textproduct: Gray - Portland

WHAT HAS CHANGED

Trends for the late week system continue downward and more toward a low impact system with significant snowfall amounts confined to the higher elevations.

KEY MESSAGES

1. A late week coastal storm remains possible with rain and/or snow, but potential impacts remain uncertain. Confidence is high in below normal temperatures and precipitation through the first part of the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Upslope rain/snow showers will continue through tonight and potentially linger through tomorrow morning as a cold front sinks into the area. Weak low pressure riding along that front is going to clip our area which will allow for shower activity to expand outside of the mountains, but likely not to a high degree. Froude numbers from the RAP and GFS suggest mostly critical flow overnight which would keep precipitation falling closer to the foothills.

Attention then turns to the late week period as low pressure jogs East with a deep trough emerging off the East Coast, south of Long Island, on Thursday night. Any impacts to our area are going to come from development of a secondary low on Friday also developing south of Long Island and here is where models continue to diverge as the GFS and GEFS ensemble members continue to have the secondary low get swept into the Gulf of Maine, but even so QPF and thusly snow amounts have trended down in this scenario. The Euro and Canadian (and their ensembles) continue to suggest a flatter wave where the secondary low gets swept out to sea with little fanfare. Even the RRFS, which keep in mind this system is at the tail end of its window, is seemingly taking the side of the latter. With all that being said confidence in exact track and rain/snow amounts is still uncertain. However, based on the trends I have seen the past couple days I have growing confidence that this is going to be a low impact event. Significant accumulating snow outside of the mountains is looking increasingly less likely, but just about everyone still has a good chance of seeing their first flakes of the season (they may just melt on contact). As for the higher terrain a couple inches of snow is not out of the question, but again an out to sea track puts this at jeopardy as well.

Below average temperatures arrive with the aforementioned system, and remain in its wake. Upslope showers likely linger through Sunday, but high pressure building in early next week is going to trend it drier everywhere.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday: VFR expected at all terminals overnight with the exception of HIE as upslope showers keep ceilings MVFR there. VFR then continues through the day Wednesday, with HIE also likely to stay mainly MVFR.

Outlook... Wednesday night-Thursday: Ceilings thicken and lower Wednesday night with MVFR becoming more widespread heading into Thursday. Moderate confidence.

Friday-Saturday: Widespread MVFR/IFR ceiling and visibility restrictions are possible as a potential system brings rain and snow to the area. Low confidence in MVFR/IFR visibility. Moderate confidence in MVFR/IFR ceilings.

Sunday: Improving to VFR south of the mountains. HIE and LEB potentially stay MVFR. Moderate confidence.

MARINE

A passing disturbance will bring a brief period of low end SCA northwesterly wind gusts and seas to coastal waters overnight. This should subside by the morning with sub-SCA conditions than taking hold at least through the day Thursday. Thursday through the weekend is likely to see pretty rough conditions with wind gusts nearing gales as low pressure crosses in the vicinity of the Gulf of Maine. Exact track of this system is uncertain, but at least SCA conditions are likely. High pressure then begins to build in to the area early next week which is going to return sub-SCA conditions to the waters

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 10 PM this evening to 10 AM EST Wednesday for ANZ150-152-154.