textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to the forecast at this time.

KEY MESSAGES

1. A weak front passes through tonight with some showers and storms, and a continued gradual transition to drier and cooler conditions following behind the front.

2. Troughing will allow for a cooler 2nd half of the week. Showers and storms are likely on Thursday and/or Friday. High astro tides are expected, but impacts should remain minimal.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A weak area of low pressure tracks through Quebec tonight, bringing a weak cold front through the region. Showers and storms reach into northwestern locations late this afternoon and evening ahead of the front. The best chance for these will be closer to the Canadian border and the low pressure center, with gradually more scattered activity further south and toward the coast. A stronger gusty storm can't be ruled out through northern New Hampshire early this evening, but otherwise the convection is expect to weaken and decay as it moves eastward through the late evening and into the overnight hours.

Any lingering showers are expected to move offshore by dawn tomorrow, with clearing conditions to follow. Areas that do see some rain this evening stand the chance to see some patchy fog develop by morning, with the best chance being through the northern valleys.

Mainly sunny skies are expected south of the mountains tomorrow, with a few more clouds and some isolated pop up showers through the higher terrain. The airmass continues to slowly and incrementally cool with each passing front, yielding highs in the mid 70s across the north, to mid 80s along the coast and through southern NH tomorrow. Dew points will also fall back into the 50s to low 60s, keeping the airmass much more comfortable overall.

With the drier airmass, low temperatures fall into the 50s tomorrow night in most spots, with some upper 40s possible across the northern valleys. Lows around 60 degrees are more likely through southern New Hampshire where some mid to high level clouds keep temps a little warmer most of the night.

KEY MESSAGE 2 DESCRIPTION...

A broad mid-level trough will engulf the northeast by Wednesday morning. The trough should allow for cooler, more average temperatures to emerge over the 2nd half of the week. Probabilistic ensemble guidance has been a bit cooler than the most recent run of the NBM. Opted to nudge high temperatures down on Wed/Thurs by 2-3F. It should be fairly difficult for any location in the area to exceed 85F Wedensday through Friday. Temperatures should stay cooler through the upcoming weekend.

Regarding precipitation, low pressure looks to move across the region at some point Thursday or Friday. Guidance is in agreement that a trough axis swings into the area and will likely strengthen with upper-level jet stream dynamics as it exits the northeast. During its passage, rain, thunderstorms are likely and could be more widespread. However, there will not be much moisture for the storm. PWATs look to be in the range of 1.1-1.5 inches - which is quite dry with low pressure overhead. With this in mind, rainfall amounts don't look like anything special nor impactful.

In addition, we will need to keep an eye on the high tides for Thursday. Astronomical tides are high for the month, and the tide gauges will be close to reaching minor flood stage. Light offshore winds and very low wave heights should prevent gauges CASM1 (Portland) and HPMN3 (Hampton) from reaching minor flood stage. Impacts should be minimal, but some high water along the coast is likely.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Mainly VFR prevails into the evening, with brief restrictions possible in showers and a thunderstorm this evening at HIE, LEB, AUG, and RKD. A shower can't be ruled out at all other terminals. Valley fog is then likely after midnight at LEB and HIE, and possible at RKD should a shower move through in the evening. VFR prevails tomorrow, then valley fog is possible and LEB and HIE again Tuesday night.

Outlook:

Wednesday: VFR expected.

Thursday-Friday: At least MVFR restrictions are likely due to trough axis bringing rain and thunderstorms. Conditions improve to VFR after the aforementioned trough axis exits the area.

Saturday: VFR expected.

MARINE

A weak front crosses the waters tonight, with a slight chance of a thunderstorm near the coast late this evening to shortly after midnight. Broad high pressure then gradually builds in on Tuesday, keeping fair conditions ongoing through at least Tuesday night. Winds and seas will largely remain below SCA criteria through the week as a series of generally weak cold fronts cross the waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.