Marine Weather and Tide Forecast for Topsham, ME

KEY MESSAGES
1. Above normal temperatures continue through midweek across all of New Hampshire and western Maine, especially Wednesday when forecast highs are mainly in the 40s.

2. A weak disturbance will lead to increasing light precipitation chances tonight. Snow is likely over the mountains, portions of the foothills, and central New Hampshire while mainly rain is expected across the Interior, coastal Maine, and southern New Hampshire.

3. Low pressure brings a mix of rain and snow to the area Wednesday evening into Thursday. Amounts will be light, but slick travel is possible across northern NH and the western ME mountains, where precipitation type is expected to be mostly snow.

4. Below normal temperatures likely Friday through early next week with multiple chances for light snow, but significant precipitation and impacts are not expected at this time. Winds chills below zero are possible for much of the area early Friday morning.

DISCUSSION
KEY MESSAGE 1 DESCRIPTION...

A ridge axis will continue to move across the region today and we transition back into southwest flow aloft by later this afternoon or this evening. This pattern will continue leading to above normal temperatures for this time of year through midweek. Today's highs will mainly range from the lower 30s to the lower 40s. Lows tonight will range from mid 20s to the mid 30s. Wednesday should then be the warmest day of the forecast period as we remain in persistent southerly flow at the surface and aloft. Nearly everyone outside of the mountains should see highs in the 40s.

KEY MESSAGE 2 DESCRIPTION...

As a mean longwave trough to our west continues to slowly nudge closer, a surface low will deepen near the border of southern Ontario/Quebec this evening. A cold front will extend to the southwest of this low, a surface trough to the south, and a warm front will be draped to the east southeast. The initial push of broad precipitation this evening will likely be associated with the warm front as it lifts north across New Hampshire and western Maine.
CAMs then suggest we could see a little bit more precipitation as the surface trough moves through, but this activity appears to be more spotty as the best upper forcing support moves out to the north. Snow will be the most likely precipitation type across the mountains and into portions of the foothills/central New Hampshire.
Rain will be most likely across the Interior, coastal Maine, and southern New Hampshire. The fringes of these regions may see a rain/snow mix at times. All that said, precipitation amounts tonight appear fairly light with liquid QPF amounts likely only maxing out around a few hundredths of an inch or so. A fresh dusting of snow to an inch or two will be possible over the higher terrain.

As the initial shortwave moves off into the Canadian Maritimes, the mean longwave trough continues to push east. We could see a few showers lingering through the day on Wednesday but the stronger wave will not approach until late in the day.

KEY MESSAGE 3 DESCRIPTION...

An upper-low approaches and crosses the Great Lakes Wednesday night into Thursday while a surface low develops and lifts northward across Maine. Precipitation is likely across most of the area beginning Wednesday evening and continuing through the first part of Thursday as lift increases from the approach of the upper low and WAA. Temperature profiles support mostly snow across northern NH and the western ME mountains (where slippery travel is possible) and mostly rain to the south, although snow could mix in at times Wednesday night. As the surface low begins to lift into northern ME on Thursday, the westerly flow on the backside will begin pulling in drier and colder air, but it's possible that there is a switch to snow from the foothills southward before precipitation tapers off Thursday afternoon.
Across the mountains, snow may last into Thursday evening with total snow accumulations of a few inches possible.

Winds become breezy in the afternoon and evening with gusts of 20-30 mph as temps continue to fall. This will bring an extra chill to the air with wind chills in the single digits possible by Thursday evening.

KEY MESSAGE 4 DESCRIPTION...

Colder and drier air continues to spill into the area Thursday night and into Friday morning with winds remaining breezy. Based on the latest wind and temperature forecast, winds chills look to be below zero for much of the area to start out Friday morning and possibly in the -10F to -20F range in the mountains. Winds will ease going into the afternoon as high pressure begins to build overhead to relax the gradient, but highs will be limited to 20s for much of the area and even 10s in the mountains.

Weak disturbances will bring a low chance of snow showers (20%)
Friday night and Saturday, but most will stay dry during this time.
For the rest of the weekend and into early next week, longwave troughing will engulf the eastern half of the CONUS favoring below normal temperatures. Even colder air may be lurking just beyond the forecast period toward the middle of next week. This longwave troughing also keeps the weather pattern active with several shortwaves crossing through the region, bringing multiple chances for snowfall. However, most of the ensemble guidance favors light amounts with little to no signal for significant precipitation at this time. Also, it's difficult to time these shortwaves, and the broad brush low PoPs of 20-30% from the NBM probably reflect the uncertainty in that.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
Through 18Z Wednesday...VFR conditions are generally expected at all terminals through this afternoon with some lower VFR ceilings at HIE and LEB. The next precipitation maker approaches this evening which could lead to some more MVFR to IFR conditions in snow showers across the mountains (mainly impacting HIE and possibly LEB). Outside of the mountains, precipitation will mainly be rain or a rain/snow mix. A brief MVFR visibility restriction is not out of the question.
Restrictions could linger in the mountains through the day on Wednesday. Finally, some enhanced low-level wind shear will be possible tonight with the best chances mainly over New Hampshire terminals.

Outlook:

Wednesday night and Thursday: MVFR to IFR restrictions possible.
HIE and LEB expected to see light snow while other terminals are expected to see mostly rain, possibly mixed with light snow at times. Winds may gusts up to 25 kt out of the west Thursday afternoon and evening.

Thursday night through Saturday: Mostly VFR, but a low (20%) chance of snow showers Fri night into Saturday may cause brief restrictions.

Saturday night and Sunday: Light snow with IFR to MVFR restrictions possible.

MARINE
Today-Wednesday...After a brief break, SCA conditions return tonight as low pressure crosses through the Gulf of Maine. SCA conditions will then continue through the day on Wednesday, likely lingering into the evening.

Thurs-Tues...SCA conditions appear likely Wednesday night and Thursday as low pressure lifts northward across Maine and deepens as it approaches the Canadian Maritimes by Thursday night. The west to southwest flow may see gusts to gale force late Thursday into Thursday night. SCA conditions continue into Friday but may briefly fall below criteria as high pressure briefly builds in. Additional periods of SCA conditions are likely over the weekend into early next week as multiple low pressures/fronts approach and cross through New England.

GYX WATCHES/WARNINGS/ADVISORIES
ME...None.
NH...None.
MARINE...Small Craft Advisory until 10 PM EST Wednesday for ANZ150-152- 154.
Small Craft Advisory from 10 PM this evening to 1 PM EST Wednesday for ANZ151-153.