October 17-18, 2012: Two Days Of Strong Northwest Winds

October 17-18, 2012

Two-Day High Wind Event

Intense Northwest Winds Impact All of South Central Nebraska and North Central Kansas On Both Days, with the 18th Featuring the Strongest Sustained Speeds Commonly 35-45 MPH With Frequent 
Gusts 50-65 MPH
 

Between Wednesday and Thursday, Oct. 17th-18th, 2012, much of South Central Nebraska and North Central Kansas experienced its windiest back-to-back days in quite some time, blowing out of the northwest on both days. Of the two days, the 18th featured the overall strongest winds with widespread sustained speeds of 35-45 MPH and frequent gusts of 50-65 MPH, and locally higher. On both days, visibility restrictions due to blowing dust were common, and at least a few fires got out of control. On the afternoon of the 17th, a large fire in western Fillmore County near Sutton burned around 3,000 acres and engulfed several outbuildings (see radar image with smoke plume below). The more intense winds on the 18th resulted in various instances of powerline damage along with primarily minor building and tree damage across the area, including a report of a trailer home with half its roof torn off in Cozad.  These intense winds occurred in response to a very large surface pressure gradient between a deep low pressure system in Minnesota and strong high pressure centered over the Central Rockies. 

The table below highlights peak sustained winds and peak gusts recorded on Thursday, Oct. 18th by automated airport sensors (ASOS or AWOS) across the NWS Hastings coverage area. Just to put these wind speeds in perspective, the NWS issues Severe Thunderstorm Warnings for the expectation of thunderstorm winds of 58 MPH or greater, so several sites actually exceeded this "damaging wind" threshold during this event:

Below are images related to this high wind event...

• Left image: The combination of the strong winds, along with very low relative humidity values dropping to under around 20% promoted elevated to critical fire danger across much of the region. Often, NWS Doppler Radar is able to detect smoke plumes from ongoing fires as smoke rises well into the atmosphere. This radar image from 5:04 PM on Oct. 17th clearly captures the smoke plume from the large fire in Fillmore County east of Sutton. Due to the strong northwest winds, this smoke plume can be seen stretching off several counties to the southeast, all the way into Kansas! The radar beam, originating from the dark "black dot" near Blue Hill at the very bottom of the image, is detecting the smoke plume in Fillmore County at altitudes of 2500-3000 feet.

• Center image: This is a visible satellite image of the north central United States from the late morning of the 18th. The blue lines overlaid across the region indicate mean sea level pressure (MSLP), measured in units of millibars. Put in very general terms, wind speed is often directly related to how much of a gradient, or how much of a difference, exists in sea level pressure across a given area. If the pressure difference is small, winds are often light, and if this difference is large, winds blow stronger to help equalize this difference. By counting the number of blue lines of sea level pressure on the image, one can see that a roughly 20 millibar difference in pressure was in place across the state of Nebraska, ranging from around 1016 millibars in the southwest corner of the state to around 996 millibars in the extreme northeast corner around Sioux City. Fortunately, there are only a few days each year that feature pressure differences of this magnitude or higher, and these are inevitably the windiest days of the year (aside from any thunderstorm activity, of course).

• Right image: This is a satellite image taken around 1:30 p.m. on the 18th.  The very dry soil conditions, combined with the strong winds, resulted in the development of a large area of blowing dust, and the area can be seen inside of the pink circle.  Extending from southwestern Nebraska into central Kansas, low visibilities dropping to less than a half mile at times were reported.
   
  Click Images To Enlarge

  Smoke plume visible on radar from the fire near Sutton on Oct. 17th.	Visible satellite image combined with surface pressure contours from Oct 18th.	Satellite image taken  around 1:30 p.m. on the 18th.