Temperatures across the U.S. on Thursday afternoon, showing winter in the West and summer in the East.
From a late season snowstorm in Colorado and Wyoming to a Great Plains tornado outbreak and record heat in the East, Thursday is bringing out the "extreme" in U.S. spring weather.
For weather nerds, it’s time to truly geek out and observe the clashing of air masses and intense weather systems, but for anyone living in a zone of "moderate" to "high" risk of severe thunderstorms, including violent, long-lasting tornadoes, Thursday is also a time to prepare to seek shelter if necessary later in the day or overnight.
The dangerous outbreak of severe thunderstorms — including damaging winds, large hail, and violent, "long-track" tornadoes — is directly connected to a weather system annoying millions in Colorado with a return to winter. While a few inches of slush is piling up in Denver and its nearby suburbs, higher elevations are getting dumped on with upwards of 2 feet of snow.
Although late season snowstorms are not uncommon in this part of the country, mid-May heavy snows are relatively rare at lower altitudes in Denver and nearby foothills, such as Boulder.
The pinwheeling storm bringing the snow is also helping to draw a rich plume of moisture northward from the Gulf of Mexico, providing the fuel needed for severe thunderstorms to develop all the way from Texas to Vermont. However, the worst of the severe storms are targeting areas thought of as being in the heart of tornado alley, such as the Texas Panhandle, much of Oklahoma and Kansas.
The trigger for these storms will come from upper level winds and boundaries separating drier, cooler air to the west from warm, humid air to the east, with the battle zone setting up across Kansas and Oklahoma.
The Storm Prediction Center (SPC) in Norman, Oklahoma, which is responsible for issuing severe weather outlooks and tornado watches, has designated Thursday a rare high risk day for severe weather. The high risk zone encompasses about 930,000 people, according to SPC data.
This is the fourth such day to occur in 2017, and although this outlook is no guarantee of a large-scale tornado outbreak, forecasters are warning that the ingredients necessary for producing multiple strong tornadoes, along with widespread damaging winds and large hail, are likely to come together.
Since 2010, only 21 days have been designated as high risk days, weather.com reported.
According to Patrick Marsh, the warning coordination meteorologist at SPC, "a high risk is a forecast of at least 30 percent coverage of tornadoes and at least 10 percent coverage of significant tornadoes (EF-2 or stronger)."
Image: weatherbell analytics
Simulated radar evolution showing the snows over Colorado (blue) and severe storms in the Plains (red).
There is a concern in the weather community that high risk days are becoming more common, and that they bust more frequently. Marsh told the Washington Post that this is partly due to the improving technology at their fingertips, which allows his colleagues to zero in on relatively small regions with the greatest threat.
"A consequence of how we define a high risk is when SPC forecasters identify a small area, it no longer takes 100+ tornadoes to achieve at least 30 percent coverage," Marsh said. "The lack of large numbers of tornadoes can lead to the perception of an over forecast, despite the forecast verifying statistically."
The area at greatest risk of tornadoes Thursday and Thursday night lies from Wichita to just east of Garden City, Kansas, south to Woodward Oklahoma. Oklahoma City is not in the high risk area but is likely to still see severe thunderstorms roll through by Thursday evening.
While the tornado potential will dominate headlines, there is a greater chance of strong, damaging winds and hail of up to 4 inches in diameter, which can damage everything from crops to cars and homes.
Image: levi cowan
Air pressure and atmospheric spin at about 15,000 feet on Thursday.
Thursday marks the continuation of a week of destructive storms which have killed at least 2 and injured dozens across the Central U.S., and more severe weather is expected on Friday as well.
While the thunderstorms rumble across tornado alley, warm, humid air has brought mid-summer-like weather to the East Coast. New York City saw temperatures spike to above 90 degrees Fahrenheit on both Wednesday and Thursday, setting daily high temperature records.
Records were also set on Wednesday in Hartford, Washington, D.C., Burlington, Vermont, and Albany, New York. High temperatures on Thursday may reach 30 degrees Fahrenheit above average for this time of year in New England, before a weekend cool down sets in.