923
FXUS63 KARX 030758
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
258 AM CDT Thu Jul 3 2025

.KEY MESSAGES...

- Low end (20-40%) storm chances through tonight. Where
  realized, some could be strong to marginally severe. The main
  severe threat will be damaging winds. Most locations will
  likely stay dry.

- Hot and humid for the 4th of July with heat indices topping
  out in the upper 90s to near 100 degrees.

- Areas of showers/storms continue to look likely for portion of
  the holiday weekend as cold front approaches the area late
  Saturday into Sunday. Near normal temperatures in the upper
  70s to mid 80s expected to follow into mid next week.

&&

.DISCUSSION...
Issued at 249 AM CDT Thu Jul 3 2025

Today: Chances for Storms Continue, Some Strong Storms Possible


Our area remains in northwest flow aloft as ridging builds across
the Plains. In the low levels, southerly to southwesterly winds are
continuing to pull low level moisture into the region. Where we see
storms fire today will be impacted by mesoscale details that aren`t
totally clear just yet. The first chance for showers and storms
looks to come during the morning hours across portions of north
central Iowa. These storms would be non-severe and many CAMs do not
even have these storms reaching our area but have included some
slight chance PoPs to account for the possibility. The next chance
looks to come later this afternoon as we start to see some shortwave
ripples in the flow aloft and a weak frontal boundary draped across
the area. This front is currently to the north of our area but is
expected to slowly sag south. CAMs are hinting at the possibility of
seeing some storms develop in the same general area as they did
today (mainly southeastern Minnesota and northeastern Iowa). Storms
look to fire south of the aforementioned weak surface boundary with
coverage being isolated to scattered at best. Some of these storms
could become strong to severe with ample instability in that region,
as noted by forecast MLCAPE values in the 1000-2500+ J/kg range. Low
level shear is sub-par at less than 20 kts but bulk shear is a bit
better at 30-40 kts with increasing upper level winds. Hodographs
will be similar to yesterday in that they should be long, straight,
and oriented to the southeast. Mid level lapse rates look poor with
the main threat likely being damaging downburst winds with ample
DCAPE noted in areal soundings. 03.00Z HREF members are having a
hard time agreeing on when storms fire and how much develops with
some having little to no activity (likely due to better low level
capping). Have broadbrushed low PoPs for this afternoon with
significant uncertainty in where/if storms will come to fruition.
These will need to be refined through the day as some of the low
level forcing mechanisms come more into focus.

The next set of storms looks to come in the late evening to
overnight timeframe as the front is expected to lift back to the
north. CAMs are in much better agreement with the formation of these
storms with only minor differences in location and overall extent.
This time period looks to have some more significant
perturbations through the flow aloft and MLCAPE values should
still be well over 1000 J/kg across West Central Wisconsin.
Similar to the afternoon hours, damaging winds would be the main
threat with DCAPEs over 1000+ J/kg. These storms would drift
east towards eastern Wisconsin overnight and into early Friday.


4th of July Weekend and Beyond: Hot and Humid Holiday with
Unsettled Pattern Going Forward


The upper level ridge axis will be right over our area during the
day on Friday which looks to keep our area largely dry for 4th of
July festivities. As we move towards Saturday, an upper level
shortwave trough begins to move towards our area. Out ahead of this,
southwesterly low/mid level flow will tap into rich gulf moisture
and advect it northwards into the Upper Mississippi Valley. 02.12Z
NAEFS shows above normal invigorated water transport into the area
late Friday into Saturday and mean pWats in the 1.25-1.5 ranges.
Deterministic mid range models are indicating the potential for
pWats to climb into the 1.75-2+ inch range by Saturday. A cold front
extending well south of a Canadian low pressure system is expected
to move through the Upper Midwest Saturday into Sunday with chances
for precipitation highest with the frontal passage late Saturday
afternoon into the overnight hours. Showers and storms will be
possible ahead of this cold front earlier in the day on Saturday
with the help for low level warm air advection and upper level
support with the aforementioned shortwave trough. All of these
showers and storms look to be efficient rainfall producers with warm
cloud depths over 3 kft and ample moisture through the boundary
layer as noted by the high pWats. The main note preventing this
event from having higher flooding concerns given the recent abundant
rainfall looks to be the progressive nature of the front with rain
chances largely ending for areas west of the river by daybreak
Sunday and areawide by late Sunday afternoon. A weak surface high
pressure should build in behind the cold front, keeping Monday dry
across the area. Unfortunately, this will be pretty short lived.
The upper ridge is expected to become more east-west oriented
across the southern CONUS this weekend and into next week,
leaving quasi-zonal flow across our area. Any shortwave
perturbations that move across the area will have the chance to
set off some rain showers/storms. These are obviously not well
resolved this far out but could make for some activity mid-next
week so have left the broadbrushed NBM PoPs as is for now.

Temperature wise, Friday is expected to be the hottest with ambient
temperatures in the upper 80s to lower 90s. With dew points in the
upper 60s to lower 70s, heat indices will top out in the mid to
upper 90s, approaching 100 degrees. This means it will feel very
uncomfortable during your outdoor 4th of July activities. While
we`re not expecting heat advisory criteria to be met at this time,
we still want to emphasize practicing heat safety and having
multiple ways to stay cool. We know telling people to stay inside
during the 4th isn`t the most practical but try to limit your
time outdoors and avoid extended periods outside, especially if
you`re doing any strenuous activities and don`t have methods of
cooling like plenty of water or shade. As rain chances increase
and the cold front approaches for Saturday, most locations will
see temperatures limited to the 80s. Behind the cold front
Sunday through mid-next week, temperatures will be seasonable in
the upper 70s to mid 80s

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1243 AM CDT Thu Jul 3 2025

VFR conditions should prevail over the next 24 hours.
Uncertainty once again focuses on potential for thunderstorms
after 18z but the probability for these (25%) is too low for a
mention at RST/LSE with this issuance. While light winds will be
present overnight once again, near-surface moisture appears too
low for valley fog to occur outside the usual trouble spots
(BRF/OVS) especially considering the small number of nighttime
hours so soon after the summer solstice.

&&

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

&&

$$

DISCUSSION...Barendse
AVIATION...Ferguson