666
FXUS63 KGRB 180806
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
306 AM CDT FRI APR 18 2025
FORECAST DISCUSSION FOR ROUTINE MORNING FORECAST ISSUANCE
KEY MESSAGES
- SCATTERED RAIN/STORM ACTIVITY WILL CONTINUE MAINLY SOUTH OF
HIGHWAY 29 THROUGH THE MORNING.
- FOLLOWING A BRIEF LULL IN PRECIP, ADDITIONAL STORM CHANCES
RETURN THIS AFTERNOON. SOME STORMS COULD BECOME STRONG IN AND
AROUND THE FOX VALLEY, WITH LARGE HAIL AND GUSTY WINDS BEING THE
PRIMARY CONCERNS.
- NEXT CHANCES FOR WIDESPREAD PRECIPITATION ARRIVE SUNDAY NIGHT
INTO MONDAY. RAIN/SNOW MIX POSSIBLE.
DISCUSSION
ISSUED AT 305 AM CDT FRI APR 18 2025
SHORT TERM...TODAY...TONIGHT...AND SATURDAY
SHOWERS HAVE GRADUALLY TAPERED OFF DURING THE OVERNIGHT HOURS
WITH THE LOSS OF ELEVATED INSTABILITY, ALTHOUGH IMPRESSIVE DEEP-
LAYER SHEAR ALLOWED FOR SOME EMBEDDED THUNDER ACTIVITY TO
STICK AROUND. WEAK WAKE LOW DEVELOPED OVER CENTRAL WISCONSIN AS
STORM COMPLEX PROPAGATED EAST, AS EVIDENCED BY PRESSURE RISE/FALL
COUPLET SHOWN BY RAP MESOANALYSIS. GUSTS TO 30 MPH WERE REPORTED
ALONG THE REFLECTIVITY GRADIENT NEAR MARSHFIELD.
STILL SOME UNCERTAINTY WITH HOW STRONGER STORM POTENTIAL WILL PLAY
OUT THIS AFTERNOON DUE TO ONGOING SHOWER ACTIVITY IN THE MORNING.
LOW-LEVEL DESTABILIZATION COMES INTO QUESTION AS PREVIOUSLY WORKED
OVER AIRMASS/REMNANT POCKETS OF WAA LOOK TO KEEP CLOUD COVER
AROUND THROUGHOUT THE DAY. LOW TRACK HAS ALSO TRENDED FURTHER
SOUTH, SHUNTING THE BRUNT OF THE WARM SECTOR OFF INTO SOUTHEAST
WISCONSIN. THIS BEING SAID, CAM CONSENSUS APPEARS TO HONE IN ON
AROUND 21Z FOR CONVECTIVE INITIATION AS 850 MB LLJ NUDGES SURFACE
DEWPOINTS IN THE UPPER 50S INTO EAST-CENTRAL WISCONSIN. CONVECTIVE
MODE WILL BE DIFFICULT TO DISCERN UNTIL RADAR TRENDS COME INTO
FOCUS, WITH ELEVATED NATURE OF STORMS FURTHER COMPLICATING CAM
OUTPUT. INITIAL IMPRESSION IS THAT STORM MODE STARTS OFF MORE
CELLULAR, ALTHOUGH CORFIDI DOWNSHEAR VECTOR APPROACHING 100 KNOTS
WOULD SUGGEST SOME SORT OF AMALGAMATION OR UPSCALE GROWTH OF
STORMS INTO A LINE OR COMPLEX. CAVEAT WILL BE OVERCOMING LOW-
LEVEL CAP SET UP BY STABILIZING SOUTHEAST FLOW OFF OF LAKE
MICHIGAN.
MAIN THREAT WITH ANY STORMS THAT DO MANAGE TO BECOME STRONG OR
SEVERE STILL LOOKS TO BE LARGE HAIL. THOUGH BETTER SYNOPTIC
FORCING LOOKS TO BE A LITTLE EARLIER IN THE DAY, THERE REMAINS NO
SHORTAGE OF DYNAMICS WITH THIS SYSTEM. UPPER-LEVEL SUPPORT COMES
IN THE FORM OF THE RIGHT FRONT QUAD OF A 130 KNOT JET WITH
CONJUGATE POSITIVELY-TILTED TROUGH. CORRIDOR OF MUCAPES ~1,500
J/KG LIKEWISE WORK THEIR WAY INTO EAST-CENTRAL WISCONSIN MID-
AFTERNOON AS LAPSE RATES STEEPEN TO 8+ C/KM. LARGE HAIL
DEVELOPMENT WOULD BE FURTHER SUPPORTED BY ELONGATED HODOGRAPHS
AND FRONT-PARALLEL SHEAR. NCAR ML ALGORITHM FLAGS AROUND A 5 TO
10% CHANCE FOR SEVERE HAIL OCCURRENCE IN AND AROUND THE FOX
VALLEY THIS AFTERNOON.
LONG TERM...SATURDAY NIGHT THROUGH THURSDAY
OUR NEXT WEATHERMAKER ARRIVES IN THE FORM OF A COLORADO LOW LATE
THIS WEEKEND AS CLOSED 500 MB ENERGY EJECTS FROM THE FOUR CORNERS
REGION INTO THE MIDWEST. ISENTROPICALLY-FORCED PRECIP SHOULD
START AS RAIN WITHIN WAA REGIME SUNDAY AFTERNOON AS UPPER TROUGH
BECOMES NEGATIVELY-TILTED, WITH A LIKELY CHANGEOVER TO SNOW MONDAY
MORNING AS COLDER AIR WRAPS IN FROM THE NORTHWEST. HOW MUCH SNOW
NORTHERN WISCONSIN RECEIVES WILL HINGE ON THE EXACT TRACK OF THE
SURFACE LOW, WITH ENSEMBLE SPREAD STILL RELATIVELY HIGH AT THIS
TIME. MOST RECENT SUITE OF PROBABILISTIC GUIDANCE SHOWS A 20 TO
40% CHANCE OF RECEIVING TWO INCHES OF SNOWFALL ACROSS NORTH-
CENTRAL WISCONSIN THROUGH MONDAY AFTERNOON. NEXT SYSTEM THEN COMES
RIGHT ON THE HEELS OF THE PREVIOUS, ALTHOUGH THERE IS STILL
SIGNIFICANT DISCREPANCIES IN TIMING/TRACK THIS FAR OUT IN THE
FORECAST PERIOD.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 1018 PM CDT THU APR 17 2025
SHOWERS AND SCATTERED THUNDERSTORMS WILL MOVE ACROSS THE AREA
THROUGH 09Z, THEN A LULL OR BREAK IN THE RAIN UNTIL MID TO LATE
MORNING WHEN ANOTHER ROUND OF SHOWERS AND STORMS WILL IMPACT
CENTRAL AND EAST-CENTRAL WI. A STEADIER RAIN IS EXPECTED FRIDAY
AFTERNOON, WITH SCATTERED THUNDERSTORMS AT TIMES ACROSS EAST-
CENTRAL WISCONSIN. SOME OF THE STRONGER STORMS MAY PRODUCE SMALL
HAIL TONIGHT, WHILE LARGE HAIL MAY BE POSSIBLE ACROSS EAST-CENTRAL
WI FRIDAY AFTERNOON. THE OTHER BIG QUESTION IS WHEN THE LOW
CLOUDS ARRIVE (MVFR/IFR OR LOWER) ARRIVE LATE TONIGHT INTO FRIDAY
MORNING AND SHOULD CONTINUE THROUGH FRIDAY AFTERNOON. CIGS SHOULD
GRADUALLY IMPROVE FRIDAY NIGHT AS THE PRECIPITATION COMES TO AN
END.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....GOODIN
AVIATION.......ECKBERG
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