FXUS63 KARX 172337
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
637 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Saturday afternoon and early evening brings potential for showers 
and thunderstorms to mainly west central Wisconsin. If thunderstorms 
do develop, a severe storm cannot be ruled out.

- While it remains difficult to narrow down timing, next week
  looks to feature multiple rounds of showers and thunderstorms.
  Additionally, next Tuesday may feature the ingredients for
  severe thunderstorms but these are currently favored to
  develop south of the forecast area. Please keep up to the date
  with the forecast for next week.

&&

.DISCUSSION...
Issued at 425 AM CDT Fri May 17 2024

Saturday thunderstorms:

A shortwave looks to eject northeastward over ND to western Ontario. 
An associated cold front will sweep eastward through MN toward the 
CWA. Plume of moist advection ahead of this front should lead to an 
axis of around 1000 J/kg of MLCAPE by the afternoon hours. As the 
front arrives, a few showers and thunderstorms may develop. Model 
soundings suggest warm temperatures at 750mb will likely limit the 
ability for deep convection to develop, especially in southern parts 
of the CWA. Additionally, with better winds aloft remaining to our 
north, deep shear of only around 20 knots suggests convective 
organization will be lacking. Thus, severe risk appears limited to a 
stray severe hail or wind event.

Sunday night through Friday precip:

Next week brings an extended period with west-southwesterly to 
southwesterly flow aloft with a series of shortwaves embedded in 
this flow. With good 700/850mb moist advection seen ahead this 
waves, multiple rounds of showers and thunderstorms will occur. PoPs 
are once again spread across a much larger time period than will be 
affecting, owing to low predictability in the timing of the 
aforementioned shortwaves.

Of particular note is Tuesday, which looks to feature a rather 
potent shortwave with most guidance bringing this northeastward during 
the afternoon and evening hours. Ahead of this feature, moist 
advection tracing back to the Gulf of Mexico could lead to large 
amount of instability. With stronger winds aloft favored, this could 
lead to a risk for severe thunderstorms. Primary uncertainties 
surround the exact track of the system - if the system tracks just a 
bit too far to the south, the forecast area would fail to 
destabilize owing to ongoing rain during the morning hours. As of 
this time, LREF joint probabilities suggest the best overlap of 
shear, potential instability, and low convective inhibition is more 
probable just to our south, but will need to keep a close eye on 
this over the coming days.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 637 PM CDT Fri May 17 2024

VFR conditions are expected through much of the TAF period with 
intermittent middle to high level clouds. Winds will decrease 
overnight marginally as diurnal mixing subsides. Ahead of an 
incoming frontal boundary, winds will increase again from the 
south on Saturday to around 15-20 kts with gusts of up to 30 
kts. As the front approaches, available low-level moisture will
allow for some shower/storm activity to get going during the 
afternoon. However, questions remain on how vigorous any 
convection will get as short-range model guidance varies 
considerably. As a result, opted to hold with a VCSH at both TAF
sites for now. Winds will shift to west/northwest behind the 
frontal passage and begin to diminish going into Saturday 
evening. 

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Naylor