Saturday, April 6, 2013

Severe Thunderstorm and Funnel Cloud in Walla Walla

The inmates of Walla Walla State Prison were provided a major meteorological show Thursday night around 7 PM as a severe thunderstorm complex moved through southeast Washington.  Kevin Pogue of the geology department at Whitman College sent me this spectacular image taken at that time, which clearly shows a shelf cloud associated with this convection and strongly suggests incipient funnel cloud.  The prison complex is also evident.


A line of strong thunderstorms moved across northeast Oregon/southeast Washington late Thursday afternoon/early evening and were starkly evident in the  NWS radar at Pendleton (see below for 6:49 PM).  The heaviest precipitation is shown by the red colors.

Strong winds gusting above 50 mph accompanied the thunderstorms and to illustrate this, here are the Doppler winds from the Pendleton radar (shows the wind velocities towards or away from the radar) at 7:24 PM for the lowest (.5 degree) scan angle. Some winds exceeded 30 knots at this level (undoubtedly stronger winds below).


Here are the wind observations at Walla Walla Airport (sustained winds shown by the line, gusts by marker) on Thursday.   Gusts got up to roughly 55 mph!  There was a number

reports of damage, mainly to trees, and Pacific Power reported 2841 customers lost power in Weston, Milton-Freewater, and Walla Walla due to broken power poles and power lines down from the wind.

Getting back to the shelf cloud, here is another example from the storm provided by Ryan Mclaughlin.  These features are often called arcus or roll clouds.   They represent the forward edge of the gust front of the thunderstorm.   Cool downdraft air moves outward from the thunderstorm, causing warmer air in front of it to rise and form a linear cloud feature (see the schematic below).  They do look very ominous and are associated with very large vertical wind shear...so NEVER dry to fly through one of these if you are a pilot. 





 Let me finish with this by adding another amazing picture from Kevin Pogue.

We are in for a wet period during the next day as a low pressure system moves across northern Oregon.  Here is the 24-h rainfall ending 5 PM on Sunday....a soaker in the Cascades and western Oregon.  This represents a relatively rare pattern where eastern Washington  gets plenty of precipitation.   Want to be dry?  Head to British Columbia or the NW tip of the Olympic Peninsula. 



4 comments:

Unknown said...

Cliff, as a pilot I found this post very interesting. Where can I find the Doppler wind charts like the one you showed?

Gregulator said...

Hi Unknown -

atmos.washington.edu is a great resource. If you head there and go for the Current Weather dropdown -> Data and Forecasts -> Radar, you'll end up here:
http://www.atmos.washington.edu/data/data.php?loc=radar

And from there you can choose a radar station and then base radial velocity.
http://www.atmos.washington.edu/nnexrad/latest.cgi?ATX/NVEL1

orv said...

In some places where glider pilots soar in mountain wave conditions, it's common practice to be towed through or near the rotor -- a formation very similar to a roll cloud where the air eddies in the lee of the wave. The turbulence there can be quite powerful. A tow pilot once remarked to me that there are two kinds of rotor turbulence: "one-handed turbulence," where you have one hand on the controls and the other on a fuselage strut to help keep you in the seat, and "two-handed turbulence," where you have both hands on the fuselage struts. ;)

DRYSIDECOUG said...

We were driving back from shopping at IKEA in Renton Thursday evening when this storm rolled over Connell. This storm and the setting sun gave us one the most beautiful double rainbows I have ever seen.