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.