textproduct: La Crosse

KEY MESSAGES

- Besides low precipitation chances mostly Monday evening along southwestern peripheral counties of Floyd/Mitchell Counties in northeast Iowa and northern peripheral county of Taylor County in central Wisconsin, dry through Tuesday morning. - Persistent temperatures through Tuesday night with daytime highs in the mid 70s and overnight lows in the mid 50s. - Widespread precipitation and storm chances Tuesday night through Wednesday morning. Chance for severe storms remains low.

DISCUSSION

Issued at 140 AM CDT Sun Aug 31 2025

Dry & Slightly Cooler Than Normal Today:

A relatively persistent forecast expected for the start of the new week as the Upper Mississippi River Valley remains situated between a synoptic axis of dilatation upstream from the Canadian Rockies through the southeast CONUS and an area of cyclonic rotation downstream over the northeast CONUS. Areas of reflectivity accompanying this axis of dilatation are expected to mostly remain southwest of the local forecast area through today as the pattern is reinforced by anticyclonic synoptic flow sagging southeast through southern Canada.

May see some scattered storms sag south into northern peripheral counties in central Wisconsin later today due to added moisture from Lake Superior. Although, the passing high and east winds will drastically hinder any storm activity, advecting dry low level air towards any storms that form over northern Wisconsin. Very limited confidence and impacts leave PoPs out of local forecast through today.

Slightly Below Normal Temps Through Tuesday Night:

Lack of synoptic forcing will keep a plume of decreased low level theta e from New England to near the Missouri River Valley through Monday, providing daytime highs in the mid 70s locally and highest precipitation chances southwest, in closer proximity to the aforementioned synoptic axis of dilatation and low level theta e boundary. While confidence is quite high, a 2-3 degree 25th-75th percentile spread in NBM MaxTs through Tuesday, variability in behavior of synoptic cyclonic flow rejoining parent flow over the northeast CONUS Monday through Tuesday may cause slight temperature forecast changes. Besides affecting strength and location of a subsequently digging trough through the central CONUS, main impact would be slightly cooler temperatures Tuesday morning evident in 1-2 degree decreasing trend in LREF members from the 30.12Z to 30.00Z runs. Most noticeable difference locally would be felt in central Wisconsin, in closer proximity to the residual, cooler airmass. Regardless of the minimal confidence with convective machine learning models (Pangu/Fengwu) 500mb isoheight plots only tied into this solution in one (29.00Z) of the last few runs, overall higher precipitation/storm impacts expected to remain well to the west of the local forecast area. Expect LREF members to continue increasing agreement on exact location of lowering heights, subsequently increasing confidence in location of potential convective impacts and local temperature forecasts through Tuesday.

Storm Chances Tuesday Through Wednesday:

An eventual synoptic upper level trough, currently distinguished by meager cyclonic mid level flow over the Beaufort Sea on early morning GOES West Alaska sector(s) water vapor imagery loops, dives south through the Central Plains into midweek (LREF probs 500mb heights). Resultant precipitation and storm chances increase locally Tuesday night through Wednesday morning as the attendant frontal boundary tightens. Current forecast confidence in storms is minimal due to transient nature of the amplifying upper level trough and overnight timing limiting diurnally influenced instability. Lack of confidence most evident in individual LREF member soundings plumes and accompanying hodographs covering 2/3 of the unit circle. Similar to early week temperatures, will also be dependent upon rejoining of lingering cyclonic flow over the eastern CONUS to the diving mid level trough. Accompanying machine learning (day 4 @ 30.00Z) and SPC severe storm categorical outlook (day 3) keeps probabilities and confidence below marginal thresholds.

Precipitation chances expected to linger through Wednesday as a stronger solution to the low in LREF members brings 30-50% probabilities for 0.5" of QPF in Wisconsin, a more widespread 10% to 20% increase over previous runs.

Colder Midweek Into The Weekend:

Higher confidence impacts will be cooler air Wednesday through the weekend due to the ushering in of a Canadian polar airmass through the Upper Mississippi River Valley. Coldest temperatures expected Wednesday night through Thursday with overnight lows near 40 and daytime highs in the 50s. Confidence in impacts is low however due to a 10 degree spread in 25th to 75th LREF and NBM minimum temperatures. Coldest mean solution seen in the GEFS with the 40 degree isotherm enveloping the local forecast area early Thursday morning while the EPS keeps area wide temperatures near 50. While the coldest solutions will be quite capable of causing frost, increased low level CAA would sustain low level winds, mixing the lowest layers, and abating widespread frost concerns. As for cold records, while overnight lows are expected to remain warmer than previous records in the low to mid 30s, daytime cold highs could be in jeopardy on Thursday. NBM probabilities suggest a 30% chance for daytime highs below 58 degrees at La Crosse, WI and 50% chance for cooler than 60 degree daytime highs at Rochester, MN. Similar LREF probabilities are 65% and 80% for 1:00PM CDT Thursday, respectively.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 554 AM CDT Sun Aug 31 2025

The mainly valley fog should dissipate around 31.14z.

Like this morning, there will be a deep layer (up to 450 mb), low temperature and dew point departures, and a nocturnal inversion. This will result in valley fog. However, there remains uncertainty on whether KLSE will see it or not. For now, just introduced a MVFR fog.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...None.