Multi-storm system across U.S. to bring snow, possible twisters
A pair of storm systems will sweep across the Lower 48 states this week, featuring characteristics more typical of spring than winter in many places. While snow will fall from the Southern Rockies to the Great Lakes, severe thunderstorms may be the big story — affecting parts of the Deep South and Ohio and Tennessee Valley Wednesday and Thursday.
The first storm was set to slide from Southern California to the southern Plains on Monday and today before sweeping northeastward into the Upper Peninsula of Michigan on Wednesday. It will generally produce light precipitation, but a strip of moderate snow could fall on its back side in the cold air over the northern Plains and western Minnesota. Winds associated with this system could produce very strong gusts in New Mexico and parts of Texas.
Concern is greatest when the second of the storms begins to take shape in the middle of the country midweek, which the National Weather Service is describing as a “multi-hazard” event — bringing heavy snow, high winds, and severe thunderstorms depending on location.
The pair of storms is the latest in a conga line of strong low-pressure systems to bring the risk of severe thunderstorms to the South. January featured 123 confirmed tornadoes, third most on record for the month. Ten tornadoes have been reported this month, and that number will probably climb with the upcoming pattern.
THE SEVERE STORM RISK
As the first storm enters Canada on Wednesday, a more pronounced high altitude disturbance — a pocket of frigid air, low pressure and spin aloft — will swing in the direction of the Four Corners while energizing a surface low that will slide from Oklahoma City to near Buffalo by Thursday.
The surface low-pressure zone will draw warm, moist air northward ahead of it, and tug chilly Canadian air south in its wake. Those clashing air masses will brew thunderstorms that could become severe.
The strong jet stream overhead, meanwhile, could encourage wind shear — or a change of wind speed and/or direction with height. That could prime a few storms to rotate. Severe weather eyes areas from Dallas to Memphis on Wednesday, then expands into the Ohio Valley on Thursday.
WEDNESDAY
A level 2 out of 5 “slight risk” of severe weather has been drawn by the Storm Prediction Center. It encompasses much of the Interstate 30 and 40 corridors from northeast Texas through western Tennessee. Included are Plano and Garland, Texas, Shreveport, Little Rock and Memphis and Jackson, Tenn.
Two rounds of storms may occur. In eastern areas, a few strong afternoon thunderstorms cells are likely, but instability, or juice to fuel thunderstorms, will be weak. That means only isolated severe weather is expected.
A greater severe risk will gel late in the afternoon/evening or into the overnight. A lid of warm air a mile or so above the ground, called a “cap,” may be a limiting factor, it will tamp down surface air attempting to rise, but that may be offset by more robust thunderstorm fuel. Damaging winds, hail and a couple tornadoes will probably accompany this second round.
THE COLD SIDE OF THE TWO STORMS
As the first storm system swept across the Southwest on Monday, a few isolated snow showers were set to occur in northern New Mexico. A comma-shaped band of rainfall will form around the low today as it moves over the central Plains. As the system works north into the Upper Midwest on Wednesday, precipitation in the comma head — or cold air wraparound northwest of the low-pressure center — will fall as snow.
A half-foot or more could fall in the James River Valley of eastern South Dakota and the Interstate 29 stretch. The same is true in northwestern Minnesota.
The second storm will get going late tonight into early Wednesday dumping considerable mountain snow on parts of Utah, Colorado, northeast Arizona and New Mexico. The highest mountain summits could see several feet while several inches are predicted around Denver.
Then, this system will produce a strip of 3 to 6 inches of snow (maybe more) from western Kansas toward Kansas City and in the direction of Iowa before affecting southeast Wisconsin and northwest Illinois. Chicago could be on the fringe.