How uncommon is the current drought? • Are you finished with that?

From the Cliff Mass Weather Blog

Cliff Mass

I’ve had several nervous emails from people concerned about last month’s relatively dry spell over the Pacific Northwest.

Are such dry conditions unprecedented?

Are the late springs getting drier?

Is global warming behind it? Or El Nino?

I will try to answer the following questions.

Let’s look at the numbers, starting with Seattle. Below I have plotted the total precipitation for SeaTac Airport from May 1st to June 5th and also added a best fit trendline.

You’ll find that our last period was dry, but far from the driest.

In fact, a list of the driest periods from May 1 to June 5 shows that last month was the 11th driest since the late 1940s.

Now look at the trend line. There is NO indication that the May 1st to June 5th period will become drier. In fact, the long-term trend is toward wetter conditions. This suggests that ongoing global warming was not the reason for our lack of rain.

What about the other side of the Cascades? Consider the long-term observation site Kennewick in the Tri-Cities.

Similar story to Seattle. We have had a dry spell but this has happened many times and the trend is towards a WEATHER late spring.

According to records, this most recent period was the 10th driest period on record in Kenniwick.

The bottom line is that we have had a dry spell, but such a dry spell in late spring is not that uncommon and there is no trend towards drier conditions in May and early June. No indication that global warming/climate change is the cause.

What about El Nino?

El Nino conditions in the tropical Pacific have only really evolved in the last month, but let’s look at the NOAA Climate Prediction Center’s historical precipitation anomaly of normal for April through June during the El Nino years (below). A very mixed record in Washington state. Weather across the South West than normal.

If I’m blogging about the lack of precipitation now, KNOW what’s going to happen in the future.

Below is the current total precipitation forecast through Friday at 5:00 p.m. Lots of rain (lots of thunderstorms) east of the Cascade ridge, with maybe a few scattered showers in western Washington. Abundant rainfall in Northern California.

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