June 17, 2013

Summer Thunderstorms

An area of summer thunderstorms and cumulus convection is moving through tonight, and for many of you this is the first rain in weeks.

Let's look at recent radar imagery every two hours.

5 PM:  lots of showers on the coast and offshore.

7 PM:  the coastal showers moved inland and substantial thunderstorms hit eastern WA.

9 PM:  Puget Sound gets moistened and a very heavy show (red color) is moving through south of Yakima

The 12-h totals as of  9 PM, modest precipitation is found around the region.  Few hundredths to a few tenths in general.

The cause?  The classic NW convection pattern.  A trough or low off the coast and a trough embedded in it moving across the region (see graphic).

That plus air that was primed for convection and only required a bit of lift to get it going.  One measure of this potential is something called CAPE...Convective Available Potential Energy.  You can think of it as the amount of energy that can potentially be released by buoyant convection.  Today, the values got up to a few hundred Joules per Kilogram...quite respectable for around here (see graphic). But pathetic in the Midwest and upper Plains.

The approach of the trough/low provided the lift that released the instability.  I flew in tonight from California and was impressed that some of the convection looked like it reached 20-25 thousand feet.  Substantial for these parts.


  1. Dr. Mass

    Last year you built some interesting scenarios for our own Hurricane Sandy, a Columbus Storm Part 2 if you will.

    I was wondering if you might consider doing the same for intense thunderstorms (tornadic activity optional). Growing up here I recall a grand total of 2 serious storms. The first was 1985 I think and gave us that great photo of downtown Seattle and the huge lightning bolt above it. The second was in August 1999. Both had hours of frequent lightning strikes and thunder loud enough to set off car alarms.

    Pulling out your scenario builder, what conditions would come together to create an incredibly memorable lightning storm? Is it even possible to bring together enough temperature differences to not be put to shame by the Midwest?

  2. I have heard so many comments lately about how fresh the air is, especially from people just back from other areas of the country. I've always thought of this as a hallmark of this area-- and one of the many reasons I live here. Apparently I'm not the only one when loves to open the windows and leave them that way 24 hrs a day this time of year!
    Is it really true we have cleaner air than other places?


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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