textproduct: Gray - Portland

WHAT HAS CHANGED

Maintained visibility reduction due to fog for much of interior southern Maine through mid evening. Significant uncertainty remains regarding the system Sunday night and Monday, but the latest model runs have trended more offshore resulting in a drier trend in the NBM.

KEY MESSAGES

1. Temperatures turn sharply colder across the forecast area tonight. Increasing winds Friday morning will make for a brisk commute with wind chill values in the single digits above and below zero. Cover exposed skin to avoid frostbite amid the much cooler temperatures.

2. Snow moves through the area Saturday afternoon through Saturday evening. Rates and accumulations look light, with a rain/snow mix possible along the coast. Some slick travel is likely where light accumulations do occur.

3. We continue to closely monitor trends for Sunday night into Monday as a signal for a coastal storm still exists, but higher than normal uncertainty remains between model solutions. Otherwise, below normal temperatures through much of next week along with an active weather pattern will continue to provide chances for snow.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Low pressure makes its way into eastern Maine this evening, deepening as it enters the Canadian Maritimes Friday. Behind the exiting triple point and associated cold front, temperatures plunge tonight. Overnight lows may be some 30 degrees cooler by the time many are heading out the door for the morning commute. This would equate to teens across much of the interior and central/southern NH, with single digits across the western Maine mountains and northern New Hampshire. Values along the coast won't be spared either and temps fall towards the lower 20s and upper teens.

Winds will also be increasing tonight, further decreasing what temps feel like Friday morning. Aloft, strong 100+ kt upper and mid jets usher the low off to the north, but a tight pressure gradient near the surface will quicken background winds and gusts into Friday morning. Overnight winds remain 5 to 10 mph, but gusts may rapidly increase upon sunrise, 20 to 30 mph. Frequency of these gusts will be most notable across SE NH in proximity to growing low level wind field. Morning wind chills will have fallen to the single digits above and below zero through mid morning. Wind chill values may remain below zero for much of the daytime hours as well as temps struggle to make it out of the single digits.

KEY MESSAGE 2 DESCRIPTION... A trough begins digging into the central U.S. on Saturday which supports southwest flow over the Northeast. This pushes temperatures slightly above normal, climbing into the mid-to upper 30s in the southern half of the CWA. This will be important as low pressure approaches from the Great Lakes Region in the afternoon breaking out precipitation across the area. These marginal temperatures in the south mean much of the area may start as rain or at least a rain/snow mix at onset. For the northern half, temperatures aren't expected to rise above freezing, so snow is expected to be dominant there. However, there is some question how far north precipitation may spread. Temperatures do fall below freezing heading into the evening, so just about everyone should see some snowflakes before precipitation comes to an end Saturday night. This trough is strongly positively tilted so QPF is going to be lacking, but a coating of snow across much of the area is certainly in the cards.

KEY MESSAGE 3 DESCRIPTION... Model trends have not been a snow lovers friend in regards to the system in the Sunday night-Monday timeframe. Global ensemble suites continue to have little support for it, keeping the low well offshore. Still, some accumulating snow for the coastal plain is possible as we get clipped, but current probabilities of greater than 3" are only in the 20-30% range. The 12Z GFS is coming in as I'm writing this and even that has trended toward a swing and a miss, and closer to what the deterministic Euro has been advertising. It is something we will continue to monitor as unusually high uncertainty remains, but it seems as though models are starting to hone in on a drier solution.

Below normal temperatures return for next week as our weather pattern remains on the active side. Models suggest that clippers from the Great Lakes Region continue to traverse the area along with several upper level waves traversing the broad trough. There isn't a signal for anything impactful at the moment, and midweek looks mostly dry as high pressure noses into the region, but some chances for snow showers are in the forecast late week.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

LIFR to IFR vis and ceilings remain across most interior southern ME terminals. Fog has been slow to thin here, and will likely remain for a couple more hours into this afternoon. Gradual improvement to VFR is expected by mid to late evening with a W wind shift. Elsewhere, VFR onset is sooner as low stratus lifts south to north. HIE hangs on to low ceilings for much of the night and through Fri AM. W winds tonight increase, with some gusts to 20 kt before dawn. Expect gusts to increase further Friday morning after sunrise, 20 to 25 kt.

Outlook:

Friday night: VFR becoming MVFR/IFR cigs as clouds thicken/lower. Light SN possible late.

Saturday: IFR in light snow showers for most terminals. PSM, PWM, and RKD may stay MVFR if rain or a rain/snow mix remains the dominant precipitation type.

Saturday Night: Gradual improvement from IFR to MVFR overnight as precipitation wraps up and ceilings begin to lift.

Sunday: Ceilings may lift to VFR for a time on Sunday, but would quickly return to MVFR as another system moves into the region.

Sunday Night: MVFR for most terminals with IFR visibility restrictions possible in snow.

Monday: Conditions improve to VFR at most terminals. HIE may experience persistent MVFR.

Monday Night: VFR prevails at all terminals.

Tuesday: VFR prevails at all terminals.

MARINE

Exiting low pressure will bring increasing winds across the waters this evening and overnight. Gale conditions arrive after midnight tonight for the outer waters with bays/harbors increasing to around 30 kt tonight. Winds begin to subside Friday afternoon as low pres pulls away.

There won't be much of a reprieve from SCA conditions as seas stay around 5 ft through the day Sunday. Winds then ramp up with frequent gusts 25kt+ by Monday afternoon. These elevated wind gusts then continue through the end of the long term forecast period.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning from 3 AM to 4 PM EST Friday for ANZ150-152-154. Small Craft Advisory from 7 PM this evening to 4 PM EST Friday for ANZ151-153.