Marine Weather and Tide Forecast for Shelburne, VT

KEY MESSAGES
As of 226 AM EDT Wednesday...

1. A pair of systems expected to track through today and tomorrow. The second on Thursday will bring more potential impacts of winds and thunderstorms with embedded heavy rain and damaging winds.

2. Showery, breezy conditions are expected for the early portion of the weekend.

3. A low pressure system will likely bring widespread rain to the region on Monday, followed by seasonably warm temperatures next week.

DISCUSSION
As of 226 AM EDT Wednesday...

KEY MESSAGE 1: Today will open up with increasing clouds and some showers and thunderstorms as an upper trough lifts northeast.
Although it's not the strongest trough, it's managed nighttime convection in the Great Lakes region. South flow today should allow for moderation into the 70s to near 80 today. Despite somewhat dry dewpoints, good lapse rates in tandem with the upper trough should produce scattered to numerous shower activity. Winds aloft are not strong, but with dry air entrainment, there should be some acceleration of winds in any thunderstorms. Looking upstream at Buffalo, NY, showers and storms have produced gusts around 30-35 knots. So that could be in the cards for us too.

Thursday's activity will be more significant. A sub-990mb low will pass near to north of Ottawa. The level of synoptic support is quite strong with a near 130mb upper level jet nosing in. Isentropic ascent, some elevated instability, and large scale lift will result in a swath of moderate to heavy rain as the warm front races northeast. After the warm front lifts out of the region, the question continues to be how much wind will be able to mix to the surface after any rainfall. Winds of 45-50 knots descends to about 1500-2000 ft above ground levels. So it will not take much to mix winds to the surface; however, the warm sector has trended towards continued convection embedded within the warm sector as occlusion quickly takes place late Thursday morning into the afternoon. For now, max wind gusts are depicted reaching 30-40 mph, and locally up to 45 mph near Malone, New York. With all the leaves on the trees, this could pose a greater likelihood for downed branches. Isolated to scattered power outages will be possible on Thursday.

Next on Thursday will be the convection: The Storm Prediction Center has upgraded the Severe Weather Outlook to a Slight Risk (Level 2 of 5) for isolated strong to severe thunderstorms. The situation involves high shear in the 0-6km layer of 45-55 knots while instability of 500-750 J/kg and somewhat low equilibrium levels make it likely that activity remains short and tilted. CAMs are split on timing as well, and that will affect how much instability convection has to develop. With the fast flow, the main concern will be whether any storms can mix down the strong winds to the surface, and that will be the primary severe weather hazard. Given such a strong surface low, excellent inflow from southeast flow, and the quick westerlies aloft, rotating updrafts are possible. The HRRR/REFS indicates some helicity tracks through the region as well. However, the strong shear mentioned before may tilt updrafts too much to sustain organized convection. The system will track east Thursday evening with storms clearing the region.

KEY MESSAGE 2: Thursday's strong low pressure gets stuck near Quebec City for a few days with an upper low nearby. This will impart breezy west-northwest winds with occasional showers. The greatest chances will be along the international border given proximity to the surface low. Both days feature some tall, skinny CAPE profiles.
Given that fast flow will continue with some good low-level lapse rates, a few showers could produce gusty winds, but none are anticipated to be particularly strong. Temperatures will trend cooler heading into the weekend with a seasonable day Friday before the core of the coldest air arrives Saturday placing temperatures in the lower 60s to lower 70s.

KEY MESSAGE 3: A deep trough over the Canadian maritimes will linger through the weekend bringing showers and the occasional thunderstorm to the Northeast before finally shifting out into the Atlantic Ocean early next week. There remains the potential for a potent low pressure system to pass to our south which would produce widespread rain and embedded thunderstorms across the region on Monday and Monday night. Determinstic models continue to disagree on exact track and timing of this system, with 40-65% chance of measurable precipitation Monday afternoon and 25-50% chance of a half an inch within 24 hours during this period. With so much disagreement in the determinsitic global models, temperatures early next week may depend on precipitation, but the majority of models at this point seem to be suggesting temperatures could increase to and even reach slightly above seasonal normals by midweek with highs in the upper 60s to lower 80s and lows in the upper 40s to lower 60s.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/
Through 06Z Thursday...Isolated to scattered showers with a few thunderstorms likely Wednesday afternoon. VFR conditions are expected to be the main flight category over the next 24 hours.
There is the low chance of some fog development in the typical valley locations (SLK most likely spot) early this (Wednesday)
morning, but overall thinking light winds and clouds should keep all sites in northern New York and Vermont clear of vis and cig restrictions through the morning hours. Current light and variable winds are anticipated to increase out of the south around 09Z-15Z Wednesday to 5-15 knots. Showers and thunderstorms are likely to develop at 15Z-21Z Wednesday, though coverage will be spotty and scattered, so have utilized PROB30s farther out in time than usual.
Most likely sites to see thunderstorms will be SLK, PBG, and MSS from 16Z through 23Z Wednesday. SLK is most likely site to see occasional southerly wind gusts 15-20 knots, but any site that gets a thunderstorm could have a quick, strong gust. However, severe weather is not forecast over the next 24 hours.

Outlook...

Thursday: Mainly VFR, with areas MVFR possible. Windy with gusts to 30 kt. Definite SHRA, Slight chance TSRA.
Thursday Night: VFR. Windy with gusts to 30 kt. Chance SHRA.
Friday: VFR. Chance SHRA, Slight chance TSRA.
Friday Night: VFR. Chance SHRA, Slight chance TSRA.
Saturday: Mainly MVFR, with local IFR possible. Likely SHRA, Chance TSRA.
Saturday Night: MVFR/IFR conditions possible. Chance SHRA.
Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA.

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