textproduct: Gray - Portland

WHAT HAS CHANGED

Cold headlines remain unchanged going into this afternoon. A Winter Storm Watch has now been issued for all of New Hampshire and Western Maine, and snowfall amounts with Sunday night's winter storm have increased.

KEY MESSAGES

1. Snow showers and squalls will move through northern New England this afternoon, allowing for some areas of reduced visibility and locally slippery roads.

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. A significant snow storm will bring widespread accumulating snowfall to the region late Sunday through Monday. All snow is expected, which will bring hazardous travel conditions through the Monday morning commute. The greatest snowfall amounts are likely across the southern half of the forecast area.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION: A weak frontal boundary will move southeastward through the afternoon. Instability ahead of this arctic front will allow for convective snow showers to develop, with an isolated snow squall possible as well. Minimal accumulations are expected with these snow showers, but localized slick roads and reduced visibility are possible.

KEY MESSAGE 2 DESCRIPTION: 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 through the day Saturday and even into Sunday morning despite lighter winds. Frostbite and hypothermia can onset as quickly as 10 minutes at these temperatures/wind chills for anyone with exposed skin or inadequate shelter.

KEY MESSAGE 3 DESCRIPTION: Forecast confidence is continuing to increase that low pressure passing to our southeast will likely bring significant snowfall to much of the region Sunday afternoon through Monday evening. Latest ensemble based guidance is honing in on low pressure moving offshore of the Mid-Atlantic coastline early Sunday evening before tracking near Cape Cod early Monday morning and then traversing over the Gulf of ME late Monday before arriving in Nova Scotia by Monday night. Strong surface high pressure will be located over Quebec, supplying our area with cold air and this combined with the forecast track offshore will support an all snow event for the region. A sharp trof axis will also be arriving from the west Monday afternoon, placing our region within the jet entrance region, assisting in upward vertical motion. This will aide in a large precipitation shield and help to prolong the event with snow likely to fall for 24-36 hrs.

There remains some uncertainty in exact snowfall amounts as we are still 36+ hrs out but overall forecast guidance continues to trend upwards with double digit snowfall possible for many locations. Latest ensemble and AI based guidance shows greater than 70% probabilities for at least 0.50" of QPF for much of the area but probabilities for 1.00" of QPF are low and mainly confined to southeastern NH. Despite this, GEFS Cobb snow-liquid ratio (SLR) probabilities indicate SLRs could exceed 15:1 with some potential for SLRs approaching 20:1. As a result, QPF of at least 0.50" combined with these forecast SLRs will likely yield warning level snowfall and therefore expanded the winter storm watch to include all of western ME and NH.

Snow character will be dry, and given this light and fluffy consistency, power outages are not likely. Significant travel impacts can be expected though beginning Sunday afternoon/evening and persisting through at least Monday evening. Winds will increase Sunday night through Tuesday with gusts up to around 30 mph possible and this will likely result in some blowing and drifting snow.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Friday Afternoon: VFR, with localized MVFR likely due to scattered snow showers and squalls.

Friday night: VFR expected.

Saturday: VFR prevails at all terminals. WNW winds at 15-20 kts. Forecast confidence is high.

Sunday and Sunday Night: SN expected, especially late day through the night. IFR to LIFR restrictions are likely. N-NNE winds at 15-20 kts. Forecast confidence is moderate.

Monday and Monday Night: SN expected with IFR to LIFR restrictions likely through at least 00Z Tuesday. WNW winds at 15-20 kts. Forecast confidence is moderate.

Tuesday: VFR conditions likely with W winds at 15-20 kts. Forecast confidence is moderate.

Wednesday: VFR conditions with NW winds at 10-20 kts. Forecast confidence is moderate to high.

MARINE

Gale force westerly winds are expected tonight and will continue through Saturday morning. Seas of 5-8 ft are expected this evening through Saturday afternoon. Winds weaken to SCA levels Saturday afternoon and then to 10-15 kts by Sunday morning. Seas of 2-5 ft are expected Saturday night. Gale force NE winds are likely Sunday night through part of Tuesday as low pressure crosses over the Gulf of ME with seas outside of the bays at 6-12 ft. Winds and seas will then gradually diminish through the remainder of the week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Extreme Cold Warning from 1 AM to 10 AM EST Saturday for MEZ007>009-012>014-033. Winter Storm Watch from Sunday afternoon through Monday evening for MEZ007>009-012>014-018>028-033. Cold Weather Advisory from 1 AM to 10 AM EST Saturday for MEZ018>028. NH...Extreme Cold Warning from 1 AM to 10 AM EST Saturday for NHZ001>006-009. Winter Storm Watch from Sunday afternoon through Monday evening for NHZ001>015. Cold Weather Advisory from 1 AM to 10 AM EST Saturday for NHZ007-008-010>015. MARINE...Gale Warning until 7 AM EST Saturday for ANZ150-152. Heavy Freezing Spray Warning from 10 PM this evening to 11 AM EST Saturday for ANZ150>153. Small Craft Advisory until 7 AM EST Saturday for ANZ151-153. Small Craft Advisory until 1 PM EST this afternoon for ANZ154. Gale Warning until 7 AM EST Saturday for ANZ154. Freezing Spray Advisory from 10 PM this evening to 10 AM EST Sunday for ANZ154.