Thursday, May 7, 2020

Winter In May: A Bone-Chilling Update

It's incredibly late into the spring to be looking at a National Weather
Service snow forecast map, but here we go.  Darker shades of
blue represent two or three inches of expected snow this
weekend. Lighter blues indicate a dusting. 
Get ready folks, winter arrives, once again, Friday night.

Yes, that is hyperbole, but not by much.  When the National Weather Service in South Burlington puts out its snow forecast map this time of year, you just want to throw up your hands

That piece of the polar vortex that broke off and is heading this way is really something.  In the upper atmosphere, several thousand feet up and higher, the air will be colder than it usually is in January.

The very high sun angle, despite the clouds and wind, will of course prevent temperatures from being truly winterlike down here on the ground Saturday. But it will feel wintry enough.  

As the bitter cold settles in Friday night, a storm that's been widely forecast will move off the New England coast.  Somewhere in New England, this will be a nor'easter that drops several inches of snow. Like the start of an Arctic outbreak in January would behave.

Believe it or not, it's possible the most snow will fall mostly south and east of most of Vermont. Yeah, it's May, and we're too far north to get the heaviest snow.

However, for perspective, it IS May, and nobody is going to get feet of snow. But higher elevations could see up to half a foot, maybe.

It'll snow pretty much everywhere in Vermont with this cold blast. Even if the storm at the start of this spell entirely misses the Green Mountain State Friday night and early Saturday, the cold pool aloft will be enough to make it snow.

The high May sun will quickly create rising air currents and showers. The cold is so deep that most of those showers will come down as snow.  

In general, the NWS in South Burlington is forecast snow totals to amount to an inch or less in the valleys, two to four inches at elevations of between 1,000 and 2,000 feet, and areas above 2,000 feet collecting four to six inches of snow, maybe more on the mountain peaks.

That's the forecast as of this morning. It is subject to change.

During the day Saturday, the snow showers will go on, temperatures will stay near 40 at best, with some areas in the north remaining just barely above freezing. As that departing storm blows up over the Canadian Maritimes, it'll drive wind gusts into the 40 mph range.

This is obviously absolutely ugly for May.  This won't be the biggest May snowstorm on record for May, but it will be a shock to the system.  The snow should mostly end Saturday night, but the northwest winds will continue howling through Sunday.

I like to turn to David Ludlum's "Vermont Weather Book" to prove that it could always we worse.  We have certainly endured worst winter storms in May than what's currently in the forecast.

At least it's not May, 1834.  That year, Burlington and Rutland had a foot of snow on May 15. Two feet of snow blanketed Marshfield during that storm. Yikes!

In June, yes, June 1842, there was a dusting of snow in Burlington on the 11th that year, nad up to six inches in the high elevations. I think global warming will have prevented anything like that from happening again.

Speaking of warming, Saturday will surely be Vermont's  coldest day until November, or maybe late October.

It can't really get any colder than Saturday this time of year, so starting Sunday, we have nowhere to go but up.  It will be a slow process, though, and temperatures will stay well below normal into the middle of next week.

Sunday should make it into the 40s during the day.  A few low 50s might pop up Monday and Tuesday. But we need to be alert for the risk of frosts and freezes every night Saturday night through Tuesday night at least.  Tender outdoor plants and possibly orchards could have a tough time with this.

The warming trend seems destined to continue nicely late next week and into the following weekend. We can probably at least expect some near normal daytime temperatures in the 60s by then.]

We do often get back door cold fronts from eastern Canada this time of year, and that could temper the eventual warmup somewhat. But after this cold spell wanes in about five days, I'm pretty sure we're done with snow until next fall.

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