888
FXUS63 KARX 110906
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
406 AM CDT Fri Jul 11 2025

.KEY MESSAGES...

- Heavy rain and storms progress northeast through northeast
  Iowa, southwest Wisconsin, and central Wisconsin through the
  daytime hours. Highest rainfall amounts expected along
  southern peripheral counties where 1"+ of rainfall is possible.

- Low confidence in limited precipitation chances through start
  of new week, eventually increasing Tuesday, lasting through
  Wednesday.

&&

.DISCUSSION...
Issued at 340 AM CDT Fri Jul 11 2025

Heavy Rain & Storm Chances Through The Afternoon:

Surface low pressure situated over the Missouri River Valley on surface
observations early this morning, being driven by well-defined cyclonic
flow upstream slowly shifting east over the South Dakota-Nebraska
on GOES upper level water vapor imagery loops, is causing strong
to severe storms from eastern Nebraska through eastern Iowa. An ill-
defined frontal boundary, extending upstream to the east-northeast,
will likely determine location of storms through today. Current track
places low center along our southern periphery keeping the warm sector
(i.e., unstable air) and severe storm potential to our south while
the lows deformation area to the north affecting the local forecast
area with heavy rain and scattered storms. Exact track and northern
extent of warm sector causing discrepancies in exact location of
heaviest rainfall with a strong moisture gradient evident on early
morning POES derived PWATs from 1.2" to 1.7" bifurcating the
forecast area. Given current confidence in frontal location and
resultant low track, highest rainfall amounts locally expected
in far southwest Wisconsin into northeast Iowa with NBM&HREF
probability for 0.5" of 75% and 1" of 50%. Again, exact storm
will be important to monitor as a sharp gradient in heaviest
rainfall amounts is expected evident in HREF 24hour LPMM of 2".

Storm Chances This Evening & Tonight:

Additional influence will be an upstream longwave trough, phasing
through the Rocky Mountain West on early morning GOES water vapor
loops, initiating a line of storms through the Northern Plains
through the afternoon. The easterly influence will shunt highest
pops farther east while subsequent phasing lifts forcing for
this northern line of storms farther north. Have decreased
widespread PoPs as a result of the two separate streams,
initially along our south and subsequently grazing our
northwestern periphery tonight into Saturday morning.

Low Confidence in Limited Precipitation Chances Through Start of
the New Week:

Upper level heights build in from the west for the start of the new
week in the wake of the trough axis exiting east (LREF probabilities
for  500mb heights >582). Low level warm air advection brings surface
temperatures into the mid 80s for Sunday. GFS & CMC suggesting a line
of precipitation chances progressing from northwest to southeast
Sunday from a subsequently digging wave within wake northwest flow.
A stronger solution to the upper level jet streak in the GFS/CMC
compared to other models causing higher PoPs due to enhancement
of synoptic ascent. Current cluster analysis (10.12Z) is clouded
by 12 hour time-lag with 65% of members suggesting some
measurable precipitation from a slower, positively tilted
trailing perturbation along the main trough`s southern
periphery. Considering overall limited moisture due to a
Canadian Continental airmass and most recent (11.00Z) LREF
solutions, have kept NBM PoPs which remain dry for now.

Similar model spread in meager precipitation chances for Monday with
GEFS probabilities of 30-60% for 0.01" in 24 hours along our
northwestern half of the forecast area, a 30% decrease from its
previous run. Synoptic disagreement stems from strength of tropical
high pressure over the Gulf, resultant convergence with locally zonal
flow, and location of accompanying low level theta e plume from the
Southern through the Central Plains. Solutions vary from a
northern filament of low level theta e through the Northern
Plains to a stunted lobe in the Central Plains in the GEFS. This
EPS solution keeps measurable precipitation probabilities <30%
across the forecast area.

Precipitation Chances Through Midweek:

Increased precipitation chances (50-70%) return to the Upper
Mississippi River Valley Tuesday evening/night from a
perturbation lifting through the Central Plains along southwest
flow. Exact location of perturbation isn`t well agreed upon
within and between LREF members showing a ~200 mile N-S spread
in 25th to 75th probabilities for 500mb heights >588dam.
Strongest intra-ensemble agreement seen in the EPS although also
seen suffering from decreasing agreement in recent trends,
similar to GEPS and GEFS.

Disagreement continues regarding an upstream upper level long wave
trough, phasing through the western CONUS, persisting local precipitation
chances through Wednesday night. Current exit behavior of this
trough suggests a quasi-zonal theta e gradient along our
southern periphery which may raise a heavy rain concern. Low
confidence as pattern may remain progressive enough to limit
overall concerns. Individual LREF members and time-lagged
cluster analyses paint 50% probabilities for 0.5" over 24 hours
which isn`t overly concerning but will change.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1250 AM CDT Fri Jul 11 2025

With light surface winds and low-level saturation, patchy fog
has begun developing across much southeast Minnesota, northeast
Iowa, and western Wisconsin. This fog is expected to linger
through much of the overnight. There is some uncertainty if this
fog becomes more dense or if the mid-level clouds moving
overhead impede dense fog and a MVFR/IFR stratus deck forms
instead. Currently have 3SM and 1/2SM for KLSE and KRST
respectively. If better saturation occurs at the surface then
expect the fog to become more dense and approach IFR/LIFR. The
best chance for the lowest visibilities to occur (LIFR) would be
in portions of southeast Minnesota, including KRST, and
northeast Iowa. The best chance (40 to 60%) for showers and
thunderstorms to occur will mainly impact areas along and south
of I-90 today. Light and variable winds are expected today.

&&

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

&&

$$

DISCUSSION...JAR/Rieck
AVIATION...Cecava