377
FXUS63 KARX 110832
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
332 AM CDT Tue Jun 11 2024

.KEY MESSAGES...

- Will there be enough recovery this afternoon and early evening
  for some isolated strong to severe storms to develop? If the
  atmosphere is able to recover, the main threats would be
  damaging winds and hail up to 1-inch in diameter.

- Still some uncertainty of how long discreet supercells will
  last prior to becoming line/lines of storms. The discreet
  storms will be capable of producing tornadoes, large hail, and
  damaging winds. As cold pools coalesce, these storms will
  evolve into line/lines with damaging winds becoming the
  primary threat.

- From Fathers Day weekend into early next week, still
  uncertainty on the position of a strong 500 mb ridge. This
  impacts the tracks of mesoscale convective complexes and
  temperatures.

&&

.DISCUSSION...
Issued at 332 AM CDT Tue Jun 11 2024

Through early this evening...

A convectively induced shortwave trough will move east through
the area this morning and early afternoon. There is little CAPE
across the area during this time period, so just looking at
some showers for this time period.

From mid-afternoon into early this afternoon, a cold front will
be moving east through the area. Still plenty of uncertainty on
whether the atmosphere will be able to recover enough for
showers and thunderstorms to develop. The 11.00z LREF has up to
a 30% chance of surface-based CAPES reaching 500 J/kg and less
than a 10% chance of the surface-based CAPES reaching 1000 J/kg.
The high-resolution FV3 and 4 km NAM have the most robust storms
and greatest coverage. Meanwhile, HRRR and RAP only have
isolated showers and storms. If there is enough recovery in
CAPES in the afternoon, soundings would suggest that there could
be some damaging wind gusts and hail approaching 1-inch in
diameter.

Wednesday and Wednesday night...

The models continue to show that a 60-80 knot mid-level jet
moving along the US and Canadian border during the afternoon and
evening. The CAMs are differing on timing issues and what areas
will be impacted by strong to severe storms. Overall, they are
in decent agreement that the convection will initially start
out as discreet supercells over western Minnesota and then they
evolve into line or lines of storms. The discreet supercells
will be capable of producing tornadoes, large hail (possibly in
the excess of 2-inch in diameter) and damaging winds. The main
question is how fast will it take for the supercell cold pools
to coalesce and evolve into line/lines. Both the NAM and GFS
show strengthening winds below 3 km. This results in helicities
in the 200 to 400 range along and west of the Mississippi
River. However, there is also concern that there may be some
convective feedback in these models and this might be causing
these winds to be too high. Once the storms develop into lines,
the primary threat will likely turn more into a wind threat.

The latest CAMS are suggesting that the showers and storms will
be moving south of the area by early evening, so concerned that
the rain chances are too high for overnight Wednesday night and
Thursday morning.

Fathers Day Weekend...

The 500 mb ridge will be building north and moving east at the
same time. Still some uncertainty on how far north this front
will build. This impacts the tracks of a couple of mesoscale
convective complexes and the potential high temperatures. If
this ridge does not build as far north as expected, high
temperatures would be in the 70s and lower 80s. If the ridge
builds further north, high temperatures would range from the
mid-80s to lower 90s.

Early Next Week...

The strong 500 mb ridge will be centered somewhere from the
Mid-Atlantic to the southern Great Lakes. There continues to be
some uncertainty on the western periphery of the 700 mb
capping. This will impact the track of a series of mesoscale
convective complexes and temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1105 PM CDT Mon Jun 10 2024

VFR conditions are expected at this time. A weather system will
be moving through Tuesday morning with some showers at the
airfields.

With some instability growing in the afternoon Tuesday, some
TSRA are possible over southeastern MN late (21-22Z+). At this
time, decided to include a PROB30 with a strong convergent
signal seen on the front in the area of KRST and some
instability present and wind shear for storm organization.
Coverage is still a question - how many storms will be around to
directly hit the airfield. These storms would have the
potential to produce hail the size of nickels, larger if
instability grows larger after the morning showers. These storms
are expected to become more isolated or dissipate as they move
toward KLSE and thus the PROB30 was not included in the TAF.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...Baumgardt