textproduct: Gray - Portland

WHAT HAS CHANGED

Freezing fog accretion that will cause slick driving conditions will be mostly confined to the Connecticut River Valley.

A Gale Warning has been issued for Friday night for the outer waters from Cape Elizabeth northward and includes Penobscot Bay. A SCA has been issued for the remainder of the near shore waters.

The Saturday night and Sunday system continues to trend cooler.

KEY MESSAGES

1) A controlled melt is expected Friday through Saturday with above normal temperatures and Rain Showers. No flooding is expected except for some nuisance poor drainage issues.

2) A period of gusty winds accompany a passing cold front Friday night. The strongest gusts will impact the higher terrain, but some westerly gusts of 30 to 35 mph are possible from the foothills to the coast before daybreak Saturday.

3) Snow and mixed precipitation are likely to create slick travel conditions as it moves in Saturday night and lasts through the day Sunday.

4) Cold and breezy Monday, a brief warm up heading into midweek, then back to below normal temperatures late week.

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DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Southerly flow increases Friday morning that will bring temperatures above freezing by mid morning for all areas except the higher terrain and northeastern zones. Low pressure tracking through Quebec area will drag a cold front across the area Friday afternoon into Friday night. This front will mainly bring light rain to much of the area outside of the higher terrain, where some freezing rain is possible. Dewpoints are expected to surge above freezing which will lead to a melt period over the next 18 hours or so before the cold front brings drier and colder back into the area. Overall some snow- melt is expected across Southern NH and Coastal Maine, but further inland, it will be ripening event in the foothills and snowpack settling in the mountains. Rainfall amounts also look light, under a quarter of an inch for the region, will most areas outside of the mountains more around .10" Friday night.

KEY MESSAGE 2 DESCRIPTION... Low pressure passing well north of the forecast area will bring a strong cold front through Friday evening and overnight. Strengthening upper jet around 180kt will aid in further deepening of this low, with mid and low level jets responding. The latest mesoscale guidance mean brings a corridor of 55 to 65kt easterly winds at 850 mb across the area Friday night, with strong gusts expected for the Whites and the western Maine Mountains and coastal waters.

With the wind shifting and cold air advection increasing behind the front, it will be possible for low levels to remain mixed. This would mean occasional gusts of 30 to 35 mph at lower elevations after midnight. Impact wise not expected much in the way of power outages, maybe a limited threat in the sparsely populated Western Maine Mountains.

KEY MESSAGE 3 DESCRIPTION... Models are in reasonably good agreement vertically stacked low pressure occludes over the Great Lakes region Saturday night as it moves into New England. They are also in good agreement on the formation of a secondary low in the Gulf of Maine. This secondary low would act to pull in colder air from the northeast, as well as provide some additional moisture off the ocean, while warmer southwesterly flow overruns it aloft. With temperatures in the low to mid-40s expected south of the mountains expected during the day, I think southern New Hampshire and some extent of the coastal plain could see rain to start as cold air won't be penetrating that far south yet, but interior locations stand the best chance of seeing a mix from the get go. Locations north of the mountains quickly fall below freezing and likely see a mostly snow event.

All this being said, the system as a whole doesn't look that juicy. The global model ensembles and there respective AI counterparts, are progging QPF at around 0.25-0.50" with the higher amounts along the coastal plain, with the highest axis of moisture staying just offshore. As the system is starting to get in the NAM it is coming up a little shorter. This is likely because the NAM is resolving a "dry" slot Sunday morning. Dry is in quotations because forecast soundings show the coastal low puts plenty of low level moisture in place to continue with a period of drizzle. Precipitation type is still a big question mark within the mix. Forecast soundings from both the NAM and GFS are showing fairly deep cold layers that would be more indicative of sleet than freezing rain. Regardless a wintry mix is likely and have transitioned the weather grids to reflect that.

The precipitation should wrap up as snow for everybody Sunday night as the cold front pushes through. With the aforementioned QPF, and snow ratios on the higher side with colder air pouring in, ensembles are showing high probabilities of greater than 3 inches in the areas that see snow through the entirety of the event and, 30-50% probabilities for greater than an inch in areas that mix and/or start as rain. All this can change if temperature trends continue colder or start to swing back the other way, but ensemble guidance has been adamant about the stronger coastal low and thusly more abundant cold air.

KEY MESSAGE 4 DESCRIPTION: The pressure gradient tightens as the system pulls off to the northeast with forecast soundings that should be good for gusts in the 20-30 mph range. With colder air moving in on the heels of the system highs Monday only end up in the mid- to upper 20s in the north and low to mid 30s south. Factor in the windchills and its going to feel about 10 degrees colder.

Flow aloft turns southwesterly as a trough begins to dig into the central U.S., so highs on Tuesday and Wednesday stand to be on the warmer side again, but another arctic front pushes through late week bringing temperatures back below normal. This front may also have some accompanying snow, but extent is uncertain.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Through 06Z Saturday...Areas of dense freezing fog at TAF terminals, especially KLEB will lead to VLIFR conditions through 12z. IFR conditions are expected at other TAF terminals in freezing fog. Temperatures rise above freezing and increasing southerly flow will mix out any fog with conditions briefly improving to VFR mid morning into early afternoon.

Outlook:

Friday night: Clouds thicken and lower Friday afternoon with light rain. This will likely bring at least MVFR conditions.

Saturday: VFR, then restrictions and mixed precip possible by late afternoon across southern NH terminals.

Saturday night: IFR conditions in widespread snow and wintry mix

Sunday: IFR conditions in snow, wintry mix, and freezing drizzle

Sunday night: Conditions gradually improving to VFR overnight. MVFR ceilings likely hang on at HIE.

Monday: VFR at most terminals, HIE improves to VFR as well.

Monday night: VFR conditions prevail.

Tuesday: VFR conditions prevail at most terminals, MVFR ceilings possible at HIE.

MARINE

High pressure continues to slide eastward today as a cold front approaches and then crosses Friday night. Southerly winds will reach 25 kts by this afternoon and then shift SW Friday evening and increasing to Gale Force before shifting to the west after the cold front swings through the area. Winds and seas will trend downward through the day on Saturday with early morning Gales, trending to SCA, before becoming light and shifting to the north by Saturday evening.

SCA conditions return Sunday as low pressure passes through the Gulf of Maine. The continues to deepen as it moves through with westerly gales possible by Sunday night and seas 5-8ft. Gales ease Monday afternoon, but SCA conditions continue into at least Tuesday. The weather pattern stays active so marginal SCA conditions may continue through late week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning from 7 PM Friday to 7 AM EST Saturday for ANZ150- 152. Small Craft Advisory from 7 PM Friday to 7 AM EST Saturday for ANZ151-153-154.