Atmospheric River Bringing Heavy Rain & Potential Flooding

 FastCast—Wednesday, Oct. 27 to Sunday, Oct. 31:

Beginning Wednesday afternoon, an atmospheric river (narrow current of subtropical moisture…sometimes called a Pineapple Express) will impact Western Washington. The biggest impact will be heavy rain. Expect rain to begin Wednesday afternoon, lasting through early Friday morning. Rain totals will likely be in the 1-3 inch range in the lowlands and 3-10 inches in the mountains, as the subtropical air pushes snow levels up to the 8,000 foot range. River flooding is possible, mainly on rivers draining the North/Central Cascades and Olympics. The most rain (1-1.5”) is expected on Thursday. Gusty winds (25-40 mph) are also possible on Thursday. Rain will slowly taper and should end by Friday afternoon. Sunny conditions will return on Friday afternoon and through the weekend, with mostly sunny skies and highs in the mid 50s  expected this weekend!

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Continue reading the full blog below!

An short-lived atmospheric river is heading for Western Washington, likely to impact the area with lots of rain, heavy at times, on Wednesday and Thursday. Flooding is possible as well. 

Below is the UW forecast for integrated water vapor transport, essentially the amount of water vapor in the atmosphere, at 1 PM Thursday.

A current of deep moisture is aimed right at Western Washington. This atmospheric river will bring steady rain, heavy at times, from approximately Wednesday afternoon to early Friday morning. Below is the UW forecast for rain through 5 AM Friday.

Those are some big totals! Expect 1.25-2 inches, from Everett southward and north of Whidbey Island (note the well-defined rain shadow northeast of the Olympics). Locally higher amounts are possible. The coast receives 1.5-3 inches, and the mountains pick up 3-10 inches. 

The high rain totals and snow levels at or over 8,000 feet (due to warm subtropical air) in the mountains will aid river flooding. In anticipation of this, NWS Seattle has issued a Flood Watch (shown below) for parts of Western Washington.

In addition to potential river flooding, urban flooding and ponding is a concern. Due to recent storms, there are a ton of leaves piled up on area curbs and in/around storm drains. This could lead to potential urban flooding and ponding on Wednesday and Thursday. 

As if this isn’t enough weather…a weak low center making landfall on southern Vancouver Island will bring the potential for gusty winds to Western Washington on Thursday. At this time, gusts of 25-40 mph are possible, strongest near the water.

For those of you who are tired of rain…there is good news! Take a look at the Weather Underground forecast for Federal Way. 

Yes…those are sun icons! A great fall weekend is in store…with mostly sunny conditions and highs in the mid 50s! Mornings will be chilly from Saturday on, with lows in the upper 30s to low 40s.

Stay tuned for more information…I will do a short update Wednesday evening with the latest forecasts regarding the atmospheric river!