- Another omega blocking pattern will keep weather conditions stagnant this week.
- California will experience unusual thunderstorms in June. The Plains and Rocky Mountains will also see storms.
- There will also be a split in temperatures for most of the week.
A weather pattern known as the Omega Block returned to the United States this week, bringing an unusual threat of June thunderstorms to California, hot temperatures in the Northwest and northern Plains and relatively cool conditions in parts of New England.
Here's how it works: There are two southward dips of the jet stream — one associated with a low-pressure system near California and the other over the Northeast. Between them is a ridge of high pressure, or northward bulge in the jet stream, found from the northern Plains and northwest into Canada.
(More: Smoke from Canadian wildfires pushed to the northeast due to low pressure)
The jet stream pattern resembles the Greek letter Omega. Notice how the jet stream pattern — that ribbon of rapidly flowing air about 30,000 feet above the Earth's surface — described above and pictured below resembles the Greek letter omega: Ω.
The term omega block may sound familiar because the pattern also developed in May.
The term omega mass is not new – it is often taught in basic meteorology courses. This is one of several blocking patterns that meteorologists are familiar with. Two others are called the Greenland Block and the Rex Block.
They all involve an exaggerated north-to-south alignment of the jet stream that causes weather patterns to move slowly for some time, which is where the term “cluster” comes into play. Essentially, the weather pattern is blocked, and this prevents weather systems from advancing at a steady pace from west to east as usual.
Ban patterns usually come and go, but the United States has been stuck in a rut with various forms of bans since the beginning of May.
It creates an unusual thunderstorm threat in June in California. The first month of summer is typically dry in California, but with enough moisture and lows in place, we will see several days of rain and thunderstorms in the state this week. The greatest chance of measurable rainfall and localized flash flooding is at high elevations such as the Sierra Nevada, but lower elevations can also see isolated storms.
The Rockies and Plains will also be hot spots for thunderstorms. Disturbances from the same upper low near California will ignite bouts of rain and storms in the Rockies and Plains through much of this week. Heavy rain in some of these storms could lead to localized flooding.
Omega block will create a temperature split. Temperatures in the Northwest and Northern Plains will remain persistently high this week due to high pressure in the upper level. Highs are in the 80s and 90s in Portland, Oregon, several degrees above the average high of 73.
The flip side is that the Northeast, especially New England, will see another bout of near-average or somewhat cooler-than-average temperatures in early June. Take Boston, which will remain stuck in the 60s on Wednesday and Thursday compared to its average high near 74 degrees.
This stuck pattern with the upper low over the Northeast will continue to push wildfire smoke from Canada to the east. The latest news on smoke and air quality can be found here.
Chris Dolce He has been a senior meteorologist at Weather.com for over 10 years after starting his career with The Weather Channel in the early 2000s.
The Weather Company's primary journalistic mission is to report on breaking weather news, the environment, and the importance of science in our lives. This story does not necessarily represent the position of our parent company, IBM.
