068
FXUS63 KARX 061740
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1240 PM CDT Mon May 6 2024

.KEY MESSAGES...

- Sunny Today, Showers and Thunderstorms Tonight

- Active pattern continues with additional thunderstorms Tuesday
  afternoon and again Wednesday night.

- Cooler Weekend, Potential Shower or Two

&&

.DISCUSSION...
Issued at 311 AM CDT Mon May 6 2024

Today: Sunny, Breezy West of the Mississippi

Weak surface high pressure over the Upper Great Lakes this morning
slowly shifts into southeastern Ontario through the day as a low
pressure system along the Front Range lifts north into the Dakotas.
Southeasterly winds will increase with gusts in the 20 to 25 mph
range west of the river by this afternoon. Daytime highs climb to
near 70 and into the mid 70s for the warmer locations. Look for
clouds to be on the increase from the west in the evening as
influence from the Dakotas low pressure system moves overhead.

Tonight through Wednesday: Showers and Thunderstorms

The low pressure system over the Dakotas and its negative tilted
trough moves across the region tonight. The best forcing moves into
our local region around midnight or so, well after diabatic heating
has ended. MUCAPE values on the order of 100-300 J/kg won`t be
enough energy to bring much of a threat across our area, but CAMs
are in great agreement for a line of showers and thunderstorms to
move from WSW to ENE overhead tonight.

On Tuesday, early morning showers and thunderstorms lift north as
the low pressure system from the Dakotas elongates from the northern
Rockies into the Upper Great Lakes. Better clearing is expected
across our area on Tuesday afternoon with diurnal heating expected.
At the same time, the low pressure system pivots and mid-level lapse
rates increase from 6C/km to closer to 8-8.5C/km with CAPE
increasing to around 500-700J/kg. SPC has introduced a marginal risk
(threat level 1 out of 5) across our region with this increase
instability. Marginal hail appears to be the primary threat as the
better shear exits to the north and east before better instability
begins.

Wednesday Night into Thursday: Another Round of Thunderstorms

As the remnant sfc low and longwave trough from the Dakotas dives
south Wednesday it brings upper-level divergence and fgen forcing
across southern MN and northern IA. An inverted trough and Fgen
forcing along 850 to 600mb coupled with a mid-level low shifting
over IA and a skinny CAPE profile will bring the potential for more
showers and thunderstorms and potentially a localized heavy rain
threat. This threat will diminish overnight Wednesday as colder air
moves in behind the exiting trough.

Into the weekend: Cooler Air, Some Showers

Long wave trough drops south from Canada across the Upper Midwest
into the weekend bringing temps into the low 60s with scattered
showers (20 to 30%) as the upper level low pivots overhead. Will
have to wait and see how we exit this blocky pattern during the
middle of the week for more weekend specifics.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1241 PM CDT Mon May 6 2024

VFR conditions will begin the TAF period with winds at around 12-17
kts with just a few high clouds present. As a weather disturbance
approaches from the southwest, sky cover will begin to increase with
cigs decreasing through the later evening and overnight hours.
Eventually, cigs will drop to MVFR just ahead of shower onset
past midnight with visbys likely reaching MVFR, potentially IFR
(10-20% chance) in more robust showers and isolated storms.
However, have opted to keep out any mention of VCTS in the
current TAF issuance due to lower confidence in how minimal
instability will manage to maintain storms as they progress into
our region. As precipitation moves out during the morning, cigs
will begin to improve somewhat before returning to low-VFR at
around 18z on Tuesday.

&&

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

&&

$$

DISCUSSION...JAW
AVIATION...Naylor