textproduct: Gray - Portland

SYNOPSIS

A white Christmas is looking more likely for much of the area as a system moving through Tuesday brings the potential for accumulating snowfall. The downside is that this may impact some of the late holiday travelers. Somewhat quieter and seasonable weather then returns for Christmas Eve and Christmas Day. Another system is then possible towards the end of next week.

NEAR TERM /THROUGH TONIGHT/

An Alberta Clipper will continue to track north of the forecast area through the afternoon as a trailing cold front moves out over the waters. Given a tight pressure gradient, cold air advection, and steep low-level lapse rates, winds will remain gusty (20 to 30 mph) through the afternoon out of the northwest behind the front. A few lingering upslope snow showers will remain possible across the mountains but we should start to see this activity diminish in the evening and nighttime hours as an upper ridge starts to nudge in.

It will become quite chilly tonight as we clear out a bit outside of the mountains. Lows will generally range from the lower single digits across the north, to the mid to upper teens south. Additionally, the pressure gradient remains tight through the night so northwest winds will remain gusty, leading to some frigid wind chills ranging from around 10 below zero over the far north, to around 10 above across southern New Hampshire and coastal Maine.

SHORT TERM /MONDAY THROUGH MONDAY NIGHT/

Monday will remain cold but the wind should be gradually diminishing through the day with dry conditions as high pressure moves into the region. Highs are mainly forecast to range from the lower teens north, to the upper 20s and lower 30s south.

The next clipper begins it's approach Monday night, flattening the upper ridge as it comes. In the late night hours we will see at least some low light snow chances return to New Hampshire before increasing and spreading east on Tuesday. Overnight lows are forecast to range from the single digits above zero north, to the mod to upper teens south.

LONG TERM /TUESDAY THROUGH SUNDAY/

Pattern Overview: The pattern remains fairly active through the long term as a ridge builds in the western U.S., with a trough just off the East Coast. Several disturbances rotate through this trough, the first of which looks to bring a great chance for a white Christmas to those areas that lost their snow on Friday. Beyond that chances for precipitation continue, but there is no strong signal for anything overly impactful at this time. Impacts and Key Messages: *Accumulating snow may bring some impacts to holiday travel on Tuesday Details: Tuesday: Confidence is increasing in at least a few inches of accumulating snow Tuesday as a low pressure rides along a stationary boundary draped over the Northeast. This low is then strengthened by a sharp shortwave trough digging into the region as it moves southeastward Tuesday night. Forecast soundings show a deep DGZ bisected by Omega values -0.5 to near -1. This suggests rates won't be all that high, but may be moderate, and with the entirety of the column falling well below the freezing mark, this snow likely ends up on the fluffier side which will help boost accumulations as well. Probabilities of greater than 3 inches are increasing with the latest Euro and GFS ensemble suites giving 40-60 percent chances across much of the northern half of New Hampshire and Maine. Southern New Hampshire and far southern Maine may end up on the lower end of snowfall totals depending on the low track. The higher end of snowfall totals may be found on the Maine coastal plain as guidance has been suggesting that the low pressure continues to deepen as it moves off the coast and forms an inverted trough that would help to enhance snowfall for a localized area. The global models have been targeting the Midcoast, but they have also been bullish on amounts. The 12Z NAM has the footprint for higher amounts also on the Midcoast, but topping out around 5 inches. With all that being said the NBM tried to be heavy handed with the QPF in that area, but I'm not ready to go all in yet with plenty of uncertainty still present among ensemble members. I lowered it to get a solid middle ground solution that agrees with the messaging I'm going for here of a potential advisory level event in that footprint of higher totals on the southern Main coastal plain, but low confidence that anyone sees warning level snowfall. The earlier you can travel the better as the timing favors the late evening and overnight for the more moderate snowfall rates. Christmas Eve and Christmas: Snow tapers off and skies clear Wednesday as low pressure continues moving off to the east. High pressure builds in at the surface Wednesday night giving Santa great travel weather as he makes his way to us. Northwesterly flow brings in some clouds and colder air with temperatures dropping into the teens across the area. Christmas day looks pleasant as high pressure remains nosed into the area. Southern New Hampshire and the coastal plain look to see temperatures climb into the mid- to upper 30s, with upper 20s and low 30s to the north. Continued northwesterly floe won't allow skies to clear much, and mostly cloudy skies Thursday night keep temperatures in the low to mid 20s in the south and in the mid- to upper teens north. Friday-Sunday: Broad troughing continues into the weekend with a chance for a clipper bringing light snow and rain, and then models try to hint at a more organized system late in the period, but at this point they have no real agreement in much of anything regarding its evolution.

AVIATION /18Z SUNDAY THROUGH THURSDAY/

Short Term...Mainly VFR conditions are expected through Monday night, with the possible exception being at KHIE this afternoon and tonight due to the potential for some MVFR ceilings and a passing snow shower. Low snow chances and MVFR ceilings will then be on the increase late Monday night as the next clipper approaches. West winds will generally prevail in 10 to 15 kt range, gusting to 25 kts.

Long Term...Tuesday looks to start MVFR as ceilings lower ahead of a disturbance moving into the area. Light snow begins to overspread the region Tuesday night which will begin to bring about some IFR restrictions at terminals. During the overnight period is when snowfall rates will peak with coastal terminals susceptible to a period of LIFR or lower conditions. Conditions then quickly return to VFR Wedensday morning which will then prevail through the day Thursday. There is a chance for another clipper system to bring some light snow and rain showers to the area Thursday night and Friday and thusly may bring about some MVFR or lower restrictions as well.

MARINE

Short Term...West to northwest gales are expected through tonight outside of the bays before slowly diminishing on Tuesday. Seas of 6 to 10 ft are expected outside of the bays with 1 to 4 ft waves in the bays.

Long Term...Winds and seas build above SCA criteria early Wednesday morning on the backside of the system moving through Tuesday/Tuesday night. They fall below Wednesday night with the potential for SCA conditions to return at the beginning of the weekend as a another system passes through.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning until 7 AM EST Monday for ANZ150-152-154. Small Craft Advisory until 7 AM EST Monday for ANZ151-153.