Thunderfest

Last night brought substantial lightning, thunder, and showers as a band of convection moved northward across Washington. As I will discuss later, these thunderstorms are associated with a upper level low that is moving northward across the Northwest this weekend.

The thunderstorms hit the Puget Sound area around 1:30 PM...here is a nice radar image at 1:57 AM Saturday. You see a line of heavy showers (reds/oranges), with lighter precipitation (green) following behind.

Here is a wonderful picture of the lightning taken over downtown Seattle by Rod Hoekstra.

There was lots of lightning over eastern Washington and unfortunately some ignited new fires (as warned by the National Weather Service). Here is a picture (by Draysen Brooks Bechard) of a new fire near Wenatchee.

Tonight may see a repeat. Take a look at the upper level forecast map (at 500 hPa, around 18,000 ft) at 5 PM Saturday. You can see an upper level low over Oregon and a lobe of low pressure, just south of the Oregon/Washington border, that is rotating around it. Those lobes are associated with upward motion that can force new thunderstorms.

In fact, the latest visible satellite imagery at around 3 PM shows thunderstorms building over eastern Washington, as does the radar (see images).

One of the most useful forecasting tools over the next 6-12 hours in the NOAA/NWS High Resolution Rapid Refresh (HRRR) modeling system. Here is the forecasting for 11 PM Saturday of a simulated radar image. You will see a band of thunderstorms moving north across Washington, really reminiscent of last night...so be prepared for more thunder!

The low will move northward on Sunday and the weather should calm down with a return to typical (and dry) midsummer conditions.

Update at 5:30 PM Saturday: lighting is widespread over northern Oregon and in a strong cell over the central Washington Cascades.