Strong Cold Front, Chance of Thunderstorms This Weekend

Reflection: Posted on Monday 5/4

Due to plentiful clouds on Saturday, instability for thunderstorms failed to develop. The cold front on Saturday also moved slower than expected, making it harder for storms to form on the frontal boundary.

Sunday also failed to produce enough instability for thunderstorms. It was a hit-or-miss day in terms of rain showers.

Sunny and 75-80 likely at the end of the week...stay tuned!!

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Showers are moving in to Puget Sound as part of a warm front begin to come in off the coast. However, Saturday is when the weather gets interesting. Let's examine it...

Stage One: Pre-frontal Showers

Before the front moves through, showers will be present in the area, along with instability in the atmosphere. Around 5 AM tomorrow, showers will start to increase. Inside these showers will be heavy rain, gusty winds, and possible hail & lightning.

I would expect these showers to continue until around noon on Saturday.

Stage Two: Cold Front With Embedded Thunderstorms

Around 1 PM tomorrow, an unseasonably strong cold front will move through Western Washington. This forecast model shows the simulated radar at 2 PM Saturday. 

I made a pink line that shows the back of the cold front and what approximate direction it is moving. You will notice that the rain inside this front is heavy at times. 

As the front is moving through Western Washington, the air will be unstable. The model below (also for 2 PM Saturday) shows instability, or CAPE (Convective Available Potential Energy).

It is very interesting that at the same time that the front is moving through Western Washington, there is an area of increased instability. The CAPE values in the front are 200-300 j/kg. Winds will also gust 20-30 mph during the frontal passage, with higher gusts possible.

Those values are enough to cause thunderstorms in Western Washington. Please be prepared for heavy rain, strong winds, lightning strikes, and hail. 

There is a potential for stronger-than-normal thunderstorms, and there is a marginal risk of sever thunderstorms in parts of the Pacific Northwest tomorrow. Take a look at this map below from NOAA's Storm Prediction Center.

Notice the darker shade of green over parts of Oregon and Eastern Washington. That means an increased risk of severe thunderstorms (damaging winds, severe hail, heavy rain, very low tornado possibility).

There is a chance that a stray strong thunderstorm will make its way in to Western Washington. That's why we should always be prepared!

Stage Three: Sunday Thunderstorms

After the front moves through on Saturday, instability will remain. At this time, the highest chance of thunderstorms will be from 11 AM to 10 PM on Sunday. Additionally, there is a higher chance for storms from 5-10 PM. 

This entire weather sequence will drop 0.7-1.1 inches of rain. 

Remember to be prepared for thunderstorms, hail, gusty winds, and heavy rain.