An omega block is ruling our weather. When will it finally budge?
- This pattern disrupts typical west-to-east jet stream flow, causing stagnant weather conditions, including cool, showery weather in the East and West, and mild, clear conditions in the north-central U.S.
- A shift to a "zonal" flow of air, where weather systems move west-to-east across the country, is needed to break the pattern, but there's no indication of this happening soon.
Your current weather may be around awhile.
The large-scale weather pattern that's now influencing much of the USA's weather – known as an omega block because of its resemblance to the Greek letter omega – isn't budging right now.
Forecasters say the overall pattern could last at least until next weekend, and perhaps beyond. "We could be stuck for a while," Weather Prediction Center meteorologist Brian Hurley told Paste BN on May 5.
What is an omega block?
According to Weather.com meteorologist Jonathan Erdman, "if you trace the path of the jet stream across the U.S. from the West to the East, you will trace out the Greek letter omega (Ω)."
"This configuration blocks the typical west-to-east flow of the jet stream, much like a large rock in a small stream forces the flow of water around it," he said. "That's why meteorologists call it a blocking pattern."
Hurley told Paste BN that you see this pattern sometimes in April and May, when upper-level low pressure areas are "cut off" from the main flow of air.
This setup tends to prevent the normal west-to-east movement of weather systems and tends to lock in chilly, unsettled conditions in some areas, while other locations have an extended period of dry and warm conditions, AccuWeather said.
What's going on weatherwise?
The pattern is bringing cool, showery, cloudy weather to the East and West, and mostly clear, mild conditions to the north-central U.S.
According to the Weather Prediction Center, a "blocky pattern remains in place over the Lower 48 to start the week with a slow moving upper-low over the Ohio Valley, another slow moving upper-low over the Southwest and an upper-level ridge over portions of the northern Plains/Upper Midwest in between."
A ridge is an area of high pressure that typically brings fair conditions.
The omega block pattern will continue to lead to areas of both well below normal and well above normal temperatures this week, the Weather Prediction Center said.
How long will the omega block pattern last?
Hurley said a temporary breakdown of the pattern could come by mid- to late week before it re-establishes itself by next weekend.
"By late week into early next week, (Monday May 12) we could be looking at a closed upper low in the Mississippi Valley and another one in the West Coast," he told Paste BN. This would bring similar weather to what we're seeing now.
As for what it will take to finally break the pattern for good, he said we need a switch to what's known as a "zonal" flow of air, where systems zip west-to-east across the country.
However, "we're not really seeing that now," Hurley said.