Londonderry, VT Weather

What Has Changed

Continued trend to lower dewpoints during the afternoons on the weekend with the surface high and dry air mass in place.

Added some patchy valley fog Sun night/Mon morning with dewpoints rising and the surface anticyclone just south and east of the region.

Key Messages

1) High confidence in dry conditions persisting through at least the middle of next week.

Discussion

KEY MESSAGE 1...

A strong surface high around 1035 hPa continues to build in over southern Quebec, NY and New England tonight. Near ideal radiational cooling conditions set-up with mostly clear to partly cloudy skies and light to calm winds, as some cirrus may drift in over the top of the mid and upper level ridge after midnight. The low-levels are very dry with PWATS close to 0.25", which are 1-2 STDEVS below normal based on th latest NAEFS guidance. Lows will fall into the 20s to around 30F (close to a MAV/MET/NBM blend). The coldest readings may be over the southern Dacks and the sheltered valleys north of Albany. The thin cirrus should diminish tomorrow morning with the sfc anticyclone centered over NY and New England with mostly sunny skies by the afternoon and light winds. Max temps will be seasonable with 50s to around 60F in a few locations. Another chilly night is expected with ideal radiational cooling conditions once again with mostly clear skies/light to calm winds with lows falling into the mid 20s to lower 30s. Not much change with the sensible weather to close the weekend with the H500 ridge over the lower MS River Valley folding over into the Northeast, and the sfc high very slowly drifting south and east of the forecast area heading into Sunday night. Temps rise slightly above normal to close the weekend in the 50s to lower 60s across the forecast area.

The mid and upper level flow becomes more zonal aloft to start the week, as the H500 ridge is slightly surpressed to the south and east. Some patchy valley fog may develop Mon morning with the sfc anticyclone south/southeast of the region. Low temps look more seasonable. A mositure-starved cold front approaches Mon with limited low-level moisture. Some of the deterministic guidance and ensembles have some light showers impacting the western Mohawk Valley and western Adirondacks late Mon, but have maintained a dry forecast based on the NBM for now. The cold front brings a reinforcing shot of cold advection, as a Canadian surface high builds in again for Tue-Wed with temps near to slightly below normal and continued dry conditions. The next best chance of showers may not occur until late Thu into Fri with a northern stream systems warm and cold fronts approaching from the southwest/west based on some of the medium range deterministic/ensemble/NBM guidance. Precipitation looks light with this system.

Aviation

Through 00Z/Sunday, VFR conditions are expected, with just a period of high-level clouds late tonight into early Saturday morning. Light/variable winds are expected through the next 24 hours, with a period of calm winds at many TAF sites later tonight into Saturday morning.

Outlook...

Saturday Night to Wednesday: No Operational Impact. NO SIG WX.