textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. An unsettled pattern continues over the weekend with daily chances for showers and storms, mostly in the mountains.

2. Low pressure tracks near New England Monday likely bringing widespread rainfall through Monday night.

3. Drying trend Tuesday into Wednesday, while pattern likely remains unsettled through the end of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A 500mb low, currently centered to our north, will gradually move eastward into the Canadian Maritimes tonight and Saturday. Broad cyclonic flow and embedded shortwaves from this low will keep the weather pattern unsettled through the weekend, bringing daily chances for showers and storms with small hail possible in some of the storms.

Highest chances will be in and around the mountains with low-level upslope flow, but high Froude numbers suggest a few showers/storms could make it downwind this afternoon and again during the day Saturday while also bringing periods of mostly cloudy skies. In addition to this, a better defined shortwave will cross through the area tonight into Saturday morning, likely providing a boost in shower activity in the mountains but possibly bringing a few to areas south as well.

Similar to today, wind gusts of 25 to 35 mph are likely again during the day Saturday but this time more out of the northwest. High temperatures will be in the 70s on Saturday, except 60s in the mountains due to more cloud cover.

For Sunday, areas south of the mountains may see more coverage of showers and storms with model forecast soundings depicting more instability to work with. The potential for severe storms is low with not much shear...but not zero. CAPE approaching 1000 J/kg suggest the possibility of hail and/or gusty winds.

KEY MESSAGE 2 DESCRIPTION... Ensembles continue to suggest that widespread rainfall will be likely Monday afternoon into Tuesday morning while there continues to be a large variability in amounts. Latest spread in the interquartile range is around 1.0 inches. The source of this spread is tied to the strength and track of low pressure emerging out of the Ohio Valley and this will be tied to how well southern stream energy merges with an upper low over SE Canada. The deterministic GFS and RRFS keep the upper level features separated enough that the bulk of rainfall misses south while several GEFS members bring an axis of at least moderate rainfall across the area. The majority of other models show better phasing and an organized area of low pressure tracking across New England. The latest NBM brings PoPs 75 to 90 percent starting Monday afternoon through Monday night with QPF amounts of 0.5 to 1.5 inches north to south. The primary potential impact from this system will be heavier rainfall amounts with a plume of PWATs approaching 2 inches to the south and some ensemble members bringing upwards of 2.5 to 3.0 inches of rain. Winds do look to be an issue with this system and most model solutions keep the warm sector south of the area limiting the threat for any severe convection. Steady rain will end Tuesday morning with showers lingering into the afternoon, mainly in the mountains.

KEY MESSAGE 3 DESCRIPTION...

High pressure builds in Tuesday night into Wednesday for mostly fair weather. Wednesday looks to be the best weather day of the week with mostly sunny skies and highs ranging from mid 70s north to mid 80s south with comfortable humidity levels. Daily chances for showers return Thursday and persist through the end of next week with broad troughing over the Great Lakes to Northeast.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through OOZ Sunday...Mainly VFR with brief instances of MVFR cigs and visibilities at HIE and LEB with scattered showers or an isolated storm. Can't rule out a brief shower elsewhere, but chances are too low for TAF inclusion. Breezy W/WNW winds continue to gust 25-30kt through around 00Z this evening, but these will then diminish as the night goes on. For winds Saturday, gusts out of the west to northwest are expected to be around 25 kt, possibly up to 30 kt on occasion.

Outlook:

Saturday night: Mainly VFR, except MVFR ceilings and visibilities possible at HIE with -SHRA.

Sunday: Mainly VFR. However, scattered showers and isolated storms during the afternoon could produce TEMPO MVFR to IFR restrictions.

Monday-Tuesday: Low pressure may bring more widespread IFR and rain showers, centered on Monday afternoon through Tuesday morning.

Wednesday: Mainly VFR.

MARINE

SCA conditions continue over portions of the nearshore waters into parts of Saturday, mainly due to seas. Southwest winds may occasionally gust 20-25 kt through tonight and again out of the west closer to the coast on Saturday. Winds and seas remain below SCA levels for Saturday night and Sunday.

An area of low pressure may develop near coastal New England Monday bringing the potential for at least SCAs Monday night. High pressure builds in late Tuesday into Wednesday allowing winds and seas to stay below SCA thresholds.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 2 PM EDT Saturday for ANZ150. Small Craft Advisory until 10 AM EDT Saturday for ANZ152.