textproduct: Gray - Portland

WHAT HAS CHANGED

Models are coming into closer agreement with winter weather across northern New England tomorrow. Increased snowfall amounts to accommodate these changes, and Tuesday evening's commute could be slick in southern NH.

KEY MESSAGES

1. A weak system brings measurable snowfall and perhaps a snow squall to the area on Tuesday.

2. Starting Wednesday, it will mainly be dry through the rest of the work week with a warming trend expected into the weekend. The next widespread chance for precipitation comes Friday night into Saturday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A late season Alberta Clipper moves in from the northwest. This clipper in particular is unique - it looks to have more convective characteristics. Usually earlier in the winter, Alberta Clippers tend to be more stratiform in nature. This difference will be crucial as it moves across New England. The low looks to undergo secondary cyclogenesis as it passes over Vermont and New Hampshire. This will do two things: First, it will allow for colder, below freezing air to remain over the thermal column with most precipitation likely staying snow over the area. Secondly, it will redevelop over the Gulf of Maine, keeping its more dominant slug of precipitation out of northern New England.

So while this transition is occuring, some pockets of sunshine may poke out across locations south of the mountains. This should create some modest wintertime low-level instability, creating the opportunity for snow squalls early Tuesday evening. Snow squalls may cause slick travel across southern NH during the Tuesday evening commute. Snow squalls will start to fall apart with sunset and some snow showers may not even make it to the coast. Skies will be quick to clear up after the snow tapers off.

Within these couple rounds of snow squalls, I am expecting about 1-2 inches of snow, mostly accumulating on grassy surfaces. A localized total or two of 3 inches of snow can't be ruled out across the southern 2/3rds of New Hampshire, especially if squalls track over the same areas.

KEY MESSAGE 2 DESCRIPTION...

High pressure and upper ridging dominates the weather pattern Wednesday before the next longwave trough starts to approach the region and we transition back into southwest flow aloft to end the work week. While specifics are still unclear this far out, it looks like we will see the next chances for widespread (but low impact) precipitation Friday night into Saturday. Most guidance then has us drying out on Sunday before the next precipitation chances arrive for the beginning of the next work week.

The warmup begins in earnest on Wednesday with highs in the upper 30s and lower 40s north, to the low to mid 40s across coastal/interior Maine, and to the mid to upper 40s over southern New Hampshire. Afternoon dewpoints are also likely to mix out fairly well on Wednesday so we will end up fairly dry with widespread minimum relative humidity values in the 20 to 30 percent range. The driest conditions will generally be over portions of central and southern New Hampshire. The one good thing is that winds will be fairly light. By Friday highs are forecast to range from the mid 50s north, to 60s south. While NBM spread increases into next week, it does appear that above to well above normal temperatures should generally stick around.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

VFR conditions forecast thru tonight. CIGs begin to lower in the morning and are most likely to drop to MVFR across the southern half of the forecast area. Where exactly it snows hard enough to reduce VIS to IFR or lower is a little harder to pin down, but at this time southern NH into southwestern Maine is most likely. MVFR CIGs are expected thru most of the day Tue before improving.

Wednesday-Friday: VFR prevails for much of the week as we enter a period of quiet weather. HIE may begin to see MVFR become more prevalent for Friday.

Friday night: May see some expansion of MVFR ceilings outside of the mountains as rain approaches the area.

Saturday: IFR/MVFR possible under precipitation in the morning with conditions improving through the day.

MARINE

Westerly sub-SCA winds and 3-5ft seas look to continue this afternoon. A low quickly moving across the Gulf of Maine on Tuesday will allow for more variable sub-SCA level winds. Winds then shift to northwesterlies Tuesday night. Seas of 2-4ft are expected Tuesday through Wednesday morning.

By Thursday, high pressure begins to pull away and a tightening pressure gradient will see wind gusts 25-30 knots and seas 6-8 feet make a brief return. Wind gusts relax on Friday, but seas could stay elevated as low pressure returns to the region and a front crosses the waters on Saturday. Sub-SCA conditions should return Sunday as high pressure moves back over the waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.