National Weather Service United States Department of Commerce

Prepare yourself for some outstanding weather through the remainder of the week and especially this weekend!  Unfortunately, you folks near Lake Michigan know the drill.  It will be cooler by you at times.  This fine weather is a result of a blocking weather pattern called an "Omega Block".  This is nothing new to meteorologists, kind of meteorology 101 stuff.  It is one of the many types of weather patterns that can set up and be stubborn to move.  Sometimes they bring us great weather, sometimes not (Colorado will see the latter).

Much of our weather is driven by what is happening in the mid levels of the troposphere, about 15-18,000ft above the ground.  You remember the troposphere from your 5th grade weather unit, it's where all of our weather happens. The troposphere stretches from the ground up to the tropopause, or roughly 32,000ft.  All those other "sphere" layers are above that (stratosphere, mesosphere, thermosphere, etc).

The Omega Block developing over the U.S. over the next few days features low pressure over the western U.S., high pressure extending through the Mississippi River Valley and Great Lakes, then low pressure just off the east coast.  We call this an omega block because it looks like the Greek letter omega.  See the image below.  This is how the weather pattern (in the mid levels of the atmosphere) will look this Saturday, April 16th. 

Below is the textbook diagram used to describe the pattern...the similarity is clear.

For southern Wisconsin, we'll be sitting under the high pressure portion of the block.  That means temperatures climbing into the mid and upper 60s on Friday (50s by the lake), and upper 60s to lower 70s Saturday and Sunday.  This will come with dry and mostly sunny skies.  The people living closer to the low pressure out west will not be so lucky (see Wyoming and Colorado).  It will be much colder with lots of precipitation.  See the temperature map below for this Sunday, April 17th. 

Below are the Climate Prediction Center's 6-10 day and 8-14 day outlooks.  The above normal weather could stay through the rest of April.  Then it's May!