textproduct: Gray - Portland

WHAT HAS CHANGED

A Gale Watch has been issued for the outer waters from Cape Elizabeth northward and includes Penobscot Bay tomorrow night through Friday.

KEY MESSAGES

1. Low pressure brings light rain at lower elevations and accumulating snow, mainly above 2500 feet, tonight into Thursday. Colder air arrives Thursday afternoon that may allow for light accumulations of snow to northern valley floors. 2. Snow lifts north through the forecast area Saturday with light accumulations possible from the coast to the mountains. Locations with cooler daytime temperatures, like the foothills and mountains, may experience more slick spots than the coast.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Current surface analysis places an area of low pressure across Quebec with a cold front draped southwestward through the eastern Great Lakes. Broad southwest flow has allowed temperatures to rise into the upper 30s north of the mountains and mid to upper 40s south of the mountains. A short wave swinging across Michigan will lead to a wave of low pressure forming along the cold front and will track across northern New England tonight. Temperatures are expected to remain above freezing at lower elevations across the entire area this evening when precipitation breaks out. Mainly light rain is expected tonight as the best forcing for ascent moves over the area, while areas above 2500 feet will see potential for a few inches of accumulating snow. Warm and moist air moving over the snowpack tonight will also likely lead to fog development.

Drier air aloft will move in Thursday morning allowing for rain to taper off south of the mountains, while valley rain and mountain snow continues across northern NH and western Maine Mountains. As low pressure moves north of the area tomorrow afternoon, colder air will work in that will allow for rain showers to change to snow showers down to the valley floors. Generally less than an inch is expected within northern valleys that could create some slick travel.

KEY MESSAGE 2 DESCRIPTION... Low pressure pivoting over the northern Great Lakes Friday night will help advect moisture and moderating temperatures into the region Saturday. With a strong mid/upper level jet overhead, there will be some convergence at the surface to produce light precipitation through Saturday evening. Absent any nearby pressure system however, do not anticipate significant QPF.

With no warm nose aloft, precip type seems clear cut at rain/snow. Snow is more confident across the interior, foothills, and mountains, but sfc temps warm enough to support rain at the coast. However, with dewpoints falling into the upper 20s, have reason to believe flakes would be the result all the way to the coast. Accumulation may be hampered here, especially on treated surfaces, thus the chance for travel impacts lies to the north across the foothills and mountains. Barring any significant change in disturbance progression and change to QPF, a dusting to two inches seems like a likely range at this time.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through Thursday...Clouds thicken and lower through 00Z with light rain and fog likely tonight resulting in widespread IFR to LIFR conditions. Low cigs likely continue IFR to MVFR from 12Z to 18Z Thursday with conditions improving south to north Thursday afternoon. The exception will be KHIE where low cigs and SHRA changing to SHSN will likely continue at least MVFR through Thursday evening.

Outlook:

Thursday night: Mainly VFR with west winds gusting to 25 kts. KHIE may continue to see MVFR cigs with 30 percent chances for snow showers. Friday and Friday Night: VFR. No sig wx. W winds gusting around 20 kts during the day. Saturday: Becoming MVFR with light SN arriving south to north. SN tapers off in the evening. Saturday Night: MVFR with some IFR cigs. Sunday: VFR. No sig wx. Sunday Night and Monday: Uncertainty regarding passing low pressure could bring SN with vis restrictions or only some lowered cigs.

MARINE

Through Friday... Seas will continue a downward trend through this evening. Conditions will remain below SCA thresholds tonight through Thursday. A frontal system crosses the waters Thursday night bringing the potential for westerly Gales through Friday.

Conditions slowly trend toward SCA into Friday evening as winds become SW. Wave heights remain 5 to 7 ft through Saturday, with 3 to 5 ft waves by Saturday night. Will keep an eye on the potential for low pressure to track into the Gulf of Maine in the Sunday night/Monday time period...but confidence is low on the exact track.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ150- 152-154. Gale Watch from 1 AM EST Friday through Friday afternoon for ANZ150>152-154.