785
FXUS63 KGRB 181147
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
647 AM CDT WED JUN 18 2025
UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE
KEY MESSAGES
- RISK OF WIDESPREAD HEAVY RAIN AND SEVERE WEATHER HAS SHIFTED OUT OF
THE AREA TODAY. ANY STORMS COULD STILL PRODUCE GUSTY WINDS,
SMALL HAIL AND HEAVY DOWNPOURS.
- THUNDERSTORMS WILL BE POSSIBLE AT TIMES FROM THURSDAY THROUGH
SATURDAY. MOST FAVORED WINDOWS FOR SEVERE THUNDERSTORMS ARE
THURSDAY AFTERNOON AND EVENING, THEN AGAIN FRIDAY AFTERNOON INTO
SATURDAY MORNING. THERE IS A CHANCE OF THUNDERSTORMS EARLY NEXT
WEEK, HOWEVER IT IS TOO EARLY TO DETERMINE IF THE STORMS WOULD
BECOME SEVERE.
- PROLONGED PERIOD OF DANGEROUS HEAT IS EXPECTED SATURDAY THROUGH
MONDAY AS HOTTEST TEMPERATURES OF THE YEAR OCCUR. HEAT INDEX
VALUES MAY REACH THE MIDDLE 90S TO AROUND 100 DEGREES EACH
AFTERNOON. LOW TEMPERATURES IN THE 70S WILL PROVIDE MINIMAL RELIEF
TO THE HEAT AND HUMIDITY.
DISCUSSION
ISSUED AT 310 AM CDT WED JUN 18 2025
SHORT TERM...TODAY...TONIGHT...AND THURSDAY
SHORTWAVE TROUGH OVER THE CENTRAL CONUS THAT HELPED DEVELOP STRONG
MCS OVER THE SOUTHERN PLAINS STILL ONGOING EARLY THIS MORNING LIFTS
ACROSS WESTERN GREAT LAKES TODAY. CONVECTIVELY MODULATED LOW COMING
OUT OF THE NORTHERN PORTION OF THE MCS IS NOW FORECAST TO TRACK
WELL TO THE SOUTHEAST OF OUR AREA, APPROXIMATELY FROM CHICAGO TO
SOUTHERN LOWER MICHIGAN. RESULT IS LESS POTENTIAL FOR SEVERE WEATHER
OR WIDESPREAD MODERATE TO HEAVY RAIN TODAY AS SHOWN BY TRIMMING OF
SPC DAY1 CONVECTIVE OUTLOOK AND WPC DAY1 EXCESSIVE RAINFALL OUTLOOK.
STILL COULD BE SHOWERS AND ISOLATED STORMS, ESPECIALLY DURING THE
PEAK HEATING OF THE DAY. SHORTWAVE TROUGH DROPPING ACROSS NORTHERN
LAKES THURSDAY AFTERNOON WILL BRING NEXT CHANCE OF SHOWERS AND
STORMS.
STORMS/SEVERE WEATHER POTENTIAL...MODELS ARE IN GOOD AGREEMENT
TRACKING MAIN COMPACT SFC LOW GENERALLY SOUTH OF WI TODAY. THUS,
GREATER BACKED FLOW AND EFFECTIVE SHEAR/HELICITY THAT IS EXPECTED
TO BOOST SEVERE WEATHER POTENTIAL WILL REMAIN WELL TO THE SOUTHEAST
OF HERE, CLOSER TO WHERE SPC HAS OUTLINED ENHANCED RISK OF SEVERE.
WEAK WAVE IN NORTHWEST FLOW ALONG WITH DAYTIME HEATING AND BUILD
UP OF SBCAPES TO 500-750J/KG WITH EFFECTIVE SHEAR OF 25-30KT COULD
RESULT IN ISOLATED STRONGER STORMS THIS AFTERNOON FROM NORTH-CENTRAL
TO CENTRAL WI. THOUGH NO SEVERE STORMS ARE EXPECTED, STRONGER STORMS
MAY PRODUCE GUSTY WINDS, SMALL HAIL AND BRIEF HEAVY DOWNPOURS.
REMNANTS OF THESE SHOWERS AND STORMS MAY LINGER MUCH OF THE NIGHT
AS SHORTWAVE TROUGH AXIS CROSSES.
ON THURSDAY, SHARPER WAVE IN NORTHWEST FLOW ALOFT (ALONG WITH MORE
DEFINED LOW-LEVEL JET) WILL BRING AN INCREASE OF SHEAR. INSTABILITY
FORECAST TO BE GREATER WITH BETTER SHOT OF SEEING SBCAPES AROUND
1000J/KG MID TO LATE AFTERNOON. ISOLATED TO PERHAPS SCATTERED
STORMS WILL FORM OVER UPPER MICHIGAN, NORTH-CENTRAL WI INTO FAR
NORTHEAST WI DUE TO WEAK CONVERGENCE WHICH MAY BE ENHANCED BY
LAKE BREEZES OFF SUPERIOR AND EVEN THE BAY AND NORTHERN LAKE
MICHIGAN. ACTIVITY WILL SINK SOUTHEAST INTO THE EARLY EVENING,
MAYBE REACHING THE FOX VALLEY IF SOME OF THE MORE AGGRESSIVE
MODELS (IN TERMS OF SOUTHERN EXTENT) VERIFY. THURSDAY SHOWING
HIGHER PROBABILITIES OF SEEING SUFFICIENT SHEAR AND INSTABILITY
TO SUPPORT AT LEAST ISOLATED SEVERE RISK IN STRONGER STORMS. NOT A
SLAM DUNK, BUT ELONGATED HODOGRAPHS AND WET-BULB ZERO HEIGHTS
AROUND 9KFT POINT TO RISK OF LARGE HAIL IN STRONGEST STORMS.
SFC-DELTA THETA-E VALUES OVER 20 AND LOW-LEVEL LAPSE RATES UP TO
8-9C/KM COULD SUPPORT DAMAGING WIND GUSTS. SPC DAY2 CONTINUES TO
HIGHLIGHT OUR AREA FOR A MARGINAL RISK (LEVEL 1 OF 5) OF SEVERE
STORMS.
TEMPERATURES/FOG...BUMPED HIGHS UPWARD NORTHEAST AND EAST-CENTRAL
TODAY GIVEN LESS CHANCE OF WIDESPREAD RAIN AND STIFF NORTHEAST
WINDS WITH THE SFC LOW TRENDING FARTHER SOUTHEAST. HIGHS OVER
CENTRAL TO NORTH-CENTRAL WI WILL HAVE CHANCE TO MAKE RUN AT 80.
MARINE FOG IS NOTED OVER NORTHERN DOOR COUNTY EARLY THIS MORNING
WITH OBS AND WEBCAMS SHOWING LOCALLY DENSE FOG AT TIMES. NOT SURE
ON EXTENT OF THE FOG BACK ACROSS THE LAKE, BUT CARRIED AREAS OF
FOG FOR THESE AREAS THROUGH MID MORNING FOR NOW. ALSO SEEING SOME
PATCHY RADIATIONAL GROUND FOG OVER NORTH-CENTRAL WI, SO HAVE ADDED
THIS IN THROUGH DAYBREAK THIS MORNING. MAY SEE SOME OF THIS IN
SIMILAR AREAS TONIGHT ESPECIALLY WHERE SHOWERS AND STORMS DEVELOP
THIS AFTERNOON. ON THURSDAY, MAJORITY OF DAY WILL FEATURE WESTERLY
WINDS KEEPING LAKE MODIFICATION AT BAY. MIXING TO 850MB SUPPORTED
PUSHING HIGHS INTO THE MID 80S ALL THE WAY TO THE SHORELINE. LAKE
BREEZES DEVELOP LATER IN THE DAY WHICH WILL LEAD TO LOCALIZED
COOLING NEAR THE BAY AND LAKE MICHIGAN.
LONG TERM...THURSDAY NIGHT THROUGH TUESDAY
A FAIRLY ZONAL FLOW IS NOTED AT 500MB AT THE BEGINNING OF
THE PERIOD, WITH SEVERAL WEAK UPPER LEVEL DISTURBANCES MOVING
WITH THE MEAN FLOW. OVER THE UPCOMING WEEKEND, 500MB RIDGE WILL
BUILD ACROSS THE SOUTHEAST UNITED STATES WHICH WILL RESULT IN
THE HOTTEST TEMPERATURES SO FAR THIS YEAR. BASED ON THE LATEST
GFS/ECMWF MODELS, THE AREA WILL REMAIN IN THE RING OF FIRE
THROUGH THE MIDDLE OF NEXT WEEK WHICH WILL RESULT IN AT LEAST
A FEW ROUNDS OF THUNDERSTORMS. AT SOME POINT NEXT WEEK, OUTFLOW
BOUNDARIES FROM ONE OF THE COMPLEXES OF STORMS WILL LIKELY PUSH
THE SURFACE FRONT SOUTHWARD AT SOME POINT.
FOR THURSDAY EVENING, A WEAK IMPULSE WILL BE MOVING ACROSS THE
REGION WHICH WILL RESULT IN THE CHANCES OF SHOWERS AND STORMS
LINGERING INTO THE EVENING. A FEW STRONG OR SEVERE STORMS ARE
STILL POSSIBLE THROUGH MID EVENING. AS THE IMPULSE MOVES AWAY
FROM THE AREA, THE NEXT FOCUS FOR CONVECTION WILL BE ALONG A
WARM FRONT WHICH THE MODELS HAVE A LITTLE BIT FURTHER SOUTH
TONIGHT COMPARED TO LAST NIGHT. THE NEXT IMPULSE MOVES ACROSS
THE REGION FRIDAY AFTERNOON, COMBINED WITH DAYTIME HEATING WILL
RESULT IN SURFACE CAPE VALUES OF 1,000-2,000 J/KG AND 0-6 KM
SHEAR VALUES OF 30-40 KNOTS TO SUPPORT THE POTENTIAL FOR STRONG
OR SEVERE STORMS FRIDAY AFTERNOON AND EVENING.
ATTENTION THEN TURNS TO LATE FRIDAY NIGHT AND SATURDAY MORNING AS
MODELS ARE DEPICTING A COMPLEX OF THUNDERSTORMS MOVING ACROSS THE
UPPER MIDWEST. THERE IS STILL A GREAT DEAL OF UNCERTAINTY IN THE
SOUTHWARD EXTENT OF THE COMPLEX, THUS HIGHEST CHANCES FOR RAIN
WILL BE ACROSS THE NORTH. RAIN CHANCES LINGER INTO SATURDAY
MORNING UNTIL THE COMPLEX PUSHES EAST OF THE AREA. FOR SATURDAY
AFTERNOON, STRONG CAPPING NOTED ON BUFKIT SOUNDINGS. IF A STORM
DID BREAK THROUGH THE CAP, AT LEAST 4,000 TO 5,000 J/KG OF CAPE
AND SPEED SHEAR OF AT LEAST 30 KNOTS WOULD SUPPORT ANY STORM
DEVELOPMENT TO GO SEVERE QUICKLY.
THE MAJOR STORY FOR THE WEEKEND WILL BE THE HOTTEST TEMPERATURES
OF THE YEAR. WITH THE RECENT COOL SPELL OVER THE PAST MONTH,
THE BUILDING HEAT WILL BE A CONCERN AS HIGHS IN THE UPPER 80S
TO MIDDLE 90S WITH HEAT INDEX READINGS IN THE 90S TO AROUND 100
DEGREES ARE EXPECTED SATURDAY AND SUNDAY, AND POSSIBLE MONDAY
ACROSS EASTERN WISCONSIN. IT IS POSSIBLE HEAT HEADLINES WILL BE
NEEDED SINCE CRITERIA FOR AN ADVISORY IS 100F. TO COMPLICATE
MATTERS, LOW TEMPERATURES SATURDAY NIGHT AND SUNDAY NIGHT WILL
LIKELY BE IN THE 70S PROVIDING LITTLE RELIEF FROM THE HEAT.
A COLD FRONT WILL APPROACH THE AREA MONDAY, BRINGING ANOTHER ROUND
OF THUNDERSTORMS. FOR TUESDAY AND WEDNESDAY, THE ECMWF HAS THE
FRONT MEANDERING ACROSS THE REGION WHICH SUPPORT SEVERAL ROUNDS
OF THUNDERSTORMS. WITH THE AMOUNT OF HEAT AND INSTABILITY AROUND,
IT IS POSSIBLE SOME THESE STORMS COULD BECOME STRONG OR
SEVERE MONDAY AND TUESDAY. AT SOME POINT, IT IS LIKELY ONE OF THE
COMPLEXES OF STORMS WILL PUSH THE FRONT FAR ENOUGH SOUTH TO PUSH
THE AXIS OF HEAVY RAIN SOUTH OF THE AREA.
AVIATION
FOR 12Z TAF ISSUANCE
ISSUED AT 647 AM CDT WED JUN 18 2025
LOW PRESSURE TRACKING SOUTHEAST OF THE REGION THROUGH THIS
AFTERNOON WILL BRING OCCASIONAL LIGHT TO MODERATE SHOWERS AND
POSSIBLE AN EMBEDDED STORM OR TWO TO THE SOUTHEAST HALF OF THE
FORECAST AREA. MARINE STRATUS AND FOG MAY SKIRT THE LAKE MICHIGAN
SHORELINE THIS MORNING, INCLUDING MTW. DEEPER INTO THE AFTERNOON,
EXPECT SCATTERED THUNDERSTORMS TO DEVELOP FROM CENTRAL AND NORTH-
CENTRAL WI TO FAR NORTHEAST WI. THESE SHOWERS AND STORMS WILL THEN
DRIFT SOUTHEAST THROUGH THE EARLY EVENING. POSSIBLE TRIGGERS
INCLUDE A LAKE BREEZE OR OUTFLOW BOUNDARY, AND THE RRQ OF AN UPPER
JET STREAK. WILL CONTINUE THE TEMPO GROUPS FOR THUNDERSTORMS AT
RHI/AUW/CWA TAFS, WITH MINOR ADJUSTMENTS TO THE PREVIOUS TIMING.
MAY ALSO SEE RUMBLES OF THUNDER ON THE NORTH EDGE OF WIDESPREAD
RAIN TO THE SOUTH IMPACT MTW LATE THIS AFTERNOON INTO EARLY EVENING.
WINDS WILL BE LIGHT AND VARIABLE ACROSS MOST OF THE AREA, WITH A
PREVAILING EASTERLY COMPONENT NEAR LAKE MICHIGAN DURING THE
DAYTIME. WINDS WILL SWITCH TO THE NORTHWEST OVERNIGHT TONIGHT.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....JLA/ECKBERG
AVIATION.......JLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page