textproduct: Gray - Portland

SYNOPSIS

Some lingering light snow continues as our winter storm departs into the Atlantic. In its wake we are left with a white Christmas but also some bitterly cold temperatures on the way. A cold front will cross the region on Christmas Day and aside from some light snow or snow showers much colder weather will be on the way for Friday. Temperatures will remain in the teens for most areas and with a steady breeze will feel even colder than that. The next storm looks most likely to miss our area to the south, but some light snow is possible over far southern New Hampshire Saturday. Then a more robust winter storms sets its sights on New England Sunday night into Monday. While this storm does not appear likely to remain all snow this time, significant travel disruptions are likely given the high volume of holiday travelers.

NEAR TERM /THROUGH TONIGHT/

Light snow comes to an end this afternoon as low pressure slides southeastward out the Gulf of Maine. A gusty north wind eases this evening as the low pressure departs.

Temperatures fall into the teens through the evening, but then increasing clouds put a cap on how far temps fall tonight. Clouds increase from the northwest as a weak area of low pressure moves through Quebec and into northern Maine. With this low, an Arctic front moves southeastward overnight, with snow showers moving into northwestern areas after midnight. These snow showers likely reach into most areas outside of southern New Hampshire by daybreak tomorrow. Snowfall will remain light from this system, but will provide a festive ambiance for Christmas morning for much of Maine, as well as central and northern New Hampshire. With Rudolph leading the way, Santa will have no trouble traveling tonight in the clouds and snow showers.

SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/

Light snow continues to spread southward through the morning hours. Coatings are likely in most areas, but 1-2 inches will be possible across the higher terrain, as well as through central Maine and into the MidCoast. In these areas, some slick travel is possible from the light snowfall.

The Arctic front pushes offshore during the afternoon hours. Breezy conditions follow the front late tomorrow afternoon through the overnight, with gusts to around 30 mph. Temperatures also fall quickly through the evening, bringing very cold wind chills overnight. Lows drop into the single digits along the coast and south, with winds chills in the -0s to -10s. Negative single digits are expected across the north, with wind chills in the -10s to low - 20s possible in spots.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

Overview: Near to below normal temps continue thru the extended. Bitterly cold Fri/Sat. Messy winter storm possible Sun night into Mon with travel impacts anticipated.

Key Messages:

-Well below normal temps expected Fri and remaining colder than normal Sat. Fri morning wind chills will be below zero and only climb into the teens and single digits during the day.

-Signal continues for widespread wintry precip Sun night into Mon. At the end of the holiday weekend that could bring significant travel impacts if it were to occur.

Forecast Details: Largely did not stray too far from the NBM guidance with it having a fair handle on any ensemble signal for anomalous weather.

One such signal is for well below normal temps Fri and through warming up slightly Sat...still below normal. Fri however is a good candidate for temps even in the warmest locations to struggle to 20 degrees. While not windy...a steady breeze will make it feel more like the single digits in most locations.

Fri into Sat a shortwave trof diving thru the Northeast will bring some light snow to parts of the region. However strong high pressure anchored to the north means the likelihood is that this passes mainly to our south. Some light snow may brush southern NH...but it is hard to tease much more out of the available ensemble guidance. Cluster analysis shows that stronger the shortwave the more likely it is to dive farther south...and even the weaker members do not give much in the way of accumulation.

Most of the focus is on the Sun into Mon storm system. Current ensemble forecast systems feature a closed or nearly-closed 500 mb low tracking north of the Great Lakes with no real confluence present ahead of it across Quebec or the Canadian Maritimes. This sort of set up then favors a warmer storm with little to hold the cold air in place besides the inertia of cold air. So with the expectation that at least low to mid levels aloft warm up...I have added mixed precip to the forecast for this window. I am not confident on any given ptype in the forecast...but there is a chance for a mix to occur...along with some light snow even in the warmest scenarios. The main concern will be timing...especially regarding Sun...as return holiday travel could be impacted. So this is the period to keep the closest eye on in the extended.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Short Term...Lingering MVFR conditions gradually improve to VFR this evening, except at HIE where MVFR ceilings likely linger in upslope flow through Thursday night. A period of MVFR ceilings and light snow is possible across Maine terminals and HIE Friday morning and early afternoon. VFR then returns by late tomorrow afternoon, with northerly wind gusts around 25 kt Thursday afternoon and night.

Long Term...VFR conditions to start the period on Fri. Some light snow may skirt southern NH on Sat...and it is possible that MHT could see VIS reduced as a result. Confidence is low...but if it were to snow some areas of IFR are possible. VFR conditions return to the entire area until late Sun when the next storm moves in. Widespread IFR or lower conditions are expected. The lower confidence part of the forecast is precip type. All precip types are possible. At this time the most likely scenario is for snow initially changing to a mix or rain by Mon midday.

MARINE

Short Term...SCA conditions linger through Thursday afternoon as low pressure moves out into the Atlantic. A cold front approaches late tonight, crossing the waters Thursday afternoon. Northerly gales develop behind the front across the outer waters, and persist through Thursday night. Moderate freezing spray is likely across the Bays, central waters, and eastern waters Thursday night.

Long Term...As high pressure builds in winds and seas will continue to diminish...falling below SCA thresholds Fri night. As a warm front crosses the waters Sun night...winds and seas will increase with increasing southerly winds Mon. SCA conditions are possible Mon early...and then gales possible late Mon into Tue as winds shift to offshore.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning from 4 PM Thursday to 10 AM EST Friday for ANZ150- 152-154. Freezing Spray Advisory from 10 PM Thursday to 10 AM EST Friday for ANZ150>153. Small Craft Advisory until 4 PM EST this afternoon for ANZ151- 153.