textproduct: Gray - Portland

WHAT HAS CHANGED

Very little has changed in the near/short term portion of the forecast (Thursday though Friday). Any light snow should be finished by the morning commute today. We'll get a reprieve from the cold air too as most lower elevations get to 35 to 40F.

Increased snow chances early next week as north trend in low pressure continues to hold.

KEY MESSAGES

1. A cold front will approach from the west today. A few snow showers and squalls may make for local slippery conditions during the late morning and afternoon hours, especially across northern NH eastward into central ME.

2. An Arctic blast will bring dangerously cold weather to the region this weekend. Sub-zero wind chills begin Friday night and last through the day Saturday. It will still feel below zero come Sunday morning despite lighter winds. Frostbite and hypothermia can onset quickly at these temperatures for anyone with exposed skin or inadequate shelter.

3. Low pressure exiting the Mid-Atlantic coast will bring accumulating snow to the region. The highest totals are most likely in the southern half of the forecast area, with all snow expected. Those with travel plans Sunday night through Monday should continue to follow the forecast and plan for slick conditions.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION: Despite a relatively warm day, a cold front will quickly approach from the west today, spreading snow showers and a few squalls across western zones by about noon, spreading eastward during the afternoon and evening hours. Slippery spots will be possible. The threat will gradually wane during this evening.

Some light snow or snow showers may accompany arctic front passage on Friday.

KEY MESSAGE 2 DESCRIPTION: Broad and strong high pressure pushes into the Upper Midwest and Great Lakes Friday night. Northern New England will be squarely downstream of a frigid airmass advecting across continental Canada into the weekend. While temperatures will be decreasing, winds will be increasing as the pressure gradient between the aforementioned high pressure and low pressure over the Canadian Maritimes tightens.

The combination of cold temperatures and winds will create a period of dangerously low temperatures for the forecast area. Of main concern will be northern NH and the western ME mountains where Friday night winds chills plummet to 30 to 40 below zero. Here, frostbite can occur in as little as 10 minutes for exposed skin. Elsewhere, values fall to the teens and 20s below zero when factoring in wind. Frequent gusts of 20 to 30 mph are likely overnight.

While these cold conditions look to bottom out Friday night/Saturday morning, wind chill values remain below zero through the daytime Saturday. Daytime high temperatures in the single digits above and below zero are likely for the area. Winds lighten as the day goes on and pressure gradient relaxes, but the cold air mass settles nearby Saturday night. What we lose in winds in proximity to the high, we gain in potential radiational cooling for cloud-free portions of the area. Right now, there is uncertainty exactly how much cloud cover there may be, but do expect a consecutive night of temperatures below zero for the entire forecast area.

KEY MESSAGE 3 DESCRIPTION: Recent guidance trend has to bring a quick but strong area of low pressure through the TN Valley Sunday before consolidating off the Mid-Atlantic coast Sunday night into Monday. This track, which has trended northward quickly over the past 24 hours, presents a snowy outcome for the forecast area into the beginning of next week.

Amid a cold air mass, an all snow outcome is fairly certain barring any continued northward shifts. Will be monitoring forcing, how long precipitation is present, and any additional shifts in the low's track to hone in on forecast totals. At this range, swings and shifts are not uncommon.

Will want to watch timing of sharp trough arriving through the Midwest Sunday evening. This could orient mid level jet coupling to further deepen the parent low as jet strengthens across the Mid-South. With a lot of strong features (high and low) to materialize over the CONUS over the next 48 hours, shifts in thoughts are likely, but accumulating snow is a likely outcome.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Through 06Z Friday...Conditions improve to VFR after 12Z today if not well before. Winds gusts pick up this afternoon and evening with most terminals seeing gusts 20-25kts. VFR largely prevails after 12Z today, but briefly heavy snow showers or squalls may impact some terminals later this morning and afternoon. evening. These would bring about quick wind changes and IFR visibilities.

Outlook...

Friday: Widespread VFR, with local MVFR possible at HIE. A few heavy snow showers or squalls may bring brief IFR conditions.

Friday Night: Widespread VFR, with local MVFR possible at HIE. WNW gusts 15 to 25 kt.

Saturday: VFR prevails at all terminals. WNW gusts 15 to 20 kt.

Sunday and Sunday night: SN likely, MVFR to IFR, potential LIFR vis at southern terminals.

Monday: IFR/MVFR in SN.

MARINE

SCA conditions continue across the bays through Friday, and westerly gales are likely from this afternoon through Friday.

Gale force westerly winds will continue Friday night through Saturday morning. Moderate to heavy freezing spray Fri night into Sat AM. Winds slacken to SCA levels during the day Saturday, with winds shifting to northerlies into Sunday. SCA winds continue through early next week. Seas of 5-8ft expected on Friday and Saturday, lowering to 2-4ft by Sunday morning.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Extreme Cold Watch from late Friday night through Saturday morning for MEZ007>009. NH...Extreme Cold Watch from late Friday night through Saturday morning for NHZ001>003-005. MARINE...Small Craft Advisory until 7 AM EST this morning for ANZ150- 152. Gale Warning from 3 PM this afternoon to 7 AM EST Saturday for ANZ150-152. Small Craft Advisory until 7 AM EST Friday for ANZ151-153-154. Gale Watch from Friday afternoon through Saturday morning for ANZ154.