657
FXUS63 KARX 181640
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1140 AM CDT Sat Oct 18 2025

.KEY MESSAGES...

- A fairly active pattern with systems moving through every couple
  of days into mid-week. Rain chances have been increased tonight
  (~60-70%), with a dry Sunday expected. Rain chances again Monday
  into Tuesday, mainly in WI (20-50%).

- Weather systems will bring windy periods with Sunday and Tuesday
  afternoons gusts of 30-35 mph looking probable (60-80% chances).

- Forecast remains consistent of a moderate chance (50%) of a
  widespread frost across the area Wednesday morning. High
  temperatures are in the seasonal/normal 60s for highs with colder
  days Sunday and Tuesday/Wednesday (50s).

&&

.DISCUSSION...
Issued at 237 AM CDT Sat Oct 18 2025

Rain Looking Likely Tonight For Most

GOES Water Vapor is looking quite fall-ish this morning with an impressive
large scale trough digging southeast through MT with a band of showers
on the MT/SD border westward to the Continental Divide. This matches
well to a QVector convergence signal in the 300-500mb layer per RAP analysis.
Good agreement exists on the phasing of this wave with the s/sw U.S.
wave energy, causing rapid cyclogenesis over the Great Lakes. By Sunday
morning, model consensus places a surface low around 990 mb over northern
MI. As these waves phase, the excellent lift suggested by the QVector
convergence moves over the area tonight bringing rain chances.
Much of the QVector convergence signal in the lowest levels is centered
across eastern IA and southern WI...suggesting that area should have
the highest rain chances. Teaming up with the Qvector convergence
is a moderate intensity mid-level frontogenesis band consistent
across CAMS and deterministic solutions that drags across the area
tonight. Many 18.00Z CAMS suggest a narrow rain band with this
feature being the key forcing mechanism. Have increased the rain
chances to ~60% along a N-S band shifting east across the area:
early evening MN/IA -> late evening+ WI, drying Sunday. Most rain
amounts will be around 0.10 to 0.20 inches with the progressive
nature to this system. Most of the action (rain) is to the east of
the area in the Great Lakes.

Winds Ramp Up on Sunday

As the surface low deepens over Michigan Sunday and low-level lapse
rates steepen locally, wind gusts will kick in late morning. 17.12Z
ECMWF ensemble suggesting much of the area has a 60-80% chance of wind
gusts over 35 mph Sunday afternoon, however this family is on the higher
end of the solutions. 18.00Z HREF guidance shows 90%+ chances for 30+
mph gusts, but probabilities rapidly drop to 30-50% for 35+ mph. Have
increased the forecast wind gusts above the NBM guidance on Sunday afternoon
into the lower 30s mph.

Rain Chances Monday-Tuesday, Windy Tuesday Afternoon

After ridge building on a cooler, breezy Sunday, another strong system
moves in for early in the week from the west in the continued progressive
pattern. This system again has moderate amplitude, a nice
warm/cold advection signal in the low levels and moderate-strong
QVector convergence aloft. These low/high level forcings are about
12 hours out of phase, but the cold frontal forcing is in concert
with the QVector forcing aloft by late Monday. Drier air in the
wake of tonights wave causes some of the lift to work to saturate.
Model QPF from the forcing signals in the 18.00Z deterministic models
arent consistent with the forcing, sans the 18.00Z ECMWF which is
more in line with the 17.12Z LREF guidance suggesting a very light
rain period Monday. LREF guidance has a 60-70% of 0.01" but only
10-20% for over 0.10" Monday afternoon. However, there is still
uncertainty about this wave and the surface cyclone intensity and
placement.

It appears the main impact will be wind gusts in the 30-40mph range,
with the 17.12Z ECMWF ens suggesting a 30-40% for 40 mph gusts in
southeast MN and northeast IA. The 18.01Z NBM suggests a less than
10% chance of 40+ mph gusts. The forecast will remain with the NBM
guidance of 30-35 mph gusts and rain chances of 30-50%. However, it
is very possible these rain chances will increase based on the signals
in the forcing.

Frost or Freeze Possible By Mid-week

Some of the seasons coldest air will settle in for Wednesday morning.
It appears skies could be clear southwest of I-94, but winds may
still be around 10 mph. This would limit frost production, but
temperatures will probably be in the lower 30s in many locations
outside the Miss river valley.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1140 AM CDT Sat Oct 18 2025

CIGS: increasing mid level deck tonight, associated with a cold
front and upper level shortwave. Should stay VFR. Cigs don`t hang
around long and expect mostly SKC conditions Sunday.

WX/vsby: Thin band of showers will work in from the west this
evening. Won`t stick around for long (a few hours at best) with
minimal vsby restriction and QPF (under 1/10").

WINDS: Tightening pressure gradient moving in Sunday will promote
northwest gust into the mid 20 kts. A couple more rounds of windier
conditions looking likely on Mon/Tue. Some 35+ kt gusts currently
possible Tue.

&&

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

&&

$$

DISCUSSION...Baumgardt
AVIATION.....Rieck