Strong winds and thunderstorms to end quiet week

 

For the second time this month the high temperature has reached 60 degrees. Our first 60-degree (plus) day came just this past Monday when the temperature reached 69 degrees. Under mostly clear skies Wednesday night temperatures will fall into the low 30s, rising back into the mid-60s Thursday afternoon. Throughout the day we'll see a gradual increase in cloud cover as a warm front, currently across central Illinois, rapidly lifts north.

There will be some moisture that follows which may briefly lead to a period of mostly cloudy skies early Friday. But with a rapidly strengthening low pressure system to the west the warm front should quickly lift north into Wisconsin later in the morning, allowing mostly sunny skies to prevail Friday afternoon.

This will set the stage for a rather warm and windy Friday afternoon. Temperatures are forecast to rise well into the 70s, possibly close to 80 degrees for areas to the south. But the warmth will also come with gusty south/southeast winds. Wind gusts during the afternoon and evening, outside of any thunderstorms, could reach 35-45 mph. 

Thunderstorms are expected to rapidly develop over Iowa and Missouri late Friday afternoon and evening along what is known as a 'dry line'. This is a boundary separating dry and moist air masses. The Storm Prediction Center has outline most of southern Wisconsin and all of northern Illinois in a 'slight' risk for severe storms for late Friday evening. This means that scattered severe storms may occur within the outlooked area. Just to the south, however, is an enhanced risk as there is higher confidence in the possibility of more widespread severe storms.

Instability will be highest to the west during the day where the storms will initially begin. Through the evening and after sunset is when we will begin to lose instability locally. The amount of moisture we're also able to maintain is in question because the stronger winds aloft could help mix down some drier air, lowering our surface dew point temperatures. If that occurs, we may lose some of the moisture needed for storms to maintain their strength once they cross into northern Illinois. 

However, very strong winds aloft could help offset that which would keep the damaging wind threat with any storm that moves through. If the line of storms to the west is able to maintain its structure and strength, there is also a low-end risk for an isolated, spin-up, tornado.

The main message with Friday evening is to remain alert and pay attention to the forecast. This is our first risk for any sort of strong to severe storms this season, and it won't be our last. The timeline for the storms locally will likely range from 6pm-7pm (west) through 12am-1am (east).