National Weather Service United States Department of Commerce

Do you remember the article we shared about something called an "Omega Block" about a month ago? Maybe not, but I'm willing to bet that you do remember the warm and sunny weather that we had right around that time. Well that beautiful weather was thanks to a weather pattern called an Omega Block, and lucky for us, it's back!  Below, you'll find the article we shared last month, with some updates to the graphics and some of the dates. I hope you enjoy the article, and more importantly, the weather!



Prepare yourself for some outstanding weather through the 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.

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 Great Plains, then low pressure over the eastern US.  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, May 21st. 

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 low to mid 70s today (60s by the lake), and the mid to upper 70s on 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, where it will be much cooler with lots of precipitation.  See the temperature map below for this Sunday, May 22nd. 

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 May.  Then it's June!