Watching two systems; One tonight with the bigger of the two tomorrow

Two low pressure systems will impact our weather with the first beginning later this afternoon and evening.  The second low will have a greater impact on the weather in the Great Lakes as it comes through late Wednesday.

A weak area of low pressure is currently moving into Iowa and will swing through northern Illinois after sunset tonight.  Warm air moving north ahead of the low has produced a few light showers across northern Wisconsin and Minnesota.  As the low moves closer this evening it may generate enough lift in the atmosphere to produce a few showers and even a thunderstorm or two in northern Illinois.  Instability remains fairly weak with limited moisture flow from the gulf but don't be surprised if a shower or two develops later this afternoon.

The bigger of the two systems will quickly move out of the Pacific Northwest and into our direction early Wednesday with winds in the jetstream racing southeast around 130 knots (150 mph)!  This will allow for another low pressure system to develop across the High Plains and move into the Great Lakes by late Wednesday night.  A cold front will sweep through the Stateline between noon and 6pm Wednesday bringing with it the threat for showers and thunderstorms.  Right now, the severe threat doesn't appear to be too great across the region because gulf moisture won't have enough ample time to set up and move north.  This system will, however, have a little Pacific moisture to work with so there may be a few bouts of heavier rainfall as the front moves through.  Another limiting factor to the severe potential Wednesday is the fact the system will begin to occlude as the upper level low moves directly overhead the surface low.  This limits the amount of lift in the atmosphere to generate thunderstorms.  Now, even though the gulf moisture is limited and the surface low remains detached from the cold front the jetstream winds will continue to be strong so this could get a few stronger storms to build; especially to the south in central and southern Illinois.  This powerhouse of a system has now just moved onshore in the northwest so with the model data this morning and especially the data this evening we'll have a better handle on exact timing and placement of this storm.

As Meteorologist Brandon Arnold mentioned in a previous post temperatures will tumble behind the front with highs Thursday and Friday in the low 50s.  The low will remain fairly stationary through the end of the week keeping the cloud cover and scattered showers through Friday evening.