661
FXUS63 KGRB 171751
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
ISSUED BY NATIONAL WEATHER SERVICE MARQUETTE MI
1251 PM CDT THU APR 17 2025
UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE
KEY MESSAGES
- RAIN/STORM CHANCES RETURN THIS AFTERNOON AND CONTINUE THROUGH
FRIDAY. SOME STORMS FRIDAY AFTERNOON COULD BECOME STRONG TO
SEVERE IN AND AROUND THE FOX VALLEY, WITH LARGE HAIL BEING THE
MAIN THREAT.
- NEXT CHANCES FOR WIDESPREAD PRECIPITATION ARRIVE SUNDAY NIGHT
INTO MONDAY. MIXED PRECIP TYPES POSSIBLE.
DISCUSSION
ISSUED AT 200 AM CDT THU APR 17 2025
SHORT TERM...TODAY...TONIGHT...AND FRIDAY
QUIET WEATHER PERSISTED OVERNIGHT WITH GOES IR IMAGERY SHOWING
SCATTERED MID-LEVEL STRATOCU DECK GRADUALLY THINNING OUT.
TEMPERATURES WERE ABLE TO DROP DOWN INTO THE LOW 30S ALONG THE
UPPER PENINSULA BORDER WHERE CLEARING WAS MORE PROLONGED.
THIS EVENING THROUGH FRIDAY... SHORT-TERM FORECAST CONCERNS ONCE
AGAIN RESIDE WITH RAIN/STORM CHANCES BEGINNING THIS EVENING,
RAMPING UP INTO FRIDAY AFTERNOON. THERE IS CERTAINLY NO SHORTAGE
OF DYNAMICS WITH THIS SYSTEM AS A POSITIVELY-TILTED TROUGH PHASES
WITH AN UPPER-LEVEL DISTURBANCE ORIGINATING FROM CANADA, TRACKING
THROUGH THE UPPER MISSISSIPPI VALLEY FRIDAY EVENING. SURFACE LOW
ORGANIZES OVER THE CENTRAL PLAINS DURING THIS TIME, EVENTUALLY
BRINGING OUR FIRST ROUND OF SCATTERED SHOWERS AND STORMS WITHIN
WAA REGIME THURSDAY AFTERNOON. 45 TO 50 KNOT LLJ NOSES INTO
CENTRAL WISCONSIN DURING THIS TIME AS ELEVATED INSTABILITY (1,000+
J/KG MUCAPE) WORKS IN AHEAD OF THE COLD FRONT, RESULTING IN
POTENTIAL FOR ELEVATED STORMS MAINLY ALONG/SOUTH OF HIGHWAY 29
THURSDAY EVENING AND OVERNIGHT. STRONG DEEP-LAYER SHEAR (50 TO 55
KNOTS) AND DECENT LAPSE RATES (~7 TO 8 C/KM) WOULD SUPPORT AT
LEAST SMALL HAIL AS A THREAT WITHIN EMBEDDED STORMS. PERIODS OF
HEAVY RAIN WILL ALSO BE POSSIBLE AS PWATS EXCEED ONE INCH, WITH
PROBABILISTIC GUIDANCE SHOWING A CONSISTENT SIGNAL (40 TO 60%) FOR
0.5" OF QPF. HOWEVER, SUSPECT THAT HEAVY RAIN WILL MOSTLY BE
CONFINED TO AREAS OF CONVECTION GIVEN DISJOINT BETWEEN UPPER AND
LOW-LEVEL MOISTURE.
STORM STRENGTH AND COVERAGE BECOME MORE UNCERTAIN FRIDAY
AFTERNOON GIVEN ONGOING SHOWER ACTIVITY AND CLOUD DEBRIS FROM
PREVIOUSLY WORKED OVER AIRMASS. DYNAMICS REMAIN IMPRESSIVE, WITH
STRONG FORCING PROVIDED BY RIGHT EXIT REGION OF 120 TO 130 KNOT
JET IN CONJUNCTION WITH SURFACE COLD FRONT. BETTER INSTABILITY
(APPROACHING 2,000 J/KG MUCAPE) AND LAPSE RATES (8+ C/KM) LIKEWISE
WORK THEIR WAY INTO EAST-CENTRAL WISCONSIN DURING THE AFTERNOON.
WHEN COMBINED WITH DECENT ASCENT IN THE HAIL GROWTH ZONE, THIS
WOULD BE A TIME TO WATCH FOR LARGE HAIL DEVELOPMENT WERE ANY
STORMS TO BECOME STRONG OR SEVERE. CAVEAT WILL BE OVERCOMING LOW-
LEVEL CAP SET UP BY STABILIZING ONSHORE FLOW OFF OF LAKE MICHIGAN.
ADDITIONALLY, BETTER HEATING WOULD REMAIN OFF TO OUR SOUTH IN THE
BRUNT OF THE WARM SECTOR. CAMS STILL BRINGING SEVERAL DIFFERENT
SCENARIOS TO THE TABLE REGARDING STORM TIMING, COVERAGE, AND
INTENSITY. THIS BEING SAID, SPC EXPANDED THE DAY 2 MARGINAL
OUTLOOK SLIGHTLY NORTH/WEST ACROSS GRB FORECAST AREA.
LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY
UNSETTLED PATTERN CONTINUES INTO NEXT WEEK, WITH NEXT CHANCES FOR
WIDESPREAD PRECIPITATION ARRIVING SUNDAY NIGHT INTO MONDAY AS LOW
PRESSURE TREKS INTO THE SOUTHERN GREAT LAKES. IN THIS CASE,
WINTER WILL ONCE AGAIN PROVE THAT IT'S NOT QUITE DONE WITH US YET
GIVEN THE POTENTIAL FOR BOTH RAIN AND SNOW. MORE DETAILS TO COME
AS WE HEAD INTO THE WEEKEND.
AVIATION
FOR 18Z TAF ISSUANCE
ISSUED AT 1250 PM CDT THU APR 17 2025
VFR CONDITIONS ARE OBSERVED AT ALL TAF SITES THIS AFTERNOON. AN
APPROACHING SYSTEM WILL BRING MVFR AND EVENTUALLY IFR CONDITIONS AS
RAIN IMPACTS ALL SITES THIS EVENING. SOME EMBEDDED TS ARE EXPECTED,
THOUGH PROBABILITIES OF THUNDERSTORMS AT ANY GIVEN TIME ARE TOO LOW
(GENERALLY AROUND 30% OR LESS) TO INCLUDE PREVAILING TSRA AT THIS
TIME. SHOULD ANY TSRA IMPACT A TAF SITE, EXPECT BRIEF LOW CEILINGS,
POTENTIAL FOR SMALL HAIL, VARIABLE GUSTY WINDS, +SHRA, AND TEMPORARY
LOW VIS. AS THIS SYSTEM PASSES THROUGH THE REGION, A LLJ WILL CREATE
A LLWS HAZARD AT MULTIPLE SITES INTO FRIDAY. A LULL IN PRECIPITATION
IS POSSIBLE IN THE FRIDAY MORNING TO EARLY FRIDAY AFTERNOON PERIOD
AS CHANCES OF RAIN FALL TO BELOW 40%, BUT CHANCES OF RAIN SHOWERS
WITH SOME THUNDERSTORMS INCREASE AGAIN JUST AFTER 18Z FRIDAY.
HOWEVER, DESPITE THE LULL IN RAIN SHOWERS, LOW-END IFR TO LIFR
CEILINGS ARE EXPECTED FRIDAY MORNING INTO THE AFTERNOON AS
LINGERING MOISTURE IS TRAPPED NEAR THE SURFACE.
GRB WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION.....GOODIN
AVIATION.......WFO MQT GS
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