La Crosse, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

134
FXUS63 KARX 152345
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
645 PM CDT Fri May 15 2026

.KEY MESSAGES...

- Storms develop this evening west of the Mississippi River and
  push east overnight. Storms may become strong to severe with
  large hail being the primary threat initially before
  transitioning to a damaging wind threat later into the
  evening.

- Additional storms are likely both Saturday evening/night and Sunday
  evening. While strong to severe storm potential appears more
  limited on Saturday night, severe potential increases more on
  Sunday with much of the area in a slight risk (level 2 out of
  5) for severe weather.

- Monday currently has the greatest risk for severe weather over
  the next four days across the entire local area. Large hail,
  damaging wind gusts and tornadoes are on the table in this
  setup as storms move through the region on Monday.

- With multiple rounds of storms expected this evening through Monday,
  rises on area rivers into flood stage will be possible where
  storms frequent the same locations.

&&

.DISCUSSION...
Issued at 135 PM CDT Fri May 15 2026

This Evening & Tonight: Storms Likely, Several Strong to Severe
Possible

A fairly notable increase in convective coverage has been
observed across the CAMs over the past couple of forecast
cycles resulting in increasing confidence for strong to severe
storms later this evening and into the overnight hours.
Currently, dewpoints have noticeably increased this morning,
reaching into the 50s as of noon for many locations. While
dewpoints are increasing, soundings at this point remain well
mixed with a fairly dry boundary layer. As we head over the next
few hours, the conceptual model in this case will essentially
be a waiting game for the boundary layer to become saturated
sufficiently such that you can lift saturated parcels into the
deepening convective layer. Once this occurs, expecting storms
to develop quickly (around 6-8pm as shown in the CAMs) along a
stationary boundary over portions of northern IA through
southeast MN and into western WI. At convective initiation, the
environment seems primed for supercells at first, capable of
large to even very large hail with mid-level lapse rates to
around 7 C/km and very elongated hodographs. This coupled with
deep inverted-v soundings would suggest damaging wind threat
with any RFD in developing supercells.

However, as we head later into the evening and storms move eastward,
deep-layer shear begins to weaken which will result in storms
clustering and trending more linear with time as they approach the
Mississippi River as hinted at in a number of the CAMs. As a result,
expecting the threat for hail to decrease with a maintaining
damaging wind threat. Some tornado potential cannot be ruled out
during this period either as low-level hodograph curvature increases
as the low-level jet ramps up in addition to greater saturation in
the boundary layer after dark. However, this is contingent on if we
can get saturation closer to the surface as LCL heights at
convective initiation would not be conducive for tornadoes.
Eventually, storms begin to push eastward into western WI and
eventually exit the area after midnight. Not anticipating any
flooding concerns with this first round of rainfall with amounts
generally ranging in the 0.25" to 1" range with storms being fairly
progressive in their movement.

This Weekend: Additional Rounds of Storms

As we head into tomorrow, skies clear out for the morning and
afternoon hours on Sunday with zonal flow persisting aloft. However,
as we head into the evening and overnight hours in particular on
Saturday, a weak axis of 850mb moisture transport transverses a
stationary boundary situated across portions of northeast IA and
southwest WI. As this occurs, some of the CAMs initiate convection
across portions of eastern IA that slowly pushes northward through
the overnight and into Sunday morning. Overall, the environment is
not overly favorable during this period as instability is relatively
limited, generally under 1000 J/kg. Consequently, this coupled with
weak deep layer shear should keep this to more of a stratiform
precipitation band with embedded convective cells with limited
severe potential.

The more significant implication of this round of convection on
Sunday morning will be how much we recover going into the
afternoon and evening on Sunday. Currently, the synoptic
factors in play to advect moisture into the region are quite
favorable as there is a profound 850mb moisture transport axis
that pushes north into the local area on Sunday evening. As a
result, instability values (2000- 3000 J/kg of MLCAPE) increase
rather quickly during the late afternoon and into the evening
with the moisture transport axis aiding as a focus for
convective development. Shear profiles are somewhat displaced
from the instability with the main synoptic trough situated over
the rockies still with a stronger upper-level jet streak to the
north. As a result, storm updrafts may struggle to maintain,
however given the aforementioned ample instability and mid-
level lapse rates of 8-9 C/km, this would certainly still favor
a severe hail risk. Damaging wind gusts cannot be fully ruled
out with any descending hail cores, however given a noticeable
capping inversion in the NAM/GFS soundings during this period,
storms will likely be elevated in nature which would also
minimize the tornado threat as well.

Monday: Potential for Severe Storms Areawide Monday

Monday currently appears to have the greatest risk for severe storms
areawide over the next 4 days as the previously advertised upper-
level trough pushes through the Great Plains and into the Upper
Midwest and becomes neutral to perhaps negatively tilted on Monday
evening. As this occurs, cyclogenesis occurs at the exit region of
this feature with a pronounced cold front in eastern MN. This
coupled with a fairly profound 850mb moisture transport axis into
the region will enable ample moisture to push northward through the
area with the grand ensemble (GEFS/EC/Canadian ensemble) having very
high probabilities (80-100%) for dewpoints over 65 degrees. As a
result, instability profiles are fairly impressive across
deterministic and ensemble guidance with modest probabilities (50-
70%) for MUCAPE exceeding 1500 J/kg on Monday evening in the EC
ensemble. The one question that remains is exactly how shear
profiles will manifest as the 250mb jet streak is somewhat displaced
from the main 500mb shortwave. As a result, while hodographs exhibit
some low-level and mid-level elongation, the upper-levels are more
disorganized. Consequently, this may result in a QLCS storm mode
assuming upper-level support continues to remain absent which would
favor a damaging wind and embedded tornado threat. That being said,
ample instability and mid-level lapse rates of 7-8 C/km in the
recent GFS would suggest at least some severe hail is possible as
well, particularly if we can get any supercellular structures going.

The environment for heavy rainfall in this particular setup seems
rather favorable as well with precipitable waters pushing over 1.5"
which are about the climatological maximum based on KDVN sounding
climatology. The key question from a heavy rain/flooding perspective
will be: 1. How the rainfall from the previous rounds of storms
manifests and 2. How progressive the storm evolution is on Monday
evening and if we have multiple rounds of discrete and linear modes
throughout this timeframe. Overall, the inter-quartile range in the
grand ensemble (GEFS/EC/Canadian) for rain amounts with just this
Monday round ranges from 0.25" to 1" with 95th percentile values up
to 2". So certainly could contribute further to any flooding
potential where storms occurred from previous rounds.

In all, Monday appears to be a fairly active day from a severe
weather perspective with all hazards on the table depending on how
all the various severe weather ingredients shake out. Now is the
time to be thinking about your severe weather safety plan and have
multiple ways of receiving warnings if you have not already done so,
especially considering each day from this evening through Monday
contains at least some degree of risk for severe weather.

Tuesday - Thursday: Cooling Trend

As we head past Monday and head later into the week, cold air
advection behind the front will allow for cooler temperatures to
move in for the middle of the upcoming week. As a result, the
10th to 90th spread for highs in the NBM falls to the upper 50s
to upper 60s for much of the local area on Wednesday, likely
our coolest day for the upcoming week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 638 PM CDT Fri May 15 2026

The main concern the next 3 to 5 hours is thunderstorms moving
through both terminals. Thunderstorms are hanging around the
vicinity of RST and there will likely be intermittent periods of
VCTS and thunderstorms overhead with MVFR visibilities and
possibly ceilings. A similar situation at LSE, except delayed by
about an hour. Expect gusty and erratic winds during and in the
vicinity of thunderstorms. Thunderstorms may eventually become
more organized as a final round passes through the terminals,
likely ending no later than 05z. After that, expect VFR
conditions with clearing skies and lightening winds. Winds will
gradually shift to northwesterly by Saturday morning.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...DLH