663
FXUS63 KARX 070342
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1042 PM CDT Thu Jun 6 2024

.KEY MESSAGES...

- Hit and miss showers and winds diminishing this evening.

- Dry and breezy with seasonable temperatures for Friday.

- Below normal temperatures persist into this weekend, temperatures
warm up next week.

- Showers, possibly a storm (15-25% chance), this weekend will bring
rainfall amounts of up to 1/3" overnight Friday and into Saturday.

&&

.DISCUSSION...
Issued at 248 PM CDT Thu Jun 6 2024

Overview:

Water vapor satellite imagery, 500mb heights, and lightning showed
an area of closed low pressure over Ontario, Canada with the
troughing extending southeastward through eastern Great Lakes and
Ohio River Valley. Convection was mostly confined to the Gulf
States, however a line of storms was noted on the east side of
the Western U.S. ridge over parts of Kansas.

Hit and miss showers and winds diminishing this evening.  Dry and
breezy with seasonable temperatures for Friday:

At 18Z...surface high pressure was located over the Rockies with
surface low pressure over Ontario.  The local area was under
northwest flow aloft with the thermal 850mb trough moving through
WI.  Temperatures aloft to the west were already moderating. Deeper
moisture in the low-to mid levels of the atmosphere is pushing
south and east with the thermal trough. With heating today
clouds continue to form and should see some hit and miss showers
increase with the heating in the 60s to lower 70s. The most
recent WSR-88D mosaic had the showers north of I94. This should
continue to be the area where spotty showers occur with a few
sprinkles possible farther west. There are some hints that an
area showers could re- develop this evening with weak warm air
advection aloft. There is an uptick in the 900mb winds going
from 28 to 30kts to 30 to 40kts. For now have some sprinkles
mentioned, but left out measurable precipitation.

A wind advisory is in effect until 6pm.  Several sites in southeast
MN and northeast IA had sustained winds around 30mph.  Gusts mostly
35 to 50 mph.  Farther north and with increased cloud cover, with
was still breezy to windy, but more intermittent.  The winds should
decouple this evening as they become less mixed and uni-directional.

The ridge builds in more for Friday with temperatures in the 60s to
mid 70s. Fewer clouds, but it does look like northwest winds will be
on the increase.  The winds aloft are not as strong.  The winds are
actually stronger in the morning over Wisconsin and drop off, but it
should not be as windy, but should still see gusts 20 to 30kts.

Friday Night - Sunday: Cool with Showers, Maybe a Storm

A fairly persistent upper-level pattern will continue into the
weekend with a parked upper-level trough situated to our west
allowing for predominantly northwest upper-level flow to remain in
place across the region.  Friday night and into Saturday will
feature a piece of shortwave energy that will progress
northwest of the region in the aforementioned northwest flow
regime. Consequently, associated lift with the wave will help to
instigate broader coverage of convective development (mainly
showers) across much of the region overnight Friday and into
Saturday. Currently, a ribbon of weak instability (up to around
500-750 J/kg as shown in the 06.15z RAP) is advected into
portions of our region, primarily across northeast Iowa on
Saturday morning. However with quite a bit of spread amongst
guidance how thermodynamic profiles will manifest, confidence is
still on the lower side for if any storms will result.
Regardless, this shortwave could bring some rainfall totals of
up to 1/3" or so, primarily north of I-90. This is further
suggested in the 06.12z GEFS/EC ensemble which has high
probabilities for over 0.1" (60-90% chance).

Otherwise, Saturday and Sunday will trend below normal for
temperatures with 06.00z grand ensemble (GEFS/EC ensemble/Canadian
ensemble) showing the vast majority of ensemble members (almost
100%) keeping temperatures below the daily average high of
roughly 80 degrees at La Crosse for both Saturday and Sunday,
with median high temperatures in the upper 60s to middle 70s
across the local area for the weekend. Additional showers are
possible (15-25% chance) into Sunday as well with cyclonic flow
and weak instability still in place.

Next Week: Mild Beginning with a Warming Trend, Some Rain Chances

As we start next week, temperatures will remain mild relative to
average as the aforementioned broad upper-level trough begins to
slide further east. While this occurs, deterministic guidance hints
at a possible secondary smaller scale trough that sneaks into the
region early Tuesday. Currently, deterministic and probabilistic
guidance is all over the place with this system as the deterministic
06.12z GFS develops a very strong upper-level trough into the
region. This is contrasted heavily by the 06.12z EC which has a
much weaker shortwave. Consequently, the 06.12z GEFS/EC
ensemble have probabilities for measurable precipitation that
reflect this (40-60% chance), suggesting that there is large
disagreement between various ensemble members. As a result, hard
to totally buy into any rain chances early next week but will
keep chance (roughly 30%) mention for precipitation chances for
Tuesday. Regardless on the impact of this trough to our region,
guidance suggests that the large scale ridge further west will
push into our region but flatten as it progresses beginning in
the middle of the week. Consequently, temperatures will begin
warming by the middle of next week with increasing confidence
(60-90% chance in the 06.12z GEFS) in highs reaching 80 during
the second half of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1040 PM CDT Thu Jun 6 2024

VFR expected across the local forecast area from southeast
Minnesota, northeast Iowa, and western into central Wisconsin.
Increased winds through Friday, albeit not as strong as
Thursday. Subsequent flight impacts and precipitation overnight
Friday into Saturday morning.

&&

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

&&

$$

DISCUSSION...Naylor/Zapotocny
AVIATION...JAR