Heat Slowly Subsides as Cold Front Sags South, Setting up Unsettled Pattern

A cold front, which is slowly working through northern New England this morning, will continue to make its way southward through the region throughout the day today. This will bring lower temperatures and humidity, though temperatures aloft will remain very warm, so it will be another rather hot day with widespread 80s north to mid 90s south.

Today will act as a transition day from a heat dome to a stalled frontal boundary set up as the heat dome slowly gets suppressed to the south and west of the region. While this will be a dry frontal passage for most, some pop-up showers or storms will be possible in the afternoon and evening. Cloud cover will also increase as the boundary approaches.

While still very warm in many places, it will still be a couple notches lower than Tuesday, which (expectedly) saw numerous daily record highs broken. Widespread temperatures in the mid 90s to low 100s were observed across southern and central New England. At least four cities (Boston, Providence, Portland & Augusta) set a new all-time hottest temperature recorded in the month of June. Bangor tied their monthly record.

Heat index values soared into the 110-115° range as dew points rose to the mid to upper 70s. Some cities came close to all-time highs. Boston and Concord fell 2° short and Manchester fell 1° short of tying all-time highs. This was heat not too often seen in New England as a heat dome set up nearly perfectly to pump nearly the full force of the system into New England.

The full relief from this incoming frontal boundary will be felt on Thursday. The boundary will likely be to the south of New England, remaining nearly stationary. A wave of energy will traverse the boundary, bringing the increasing clouds and scattered showers in the afternoon and especially the evening. Multiple waves of energy will likely ride along the boundary through early next week.

The most organized of these waves will likely cross New England later Friday through Saturday. While there's a spread in exactly where the boundary will be set up, it continues to look like northern New England will see better forcing for showers,leading to wetter conditions the farther north in New England you go.

Below: Current precipitation forecast through Saturday morning:

Areas which see the greatest forcing for showers will be favored to see scattered torrential downpours later Friday into Saturday. Again, this looks to be across the northern tier of New England, with northern Vermont currently forecast to see 1-2 inches of rain during this time frame. A thermal boundary set up across the area with an unseasonably strong jet streak set up across southern Canada will help enhance rainfall 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. These factors may line up to create the potential for downpours and isolated flash flooding across northern New England. Minor river flooding will also be possible. Trends will be watched closely as this threat could increase or decrease over the next 36 hours or so as a large spread in guidance remains.

In the temperature department, the frontal boundary suppressing the heat dome combined with high pressure moving eastward will create a prolonged period of an onshore flow, bringing much cooler temperatures to New England through Saturday, with 70s dominating. Areas closer to the coast as well as areas that see more rainfall may struggle to break out of the 60s Friday and Saturday.

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 major heat wave is unlikely, but temperatures will be building back up next week. This Sunday may be the transition day and there's a large spread in what temperatures will be that day as it's unclear whether an onshore flow and cooler temperatures win out or if the warmer pattern kicks in during the afternoon.