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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