859
FXUS63 KARX 100900
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
400 AM CDT Thu Jul 10 2025

.KEY MESSAGES...

- Low to moderate (50%) confidence for storms today into tonight
  with low (20%) confidence in exact location or associated
  timing.

- Ongoing early morning storms primarily affect counties along
  and east of the Mississippi River Valley from northeast Iowa
  into southeast Minnesota.

- Heavy rain will be the main concern as storm chances continue
  into Saturday. Flash flooding concerns where storms frequent.
  Current confidence (20-50%) places highest accumulations
  locally in southwest Wisconsin and northeast Iowa.

&&

.DISCUSSION...
Issued at 340 AM CDT Thu Jul 10 2025

Ongoing Early Morning Convection:

A meridionally oriented line of storms decaying whilst
advecting east on radar loops followed an upper level
perturbation on GOES upper level water vapor loops steered by
synoptic anticyclonic flow centered over the Desert Southwest
yesterday (Tuesday). As the perturbation rounded the periphery
early this morning, a north-south separation in storms occurred
overnight with strongest storms in the southernmost line jogging
southeast through the Central Missouri River Valley.

Within this separation, easterly propagating storms have been
initiating and filling in on a meager zonally-oriented low level
boundary from northern Iowa into southern Minnesota most
evident on VWPs. Supplemented by outgoing cold pools,
reinvigoratedconvection has been initializing along the Iowa-
Minnesota border heading east towards the Upper Mississippi
River Valley, providing local morning storm chances primarily
west of the Mississippi River Valley in southeast Minnesota and
northeast Iowa. Easterly limiting factor is a well-defined low
level frontal boundary bifurcating the forecast area on VWPs.
If storms do affect counties along and just east of the
Mississippi River Valley, expect limited coverage in a
disjointed arc in a limited timeframe as a filament of Fgen has
been initiating storms ahead of the line all morning.

Through today, any minute differences in any mesoscale
influences will exert a large impact over time and downstream.
This will in turn limit overall predictability with subsequent
rounds of convection. This is quite evident in high resolution
model reflectivity solutions and accompanying trends for today.

Storm Chances Through Tonight:

The eastern progressivity of the synoptic pattern through the
late morning into the early afternoon pushes the aforementioned
frontal boundary east, allowing more moist air locally, and
limited storm chances pushing east of the Mississippi River
Valley; eventually reinvigorating through central Wisconsin
concurrent with diurnal heating building instability.

While trends in high resolution forecast models have been to limit
additional storm chances for counties in southeast Minnesota and
northeast Iowa at this time, they can`t be ruled out as a
trailing MCV over the South Dakota-Minnesota border at AFD
issuance and subsequent deformation axis may be supplemented by
building instability should sky cover somewhat clear. Regardless
of exact location of initiation, this storm possibility persists
through the afternoon into the evening, again conditional on
location of clearing concurrent with mesoscale forcing.
Additional strong to severe storm chances this evening into
tonight dependent on multiple bouts of storm chances through
today.

Strong to Severe Storm Potential Today:

The many potential mesoscale boundaries strewn over the forecast
area present infinite challenges in nailing down specifics
surrounding severe storm potential today and tonight. While there
will be ample CAPE 1000 J/kg+, there is little to no shear until
this evening through tonight when the anticyclonically curved
mid to upper level wave with stronger winds progresses through
the Upper Mississippi River Valley. Therefore, shear dependency
will be on mesoscale influences from floating boundaries and
various circulations potentially providing some stronger to
severe storms. All remains conditional on clearing skies and
strength/location of boundaries.

Heavy Rain, Potential Flash Flooding Impacts Today:

Higher concern will be heavy rain with 90th percentile PWATs
(1.5"+) in the 10.00Z RAOB at Aberdeen and warm cloud depths
11,000+ ft in high resolution soundings. Storm motion will
remain dependent on nebulous mesoscale influences and with
stunted, near circular hodographs, flash flooding will be a
concern should storms frequent the same areas.

Overall moderate confidence (~50%) for 0.5" of rainfall before
Friday morning across the forecast area. A wet tail in 25th
(~0.1") to 75th (1.5") percentile box and whiskers shows lower
confidence for higher amounts. Most models suggest highest
rainfall amounts locally from northeast Iowa into southwest
Wisconsin. Exact location of highest rainfall amounts widely
varies both between and within model trends. Evident in a nil
trend for histograms and recent HRRR runs with bullseyes of 4"
(10.00Z) to 7" (10.06Z) by Friday morning. All goes to say flash
flooding will be a concern to monitor while storms are ongoing.

Storms Through Friday:

Overall confidence for storms increase through Friday morning as a
the synoptic trough over the Rocky Mountain West on early morning
GOES water vapor imagery progresses through the Northern Plains.
Unfortunately, there remains much to be ironed out as many unknowns
remain. Can expect a southwest-northeast oriented line of storms
associated with a defined frontal boundary from the Central to
Northern Plains pushing east/southeast and a potentially quasi-zonal
line of storms pushing east/northeast along and south of the
forecast area through afternoon and evening on the remnants of
tonight`s ill-defined quasi-zonal frontal boundary. Remains quite a
moist airmass (1.5"+) persisting heavy rain concerns. Location of
remnant frontal boundary and eastern extent of upstream prefrontal
moist air plume leave no confidence in location of higher
instability or shear for that matter.

Cooler Next Week, Low Confidence In Precipitation:

Storm chances depart through Saturday as a continental Canadian
airmass comes into the Upper Midwest keeping daytime highs from the
70s into the low 80s on Saturday. The butterfly effect theme
continues through the week given low (20-40%) LREF confidence in
quasi-zonal flow and accompanying perturbations progressing through
the central CONUS. Outside of Wednesday when confidence for
measurable precipitation in 24 hours is 70-100% in all LREF members
(GEFS/EPS/GEPS), probabilities vary from 0-100% during any 24 hour
period between members. Slightly higher confidence for slightly
cooler than normal temperatures with 100% confidence for the 80
degree surface isotherm lieing along and to the south of the
forecast area (LREF).

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1234 AM CDT Thu Jul 10 2025

Line of storms at 10.06Z TAF issuance seen over the SD-MN
border progressing east at 40mph and expected to weaken as they
approach the local forecast area in southeast Minnesota and
northeast Iowa through the morning hours. Low to moderate
confidence (30-50%) in precipitation primarily west of the
Mississippi River Valley keeps mention out of either TAF but
immediate term amendments may be needed should storm intensity
persist.

Similar confidence across the forecast area through most of the
10.06Z forecast period as multiple bouts of storms, some
strong, will be possible. Again, haven`t included 18+ hours of
PROB30 in TAFs and will require ongoing amendment when
confidence increases. Where storms do form, visibility
restrictions <1SM from heavy rain will be possible and MVFR-IFR
ceilings.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...JAR