textproduct: Gray - Portland

WHAT HAS CHANGED

Seas have dropped below 5 feet and have cancelled the remaining Small Craft Advisory. Otherwise minor tweaks to PoPs through today based on latest hi res guidance.

KEY MESSAGES

1. An unsettled pattern continues over the weekend with daily chances for showers and storms, mostly in the mountains. Gusty NW winds today up to 30 MPH.

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

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Much of the latest model suite continues the idea of mean troughing over New England this weekend with occasional weak short wave trough passages. This will keep things variably cloudy, especially during the afternoons with shower chances, especially on Sunday.

Today, deep NWLY cyclonic flow will continue with the best chances of showers and perhaps a storm in the mountains. Downsloping winds to the east and southeast of the mountains will tend to keep lower elevations dry with gusty winds around 30 MPH. Highs will only be in the 60s in the mountain zones but downsloping flow toward lower elevations will aid in highs reaching well into the 70s.

On Sunday yet another weak short wave will pass across the area. 500mb temps will lower to about -18 C which is pretty cold for this time of year. This coupled with an increase in low level dewpoint values will aid in SBCAPE values 1000+ J/KG by early Sunday afternoon. Weak forcing in this environment will be supportive of scattered thunderstorms pretty much anywhere from about noon onward. With the cold air aloft and steep low level lapse rates in place, we can't rule out a few strong wind gusts and perhaps some small hail in the strongest storms. Highs will be well into the 70s to around 80 in some spots.

KEY MESSAGE 2 DESCRIPTION... Monday, low pressure looks to emerge from the Ohio Valley and enter southern New England. As mentioned previously, there remains a wide a spread of solutions regarding speed and positioning, which impacts forecast rainfall amounts and how quickly rain exits Tuesday.

Dynamics are largely driven by an incoming trough from the northern Great Lakes meeting with southern stream jet and moisture. These two parties are forecast to eventually phase east of the CONUS, so it's effects on NH/ME will be leading up to that event. The upper jet that will be draped across NY and New England to Nova Scotia isn't that impressive, think dynamics will largely be driven by how well the LLJ and eventual surface low progress.

NBM IQR spread has actually increased in value and area since this morning's guidance, with two main camps. The first, populated with a bulk of Euro and Canadian solutions, is slower and further along in developing a surface low into New England than the second camp. This results in better lift amid a moist environment and thus greater precipitation values (over an inch) into the southern half of NH and far southern ME. The second camp is largely GEFS with some Canadian support, but delays deepening of the surface low with a flatter, more progressive system. This keeps amounts greater than an inch to the south.

Given an unimpressive EFI/shift of tails signal, limited upper level support, and instability values remaining to the south in both camps, think rainfall amounts greater than an inch are most likely across southernmost zones in NH to the immediate southern ME coast.

While the bulk of precipitation pushes east by Tuesday afternoon, gradient flow and remaining low level moisture may still be enough to bring about scattered showers Tues, and then additional showers north of the foothills Wednesday. Would think the maturing low and increasing NW winds should bring about some dry air to limit shower efficiency, but this window could be short lived as zonal flow to the west looks to keep some semblance of a moisture feed to the East Coast through Midweek.

AVIATION /14Z SATURDAY THROUGH WEDNESDAY/

Through Sunday...Mainly VFR with instances of MVFR cigs and visibilities at HIE and LEB with scattered showers or an isolated storm today. Breezy W/WNW winds continue to gust 25-30kt today. Lighter winds are expected Sunday but showers and thunderstorms may be a bit more numerous. Localized brief lower conditions will be possible in these along with some small hail and gusty SFC winds.

Outlook:

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

Wednesday: A trend towards VFR likely, but some SHRA still possible NW of the mountains.

MARINE

Seas have dropped below 5 feet this morning. Southwest winds may occasionally gust 20-25 kt out of the west nearshore today. Winds and seas remain below SCA levels for tonight 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...None.