748
FXUS63 KGRB 172046
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
ISSUED BY NATIONAL WEATHER SERVICE MARQUETTE MI
346 PM CDT THU APR 17 2025
FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE
KEY MESSAGES
- RAIN/STORM CHANCES 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, ESPECIALLY NORTH AND WEST OF
US-8.
DISCUSSION
ISSUED AT 345 PM CDT THU APR 17 2025
RAP SURFACE ANALYSIS SHOWS AN ELONGATED 992-997 MB SURFACE TROUGH
EXTENDING FROM COLORADO TO SOUTH-CENTRAL MN, WITH GOES-EAST DAY
CLOUD PHASE RGB IMAGERY SHOWING A LINE OF CUMULUS WITH SOME
OVERSHOOTING TOPS DRAPED ACROSS NORTH-CENTRAL WISCONSIN. FREQUENT
LIGHTNING HAS BEEN SHOWN WITH THESE STORMS, ESPECIALLY PRICE
COUNTY AND NORTH, THOUGH LIGHTNING TRENDS HAVE DECREASED WITH
FURTHER PENETRATION INTO WISCONSIN FROM MINNESOTA AS THE AIRMASS
OVER ESPECIALLY NORTHEAST WISCONSIN REMAINS STABLE. MORE UNSTABLE
AIR IS ADVECTING IN, WITH THESE STORMS RIDING A MUCAPE GRADIENT
RANGING AROUND 250-1000 J/KG. CAMS HAVE STRUGGLED TO CAPTURE STORM
BEHAVIOR TODAY ON THE NORTHERN END BUT HAVE BEEN MORE CONSISTENT
IN CAPTURING STORMS KICKING OFF CLOSER TO THE SOUTHERN MN PORTION
OF THE SURFACE TROUGH. CAMS DO CONSISTENTLY SHOW THESE STORMS
BEING THE PRIMARY THREAT INTO THE EVENING AND OVERNIGHT HOURS. THE
12Z HREF SUITE STRUGGLES TO KEEP MUCH ELEVATED INSTABILITY FOR
THESE STORMS WITH MEAN MUCAPE VALUES ONLY IN THE 100-250 J/KG
RANGE, BUT SHEAR PROFILE IS OUTSTANDING WITH SOUTH TO SOUTHEAST
SURFACE WINDS VEERING TO SOUTHWEST AT NEAR 50 KT BY MIDNIGHT
TONIGHT AT 850MB. 0-6KM BULK SHEAR VALUES OF NEAR 50 KT WILL KEEP
ORGANIZED WHAT STORMS DO MAKE IT INTO THE REGION, THOUGH THE
MEAGER INSTABILITY WILL LIMIT THE CEILING OF IMPACTS TO SMALL TO
BORDERLINE SEVERE HAIL AND GUSTY WINDS.
MOVING INTO THE MORNING HOURS OF FRIDAY, A LULL IN THE PRECIPITATION
IS GENERALLY EXPECTED BEFORE CAMS INDICATE CONVECTIVE INITIATION AS
BETTER INSTABILITY IS PRESENT (MUCAPE CLOSER TO 1000 J/KG) AND STILL
SUPPORTIVE SHEAR PROFILES (0-3KM SRH NEAR 300). HOWEVER, WITH THE
BEST SYNOPTIC FORCING MOVING PAST THE REGION DURING THE DAYTIME
HOURS, IT IS NOT COMPLETELY CLEAR WHETHER THE GOOD INGREDIENTS FOR
STORMS CAN COME TOGETHER. THERE IS ALSO SOME QUESTION AT THE ABILITY
FOR THE LOW LEVELS TO BE DESTABILIZED AS THE PRECIPITATION-MOISTENED
LOW LEVELS ARE EXPECTED TO KEEP CLOUD COVER OVER THE REGION EVEN
DURING THE LULL IN PRECIPITATION. STILL, THE PRESENT DANGER FOR
DAMAGING WINDS AND SEVERE HAIL SHOULD INITIATION OCCUR IS HIGH
ENOUGH TO WARRANT AN SPC MARGINAL RISK (1/5). REGARDLESS OF EXACTLY
HOW THINGS SHAPE OUT, HIGH PRESSURE ENCROACHING ON THE REGION WILL
QUICKLY EXTINGUISH SHOWERS OVERNIGHT FRIDAY INTO SATURDAY, WITH GEFS-
MEAN 1028MB HIGH PRESSURE RESIDING OVER THE REGION BY SATURDAY
EVENING.
AFTER A DRY SATURDAY WITH HIGHS CLIMBING BACK INTO THE 50S,
ATTENTION TURNS UPSTREAM TO A CUTOFF 500MB LOW ALOFT IN THE FOUR
CORNERS REGION AT 12Z SATURDAY, NEGATIVELY TILTING AS IT REACHES THE
CENTRAL PLAINS SUNDAY AFTERNOON. ISENTROPICALLY-FORCED PRECIPITATION
AHEAD OF THE RESULTING SURFACE LOW OF 1000-1010 MB WILL BEGIN TO
RAMP UP POPS SUNDAY EVENING FROM THE SOUTH AND WEST. GIVEN THE
COMPLEXITY OF THE CURRENT SETUP, ENSEMBLE SPREAD IN THE TRACK OF
THIS SYSTEM AND THE FOLLOWING SYSTEM (SHORTWAVE-FORCED LOW FOLLOWING
THE INTERNATIONAL BORDER) IS HIGH. WINTER WEATHER CHANCES ARE NOT
QUITE DONE FOR THE SEASON, AS CHANCES FOR ACCUMULATING SNOW CLIMB TO
20-40% NORTH AND WEST OF A LINE FROM RHINELANDER/TOMAHAWK TO
FLORENCE/AURORA BY MONDAY MORNING. AFTER BRIEF RIDGING MOVES OVER
THE AREA IN THE WAKE OF THAT SYSTEM, THE AFOREMENTIONED TRAILING
SYSTEM APPROACHES FOR THE MIDWEEK PERIOD OF NEXT WEEK, BUT SPREAD IN
THE GUIDANCE IS QUITE HIGH AT THIS TIME.
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.....WFO MQT GS
AVIATION.......WFO MQT GS
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