Dreary Weekend on Tap for Most With a Cold Rain and Some Snow

Heading into Saturday, a coastal storm system will form across the Mid-Atlantic and slowly meander its way up the coast. This system will likely wobble around to the south of New England through the weekend before continuing its journey northeast on Monday. This will bring another round of cold rain and a light spring snow to New England through Sunday. With the storm remaining offshore of New England, a stiff and chilly northeast wind will add to the dreariness of the day.

This will be a cutoff low, which inherently lowers confidence in the outcome, even at this near-term stage in the forecast. With that said, some agreement on the timing of the system is starting to emerge among guidance. Initial rounds of precipitation will likely rise into southern New England during the pre-dawn hours Saturday.

Below: HRRR showing potential weather in the pre-dawn hours Saturday:

Bands of rain and snow will continue to lift northward through Saturday morning. By the afternoon, most of New England will likely be seeing at least light and scattered precipitation. Rain and snow will be most numerous across southern New England with coverage gradually decreasing moving northward.

Below: Potential weather around mid-morning Saturday (1st image) and mid-afternoon Saturday (2nd image):

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. Being mid-April, any snowfall will be highly elevation-based. As of now, the Berkshires, Worcester Hills, southern Greens, Monadnocks and maybe the Litchfield Hills will stand the best chance at seeing a few inches with locally higher amounts farther up in elevations. The lower elevations/valleys/coastal plain will be more apt to see slushy coatings to maybe an inch.

Given the way recent trends have gone, there is room for the amounts above to increase further over the next 12-18 hours. 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: HRRR showing hourly temperatures from about 6am to 6pm Saturday:

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. This potential can be seen on the Storm Prediction Center's hourly snowfall Rate potential. It currently shows low to moderate probabilities of snowfall rates reaching or exceeding an inch hour for a time Saturday morning. In mid-April, snowfall rates of this magnitude will be needed to get much of any accumulations.

Below: Storm Prediction Center likelihood of at least 1" an hour snowfall rates:

With all of that said and out of the way, mid-April doesn't lend itself to much of a snowstorm. Conditions need to be perfect and the storm needs to get pretty strong. With that said, minor accumulations are likely across the higher terrain, as mentioned above. A winter weather advisory has been issued for Berkshire county. National Weather Service offices in both Boston and Gray, Maine have floated the possibility of winter weather advisory expansions later today should last night's overnight trends hold up through today.

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. It should also be noted that roadways are much milder now and snow will quickly begin to melt after snowfall rates calm down. Outside of the snowfall, a steady, cold rain will be falling for southernmost New England and along the coastal plain.

Heading into Sunday, a second low pressure system will follow up the coast as the first low from Saturday deteriorates. This low will likely move a bit farther offshore than Saturday's and will likely have less moisture to work with resulting in lighter precipitation. Exactly how close to the coast this system gets will determine how far inland precipitation is able to push. As of now, the coastal plain and much of Maine will stand the best chance to see more numerous showers. Showers may be snow for interior Maine, with the potential for light accumulations.