The Most Valuable Precipitation of the Year

Precipitation at some times of the year is more valuable than at others.

Here in the Pacific Northwest, March and April precipitation is by far the most prized and valued.

Fortunately, the latest forecasts suggest we will enjoy bountiful amounts during this period, which should be a relief to those worried about the water supply.

Why is spring precipitation so important?

It can moisten the soil and help fill the rivers before our dry summers.

It can build up water behind our dams and in our reservoirs, providing water and power during the summer.

For years without good snowpack (e.g., 2024), it can provide needed water.   

It doesn't make much difference if we fill our reservoirs with melted snow or spring precipitation.

As you can see from the average cumulative precipitation at Olympia (below), quite a bit of the annual precipitation at this station occurs in March and April (between the red bars).  

Bottom line:  it is not too late to get substantial precipitation, even in a normal year.

Although there has been a lot of gnashing of teeth about this year's precipitation, the water year totals (from October 1 to now) are actually near normal, something shown by the cumulative precipitation at Seattle and Yakima below (red is normal and green is this year).

The issue is that the snowpack is about 50% of normal as of today.  However, reservoirs are in very good shape, with some well above normal (e.g., the Yakima reservoir system).

As I have noted before, the prediction models have been emphatic about our progression into a far wetter pattern.

To illustrate, below is the total precipitation forecast from the European model through Friday, March 20th, over the Northwest.   Quite a lot over the Cascades!

Much of that will be snow, as shown by the totals through March 19th

The latest extended forecast from the NOAA Climate Prediction Center is for wetter than normal conditions for the second half of the month.

With La Niña rapidly weakening, there is no reason to expect that we will get a persistent dry pattern, as in January.  

I suspect our summer water situation will be fine.