After weekend of storms, severe weather risk expands to East Coast

It’s the first taste of what looks to be an increasingly active weather pattern heading into mid-March, with several additional storm systems that bear watching in the coming weeks.

A weekend of violent storms

The weekend began with a major tornado outbreak in Iowa that left seven people dead, including six from a wedge tornado that carved a lengthy path south of Des Moines. Parts of Winterset, a small city about 25 miles southwest of Des Moines, was leveled, with damage observed to be at least EF3 strength on the 0 to 5 scale for twister intensity. That would correspond to winds exceeding 136 mph, though the National Weather Service has yet to release their final rating.

That tornado may have been on the ground semi-continuously for an hour or more, the parent thunderstorm tracking 150 miles through southern and central Iowa. Another deadly tornado, rated an EF3, impacted Chariton, Iowa, about 50 miles south-southeast of Des Moines, with a path length confirmed at 16.5 miles. Now, a plastering of snow blankets tornado damage.

On Sunday, the instigating cold front sagged south, where it encountered warm, moisture-rich air over Arkansas and southern Missouri. Four additional tornadoes were reported, though a number of tornado-warned storms continued their malicious prowl overnight, and more twisters will probably be confirmed as damage reports stream in.

Five people were injured near Zion, Ark., about 125 miles north of Little Rock, as a severe thunderstorm with a possible tornado damaged two homes.

The setup for Monday’s storms

The thunderstorms are tied to an advancing cold front and “shortwaves,” or lobes of high-altitude cold air, low pressure and spin, swinging around a larger blob of cool weather to the west. As each one propagates northeastward, it enhances upward motion ahead of it, helping storms to blossom.

Ahead of the cold front, southerly winds are pumping in anomalous and, in some locales, record-breaking warmth. Washington should hit 80 degrees today, eclipsing the record of 77 set back in 1961. Philadelphia should break their record of 74 degrees too, and Baltimore is in line for a record as well.

Humidity and instability, or “juice” for thunderstorms, will be limited — but plentiful jet stream energy aloft will provide momentum so that downpours will mix to the surface in the form of strong gusts. A squall line will continue to take shape through the afternoon, pushing east.

The National Weather Service Storm Prediction Center has issued a level 2 out of 5 slight risk for severe weather, which includes Philadelphia, Washington, Baltimore, and Atlanta. That’s where gusty to locally damaging winds will be scattered about.

Areas to the west will see storms earlier, with boomers arriving along the Interstate 81 corridor by 4 p.m. and approaching Interstate 95 around 6 or 7 p.m. Damaging winds are the main concern, with a few embedded pockets of 50 to 60 mph gusts probable.

Flooding concerns are negligible, since the storms are progressive, meaning they’ll be moving swiftly through the area and won’t linger.

Behind the cold front and attendant storms, temperatures will tumble Monday night, falling back through 40s across the Mid-Atlantic, with 30s in interior zones.

Beyond Monday night, two opportunities for active weather appear probable. First, there may be some vigorous storms from the Deep South to the Mid-Atlantic late this week into the weekend.

Thereafter, we’ll see cold air linger across the central and eastern U.S. for several days until the middle of next week, when an insurgence of warm, moist air will waft over the southern Plains and perhaps Mid-South. With signs that a more significant storm system will roll in from the west, there will probably be more severe weather in the March 15-19 time frame.