Thunderstorms Bring Strong Winds, Road Closures, and Power Outages over Northeast Washington

The line of strong thunderstorms that hit western Washington around midnight Sunday/Monday continued into eastern Washington, where some of the convection revved up into intense storms.    Over limited areas the winds were extraordinary, gusting to well over 60 mph and I suspect more in some locations.

An idea of the intensity of some of these storms was made clear over Ferry County of northeast Washington, where extensive power outages and downed trees were noted.   State Route 20 was closed by a large number of fallen trees at a location about 4 miles west of the town of Republic (see pictures and location map below).

Picture Courtesy of Andy of TroutStreaming

The strong winds were associated with a line of strong thunderstorms.  Let me illustrate by showing a series of composite radar images from the Spokane radar from 1102 UTC Sunday (4:02 AM PDT) to 1231 UTC (5:31 AM).  The maximum reflectivity (how much of the radar signal is returned to the radar) was very, very large (values reaching the mid-60s), which is associated with hail and VERY heavy precipitation.

The radar can tell us about the top of the radar echo (see below), which reached around
40,000 feet---which is very high for our area (folks in Oklahoma would yawn at it).

So what kind of wind reports did we get?   The problem with NE Washington is that observation density is sparse....but we get some suggestive reports.  For example, the USDA RAWS site at Oroville, WA has a very sudden gust to 61 mph at the time of the convection line passage.

The RAWS site at Aeneas, WA, just a few miles from the SR-20 blowdown had a gust to 64 mph.

A weatherunderground station in Republic got a piece of the action (see plot below), with a surge of wind to 26 mph, accompanied by a sudden jump of pressure and a burst of rain.

 The really strong winds early Monday morning were localized over the Republic area of NE Washington.   The max wind gusts overnight  in the regional plot showed lots of blustery conditions (winds gusting to 20-35 mph), put little evidence of a major area of greater 50 mph.

So what happened around Republic?   There is no reason to suspect a tornado, particularly since the strong winds appeared to occur over a region of roughly 10 miles in size. 

Strong thunderstorms can produce strong "straight line" winds even without a tornado vortex.  For example, powerful thunderstorms can have strong gust fronts of descending outflow air, with wind speeds reaching 40-80 mph.   Dry air under the thunderstorm air can aid in producing a strong

 gust front, and the vertical radiosonde sounding at Spokane Airport for 5 AM, did show a low-level dry layer (see below, temperatures in red and dew point in blue, the more they are separated, the drier the air).  Dry air encourages evaporation and cooling, with cooler/denser air sinking more rapidly before it spreads out along the ground.  Strong downdrafts can also mix higher momentum air from aloft down to the surface.

An unusual event with strong thunderstorms on both sides of the Cascades.




from Cliff Mass Weather and Climate Blog https://ift.tt/2Ke6Ge0