Heat Peaks Before a Cold Front Stalls Over New England Thursday

Temperatures aloft will likely peak on Tuesday, making Tuesday a notch hotter than Monday for most. Increased humidity will bring feels-like temperatures into the low 100s for southern and central New England. While humidity levels will be elevated during this time, they likely will not be able to reach their full potential given the overall setup.

A subtle front will drop through New England on Tuesday, switching the wind direction to northwest rather than due west. This will try to advect drier air into the region aloft. With good mixing, this drier air may keep humidity at bay somewhat. It'll still be humid with dew points into the 60s for many, but it could have been much higher.

The ridge bringing this heat will begin to break down on Wednesday, leading to a more zonal flow developing. A frontal system will likely approach Tuesday night before crossing New England on Wednesday into Thursday. This system will lift its warm front into the region, raising moisture content, before a cold front slides through later in the day. This will set the stage for a round of scattered thunderstorms in the afternoon and evening.

The overall progress of the cold front has trended slower over the past 24 hours. This slowing trend has allowed temperatures to trend upward for the southern half of the region. Heat advisories for much of southern New England have been extended into Wednesday. as temperatures may again approach the mid 90s. The slowing of the front will also likely mean that coverage of storms will be greater across northern New England with more isolated activity focused later in the day for southern New England.

Below: HRRR showing potential weather Wednesday afternoon:

The threat for strong to severe storms Wednesday is on the low end, currently. The biggest limiting factor will be the fact that instability will be marginal at best and the front providing forcing has slowed down. The region may struggle to build up to 1,000 units of CAPE. With that said, shear will be rather strong, so if trends head in the direction of higher instability, the threat for severe storms will increase. As of now, severe weather looks to be very disorganized Wednesday at worst and non-existent at best.

Moving into Wednesday night and Thursday, the cold front will likely slow down further and stall either over southern New England or just south of New England, resulting in the potential for unsettled weather throughout the day for the southern half of the region. Waves of low pressure will likely ride along the stalled out front, bringing clouds and bouts of showers, storms and potentially downpours.

Given the uncertainty in where exactly the front will stall out, there's a spread in the northern extent of scattered showers and thunderstorms for Thursday. Should the front stall south of New England, the threat would be focused over southernmost New England. If it trends farther north, the showers would trend farther north as well. Some guidance shows the front stalling as far north as the northern Massachusetts border. Models have not been able to agree on this boundary's placement, and a decent spread remains as of Tuesday morning.

Below: Euro (1st image) and GFS (2nd image) showing the northernmost extent of this system:

Moisture will be highly elevated during this time, with precipitable water (PWAT) values approaching 1.5 to 2 inches. PWAT is a measure of water vapor contained in a column of air if it were to be condensed and collected. Basically, the higher the PWAT value, the more rain could fall, if a forcing mechanism for rain (low pressure system, frontal boundary, etc.) is present.

Below: Potential PWAT values Thursday:

With a stalled boundary, multiple rounds of rain with embedded downpours will be possible. The area where the frontal boundary sets up could see 1-2 inches of rain, with locally higher amounts where localized downpours set up. The area most likely to see the highest rainfall amounts is currently interior southern New England, however, given the spread, this could still shift in the next 24-36 hours. Overall, rainfall amounts will likely end up highly varied given the scattered nature of potential downpours.

Below: Current precipitation forecast through Friday:

The general timing of all of this is coming into better agreement despite the spread in location. Rounds of rainfall and downpours will likely move along the front beginning Wednesday night and last through Thursday, likely peaking in the afternoon. Showers will likely continue through Thursday night and slowly pull southward Friday morning, clearing out from north to south. During this time temperatures will be much cooler, with humidity dropping off Friday once the moist air mass is pushed south.

This upcoming weekend is currently shaping up to be a great summer weekend. A large ridge of high pressure looks to build into New England. This is poised to bring dry conditions, seasonable temperatures and low humidity. There's currently not a whole to say about this upcoming weekend in the weather department, with a beautiful stretch of weather once the front clears.