Diving Into New England's Mid-Spring, Quick Hitting Snowstorm

For a fleeting few hours on Saturday morning, it seemed like a full-fledged, mid-winter type snowstorm across portions of southern New England in the middle of spring. While this kind of snow this time of year wouldn't be too out of the ordinary within the mountains of northern New England, this storm's jackpot zone set itself up over the moderately higher terrain of central Massachusetts. This jackpot zone saw a narrow band of 6-10 inches of snow when generally 1-4 inches was expected.

A scene reminiscent of the middle of winter, not the middle of April. Photo by Cam Jandrow

Throughout the week, Saturday's forecast remained very changeable as this system involved a cutoff low, a low that has been cut off from the main flow. Cutoff lows become more common in springtime as the overall pattern transitions from the colder months to the warmer ones. These storms are almost always a challenge for guidance to hone in on since they're separated (or cut off) from the main flow and can move independently of it.

With the confidence in potential outcomes decreased from the overall setup of the storm, there were two main factors to focus on for potential snowfall. Both of these factors began moving in the direction of the storm producing more snowfall. In Friday morning's forecast post, we wrote:

"There have been some rather distinct trends within guidance over the last 24 hours or so involving dry air and the potential for a strengthening storm system, both of which lends itself to entertaining the idea of a bit more snowfall...Diving into the reasons behind this potential bump in precipitation, the system will be entering a dry air mass with high pressure just north of New England. This lends itself to the potential for evaporational cooling. Evaporational cooling is the process of an air mass cooling as water evaporates within it (as water changes from a liquid to a vapor, it absorbs heat). Since the precipitation will be arriving in a dry air mass, initial precipitation will evaporate, allowing temperatures to cool. With marginal temperatures in place, enough cooling will likely occur to allow for snowfall Saturday morning."

Below: A graphic we used in forecasts, showing the high pressure directly north of New England. This high created a dry air mass for the storm to enter into (as well as allowed colder air to drain from the north):

The other main factor being watched with this storm was the potential strengthening as it moved up the coast. Heading into this storm, trends began heading toward a period of frontogenesis occurring, along with a band of moderate to heavy precipitation. With the stage set for a colder air mass when the system fired up, this would come in the form of snowfall. In Friday morning's forecast, we also wrote:

"Another potential factor working for the system will be the possible strengthening of the storm as it moves closer to New England. This could lead to a band of heavier precipitation rates forming across southern and central New England as frontogenesis forms, which is basically the formation and strengthening of a frontal boundary (which can lead to stronger precipitation rates). Should this occur (and it's certainly not a guarantee), a brief period of moderate snowfall will be possible. In mid-April, snowfall rates of this magnitude will be needed to get much of any accumulations."

In that article, we mentioned that on Friday morning, a winter weather advisory was only in effect for Berkshire county, but expansions were very possible given the trends being shown Friday morning would hold up. These trends certainly did hold up, which can be seen on the Storm Prediction Center's hourly snowfall rate potential. In the morning, the potential for an inch hour rates were around 20%. By the evening, the chances had grown to 50% and covered a much wider area.

Below: Storm Prediction Center hourly snowfall rate potential from Friday morning (1st image) and Friday evening (2nd image). While the evening area was positioned slightly too far north, it shows the general trend toward an increasing chance of heavier snowfall rates:

These factors came together to create a band of snow with heavy snowfall rates. Hourly snowfall rates as high as 3 inches an hour were reported across Worcester Hills, more than enough to overcome mid-April factors that work against piling up snow. Thundersnow was reported in the Worcester area. This allowed for a rather widespread 3-6 inches of snow in places with a narrower band of 6-10 inches.

Being the middle of spring, snowfall was highly elevation-based, with the Worcester Hills, Monadnocks and Berkshires seeing the most snow with far less in the valleys and very little to none along the coastal plain. Snow accumulations were aided in these areas as the strongest snow bands arrived early in the morning, before the strong sun angle took hold, which is what kept snowfall amounts down for the higher elevations farther north in New England.

Despite the trends described above, it was still hard to latch onto any idea with much confidence, especially regarding high levels of snow accumulation this time of year. In Friday morning's article, we wrote:

"Given the way recent trends have gone, there is room for amounts to increase further over the next 12-18 hours...mid-April doesn't lend itself to much of a snowstorm. Conditions need to be perfect and the storm needs to get pretty strong. Given how wobbly guidance has been with this system all week long, it's difficult to jump onto what anything is showing with a high amount of confidence."

The approach taken in our forecast was to leave the door open for higher accumulations while not fully jumping on the potential for high snow accumulations. In the end, the factors lined up nearly perfectly to create quite a winter storm for a brief period of time. The highest snowfall was 9 inches, recorded in Princeton and Ashburnham, Massachusetts. Should this storm have entered New England two months ago, this would have been a big one for much of New England. Should-a, could-a, would-a.