373
FXUS63 KARX 161824
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
124 PM CDT Sat May 16 2026

.KEY MESSAGES...

- Hail threat lowers late tonight and Sunday morning.

- Severe weather threat on Sunday and Sunday night shifts west.

- Severe weather threat from Monday into Tuesday morning is
  becoming more uncertain.

&&

.DISCUSSION...
Issued at 124 PM CDT Sat May 16 2026

This Afternoon

A dry line will continue to slide south through northern Iowa,
southern Wisconsin, and northern Illinois this afternoon. Surface
dew points will fall into the 30s and 40s north of this dry line.
This will lower the afternoon relative humidities into the teens and
20s for much of the forecast area. The dew points were lowered
closer to the CONShort which seems to be handling this dry air the
best. Even then, the dew points are not low enough south of
Interstate 90.

Further south across northern Missouri and central Illinois is
the outflow boundary from the storms that moved through our area
last evening. With convection continuing along this boundary,
it will likely remain quasi-stationary.

Tonight and Sunday

The boundary across northern Missouri will move slowly north as a
warm front in response to the nocturnal jet tonight and the surface
low lifting northeast out of the Central Plains on Sunday. While
there is good 1 to 7 km shear located north of the warm front, the
instability stays south of the warm front. As a result, we have seen
a significant drop in the probabilities of seeing elevated hail for
tonight and Sunday morning.

In an interesting development in the 16.16z HRRR, a MCS develops
over eastern Nebraska and western Iowa tonight. As this system moves
toward our area, it gradually weakens. One thing that will have to
be watched is whether the rain-cooled air produced by this MCS
will limit the northern extent of the warm front on Sunday. This
could potentially keep the high temperatures in the lower to
mid-60s north of Interstate 94. This would be 10 to 15 degrees
cooler than the NBM.

Sunday night

Plenty of uncertainty is showing up in the CAMs. While many are in
general agreement that storms will initiate over western Iowa,
eastern Nebraska, southwest Minnesota and eastern South Dakota
during the late afternon/evening, they then diverge on their
solutions. Some show a line developing as their cold pools
coalesce and others show clusters of storms. In either scenario,
the storms are trending to weaken as they move into the Upper
Mississippi River Valley due to weakening instability and
shear. As a result, the Day 2 slight risk has been shifted west.
It now is located along and west of the Mississippi River

Monday into Tuesday morning

Much of uncertainty exists on the timing of the cold front moving
through the area. This ultimately affects the location of the warm
sector. The GFS and many of its ensemble members move the front
across the area on Sunday night or Monday. The 16.12z operational
GFS was further west than its 16.16z run. It has 1500 to 3000
J/kg CAPEs in northeast Iowa, and southwest and central
Wisconsin. While there is more instability, the better deep
shear is post frontal. The operational ECMWF and many of its
ensembles has its cold front moving through on Monday night.
With this timing, the instability (up to 750 J/kg) is much less
ahead of this cold front. Its has deep shear over 40 knots north
of Interstate 94, so there may be some supercells in this area
during the evening.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1256 PM CDT Sat May 16 2026

No impacts to aviation are expected through this afternoon. As
we head into the evening hours, after 00z, showers and storms
begin to move northward into northeast Iowa and southwest
Wisconsin (20-40%), but confidence in how far north they can
progress is low. They may only pose an isolated hazard into the
overnight hours for those sites south of Highway 18. Northwest
winds this afternoon begin to veer to the southeast tonight.

Confidence in showers and perhaps a thunderstorm increases Sunday
morning as a line of showers/storms moves northward (60-80%).
MVFR to IFR conditions are expected to accompany these
showers/storms as cloud bases fall to near 1kft. Visibilities
are expected to fall generally to 4-5SM, but more vigorous areas
of precipitation may result in IFR visibilities. Winds will
also increase during this period, with southeast gusts of
15-25KT for most while those west of the Mississippi River may
see gusts upwards of 30KT.

&&

.HYDROLOGY...
Issued at 440 AM CDT Sat May 16 2026

Storm chances increase daily, initially tonight through Sunday
morning. The accompanying anomalously moist airmass raises heavy
rain concerns with a widespread 1" to 2" of rainfall expected
through Monday. While low lower confidence in specific repeat
storm locations over the next 72 hours limits overall confidence
in location of higher rainfall amounts, 2" to 3" will be
possible should storms repeat over similar areas.

Resultant currently low confidence (10-20%) for minor river
flooding impacts limited to flashier creeks and rivers in
northeast Iowa such as the Turkey River at Garber and Elkader.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...Falkinham
HYDROLOGY...JAR