185
FXUS63 KARX 111950
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
250 PM CDT Tue Jun 11 2024

.KEY MESSAGES...

- Isolated thunderstorms possible this afternoon, some of which
  could produce small hail and gusty winds.

- Complex severe weather setup for Wednesday afternoon and
  evening with the potential for multiple rounds of storms.
  Large hail, damaging winds, heavy rainfall and possibly a few
  tornadoes are all on the table depending on how storms unfold.

- Warmer weather on the docket for early next week with highs
  pushing into the upper 80s to low 90s from Sunday through
  Tuesday.

&&

.DISCUSSION...
Issued at 250 PM CDT Tue Jun 11 2024

This Afternoon and Evening: Isolated Storms

Current radar mosaic this early afternoon shows this morning`s
showers continuing to exit eastward out of the local forecast area.
GOES satellite imagery and RAP progs show an upper level trough
continuing to move towards the region, with surface observations
showing an approaching (currently draped down through central MN)
surface cold front. As the front moves across the area, model
guidance continues to suggest the potential for isolated to widely
scattered showers and storms to develop this afternoon/evening.
However, there still remains some uncertainty in just how much
instability will be able to build ahead of the front.

Hi-res guidance would suggest the potential for a very narrow
axis of instability with CAPE values generally around/under 1000
J/kg. If storms do develop, stronger storms may be capable of
producing small to marginally severe hail and gusty winds.
However, as we lose daytime heating the storm threat will
quickly decrease. There is still quite a bit of variability in
solutions on location/timing of initiation of storms, so will be
monitoring near-term satellite and radar trends closely through
the afternoon and evening.

Wednesday Afternoon and Evening: Severe Weather Details

A zonal pattern becomes established for tomorrow with a
seasonable strong 120-kt jet working over the Dakotas in the
wake of subtle perturbation in the flow. The surface boundary
sliding southeastward this evening quickly washes out overnight
with southerly flow becoming reestablished up through Minnesota
by sunrise tomorrow. Steepening mid-level lapse rates and
increasing surface theta-e values result in SB/MLCAPE values
approaching 2000 J/kg by the mid-afternoon while elongated
hodograph will be supportive of organized storm structures.

The main question revolves around convective mode and timing.
The latest 12Z HREF members are rather locked in on having
elevated convection develop on the nose of a weak low-level jet
towards sunrise in western Minnesota, with this complex and its
convective debris/cold pool serving as the focus for renewed
development during the early afternoon hours in central/eastern
Minnesota and western Wisconsin. The hodographs would be
supportive of supercellular structures and all storm hazards,
though the explicit composite reflectivity progs show rapid
upscale growth along the line into an MCS that propagates SSE
with the Corfidi vectors during the afternoon.

However, with the main synoptic forcing still off to the west,
renewed development is likely along the western flank of this
MCS cold pool that would result in multiple rounds of
thunderstorms training over the same area throughout the late
afternoon and evening hours along a northwest to southeast axis.
This would point to a potential heavy rain and flooding threat
somewhere in south-central Minnesota to northeast Iowa, but it
remains too early to pin down the exact area as such a threat
will rely heavily on how storms behave earlier in the day.

Hodographs become quite favorable for tornadoes as we move
through the evening hours, but the main question will revolve
around the surface airmass thermal characteristics given the
passage of the MCS earlier in the day. Any areas that do manage
to recover may realize the over 500 m2/s2 of 0-1-km SRH and pose
a tornado threat. At this stage, given the trajectory of the
afternoon MCS, such a threat might be limited to south-central
Minnesota and north-central Iowa.

Thursday and Friday: Cooler and Drier

Northwesterly flow settles in for the latter part of the week
in the wake of our midweek storms and holds temperatures near
seasonal norms for this time of year. With low level moisture
slow to depart during the day on Thursday, steepening low-level
lapse rates may result in diurnal showers developing during the
day, with the showers sliding southeastward as drier air filters
south during the afternoon. Friday is shaping up to be the
coolest and driest day of the forecast period as a 1020-mb
surface high pressure slides through, but highs should still top
out near 80 degrees.

Saturday and Sunday: Next Round of Stronger Storms

Return flow builds in behind the departing ridge early Saturday,
with surface dewpoints rebounding into the 60s by Saturday
afternoon. The medium range solutions are in modest agreement
with a sharp shortwave impinging on the backside of the
synoptic ridge and thus we should see strong to severe storms
somewhere across the Upper Midwest, but enough differences exist
in the placement of the surface baroclinic zone make it
difficult to nail down any further specifics on threats and
locations. How convection unfolds on Saturday and the timing of
the shortwave passage will play a role in the threat area for
Sunday, though the southwesterly flow is strong enough that the
warm sector may have time to recover on Sunday and result in
repeated rounds of storms each day. Stay tuned for more details.

Next Week: Warming Up

Upper ridging amplifies over the central and eastern CONUS for
much of next week, resulting in southwesterly flow across the
region and with it the first real surge of summertime heat.
There exists some modest synoptic differences with the various
ensemble members with respect to the strength of the ridge,
with the more amplified solutions resulting in warmer and drier
conditions whereas the flatter solutions bring periodic bouts of
thunderstorms and cooler temperatures as shortwave
perturbations ripple northeastward over the Dakotas. The
resultant precipitation forecast contains a smattering of 20 to
40 percent probabilities for the end of the forecast period, but
these will be honed in over the coming days as the strength of
the ridge is better analyzed. What is more certain is that we
will see above average temperatures with over 70 percent of the
available guidance pushing the mid-80s for highs and 20 to 30
percent of the members exceeding 90 degrees.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1259 PM CDT Tue Jun 11 2024

VFR conditions have prevailed through this early afternoon
across the forecast area, with this mornings showers continuing
to exit eastward. As a cold front pushes across the region,
there remains potential for the development of isolated to
widely scattered showers and storms this afternoon and evening.
Confidence still remains low on exact impacts to the TAF sites,
especially due to uncertainties in coverage. With this have left
the mention of thunder out right now and will monitor
conditions through the afternoon/evening. Expect there will be
near/short term updates, especially to any restrictions/thunder,
as details become more clear. Otherwise, increased winds this
early afternoon will ease tonight before increasing into the day
on Wednesday.

&&

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

&&

$$

DISCUSSION...EMS/Skow
AVIATION...EMS