664
FXUS63 KARX 131743
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1243 PM CDT TUE MAY 13 2025
KEY MESSAGES
- ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED TODAY
AND TOMORROW. ASIDE FROM THE LIGHTNING RISK, NO IMPACTS ARE
EXPECTED.
- SEVERE STORMS CONTINUE TO LOOK POSSIBLE FOR THURSDAY AFTERNOON
WITH A RISK FOR LARGE HAIL AND DAMAGING WINDS. DETAILS THAT
WILL DETERMINE IF A TORNADO RISK WILL BE PRESENT REMAIN
UNCERTAIN. MONITOR FUTURE FORECASTS AS THURSDAY APPROACHES.
DISCUSSION
ISSUED AT 343 AM CDT TUE MAY 13 2025
SPOTTY ORDINARY THUNDERSTORMS TODAY AND TOMORROW:
TODAY, DISTURBANCES IN THE EASTERLY FLOW ALOFT ON THE NORTH SIDE OF
AN UPPER LOW CENTERED OVER THE TN VALLEY MAY KICK OFF ISOLATED TO
SCATTERED CONVECTION, PRIMARILY THIS AFTERNOON AS BOTH SURFACE
HEATING IS MAXIMIZED AND THE CONTINUED SOUTH-SOUTHEASTERLY SURFACE
WINDS BEGIN TO ADVECT MOISTURE NORTHWARD. WHILE GUIDANCE BROADLY
DEPICTS AROUND 500-750 J/KG OF SBCAPE PER 13.00Z HREF AND INSPECTION
OF INDIVIDUAL MODEL RUNS SUGGESTS THIS SHOULD BE REALIZED WITH
MINIMAL CIN, RESULTING INSTABILITY PROFILES ARE SKINNY. THUS,
EXPECTATION IS THAT MANY CONVECTIVE ATTEMPTS WILL OCCUR BUT
ULTIMATELY FAIL WITH AT LEAST A FEW STORMS MANAGING TO DEVELOP WITH
THE RELATIVE PROBABILITY OF SUCCESS HIGHEST EAST OF THE MISSISSIPPI
RIVER. PAST 3 RUNS ARW/FV3/NAMNEST ALONG WITH SEVERAL HRRR/RAP RUNS
HAVE CONSISTENTLY REFLECTED THIS - EACH HAS VERY SPOTTY CONVECTION,
MAINLY ALONG AND EAST OF THE RIVER. AM THUS CONFIDENT THERE WILL BE
CONVECTION THAT WILL BE LIMITED IN SCOPE - HAVE THEREFORE ELECTED TO
BROAD BRUSH 15-20 POPS ACROSS A GOOD CHUNK OF THE CWA AND SWITCHED
TO COVERAGE WORDING IN WEATHER OUTPUT. AS FOR IMPACTS, PROGGED DEEP
SHEAR VALUES IN THE 13.00Z SUITE ARE GENERALLY 5 KNOTS OR LESS, SO
ORGANIZED CONVECTION IS NOT EXPECTED.
WEDNESDAY, DEPARTING DISTURBANCE AND MARGINALLY HIGHER LOW LEVEL
MOISTURE MAY ALLOW FOR MORE CONVECTIVE COVERAGE TO DEVELOP DURING
THE AFTERNOON, ONCE AGAIN PRIMARILY IN OUR EAST. HAVE THUS GONE WITH
RELATIVELY HIGHER POPS, WITH NBM VALUES OF 15-35% DEEMED SUFFICIENT.
ONCE AGAIN, MINIMAL SHEAR SUGGESTS ANY IMPACTS FROM THUNDERSTORMS
WILL ALSO BE MINIMAL.
SEVERE THUNDERSTORM POTENTIAL THURSDAY:
LARGE SCALE PATTERN REMAINS ON TRACK FOR THURSDAY WITH AN AXIS OF
LOW LEVEL MOISTURE BEING ADVECTED NORTHWARD AHEAD OF A STRONG UPPER
WAVE AND AN ASSOCIATED COLD FRONT. COOLING ALOFT ASSOCIATED WITH
THIS WAVE AND LOW LEVEL CONVERGENCE ALONG THE FRONT SHOULD ALLOW FOR
WIDESPREAD SHOWERS AND THUNDERSTORMS TO DEVELOP DURING THE AFTERNOON
HOURS WHERE WEAK CONVECTIVE INHIBITION ALLOWS PARCELS TO RISE. ROBUST
INSTABILITY SHOULD BE IN PLACE BY THE AFTERNOON WITH MEAN 12.12Z
LREF VALUES SUGGESTING GREATER THAN 2000 J/KG WILL BE PRESENT
FOLLOWING A MORNING FREE OF CONVECTION DUE TO A STRONG INVERSION IN
THE 600-900MB LAYER. WITH INCREASING WINDS ALOFT LEADING TO SFC-6KM
BULK SHEAR OF AROUND 45 KNOTS, SEVERE STORMS WOULD BE POSSIBLE. FOR
THIS RISK TO BE REALIZED IN OUR NECK OF THE WOODS, UNCERTAINTY
FOCUSES ON HOW FAR EAST THE COLD FRONT WILL ADVANCE BY THE TIME
ENOUGH INSTABILITY IS PRESENT TO OVERCOME THE AFOREMENTIONED
INVERSION. OPERATIONAL 13.00Z GFS/NAM/CMC/EC RUNS ARE BROADLY
ILLUSTRATIVE OF THE WIDE RANGE OF OUTCOMES, WITH CMC/EC PLACING A
MAJORITY OF THE CWA IN PLAY, THE NAM OUR EASTERN TWO THIRDS, AND THE
GFS LIMITING RISK TO AREAS EAST OF THE MISSISSIPPI RIVER. 12.12Z TO
13.00Z NAM AND 11.12Z TO 13.00Z EC TREND HAS SLOWED THE PROGRESSION
OF THIS FRONT. THUS, AM INCREASINGLY CONFIDENT AT LEAST OUR WI
COUNTIES WILL END UP WITH A RISK FOR SEVERE STORMS AND THIS RISK
EVENTUALLY ENCOMPASSING AREAS WEST OF THE RIVER SEEMS TO BE A DECENT
BET.
AS FOR WHICH SEVERE HAZARDS WOULD BE IN PLAY, PROGGED INSTABILITY
AND SHEAR APPEAR SUFFICIENT FOR ROTATING UPDRAFTS WITH AN ATTENDANT
RISK FOR LARGE HAIL. RAPID - PERHAPS 50 MPH - FORWARD MOTION OF
STORMS COUPLED WITH DCAPE AROUND 1000 J/KG SUGGEST DAMAGING WINDS
WOULD BE IN PLAY AS WELL. ON THE SUBJECT OF TORNADOES, ORIENTATION
OF DEEP SHEAR IN RELATION TO THE COLD FRONT WILL BE CRITICAL IN
DETERMINING WHETHER OR NOT DISCRETE CONVECTION AND THUS A NOTABLE
TORNADO RISK DEVELOPS. ORIENTATION REMAINS UNCERTAIN - THE 13.00Z
GFS SUGGESTS A MORE ALONG-BOUNDARY ORIENTATION WHILE THE
CORRESPONDING NAM RUN SUGGESTS THIS VECTOR WILL BE NEARLY ORTHOGONAL
TO THE FRONT, LEADING TO RAPID UPSCALE GROWTH OR DISCRETE
CONVECTION, RESPECTIVELY. THIS SUGGESTS THAT, AS IS USUALLY THE
CASE, WILL NEED TO WAIT FOR DETAILS TO BECOME CLEARER - OFTEN
WITHIN 24 HOURS OF THE EVENT - TO MAKE LARGE PRONOUNCEMENTS
ABOUT TORNADO RISK.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1223 PM CDT TUE MAY 13 2025
PRIMARILY VFR CONDITIONS ACROSS THE AREA THROUGH THE NEXT 24
HOURS. A SCT-BKN DECK OF CUMULUS AROUND 5KFT HAS DEVELOPED THIS
AFTERNOON AND IS EXPECTED TO REMAIN THROUGH THE REST OF THE
DAYLIGHT HOURS, BEGINNING TO DISSIPATE THIS EVENING. THERE IS
THE CHANCE (15-30%) FOR SOME ISOLATED TO SCATTERED SHOWERS AND
STORMS THIS AFTERNOON AND EVENING, MAINLY FOR AREAS EAST OF THE
MISSISSIPPI RIVER, BUT IMPACTS ARE EXPECTED TO BE BRIEF. THERE
REMAINS THE POSSIBILITY THAT SHOWERS/STORMS MAY IMPACT LSE THIS
AFTERNOON AND HAVE LEFT THE PROB30 GROUP IN THE TAF TO HIGHLIGHT
THIS POTENTIAL.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...FERGUSON
AVIATION...FALKINHAM
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