531
FXUS63 KARX 231814
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
114 PM CDT Thu May 23 2024

.KEY MESSAGES...

- Organized showers/storms will spread east late tonight into
  Friday. Confidence remains on the low side for severe weather,
  but a few strong to severe storms could not be ruled out late
  tonight or Friday.

- The holiday weekend will start out dry, but the latter half of
  the weekend may be unsettled at times.

&&

.DISCUSSION...
Issued at 310 AM CDT Thu May 23 2024

Today-Friday:

Although gradual height rises and mid-level warming will occur
today ahead of a shortwave trough across the northern Rockies,
there is a weak signal for a few showers/storms to develop
towards central WI this afternoon within a diurnal cumulus
field. RAP/HRRR soundings become uncapped with cool mid-level
temps contributing to modest destabilization. Although lift is
nebulous, did add a small (20%) chance for a shower/storm into
central WI this afternoon. Small hail could occur with any
storms.

Otherwise, convection will likely organize to the west this
afternoon/evening, approaching the area late tonight. There is some
question how intense these storms will be as they approach, given
the diurnal minimum in instability, but strong moisture
transport/warm advection could help sustain stronger storms,
likely elevated, early Friday morning, especially if a more
linear organization occurs. The higher chances for severe storms
look to hold west of the area tonight, but trends will need to
be monitored through the day/evening with lower confidence in
convective evolution.

The band of showers/storms will move across the area Friday morning,
in conjunction with the weakening low-level jet and warm advection.
Although the stronger synoptic support will be displaced to the
north and west, closer to the trough, some daytime destabilization
could occur ahead of the front (30 to 60% for >1000 J/kg SBCAPE
across western WI per the HREF) with seasonably strong mid-level
wind fields. There is some question on the extent/intensity of re-
development as the parent trough lifts into southern Manitoba and
the low-level jet/moisture transport weakens through the day ahead
of the front. Right now the lower end severe weather risk (level 1
of 5) from SPC seems reasonable for this scenario, primarily across
northeast Iowa through central Wisconsin. Any lingering storms
should exit central Wisconsin during the evening. The progressive
nature of this system should limit rain totals, but localized 1-2"
amounts could occur with any more intense storms


Saturday-Monday:

Weak ridging should provide a dry start to the holiday weekend on
Saturday before mid-level troughing in conjunction with a few
interacting shortwave troughs develops across the Mid to Upper MS
Valley later in the holiday weekend. There is still a fair
amount of uncertainty with exactly how the details of this
pattern will evolve. Have continued to lean on the blended NBM
rain chances, given the degree of spread present with generally
30 to 60% rain chances Sunday/Memorial Day. Overall,
instability is forecast to be higher south of the region on
Sunday, which would tend to keep the higher chances for severe
weather farther south this weekend.


Tuesday-Wednesday:

Looking ahead towards the middle of next week, a transition to
northwest flow aloft is expected with the longwave pattern featuring
ridging across the Rockies and high plains and a trough over the
Northeast. Broadly speaking, global ensembles broadly support drier
conditions through the middle to end of the week as ridging works
east, but there is some uncertainty in placement of any shortwaves
traversing the periphery of the larger trough earlier in the week
within the northwest flow pattern. As a result, at least low end
rain chances persist into mid-week. Temps should be fairly
seasonable for late May.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1258 PM CDT Thu May 23 2024

VFR expected for most of the TAF period. Increasing upper level
cloud cover seen on satellite imagery early this afternoon is
mostly associated with widespread storms in the Northern Plains.
Other scattered, more local cumulus cloud cover associated with
a more moist are mass moving to the northeast into central
Wisconsin interacting with a drier air mass. Given the scattered
nature, limited impact, and location mostly in central
Wisconsin, have not introduced anything at either TAF site
(KRST & KLSE).

Widespread precipitation and storm chances reach the Upper
Mississippi River Valley late tonight from the west, eventually
traversing the local Mississippi River waterway into early
Friday morning. Have accounted for meager confidence in initial
precipitation and associated storm chances with PROB30 (30%
probabilities). Lower ceilings eventually move from west to east
with these precipitation and storm chances.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...JAR