Sunrise 5:45 AM   Sunset 8:16 PM Moonrise 4:15 AM   Moonset 7:10 PM

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FXUS63 KARX 071913 AFDARX

Area Forecast Discussion National Weather Service La Crosse WI 210 PM CDT Tue May 7 2024

KEY MESSAGES

- Scattered storms into the evening, mostly along and east of the Mississippi River. A few could be strong with small hail, gusty winds...but can't rule out a funnel cloud or two in western WI.

- Active weather pattern with a series of shortwave troughs promising periodic rain chances into next week. Severe threat looks low. Rainfall from today through next Thu could reach 1 1/2 to 2".

- Cool Thursday, mostly around the seasonable normals after that.

DISCUSSION
Issued at 210 PM CDT Tue May 7 2024

OVERVIEW: wagon train of upper level shortwaves are looking to drive across/near the upper mississippi river valley through the weekend, and much of next week. While there are some differences in timing/placement of the upper level features in the GEFS and EPS, they both agree the pattern should stay "active". There doesn't look to be much/if any tap to gulf moisture after today, but the model blend suggests amounts (including today) upwards of 1 1/2 to 2" through next Thu. A 10 to 20% to exceed 3" for a few locations.
After today, instability is looking meager through the period for most days, keeping any severe threat low (to none).

REST OF THE AFTERNOON/TONIGHT: Additional Showers & Storms This Afternoon and Evening

As our morning line of storms continues to exit the region, clearing skies with occasional bands of low-level clouds on GOES-16 visible satellite imagery can be noted pivoting around a clearly defined low pressure center. As we continue through the afternoon, clearing skies will allow for destabilization to take place with the 07.15z RAP ramping up MLCAPE values to around 1000-1500 J/kg later into the afternoon. As of 1830z, satellite imagery shows some aggravated cumulus with a few weak convective cells popping up east of the Mississippi River. While the instability later today is fairly conducive for convection, however, 0-6km bulk shear profiles (around 10 kts) in the CAMs would suggest a more pulse storm environment. In short, expecting cells to develop quickly when any localized surface boundaries are utilized but will struggle to maintain their cores aloft. Consequently, there may be some small hail and gusty winds with the most robust updrafts when considering relatively low freezing levels to around 8kft. With surface flow changing to southwest by 21z, will have to watch for some non-supercell funnel/tornado threat as 0-3km CAPE approaches 300 J/kg. Therefore, the RAP increases the non-supercell tornado parameter substantially for a few hours this afternoon and evening. Currently, the CAMs suggests showers and storms to move northeast with the mean wind through the later evening hours and weaken as instability wanes.

WED AFTERNOON/THU: an occlusion still set to lay northwest of its parent sfc low tracking east across the Ohio River Valley Wed afternoon/evening. A loft, shortwave energy set to spit east from the plains while a ripple in the upper level flow drops southward out of Canada. The features will interact to spark areas of showers - mostly favored along/south of I-90. These will sink south/southeast with the shortwave movement/exit of the sfc trough Thu. Meager instability with the bulk of the deep layer shear farther south. Some turning in the the lowest 0-1km per RAP bufkit soundings, and there is sfc convergence along the occlusion. With a cold core upper level low association, there does lie some low end risk for tornadoes near the sfc convergence Wed afternoon. Overall, the bulk of the severe threat lies south of the local area.

FRIDAY: the long range guidance has been in good agreement with taking a shortwave trough out of southern Canada south/southeast, dropping it across the upper mississippi river valley Fri afternoon/evening. Weak low level warming and a little Fgen will help the feature spark another area of showers as it spins across the region. 250-500 J/kg of SCAPE in the GFS and NAM support some scattered thunder chances while deeper shear is displaced to the west. No severe expected at this time. With no southern tap to deep moisture, rainfall amounts trending less than 1/4".

SUNDAY/START OF NEXT WEEK: more bits of upper level energy currently progged to slip across/near the region in the GEFS and EPS, bringing additional rain chances. Some differences in timing and location, but the long range guidance keeps it active and potentially wet through the middle part of next week.

TEMPS: Thu still trending to be the coolest day of the week with an upper level trough dropping across the region - bringing colder air along with cooling from areas of rain. Probabilities in the LREF sit at 10-20% to warm out of the 50s - although the EPS is a bit more optimistic that a few locations could break 60 degrees.

After that, the EPS and GEFS settle in to temperatures plus/minus 5 to 10 degrees around the seasonable normals.



AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
Issued at 1241 PM CDT Tue May 7 2024

VFR conditions are generally expected through the TAF period with showers and a few storms possible (20-50% chance) later this afternoon and evening. As a result, included some VCSH mention in the KLSE TAF from 21z to 02z to account for anything that may initiate. However, confidence is low in exact coverage of showers/storms and where they will initiate due to uncertainty on where localized boundaries will setup. Otherwise, cigs will vary throughout the TAF period between middle and high-level clouds, perhaps a few low-VFR cigs to begin the TAF period. Southwesterly winds will diminish late this evening and overnight to around 5 kts.

ARX WATCHES/WARNINGS/ADVISORIES
WI...None.
MN...None.
IA...None.

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