594
FXUS63 KARX 281059
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
559 AM CDT Sun Apr 28 2024

.KEY MESSAGES...

- Heavy rain axis has shifted south of the area. A more
  widespread rain of 0.5-1" is expected through Monday, with
  most falling during the afternoon and evening today. The risk
  of storms being severe is low.

- An active week is expected with periodic rain and storm
  chances with the next chance coming Tuesday/Tuesday night.

&&

.DISCUSSION...
Issued at 318 AM CDT Sun Apr 28 2024

Widespread Storms Today into early Monday:

As the surface low moves northeast towards the Upper Midwest region,
dewpoints and lift will increase. Dewpoints increase as the warm
sector pushes northward, while lift increases due to waves of energy
originating from the surface low passing through the area. Current
CAM guidance has a swath of widespread showers and storms moving
into northeast Iowa and southern Wisconsin by mid-morning today and
pushing northward through the afternoon. As this band moves
northward during the afternoon, moisture advection increases from
the south, resulting in PWAT values between 1" and 1.4". These
values are in the NAEFS 90th to 99th percentiles for PWATS. The
highest PWATs will be along the stationary boundary in far southern
Wisconsin, northern Illinois and eastern Iowa. Not much is in the
way for instability, as the boundary stays to our southeast for
most of the day, at least with this first round of storms.
Instability will increase a little as the surface low pushes
northeastward. SBCAPE and MUCAPE will be around 500J/kg heading
into the late afternoon and lasting through the evening. This
appears to be the most likely time for any severe weather to
occur. Not much is expected given the lack of instability and
daytime convection, however with the surface low close by and
good amounts of shear, there remains a marginal risk for severe
weather along and south of I-94. As far as precipitation goes,
most areas look to have 0.5 to 1" of rain from today into
Monday. The latest HREF probabilities have between a 20 and 40%
for at least an 1" of rain to occur.

Active Pattern Next Week:

Next week is looking like another active period as the region ends
up being in a predominant zonal flow. This flow pattern will result
in periodic shortwave disturbances to bring more precipitation
chances throughout the week. The first wave to move through is
expected on Tuesday. Current guidance has a compact shortwave moving
through the area. This will be accompanied by good moisture
advection from the Gulf of Mexico ahead of a cold front Tuesday
afternoon/evening. By Tuesday afternoon, the cold front will be near
I-35, where the greatest lift and instability will be at, due to
being in close proximity to the shortwave. MLCAPE values of around
500J/kg are expected across southern Minnesota at this time as well.
Given these dynamics, SPC has gone with a Marginal for portions of
southeast Minnesota. CSU severe probabilities also have a 5 to 15%
chance of severe weather occurring late Tuesday.

There is a lot of uncertainty with what happens after Tuesday. Zonal
flow will continue. Ensemble guidance has differing solutions with a
slight lean into a trough moving through the region on Thursday and
another on Saturday. Confidence is not low, however the week will
remain active with multiple chances of precipitation.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 559 AM CDT Sun Apr 28 2024

Showers will increase in coverage through the morning and
continue at least into this evening before coverage begins to
lessen. Isolated storms are possible this afternoon into tonight
(20-40% chance), but confidence in timing/coverage is too low
to mention. Flying conditions will deteriorate with ceilings
likely trending LIFR/IFR through the day, possibly MVFR at times
at KLSE with IFR/MVFR visibilities at times as low-level
saturate with showers. Winds will increase from the east with
some gusts in the 20-30 kt range before diminishing this evening
and shifting south/southeast.

&&

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

&&

$$

DISCUSSION...Cecava
AVIATION...JM