Omega block pattern shift brings 4 changes in the week ahead

Omega Pattern to Bring Major Change Across US


Changes are coming this week due to a shift in the weather pattern that includes the redevelopment of the omega block weather pattern across North America. The changes will be particularly welcome to the severe-weather weary central U.S., but may not be cheered in the East.

READ MORE: Deadly Flooding Strikes Texas

This is the second time in the last several weeks that we will have seen an omega block weather pattern develop. This time around the configuration of the omega block will be in a different geographic location and less extreme than what we saw in mid-April.

Omega Block Midweek: Two areas of low pressure develop, one on the East Coast and another on the West Coast. In between, the jet stream bulges northward.

Here's how it works: an area of low pressure aloft will anchor itself in the East by midweek while another separate area of low pressure develops on the West Coast. In between will be a ridge of high pressure, or a northward bulge in the jet stream near the Plains and Rockies. Now, 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 to the right resembles the greek letter omega shown here: Ω.

1) Wetter, Cool Northeast

Jet-stream pattern in place late in the week, featuring a deep, closed upper-level low in the East.

It's been a dry spring so far in most of the East, but the pattern change will flip that around the first week of May.

First up, through Tuesday, waves of low pressure and upper-air disturbances will bring periods of rain to the Northeast.

MAPS: 7-Day Weekly Planner

Then, a sharp plunge of the jet stream will nosedive out of central Canada and form a slow-moving gyre of low pressure over the Northeast late in the week into the Mother's Day holiday weekend.

It's not yet clear whether this late-week system will produce heavy rainfall in any locations, but persistent clouds and periods of rain look to be in the cards much of the week.

FORECASTS: NYC | Boston | Philly | Wash. D.C. | Syracuse

If any area of low pressure at the surface is able to strengthen off the East Coast, that would enhance the heavy rain threat. Again, that is not clear at this point.

Temperatures will also stay cooler than average through much of this week in the East. Highs will only be in the 50s and 60s from the Great Lakes into the Northeast. Milder temperatures may then return next weekend.

2) Drier Days Ahead For South-Central States

The threat of severe thunderstorms and flash flooding will continue into Monday in parts of the South. This next round comes after storms have already brought severe weather to the region last week.

Thunderstorms are likely, especially toward the Gulf Coast, but the chance for severe thunderstorms will decrease.

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Omega block pattern shift brings 4 changes in the week ahead
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By midweek, the risk of showers and thunderstorms will be confined to the Southeast. High pressure will move into the Plains, bringing a welcomed stretch of dry weather to the south-central U.S. starting Tuesday.

This is good news for the water-logged areas of the South, as this weather pattern will give areas the opportunity to dry out a bit and clean up any storm damage.

READ MORE: Deadly Flooding Strikes Texas

3) Spring Returns to the South

Portions of the South have enjoyed a taste of summer this past week due to high and low temperatures that have been 10 to 15 degrees above average.

Highs soared into the 80s and even a few lower 90s last week, serving as a reminder that summer is right around the corner. These warm temperatures were courtesy of high pressure, which allowed a southerly flow to bring the warmer conditions into the South.

The warm temperatures have begun to come to an end, however, as the ridge of high pressure is sliding eastward and an area of low pressure is approaching from the west. The result will be slightly cooler temperatures, along with the chance of showers and thunderstorms.

FORECASTS: Atlanta | Charleston, South Carolina | Jackson, Mississippi

Temperatures will be closer to average for early May, but for many areas the temperature difference will be 10 to 15 degrees compared to the end of this last week. Highs this week will typically be in the 70s by Tuesday, with 80s toward the Gulf Coast. Parts of the Southeast may not rise out of the 60s late this week due to the incoming jet stream dip in the East.

4) Warmer Days Ahead in the Rockies

Another area of the country that will see some of the big changes this week are the Rockies.

An area of low pressure brought snow to Rockies and parts of the High Plains to end April. Parts of western Nebraska and the Colorado Rockies saw near a foot of snow.

Accompanying the snow have been chilly temperatures. High temperatures were 20 to 30 degrees below average in Denver and other parts of the Rockies and the adjacent High Plains this past weekend into late last week.

Mid-to-late week, the upper-level trough will be replaced by an upper-level ridge of high pressure. This will translate into warmer and drier conditions for the region.

MAPS: 10-Day Forecast

High temperatures will be up to 20 degrees above average by late this week in the Rockies and northern Plains. Temperatures are expected to climb into the 80s as far north as Montana. Denver will go from seeing a high of 40 degrees on Sunday to highs near 80 by Thursday.

RELATED: More flooding earlier this year

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Omega block pattern shift brings 4 changes in the week ahead

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