045
FXUS63 KARX 181842
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
142 PM CDT Fri Apr 18 2025

.KEY MESSAGES...

- Some afternoon showers are expected to develop, mainly over
  Wisconsin. These push off east through the evening.

- Widespread rain is still looking on track for Sunday afternoon
  into early Monday. Amounts around an inch are likely with
  river rises, and worst case scenario suggesting a very low
  chance for reaching minor flood stage on some WI rivers (less
  than 10%). Snow may mix in, but looks unlikely to accumulate.

- Warming next week into at least the 60s.

&&

.DISCUSSION...
Issued at 140 PM CDT Fri Apr 18 2025

Shower Chances Into the Evening, Mainly Wisconsin

Abundant clouds have filled in over the area per observations
and GOES visible imagery at 18Z. Radar continues to show some
spotty light echoes north of a surface low center southeast of
Waterloo IA. As this low progresses northeast today, some
frontogenesis is expected to develop showers over mostly
Wisconsin. The air mass is fairly saturated in the lowest levels
with some surface-based instability developing in the warmer WI
air this afternoon below an inversion near 800 mb. Should be a
popcorny shower look across Wisconsin by mid-late afternoon.
Late this morning the precipitation chances were updated higher
to account for higher confidence. There is fairly good
agreement in the 12Z/latest CAMS that these showers develop
today. There should be no impact. These showers will dissipate
and shift east this evening. Saturday should have more sun with
northwest breezes at 10-20 mph.

Easter Sunday and Monday

A vigorous system lifts through the Upper Miss Valley / Great Lakes
on Sunday with probabilities for rain increasing during the
afternoon but peaking Sunday night across the entire area. The
rainfall looks to move out Monday morning. Reviewing some of the
latest ensemble probability data for rainfall amounts from the
18.06Z ECMWF and GEFS, general agreement exists with high
confidence of at least 0.50" across the area. Probabilities for
an inch or more are in the middle ranges of 40-60% - with the
EC (GEFS) on the higher (lower) end of the range. The GEFS
M-climate comparison to the 2000-2019 period also suggests an
"above normal" event but not record for rainfall (which are
mostly 1.5-2" for this time of year). Details on the amounts and
location will still depend on the system track and intensity of
the low, but with a negatively tilted system with strong
meridional moisture advection and excellent curvature to the
height field aloft...favorable ingredients are in place. The
climatology rank for the precipitable water inflow to the lift
(at DVN) is 92-98th percentile for values of 1-1.2" per both
ensemble systems. See the river response discussion in the
Hydrology section below.

Surface-based instability remains well south of the area (I-80
or so) with some limited instability aloft for embedded
thunderstorms Sunday night per ensemble guidance. The 18.06Z
ECMWF ens suggests a 20% probability of MUCAPE of 200+ J/Kg
toward the moisture source south of I-90. Thus, this is mainly a
rain system without a severe thunderstorm threat.

There is a very small probability of snow on the north side
deformation zone of the cyclone which would possibly affect the
I-94 corridor into southeast MN (worst case scenario). The
latest 18.12Z GEFS has a 10% chance for 1"+ of snow by Monday
morning from Rochester MN to Wausau WI and north, with the EC
ens suggesting those probabilities are in northern WI.

Warmer Next Week!

It seems the area will break out into a bit warmer temperatures
Tuesday-Friday with more sun than clouds and some small rain
chances. The National Blend of Models suggests there is a 75% chance
of being above the low 60s for high temperatures. The highest
rain chances of the week look like Tuesday and Tuesday night (~50%).

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1222 PM CDT Fri Apr 18 2025

MVFR to IFR cigs will persist throughout much of the afternoon with
the recent HREF having very high probabilities (80-100%) for MVFR
cigs through 00z with the low-level cloud field slowly pushing
eastbound into the evening. Occasional showers will be possible
across western WI during the late afternoon. Consequently, have
included a tempo at KLSE to address this potential. While some
elevated instability is present across western WI, do not have
enough confidence to mention TS in the TAF but cannot completely
rule it out (10-15% chance). Cigs will gradually improve to VFR late
evening/overnight and clear out for the daytime hours on Saturday.
Winds will begin the TAF period at 10-15 kts with occasional gusts
to 20 kts across southeast MN and northeast IA. Winds will diminish
slightly overnight but will remain from the northwest through the
TAF period.

&&

.HYDROLOGY...
Issued at 140 PM CDT Fri Apr 18 2025

River rises are expected from the rain Sunday into early Monday,
especially with some rains this morning of 1-2" across the area
making for more moist soils. The latest River Forecast Center
ensemble river forecasts suggest the event total rainfall
amounts would have to get closer to 2" for rivers to be put into
minor flood stage...and that is mainly for rivers in Wisconsin.
At this time, that would be a less than 10% chance, and near
daily rainfall records.

&&

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

&&

$$

DISCUSSION...Baumgardt
AVIATION...Naylor
HYDROLOGY...Baumgardt