This morning's Alberta Clipper continues to move through the Gulf of Maine and across Nova Scotia through this afternoon. A trailing mid-level disturbance will cross northern New England as it does so. This will drag a cold front across the region, leading to the redevelopment of scattered snow showers and squalls. The setup this afternoon is similar to yesterday in regards to the front, just delayed a few hours.
The trailing disturbance will likely cross New England near the Canadian border beginning early this afternoon. This will create more numerous snow showers across the northern tier this afternoon. Farther south, more scattered activity is expected along the cold front, which will cross from west to east through the afternoon. Scattered activity will likely move west to east across New England from midday to about 5pm. Eastern Maine will get whatever's leftover in the evening.
Below: NAM showing potential around mid-afternoon today:
This afternoon is rather similar to a thunderstorm day in the summer. Since its January, the scattered storms and showers are replaced with scattered squalls and snow showers. Conditions appear favorable for briefly heavy snow showers and gusty winds as the front pushes through. Daytime heating ahead of the front will steepen lapse rates (the rate of decrease of temperature with altitude). This will create an unstable environment.
Combine the unstable environment with the lift and forcing from the cold front/disturbance and a saturated snow growth zone, and the recipe is there for additional snow squalls to pop up this afternoon. The biggest limiting factor for southern and central New England will be temperatures, which will rise well above freezing prior to the front's arrival. While snowfall rates within a squall should be enough to bring snow all the way down to the surface, it is still possible for some mixing or rain showers, especially near the coast. Not everyone will get one, like yesterday.
Below: Snow squall parameter forecast this afternoon showing values around 5, which indicates a favorable environment:
Outside of the snow shower/squall threat, a period of gusty winds will accompany the frontal passage. Temperatures will turn sharply colder behind the passage. Temperatures may drop 10-15° within a couple hours around sunset as the fresh Arctic air mass settles into the region. Gusts of 40-55mph will be possible as the front moves through and after the passage. After yesterday's winds over-performed, a wind advisory has been posted for southern New England this afternoon and tonight.
New England's next Arctic blast will settle in on Thursday, with wind chills below zero Thursday morning for most, and approaching -30° across the north. High temperatures will range from the low teens north to mid 20s south. Winds will remain blustery all day, keeping wind chills very low throughout.
Another northern stream system with limited moisture will pass to New England's north Thursday night into Friday. This will lift a warm front across New England, bringing a quick end to Thursday's Arctic blast. While it won't actually get truly warm, or even mild, it will be noticeably warmer than Thursday. Later Friday, a southern stream system will approach New England. A split-flow setup will allow the northern and southern stream systems to remain separated. This will result in another minor-impact storm with lighter precipitation totals likely.
The two big questions surrounding this storm over the past few days have been how far north will the precipitation be able to spread and what will the precipitation type be? For the first question, recent trends have been toward less of a drier upper-level flow, which would no longer restrict the northward advancement. Even the driest CMC model, which was pitching a shutout for precipitation yesterday, now has precipitation extending well into northern New England.
As far as precipitation type goes, it continues to depend on the exact track of the storm. As of now, mostly snow is favored across most of northern New England, except for southern New Hampshire, where more mixing issues could come into play. This is despite rather warm thermal profiles in northern New England; it just doesn't appear to be warm enough to change snow to a mix across the north.
Below: Model roundup (Euro, GFS, CMC & GraphCast) for Friday evening:
For southern New England, a warm nose of air aloft will push into at least part of the region. The northward extent of this warm nose will be dependent on the storm's final track. This could be a messy mix type of storm across southern New England with a variety of precipitation types draped across the area (plain rain, sleet, freezing rain, snow). This will all depend on the depth of the warm nose aloft and surface temperatures. Areas south of the Mass Pike will likely see primarily rain while areas north will stand the best chance to see some mixing.
The track and timing of precipitation will help determine precipitation. The system will be deamplifying as it moves toward New England. This will allow the storm to go from a more south to north motion to a more west to east motion. This will create a more progressive a quick-moving system. The big question remains how far north it will get before shearing off to the east. A more northerly track would pull the rain/snow line further north and vice versa.
The amount of dry air in place ahead of the storm will also matter. Should dry air be resilient and allow for a later start time, it would allow the warmer air aloft to push further and deeper into New England, particularly southern New England. This would result in plain rainfall being more widespread.
As far as how much goes, this isn't shaping up to be a major storm anywhere in New England. Preliminary estimates on snowfall for areas that remain all snow are 1-3 inches for many areas across the northern tier with a potential jackpot zone over eastern Maine, where 3-6 inches may be possible. These numbers are preliminary and could increase should the system take a more northerly track.
Below: Current probability of at least 2 inches of snow Friday afternoon and night. These probabilities will likely shift around some:
As stated before, this is a progressive system and will likely be gone by Saturday morning. This fact will also help keep precipitation totals on the lower end. Strong high pressure advects into New England afterward, setting up a cold weekend with very low overnight lows for Saturday night.
Another clipper appears poised to move through New England Sunday into Sunday night, bringing another round of widespread light snow to the region. There are timing differences with this one, which will affect precipitation type. The longer it takes for the system to move through, the better the chance of mixing or rainfall as opposed to all snow from beginning to end.
Below: Current weather map for Monday morning (February 3):
One last note about this active forecast is the changeable temperatures. With a succession of ridges and troughs punching through New England, it will lead to whiplash with up and down temperatures. With Arctic intrusions quickly being replaced with warm air advection and vice versa, temperatures will be all over the place through at least early next week.
Kommentare