Extreme Heat Followed by Showers and Thunderstorms

Today was a day of amazing contrasts, with record high temperatures followed by thunderstorms and light rain.

Picture courtesy of NWS Seattle

A line on showers and thunderstorms moved through tonight... welcome relief from a record-breaking day of heat.  The models had been suggesting for days that a line of showers/thunderstorms would move up the east side of the Cascades, but with only a small chance of reaching the western lowlands.

The cause?  A weak upper level disturbance that helped release the instability inherent in the warm air present over the region (see map, the arrow indicates the disturbance).

The upward motion associated with the upper level feature was apparent in the high clouds that spread over western Washington this afternoon.  And the mid-level instability was suggested in some altocumulus clouds that began to form mid-afternoon (both apparent in the SpaceNeedle cam around 2 PM shown below

By 7 PM, the cloud mass associated with convection and thunderstorms was pretty impressive (see below).

And the radar image at 8 PM clearly indicated the showers and thunderstorms.

I saw a few lighting strikes myself and the lightning network provided further evidence.

The morning forecasts did not suggest too much moving into western Washington, but the 5 PM NOAA/NWS HRRR model forecast, the highest resolution modeling system run by the NWS was reasonably good (see forecast below for 9 PM).   My research group at the UW is working on more advanced lightning forecasting technology, combining state-of-science model output with machine learning, that should be able to do better.  This research is sponsored by Seattle City Light, which is concerned about lightning for obvious reasons.

Finally, just wanted to note the extraordinary high temperatures today, with several locations getting to 100F (see below, click toe expand).   Some significant records were broken today, with many daily records surpassed.  Thankfully, tomorrow should be about 10F cooler.

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from Cliff Mass Weather Blog https://cliffmass.blogspot.com/2020/08/extreme-heat-followed-by-showers-and.html