• Click here to read a National Weather Service report on the destructive high winds that battered the Plains, including Nebraska, on Oct. 17-18.
Autumn and spring are the times of year when deep low-pressure systems are most likely to occur in the Great Plains.
In a review of October's weather, two things stand out: It was a fairly benign month except for the destructive winds that accompanied a particularly deep low-pressure system.
All across the Earth the atmosphere is swirling and billowing as air masses of different density seek to reach a balance. Two opposites — high-pressure and low-pressure systems — are a result, and one of the things they do is drive local wind patterns.
A low-pressure system is an area where air is lifting up from the surface, leaving a sort of vacuum behind that winds rush in to fill.
On Oct. 17-18, extreme wind accompanying a low-pressure system wreaked havoc across the Great Plains.
The winds whipped up devastating wildfires and stirred up a dust storm that stretched from southwest Nebraska into Oklahoma.
In Nebraska, the wildfires combined to burn more than 90 square miles, and the dust storm caused a pileup on Interstate 80 that left several people injured.
Similar problems occurred in other Great Plains states.
Ryan Pfannkuch, meteorologist for the National Weather Service in Hastings, Neb., said winds from that low-pressure system were stronger than the those typically associated with severe thunderstorms. The National Weather Service sets the threshold for wind speed associated with a severe thunderstorm as 58 mph, he said.
Of the two days, Oct. 18 was the windiest, he said. On that day in central Nebraska, sustained wind speeds commonly reached 35 to 45 mph, and gusts of 50 to 65 mph were frequent.
Peak wind speeds on Oct. 18, based on region:
— Nebraska Panhandle, 67 mph in Sidney.
— West-central Nebraska, 73 mph in Rock Springs and 70 mph near Big Springs and Broken Bow.
— Central Nebraska, 70 mph at Ord and 63 mph at Grand Island.
— Eastern Nebraska-western Iowa, 58 mph in Douglas County and 64 mph in Pottawattamie County.
Pfannkuch said low-pressure systems become their most intense during spring and fall because those are seasons with the greatest changes in temperature.
Temperature and moisture affect the density of air, and wind is essentially the result of the Earth's atmosphere trying to balance out.
The low-pressure system that generated the winds was located over Minnesota. Winds associated with a low-pressure system blow clockwise, so in Nebraska the winds blew down out of the northwest. Those wind patterns were visible from space — in the path of the dust storm and of smoke from a wildfire.
Source: National Weather Service