'Omega Block' To Keep Northern US Comfortable As Heat Dome Keeps South Blazing Hot

A weather pattern called an "omega block" in western Canada will keep parts of the northern U.S. feeling comfortable by August standards as a heat dome continues to bake Texas and the Southwest.

Here's what the omega block means: An area of high pressure in the upper atmosphere is parked over western Canada. That's forcing southward plunges of the jet stream on both sides of that high, including one dipping south across much of the northern U.S.

Notice how the jet stream pattern – that ribbon of fast-flowing air some 30,000 feet above the ground – described above and depicted in the image below resembles the Greek letter omega: Ω.

The term "omega block" is not new (we've talked about it before earlier this year) and is often taught in basic meteorology courses. It's one of multiple blocking patterns that meteorologists learn about, and all of them feature an exaggerated north-to-south jet stream alignment that causes weather patterns to move slowly for a time.

H​ere's what this omega block means for your temperatures: As you can see below, areas from the northern Rockies into the Midwest and Northeast will generally see highs that are near or below average for early August. That's because the blocking high in western Canada will help to force relatively cool air by August standards from northern latitudes southward into those regions.

But this pattern shift won't eradicate the heat dome that's been searing parts of the southern U.S. since July. Areas from the Desert Southwest into Texas, the Gulf Coast and Florida will continue to be hotter than average.

T​he most significantly below-average highs will be from the northern Rockies into portions of the Plains and Midwest. Cooler air will spread into the Ohio Valley and Appalachians on Monday and Tuesday. You can see how the forecast highs compare to the daily average for select cities below.

O​n top of that, lows will dip into the comfortable 50s and lower 60s as the cooler air spreads eastward through the Plains and Midwest.

Heat fatigued areas from Texas to the Southwest won't see any relief. Triple-digit highs will continue to be commonplace in Texas, including more daily records, particularly in central and South Texas. The heat dome will pile on to last month's all-time record heat in the Desert Southwest, including Phoenix, which will be in the midst of a new stretch of 110-plus-degree highs.

(​MORE: July Was Record Hot In Phoenix And Other Southwest Cities)

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.

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