Saturday weather breakdown

After Thursday's weak cool front all eyes will turn west towards California as the next potent storm system moves onshore.  Already bringing flooding rain and thunderstorms to the southwest, this storm system will move out of the Rockies and into the Plains by Saturday morning.  The weather will remain quiet both today and tomorrow but thunderstorms, some strong to severe, are becoming more likely for the Midwest.

Here's the breakdown and what you need to know for this weekend:

The cool front passing through today will settle south as high pressure moves in Friday.  That same frontal boundary will then lift back north as the low pressure system moves out of Colorado.  Already dew points in the 60s and low 70s can be found across the far southern Plains and once that front begins to lift back north Friday night moisture will come streaming into the Midwest.  Our weather computer models were in fairly good agreement concerning the timing of this system, however, they've started to diverge a bit on not only the timing but also how many shortwaves, or mini lows, will form ahead of the main upper level low.  If any one of the 'mini lows' move through this could allow for additional storm development. 

Winds increase significantly behind the warm front Saturday with winds just a few thousand feet above the surface streaming in around 58 to 70 mph!  This is what's know as the low level jet and it will help transport the gulf moisture northward late Friday night and early Saturday morning.  Thunderstorms will likely be ongoing across eastern Iowa and maybe even northern Illinois at the start of Saturday as the warm front pulls through.  If the warm front lifts far enough north into Wisconsin we'll dry out some for the afternoon and temperatures will rise well into the 70s.  If we don't clear out and the warm front remains just to the south of the Wisconsin/Illinois border the cloud cover will likely persist with temperatures only rising into the 60s.

Along with the strong winds a few thousand feet above the surface winds within the jetstream will also come roaring in and actually move over what we call the 'warm sector' of the storm system.  The significance of this is when there is a change in wind speed with height and also a change in wind direction with height it can enhance the shear in the atmosphere which is what's needed to allow thunderstorms to rotate.  If winds at the surface are from the south but just a few thousand feet above they're now from the west/southwest supercells are more likely to form rather than thunderstorms that develop into a line.

As of right now the most favored regions for severe storm develop Saturday appear to range from eastern Nebraska and Kansas to central and northern Missouri into Iowa with southern Minnesota, southwest Wisconsin and northwest Illinois possibly being impacted.  The weather here Saturday afternoon and evening greatly depend on how quickly storms from the morning move out, where the placement of the warm front is and if there are any lead shortwaves (mini lows) ahead of the main system.  The Storm Prediction Center has placed northern Illinois and southern Wisconsin under a slight risk for Saturday.  Continued updates will be found here as the weekend gets closer and the details become a little more clear.  Since we're now in the 'off season' for severe weather it's important for you to be weather aware and informed as to what may occur this weekend.