A powerful storm front is moving through the lower 48 US states, causing widespread snowfall in the Mountain West, the threat of high-intensity fires in the Plains and the possibility of strong storms in the Midwest. It is the first of two storm systems that will sweep across the country over the next week as weather patterns begin the transition to spring.
In the plains and the center of the country, the entry of warm, dry air near the front will reduce moisture from the ground, raising fears of rapid fires between Monday and Tuesday. Red alert warnings for dangerous fires extend from the US-Mexico border in Texas to the outskirts of Chicago, affecting nearly 20 million people.
Ahead of the front, abnormally warm and humid air blowing northward in the Midwest will allow thunderstorms to develop on Tuesday, some of which may produce hail, damaging winds and a pair of tornadoes. The highest risk area is between Chicago and Detroit and south towards St. Louis.
Behind the front, temperatures plummet. That’s why winter storm watches and winter weather warnings cover the high terrain of the Mountain West, affecting more than 5 million people. The National Weather Service is warning a vast area from Nevada and Montana to Colorado and Wyoming to expect “widespread mountain snow, strong winds and hazardous travel.” As temperatures cool eastward through Tuesday, snow will also spread into North Dakota and northern Minnesota, where winter weather advisories are in effect.
Most of the active weather will be in the vicinity of the front, which currently stretches from northern California to North Dakota. It is expected to move east and south through midweek before leaving the east coast. Ahead of it, record heat will spread northward. Behind it, cold, dry air with low temperatures will collide with the south within a trough in the jet stream.
Colliding air masses will cause strong storms in the Midwest along and ahead of the cold front, while enveloping moisture in the back of the storm system will cause snowfall. Dry air in the storm system’s “dry slot” – or wedge of arid air spiraling in from the southwest – will spread over the Plains. This will create a climate conducive to fires.
Risk of strong storms in the Midwest
Thunderstorms, some severe, will form along and ahead of the cold front on Tuesday in the Midwest. They will have a limited fuel supply, but ample wind dynamics. With the jet stream shearing overhead, a dramatic change in wind speed and/or direction with height, known as shear, will be present.
Some rotating supercells will be possible, with threats of large hail, damaging winds and tornadoes. The Weather Service’s Storm Prediction Center has drawn a level 2 out of 5 slight risk of severe storms. It extends from Milwaukee south to Detroit and south toward the southern tip of Illinois and eastern Missouri. Chicago; Springfield, Ill. Indianapolis; Toledo; and St. Louis are all in the area to watch.
There is an increasing likelihood that a Level 3 of 5 enhanced severe weather risk will be introduced in later forecasts, most likely from Chicago eastward. That’s where a warm front moving north will impart a little extra spin, helping storms rotate.
Wind-swept snowfall for Mountain West and northern Plains
A disruptive combination of snow and wind means travel problems across the Mountain West through Tuesday, extending to the northern plains. Blizzards are occurring in the Oregon and Washington Cascades, with snowfalls of 2 to 5 centimeters per hour crippling travel through mountain passes. Totals of 60 centimeters or more are possible in the Cascades above the rain-snow line, with up to 1.2 meters on the mountain’s highest peaks.
Moderate to heavy snow will move into the Great Basin and central Rockies, with winds gusting to 80 to 100 kilometers per hour in the highest areas. This will cause blizzards and make travel almost impossible. The Weather Service writes that much of the higher terrain has a 70% or greater chance of seeing accumulations of a foot or more.
Freezing air will crash south behind the front, with temperatures plummeting into the teens and single digits, even across the northern Plains. Strong winds and several inches of snow are expected for eastern North Dakota and northern Minnesota on Tuesday, February 27.
Dangerous fire weather on the Plains
As hot, windy weather moves northward ahead of the front, dangerous fire weather is already present in West Texas, southeastern New Mexico, and the Oklahoma and Texas Panhandles. That’s where the Storm Prediction Center has flagged a “critical” wildfire risk through Monday. A lower, but still significant, wildfire risk extends to Nebraska and Iowa.
In the Plains, the main factors of fires are two:
Temperatures are unusually warm several degrees above average. This means temperatures between 26 and 32 degrees Celsius in eastern New Mexico and Texas, and between 15 and 21 degrees in the rest of the Plains, something very unusual for February. Higher temperatures evaporate more moisture from the soil, depriving vegetation of moisture and drying out the landscape.
Downsloping winds, or air blown from high in the Rocky Mountains to a lower elevation over the Plains. A belt of strong westerlies associated with the airborne jet stream mixes at the surface and enhances strong westerlies in the Rockies and western Plains. As air descends from higher to lower areas, it is compressed, heated, and dried. This keeps humidity levels very low.
A huge area of low relative humidity is expected to spread across the Plains on Monday afternoon, meaning the air will hold very little moisture. Combined with westerly winds gusting from 30 to 40 miles per hour, any fire that ignites could spread very quickly.
“Use caution if you engage in activities that could cause a fire,” the Weather Service advised. Further east in the Corn Belt, severe to extreme drought conditions will exacerbate fire risk. Wildfires will continue to be a problem through Tuesday, especially in the High Plains.
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