487
FXUS63 KARX 150742
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
242 AM CDT Tue Sep 15 2026

.KEY MESSAGES...

- Mostly dry and cool today with limited potential for scattered
  storms along southern peripheral counties dependent on exact
  location of overnight frontal boundary.

- Low-moderate confidence (20-60%) in subsequent precipitation
  overnight Wednesday into Thursday morning increases in amounts
  (1" - 2") and confidence (60-80%) Friday into Saturday.
  Location of highest rainfall rates limits confidence for areal
  and river flooding (<10%), potentially higher for flashier
  rivers in northeast Iowa (Turkey) and southwest Wisconsin
  (Kickapoo) should highest amounts be realized in these spots.

&&

.DISCUSSION...
Issued at 227 AM CDT Tue Sep 15 2026

Overnight Storms & Heavy Rain Potential:

The low level boundary, evident in a southwest to northwest
wind shift on low level VWPs between the Mississippi and
Missouri River Valleys, will continue instigating storms along
a parallel (southwest to northeast) orientation overnight. A
slight eastern shift in the backing wind profiles resulted in
the line of heaviest rainfall and strongest storms slowly shifting
east of the local forecast area into central Wisconsin through
the early in the overnight hours. However, a more northerly
component of the trajectory to parent mid-upper level low over
southern Canada overnight is gradually decreasing southerly
advection of the boundary through Tuesday morning, raising
slight concern for reinitiation of storms capable of heavy rain
northwest of current (15.08Z) RADAR imagery where heavy
rainfall totals nearing 2" have been observed. Therefore,
overnight flooding concerns cannot be completely ruled out until
the frontal completely exits the area through early Tuesday
morning.

Drier & Cool Today, Limited Rainfall Potential:

The aforementioned upper level low eventually abandons the boundary
along the southeastern periphery of the local forecast area through
Tuesday. Exact southern extent will determine lingering heavy rain
potential in select peripheral counties as storms potentially burble
along the boundary until anticyclonic flow further shunts moisture
southward into Tuesday night. Outside of the select counties in
northeast Iowa into far southwest Wisconsin, a drier, cooler
upstream airmass, evident in overnight surface dewpoint observations
in the mid to low 50s and temperatures from the upper 50s to low 60s
at 15.06Z spreads east across the forecast area through today.
Daytime temperatures from the upper 60s along our northwestern
peripheral counties to low 70s elsewhere expected.

Midweek Heavy Rain & Storm Potential:

Low level anticyclonic flow traverses the forecast area overnight
into Wednesday, resulting in return flow returning the warm, moist
airmass across the Upper Mississippi River Valley into
Wednesday night. Confidence in local precipitation chances
remains low- moderate (20-60%) as GEFS (15.00Z) presents a drier
solution than the GEPS/EPS due differences in strength of upper
level jet streak providing enhanced ageostrophic ascent within
the equatorward entrance region, an accompanying lobe of mid
level shear vorticity, and entrained drier air in the mid levels
according to associated individual ensemble member sounding
plumes. Should the stronger forcing solution in the GEPS/EPS
come to fruition, another 0.5" - 1" of rainfall will be possible
overnight Wednesday into Thursday morning. While overall
amounts aren`t overly concerning, potential subsequent flooding
impacts into the weekend will be impacted by this supplementary
midweek rainfall.

Heavy Rain & Flooding Concerns Through Friday:

Synoptic confluence through late week funnels the anomalous moisture
in a narrow corridor, similar albeit slightly lower than
current areal observations, through Friday into Saturday with
LREF probabilities for 2" PWATs decreasing/increasing and
shifting south/north in most recent runs of the GEFS/EPS placing
temporarily maxima of 40%/70% near the southwestern half of the
forecast area. While the longer forecast hour combined with
aforementioned low-moderate confidence rainfall midweek limits
overall confidence in flooding concerns, LREF sounding plumes
suggest anomalous freezing levels and thick warm cloud depths,
reraising concern for areal and river flooding potential late
Thursday night through Friday into Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1243 AM CDT Tue Sep 15 2026

Showers and storms continue for portions of southwest Wisconsin
and northeast Iowa through the early morning hours before
exiting by mid-morning. Some lingering showers are possible in
portions of northeast Iowa and far southwest Wisconsin through
the early afternoon, however those chances will continue to dip
further south as the morning and afternoon progress. MVFR to IFR
CIGS and visibilities will move into most locations during the
early morning hours and then exit southwest Wisconsin by mid-
morning. Southerly winds will gradually shift more westerly and
then northwesterly as a front moves through between 12 and 16Z.
Expect wind gusts between 25 and 30 mph when the front moves
through then for the remainder of the day the northwest winds
will be sustained at 5 to 15 mph. Wind shear is also possible
before the frontal passage as strong westerly winds at 2000ft
will be around 35 to 45kts over the next few hours.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...Cecava