Weird Spring Heat Waves Happening More Often

New spring plants emerge from mud and melting ice in
St. Albans, Vermont Thursday amid unseasonable 
mid-60s warmth and sunshine. 

What a gorgeous day across northern and central Vermont Thursday!

Temperatures reached the mid-60s under mostly sunny skies.  I was out there in the yard in big mud boots, and summer shorts doing some work. 

Yesterday's warmth was not nearly as extreme as some other recent Vermont late winter and spring heat waves. But these early hot spells are hitting with increasing frequency.

We got what I would argue is our first weird spring hit way back in April, 1976.  Until then, the earliest 90 degree reading on record in Burlington was on May 21. But on April 18 and 19 of that year, it got up to 91 degrees.

That weird hot spell seemed like a fluke for well over a decade after it hit.  Then, in 1990, temperatures soared into the mid 70s to near 80 degrees on March 16, shattering records for hottest for so early in the season. 

Since then, record late winter and spring heat has been coming fast and furiously to Vermont. In 1998, temperatures soared to 84 degrees in Burlington, tying the record high for the month.  On that same day it was 88 degrees in southern Vermont, setting a state record for heat for the month of March. 

 I thought that earliest 90 degree record set in April, 1976 would never be touched, but on April 17, 2002, it was 90 degrees in Burlington. 

I also thought that the record for earliest 70 degree weather in March from 1990 was untouchable, but then it was 70 degrees in Burlington on March 9, 2016.  And then, the next year, on February 25, 2017 it was a whopping 72 degrees in Burlington and Bennington. 

And I just skipped over March, 2012, in which set seven daily high record temperatures and featured five days in a row with highs of at least 76 degrees, including three days in a row with 80 degree readings. That month was by far the warmest March on record in Vermont. 

There's been some odd May hot spells, too.  May 25, 2020 reached 95 degrees in Burlington, breaking the old record for hottest May day by two degrees.

All this is not to say that record warmth is limited to spring.  We've been getting odd warm spells at all times of year as the climate warms. 

Also, as we all well know, an occasional spring warm spell like we had Thursday does not guarantee warmth all the time. 

Two weeks after that 70 degree February weather in 2017, we endured the Pi-Day blizzard which dumped two to three feet of snow on much of Vermont. 

I noticed the record low for yesterday's date was recent. It was 8 below on March 17, 2014.

I theorize that spring heat waves, like the example above, are boosted not only by climate change but also by the lack of leaves on the trees and drier air in the spring than in the summer.

Leaves add moisture to the air, which would help temper heat, but also make things more humid. Also, during spring heat waves, the air comes from the southern and central Plains, which tend to be quite dry in March and April. Drier air can heat up faster than more humid air. The strengthening sun this time of year can really heat up a dry air mass.  

To an extent, that's what happened over northern Vermont on Thursday. 

We obviously don't know whether we'll have any more big warm bursts this spring.  A weak cold front today will hold temperatures down slightly in northern Vermont with expected readings in the 50s. But central and southern Vermont will see highs well into the 60s this afternoon, maybe touching 70 in the warmest towns.

Then it's back to reality with seasonable temperatures (daytime highs in the 40s) for the next several days, starting tomorrow.