4 Jaw-Dropping Facts About Winter Storm Ulmer

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W​e examine each of those factors below:

Ulmer Underwent Bombogenesis and Broke a Few Pressure Records

Winter Storm Ulmer was a massive low-pressure system that became a bomb cyclone on Wednesday, March 13. A bomb cyclone refers to a strengthening area of low pressure that undergoes bombogenesis, meaning its minimum surface pressure drops at least 24 millibars in 24 hours or less.

Ulmer dropped 26 millibars in 16 hours, achieving bombogenesis, when its central pressure dropped from 994 millibars around 8 p.m. MDT March 12 to 968 millibars around 1 p.m. CDT March 13.

Unofficial all-time low-pressure records were set or tied in at least four locations, Pueblo, Colorado, Alamosa, Colorado, Amarillo, Texas, and Clayton, New Mexico.

Ulmer Brought Widespread Powerful and Damaging Winds

When the central pressure in a storm system decreases, winds increase and when the pressure drop is rapid and reach levels as low as Ulmer did, very strong wind gusts often occur. This was the case on Wednesday in the Plains.

In Texas, San Augustin Pass reported a gust of 104 mph and Pine Springs measured a wind gust of 103 mph. In the Texas Panhandle, tractor-trailers were blown over and a dust storm developed in West Texas. A wind gust of 100 mph was estimated in Cloudcroft, New Mexico.

Colorado Springs reported a gust of 97 mph Wednesday afternoon, while winds gusts up to 80 mph were observed at Denver International Airport.

Wind gusts over 85 mph were also reported in western Kansas and western Nebraska.

Blizzard Criteria Was Reached in at Least 8 Locations, 4 States

To be considered a blizzard, winds must frequently gust to at least 35 mph and considerable falling or blowing snow must reduce visibility to a quarter mile or less for at least three hours.

At least eight locations met that criteria Wednesday. Two spots that reached official blizzard criteria in Colorado (Denver and Colorado Springs), two locations in Wyoming (Cheyenne and Torrington), three places in Nebraska (Alliance, Valentine and Sidney) and one in South Dakota (Pierre).

A few locations in the Dakotas will also likely reach blizzard criteria Thursday.

Blizzards cause treacherous travel. Hundreds of miles of interstates were closed Wednesday, which left more than 1,000 drivers stranded in Colorado.

Record-High River Levels Resulted in Major Flooding

Milder temperatures surged northward ahead of Winter Storm Ulmer, which had two effects. One was to allow snow that was already on the ground to melt and for ice on rivers to break up and the other was that additional precipitation fell in the form of rain.

This caused flooding as river levels rose late Wednesday into Thursday.

At least six locations set record crests in parts of Iowa, South Dakota and Nebraska with more than 20 river gauges in major flooding.

Many evacuations were issued, including a third of the 24,000 residents in Norfolk, Nebraska, on Thursday due to concerns of flooding as the city's levee system was near its top.

Flooding concerns may linger into next week as rivers, creeks and streams are expected to rise in parts of the Plains and upper Midwest.