-- Discussion containing changed information from previous version are highlighted. --
754
FXUS63 KARX 110407
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1107 PM CDT Mon Jun 10 2024

.KEY MESSAGES...

- Following more widespread showers earlier in the day, a few
  storms are possible (20-40% chance) Tuesday afternoon with a
  hail/gusty winds risk (level 1 of 5 for severe), mainly west
  of the Mississippi River.

- Severe storm risk (level 2 of 5) increases late
  Wednesday/Wednesday evening with a damaging wind/hail threat.
  Details/magnitude of this risk will be refined as confidence
  increases.

- Some lingering storm risk possible into Thursday depending on frontal
  timing with drier, seasonable conditions into late week and
  warmer, potentially more unsettled conditions by the weekend.

&&

.DISCUSSION...
Issued at 240 PM CDT Mon Jun 10 2024

Tuesday: Shower/Storm Potential

Dry, Canadian high pressure will be shunted east overnight ahead of
a progressive shortwave trough. A band of showers likely will work
east through the day in conjunction with warm advection/modest
moisture transport, but instability looks minimal, supporting a
limited thunder risk at best. Rain amounts also should be fairly
light with this precip, around 0.1 to 0.2" or less for most
areas.

In the wake of these showers, a narrow instability axis may
develop ahead of a weak front progressing east across Minnesota
and Iowa. HREF mean surface-based CAPE values remain mostly
under 1000 J/kg within the instability axis across southeast
Minnesota and northeast Iowa. However, some enhancement (40-50
kts) of mid-level flow could support storm organization for
isolated to widely scattered storms during the mid/late
afternoon hours into early evening, potentially producing small
to perhaps marginally severe hail in the strongest storms,
given elongated straight hodographs. Gusty winds are also
possible, especially if stronger warming/mixing occurs. Overall,
weak forcing and seasonably weak instability look to be
mitigating factors for stronger storms.


Wednesday-Thursday: Severe Storm Potential

Warm advection and breezy southerly flow will develop on
Wednesday ahead of a shortwave passing along the Canadian
border. A pool of instability will build across MN/IA into
western WI, especially by later afternoon/evening as a low-level
jet/moisture transport increases, with the CAPE dependent on
low-level moisture advection strength and degree of mixing.
However, deep layer shear of 40-50 kts across MN into northern
WI will provide a favorable kinematic environment for
potentially strong to severe storms. Details on evolution remain
somewhat unclear, but storms may develop later in the afternoon
ahead of a surface boundary working southeast, being fed by a
low-level jet/warm advection. In this scenario, initial storms
may develop into a cluster or clusters of storms into the
evening with more of a hail threat initially storms perhaps
transitioning into an increase in wind if a larger cold pool
develops.

In addition, warm cloud depths exceeding 3.5 km and higher
precipitable water values focused on the nose of the moisture
transport could support a heavy rain threat, although the system
is progressive, and the low level jet will pivot east through
the night. Mesoscale details will impact storm development/evolution,
including placement, so continue to monitor for updates over
the next day. As the front continues to sag south into Thursday,
the higher threat for storms looks to shift farther south into
Iowa. However, will have to continue watch frontal timing,
especially across northeast Iowa into southwest Wisconsin.

Friday-Monday:

High pressure will build back into the region for Friday as the
upper flow briefly transitions northwesterly. However, medium range
guidance supports mid-level ridging expanding into the Upper
Midwest/Great Lakes through the weekend into early next week. This
would lead to temps warming above average by early next week and
increasing moisture/instability. High temps may approach 90 by
Sunday with more summer-like lows in the 60s. There is some signal
for a shortwave trough to eject northeastward over the weekend from
the southern Rockies, with global ensembles (GEFS/EPS/CMC) showing
the footprint for higher 24-hour rainfall amounts (at least 0.5")
from eastern SD through central MN Saturday/Saturday night. At
this range, though, forecast confidence remains on the lower
side, and it is too early to highlight any potential targets for
heavy rain/severe storms.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Baumgardt