Chelmsford, MA Weather

What Has Changed

No meaningful changes to the forecast, with an extended stretch of quiet and dry weather ahead.

Key Messages

- Prolonged stretch of dry weather across southern New England. Moderating afternoon temperatures this weekend, though chilly mornings will bring widespread frost away from the immediate coast.

Discussion

KEY MESSAGE 1...Prolonged stretch of dry weather across southern New England. Moderating afternoon temperatures this weekend, though chilly mornings will bring widespread frost away from the immediate coast.

If the forecast discussion starts sounding like a broken record over the next several days, you can thank strong high pressure for that! An extended stretch of dry weather is expected, with some day-to-day variability in temperatures, but otherwise not much excitement on the horizon. In fact, global ensembles paint a rather parched picture for southern New England, with cumulative probabilities of measurable precipitation (0.01 inches or greater) generally less than 10 percent through much of next week.

An expansive area of surface high pressure, around 1035 mb, remains anchored across the region this weekend, with some guidance suggesting pressures could approach 1040 mb Saturday night. This will promote plenty of sunshine, light winds, and generally quiet conditions. Temperatures at 925 mb warm to +6C to +9C this afternoon, supporting highs in the upper 50s to lower 60s. If this were a few weeks earlier, with a higher sun angle, we'd likely be talking about highs in the middle to upper 60s. But here we are, nearing the end of October! Temperatures aloft continue to moderate Sunday and Monday, with 925 mb temperatures approaching +10C Sunday and +13C Monday. This should support highs in the lower to middle 60s Sunday, with some locations potentially reaching 70F Monday.

Overnight temperatures, however, are a different story. Clear skies and light to calm winds beneath strong high pressure will promote efficient radiational cooling. Opted to trend overnight lows below NBM guidance, which typically runs too warm in these setups. Saturday and Sunday mornings, and to some extent Monday morning, will be quite cold, with lows in the 20s to lower 30s and widespread frost away from the immediate coast and urban heat islands. Be sure to protect those mums and Halloween pumpkins! One interesting feature of this setup will be the potential for significant temperature differences between sheltered valleys and higher elevations. With clear skies and light winds promoting strong radiational cooling, colder air will settle into the valleys, while some elevated locations may remain several degrees warmer within the nocturnal temperature inversion.

Looking ahead, a moisture-starved cold front approaches from the north-northwest late Monday night into early Tuesday. However, persistent high pressure and dry air will likely limit the front to little more than some additional cloud cover and a cooler air mass. Highs return to the 50s Tuesday and Wednesday before potentially rebounding into the 60s Thursday and Friday. Overnight temperatures should trend closer to seasonable levels, although confidence is lower given uncertainty surrounding cloud cover and winds, both of which could limit radiational cooling. Fingers crossed this dry pattern holds just a little longer and gives us a dry All Hallows' Eve!

Aviation

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

06Z TAF Update:

Today through Sunday...High confidence in flight categories, moderate confidence in wind direction and speed.

High pressure brings dry weather and clear skies, with VFR conditions prevailing through the period. Wind direction and speed are a bit more challenging given the weakly forced environment. Winds around 2 kft are generally NW to N near 10 kt, though daytime heating and temperature differences between land and water may allow a weak sea breeze to develop along the coast. Confidence in sea- breeze development remains low. Regardless of direction, surface winds should remain light, generally 4 to 8 kt. Tonight, winds become calm to light and variable, generally less than 3 kt. More of the same is expected Sunday, with winds around 2 kft shifting to the west at 5 to 10 kt, while surface winds remain light, generally 4 to 8 kt.

KBOS Terminal...High confidence in flight categories, moderate confidence in prevailing winds, but low confidence in sea-breeze development.