPECTED TO  
OCCUR DURING THE EARLY TO MID AFTERNOON HOURS ALONG AND JUST AHEAD  
OF THE FRONT. INITIAL MODE WOULD LIKELY BE DISCRETE TO SEMI-  
DISCRETE, WITH MORE THAN SUFFICIENT SHEAR PROFILES FOR SUPERCELLS.  
TORNADOES AND LARGE TO VERY LARGE HAIL WILL BE POSSIBLE WITH ANY  
SUSTAINED SUPERCELLS. WITH TIME, CONVECTION SHOULD BECOME MORE  
LINEAR IN NATURE, LIKELY FROM NORTH TO SOUTH, SINCE FRONTAL AND  
UPPER LEVEL FORCING WILL BE STRONGER ACROSS THE NORTHERN HALF OF THE  
STATE. THE RISK FOR STRAIGHT LINE WINDS WILL INCREASE WITH ANY  
LINEAR SEGMENTS, ALONG WITH A CONTINUED HAIL AND A QLCS TORNADO  
RISK.  
 
CONVECTION IS EXPECTED TO MOVE EAST-NORTHEASTWARD, AND IF CURRENT  
TRENDS HOLD WOULD BE EXPECTED TO CROSS INTO THE COOLER LAKE-INDUCED  
AIRMASS AND EVENTUALLY OVER LAKE MICHIGAN BY LATE EVENING (10 PM-  
MIDNIGHT).  
 
QUIET WEATHER IS EXPECTED THURSDAY NIGHT AND EARLY FRIDAY MORNING AS  
A SUBTLE SURFACE RIDGE PASSES THROUGH THE AREA. BY LATER FRIDAY,  
ADDITIONAL CONVECTION WILL BE POSSIBLE AS THE UPPER LOW BEGINS TO  
PIVOT SOUTHEASTWARD INTO MINNESOTA, AND ASSOCIATED SURFACE ENERGY  
PUSHES ACROSS THE STATE. WHILE DEWPOINTS WILL ONLY BE IN THE LOW  
50S, CONTINUED STEEP LAPSE RATES AND FAST FLOW ALOFT WILL SUPPORT  
1000+ J/KG OF MLCAPE AND AROUND 30 KNOTS OF DEEP LAYER SHEAR FRIDAY  
AFTERNOON. HAIL SHOULD BE THE GREATEST RISK WITH THIS ACTIVITY,  
THOUGH A POTENTIALLY WELL MIXED BOUNDARY LAYER (I.E., RELATIVELY  
HIGH CLOUD BASES) MAY ALSO BE SUPPORTIVE OF DOWNBURSTS.  
 
THE UPPER LOW IS THEN EXPECTED TO FINALLY MOVE THROUGH THE REGION ON  
SATURDAY, WITH CONTINUED CHANCES FOR SHOWERS, BEFORE RAIN CHANCES  
END SATURDAY NIGHT.  
 
HIGH PRESSURE IS EXPECTED TO BUILD SOUTH FOR SUNDAY AND POTENTIALLY  
INTO MONDAY. BY THE EARLY PORTION OF NEXT WORKWEEK, ADDITIONAL  
SHORTWAVE ENERGY WILL BRING RENEWED CHANCES FOR SHOWERS AND  
THUNDERSTORMS TO THE WESTERN GREAT LAKES.  
 
BOXELL  
 
 
   
AVIATION /00Z TAFS THROUGH 00Z THURSDAY/  
 
ISSUED AT 659 PM CDT TUE MAY 13 2025  
 
MAIN CONCERN OVERNIGHT WILL BE MOISTURE FLOW OFF LAKE MICHIGAN  
CREATING LOW CEILINGS AND FOG. ONSHORE WINDS AT MTW HAVE ALREADY  
LED TO REDUCED VISIBILITIES AND LIFR CEILINGS, WITH THOSE  
CONDITIONS EXPECTED TO MOVE INLAND TONIGHT, AFFECTING THE FOX  
VALLEY AND LAKE MICHIGAN AREAS. FARTHER WEST AND NORTH, STILL  
ANTICIPATING FOG DEVELOPMENT, BUT ANY IFR/LIFR CONDITIONS WILL  
REMAIN PATCHY. IN NORTH-CENTRAL WISCONSIN, EXPECTING ANY FOG  
DEVELOPMENT TO KEEP VISIBILITIES IN THE MVFR RANGE, BUT STILL  
EXPECTING LOW CEILINGS DURING THE LATE OVERNIGHT TO EARLY  
WEDNESDAY MORNING TIMEFRAME.  
 
WINDS BECOME STEADY AND SOUTHEASTERLY INTO WEDNESDAY MORNING,  
ALLOWING FOG AND CLOUDS TO MIX OUT BY THE AFTERNOON HOURS.  
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TO  
DEVELOP IN NORTH-CENTRAL TO CENTRAL WISCONSIN DURING THE  
AFTERNOON HOURS, ENDING AROUND SUNSET ONCE AGAIN.  
 
MH  
 
 
   
MARINE  
 
ISSUED AT 1019 AM CDT TUE MAY 13 2025  
 
EXPANDED THE MARINE DENSE FOG ADVISORY NORTHWARD ONE ZONE TO  
INCLUDE AREAS SOUTH OF STURGEON BAY. THE MARINE FOG IS EXPECTED  
TO STICK AROUND THROUGH AT LEAST WEDNESDAY MORNING DUE TO LIGHT,  
MOIST EASTERLY FLOW OVER THE COLD OPEN WATERS. AN ADDITIONAL  
NORTHWARD EXPANSION TO INCLUDE THE DOOR PENINSULA WILL BE  
POSSIBLE, BUT MORE UNCERTAINTY REMAINS.  
 
 
   
GRB WATCHES/WARNINGS/ADVISORIES  
 
WI...DENSE FOG ADVISORY UNTIL 10 AM CDT WEDNESDAY FOR WIZ040-050.  
MARINE...DENSE FOG ADVISORY UNTIL 1 PM CDT WEDNESDAY FOR LMZ542-543.  
 
 
 
 
 
DISCUSSION...  
AVIATION...  
MARINE...  
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