Weekend weather update

500 mb Flow Chart

The cloud cover from this morning has hung around through the better part of the afternoon and it's only in northwest Illinois that the clouds have thinned enough to allow filtered sunshine.

An ongoing MCS (cluster of storms) from this morning in the Plains has regenerated itself and is pressing to the east across the Minnesota/Iowa border.  Currently a Severe Thunderstorm Watch is in place for southern Minnesota and northern/northeast Iowa.  The first image on the left is an analysis of the 500mb level.  The solid black lines are pressure and the dashed red lines are temperatures (in °C).  Current wind flow at this level is almost from west to east.  In fact, there is a ridge of high pressure across the western Great Lakes.  Winds then shift to the south in southern Wisconsin and northeast Illinois.  It's important to look at the wind field at this level because this gives us an idea of where potentially the storms will go.  Storms in Minnesota will continue to move east into Wisconsin and will likely weaken before turning southeast due to more of a stable airmass because of an east wind at the surface, cooler temperatures and dew points and lack of sunshine today.

Another factor against any big storm threat tonight is also the fact that instability isn't too great across the area.  The greatest instability remains to the west in Iowa where almost a full day of sunshine was seen.  We will, however, have to watch the southern edge of this complex because it's possible it may dive southeast and hit sections of northwest/western Illinois as it follows an bit of an instability axis later this evening.

Of a greater concern will potentially be the weather for Sunday.  A developing low pressure system in the Plains will move either right over or just to the south of the area late Sunday.  Depending on how storms evolve/move tonight and if we see more sunshine Sunday afternoon as the associated warm front and cold front move through strong to severe storms remain possible across all of southern Wisconsin and northern Illinois.  Greatest threat appears to be from south-central Wisconsin across Illinois and back through Missouri.

Eric Nefstead is in the FirstWarn Weather Center this evening and will have all the latest on the news at 6pm and 10pm.  Of course, I'll continue to monitor things from home and we'll keep you updated on the weather for tonight as well as this weekend. -CK