textproduct: Gray - Portland

WHAT HAS CHANGED

Minor update to increase PoPs in the mountains based on latest radar trends showing continued snow shower activity.

KEY MESSAGES

1. There are a couple chances for snow showers early in the forecast period, but otherwise mostly dry weather continues into midweek with temperatures trending slightly above normal.

2. The pattern in the extended forecast period supports active weather with generally zonal flow and the suggestion of some shortwaves crossing the area. One or two widespread precipitation events are possible, but models are waffling so the details are still uncertain.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... An upper low tracks southeastward through northern Maine this evening dragging a cold front with it. This front looks like it is going to be moisture starved, but increasing northwesterly flow could get some showers going in the Western Maine Mountains. CAMs have been honing in on this, as well as the potential for them to be briefly heavy. With the lack of moisture and front being on the weaker side I don't expect them to rise to the level of squalls, but wouldn't be surprised to see some quick bursts of heavier snow from them as they go along down through Central Maine.

Northwesterly flow may keep light snow showers going in the mountains, but the aforementioned snow shower activity should come to an end shortly after midnight. Skies clear overnight and mostly sunny conditions should prevail through the day Sunday. The airmass behind the front is a little cooler, but full sun should allow temperatures to warm into the upper 20s and mid-30s. Low pressure deepens off the coast of Nova Scotia which may make for some breezy conditions in Central Maine, but the gustier winds look to stay over the waters. Clouds begin to build in Sunday evening as strong low pressure is set to cross to our southeast. There has been a notable trend northward in the guidance with this, but not enough to raise any concerns. I only say this to justify keeping isolated snow showers in southern New Hampshire Sunday night as a sharp shortwave should provide sufficient forcing if we end up with some of the moisture from it. A weak wave may bring some light snow Monday night as well. Otherwise, the majority of the area stays dry into midweek with temperatures trending above normal (potentially topping out in the low to mid 40s across much of the area Tuesday!).

KEY MESSAGE 2 DESCRIPTION... There are two time frames of interest in the extended forecast period: Wednesday night into Thursday, and Friday night into Saturday. For the first one, low pressure looks to ride a stationary boundary across the northern CONUS and make a run at the northeast. However, there is some suggestion that the frontal boundary is more progressive in the northeast which would slide the low pressure and the accompanying precipitation to the south. The problem is that the deterministic model runs have been taking turns with each solution and ending up in complete disagreement. Looking at the ensembles for guidance isn't much clearer as the spread in low locations is still large, but there has been some consistent clustering in the Northeast in the Euro suite and the 500mb pattern is certainly supportive so I am leaning toward a hit. Then the question becomes what we could see out of it, and that is where the low pressure location becomes important again. High pressure to the north is going to provide a feed of cold air so snow seems like the best bet for the northern half of the CWA, but depending on where the low tracks we could see rain or a mix introduced somewhere in the southern half. Keep an eye on the forecast as details should become clearer over the next couple of days.

For the late week time frame, I will just say that it looks active, but there is even more uncertainty as models are showing two completely different synoptic patterns. Currently the Euro and Canadian favor a coastal storm, while the GFS has a similar set up to midweek. Until there is some sort of agreement, this is really only worth the acknowledgement for planning purposes.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through 00Z Monday...VFR prevails at all terminals through tomorrow with 20kt wind gusts possible at RKD.

Outlook...

Sunday night: Ceilings thicken and lower, with MVFR possible at HIE and LEB as well as light snow showers possible at all New Hampshire terminals.

Monday: MVFR to start trending toward VFR for the afternoon. Ceilings than return to MVFR monday night as a disturbance moves through that will bring a chance of light snow for most terminals.

Tuesday: Ceilings trend back to VFR for Tuesday, except that HIE may stay MVFR.

Wednesday-Thursday: Confidence is low at the moment, but another disturbance may cross Wednesday night into Thursday that would bring a mix of rain and snow as well as a mix of ceiling conditions.

MARINE

Mostly sub-SCA conditions across the waters through Sunday with northwesterly winds. The exception will be in the waters south of Penobscot bay where deepening low pressure off the coast of Nova Scotia may allow for gusts 25-30kts. Winds than shift around easterly by daybreak Monday.

Winds are expected to stay below SCA criteria through Thursday, but a system passing out to sea Tuesday builds seas 4-6 ft. Elevated seas potentially linger through Thursday depending on the track of another disturbance midweek.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 1 AM to 1 PM EST Sunday for ANZ150.