721
FXUS63 KARX 150711
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
210 AM CDT THU MAY 15 2025
KEY MESSAGES
- SEVERE THUNDERSTORMS LIKELY ACROSS PORTIONS OF THE REGION TODAY
INTO TONIGHT. LOCALLY, THE HIGHEST THREAT LIES IN WESTERN WI, BUT
ESPECIALLY ALONG AND EAST OF I-94. VERY LARGE HAIL (2+"), TORNADOES
AND DAMAGING WINDS ARE ALSO.
- BECOMING COOLER WITH SHOWERS AND WINDY CONDITIONS FRI/SAT.
- MORE ACTIVE WEATHER PATTERN FOR NEXT WEEK WITH TUE-WED BRINGING
THE NEXT SHOT FOR WIDESPREAD RAIN. TEMPS GENERALLY AT OR BELOW
NORMAL.
DISCUSSION
ISSUED AT 210 AM CDT THU MAY 15 2025
> TODAY: SEVERE STORM THREAT. STILL SOME QUESTIONS IN WHEN
INITIATION TAKES PLACE, BUT LIKELY ACROSS THE LOCAL AREA PLUS/MINUS
1 TO 2 HOURS AROUND NOON.
- SETUP: UPPER LEVEL TROUGH STILL ON TRACK TO LIFT NORTHEAST OUT OF
THE DESERT SOUTHWEST, DEVELOPING A NEGATIVE TILT AND CLOSED 500 MB
LOW AS IT MOVES OVER THE CENTRAL/NORTHERN PLAINS THIS MORNING. AT
THE SFC, AN ATTENDANT WEST-EAST ORIENTATED WARM FRONT WILL BE
DRIVING NORTHWARD ACROSS IA/MN THIS MORNING. CLUSTERS OF
SHOWERS/STORMS ASSOCIATED WITH THIS, BUT THE BULK OF THE CAMS
SUGGEST IT WILL STAY WEST. IF NOT, COULD HAVE A SEVERE RISK.
WARM AND MORE MOIST AIR WILL FLOW NORTH SANS THE DEPARTING WARM
FRONT WITH SFC TDS EXPECTED TO CLIMB INTO THE MID 60S. A RICH SOURCE
OF INSTABILITY POOLS ACROSS THE AREA WITH "ALL" THE CAMS PUSHING
SBCAPES TO 3000+ J/KG.
THE SYSTEM'S COLD FRONT, RUNNING FROM THE NORTHWEST TO THE
SOUTHEAST, SET TO DRIVE EAST/NORTHEAST THIS AFTERNOON. THE UPPER
LEVEL SHORTWAVE ENERGY LAGS BEHIND THE FRONT INITIALLY, BUT LOOKS TO
CATCH UP TO IT BY MID/LATE AFTERNOON - DEEPENING THE LIFT ALONG THE
FRONT. SHORT TERM GUIDANCE EXITS THE FRONT/LEADING EDGE OF THE
TROUGH INTO EASTERN WI THIS EVENING.
- INITIATION: ONE OF THE BIGGEST, IF NOT THE BIGGEST QUESTION WITH
THIS SYSTEM IS WHEN/WHERE CONVECTION INITIATES ALONG THE COLD FRONT.
THE MODELS HAVE BEEN FAIRLY CONSISTENT IN SPARKING IT ACROSS THE
LOCAL AREA, BUT HAVE SHOWN SOME "BACK AND FORTH" ON TRIGGERING WEST
OF THE MISSISSIPPI RIVER TO WAITING UNTIL THE I-94 CORRIDOR IN
WESTERN WI. THERE IS A CAPPING INVERSION TO DEAL WITH FIRST, MORE
STOUT THE FARTHER SOUTH ALONG THE BOUNDARY YOU MOVE. CONSENSUS IN
THE CAMS IS TO TRIGGER ALONG NORTHERN PORTIONS OF THE BOUNDARY AS IT
MOVES INTO NORTHWEST WI BETWEEN NOON AND 2PM. CONVECTION THEN ERUPTS
IN THE 2 TO 4 PM WINDOW DOWN THE SOUTHERN FLANK OF THE BOUNDARY AS
THE CIN IS OVERCOME (AND THE UPPER LEVEL SHORTWAVE MOVES IN). ON THE
WHOLE, THIS HAS BEEN THE MOST FAVORED SCENARIO AND WILL PAINT THE
OUTLAY OF PCPN CHANCES WITH THIS IN MIND.
OBVIOUS IMPLICATIONS TO STORM CHANCES AND RELATED SEVERE THREAT AND
A VERY CLOSE EYE WILL BE KEPT ON THE NEAR TERM ENVIRONMENT AND
CURRENT EXPECTATIONS ADJUSTED IF TIMING TRENDS DIFFERENTLY.
- RISKS: 3+K J/KG OF SBCAPE AND 35-40+ KTS OF 0-6 KM SHEAR WILL
SUPPORT SUPERCELLS ON INITIATION. STORMS COULD UPSCALE QUICKLY,
GOING FROM "ZERO" TO SEVERE HAIL IN AS LITTLE AS 1/2 HOUR. THE MODE
MAY STAY AS DISCRETE CELLS UNTIL THEY EVOLVE INTO A LINE AS THE
SYSTEM MOVES OVER EASTERN WI.
THE FAT CAPE PROFILES AND HEFTY MID LEVEL LAPSE RATES SUPPORT VERY
LARGE HAIL (2+ INCHES). CURVING HODOGRAPHS IN THE 0-1KM LAYER WITH
20 KTS OF SHEAR IN THAT LAYER AND UPWARDS OF 200 M2/S2 OF SRH
SUPPORT TORNADIC DEVELOPMENT. DAMAGING WINDS ALSO POSSIBLE.
IF THE CURRENT CAMS PREFERENCE IS REALIZED, THE BULK OF THE SEVERE
WEATHER WILL BE FOCUSED FROM THE I-94 CORRIDOR IN WESTERN WI
EASTWARD.
> FRIDAY-SATURDAY: COLDER, WINDY WITH SHOWERS.
THE UPPER LEVEL LOW WILL BE SITTING ACROSS NORTHERN MN EARLY FRI
MORNING, SLOWLY TRACKING EAST TO ACROSS THE EASTERN GREAT LAKES BY
00Z SUN. CYCLONIC FLOW, RIPPLES IN THE UPPER LEVEL FLOW, LOW LEVEL
COLD AIR ADVECTION AND FAVORABLE LOW LEVEL LAPSE RATES WILL WORK ON
AMPLE SATURATION TO TRIGGER SCATTERED/AREAS OF SHOWERS (MORE
WIDESPREAD FRIDAY).
PERIODIC, RELATIVELY DEEP UNIDIRECTIONAL MIXING OF THE WINDS IN THE
LOW LEVELS SUGGEST GUSTS IN THE LOW TO MID 30 MPH FRI INTO SAT.
WINDS COULD BLOW AS MUCH AS 70 MPH FRI AT THE TOP OF MIXED LAYER,
BUT DON'T ANTICIPATED BRINGING THOSE SURFACEWARD. IN ADDITION, THE
SFC PRESSURE GRADIENT TIGHTENS UP POST THE STORM SYSTEM'S SFC LOW,
KEEPING SUSTAINED WINDS MOSTLY FROM 15 TO 25 MPH. FRI IS LOOKING TO
BE THE WINDIEST OF THE DAYS. CURRENT FORECAST HOLDS EXPECTATIONS
UNDER WIND ADVISORY CRITERIA.
COLDER, BUT CLOSER TO THE SEASONABLE NORMS, AIR FLOWS IN FROM
WEST/NORTHWEST AS THE SYSTEM EXITS EAST. HIGHS FRI LOOK TO BE ABOUT
10 TO 15 COLDER THAN TODAY, LOPPING ANOTHER 5 TO 10 DEGREES OFF SAT.
SAT SHAPING UP TO BE BELOW NORMAL FOR A CHANGE.
> NEXT WEEK: BUSIER, MORE ACTIVE WEATHER PATTERN (AKA, RAIN
CHANCES), COOLER.
GEFS AND EPS REMAIN IN GOOD AGREEMENT WITH TRANSITIONING FROM THE
BLOCKING RIDGE PATTERN TO ONE THAT IS QUICKER, MORE PROGRESSIVE, WITH
PERIODS OF TROUGHING AND PERIODS OF RIDGING.
WHILE THERE IS SOME EXPECTED VARIATIONS IN TIMING/POSITIONING OF THE
VARIOUS WEATHER ELEMENTS MOVING OUT INTO NEXT WEEK, THE WPC CLUSTERS
ARE ALL IN FAVOR OF DRIVING A SHORTWAVE TROUGH NORTHEAST OUT OF THE
DESERT SOUTHWEST, SPINNING ACROSS THE MID MISSISSIPPI RIVER VALLEY
WED. BITS OF UPPER LEVEL ENERGY PROGGED TO SPIT NORTHEAST OUT OF THE
TROUGH WHILE LOW LEVEL THERMODYNAMICS MEET UP WITH NORTHWARD MOVING
850 MB MOISTURE TRANSPORT. TUE AND WED SETTING UP TO BE THE NEXT
BEST PERIOD FOR WIDESPREAD RAINS. SOME THUNDER CHANCES ALTHOUGH THE
MAIN POOL OF INSTABILITY CURRENT PROGGED TO HOLD WELL SOUTH. AS FOR
RAIN, LATEST MODEL BLEND SUGGESTS 1/2" ON AVERAGE FOR TUE-WED, BUT
HAVE 20-40% PROBS FOR 1+".
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1228 AM CDT THU MAY 15 2025
UPSTREAM VFR CLOUD DECK SEEN MOVING EAST THROUGH THE MISSOURI RIVER
VALLEY AT 15.06Z TAF ISSUANCE. EXPECT VFR CONDITIONS TO CONTINUE
EARLY THIS MORNING AS MVFR POTENTIAL INCREASES FROM SOUTH TO NORTH
LATER THIS MORNING.
AN INITIAL ROUND OF SHOWERS ACCOMPANIES INCOMING MVFR CLOUD DECK,
PROGRESSING NORTHEAST THROUGH SOUTHERN MINNESOTA EARLY THIS MORNING.
HIGHEST CONFIDENCE FOR IMPACTS LIES WEST OF THE MISSISSIPPI RIVER
THROUGH NORTHEAST IOWA AND SOUTHEAST MINNESOTA LOCALLY. CONFIDENCE
FOR POTENTIAL IMPACTS AT EITHER TAF SITE (KRST/KLSE) IS LOW AS
SOUTHERN EDGE OF SHOWERS AND STORMS IS MAY GRAZE BOTH. THEREFORE,
WILL BE AN IMMEDIATE CONCERN TO MONITOR AS ANY SOUTHERN BUILDING
ALONG THIS INITIAL LINE MAY REACH KRST AND THEN SUBSEQUENT KLSE.
CONFIDENCE IN THE SUBSEQUENT LINE OF STORMS EARLY THIS AFTERNOON
INCREASES TO ~75%. A NORTHWEST TO SOUTHEAST ORIENTED LINE OF STORMS
EXPECTED TO DEVELOP NEAR THE MISSISSIPPI RIVER VALLEY, QUICKLY
STRENGTHENING TO SEVERE. SIMILAR TO MORNING STORMS, CONFIDENCE IN
EXACT LOCATION RELATIVE TO EITHER TAF SITE WAIVERS SOME DUE TO
INITIAL DEVELOPMENT EXPECTED BETWEEN KLSE AND KRST: NEAR KEAU.
FURTHERMORE, KLSE AND SMALLER AIRPORTS IN WESTERN WISCONSIN MAY
INITIALLY BE ON THE SOUTHERN EDGE OF THE QUICKLY PROGRESSING
NORTHEAST LINE OF STRONG TO SEVERE STORMS. THEREFORE, HIGHEST
CONFIDENCE FOR IMPACTS LOCALLY WILL BE AT KBCK, KMDZ, AND K82C.
LIGHT SOUTHEAST WINDS AT 15.06Z TAF ISSUANCE EXPECTED TO INCREASE
THROUGH THE EARLY MORNING HOURS, GUSTING NEAR 20KTS BY DAYBREAK. AS
THE SURFACE FRONT RESPONSIBLE FOR THE STORMS PROGRESSES EXPECT A
CLOCKWISE ROTATION TO SOUTH WINDS GUSTING NEARS 30KTS. FURTHER
ROTATION THROUGH THE EVENING TOWARDS THE END OF THE TAF PERIOD
BRINGS WESTERLY WINDS WEAKENING THROUGH THE NIGHTTIME HOURS.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...RIECK
AVIATION.....JAR
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page