Marine Weather and Tide Forecast for Shelburne, VT

KEY MESSAGES
As of 233 AM EDT Friday...

1. Quieter and mild weather for today and tonight with perhaps some patchy valley fog tonight.

2. Warm and breezy weather on Saturday will give way to much cooler, blustery, and rainy conditions on Sunday. Brief mountain snow will be possible as temperatures drop well below normal.

3. Much colder but mainly dry to start next week, trending warmer with chances of rain by mid week.

DISCUSSION
As of 233 AM EDT Friday...

KEY MESSAGE 1: The frontal boundary that helped produce the showers and thunderstorms yesterday is drifting southward early this morning and will clear the region by this afternoon, replaced by high pressure nosing in from Hudson Bay and upper ridging building. A few lingering showers are expected early this morning, mostly before sunrise, then today looks like a fairly dry day overall, save the odd shower in the Connecticut River Valley. Northerly winds will increase throughout the day as cloud cover decreases. Gusts 10-20 knots are likely by the late morning and early afternoon, keeping temperatures cooler than yesterday with highs in the mid 60s to lower 70s, but still above seasonal normals under increasing sunshine. Tonight we'll see a return of overall southerly flow ahead of our next frontal system, which should keep temperatures relatively mild in the upper 30s and 40s despite partly to mostly clear skies. As we do typically see temperatures fall quickly in high pressure and clear skies, there is the potential for it to be a touch cooler than anticipated, and this may result in some patchy valley fog, but not nearly as dense and widespread as previous nights' fog and low cloud have been.

KEY MESSAGE 2: Surface low pressure over the Hudson Bay and associated upper level closed low in Ontario on Saturday will drag a cold front through northern New York and Vermont Saturday night as it moves northeastward. Ahead of this frontal passage, Saturday will feature increasing southerly to southeasterly winds, drawing warmer air into the region. Highs Saturday will reach into the 60s and lower 70s, with warmest temps across the St. Lawrence Valley where the low level jet will peak overhead winds will be more southwesterly and channel through the valley, while coolest temps will linger east of the Greens in Vermont. Widespread wind gusts are expected to reach around 15-35 knots, highest in the St. Lawrence and Champlain valleys. The cold front approaches from the west late in the day and then crosses the forecast area Saturday night into early Sunday. As such, expect we'll have a period of non-diurnal temperatures, with temperatures rising or holding steady overnight, then falling or holding steady on Sunday under strong cold air advection. Widespread showers will likewise spread from west to east along/ahead of the front, with the bulk occurring overnight Saturday night through Sunday morning. Moisture will be ample ahead of the front with PWATs approaching 1.50 inch, or near/above the 99th percentile. There could be some briefly heavy rain as the front moves through. Much drier air will follow the front, ending the bulk of the showers by early Sunday afternoon. However, some isolated to scattered activity may linger into the Sunday evening hours as a secondary front crosses the region. As mentioned above, expect temperatures to be much colder Sunday than Saturday (topping out in the 40s and lower 50s, below seasonal normals), and likely dropping in the afternoon, especially on the higher summits. Therefore, any lingering showers could mix with and/or change over to snow by late in the day, though any daytime accumulation would be limited to 2500 ft or higher.
Total rainfall will range from around 0.45 inch to around 1.10 inch in most areas, with highest amounts along the spine of the Green Mountains. Winds Sunday will become blustery out of the W/NW, only adding to the chilly, raw feel of the day.

KEY MESSAGE 3: Following a cold front on Sunday, a cooler and drier air mass will filter into the region for the start of next week with perhaps some snow shower chances early on Monday. Brisk northwest flow will draw cooler and drier Canadian air as high pressure begins to shift east out of the Great Lakes. A trailing shortwave on the backside of the departing Sunday trough will shift south on the leading edge of the high with a few chances for snow showers in the higher terrain. With 925mb temperatures Monday to -5C to -9C, sfc highs will struggle to reach 40 areawide, with the higher terrain hugging the freezing mark. The GFS model progs the 520dam line to sag south into the Mohawk Valley of New York and southern Vermont further supporting cold surface temperatures and cool enough mid level atmospheric profiles to support a saturated thin DGZ. Snow growth will be limited, however, due to a low equilibrium level to 700mb and a significantly dry low level. Any snow showers that do form will likely fall as virga for most of the region, outside of the higher summits. Strong radiational cooling looks likely Monday night with cresting high pressure. Overnight lows will plummet across the region with lows in the low to mid 20s, with perhaps some isolated upper teens in the colder hollows of the Adirondacks, Northeast Kingdom, and Lamoille Valley.

Towards mid week, temperatures will moderate back to near climatological normals in the upper 40s to 50s. Model agreement has generally trended towards a weak frontal system traversing the region Tuesday night/Wednesday. Temperatures aloft may be conducive for some mountain snow, but most of the region should see a cold rain from this system as surface temperatures will be seasonably cool in the upper 40s to low 50s.

AVIATION /12Z FRIDAY THROUGH TUESDAY/
Through 12Z Saturday...Low level clouds and patchy fog remain across most sites this morning. Low IFR/LIFR ceilings will likely remain through 14Z for most terminals, but should slowly improve between 14-16Z as drier air pushes south eroding our low level moisture. As moisture decreases, already dry mid to upper levels will allow for widespread VFR today with clear skies at times between high scattered clouds. Skies will remain VFR through the end of this TAF package. Winds are beginning to turn to the north/northwest as the stationary boundary slowly drifts south reaching RUT by 08-09Z. Wind speeds will remain light and variable (< 10 knots) outside of BTV, where an occasional gust to 15-20 knots is possible through 12Z.

Outlook...

Saturday: VFR. Windy with gusts to 30 kt. NO SIG WX.
Saturday Night: Mainly MVFR, with local IFR possible. Definite RA, Slight chance SHRA.
Sunday: MVFR/IFR conditions possible. Definite RA, Likely SHRA.
Sunday Night: VFR. Chance SHRA, Chance SHSN.
Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.

BTV WATCHES/WARNINGS/ADVISORIES
VT...None.
NY...None.