April 19, 2020

Forecast: April 19th, 2020

By Matthew Charchenko

Good morning Huskies!

Yesterday’s 0.05 inches of rain at SeaTac marked the end of a very unusual two week dry spell in Seattle. Currently we are at 0.06 inches of rain so far this month, which is well below our month to date average of 1.77 inches of rain. Our lengthy dry spell has been thanks to a very persistent ridge high pressure that has been sitting over the West Coast, keeping us mainly dry and steering storms well off to our north and south. This pattern will remain in place for the next couple of days but big changes are ahead.

In the meantime expect to see decreasing clouds during the day on Sunday as the system associated with yesterday’s rainfall continues to make its way out of the region. Sunshine should make a triumphant return by this evening with temperatures making it into the mid 60s. That ridge of high-pressure will be parked directly over Washington on Monday making way for a beautiful day with mostly sunny skies and highs again in the mid 60s.

One of the model output’s that meteorologists look at to get a better idea of the temperature of the atmosphere is geopotential height. Height’s vary based on the temperature of the layer with lower heights associated with cooler temperatures and troughs, while higher heights are associated with warmer temperatures and ridges. Looking at the geopotential heights on Monday, you can see the large ridge of high pressure over the West Coast, bringing us sunny skies and warmer temperatures.

Heliophile’s, this is where you might want to look away.

The pattern begins to shift Monday night into Tuesday as our stubborn ridge of high pressure starts to break down. Tuesday should remain mainly dry with increasing clouds and highs around 60 degrees. Taking a look at our 500mb geopotential heights on Tuesday, you can see that while that ridge of high pressure is still present, it has started to break down.

By Wednesday that ridge has flattened out completely and we return to zonal (west-east) flow, which will open the door for storm systems from the Pacific to make their way into the Northwest. Pluviophiles rejoice! Wednesday will start off with steady rain, then tapering to scattered showers by the afternoon. High temperatures will be much cooler than what we’ve been used to so far this month with highs only reaching the mid to upper 50s.

Reach forecaster Matthew Charchenko at theuwdawgcast@uw.edu. Twitter: @mcharchenko

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