textproduct: Gray - Portland

WHAT HAS CHANGED

Active pattern will bring at least two systems across the region from late Friday through Monday morning. While rain will be the dominant precipitation type south of the foothills, model solutions have trended colder with more available moisture. Chances for accumulating snow have increased for Sunday into Monday system with impacts possible to both commutes.

KEY MESSAGES

1. A cold front cross tonight bringing scattered snow showers followed by a wave of low pressure crossing Friday afternoon into Saturday morning. A few inches of snow in the mountains could bring some slick travel in the mountains Friday evening.

2. Active weather continues Sunday into next week with multiple chances for widespread precipitation. The system Sunday into Monday could bring accumulating snowfall to much of the region. Amounts are uncertain, but impacts to the Monday morning and evening commutes are possible.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Onshore flow ahead of a cold front had produced a localized band of ocean effect snow in the vicinity of Sagadahoc and Kennebec Counties for much of the morning. Latest radar trends show this band is weakening while surface temperatures have warmed to near or above freezing. Therefore, little in the way of additional snow accumulations are expected with this feature. As the cold front crosses overnight there will be chances for scattered snow showers, mainly in the mountains.

Friday will start off mostly dry with partly to mostly sunny skies. Clouds will quickly increase west to east Friday morning as a wave of low pressure tracks east out the Great Lakes. This low will track across the forecast area Friday night and quickly exits Saturday morning. Temperatures will rise into the 30s north of the mountains and into the 40s south of the mountains before precipitation begins Friday afternoon. Precipitation will likely be rain along and south of the foothills through Friday night. However, some dynamic cooling may allow for rain to change to snow across portions of Androscoggin, Kennebec, and northern Waldo Counties that could bring some slick travel Friday evening. In the mountains and points north precipitation will likely stay all snow with a couple inches possible down to the valley floors and several inches above 2500 feet. Dry air aloft will work into the DGZ Friday night that may allow for patchy freezing drizzle across the mountains and north into Saturday morning while confidence is not high enough to put this in the gridded forecast. Drier air arrives Saturday allowing for clearing skies.

KEY MESSAGE 2 DESCRIPTION...

Global models show a busy 500mb wave pattern from Saturday night into next week with a quick progression of shortwaves and ridges crossing through the Northeast.

The next system of interest is Sunday into Monday with a strong signal in the ensemble guidance for widespread precipitation as low pressure crosses the Great Lakes and heads for New England. There's still timing discrepancies in onset/end times and does have potential to be longer duration, so the NBM PoPs covering a larger time window of 40-70% seem reasonable.

For Sunday, precipitation type favors snow in and around the mountains with both rain and snow possible to the south, but colder air working in as winds turn more north to northeast could change this to all snow later in the day into Sunday night and Monday. Depending on the track of the low it's possible somewhere will see a period of sleet or freezing rain as well. While it's too early to pinpoint amounts, there's increasing potential for accumulating snowfall as ensemble means for QPF are on the order of 0.25" to 0.75". We'll see how models trend in the coming days, but impacts to both Monday commutes are on the table, especially the morning.

Based on latest guidance, precipitation should come to an end Monday night with shortwave ridging building in for Tuesday bringing mostly dry conditions.

Another wave brings a chance for lighter precipitation Tuesday night or Wednesday followed by with what looks to be a wetter system and a better chance for widespread precipitation approaching the region around next Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Through 18Z Friday: Mainly VFR through Friday morning. The exception will be occasional MVFR at KAUG and KRKD.

OUTLOOK: Friday Afternoon through Saturday...Snow north and rain south overspreads the area bringing MVFR to IFR into Saturday morning. Skies clear through the day with conditions returning to VFR.

Saturday night: MVFR possible with -SN.

Sunday-Monday: IFR is looking more likely with a chance for widespread precipitation. Mostly snow is favored across the north, and precip could be a rain/snow mix possible to the south before a change to snow. There may also be a period of PL/FZRA, but confidence is low on details.

Monday night and Tuesday: Return to VFR Monday night with mostly VFR Tuesday, except MVFR possible at HIE.

MARINE

Winds and seas remain below SCA thresholds through Friday morning. Southerly flow increases ahead of an area of low pressure Friday afternoon shifting to the northwest Saturday morning. SCA conditions will exist from Friday afternoon through Saturday.

SCA conditions are possible from Sunday into Tuesday as low pressure crosses New England and then lifts into the Canadian Maritimes. There remains uncertainty in the track and timing of the low, and a period of gales can't completely be ruled out. The pattern remains active toward the middle and and later parts of next week with a couple of additional potentially bringing more increased winds and seas.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 5 PM Friday to 8 PM EDT Saturday for ANZ150-152-154.