Steamy summer of 2018? Why our hot May statistically predicts a hot summer

We often look for predictive seasonal trends in weather. Some of you have asked me if our seemingly endless winter tells us anything about this upcoming summer? It turns out the answer to that question historically is, not much.

But multiple days of 90-degree May heat in Minnesota strongly favor more 90 degree days in summer.

Hot May 

So far May is running over 6 degrees warmer than average in the Twin Cities and most of Minnesota.

The Twin Cities hit 92 degrees Thursday. It was our first 90 degree day since September 24th of last year. We've already hit 90 again today, marking our second 90 degree days this May. Looking at the forecast, we'll probably add 3 more 90 degree days this Memorial Day weekend.

The Minnesota DNR Climate Working Group crunched the numbers on multiple days of 90 degree heat in May in the Twin Cities. And they found some interesting statistical trends that favor a hot summer this year in the Twin Cities and Minnesota.

• The Twin Cities averages 13 days of 90 degree heat each year.

• Only 1 in 3 years features 90 degree heat in May in the Twin Cities.

• Mays that recorded two or more 90 degree days averaged 23.4 days of 90-degree heat that year.

• 74% of Mays that recorded two or more 90 degree days produced 20 or more 90 degree days that summer!

Below is a listing of the years that produced two or more 90 degree days in May, and the resulting total of 90 degree days that summer. In those year the Twin Cities average 23.4 days of 90 degree heat.

Here's more from the Minnesota DNR Climate Working Group.

90-degree readings in the Twin Cities during May have occurred in 48 out of 146 years on record, or about 33% of the time. Only 23 years, however, or about 16%, have had more than one 90-degree day during May. Of those years, May of 1934 was by far the most extreme, with eight daily highs of at least 90 degrees, including a reading of 106 on May 31st.

We find that years with multiple 90-degree days during May have tended to be followed by summers that also have relatively high numbers of 90-degree days. The Twin Cities airport averages about 13 90-degree days per year, and 26% of years historically have had 20 or more such days. For years with at least two 90-degree days during May, however, the average number of 90-degree days for the year jumps to 23.4 (an 80% increase), and 74% of those years go on to have at least 20 90-degree days.

Kenny Blumenfeld at the Minnesota DNR Climate Working Group elaborates the data in an email to me today.

Hi Paul, I thought I’d share this with you.

Poking around with some stats yesterday, we came across something pretty amazing. Basically, there is a strong historical association between seeing multiple 90+ days during May summers with lots of 90s. This is odd because we know that early snowfalls don’t tell you anything about the coming winter, and that warm spells in late winter don’t foretell a hot summer ahead. In general, when it comes to relating what happens in one month to some larger seasonal pattern after it, we have learned to be doubtful.

But May heat maps really well to the rest of summer. Typically, one in three years has a 90+ reading during May at MSP. But only 23 out of 145 years have had two or more such days. Those 23 years went on to produce an average of 23.4 days with 90-degree highs for the whole season (13 days is average), and 17 of them (74%) went on to produce 20 or more 90-degree readings (using the whole record, only 16% of seasons have had 20 or more 90-degree days).

So historically, years with two or more 90-degree highs during May at MSP averaged 80% more 90-degree days for the season, and were over four times as likely to record 20 or more 90-degrees days at MSP…compared to average. Our story is here.

Have a great long weekend, Paul!

Kenny

Hot summer ahead

It looks like we'll have at least 5 days of 90 degree heat in the Twin Cities and much of Minnesota this May. Historically speaking, Mays with at least  2 days of 90 degree heat produced, 20 days of 90 degree heat in the following summer in 74% of years.

Fire up the AC or hit the beach folks. The statistical weather odds favor a hot, steamy summer ahead.