NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION. Privacy and Cookie policy

FXUS63 KARX 071659 AFDARX

Area Forecast Discussion National Weather Service La Crosse WI 1059 AM CST Thu Dec 7 2023

DISCUSSION
(Today through Thursday)
Issued at 255 AM CST Thu Dec 7 2023

Key Messages:

- Relatively warm today/Friday...10 to 20 degrees above normal

- Precipitation likely for most/all of the area late Friday night through Sat. Bulk of accumulations fall as rain, but some snow could accumulate on grassy/cold sfcs. Lots of uncertainty with snow potential with near sfc temps having considerable influence. Expect refine to forecast as we move into Friday.

- Colder weekend, persists into start of new work wee.

* MILD THE NEXT COUPLE DAYS - 10 to as much as 20 degrees above normal for some

Abnormally warm air a loft spreads across the region today, lingering into Friday. NAEFS and EPS anomalies still pushing +2 for 850 mb. Questions arise in how much that warm air will factor in the near sfc temps as the low level mixing is only progged to extend to about 1000 ft (per the RAP). NBM has generally been a few degrees too cool the past couple days - with the NBM75 (75 percentile)
closer to reality. Little if any snow cover to temper warming. Will trend highs toward the 75th percentile with this in mind today/Fri.
Some real mild days for early Dec (today likely the warmest), but perhaps not as mild as the air a loft would suggest.

* PRECIPITATION FRIDAY NIGHT-SAT: rain and snow both expected, but bulk of accumulations likely liquid. Still expect some snow, but how much very dependent on temps. Expect refinement to forecast over the next couple days.

Medium range guidance remains in decent agreement with the over arching expectations for Friday night-Sat...ejecting a shortwave trough northeast out of the southern plains, spinning across eastern IA/southeast WI Friday night/Sat morning. Cyclogenesis occurs with accompanying sfc low tracking over eastern IA and then across eastern WI by 12-15z Sat. Deep QG convergence with the system is quick hitting, focused around 06z Sat. Swath of isentropic upglide along the 285:295 K sfcs highlighted during the night time hours too...much of which could/will go into helping to saturate the near sfc layer. Speaking of which, GFS soundings/time-height x-sections show a pronounced dry layer sub 700 mb, which could take a couple hours to saturation before any pcpn could make it to the sfc.

Track of the system continues to favor higher QPF across northeast IA into central WI where temperature profiles would make rain the pcpn type. Moving northwest the warm layer starts to shallow out, bringing a rain-snow to snow ptype into the mix. How soon this would occur isn't clear and just a few degree swing in temp (ala a shift in the storm) would result in corresponding change in ptype.
Short/med range guidance continues to hold snow chances mostly late overnight Fri through Sat, from southeast MN into north-central WI.
QPF is lower here while warmer grounds and still relatively high Tw would work to limit snow accumulations. That said, there is the potential for focused banding with good Fgen response in the 600:700 mb layer via several of the short/med range models - likely within the favored snow type region (northwest of the sfc low). Snowfall rates could overcome any near sfc warming, thus a bit more in accumulation - although more likely on cold, grassy surfaces.
Ensemble mean paints only a 20% shot for more than 1 inch, and has shown some fluctuation over its last few runs.

Overall, confidence relatively high that the local area will see accumulating pcpn late Friday night through Sat...with higher amounts (mostly liquid) in the south and east. How much snow is realized is a lot less clear with several factors (but mostly near sfc temps) playing roles. Look for continued refinement in chances/amounts as we move into Friday.

Quick side note - a shortwave in the northern stream is progged to drop southeast across the area Sat/Sat night, just behind the departing southern system. This look like a low QPF, higher POP kind of scenario where much of the forecast area could/would see some light snow, but accums would be minimal.

* COLDER WEEKEND, START TO THE NEW WEEK...albeit, closer to the early December normals

A slug of much colder air, but closer to what is expected for early December, flows southward out of Canada Saturday. The GEFS and EPS members then trend toward northwest flow a loft for the rest of the weekend, into the start of the new work week - with support from all the WPC clusters. Temps will take a tumble back to the early December normals - perhaps a few degrees below - as a result. Not much spread in the EPS and GEFS 20-75% percentiles for temps, which has been a consistent signal over the past several runs of both model suites (increasing confidence in likely outcomes). Not a significant cool down by any means, but going to "feel" a lot colder compared to recent spate of mild days.

Clusters and latest deterministic runs of the GFS/EC suggest a west coast upper level ridge could build eastward across the local area for the latter half of the new week - bringing another round of milder conditions. A lot more spread in the ensemble members here, but suggestive that we could return to a more milder regime - at least for a few days.

AVIATION
(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1058 AM CST Thu Dec 7 2023

VFR conditions through the TAF period. A surface warm front is lifting into the area, however washes out. Generally some patchy high clouds today. A pocket of moisture per the HRRR short term models increases some low level and mid level cloudiness after 22Z before the 850mb winds shift to the west. Due to low confidence in the coverage of these low/mid clouds, just included a scattered deck. Surface winds are southeast to south 3 to 13kts, gradually veering more west Friday morning as a surface low tracks well to the north across southern Ontario. Most gusts during the period; 5 to 15kts, however this afternoon toward RST gusts should increase 10 to 20kts.

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

toggle option: (graph/table)

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

La Crosse, WI,