Plaincast

Messages

Isolated to scattered shower and thunderstorm chances along and west of I-90 corridor this evening.

Very warm and muggier conditions continue Saturday with heat indices in the 90s, but remaining below heat headlines.

Wildfire smoke from across northern MN and northwestern Ontario will continue tonight into Friday contributing to very unhealthy/hazardous air quality. Thus WI DNR issued air quality alert for all southern WI through noon Friday when southwesterly winds help improve conditions briefly before returning this weekend.

Increased shower and storm chances Friday afternoon/evening and Saturday and again for the start of next week.

Update

Isolated showers and storms will remain possible this evening, mainly southwest of a line from the Wisconsin Dells to Burlington. Otherwise, continued smoke will be the story through the rest of the evening and overnight. Outside of the far southwest forecast area, smoke with visibilities of 1 to 3 miles is likely to persist into Friday morning. No significant updates to the forecast are anticipated for the remainder of the night.

Short Term

Smoky conditions and very unhealthy/hazardous air quality continues, but gradually improves from southwest to northeast late this afternoon/evening as a warm front lifts and stalls across southwestern portions of the forecast area. This boundary will be the focus for pulse-type shower and thunderstorm development this afternoon and evening as hotter, more moisture air results in higher instability across southwestern corner of the forecast area. This is proving to be enough for scattered showers and storms, but given the lack of shear, any activity builds and collapses quickly. Nevertheless still may see a a few storms build tall enough to produce lightning and gusty winds if they are able to interact with the boundary along with any outflows from nearby decaying showers/storms. This activity will continue through sunset, but diminish with the loss of daytime heating.

Also looking at the this boundary to stall along the I-90 corridor tonight as prevailing easterly flow slows it progression overnight and will allow for areas to the southwest clear out from wildfire smoke a bit more compared to areas to the east where the lower visibility will continue through much of the night. Expecting smoky conditions to gradually improve through daybreak Friday as southwesterly winds pick up as the warm front progresses northward, but will linger longer along the lakeshore longer than inland areas.

Otherwise, will see temperatures and dewpoints warm through Friday afternoon behind the warm front. Given SBCAPE building to around 1000 J/kg with dewpoints in the upper 60s into lower 70s. While environment remains conductive for additional thunderstorm development as depicting by the 12-18z CAMs, tough to tell what the forcing mechanism will be the focus for initiation. Nevertheless, the potential remains for afternoon/evening shower/storm development (20-40%). Again not expecting strong activity given the lack of shear, but will monitor.

Long Term

Focus then shifts to the the upper-level trough progged to dig down across the Upper Great Lakes Saturday. The associated surface low will develop and track across northern MN/WI overnight Friday into Saturday dragging a cold front down across southern half of WI Saturday morning. This will bring some shower/storm chances along the frontal passage, but given the morning timing not expecting strong or widespread coverage. Chances will diminish through the morning with drier airmass. However, accompanying the northerly winds shift will also be a return of wildfire smoke to southern WI Saturday and lingering into Sunday as high pressure works its way across the region.

While smoke returns for the end of the weekend temperatures are looking cooler on Sunday with highs in the low to mid 80s. Then as the high shifts southeast later Sunday, expect warmer temperatures to return for the start of the week ahead of a deepening trough. This looks to be the strongest of the systems in the extended period with a sub-1000mb surface low trekking east across Ontario through the day Monday with a cold front pushing across the Upper Midwest later Monday. Will see +1000 J/kg of SBCAPE, better deep layer shear (+50 knot), and more favorable upper-level jet dynamics align over the region with this frontal passage. Thus expect increased thunderstorm chances along with potential for stronger to severe storms if these trends persist.

Behind this early week system, expect a cooler Canadian airmass to settle into the region through the middle of next week as high pressure builds. Given the extended trends, there remain the a potential to see near to below normal temperatures.