839
FXUS63 KARX 191116
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
516 AM CST Sun Jan 19 2025

.KEY MESSAGES...

- Anomalous cold with overnight minimum wind chills of 25 to 35
below zero sticks around through Tuesday.

- Cold weather advisories expanded into northeast Iowa overnight
  through Monday morning and extended in southeast Minnesota
  through western Wisconsin through Tuesday morning.

- Light snow potential midweek and next weekend.

&&

.DISCUSSION...
Issued at 319 AM CST Sun Jan 19 2025

Anomalously Cold Low Level Temperatures Through Tuesday:

10th percentile low level temperatures were seen in 19.00Z RAOBs
from the Great Basin to the Lower Mississippi River Valley.
Colder, near average minimum temperatures, were seen as far south as
Omaha (SPC climatology). Overnight POES derived 850mb temperatures
were near -20C over the Upper Mississippi River Valley, decreasing
to -30C over the southern Manitoba/Ontario border. Longwave
troughing from the Canadian Rockies through the Great Lakes on GOES
water vapor imagery with embedded perturbations will advect the
coldest air through the Upper Mississippi River Valley into Tuesday.

A bowling ball of 100% confidence for these anomalous 850mb
temperatures of -30C in the GEFS/EPS/HREF sticks around the Upper
Mississippi River Valley through Tuesday morning. Has been a
consistent signal between ensembles and their respective runs.
Center of this anomaly sits over the Upper Mississippi River Valley
Monday. Resultant 100% confidence in surface temperatures of -10F
covers the northern half of the forecast area from southeast
Minnesota through central Wisconsin nightly into Tuesday. Meanwhile,
EPS/GEFS certainty for daytime temperatures below zero envelops the
forecast area into Tuesday.
While HREF solutions are slightly warmer, confidence for the same
thresholds still remain above 80%.

Cold Surface Temperature Impacts Through Tuesday:

Similar to previous forecasts, daytime high temperatures struggle to
reach above freezing, staying as low has -10 in Clark/Taylor
counties. Overnight lows plummet to 5-20 below zero. Resultant
overnight wind chills will be 25 to 35 degrees below zero. Records
don`t look in question at this time. Regardless, have spatially
extended advisories into northeast Iowa tonight into Monday morning.
Also have temporally extended cold weather advisories in southeast
Minnesota and western Wisconsin through Tuesday morning. Areas
in northeast Iowa will need to further evaluated for meeting
Advisory criteria of -25. Coldest areas in central Wisconsin may
need to be further evaluated for meeting warning criteria of
-35.

Not As Cold From Midweek & Precipitation Chances:

A weakening ridge in ensemble height probabilities moves through the
Northern Plains midweek, allowing slight return flow and WAA to
bring in daytime highs in the mid 20s. An accompanying slight
moisture return quickly followed by a perturbation along upper level
northwest flow drives precipitation chances Wednesday through
Thursday. Similar to previous forecast, have upped PoPs from a dry
NBM solution due to a low QPF bias. Confidence is driven by 80-100%
probabilities in EPS/GEFS for 0.01" QPF within 24 hours. Has been a
constant signal between runs and models. Preciptiation type expected
to be snow. Low moisture will be limiting factor for impacts.

This pattern appears to repeat itself into next weekend according to
EPS/GEFS confidence in mid level heights and 0.01" 24 hour QPF.
Although, confidence is much lower, highest in central Wisconsin and
in the EPS over the GEFS. While it is too far out to fully
investigate potential impacts, EPS/GEFS confidence for low level
temperatures would suggest minimally impactful snow event.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 508 AM CST Sun Jan 19 2025

Forecast model guidance continues recent trend of over
saturating lower levels due to the anomalous cold. Have opted
optimistically given this recently observed bias but
observations should be monitored regardless through the 19.12Z
TAF period. Most likely impacts will be in central Wisconsin.
Very low confidence circumstance given recent model trends
compared to upstream observations.

Higher confidence for narrow streets of FEW-BKN cloud decks
potentially busting TAF. Can be observed for 19.12Z TAF
issuance at KRST. As a result, have TEMPO`ed MVFR at KRST till
19.15Z. Daytime cumulus may increase coverage, requiring more
widespread MVFR TEMPO. Potential impacts apply area wide from
northeast Iowa, southeast Minnesota, and western into central
Wisconsin.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Cold Weather Advisory until noon CST today for WIZ054-061.
     Cold Weather Advisory from 3 AM to 11 AM CST Monday for WIZ054-
     061.
     Cold Weather Advisory until noon CST Tuesday for WIZ017-029-
     032>034-041>044-053-055.
MN...Cold Weather Advisory until noon CST Tuesday for MNZ079-
     086>088-094>096.
IA...Cold Weather Advisory until noon CST today for IAZ008>011-018-
     019-029-030.
     Cold Weather Advisory from 3 AM to 11 AM CST Monday for
     IAZ008>011-018-019-029-030.

&&

$$

DISCUSSION...JAR
AVIATION...JAR