It can't be seen with the naked eye, but a curious weather pattern in the upper level atmosphere above the continental United States is forecast to generate unsettled weather and some big temperature contrasts into the weekend.
An "omega block" is expected to form from California eastward into the Ohio Valley, the National Weather Service Weather Prediction Center said on May 2. The blocking pattern is so named because its shape resembles the Greek letter omega.
The unsettled weather will begin with a swath of heavy rain, flooding and potentially severe weather from the Southern Plains into the Ohio Valley on May 2, stretching from Texas into southern Pennsylvania. The greatest risk will exist from southern and eastern Texas into Kentucky and the weather service has posted flooding advisories across southern Oklahoma.
A boundary of moist air along the cold front is forecast to stall in some areas, bringing repeated rounds of rain and storms, with a slight risk of excessive rainfall over portions of the lower Mississippi River Valley and parts of Texas, Arkansas and the southern Plains, the weather prediction center said.
Several rivers that have been flooded in Northern Texas could see a slight bump in water levels over the weekend, according to the National Water Prediction Service. Fortunately for those along the Mississippi River, water levels are forecast to continue dropping despite the predicted rain.
The front will make some progress south and eastward into Saturday, bringing shower and thunderstorm chances to the Northeast, Mid-Atlantic, Appalachians, and Southeast, the weather service said, where moderate to locally heavy rainfall is expected with some additional isolated instances of flash flooding possible.
As the pattern amplifies over the weekend, stretching from west to east, It's expected to bring big contrasts in high and low temperatures. Parts of the Great Lakes and Midwest may experience cool temperatures well below average, down into the 50s and 60s.
Next week will be a farewell to this recent summer preview in the eastern United States, thanks to a weather pattern known as a cut-off low. That's a large area of low pressure that gets "cut off" from the main jet stream and just sits and spins for days. It's forecast to bring a spell of cooler, damper weather to a region that's in desperate need of rain.
Contributing: Doyle Rice, USA TODAY
Dinah Voyles Pulver, a national correspondent for USA TODAY, covers climate change, weather, the environment and other news. Reach her at dpulver@usatoday.com or @dinahvp on Bluesky or X or dinahvp.77 on Signal.