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FXUS63 KARX 100825 AFDARX

Area Forecast Discussion National Weather Service La Crosse WI 220 AM CST Sun Dec 10 2023

KEY MESSAGES

- Back to colder, more seasonable temps for the next few days.

- Milder air returns by mid week, holding into Friday. Trending cooler for the weekend.

- Generally dry through the new work week with low end (20%)
precipitation chances creeping in for the weekend.



DISCUSSION
Issued at 220 AM CST Sun Dec 10 2023

* COLDER, BUT SEASONABLE START TO THE NEW WEEK...trending dry

With the passage of the upper level trough/sfc cold, the snow has exited east and colder air is flowing southeastward out of Canada.
850 mb temps already dropping into the single digits below zero (from closer to +10 C just a day or two ago) and look to settle in there through Tue. Today/Tue will hold highs in the low to mid 30s while a few degrees warmer for Monday, ahead of an approaching shortwave trough. All in all, much colder than the past few days, but what is expected for this time of year.

As for that shortwave trough, medium range guidance continues to slip it across far northern portions of the region. The deeper saturation looks to hold to the north with the shortwave, as does the "stronger" QG convergence. EPS/GEFS ensemble members hold all QPF (which is light) to the north. So, sensible weather outcomes locally will likely confine themselves to some clouds and a wind shift with the frontal passage.

* MILD AIR RETURNS FOR THE LATTER HALF OF THE WEEK...perhaps some pcpn chances for Friday/weekend

Broad upper level ridging starts to build in from the west by Wed, continuing to influence the region through Friday. Very consistent signal in the long term guidance. WPC clusters also support this outcome, with small differences in location of the axis and strength of the ridge. Milder air will push northward and highs look to climb back into the 40s for many/most. A few of the EPS/GEFS members suggest 50+ could be attained - although low end chances at this time (5-10%).

The EC and GFS then want to shuffle a few upper level shortwaves across/near the upper mississippi river valley. Not a lot of agreement in placement/strength, but they both suggest troughing and colder air returns. Could see some pcpn chances, depending on where these various features track. Mixed bag in the individual members for both models' ensembles with more than 1/2 trending dry or only very light QPF potential...and in different locations/timing. The grand ensemble paints about a 20% shot for pcpn for Fri/weekend, and that looks reasonable given the model differences between/within themselves.

Also, as noted yesterday, while the long range guidance is trending colder for the weekend, the deterministic GFS continues to be at the bottom of its own ensemble members - with a very cold solution.
Looks like the outlier.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/
Issued at 1107 PM CST Sat Dec 9 2023

A low pressure area will provide periods of light snow into the early overnight. This snow will occasionally produce MVFR visibilities across western Wisconsin through 10.08z. Additional snow accumulations across western Wisconsin will range from a dusting to a few tenths of an inch.

Expect sustained west winds in the 15 to 25 knot range with gust of 20 to 30 knot range overnight. These winds will then drop to around 10 knots on Sunday morning and even lower on Sunday evening.

With cyclonic flow continuing through Sunday, kept the MVFR ceilings going through 11.00z and then brought in clearing in the evening as the ridge axis moves east across the area.

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

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