A weather pattern named after the Greek letter omega is guiding the U.S. weather from May to June, forecasters said, and the pattern is expected to continue.
Indeed, be prepared for some weather deja vu over the next few days. The “Omega Block” weather pattern will remain in some form for some time, trapping cold air for some and hot air for others. It can also change the direction of the storm in unusual ways.
According to the National Weather Service, this omega block is locked into a stagnant breakup pattern. The weather is very warm and dry in the north-central United States, and cooler and wetter along the coast and in the south, with a slow-moving system increasing the risk of flooding in wetter regions.
ABC 17 meteorologist Nate Splatter wrote on his blog in late May that “blocking patterns like this are known to cause extreme weather, as high pressure blocks the jet stream and shifts the path of the storm north and south.”
This pattern can continue for several weeks.
A more open, weaker version of the Omega Block will be in place from June 4 to 12, according to AccuWeather meteorologist Paul Pastelok.
What is Omega Block?
The Omega Block is essentially a stagnation pattern in the jet stream that locks in the weather over the United States, keeping the central part of the country warm and dry while conditions along the coast remain prone to storms and flooding for days on end.
According to Pastelok, the Omega Block is a large, nearly stationary, upper-level high-pressure region sandwiched between two upper-level low-pressure regions.
This pattern is most common in April and May, when the upper-level low-pressure area is “cut off” from the mainstream air.
So what’s the name?
According to Weather.com meteorologist Jonathan Erdman, “If you follow the path of the jet stream across the United States from west to east, you’ll find the Greek letter omega (Ω).”
What does the Omega Block mean for our weather?
It depends on where you live.
The overall pattern is to have troughs in both the west and east, with ridges in between, according to NOAA’s Weather Prediction Center. This means cooler weather on these two coasts and much warmer weather in the central United States.
- Cool Northeast: The weather forecast center said unseasonably cold temperatures in the east will intensify from early to mid-week. A relatively cold air mass moving across the Northeast and Middle East United States will keep the heat and humidity in check in the South.
- The northern plains are hotTemperatures will be well above normal from central and Midwest Canada to the northern Plains, Pastelok said. As this pattern takes hold, the heat of summer has finally arrived across the northern tier, with temperatures up to 20 degrees above average and breaking nearly 50 records, Fox Weather reported.
- It rained in the south: The weather prediction center said this blocking pattern would create a very warm, moist, and unstable air mass south of the wavy frontal boundary, keeping much of the south and southeast active and bringing the possibility of rain and thunderstorms daily into early June.
- Wet and snowy West: WPC added that the western trough will close into a wide upper-level low that will circle the northern Rocky Mountains and bring heavy rain and mountain snow to low-lying areas from May 31 to June 1.
- Temperatures in the Southwest are mild: WPC says mild temperatures are expected across the Southwest this week after a period of below-average temperatures associated with increased cloud cover and precipitation. Phoenix is expected to reach 104 degrees by June 1, according to the National Weather Service.
Additionally, Pastelok warned that “dryer-than-normal conditions and higher temperatures than normal for this time of year could lead to fires, especially in the northern High Plains and central Canada.”
Doyle Rice is a national correspondent for USA TODAY, focusing on weather and climate.
