FXUS63 KARX 041906
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
206 PM CDT Sat May 4 2024

.KEY MESSAGES...

- Fog possible tonight along and east of the Mississippi River.

- An active stretch of weather from Monday night through at
  least Thursday as multiple rounds of showers move through.
  Severe weather risk for Tuesday is trending south.

&&

.DISCUSSION...
Issued at 200 PM CDT Sat May 4 2024

TONIGHT: fog, frost? 

With a day of wetting rains saturating the boundary layer and clouds 
not slated to clear until near or after sundown, decent setup for 
fog. Add in diminishing winds and the potential increases. Short 
term models aren't overly enthusiastic on the widespread possiblity 
for thick/dense fog though. HREF and RAP hold any "thicker" type fog 
to the I-94 corridor northward. Can't rule out a thin fog layer in 
the river layers too, ala what occurred a couple days ago. Will hold 
with some mention of fog mostly along, east of the Mississippi river 
for now. 

In addition, passage of a cold front will bring in colder air with 
lows expected to bottom out in the upper 30s to lower 40s. Some 
potential for frost in low lying areas as a result, mostly in 
central and north-central WI. Not widespread enough, nor high enough 
confidence, to warrant a frost adv at this time. 

Active Weather Pattern Next Week:

Shortwave ridging will be over the area through Monday. Warm 
southerly flow and increasing PWATs are expected out ahead of a low 
moving through the Upper Plains. Temperatures in the low 70s 
expected. An 850mb jet with winds between 30 and 45 kts will be over 
our area during the late evening on Monday and overnight period into 
Tuesday. Convection across the Plains is expected to begin Monday 
afternoon and push eastward throughout the day. Moisture
transport increases late in the day on Monday across eastern 
Minnesota and Iowa. As the storms push eastward into Wisconsin, 
even though shear and life potential increases, instability will
decrease. Thus the severe threat with this first round of 
storms is low. Another factor that plays into the severe threat 
is timing. These storms will push through the overnight period, 
so daytime heating and the gradually weakening warm sector will 
help to minimize the severe threat. 

After this first round moves out by early Tuesdsay afternoon, model 
guidance continues to show another round of storms forming over Iowa 
as a shortwave pushes around the main low. While this wave does look 
stronger with higher CAPE and lift potential, moisture advection is 
weaker and so is the low-level shear. Even though the ingredients 
are there to at least have some thunderstorm development, the 
biggest inhibitors for development is that environment will 
probably be worked over the morning thunderstorms and that the 
warm sector will be further southeast of our area. At the 
moment, southeastern Iowa and northern Illinois will have the 
better chances at afternoon thunderstorm development. 

From Wednesday through the rest of the week, this shortwave becomes 
a cutoff low and the original low weakens and gets absorbed by the 
new low. This cutoff low will be over the Upper Midwest providing 
the area with northwest flow and periodic chances for precipitation 
to occur.  With this flow pattern, temperatures will cool down and 
remain in the low to mid 60s from Thursday through the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1135 AM CDT Sat May 4 2024

CIGS: IFR/MVFR will hang around through the afternoon, showing some 
improvement with a increasing then scattering/clearing of the clouds 
near/shortly after 00z this evening. Mostly SKC conditions then 
expected through the night and Sunday, although some some scattered, 
flat CU could occur Sun afternoon. 

WX/vsby: radar trends and CAMS models suggest the -shra will have 
pulled east/northeast of the TAF sites by 18z and will trend the 
forecast that way. With the rainfall saturating the boundary layer, 
and clouds not expected to clear until close to sundown (or after), 
some threat for fog. Latest RAP and HREF suggest at least MVFR fog 
in the I-94 northward. NAM soundings at KLSE suggest a very shallow 
river valley fog could develop, although wind speeds just off the 
sfc would work against that reaching the airport. Tough call here 
but will lean toward the HREF for now and keep and fog related vsby 
impacts out of the forecast. Will monitor and update if needed. 

WINDS: northwest becoming light and vrb tonight with some shift back 
to the west/northwest Sun but still light.

&&

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

&&

$$

DISCUSSION...Cecava/Rieck
AVIATION...Rieck