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FXUS63 KARX 042114 AFDARX

Area Forecast Discussion National Weather Service La Crosse WI 314 PM CST Mon Dec 4 2023

DISCUSSION
(This evening through Monday)
Issued at 314 PM CST Mon Dec 4 2023

Key Messages:

- Light snow could bring minor accumulations to the area tonight with highest probabilities approaching an inch in southwest Wisconsin.

- High confidence in increased temperatures into the 40s to low/mid 50s Thursday and Friday.

- Still some uncertainties revolving around a system over the weekend. Low confidence remains in the track of the surface low and northern extent of any precipitation. Stay tuned for continued updates.

Light Snow Chances Tonight:

Next short wave trough is approaching in northwest flow and bringing yet another lower QPF /light amounts/ round of snow to the area. As wave drops out of the Dakotas heading into this evening, some deepening will take place, providing enough lift and forcing for what appears to be mainly a snow event. Better mid- level forcing aligns closer to wave and thus, highest accumulations are a bit more likely across southern areas, especially in southern Wisconsin where timing and a more prolonged period of precipitation could occur.

Given fairly mild temperature profiles, probabilities of an inch or more according to 04.12z HRRR are only around 30% but if rates in any bands that form are high enough, could see this grow with minor impacts to travel overnight. Mean amounts for a site like Platteville WI have been around an inch by ensemble members with a small range of possible outcomes.

Increased Temperatures Across The Region For Thursday and Friday:

Behind the aforementioned system, model guidance suggests an upper level ridge will be building over the central/north-central U.S. for mid-week. This looks to allow for a drier period for much of the week. The main message will continue to revolve around increasing temperatures mid-week into the end of the week. The NAEFS and ECMWF ENS continue to show 850mb mean temperatures within the 97.5 to near 99.5 percentiles of climatology for portions of the area on Thursday, with GEFS and ECMWF ens solutions suggesting 850 mb temperatures reaching up to 8 to 11 degrees C by the afternoon.
Further confidence is added as NBM and ensemble solutions show small spread (only around 2-5 degrees F) between the 25th and 75th percentiles. With this said, have maintained previous forecasts and increased high temperatures towards the 75th percentile of the NBM resulting in forecast highs in the upper 40s to mid 50s Thursday.
Though still fairly small, spread increases just a bit for Friday with some differences in details surrounding a frontal passage through the region. The current forecast leans towards highs in the low 40s to low 50s (highest across NE IA & far SW WI) right now.
Otherwise, looking into the weekend and start of early next, model guidance shows some indication that temperatures will make a downward trend through the weekend and beginning of next week.

Keeping An Eye On Precipitation Chances For The Weekend:

By Thursday model guidance suggests the ridge gets flattened (across the western/central U.S.) as shortwave energy from the western U.S.
ejects eastward. With this, an upper level trough is then forecast to develop across the western U.S. Friday and continue to move eastward through the weekend. In the early Friday time period, ensembles show a low pressure system moving across southern Canada.
Highest chances for precipitation look to mainly stay north of the forecast area with only the ECMWF ens showing low chances (<30%) for any measurable precipitation across northern portions of Taylor county. With lower confidence, have maintained the drier forecast for now. Otherwise, most attention will turn towards a system expected to develop and track across the central to eastern U.S.
through the weekend. There is still quite a bit of spread among ensemble solutions in timing, amounts, and especially revolving around the track of the attendant surface low. There remains low confidence in any one solution right now, so will maintain the NBM precipitation chances. Will be something to keep an eye on in the coming days as details become more clear.



AVIATION
(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1155 AM CST Mon Dec 4 2023

Wide variety of flight conditions across the region today with abundant low level moisture and next short wave trough approaching from the northwest. Meanwhile a whole in the lower stratus brought some VFR conditions to parts of western and southwest Wisconsin but this should gradually evolve back to MVFR as wave draws closer.

Short wave is progged to deepen a bit as it moves through the area tonight but should be enough forcing to generate fairly widespread precipitation. While confidence in where more steady snow might fall is not overly high yet, should be enough impact to bring aviation flight categories down to IFR and possibly LIFR for a time tonight into Tuesday morning. Higher impacts likely south and east of KLSE.



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

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