Late-Season Chill Arrives as Rainstorm Bears Down

The late-season chill is officially here and temperatures will continue to drop through late this week. Highs will remain in the 50s for a vast majority of New England for the rest of this week, except Thursday, when a windswept rain will likely make reaching the 50s rather difficult. Overnight lows are also pretty cold for this time of year; the overcast skies and breezy conditions are preventing temperatures from completely bottoming out given the air mass overhead. If skies were clear, frost and freezes would be an issue across the region.

Some cities will come within a few degrees of lowest daily high temperature records for the rest of this week. Daily records for most cities in New England during this time sit in the mid 40s to around 50° for May 21-23. At this point, it looks like most of these records will stand. One interesting outlier is Concord, NH. Every day in May has a record lowest high temperature in the 40s (with one in the 30s) except for May 22, which is 51° and May 31. This Thursday (May 22) is currently forecast to be 48°.

Below: RGEM showing potential temperatures Thursday afternoon:

In the midst of this cool-down will be a late-season nor-easter moving through New England late this week. A large upper-level low pressure system will begin to approach New England late in the day Wednesday. This system will likely spawn a surface low off the Mid-Atlantic coast by Wednesday night and Thursday morning. This surface low will then slowly move northeastward across New England's coastal waters for the rest of the week.

The storm currently looks to enter western New England Wednesday night and steadily spread eastward through New England during the day Thursday. The storm may not be able to reach into central and eastern Maine until Thursday evening or night. For many, the bulk of the storm will be Thursday afternoon and evening. With a blocked-up pattern in place, the system will be very slow to exit, with scattered showers continuing to cycle into New England through at least Saturday.

Below: Euro showing potential weather Thursday morning (1st image) and Thursday evening (2nd image):

The track of the surface low off the Mid-Atlantic coast will help dictate exactly how much rain and wind the region will see. The closer the system tracks to Cape Cod as it moves northeast into the Gulf of Maine, the more rain will fall and the higher the wind gusts will be, especially across eastern Massachusetts, Rhode Island, southern New Hampshire and coastal Maine. A ridge of high pressure to the north of New England may delay the rain's arrival for northernmost New England as well as limit how much rain falls.

Overall, there remains a fair spread among guidance in just how much rain falls, and how far north the heavier rain can get. Some ensemble members (mainly the GEFS) still show a track more offshore, which would limit how much rain falls. As of now, a widespread half inch to inch and a half of rain is the going forecast. A track near or over Cape Cod remains the favored outcome.

While this will be a cold, windswept rain for much of New England, some of the region's highest peaks could see some snow. Snow levels may be able to drop to as low as 3,000 feet above sea level Thursday. Wednesday night and Thursday night will continue to be very chilly as well. The record latest observed snowfall for mountainous counties in New England are all in late May or June.

This system involves a primary low moving inland through New England with a secondary low forming off the Mid-Atlantic coast and moving northeast over New England's coast. The secondary low will strengthen as the primary low transfers energy to the coastal low. This is a very winter-like storm setup and would result in a widespread snowstorm if this was a few months ago.

Being a nor'easter, gusty winds are also likely with this system. At this point, wind gusts don't look to be overly high, but 40mph+ gusts will be possible for the coastal plain. Should the storm track close to land and achieve better mixing, gusts of around 50mph will be possible, mainly for eastern Massachusetts. Winds of this strength with the trees now fully leafed would cause higher impacts than a similar storm with bare trees in the winter.

The main storm system will lift into the Canadian Maritimes by Friday morning, ending the widespread rain chances from west to east. With that said, the upper-level low which spawned this system will be much slower to depart. This will keep scattered showers in the picture, very gradually decreasing in coverage through the weekend.