Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
158 FXUS61 KGYX 061922 AFDGYX Area Forecast Discussion National Weather Service Gray ME 322 PM EDT Sun Sep 6 2026 .WHAT HAS CHANGED... Kept isolated showers for this afternoon across southern New Hampshire and central Maine. Otherwise, low impact weather continues into midweek. && .KEY MESSAGES... 1. Isolated showers remain possible through this afternoon, with drier conditions expected Monday and Tuesday. 2. A seasonably strong low pressure will cross the St. Lawrence Valley Wednesday into Thursday. Thunderstorms will be possible ahead of the trailing cold front Wednesday, and gusty northwesterly winds will be possible behind it Thursday. && .DISCUSSION... KEY MESSAGE 1 DESCRIPTION... Low level moisture in proximity to the broad low pressure over Nova Scotia will continue to produce isolated showers this afternoon. This is being helped by daytime instability, and these should dissipate as insolation decreases early this evening. Pressure gradient remains tonight, and this will keep a gentle breeze in the region. Did opt to lower overnight lows in most common radiational cooling locations as these should be more sheltered at the surface. This means some mid 40s for the northern valleys and SW NH. It will again be breezy Monday, this time with less moisture and a drier airmass to mix to the surface. Its possible dewpoints will need to be lowered further, which could result in RH values in the mid to upper 30s. KEY MESSAGE 2 DESCRIPTION... Ensemble guidance continues to place a sub-1000 mb MSLP low pressure moving thru Quebec north of the Gaspe Peninsula Wed into Thu. Precip will largely be centered around the trailing cold front in the form of showers and thunderstorms. The latest guidance has trended slower timing-wise and less favorable for widespread thunderstorm activity locally. Ahead of the front southwest winds will be breezy, owing to a modest LLJ of 40-50 knots along the coast. Forecast soundings continue to look pretty stable throughout the day, so I am not expecting significant gusts from that LLJ. It will also advect in higher moisture, and dewpoints may be able to climb towards 60 degrees across southern NH. It is possible that this may be enough for some nominal instability across interior zones, enough to support some thunder threat continuing into the evening. CSU machine learning guidance does continue to show parts of the Connecticut River Valley and mtns with a small risk of severe thunderstorms, but as the current frontal timing stands I think that is unlikely. The precip itself will be showery in nature along the cold front. So I do not anticipate widespread significant rainfall. This is yet another high Pop/low QPF type event, which is more or less what the NBM is forecasting at this time. Finally once the front crosses the area, winds shift to northwesterly as cold air advection commences. On Thu as mixing heights increase that will lead to a gusty day. Forecast soundings over much of the area continue to indicate that gusts around 30 mph are likely. However a few spots may push 40 mph across southern NH and coastal western Maine. Once that cooler airmass settles into the region, Fri night and Sat night may be chilly across many spots. Some widespread 40s are likely, and a the northern valley cold spots may be flirting with upper 30s. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Through 18z Monday...SHRA continue for central ME terminals (AUG/RKD/IWI), while N winds gust up to 20 kts. Some showers may boost winds to 30 kts briefly. SHRA decrease this evening, with valley fog developing. A light breeze may stave this off from more shallow valleys. VFR Mon with gusts again up to 20 kt from the NW. Outlook: Tuesday: VFR conditions expected. Wednesday: Local MVFR or lower conditions possible in showers and thunderstorms, especially overnight. LLWS possible near the coast. Thursday: Becoming VFR. Northwest wind gusts at or above 25 kt possible. Friday-Saturday: VFR conditions expected. && .MARINE... Below SCA conditions expected early this week as cyclonic flow weakens from departing low pressure over Nova Scotia. SCA conditions still looking possible for all waters Wed evening and overnight as southwest winds increase. NBM does have some patches of 34 kt gusts, but I think it will be too stable for gale force gusts unless the LLJ can increase in strength on modeling. Seas are expected to build above 5 ft, especially northeast of Jeffreys Ledge, with some 7 ft seas southeast of MISM1. As those slowly diminish Thu that may prolong SCA conditions thru much of the day. Winds and seas below SCA thresholds are expected Fri into the weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ DISCUSSION...Cornwell/Legro AVIATION...Cornwell/Legro MARINE...Cornwell/Legro