textproduct: Gray - Portland

SYNOPSIS

Strong southerly winds and showers continue before a strong cold front crosses the region through this evening. This will shift winds to the west...with strong gusty winds continuing tonight with temperatures sharply falling with wind chills approaching zero degrees. Winds will diminish quickly on Saturday with seasonable temperatures. A weak system will cross north of the area Saturday night, but only light snow or snow showers are expected. Another clipper is then possible by Tuesday.

NEAR TERM /THROUGH TONIGHT/

Key Messages:

- Strong to damaging southerly winds from now through 6pm.

- Turning sharply colder tonight with gusty northwest winds and wind chills falling to around 0F.

- Standing water will freeze with pockets of slick travel likely.

Primary change this afternoon was to add more zones into the longer-lasting wind advisory for areas in the foothills with strong downslope northwesterly winds expected into tonight. Otherwise...headlines look good as strongest winds are arriving attm.

Details: Winds are quickly increasing towards their peak as of this writing as 975mb low rides north and east across Quebec north of the region with peak LLJ (J9 winds 75-90kts...3kft GYX VWP winds 65kts) now overhead. Band of moderate rain associated with moisture plume in WAA regime continues to lift north and east with the ankle-deep cold air in interior western ME finally giving way to temps 50F+. Cold front will sweep east through the afternoon and evening hours with rain becoming more showery and temperatures beginning a rapid descent. Power outages have been limited thus far to mainly northern NH...but expect more issues between now and 5-6pm as the strongest winds move overhead.

Tonight...the focus will shift to plunging temps and gusty WNW winds. T8s fall roughly 20C through this evening which should allow for continued strong mixing overnight. Gusts over 40 mph are expected in the overnight advisory area while it will remain blustery everywhere. Overnight lows fall to the teens in the mountains and lower 20s to the south as winter roars back into the region. Wind chills will fall to within a few degrees either size of zero by daybreak.

Temperatures look to fall below freezing between 8pm and midnight with a flash freeze causing any standing water to freeze resulting in slick travel for the overnight. Will continue to message this in the afternoon Hazardous Weather Outlook.

SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/

Key Messages:

- Winds rapidly diminish with cooler (albeit seasonal) temperatures.

- Clouds arrive late Saturday and Saturday night with southwesterly winds strengthening in association with a passing warm front. Details: Rapid height rises continue through the morning with coldest air aloft here at daybreak...with a WAA regime developing during the day as the H8 ridge crests overhead. This should bring winds down quickly and while the morning hours will be chilly...daytime highs in the mid/upper 20s in the mountains and the mid/upper 30s to the south will be pretty seasonable albeit 20F cooler than today.

A fast-moving northern stream shortwave drops southeast towards the area Saturday night with a surface warm front pushing across the region. The primary sensible weather impacts will be 1) increasing clouds with the potential for a few snow showers near the international border and 2) increasing southwesterly winds...especially over the terrain and across the waters. With the clouds and mixing...temperatures will be warmer than Friday night...with lows in the teens from the mountains north and in the 20s to the south.

LONG TERM /SUNDAY THROUGH FRIDAY/

A weak clipper system will continue to move through the region on Sunday with a 995-1000 mb surface low forecast to be centered over south central Quebec in the morning. A cold front will trail this low to the south southwest and it will move west to east across New England through the day as the low moves off into the Canadian Maritimes. Moisture amounts will be limited for this clipper but we should still see widespread low chances (~20 to 30 percent) for mainly light snow. We will maybe see some slightly better chances over the higher terrain (40 to 50 percent), especially as the wind shifts more westerly and we see more of an upslope component later in the day.

Behind the front, guidance suggests we will see some modest pressure rises, decent cold air advection, and steep low level lapse rates. Thus, we are likely to mix down at least a portion of the velocities at the top of the mixed layer during the day, which soundings suggest top out in the 35 to 45 knot range. While it remains unclear just how much will mix down, Sunday certainly appears to be windy. Sunday should also see some above normal temperatures, especially over southeast New Hampshire and coastal/interior Maine given compressional warming ahead of the front. Highs are forecast to range from the upper 20s and lower 30s north, to the mid/upper 30s across the foothills and interior, to the lower 40s over southeast New Hampshire and coastal Maine.

Sunday night will be fairly chilly behind the front as lows dip into the lower single digits above zero north, to the mid to upper teens south. It will likely stay fairly breezy through the night so wind chills may bottom out close to 10 below zero north, to the single digits above across the south. Monday should mainly be dry as high pressure moves into the region with below normal highs ranging from the lower teens north to the upper 20s and lower 30s south. That being said, we may see the usual snow showers stick around in the mountains given upslope westerly flow.

A ridge axis crosses the region Monday night and then the next progressive clipper/shortwave moves into the area on Tuesday. This clipper should have a little more moisture to work with but amounts will still be fairly light. Given the forecast temperatures, most of this precipitation should be in the form of snow but some rain or a mix or rain/snow will be possible along the coast. The best chances for a few inches of snow will be over the higher terrain but we could see enough widespread light snow for most in the forecast area to see a White Christmas. Highs will be a bit warmer on Tuesday, ranging from the low to mid 20s north to the mid to upper 30s south. The bulk of the precipitation should move out by Tuesday evening but snow showers will likely continue into Wednesday over the mountains in northwest upslope flow.

We should mainly dry out by Wedensday evening (Christmas Eve), which should help Santa's travel across New England overnight. As of now, it appears the dry weather will continue for Christmas Day with slightly warmer temperatures. The next shortwave then approaches Christmas night into Friday which brings our next widespread precipitation chances but details remain unclear a week out. At an early glance it looks very similar to the progressive clippers we will see earlier in the week.

AVIATION /18Z FRIDAY THROUGH TUESDAY/

Short Term...A wide range of conditions across the terminals...with much of ME still in LIFR/IFR....SE NH in IFR/MVFR and LEB VFR with occasional restrictions at HIE. Strong southerly winds with continued LLWS /2kft winds to 60kts from the south/ will continue until frontal passage from 20-23Z with winds then shifting west...but continuing to be gusty /20G30-35kts/ for the overnight as conditions rapidly improve to VFR. VFR with quickly diminishing winds on Saturday. Winds begin to increase Saturday night from the southwest with lower mid and upper level clouds...but continued VFR conditions.

Long Term...A period of MVFR conditions are possible on Sunday across northern terminals as a period of light snow is possible. VFR conditions return on Monday, with another system possibly bringing more restrictions late Tuesday.

MARINE

Short Term...Storms on the waters continue into this evening with peak winds arriving over the next 1-2 hours. These will have to be transitioned to gales this evening before winds quickly slacken on Saturday with SCAs continuing as waves slowly subside. Strengthening southwesterly winds Saturday night associated with low pressure passing north of the area will likely bring a renewed round of gale force wind gusts... especially over the outer waters.

Long Term...At least SCA conditions in westerly flow are possible Sunday as an Alberta clipper tracks north of the waters. Northwesterly gales are then possible behind the front on Monday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Wind Advisory until 8 AM EST Saturday for MEZ007>009-012>014- 033. Wind Advisory until 7 PM EST this evening for MEZ018>021-023. High Wind Warning until 7 PM EST this evening for MEZ022- 024>028. NH...Wind Advisory until 8 AM EST Saturday for NHZ001>006. Wind Advisory until 7 PM EST this evening for NHZ007>015. MARINE...Storm Warning until 7 PM EST this evening for ANZ150>154.