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Heat Wave Gives Way to Unsettled Stretch for New England

A cold front has dropped into northern New England this morning. This front will continue to slowly meander southward toward southern New England before stalling out due to the heat dome now suppressed to our south. This front will bring heat relief for most of New England today. The one exception will be western Massachusetts and Connecticut, who will see another very warm day with high index values and a potential fourth day in this heat wave. A developing onshore flow will lead to cooling this afternoon for eastern areas.

Thunderstorms this afternoon will be much less widespread and generally pack less of a punch for areas that do see storms. Exactly where the cold front stalls this afternoon will play a big role in where storms are able to break out. Areas that remain south of this front, in the warm sector, will see the highest storm chances. This currently looks to be across central Massachusetts, Connecticut and Rhode Island.

HRRR showing potential weather mid to late this afternoon:

As for the severe threat, it will be lesser than it was yesterday afternoon and evening. South of the front, the ingredients will be there, but some will be muted. Lift and moisture will be sufficient, instability will be modest, with CAPE values rising to 1,000 to 1,500 in the afternoon, but lapse rates won't be all that steep. Shear will also be strongest where storms aren't expected and weaker where storms will be present. With that said, the severe threat will be isolated, but a couple cells will likely become stronger.

On Saturday, the frontal boundary will remain over New England, allowing continued low pressure to ride along it. The front will likely begin to move back northward during the day, allowing for another round of scattered showers and thunderstorms during the day. Showers will be isolated and concentrated across the northern tier of England to start before dropping south in the afternoon and evening and becoming more widespread.

The highest chance for more consistent rainfall will be across northern Vermont, the White Mountains and into western Maine. Areas farther south may see a line of showers and storms move through in the afternoon and evening, though guidance remains varied on how widespread storm activity will be across southern and central New England. The general idea is that scattered showers and storms will be around during the day, but there will also be dry times with at least partial sunshine for some.

HRRR showing potential weather around midday Saturday (1st image) and mid-afternoon Saturday (2nd image). While models remain varied, HRRR is giving a good middle ground at the moment:

Heading into Sunday, the frontal boundary continues to lift northward. This will transition the front to a warm front, putting southern New England into the warm sector. This will allow warm, and potentially very warm, temperatures to return to Connecticut, Rhode Island and western Massachusetts. Connecticut could see highs in the 90s once again. There will likely be plenty of clouds around, which will help limit temperatures. Temperatures will fall off as you head north and east. 

Depending on exactly where the area of low pressure shown above tracks, there could be a widespread rain event for northern New England, particularly the northern third of New England. With a moisture-rich environment in place within the warm sector, heavy downpours will be possible within the rainfall and thunderstorms.

Euro showing potential weather Sunday afternoon. You can see the heaviest precip near the Canadian border/northern Maine:

With widespread rain possible across the north, this could translate to an area of 2-3 inches of rain. This area is looking most likely to set up near the Canadian border with rainfall amounts steadily dropping as you move southward.

Current expected rainfall from Sunday morning to Monday morning, showing the highest rainfall amounts across northern Maine and southern Canada. This remains a low confidence forecast:

As of now, guidance has this band of heavier rain just to the north of Vermont and New Hampshire with northern Maine getting into it. This potential has led the Weather Prediction Center to put the northern tier of New England in the “slight” (level 2 of 4) category for excessive rainfall.

Should this band of rain remain mostly in Canada with a continued north trend, the southern extent of the flood risk below will need to be pushed northward. Southern New England will likely see more scattered storm activity rather than widespread rainfall, but any storm will be able to produce downpours there as well.

Another round of showers and storms will be possible across New England on Monday as the system's cold front gets dragged across the region.

Weather map for Monday (June 24):



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