Concerning pattern change and warm temperatures on the way

A major pattern change is ahead after Mother’s Day, which will bring several big changes in the nation’s weather in the new week ahead.

An omega block has influenced weather conditions across the U.S. so far this month, but this clog in the atmosphere is finally expected to break down next week.

The pattern will slowly transition to an upper-level trough, or southward dip in the jet stream, in the West and an upper-level ridge, or northward bulge of the jet stream, over the East.

The jet stream pattern is expected to change after Mother’s Day, with a trough developing in the West and a ridge over the East.
The result of this pattern change will be some welcome changes in the East, an increase in severe thunderstorms in the central U.S. and a late-season snowstorm for portions of the West.

Here’s what to watch for.

1) Increasing Risk of Severe Storms

So far this month, there has been a lack of severe thunderstorms, including tornadoes. Through Friday, there had been an estimated 63 tornadoes, below the month-to-date average of 115, according to severe weather expert Dr. Greg Forbes of The Weather Channel.

May is typically when tornado activity peaks in the U.S., but the jet stream pattern so far this month has not been very conducive for widespread severe storms because high pressure has been dominant over the Plains.

Next Week's Forecast

The upper-level pattern will shift in the new week, resulting in conditions favorable for more widespread severe thunderstorm development.

The first chance for an increase in severe storms will come on Tuesday. A jet stream disturbance is expected to swing east into the Plains, topping a moist and unstable environment for the development of severe thunderstorms.

Parts of Texas northward to the Missouri Valley have the best chance at seeing severe storms Tuesday.

A second round of severe thunderstorms is likely once again late in the week, when the large jet stream trough itself lumbers east into the Plains. The ingredients necessary for severe weather will likely be in place, including ample moisture and some instability.

This severe threat may extend into next weekend in parts of the Midwest and Northeast.

Given that this event is still roughly five days away, there are uncertainties in the forecast, so be sure to check back to weather.com for updates.

2) Late-Season Snowstorm Ahead for Parts of West

The upper-level trough over the West will allow below-average temperatures to spread across the region. High temperatures midweek will be 10 to 20 degrees colder than average, mainly in the Great Basin and Southwest.

Temperatures in the higher elevations will drop below freezing and, combined with a slow-moving area of low pressure, the result will likely be a late-season snowstorm in the higher elevations.

This strong upper-level low will dig into the Pacific Northwest Monday and into northern California by Tuesday before moving into the Great Basin and Rockies by midweek.

Snowfall Outlook

Snow is expected in the Cascades Monday night and will spread into the Sierra Nevada mountains of California on Tuesday. After that, snow will fall in portions of the Great Basin and northern Rockies through at least Thursday night.

Significant snow may fall at elevations low enough to impact the passes in the Cascades, Sierra and central Rockies, leading to hazardous travel conditions next week. Gusty winds are a concern, as well.

This will add to the already hefty snowpack in the region, which is good news for areas that depend on snowmelt for water supply in the drier, summer months, but will raise spring snowmelt flood concerns, as well.

3) Warmer Temperatures Finally Return

After one of the warmest Aprils on record in some areas of the mid-Atlantic and Northeast, May has been much cooler than average. According to the Southeast Regional Climate Center, several locations in the region are experiencing a top-10 cold May so far. This early-May chill is due to the persistent trough in the region, courtesy of the omega block that has been in place.

For those looking for spring warmth, there is good news ahead. An upper-level ridge of high pressure is expected to develop from the Plains to the East Coast in the new week ahead.

High pressure will bring drier conditions and warmer temperatures, as more of a southerly flow will develop. Above-average temperatures will spread from the Plains into the Midwest Sunday and Monday and then into the East midweek.

Forecast Highs

Highs will be 10 to 20 degrees warmer than average, with temperatures up to 25 degrees above average in parts of the Midwest. Temperatures will soar into the 80s as far north as the southern Great Lakes and into portions of the Northeast.

Low temperatures will be above average, as well. Temperatures will only drop into the 60s midweek into the southern Great Lakes and interior Northeast, with 50s for much of New England and the upper Midwest.

Dew points are also expected to rise into the 60s, making it feel more humid, too.

The other plus side is that the Northeast will finally get a stretch of dry days with sunshine.

4) Rounds Of Storms May Trigger More Flooding

An active weather pattern will bring multiple chances for rain next week in the central U.S., including areas that have recently been impacted by flooding.

A southward plunge of the jet stream accompanied by a slow-moving area of low pressure will develop over the West. Ahead of this system, a southerly flow will allow for plenty of moisture to surge northward.

Flash Flood Setup

This will result in rounds of rain and thunderstorms, including severe storms as highlighted earlier, to impact the Plains and possibly portions of the Mississippi Valley next week.

Many parts of Kansas, Oklahoma, north and central Texas, Missouri and Arkansas should see at least 1 to 3 inches of rain through late next week, with locally higher amounts where thunderstorm clusters or lines stall.

Some of these areas, especially southern Missouri and northern Arkansas, experienced record flooding in late April and early May.

Any additional heavy rain on top of already saturated ground may trigger local flash flooding, and could either trigger new river flooding or slow the recovery of areas previously experiencing river flooding.

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