Thursday, June 9, 2016

Does Hot Spring Mean Hot Summer?

Many people are starting to ask the question "With spring being so warm, does that mean that the summer will be hot as well?" Although there is no clear answer to this question, we can look at the statistics from previous years and compare them with the how the current pattern is shaping up to get a better idea at what this coming summer might look like. 

A strong El Niño formed in the equatorial Pacific during the spring of 2015, and it persisted through the summer of 2015 and this past winter before it weakened this spring. The Climate Prediction Center has issued a La Niña watch for late summer through the winter 2016-2017 which will bring a shift to the weather in the coming months. But for now, we are going to focus our attention on what June, July, and August might look like for the Inland Northwest. 

This past spring has brought temperatures much above average and for many locations in Eastern Washington and the Idaho Panhandle, the temperatures were record breaking. The above average temperatures were not confined to only our location either. Oregon, California, Montana through most of Wyoming and parts of Utah were also either above normal or much above normal based on the mean temperature that is shown below.

Before getting into the statistics, we will compare our 2016 spring to the previous year. In 2015, Spokane, Lewiston, and Wenatchee all were much warmer than normal for the months of March, April, and May (see table below). We can see that these three locations were all  more than 5⁰F above average for the summer months of June, July and August last year.  But the springtime temperatures this year we are even warmer than last year.  Does this mean that this summer will be even hotter?

Temperatures above average along with their records (listed in parentheses) comparing 2015 to 2016 for Spokane, Lewiston, and Wenatchee

As we said, last summer we had a strong El Niño that had formed during the spring and continued through the summer.  But this year, El Niño is weakening and will be replaced by a La Niña later this autumn.  When looking at past years when our climate has changed from an El Niño pattern to La Niña pattern, we can see a common trend in what our summer might look like. 

So how often does a warm Spring mean that a warm Summer will follow?  The graphs below are for years where the Spring temperature in March, April, and May was at least 2⁰F above average.  The bars show the distribution of the following Summer temperatures compared to normal.

Number of years when Spokane's spring (March, April, and May) was over 2 degrees F above average and what the summer (June, July, August) looked like following those years. 

We can see that in Spokane, there were only 4 years that occurred where the summer was cooler than average following a warm spring, while there were 17 years where the Summer temperature was above average. 

Number of years when Lewiston's spring(March, April, and May) was over 2 degrees F above average and what the summer (June, July, August) looked like following those years. 

For Lewiston, there were six years where a warm Spring was followed by a cool Summer.  The vast majority (16) of warm Springs also had warm Summers.

Number of years when Wenatchee's spring(March, April, and May) was over 2 degrees F above average and what the summer (June, July, August) looked like following those years. 
In Wenatchee, the story is about the same.There were 3 years where the summer temperature was cooler than the average following an above average spring, while there were 10 years that were warmer normal. 

The tables below show the years where there was a strong El Niño that switched to a La Niña, just like what is expected during this coming summer. For most of the years where a strong El Niño occurred during the winter months, we can see that the average temperatures for March, April, and May were above average. The average summer temperatures following those warm springs were a majority warmer than average. There were a few years, such as 1983 and 1988, where the summer was cooler than average following a warmer spring. Although 2015 was not a summer that was followed by an La Niña, it was included for purposes of comparison.

The red boxes within the table indicate a temperature that is above .5 degrees F above the average temperature for spring or summer. The blue boxes indicate that the temperature is below .5 degrees F from the average while the white boxes would be considered normal due to the fact they are +/- .5 degrees from the average. 
How the summer temperatures compared with the summer temperatures for years following a strong El Niño, excluding 2015. 2015's summer broke all records and is included to show how this year compares.

Every month the CPC (Climate Prediction Center) puts out what they expect the next 3 months to look like. The images below are what the CPC was predicting last year for the Spring and Summer. The images on the left are what they predicted and those are compared to the images on the right, which is what actually occurred during those months. We can see that for the Inland Northwest they were not too far off from what they predicted out spring and summer of 2015 to look like. 

Spring 2015

Summer 2015

So how did they do with our warm Spring this year?  The images below show that once again, the outlook from CPC was fairly accurate.

Spring 2016

And that leads us to the CPC outlook for this summer. It's not identical to last summer, as they expect warmer conditions for most of the country.  But they once again have higher confidence of a warmer-than-normal Summer for the western US.

Summer 2016

Although we cannot say directly that this coming summer is going to be hot due to the fact that spring was above average, we can say that based on statistics, there is a good chance that our summer will be warmer than normal. That does not leave out the possibility of it being a cooler summer, but the odds aren't in your favor.

1 comment:

  1. How much of an influence will the Arctic Oscillation play?