458
FXUS63 KARX 051801
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
101 PM CDT Wed Jun 5 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms develop this afternoon
  with a threat for hail and gusty winds from stronger storms.

- Windy conditions expected later today and again Thursday,
  especially west of the Mississippi River. Advisory issued for
  parts of the area today, and may be needed again on Thursday.

- Cooler than normal temperatures expected over the weekend.

&&

.UPDATE...
Issued at 307 AM CDT Wed Jun 5 2024

After further discussion with other forecast offices, some
concern about how to best handle convective induced wind threat
later today, along with increasing gradient wind setup overall.
Late decision was to include a corridor of Wind Advisories with
that possibility. Admittedly not a clear cut situation but this
will give people at least some advance notice that wind gusts
could be strong at times later in the day.

&&

.DISCUSSION...
Issued at 200 AM CDT Wed Jun 5 2024

Busy past 48 hours with convection fueled by relatively high
precipitable water values for early June but that is mainly
east of the area now as mid level trough and associated cold
front push through. Drier airmass will certainly diminish the
heavy rain threat but the overall threat for convection
seemingly has not ended for the week.

TODAY - Afternoon convection threat

Upper low across southern Canada and strong mid level wind max
rotating around trough base will strengthen troughing next 36
hours across western Great Lakes. With height falls, cooler air
aloft, and June sun angle, model soundings suggest steep lapse
develop with enough moisture for scattered afternoon and evening
thunderstorms, even with a relatively shallow instability
/CAPE/ layer. Warm cloud layer last couple days will be replaced
with cooler air aloft raising hail chances in stronger storms,
but perhaps greater risk will be wind gusts given such strong
flow in the mid levels. Any stronger storm could tap into that
wind level and mix it down to produce locally higher storm
gusts.

Marginal Risk /Level 1 of 5/ from Storm Prediction Center seems
appropriate given setup.

Gradient winds are also expected to increase this afternoon,
especially across western areas, as trough amplifies. Highest
probabilities for peak gusts at or above 40 mph via 05.00z HREF
remain from Rochester MN to Mason City IA and points west. Not
anticipating need for wind related headlines quite yet, but
Thursday could be another story.

THURSDAY - Higher winds / possible Wind Advisories

As Canadian trough amplifies even more on Thursday and drops
into Great Lakes, broad ridge builds across western CONUS. This
process spreads belt of stronger mid level winds across northern
Midwest into the Great Lakes. Seeing a bit more variability on
how strong wind gusts might get in the ensemble data so not a
slam dunk yet that headlines will be needed. But not out of the
question to see some peak wind gusts in the 35 to 45 mph range
during peak mixing of the afternoon.

UPCOMING WEEKEND - Cooler than normal with diurnal shower
chances

Large trough evolution across southern Canada and Great Lakes
will likely keep temperatures cooler this weekend along with
more unsettled weather. Details hard to pull out that far in
advance but diurnal shower activity a possibility. Luckily this
pattern limits the threat for severe weather, always a good
thing given we are approaching our climatological peak for
storms.

NEXT WEEK - Evolution of large western ridge and possible warm
up

Will certainly be watching evolution of larger upper ridge
across western CONUS and developing heat wave. Some medium range
guidance has been suggesting this will evolve east towards
latter half of next week which could bring us back into a warmer
and drier regime. Even some of the ECMWF ensemble guidance has
been hinting at this perhaps peaking in the June 18-22 time
frame.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1255 PM CDT Wed Jun 5 2024

Clear skies will give way to increasing clouds as scattered showers
and thunderstorms develop this afternoon into the early
evening. VFR ceilings fl050-150 are expected. Low confidence in
the coverage of thunderstorms. Due to their spotty nature,
included a VCTS at KLSE, but will need to watch KRST. West winds
15 to 30kts into early evening, but should see some stronger
gusts 30 to 40kts near showers and storms. The winds should
decrease this evening, but increase again Thursday from the
northwest.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory until 7 PM CDT this evening for MNZ086-087-094-
     095.
IA...Wind Advisory until 7 PM CDT this evening for IAZ008-009-018-
     019.

&&

$$

UPDATE...Shea
DISCUSSION...Shea
AVIATION...Zapotocny