Squall Line - August 25, 2013

     On August 25, 2013 a strong squall line passed through the Inland NW bringing strong damaging winds that brought trees and power lines down and caused property damage in many areas. The storm originated in the Lower Columbia Basin and quickly moved through the Baisn and into the northern mountain regions of Washington and the Idaho Panhandle. Within this write up we will examine some of the factors that went into the storm and some of the reports we received that were caused by it.

     Throughout the day, high-resolution weather models had been giving slight indications that the potential for stronger winds would be possible with storms that occur in the evening and overnight hours. With the completion of the 4pm weather balloon release from the Spokane Office, it was clear the potential for storms would be possible. The only thing necessary would be a small boost to get them started. With storms already initiating and moving north from the Pendleton, OR forecast area, it was realized the needed boost would come from the Oregon storms moving north into Washington. As was the case, the storms were able to utilize energy from the atmosphere to bring a widespread severe weather event to the Inland NW. From the images below of the satellite images from 7pm to 10pm, a linear squall line progressed from Oregon into Washington and the Idaho Panhandle. Notice in the lower images how much more defined the bowing squall line has become.

Image (Left) shows satellite view from 7pm on 8/25/2013. Image (Right) satellite view from 8pm.

Image (Left) shows satellite view from 9pm on 8/25/2013. Image (Right) satellite view from 10pm.

     As the squall line crossed into Grant, Adams and Whitman counties it continued to gain steam, impacting the Central Columbia Basin from areas near Moses Lake east to almost the State Route 195 corridor in eastern Washington. In the radar reflectivity loop below we can see the linear structure of the storm, but this does not reveal the full strength of the storm. The velocity values obtained from the radar had to be examined to see the strong winds that the line brought which showed values from 67 to 72mph only approxamatley1500 feet above ground level.

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     Notice how in the radar animation, as was the case with the satellite, that the structure takes on the bowing linear squall line as it passes into Washington. The geographical area covered by the storm dramatically increased in Washington. Something that may not be noticed in the radar animation is the storms in the Central Idaho Panhandle prior to the arrival of the main line. These storms put down hail the size of quarters, but no strong winds.

     The storm continued its track through the Spokane area pushing into the northern mountains and into the Idaho Panhandle. As it neared the Canadian border, the storm structure weakened as it pushed across the International Border. This was a long track storm that moved through eastern Washington.

The map below shows all of the Local Storm Reports received to this point. For a clickable map of this, click this link Local Storm Reports.

     Throughout the region there were multiple wind reports exceeding 60mph including at the NWS office just north of Airway Heights, WA. Property damage extended from Grand Coulee into the Idaho Panhandle associated with the strong winds that were brought by the storm. One fatality and one injury was also a result of the storms. Hail was generally small, but one storm brought severe hail to the Central Idaho Panhandle. In all, the National Weather Service in Spokane issued 13 Severe Thunderstorm Warnings throughout the evening and into the overnight hours. 9 of the warnings were associated with the strong winds, 3 warnings were for the hail threat in the Central Idaho Panhandle and the single warning in the Lower Idaho Panhandle was for hail with a storm in that area.

     Overall, this is an event was a good example of the widespread hazardous conditions that Mother Nature can bring to the Inland Northwest. For a storm of this nature to be able to march from the central part of Oregon and persist through Washington and into BC, many things had to be well aligned. Storm speed along with the gust front winds that was pushed out ahead of the storm had to be similar. Enough instability had to be present in the atmosphere to support the storm as it pushed up through the region. In this case with the prolonged dry conditions, we saw an abundance of dust picked up creating images similar to the southwestern haboobs (images shown below), but this linear storm had an abundance of rain which is often uncharacteristic of the storms in the southwest. Technically this was not a Derecho, due to the smaller size of the line in overall length.  This event did not meet the criteria of 240 miles in length or the high wind speeds common with derechos. So although we were close in some sense and the structure may have had many similarities, this was not a derecho. In summary what came through eastern Washington on August 25th was definitely a rare, strong squall line.

Dust Storm 5 miles South of Ritzville. Photos From KOMO and KHQ News.

Wind Damage to Coulee Dam Casino, courtesy of Omak Chronicle.

Downed tree in Grand Coulee, courtesy of Jim Servias

By Ryan Fliehman