Chilly High Pressure Remains Over New England This Weekend

The passage of yesterday's cold front opened the door for an area of high pressure with Arctic origins to settle over New England for this weekend. With it being mid-September, the effect of this high pressure is muted compared to winter, but it is strong enough to bring the region its first widespread frost and first freeze warnings of the season. Frost advisories and freeze warnings have expanded for tonight into Sunday morning.

Widespread highs for Saturday afternoon will remain in the 60s across much of the region. The northern tier likely won't break out of the 50s today. The high pressure will bring an overall tranquil day with light winds and sunny skies. It'll be a very fall-like weekend to close out astronomical summer. This high pressure system will also create strong radiational cooling conditions, allowing the temperatures to drop off and bottom out overnight tonight. Light winds, clear skies and low dew points will allow widespread 30s to low 40s for morning lows on Sunday.

Below: RGEM showing potential Sunday morning lows:

While the weather will be tranquil today, overall conditions do support elevated fire weather concerns. Continued bone-dry conditions and low relative humidity of 20-30% are the main drivers of the risk for this weekend. The main limiting factors for the spread of brush fires will be a lack of wind thanks to the high pressure overhead.

These conditions are not enough for a red flag warning, but most of New England has a special weather statement for the elevated risk, which is a notch below a red flag warning. Similar conditions will be in place on Sunday as well. An elevated risk of fire weather will likely remain in place until a decent rainfall.

Sunday will play out almost identically to Saturday for weather conditions considering the high pressure system will barely move. Early next week, the high pressure overhead and a trough to New England's west will shift eastward. This will allow return flow from the south and create a warming trend.

Tuesday continues to look like the warmest day of the week, with the potential for 80s to return to the river valleys. Clouds and unsettled weather expected early next week has started a slight cooling trend among guidance, however, so trends will continue to be watched.

Below: Temperature departure from average Tuesday afternoon (September 23):

The trough sliding east will drag a cold front through New England. With several waves of low pressure potentially riding along the front, multiple bouts of unsettled weather and showers will be possible across New England from Monday night through Wednesday. Guidance remains at odds over how this will all play out, which is expected given the pattern shift that will be underway.

Below: Current weather map for Wednesday morning (September 24):

The most likely outcome will be multiple periods of scattered showers Tuesday and Wednesday, with a bout of more widespread rainfall possible. Without one well-defined feature to force rainfall, timing this out will remain tricky. Forcing overall will likely remain on the weaker end, which will likely keep rain totals on the lower end. At this point, a quarter inch or less of rainfall is expected, which is less rain than what was being shown yesterday.

Below: Current five-day precipitation outlook:

That cold front will likely drop temperatures from Tuesday's highs. Another warm-up may be on the way later next week as the large-scale setup does favor above average temperatures across much of the United States. The one issue with this would be the presence of a negative NAO, which would make it more difficult for a firm ridge to develop over the east. This could put a damper on warmer weather late next week. Note that the below graphic currently covers September 25-29 (next Thursday through the following Monday).