Flooding Ahead

It is now clear that we will have a major precipitation event on Monday and Tuesday, with flooding over vulnerable areas of western Washington, such as the Snoqualmie Valley, on Tuesday and Wednesday.  Later in this event, substantial snowfall is expected in the mountains.

Overall, this will be a very positive event for water resources in our region.  

The NWS has now released a flood watch over much of western Washington, which is good (see below).  Soon they should upgrade this to a warning. 

Models, such as the UW WRF forecast system, are still going for a big event, although the totals have backed off slightly.  Still predicting ten inches or more over large sections of the Cascades and Olympics (see total precipitation through 4 PM Wednesday below). 

Perhaps what is just as impressive is where it is not precipitating.  Look more closely at the predicted totals, and you will see a profound rain shadow northeast of the Olympics.

We are talking about less than a tenth of an inch.  So ONE HUNDRED times more rainfall in the mountains than in Sequim.  Much less rain in north Seattle than at SeaTac.

Back to flooding potential, it is now highly probable for vulnerable locations such as the Snoqualmie Valley.   

The situation near Carnation is stunning, with the river reaching major flood level for THREE days (see below).    You don't see that very often.

Please...if you live in local flood plains, avoid driving through water.  And complete your preparations for flooding by early Monday.

Finally, there is a lot of talk on social media and online about the importance of rain versus snow and snowpack versus reservoir storage.   

A lot of it is not correct.  Some of the AI information is not accurate either.     I will discuss the water situation more in a future blog.

Major Flooding Coming to Western Washington

With very heavy precipitation expected next week, particularly on the western side of regional mountains, major flooding is being forecast.

Over the next five days, the UW WRF model is forecasting more than ten inches over the western side of the Cascades (see below).

 

Are you sitting down?  Ready for a shock?  Below is the ten-day accumulated precipitation forecast for the region.  Some locations are expected to receive 15-20 inches in total.  

That means flooding.

The European Center model is doing the same thing, as shown by the predicted totals through next Saturday (13 December).  For all models, the wettest day is on Tuesday.

The super-heavy precipitation on Tuesday will be associated with this region being hit by one of the strongest atmospheric rivers in a long time (Tuesday at 7 PM shown):

The Gogzilla Atmospheric River.  Trained meteorologists call this a GAR.

The Northwest River Forecast Center in Portland is predicting moderate flooding on several northwest rivers (see red dots on the map below).

For example, the Snoquamie River near Carnation will get to MAJOR flood stage (purple line) on two days (10-1lth), with levels reaching all-time high river stages on two days.

The Snohomish will reach major flood stage (red line) during the same period.

And the Skagit will approach major flood stage on December 20th.

This is a serious event, and those of you in vulnerable locations should make preparations. 

A good effect of this major precipitation event is that local reservoirs will gain an enormous amounts of water.  All the western Washington reservoirs should fill to at least normal levels and a major filling of the Yakima system will occur.