Tales of Two Slopes: Hot and Cold

There has been a lot of talk about warmth in the mountains, loss of snowpack, and inversion conditions.   

The truth is a bit more complex.  

The western side of the Cascades has been warmer than normal with significant loss of snow, but conditions have been MUCH cooler on the eastern slopes, helping to maintain snowpack on that side.

Let's explore the fascinating temperature variations of the past few days.

Below are the minimum temperatures on January 16th and 19th.

Forties on the western slopes of the Cascades, but below freezing east of the crest, with many locations in the teens.

As I have discussed in prior blogs, a pool of very cold air has been trapped in the Columbia Basin, with cold air associated with a low cloud deck of stratus and fog (see the satellite picture below).

The UW high-resolution modeling system accurately simulated this cold/warm pattern.  

For example, the model forecast for the surface (2-m above surface) temperatures at 1 PM Saturday shows warmth (red colors) on the western Cascade slopes up to the crest level, but colder air right over the crest (blue and green colors).

Note the warm temperatures on the western slopes of the Olympics and coastal mountains as well.

Next, consider the temperatures at some locations on both sides of the Cascades. 

 At Paradise (Mt. Rainier) at 5000 ft on the western slopes, the temperatures (blue bars) were well above normal (brown band) during the past week..

In contrast, it was much cooler at Holden Village on the NE slopes of the Cascades. A short period of warmth followed by normal and colder than normal conditions.

The impacts on snow melt on both sides of the Cascades were noticeable.

On the west side of the North Cascades, the Upper Skagit snow water amounts are 89% of normal and have declined during the past week.

In contrast, the Methow drainage on the eastern Cascade slopes is a 124% of normal and holding steady!

The critical snowpack on the eastern side of the Cascades, so important for agriculture, is being protected by Columbia Basin cold!

The Driest Winter Period in Northwest History?

 It hasn't rained (or snowed) in a week.  Next week will also be dry.

Dry in Washington State.  In mid-winter.

Is this the driest mid-winter period in the history of our region?

According to the National Weather Service, the last rain fell in Seattle on January 12th:

And considering the highly skillful European Center forecast, the first rain won't be until January 26:

That is 13 days without precipitation for most locations in western Washington, during the middle of the winter!

Thirteen dry days.

How unusual is this for midwinter (we do this all the time during summer)?

Let's check the numbers for the Northwest wet season (November 1-February 28)

Below is a list of other periods when Seattle has had no precipitation for 13 days in mid-winter: FIVE other years (2005, 2002, 2000, 1993, and 1985).

 What about times when Seattle had only a trace of precipitation over 13 days (a trace is when less than  0.01 inches fall)...something that can be done by a light mist?

Several other years are added.  2025, 1989, 1968, 1963, and 1956

Finally, considering years when only 0.01 inches of precipitation fell (a trace of rain...just enough to make a surface wet), we add 2013, 1994, 1989 (twice), 1976, 1974, 1992, and 1945.

The bottom line of this analysis?

Since 1945 (81 years), we have had 13-day dry periods (0.01 inch or less) about 20 times.  

So it has happened before, roughly once every four years.

Such dry years are scattered over the period and don't appear to have an obvious increasing trend.   This is not climate change.

The current dry period is expected to end, as indicated by the predicted precipitation through February 5 (see below).   

So enjoy the sun while you can.  

I know some folks who are going to be happy with the return to wettness.