A broad upper-level trough will remain over the region into Thursday night, with a cold front and an embedded shortwave passing over our region on Thursday afternoon. Surface high pressure will then build in from the northwest late Thursday night into the day on Friday.

Diurnal instability could lead to a few isolated showers and thunderstorms this evening before quickly diminishing after sunset with the loss of surface heating. Elevated winds associated with northwesterly flow behind a cold front, which passed through earlier this morning, will continue through this evening, with wind gusts well above hurricane force expected, before slowly ramping down into Thursday morning. Lingering low-level moisture and the elevated winds will likely lead to another round of intermittent summit fog this evening before slowly clearing as drier air mixes down and winds diminish. Lows will drop towards seasonal averages, but with the elevated winds, it will feel closer to freezing on exposed skin and increase hypothermia risks for those inadequately covered or prepared.

Thursday will start under fair weather skies and stiff northwesterly winds. An embedded upper-level shortwave rotating around the upper-level trough and a secondary cold front will then move in from the north late in the morning into the early afternoon, allowing for summit fog to return. The cold frontal boundary will also likely be accompanied by scattered rain showers and isolated thunderstorms Thursday afternoon into the early evening, along with gusts near the century mark. A few of these thunderstorms could become severe and produce strong, gusty winds, small hail, and frequent lightning. Surface high pressure will then begin to build in later Thursday evening into the day on Friday. Cold air diving southward behind the front will drop temperatures into the 30s, with elevated winds producing wind chill values on exposed skin down into the upper teens at times late Thursday night into early Friday morning. For this reason, a wind chill advisory has been issued and will be in effect from 11 PM Thursday night until 9 AM Friday morning. Drier air mixing in will produce a clearing trend at and above the summits later in the evening, with fair weather skies developing before sunrise on Friday. Winds will slowly begin to ease Thursday night, but will remain stiff through Friday afternoon, keeping wind chill values in the 30s through the day.

Wildfire smoke looks to be shunted mostly south of the summits by Wednesday evening by the cold front which passed through earlier this morning before rebounding northward late Wednesday night through much of Thursday. Air quality in the higher terrain will likely be affected and is forecast to reach unhealthy levels during the day on Thursday, with reduced visibility likely to result as well. Following the passage of the cold front on Thursday afternoon, air quality and visibility will likely improve Thursday night into Friday.

And with our non-profit's largest annual fundraiser taking place this weekend, we will be extending the next few forecast updates out to Saturday. Friday night, expect partly cloudy skies; winds will continue to decrease overnight to 20-35 mph as they shift W before sunrise, with temperatures dipping to the lower 40s in the evening before rising to mid-40s by sunrise. Saturday, expect increasingly cloudy skies with summit fog returning around midday. There will be a chance of showers or thunderstorms in the afternoon before becoming increasingly likely towards the evening. Temperatures will rise to the lower 50s. Winds will be from the southwest shifting south at 20 to 35 mph in the morning, increasing to 30-45 mph with gusts up to 55 mph in the afternoon.

Karl Philippoff -- Weather Observer and Meteorologist
Updated at 4:41 PM on Wednesday

AI Conditions Dashboard

Challenging Conditions Reported

5-Day Conditions Forecast

NWS Higher Summits Forecast

Mt Washington Observatory