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000
FXUS63 KARX 131733
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1230 PM CDT Sat Apr 13 2024

.KEY MESSAGES...

- Elevated fire weather conditions this afternoon with min RH
  around 25% and breezy winds, especially west of Mississippi
  River.

- Increasing shower/storm chances later Monday into Tuesday.
  Some concerns for potential severe storms Tuesday afternoon,
  mainly south of I-90.

&&

.DISCUSSION...
Issued at 317 AM CDT Sat Apr 13 2024

Warm, Dry Weekend:

As the surface ridge axis presently overhead begins to depart
by daybreak, upper level ridging over the Central Plains will
begin to move in, flattening out as it arrives. Breezy southerly
winds gusting 25 to 30 mph and increasing warm air advection
behind the departing surface ridge will lead to a pronounced
jump in temperatures. Afternoon highs look to climb into the 70s
for the bulk of the area, with upper 60s north of I-94. With
dry low level forecast sounding profiles, there is some concern
for elevated fire weather conditions this afternoon (see Fire
Weather Discussion below).

A weak passing shortwave will graze northern Wisconsin this evening.
Looks pretty moisture starved, especially in the lower levels per
forecast soundings. HREF probabilities of 20-40% for >0.01 inch
rainfall reside just north and east of Taylor County, so for our
area this may manifest as only brief sprinkles or virga across
Taylor and northern Clark counties, certainly nothing impactful.

Sunday will be another pleasantly warm day in the 60s to 70s with a
lighter breeze out of the northwest.

Increasing Chances for Showers/Storms Monday into Tuesday:

Main forecast focus will be on a more active weather pattern as the
first half of the new work week unfolds. A robust upper low coming
onshore California tonight will cross the Rockies by Monday, then
eject towards the western Great Lakes Tuesday into Wednesday. Broad
moisture transport and ascent out ahead of this system begins to
increase in our area late Monday, with rain chances likely to
steadily ramp up through the evening and overnight as the main
system slowly approaches.

By Tuesday the occluding system becomes nearly vertically stacked as
it approaches the Middle/Upper Mississippi Valley. Strong upper
level divergence and isentropic lift comes into play by afternoon
with precipitable water exceeding the 95th percentile per NAEFS, or
about 250% of normal. Exact track of the surface low makes pinning
down more specific forecast details such as severe weather potential
more difficult, still being this many days out. Nevertheless, there
is reasonably good agreement for the low to lift into eastern
Nebraska by Tuesday afternoon with the warm sector lifting somewhere
near the I-90 corridor locally. Where the warm front ends up will be
the determining factor for greatest instability and storm chances,
and GEFS/ENS ensemble members show quite a bit of spread in possible
outcomes. Probabilities for >500 J/kg CAPE have been holding rather
limited in recent runs (20 to 30% south of I-90), with the highest
probabilities residing along and south of I-80. This seems
reasonable given the high likelihood of rain through most if not all
of the morning (>50% chance for some areas seeing 1" or more
rainfall). Regardless, this will be a very dynamic system with
potential for favorable deep layer wind shear especially south
of I- 90, so will be monitoring the severe potential very
closely.

The surface low is progged to move overhead early Wednesday and then
gradually depart, with continued shower/storm chances through the
day. Second half of the week will feature another upper low near the
MN/Ontario border but also a much drier airmass that will make it
more difficult for any additional widespread rainfall. Looks like
cooler than normal temperatures for Thursday through Saturday
also.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1230 PM CDT Sat Apr 13 2024

VFR conditions will continue with mainly a wind shift adding to
forecast length. Passing trough to the north, which will create the
wind shift overnight, will also bring some mid/high level ceilings
at times mainly north of the area. Otherwise fairly quiet pattern
should continue through the weekend.

&&

.FIRE WEATHER...
Issued at 317 AM CDT Sat Apr 13 2024

Elevated fire weather conditions are likely today with a very
dry airmass overhead. Forecast soundings show very dry low
levels with deep afternoon mixing. While dewpoints will
increase a bit west of the Mississippi River today, the deep
dry mixing is likely to overcome any slight increase in
moisture. As a result, afternoon minimum RH looks to drop to
around 25 percent area wide. Breezy winds will increase out of
the south to southwest this afternoon, and with deep mixing
there could be some gusts of 30 to 35 mph at times in open areas
west of the Mississippi River, particularly near Rochester.
Fuel dryness appears to be held in check by recent rainfall with
FFMC values along and west of the Mississippi River climbing to
around 90 to 92. While a Red Flag Warning is in effect for
portions of north-central Iowa and south-central Minnesota, the
local forecast appears more like a marginal Red Flag setup for
southeast Minnesota and northeast Iowa. After collaboration with
surrounding offices, have opted to issue a Special Weather
Statement for areas west of the Mississippi River where elevated
fire weather conditions will be most likely. The day shift will
monitor trends in case conditions would deteriorate more than
currently expected.

&&

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

&&

$$

DISCUSSION...Kurz
AVIATION...Shea
FIRE WEATHER...Kurz