Godzilla-Low Pressure, Heavy Rain, and Drifting Snow Ahead for the Pacific Northwest

Northwest meteorological winter is about to begin dramatically.    

Heavy rain and massive mountain snows are on the way.  Reservoirs will begin to fill.

Those worried about El Nino drought will be able to relax.  

The forecast from the NOAA global model (the GFS) for the next week predicts a stunning persistent upper-level low along our coast, illustrated below by the average 500 hPa heights (think of it as pressure at 18,000 ft) through next Saturday. 

Blue colors indicate the deep low, which will bring showers and cool temperatures to our region.

But now prepare yourself.  

Below is the forecast for the subsequent 7 days. 

Mamma Mia!  

An intense upper-level low over the northern Gulf of Alaska.  The PERFECT configuration to moisten our region.

Consider the total precipitation predicted over the next two weeks by the NOAA model is shown below.

 Unbelievable. Massive amounts, with over ten inches of liquid water in some mountain locations.  Way more than normal for the period.

Snowfall in the mountains will be extreme.   Not feet. Yards of snow at some elevations.

I know what you are saying.....this is the U.S. global model. What about the uber-skillful European Center AI model?

Same solution.  Very wet over the next two weeks.  Let me show you.

First, the total precipitation for the same period.   Huge amounts in the mountains. 

And like the NOAA forecast model, bountiful snow.

I noted in earlier blogs that extreme El Nino years often enjoy good water resources in the Northwest.   No drought. The next two weeks may be the start of this favorable outcome.

How Unusual Has Been the Temperature and Precipitation this Fall?

 Several folks have asked about this autumn.  Has it been drier and warmer than normal?

Let's check it out by considering a representative location:  Olympia.

Below is a plot of cumulative precipitation at this location from September 1 to yesterday.  Green is this year, and the brown line is normal (the climatological values).

September was close to normal, but October has been quite dry.

No wonder I have been able to bike to work without rain gear!

Temperature is shown below, with the blue bar showing the daily highs and lows and the brown band showing the normal range.  Red indicates record highs.  

September was very close to normal, and October has been modestly above normal.

But let's get a better historical picture.  

Below is a plot of the Sept 1-October 21 precipitation totals for the past 50 years at Olympia.  A trend line for the period is also shown.

This year's precipitation is low, but many years were lower

Interestingly, precipitation increased over the period, so you can't blame climate change!

The average temperature for the entire (Sept 1-Oct 21) period was very close to normal ( this year was the 25th warmest year out of 50 years).

However, this is evidence of long-term warming, with about a 2°F warming over the past 50 years, very consistent with warming found in many studies.

What about the outlook for the rest of the month?  

The excellent European center model is predicting cooler-than-normal conditions (blue) over much of the Northwest (except for NE Washington).

In contrast, the European center model is going for drier-than-normal conditions over the Cascades and Olympics over the next week.

Biking should be relatively dry for the remainder of the month.