Published: May 12,2017
A major pattern change is ahead after Mother's Day, which will bring several big changes in the nation's weather.
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.(MORE: 6 Out-Of-Season Weather Events We Have Seen This Spring)
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 Wednesday, there had been only 45 reports of tornadoes, well below the average of 82, 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 conducive for severe storms because high pressure has been dominant over the Plains.
The upper-level pattern is finally expected to shift next week, resulting in conditions favorable for more widespread severe thunderstorm development.
Next Week's Forecast
Parts of Texas northward to the Missouri Valley have the best chance at seeing severe storms Tuesday.
(MORE: Tornado Central)
A second round of severe thunderstorms is likely once again late next 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.
Given that this event is still about a week 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.
Snowfall Outlook
Snow is expected in the Cascades Monday night and will spread into the Sierra Nevada mountains of California on Tuesday. Through Thursday, snow will fall in portions of the Great Basin and northern Rockies.
(MAPS: Weekly Planner)
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.
It is too soon to determine exactly how much snow will fall, but there is the potential for some heavy snowfall totals. 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.
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, many 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 next week.
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.
(MAPS: 10-Day Forecast)
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.
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.
Flash Flood Setup
Some of these areas, especially southern Missouri and northern Arkansas, experienced record flooding in late April and early May.
(FORECAST: Tulsa, Oklahoma | Springfield, Missouri | Little Rock, Arkansas)
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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