205
FXUS63 KARX 171741
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1241 PM CDT THU APR 17 2025
KEY MESSAGES
- SCATTERED SHOWERS, STORMS THIS MORNING - HIGHER CHANCES ACROSS
NORTHEAST IA/SOUTHWEST WI (30-60%).
- SHOWERS AND STORMS LIKELY AREAWIDE TONIGHT (70-90%) WITH A SEVERE
THREAT THIS EVENING (MOSTLY WEST OF THE MISSISSIPPI RIVER). LARGE
HAIL THE MAIN CONCERN.
- POTENTIAL STORM SYSTEM FOR SUNDAY/SUNDAY NIGHT. LOW END CHANCES
FOR ACCUMULATING SNOWS (10-30%) NORTH OF I-90 SUN NIGHT.
DISCUSSION
ISSUED AT 255 AM CDT THU APR 17 2025
THIS MORNING: SOLID SIGNAL IN THE CAMS OF NOSING THE LOW LEVEL JET
INTO NORTHEAST IA TOWARD 12Z THIS MORNING. CONVERGENCE ALONG THE
NOSE, ALONG WITH FAVORABLE MOISTURE TRANSPORT, SHOULD SPARK
SCATTERED CONVECTION ABOVE THE LOW LEVEL CAP - AND MOST/ALL CAMS
MODELS PAINT THIS. SOME AID IN THE UPPER LEVELS TOO, WITH A THIN
LINE OF NORTHWEST-SOUTHEAST ORIENTATED SHORTWAVE ENERGY RUNNING JUST
BEHIND THE LLJ. IN ADDITION, THE RAP SKETCHES OUT A POOL OF 500-1500
J/KG MUCAPE FOR THIS CONVECTION TO TAP INTO. LITTLE IF ANY SHEAR
OUTSIDE OF THE NEAR SFC, AND WITH ANY STORM ELEVATED, NOT MUCH
SUPPORT FOR SUSTAINED UPDRAFTS. STILL, ANY STRONGER STORM WOULD HAVE
THE POTENTIAL FOR SMALL HAIL. WHATEVER DEVELOPS COULD CONTINUE TO
PUSH NORTHEAST ACROSS THE REST OF THE AREA INTO THE AFTERNOON,
ALTHOUGH WILL BE MOVING OUT OF THE FAVORABLE CAPE POOL. WILL STICK
WITH HIGHER RAIN CHANCES ACROSS IA FOR NOW, BUT SPREAD AT LEAST LOW
END (20%) ACROSS MUCH OF THE FORECAST FROM LATE MORNING/EARLY
AFTERNOON.
THIS AFTERNOON/TONIGHT: FAIRLY MESSY AFTERNOON FOR CONVECTIVE
POTENTIAL WITH LOW LEVEL CAPPING REMAINING IN PLACE, WORKING AGAINST
SFC BASED CONVECTION. POTENTIAL FOR SOME BITS OF UPPER LEVEL ENERGY,
PERHAPS A LEFT OVER OUTFLOW BOUNDARY, ETC. A MIX OF LOW END POPS
STILL WARRANTED, BUT THE CRUX OF THE LATER DAY STORM CHANCES WILL
COME FROM THE LIFT ALONG THE LOW'S COLD FRONT - WHICH SLIPS EAST
ACROSS THE FORECAST AREA TONIGHT. THE LOW LEVEL JET REASSERTS ITSELF
ALONG THE FRONT TOWARD 00Z WITH A 500-2000 J/KG MUCAPE STILL
AVAILABLE FOR THE FORCING/CONVECTION TO WORK ON. STORMS STILL LOOK
ELEVATED SO WON'T FEEL THE STRONGER NEAR SFC SHEAR, BUT ENOUGH A
LOFT TO AID A STRONG/SEVERE THREAT. LARGE HAIL CONTINUES TO BE THE
MAIN THREAT WITH THE GREATER RISK WEST OF THE MISSISSIPPI RIVER.
SUN/SUN NIGHT: POTENTIAL FOR A STORM SYSTEM TO IMPACT THE REGION AND
SOME OF THE RESULTING QPF COULD COME IN THE FORM OF SNOW. A LOT OF
UNCERTAINTY THOUGH.
LATEST ROUND OF EPS AND GEFS MEMBERS TAKE A TROUGH OUT OF THE
DESSERT SOUTHWEST SATURDAY, LIFTING IT NORTHEAST ACROSS THE MID
MISSISSIPPI RIVER VALLEY SUNDAY NIGHT AND THEN CONTINUING OFF ACROSS
THE EASTERN GREAT LAKES. HOW STRONG, TIMING AND TRACK SHOW A VARIETY
OF POSSIBILITIES IN BOTH THE MODELS'S SUITE OF MEMBERS. OF NOTE IS
THE VERY SMALL SUBSET OF MEMBERS THAT DROP ACCUMULATING SNOWS IN THE
STORM'S DEFORMATION REGION. GRANDENSEMBLE HAS 15-20% CHANCES FOR
SNOW OF 1+" , HEAVILY WEIGHTED BY THE STRONGER/MORE ROBUST EPS
MEMBERS. ADDITIONALLY, EFIS VIA THE EPS HAVE A NON-ZERO SOT -
SUGGESTIVE OF A FEW "HIGH END" OUTLIERS FOR SNOWFALL AMOUNTS. SNOW
DOES FALL IN APRIL, AND WHILE THE CHANCES ARE ON THE LOWER END OF
THE SCENARIOS, THEY ARE THERE - AND BEAR WATCHING.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1232 PM CDT THU APR 17 2025
VERY CHALLENGING FORECAST AS THUNDERSTORMS BEAR DOWN THIS
AFTERNOON AND POTENTIALLY CONTINUE THROUGH THE EVENING HOURS.
LOW CONFIDENCE AS STORMS HAVE BEEN PULSING UP AND DOWN IN A
LIMITED TIME. EVIDENT IN STORMS JUST UPSTREAM OF KLSE AT 17.18Z
TAF ISSUANCE, HAD TO ISSUE A CORRECTION REMOVING TS IN FM GROUP.
A SHORT REPRIEVE IN STORM COVERAGE THIS EVENING MAKES WAY TO
MORE STORMS TONIGHT WITH MODERATE CONFIDENCE FOR SCATTERED
STORMS PROGRESSING NORTHEAST. HAVE INCLUDED FM GROUP AT BOTH
KLSE AND KRST DURING THIS TIME BASED ON HIGHER RESOLUTION
FORECAST MODELS BUT LIMITED FORCING PRESENTS PROBLEMS IN OVERALL
CONFIDENCE. CONFIDENCE BETWEEN THESE STORMS PROGRESSING
NORTHEAST AND A SUBSEQUENT FRONTAL BOUNDARY SAGGING SOUTHEAST
OVERNIGHT IS LOW. STORMS EVENTUALLY EXIT SOUTHEAST EARLY FRIDAY
MORNING. HIGHEST RAINFALL RATES EXPECTED OVERNIGHT POTENTIALLY
CAUSING LIFR-VLIFR AT TIMES. THE LINE LINGERS AT LOCALLY SMALLER
AIRPORTS IN SOUTHWEST WISCONSIN EARLY FRIDAY MORNING.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...ZAPOTOCNY
AVIATION...JAR
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