textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast update.

KEY MESSAGES

1. A series of fronts bring widespread showers and maybe a few thunderstorms late Thursday and Friday.

2. Dry weather and lower humidity returns for the weekend. Chances for showers and warmer temperatures return early next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Surface ridging continues to nose into the area today. Valley fog will begin to lift with daytime heating, but otherwise it is expected to be dry this afternoon. While the center of surface high pressure is forecast to be south of the region, it will exert its influence locally. Temps should radiate nicely overnight, which given the pattern of late the NBM guidance is picking up on. The upper ridge will also slip east of the area sometime this evening, and allow return flow to begin. This may make marine fog/stratus a little more widespread overnight, but southwest winds may also keep that banked more towards the Downeast coastline than the Midcoast.

A stray shower can't be ruled out Thursday morning as a warm front lifts through New England, with moisture increasing through the daytime. The best chance is over New Hampshire as Maine looks to remain on the periphery of high pressure departing to the east. High temperatures climb into the low 80s just about everywhere, with dewpoints in the mid-60s making it feel somewhat sticky.

The first of two cold fronts attempts to make a pass Thursday night. which will increase PoPs for the western half of the CWA, with lesser chances further east. Scattered showers and storms decrease in coverage through the evening, but will remain possible through the overnight hours still. Areas of fog and drizzle will be likely as the first front fails to bring a change of airmasses. It will take a second front during the day on Friday to usher in a cooler and drier airmass late in the day and Friday night. With the front's approach and passage, scattered showers and storms will be possible again during the day on Friday, with the best chance across the higher terrain and western areas.

KEY MESSAGE 2 DESCRIPTION... The timing of the front's progression came in a little faster on this evening's models runs, hedging towards cooler and drier air arriving early enough to drop lows into the 40s and 50s by Saturday morning. Drier air continues moving in on Saturday with high pressure building in at the surface. This makes for a mostly sunny and mostly dry weekend with high temperatures in the mid-70s to low 80s and dewpoints in the 50s across much of the area.

Global models suggest at least one upper low moves through Quebec Sunday making its closest pass Sunday night which may drag a front through the region early next week. There is still plenty of uncertainty among the global models on exactly how this plays out, but I think the chance PoPs from the NBM are fair. A warming trend then looks likely early next week as the high pressure center moves off the East Coast and ridging builds into the Northeast.

AVIATION /09Z WEDNESDAY THROUGH SUNDAY/

As of 6AM, patchy fog has started to form across NH and western Maine. While LIFR restrictions are ongiong/expected through sunrise at LEB, fog is not be as prevalent and it is unlikely other TAF sites will see the same type of fog. High pressure is expected to move overhead and will lead to VFR conditions everywhere through the rest of the day. Ahead of a frontal passage Thursday morning, there will likely be even less fog, though some patchy fog still can not be ruled out near LEB, HIE, and RKD.

Outlook:

Wednesday night: VFR conditions expected. Local IFR or lower in valley fog, including LEB and HIE.

Thursday: Morning valley fog possible, then generally VFR conditions expected.

Thursday night-Friday: Generally MVFR conditions expected with widespread showers. IFR conditions possible in fog at night.

Saturday-Monday: Mainly VFR conditions prevails, with nighttime valley fog likely at at least HIE and LEB.

MARINE

Winds and seas are expected to remain below SCA thresholds through the morning. Until the upper trough can cross the Gulf of Maine, there will be areas of marine fog/stratus that form, especially at night, but with winds generally southwesterly much of that may remain Downeast. A period of near SCA conditions are possible in southerly flow ahead of a cold front on Thursday into Thursday night. Marine fog will be possible Thursday night and Friday. High pressure then builds across the waters for the weekend, bringing an extended period of fair conditions into early next week.

GYX WATCHES/WARNINGS/ADVISORIES

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