Thunderstorm Three-Peat Looms

Get ready for round three.

Thunder and lightning are once again in the forecast for Seattle, putting us under the gun for our third thunderstorm outbreak this month. Officially, Sea-Tac Airport has already recorded four days with thunderstorms in July—the 8th, 9th, 13th, and 14th—with the storms on the night of the 8th/morning of the 9th comprising round one, and the 13th/14th gully washers round two.

We’ll go for the hat trick on Friday, as a pesky upper level low lounging off the Northern California coast finally scoots inland. The low is forecast to track northeast, first towards Portland, then Yakima, turning the upper level winds over Seattle to the southeast. This will allow thunderstorms forming over the Cascades, fueled by moisture-laden air to our south, to once again spread into the metro area from southeast to northwest.

At this point, it looks like prime time for thunderstorms will range from early morning to noon. Forecast models are still a little uncertain on the intensity of this latest round of unusual weather, with one model (the University of Washington’s WRF) calling for over half an inch of rain as the storms roll through. Other models keep the Seattle area much drier, but still light up the sky over Puget Sound through midday.

In any case, the dark clouds and storms will keep Friday’s temperatures below normal, with highs remaining in the upper 60s. Our best shot at a warm, sunny day comes tomorrow, with temperatures expected to rise into the upper 70s once the morning cloud cover burns off. Saturday should also feature some sunshine, but with another upper level low lurking to our north, clouds—and even a few thundershowers—are possible by nighttime.

Round four, anyone?