Onalaska, WI Weather

Key messages

- Increasing but still low confidence (less than 10%) in potential for strong storms Wednesday afternoon and evening across Southeast Minnesota.

- Warmer than normal temperatures continue through the forecast. Warmest, record to near record breaking temperatures expected for Wednesday.

- Rain chances continue off and on starting Friday through the weekend

Discussion

Issued at 216 PM CDT Tue Oct 27 2026

Tonight: Scattered Light Showers Continue

A weak warm frontal boundary is lifting north across the area helping to induce some light showers across the Upper Mississippi Valley this afternoon. These transient showers are producing little in the way of QPF with only a couple hundreths being reported at most in any given location. These will continue to lift to the north along with the front. In addition, a weak stationary boundary and axis of 850 mb moisture transport into our area is providing a steady fetch of light showers over Northeast Iowa and Southeast Minnesota this afternoon. This is noted on RAP 27.18 mesoanalysis with a small axis of 1+ pWats and across our area coinciding with a modestly strong 850 moisture transport vector. Even with this better fetch of moisture, still not expecting more than 0.05 inches of additional precipitation at any location. Overnight lows tonight will be on the warmer side compared to previous nights (upper 40s to low 50s) thanks to prolonged cloud cover and southerly return flow increasing low level moisture across the region.

Wednesday - Thursday: Potential Record Warmth, Rain/Storms

A low amplitude trough axis is expected to eject out of the Intermountain West and into the North Central Rockies/Plains through the day on Wednesday with strong southwesterly flow out ahead of it. At the surface, a family of weak lows, one across the southern Canadian Plains and one across the Northern Great Plains will start to move northeast, connected in part by a cold front. The low to the north is expected to become the more dominant low of the two with more support in the left exit region of the upper level jet. This setup overall: the two surface lows, the trailing cold front, the strong upper jet ahead of a upper trough axis all look to provide favorable synoptic kinematics across the region. In addition, moisture is expected to continue to pool ahead of the front with strong return flow through the day and near 60 deg dew points and surface temps in the low to mid 70s. This is a relatively anomalous setup for late October and has allowed for the chance to see some thunderstorms tomorrow afternoon/evening (a few strong storms possible) primarily across Southeast Minnesota. The thermodynamic parameter space does not look very favorable with weak mid level lapse rates below 7 deg C/km and elevated MLCAPE between 500-1000 J/kg. However, given the favorable kinematic space with 35-45 kts of effective bulk shear expected and low level curvature in the hodographs leading to increased SRH, this does give pause to the possibility supercells of all hazards being possible. Cloud cover and MLCIN will be of significant hindrance but if storms can become surface based along the front (potentially near the I-35 corridor?) some strong to severe storms may be possible. There is still significant uncertainty given this potential with only a 5% chance of severe weather in the Day 2 SPC Convective Outlook. Better chances overall look to be to our west across South Central Minnesota as the frontal boundary doesn't make it to our doorstep likely until after peak heating. This potential will be monitored closely over the next 24 hours.

After the front moves through overnight into THursday, rain chances are expected to come to an end with dry conditions expected during the day on Thursday. High temperatures will go back down much closer to normal in the upper 50s to mid 60s.

Friday - Early Next Week: Continued Rain Chances

A low confidence forecast continues for this weekend with chances for rain returning Friday and continuing off and on through the weekend and into early next week. This is due in large part to an upper trough moving northeast out of the Desert Southwest (cutoff from the main jet over the Pac NW). As this moves northeast, this will help send another surge of moisture northward into the Mid and Upper Mississippi River Valleys. There are ensemble differences as to how this cutoff trough is handled through the weekend but the general consensus is that it will provide some kind of upper support to allow for additional rainfall across the area. Finer details will be sorted out in the coming days as the trough evolution will determine local impacts.

Looking just beyond the scope of this forecast, both EC and GFS ensemble members are locking onto a relatively strong cut off low forming by early/mid next week across the Central Rockies. How this cutoff low evolves could play a significant impact across the area with the EC solutions favoring a more northward swing, bringing additional bouts of heavy rain across the area. There is still much that can change with this but it bares watching over the coming days.

Aviation

Issued at 1230 PM CDT Tue Oct 27 2026

Fairly dreary conditions remain across the Upper Mississippi River Valley this afternoon as scattered light showers continue into this evening. Showers largely come to an end after 00z as drier air makes its way northward given persistent southerly winds, but low level moisture looks to remain for those west and north of a line from KCCY to KMDZ through the overnight hours, resulting in MVFR ceilings and perhaps some light drizzle (<15%) while VFR conditions prevail elsewhere. Any MVFR ceilings lift Wednesday morning to between 5-10kft before a surface front moves into the region Wednesday afternoon/evening, bringing additional precipitation potential (20-40%).

Climate

Issued at 100 AM CDT Tue Oct 27 2026

Record or near record temperatures Wednesday (Record/Forecast):

La Crosse, WI

Date High Temperature Warm Low Temperature ----- --------------- --------------- 10/28 75F (1945) / 73F 57F (1881) / 56F

Rochester, MN

Date High Temperature Warm Low Temperature ----- --------------- --------------- 10/28 73F (2024) / 70F 54F (1989) / 54F

Watches, warnings and advisories

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