The National Weather Service's Storm Prediction Center has already released maps highlighting the increased threat of severe thunderstorms, which includes Kansas City, Mo. and Omaha on Saturday. Chicago, Milwaukee, Indianapolis and Nashville on Saturday. and Cleveland, Washington, Baltimore and Philadelphia on Monday.
The center is warning that “all severe hazards will be possible” as the storms move east, meaning damaging winds, hail and isolated tornadoes are possible. Just last week saw a series of wild storms that brought strong gale-force winds to Northwest Washington, Northern Virginia and Maryland, bringing gusts over 80 mph and knocking out power to nearly a quarter million customers.
As the storms form and move east, a low-level tornado risk may develop in the central Plains on Saturday, Chicago and the Corn Belt on Sunday, and the inland Northeast on Monday.
Even New England, which has borne the brunt of the weather in recent weeks, could see new flooding concerns in addition to severe storms Monday and Tuesday.
Location: A Level 2 out of 5 severe weather risk has been projected by the Storm Prediction Center for much of the Central Plains from Kansas and western Missouri to western Iowa and southwestern Minnesota.
Synchronization: Thunderstorms will form in eastern Nebraska and western Iowa, as well as near the Kansas-Missouri border, by mid to late afternoon. By evening, a second storm will develop across eastern Colorado, southwestern Kansas, and Texas and Oklahoma. Storms will likely build through midnight.
Risks: Damaging winds will be the primary risk, with a multi-mesoscale convective system expected. This is a fancy term for thunderstorm complexes that take the form of clusters or squall lines.
With the cluster(s) over the Corn Belt, damaging straight line winds of 65 mph are possible in the strongest storms. Some hail is also expected.
Gusts of 60 to 80 mph are possible in the western danger zone, including the southern High Plains.
Location: Much of the Corn Belt and parts of the Great Lakes and Ohio Valley are at a Level 2 of 5 risk.
Synchronization: Thunderstorms will develop in the afternoon and may persist into the evening and at least the first half of the night.
Risks: In addition to damaging straight-line winds, a few tornadoes are possible, especially near the warm front. The warm front will move up toward the Great Lakes in the afternoon. It is not clear exactly where the frontal will be installed.
There will also be some “support” winds, or a subtle easterly component to the surface winds, feeding the low pressure area developing in the area. This may strengthen the low-level helicity or twist and lead to a few tornadoes in central or northern Illinois and adjacent northwest Indiana.
Location: The National Weather Service's Storm Prediction Center took the unusual step of declaring an increased risk for severe thunderstorms for parts of the Mid-Atlantic, Northeast and northern Appalachians four days earlier.
Risks: Damaging winds will be the main concern, but a sporadic tornado or case of large hail is also possible.
There may be some lingering threat of severe weather in the northeast, but details and confidence remain low.
Instigating the storm will be the phasing or merging of two different storm systems. One — a pocket of high-altitude cold air, low pressure and spin — was sliding into Saskatchewan Friday morning. The other pushed through the northern plains.
The system over the northern plains will be infused with energy from the Canadian disturbance and strengthen over the weekend. Then a low pressure zone will intensify below it closer to the ground.
This surface low will pull in a tongue of warm, moist air from the south, which will act as fuel for the storms. A strong jet stream dive, meanwhile, will sweep the surface low, adding wind energy to the upper atmosphere. Storms can mix this momentum at the surface in the form of damaging straight-line winds. Tornadoes would also become a threat.
