Flood warnings issued as heavy rains drench mountains

Flood warnings issued as heavy rains drench mountains
SEATTLE -- A very warm, potent Pineapple Express storm was bringing heavy rains to the mountains of Western Washington Wednesday, sending some rivers over their banks and prompting flood watches and warnings to be issued.

So far as of late Wednesday morning, Flood Warnings were in effect for the Tolt, Snoqualmie, Snohomish and Stillaguamish Rivers, with other rivers that flow off the Central Cascades and Olympics at high risk of eventually being placed on flood warnings as well. As much as 4 to 7 inches of rain are expected to fall there by late Thursday.

Lesser amounts are forecast for the northern and southern Cascade rivers and a Flood Watch remains in effect there.

- Monitor the latest flood warning information from the National Weather Service

The National Weather Service is warning that the Snoqualmie River near Carnation could experience major flooding as it rises over flood stage around 7 p.m. Wednesday and crests at 58.1 feet Thursday evening. It is expected to remain over flood stage until Friday evening.

Near Snoqualmie Falls, the Snoqualmie is expected to bring moderate flooding, starting around Wednesday afternoon and cresting Wednesday night. The river is expected to fall below flood flow by Friday morning.

The Snohomish River near Monroe and Snohomish was also expected to experience "major" flooding.

Around Arlington, the main stem of the Stillaguamish River was expected to reach moderate flooding stage, going over its banks Wednesday evening and cresting Thursday morning before receding below flood stage Thursday night. The North Fork of the Stillaguamish River is expected to have minor flooding.

On the Tolt River, minor flooding was forecast starting at midday Wednesday and it was expected to reach moderate flooding at flood stage though Thursday.

Minor flooding was also expected on middle Green River upstream from Auburn.

Heavy rains are forecast to fall in the mountains through Thursday night or Friday morning, then taper off from north to south.

Not so rainy in the Seattle Metro Area

As mentioned Tuesday, the Seattle metro area was not receiving anywhere near as much rain as their mountain brethren Wednesday, thanks to the Olympic Rain Shadow.

The upper air flow is screaming at us from nearly due west, and as that air hits the western slopes of the Olympic Mountains, the air is forced upward where it condenses and, effectively, has its moisture wrung out like squeezing a sponge. Then, as the air crosses over the summits and sinks down the eastern slopes, it dries even further, leaving a large dry slot just to the east of the Olympics -- in our case, right over Seattle. Think of it as a 1400 square mile umbrella.

As of 11 a.m., Olympia had 0.53" on Wednesday, and Everett and Sea-Tac Airport each had 0.14". But Seattle's Boeing Field in the heart of the rain shadow just had 0.02". (Meanwhile, Sequim, which usually enjoys the benefit of the rain shadow, has had 0.27" of rain.)

Thus, we expect the immediate Seattle area to remain relatively dry through the day, although it'll be mild and breezy. But don't let the lack of rain fool you as it is pouring in the mountains.

The entire system will weaken and move off to the south on Friday, allowing cooler air to return and snow levels to drop back down to usual levels. We're still anticipating scattered showers over the weekend, but much lighter amounts and with snow back in the mountains, flooding concerns will end.

Follow live Tweets during the flooding via Scott Sistek's Twitter Feed @ScottSKOMO