756
FXUS63 KARX 271100
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
600 AM CDT Mon May 27 2024

.KEY MESSAGES...

- Two More Rounds Of Precipitation Today & Tonight With Highest
  Storm Potential Later This Morning Into The Afternoon With
  Primary Hazards Of Small Hail & Strong Winds

- Decreasing, Slightly Below Normal Temperatures Through Midweek

- Warming Into The End Of The Week With A Drier Forecast
  Trending

&&

.DISCUSSION...
Issued at 300 AM CDT Mon May 27 2024

Precipitation & Storm Chances Today:

Two more rounds of precipitation and storms on tap for today and
tonight as two shortwaves advect across the Upper Mississippi River
Valley along northwest flow. The initial low can be seen on upper
level GOES water vapor imagery early this morning, closed from the
Rocky Mountain West into North Dakota. This initial upper level low
is expected to continue its southeasterly trajectory through the
morning hours, eventually advecting a bowling ball of synoptic
forcing through the forecast area along the Upper Mississippi River
Valley. Ongoing precipitation ahead of this area of lower heights
will reach southeast Minnesota early this morning and cross the
Mississippi River Valley into the early afternoon hours.

Expected Impacts & Primary Hazards:

ACARS soundings show Cold Air Advection (CAA) along the northwest
flow from the Northern Plains into Minneapolis-St Paul Int`l
Airport. The CAA is steepening low level lapse rates early this
morning which will provide slight instability locally as the
low trudges southeast. Therefore, storm chances increase into
the Upper Mississippi River Valley concurrent with overall
moisture decreases. Current PWATs through the Northern Plains
are pushing 1" as this decreasing trend will drop them to near
0.75" as they traverse the local area in southeast Minnesota
later this morning. This narrow band of limited moisture will be
slightly assisted by remnants of the easterly exiting low over
the Great Lakes. Therefore, unlike Friday, heavy rain will be
less of a concern as swollen rivers are lowering early this
morning. HREF maximum QPF does push 1.0" in spots, while PMM
(Probability Matched Mean) remains less than 0.5". Besides the
decrease in moisture, the transient nature of precipitation
will also limit overall amounts. In summary, highest amounts
could push 1" over a 6 hour window within the stronger storms
that manage to for. Widespread amounts will most likely remain
in the 0.25" to 0.5" range.

As the wave passes, SB and MUCAPE from 500 to 1000 J/kg will advect
primarily from southeast Minnesota into northeast Iowa this
afternoon. The concurrent bowling ball of mid level vorticity will
provide lower level stretching as an 850mb jet potentially perks
through central Iowa. While best deep layer shear lies to the
southwest, resulting in Convective Allowing Models sustaining
potential stronger storms, non-supercell Tornadoes (NSTs) cannot be
ruled out locally. The normalized SPC NST parameter incorporates
limited ingredients which alludes to the mesoscale nature of
necessary forcing. Limiting factors, dependent on which high
resolution Convective chose to interrogate, are placement of the
surface boundary and resultant surface shear resulting in
nebulous shear concurrent with an increasing off deck jet
streak. Therefore while NSTs cannot be ruled out, necessary
mesoscale ingredients such as surface shear from the frontal
boundary or meso-gamma to beta outgoing cold pools, and lacking
deep layer shear will be important to monitor this afternoon.

With the colder temperatures providing freezing levels near 5k ft,
the primary hazard will be small to medium sized hail as well
as strong winds. Limiting factors will be overall lack of CAPE
and transient, pulse nature of any stronger storms. Again,
better forcing and shear lie to the west and southwest so our
western peripheral counties are best aligned with any hazards.
Overall, quite a conditional threat.

Second Round Of Precipitation Tonight Into Tuesday:

Subsequent precipitation chances will be tied to an appendage of the
everlasting upper level low situated over southern Canada. Moisture
remains low which will limit heavy rain potential. Long and skinny
CAPE profiles result in very limited storm potential. Overall
rainfall amounts in the hundreths expected.

Cooler Temperatures Through Midweek:

Otherwise, primary impacts will be cooling temperatures within the
CAA regime. Slightly below normal temperatures with daytime highs in
the 60s and overnight lows in the 40s from Tuesday through Wednesday
night. These slightly below normal temperatures will be short lived
as the progressive pattern pushes an amplified upper level ridge
through the Central Plains through midweek, quickly turning the
tide to slightly above normal temperatures.

Warmer Through The End Of The Week, Trending Drier:

Resolving the resultant quasi-omega block has been a challenge
between global models (GFS/GEFS/ECMWF/EPS/CMC/GEM) has been a
challenge. A general slowing trend continues for intramodel
dProg/dt. The GEM exhibits the most amplified ridge in the most
recent run (27.00z), showing  certainty (100% confidence) in mid
level heights greater than 576 dam enveloping Wisconsin into Friday.
Weakest, most transient model continues to be the GEFS, keeping
certainty for the same aforementioned parameter as far north as the
IA/MN/WI border. As a result, discrepancies surround precipitation
confidence through Friday as well as temperatures. Although,
dProg/dt for the GEFS has trended and abated in the most recent run
for 100% confidence. Instead of suggesting definite probabilities
for greater than 0.01" of 24 hour precipitation the GEFS breaks
certainty both south and north of the forecast area during the
late morning hours on Friday. As expected, the more amplified
ridge in the EPS and GEM abate confidence for 0.01" until late
afternoon. Similarly, confidence is slightly higher in the EPS
and GEM for slightly above normal temperatures.&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1052 PM CDT Sun May 26 2024

VFR conditions overnight are expected to continue through Monday
afternoon. As a system approaches from the NW Monday afternoon,
scattered showers and thunderstorms are expected to develop.
Went with a prob30 at RST and LSE for afternoon thunderstorms.
Where these thunderstorms occur, will likely see MVFR conditions
during the rain. Otherwise, VFR conditions expected through the
period.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 549 AM CDT Mon May 27 2024

Initial VFR this morning will become MVFR/IFR through the
morning hours as storms move from northwest to southeast.
Initial impacts expected to reach southeast Minnesota near
27.15Z. MVFR expected with TS chances increasing from northwest
to southeast. Storm and rain chances are quick hitting allowing
flight restrictions to depart quickly this evening.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...JAR