Frontal System to Bring Showers to New England Before Warm-Up

The most organized wave of low pressure over the next few days will likely cross New England later Friday through Saturday. This system will pass to the north of New England, lifting a warm front across New England. One of the biggest questions with this system will be how far north this front lifts, as this will determine who gets into warm temperatures, who stays cooler and how much rain falls.

Areas which see the greatest forcing for showers will be favored to see scattered heavy downpours later Friday into Saturday. For New England, this looks to be across northern Vermont, New Hampshire and interior Maine. Trends over the past 24 hours have continued to push the warmer air farther north, which likewise pushes the heaviest rain farther north. Areas near and south of the warm front will see much more scattered shower activity, milder temperatures and higher instability.

Areas well north of this front will be cooler with more widespread rain and the potential for multiple rounds of downpours. With the continued northern trends, the bulk of this rain is now expected across southern Canada, however, it will be very close to the international border. Trends will continue to be watched in this regard as further shifts remain possible as the system arrives given the way guidance has handled this event.

Below: Current precipitation forecast through Sunday morning, showing a widespread 1-3 inches of rain falling just to the north of New England:

There are a few factors that may line up that would still support northern Vermont and New Hampshire seeing bouts of heavier rainfall. A thermal boundary will be set up across the area (in the form of the frontal boundary) with an unseasonably strong jet streak set up across southern Canada, which could help enhance rainfall within showers at times. Moisture-content will be very high as well, with precipitable water values (a measure of moisture in the atmosphere) well over 1 inch, indicating a moisture-rich environment.

The overall threat of flooding across northern New England has dropped quite a bit over the past 24 hours as trends have taken the highest rainfall into Canada. With that said, these factors remain in place and any shower across New England could become briefly heavy. This could result in very localized and minor flash flooding issues. The Weather Prediction Center has taken northern New England out of the "slight" category (level 2 of 4) for excessive rainfall. This area has been dropped to the "marginal" category (level 1 of 4).

Below: HRRR showing potential weather Saturday morning:

Areas south of the warm front will get into the warm sector of the system. While there remains a spread in just how far north this front makes it, southern New England will likely see it push north by Saturday afternoon. This would set up some scattered showers mainly in the morning before becoming much more isolated in the afternoon. Areas south and west of the boundary could see breaks in the clouds and temperatures shoot well into the 70s toward the low 80s.

Areas farther north and east will remain in the 60s to low 70s. There could be a decent temperature gradient set up across the region with a narrow area separating the low 80s from the upper 60s. Exactly where this sets up is difficult to say, but it will likely occur somewhere across central New England (northern Massachusetts, southern New Hampshire and Vermont). Western New England will be the warmest and Maine will be the coolest. Overall, there's big bust potential with Saturday's temperatures.

Below: HRRR showing potential high temperatures Saturday afternoon:

The basic timing of this system will see showers across northern New England gradually expand in coverage Friday night into Saturday morning. Showers will become more scattered in nature during the day Saturday with the potential for thunderstorms. Much of Maine will see a slug of rain for the day. For southern and central New England, scattered showers are likely in the morning with the passage of the front. Showers then become much more isolated with more dry hours than wet hours in the afternoon and evening.

Early next week, a Bermuda high looks to build back, bringing a warming trend with widespread 80s and higher humidity back into the picture. At this point, another heat wave is unlikely, but temperatures will be building back up next week. The next chance for showers or thunderstorms will come on Tuesday (July 1).