280
FXUS63 KARX 211918
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
115 PM CST Fri Feb 21 2025

.KEY MESSAGES...

- At/above normal for the weekend into early next week. Highs
mostly in the 40s. A few locations could flirt with 50.

- Dry weekend, but unsettle weather pattern for the new week will
bring occasional precipitation chances (rain or snow).


&&

.DISCUSSION...
Issued at 115 PM CST Fri Feb 21 2025

OVERVIEW: quiet, milder weekend...more active weather pattern moving
into next week.

The bitter cold airmass will soon be a thing of the past as it
continues to edge east today. Broad upper level ridging/height rises
are creeping in from the west, bringing in a milder airmass for the
weekend.

No change in the expectations for the front end of next week as the
long range guidance continues to depict a broad, quasi-zonal upper
level flow with various shortwave ridges/troughs sashaying west-east
through it. A more active weather pattern when it comes to
precipitation chances as the milder airmass will also bring an
increase in moisture for those perturbations to work on.

The latter half of next week has been more problematic with stark
differences between the EPS and GEFS - EPS favored keeping it warm,
GFS preferred more trough building/colder. Latest deterministic runs
of both models has the EC aligning more with the GFS. Meanwhile, WPC
clusters are also starting to lean into the idea of more troughing.
Still way out there, but the mild start to the new week may not
linger into the latter half.


TEMPERATURES: the much talked about return to at/above normal
temperatures starts this weekend. The EPS remains the most emphatic
on the warming with 70-100% chances for 40+ degree temps Mon-Wed
through the I-94 corridor. The GEFS is still 30-40% less than that,
but has shown an increase in warming over its last couple runs.
Spreads in the 25-75% for temps from both model suites are only
around about 5 degrees - so a lot of alignment within the models on
expectations. Upper 10% also suggest a decent shot to warm to 50+ at
few locations, with the GEFS even hinting at this now.

The latter half of the week is a lot more uncertain owing to model
differences/evolution of the upper level pattern. Confidence much
lower as a result.


PRECIPITATION CHANCES: as alluded to in the overview section, the
weather pattern is becoming more "active" next week. Various bits of
shortwave energy continue to be progged to spin across/near the
upper mississippi river valley. While there have been differences in
timing/location of the features in the GEFS and EPS members, they
have both been consistent over the past several days in the uptick
in potential pcpn makers.

QPF has trended low, so the NBM is likely a tad too low for its pcpn
chances on the whole. Current probabilities in the GEFS and EPS have
20-40% to exceed 1/4" of liquid through Wed night. If there is one
day that shows the most agreement for pcpn chances in the long term
guidance its next Tue night/Wed.


RIVER IMPACTS? The warming will result in compaction/melting of the
snow pack. With frost depths at a foot to foot and a half, much of
what melts will eventually find its way into local rivers/streams.
However, a few things have to happen before we get to that. First,
the snow pack needs to warm enough to melt. Currently much of it
sits in the teens. Second, we have to compact the snow. Current snow
density is only 15 to 20% (have a long way to go). Once we warm,
compact the snow enough, then we can melt that and release it - and
eventually find the waterways. Observations of the snow pack water
equivalent is 1/2" or less south of I-94...closer to 1 to 2" north
of there. In addition, with nighttime temps expected to drop to
at/below freezing, most if not all of the melting will shut down. A
best case scenario.

However, we are also looking at increasing shots for pcpn next week.
While resulting QPF is relatively minor (current forecast favor 1/4"
or less liquid through Wed), any additional moisture will accelerate
melting/add to the runoff.

At this time, think we can expect rises on most waterways...but not
anticipating flooding (with current QPF expectations). Ponding of
water in fields, low lying locations, perhaps storm sewers where
snow isn`t cleared, etc more likely. Again, a few things need to
occur first, so probably won`t see that water until early/middle of
next week. As for ice jamming, can`t completely rule that out. Will
have to keep an eye on river levels as we move into next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1137 AM CST Fri Feb 21 2025

High confidence remains in VFR conditions persisting through the TAF
period across the region. There is the potential for some MVFR
ceilings to develop Saturday north of I-94, but the probability at
this time is only 30-40%. Southwest winds will be gusty this
afternoon, especially west of the Mississippi River where gusts will
persist into the overnight hours. Winds remain southwesterly but
begin to diminish on Saturday. Have included low-level wind shear in
the LSE TAF with this issuance owing to strong winds aloft and the
expectation of more diminishment of winds overnight in valley
locations as compared to winds in flatter areas of terrain.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...Falkinham