137
FXUS63 KARX 171711
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1211 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Shower and storm chances (20-30%) remain in the forecast for
  Saturday afternoon and evening. An isolated strong to severe
  thunderstorm cannot be ruled out if storms do develop.

- Additional shower and thunderstorm chances remain for the end
  of the weekend and into next week. Keep up to date with the
  latest forecast, especially if you have outdoor plans next
  week.

&&

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

Precipitation Chances Through Saturday Night:

A fairly quiet night so far as clouds have cleared over much of the
local area. Surface observations and GOES Nighttime Microphysics
reveal some patchy fog has developed over parts of the area and
along some river valleys this early morning. A subtle wave was also
noted in GOES satellite imagery generally moving from the Dakotas
towards Minnesota this morning, with ongoing and developing showers/
storms advancing across Minnesota. Latest hi-res models try to
develop a few echos during the day today locally as this system
continues eastward. Model forecast soundings show some mid level
moisture and elevated instability, but there is some concern with
quite a bit of dry air shown in the lower levels into the day. For
now have added in some low sprinkle/shower chances (mainly SE MN
into NC WI) to account for any precip that may be able to develop.
Otherwise, warm air advection will spread across the region today,
with high temperatures rising into the upper 70s to low/mid 80s.

As we head into Saturday an upper level shortwave trough is forecast
to move eastward across southern Canada and the Northern Plains
towards the region on Saturday. An associated surface boundary will
move through the region bringing some chances for some showers and
isolated storms to develop. Model guidance suggests increasing
instability building through the afternoon along with steepening low
level lapse rates as high temperatures rise into the 80s. Have noted
model soundings do show some capping in place across the area,
though a few models show this cap eroding in the north by the early
evening. Will need to monitor conditions especially as more hi-res
guidance continues to come in. For now, SPC has placed portions of
north-central WI in a marginal risk (1 out of 5) for severe weather.

Additional Showers & Storms Into Next Week:

As we head into the end of the weekend and into early next week,
flow aloft becomes southwesterly as an upper level trough develops
in the western U.S. A series of shortwave energy looks to eject out
from the trough and lift through the region, bringing a more active
period of shower and storm chances. Ensembles do appear to be coming
together on increasing shower and storm chances late Sunday night
into Monday and again on Tuesday. With that said, there is still
plenty of variability in details (i.e. timing, amounts) among GEFS
and ECMWF ens solutions. This variability continues to result in
broad precipitation chances in blended model guidance. However, in
reality there will be shorter more focused windows for shower and
storm chances which will be better reflected as details are refined.
Do not want to jump ahead too much, but it will be a period to watch
as WPC has highlighted a day 4-5 marginal for excessive rainfall and
CSU severe progs are beginning to highlight some probabilities
across the region. Keep an eye on the forecast for continued updates
over the coming days, especially if you have outdoor plans next
week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 650 AM CDT Fri May 17 2024

Main source of uncertainty in the upcoming TAF period is the
potential for a brief shower, mainly at RST soon after issuance
time. At this time, do not expect any kind of operational
impacts even if (10% chance) a shower briefly affects the
terminal. Otherwise, with winds a few knots stronger than last
night, do not expect a recurrence of the valley fog that plagued
LSE early the morning.

&&

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

&&

$$

DISCUSSION...EMS
AVIATION...Ferguson