The First Flooding of The Season!

Thursday, October 29, 2015
4:59 pm

Record flooding in Mt. Rainer National Park, November 2006. Credit: National Park Service

For some reason, the weather always seems to get dramatically stormier as soon as we switch from October into November. The weather could be fine for trick-or-treating, and then whammo! November rolls around, and there are more fallen branches and puddles than you can shake a stick at.

This year, our storm season will be arriving early.

From Friday night to Saturday morning, a very juicy front will sit over our area and soak the entire state. The Southern Cascades will get particularly hard hit. This morning’s National Weather Service forecast discussion called for over 15 inches in the space of two days to impact the windward slopes of Mt. Rainier. I’m not religious, but I think 15 inches of rain in 48 hours is pretty Biblical.

An ark with all the newest technological innovations! Credit: Kimmo Virtanen

This is a classic atmospheric river event. Atmospheric rivers are streams of moisture in the atmosphere that may be thousands of miles in length but less than a few hundred miles wide, and they are the events most commonly associated with flooding on our local rivers. These atmospheric rivers often occur along frontal zones where there is preexisting uplift, creating precipitation, and they often stall over an area instead of quickly brushing through. The picture below shows a massive atmospheric river stretching well west of Hawaii, and it is going to be plopped right over our area for the next 24 hours and give us a ton of rain in the process.

Valid 09:30 am PDT Fri 30 Oct 2015. Credit: UW Atmospheric Sciences

By tomorrow morning, this river will have moved a bit south, and will be positioned right over our area, giving extremely heavy rain to our region and blustery winds along the coast and on exposed peaks.

Valid 05:00 am PDT, Sat 31 Oct 2015 – 36hr Fcst. Credit: UW Atmospheric Sciences

We had a massive atmospheric river event on November 6-7, 2006, and this event caused record floods on many Cascade Rivers and caused millions of dollars of damage to Mt. Rainier National Park. While this event does not appear to be as devastating as the one we witnessed in 2006, it looks really wet. Take a look at the graphic made by the NWS below.

NWS SEW Current Weather Story

Right now, the National Weather Service forecasters up at Sandpoint are forecasting anywhere from 1-4 inches of rain in the lowlands, 4-8 inches of rain in the mountains, and 12-15+ inches of rain near Mt. Rainier. This will cause flooding on many area rivers, particularly those in the South Cascades. Thankfully, river levels are very low right now and the ground is not very saturated, so this event will not cause major flooding on our local rivers, with the exception of some rivers near Mt. Rainier, particularly the Carbon River.

The heaviest rain will arrive around 10 pm tonight and end around noon tomorrow. Trick-or-treaters may have to avoid some puddles, but they should not be trudging around in the rain tomorrow night.

By the way, after the cold front passes through at lunchtime tomorrow, snow levels will drop to 3,000-4,000 feet, and the Cascades will get significant snow. The Seattle NWS forecast discussion talked about issuing a winter storm watch from Saturday night through Sunday this afternoon, and I suspect they will do that!

Enjoy the fun weather! I’ll be posting updates throughout the night on my Facebook page! And by the way, Snoqualmie Falls is absolutely stunning during these flood events. I’d highly suggest going to check it out Saturday night or Sunday morning.

Snoqualmie Falls during a major flooding event, January 7, 2009. Credit: Bdelisle

Stay dry!
Charlie

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