044
FXUS63 KARX 240403
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1103 PM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Showers and thunderstorms return to the forecast Monday
  evening into Monday night, with a conditional risk for severe
  thunderstorms. A Slight Risk (level 2 of 5) for severe weather
  remains for Monday evening. Should everything come together
  and severe storms storms develop, significant (75+ mph) wind
  gusts could occur.

- Another brief break for mid-week before additional shower and
  storm chances return late in the period. Details to be refined
  in the coming days.

&&

.UPDATE...
Issued at 700 PM CDT Sun Jun 23 2024

Continue to monitor incoming guidance concerning the
thunderstorm threat for Monday night. Latest RAP/HRRR capping to
incoming surface-based instability is really really strong
(300-500 J/Kg of CIN) with the elevated mixed layer moving into
the region from the southwest. Using 700 mb temperature as a
proxy to capping strength, by 00Z Tuesday /7 pm Monday/, the 12C
line is well into the area running from KEAU-KDBQ, and only
warming into the evening on strong warm air advection from the
southwest. The cap weakens to the northeast with the gradient
aligning from MSP-EAU-DLL-MSN /I-94/. The latest extended HRRR
run from 23.18Z now forecasts speckles of reflectivity over the
forecast area later Monday, representative of some mid-level
saturation and very limited elevated instability, with the
convective system tracking from nrn MN into the UP/nrnWI. This
makes sense as it is riding around the capping in place further
south, although it may be a bit too far northeast. In any case,
should this strong of a cap build in, the chances really
increase for a system to track northeast of I-94.

&&

.DISCUSSION...
Issued at 205 PM CDT Sun Jun 23 2024

This Afternoon and Evening: Sprinkles and a Stray Thunderstorm

Progged soundings show modest instability this afternoon and
evening in the northern portions of the forecast area. While dry
air above the top of the mixed layer has inhibited vertical
growth thus far in our CWA, plenty of cumulus are seen on
visible satellite and, farther northwest, a couple showers and
thunderstorms have developed west of Hawyard. Have thus added
low end mentions of thunder to the forecast this afternoon and
evening.

Monday Evening and Night: Conditional Severe Risk

After one nice, sedate, temperate day with dewpoints in the
lower 60s for Sunday, warm and muggy conditions return by Monday
afternoon as southwesterly 850mb moisture advection resumes in
earnest. As this occurs, strong EML looks to advection eastward
with 700-500mb lapse rates approaching 8-8.5 C/km. Thus, expect
CAPE values to increase markedly, with progged MLCAPE exceeding
3000 J/kg in our CWA. Stout capping across the forecast area
should keep convection from developing in our area directly but,
farther to the northwest, a combination of a slightly weaker
EML and cooling aloft ahead of a shortwave may allow convection
to develop. Should this occur, progged sfc-6km shear there is
around 55 knots, so expect organized convection to develop, with
the relatively straight hodographs above 1km suggesting
splitting storms and subsequent upscale growth into an MCS would
occur. As 850mb moist fetch only ramps up across the CWA in the
evening, it is plausible that this MCS would be able to dive
southeastward through the forecast area. Given the strong shear
and very high instability, this could result in significant
(75+ mph) wind gusts were it to occur. All the above said, the
strong EML suggests that initiation is not a given and neither
is the ability for any MCS to survive the trek southeast.

For Tuesday, while blended guidance continues to show the
potential for additional convection, am doubtful this occurs as
guidance has generally sped up the passage of the front
associated with the aforementioned shortwave that may kick off
an MCS the previous night. If that MCS does occur, resulting
cold pool would likely force the boundary well south of the CWA.
In either case, while SPC has a Slight Risk (level 2 of 5) in
portions of NE IA and SW WI based on the 00z guidance suite, CSU
ML-based outlooks using the 12z suite show a notable trend away
from our forecast area in line with a faster progression.

Rest of Week: Midweek Break, Another Round Possible
Friday/Saturday

Surface high pressure in the wake of Monday night/early
Tuesday`s front and a reduction in heights aloft should serve to
keep things cooler than normal and precipitation free Wednesday
and Thursday.

Friday and Saturday, next longwave trough looks to advance
eastward just to our north. While precipitation is a good bet, guidance
shows a variety of timings with this feature, so rain mentions
are spread across Thursday night through early Saturday for now.
Additionally, severe thunderstorm risk is uncertain as well as
it remains unclear just how much instability there will be when
best upper forcing arrives.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1057 PM CDT Sun Jun 23 2024

VFR conditions are forecast for Monday. However, during the
evening hours, thunderstorms could develop over central MN and
move southeast toward the airfields. There is very warm air
above the surface which should favor thunderstorms to form
further north and east - toward KMSP to KDLL and northeast
generally. Wind shear profiles combined with the instability,
should it be released, would form severe thunderstorms with
large hail and mainly a damaging wind threat.

For now, have decided to add VCSH and a VFR BKN cloud deck for
Monday evening until confidence can grow in a given outcome.


&&

.HYDROLOGY...
Issued at 613 AM CDT Sun Jun 23 2024

Heavy rainfall over the previous couple of days has resulted in many
area rivers and streams running high or in flood stage. Flooding
concerns will last well into the week, with the Mississippi
River also continuing to rise. Fortunately, little rainfall is
expected into Monday. However, another round of showers and
thunderstorms will be possible Monday night into Tuesday.
Although some details are uncertain at this time, will need to
monitor for any further potential hydro impacts with these
storms. Please continue to reference the latest flood
statements for additional updates and details.

&&

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

&&

$$

UPDATE...Baumgardt
DISCUSSION...Ferguson
AVIATION...Baumgardt
HYDROLOGY...EMS