textproduct: Burlington

WHAT HAS CHANGED

As of 242 PM EDT Wednesday...

A Wind Advisory has been issued for the entire region outside of Orange, and eastern Windsor Counties in Vermont, from 8 AM to 8 PM Tomorrow. Winds will gust between 45 and 55 MPH, especially in the Champlain Valley and northern slopes of the Adirondacks.

KEY MESSAGES

As of 242 PM EDT Wednesday...

1. Strong gusty winds areawide are expected tomorrow as an unseasonably strong area of low pressure track just north of the area.

2. Scattered showers and thunderstorm today will taper off by this evening, with more widespread rain and thunderstorms tomorrow. Some storms tomorrow may become strong to severe with embedded heavy rain and damaging winds.

3. Unsettled weather continues this weekend with some showers and northwesterly breezes. A low pressure tracking offshore Monday, may increase winds and rain chances further.

DISCUSSION

As of 358 PM EDT Wednesday...

KEY MESSAGE 1: An unseasonably strong sub-985mb low will pass near to north of Ottawa tomorrow with strong gusty winds expected. The synoptic support is strong with a near 130 knot upper level jet beginning to nose in overnight tonight, of which will be quite elongated and nearly zonal. Convergent flow aloft will strengthen the jet as it approaches, with a deep layer tightening pressure gradient, leading to a vertically stacked low over eastern Ontario. The synoptic setup is more reminiscent of something found in our winter months, and is near record levels for overall surface pressure for this time of year. As the pressure gradient tightens and the system deepens, a low level jet at 850mb will also deepen to nearly 100 knots aloft. Such a strong jet is also quite uncommon appearing less than 1 day in 10 years for this time of year. These strong winds in model soundings continue to denote even 40-50 knot winds just off the surface at 500ft areawide. As a result a widespread Wind Advisory has been issued for all of northern New York and most of Vermont, outside of Orange and eastern Windsor Counties from 8 AM tomorrow morning 8 PM tomorrow evening. Winds may gust up to 45 to 55 MPH, in the Advisory areas, and perhaps up to 60 MPH near Malone, NY. The strongest winds will be focused in the northern Champlain Valley as winds become channeled tomorrow morning between 8 AM and 1 PM, as well as along the northern slopes of the Adirondacks near the US-11 corridor due to downsloping of southerly winds. Additional areas near the western facing slopes of the Green Mountains of Addison, Chittenden, and Franklin Counties in Vermont could also see further enhancement to 55 MPH gusts from downsloping of southeasterly winds tomorrow morning. Winds will be below Wind Advisory thresholds overall, but remaining gusty at times, in Orange County and near the Connecticut River in general due to terrain influences and weaker southeasterly winds near the surface. Impacts from these winds will be downed tree limbs and isolated to scattered power outages. Due to trees being fully leafed out, there may be more tree damage than with similar wind speeds during the colder months as the wind cannot as easily pass through the trees.

Winds will turn to the south and then southwest into tomorrow afternoon, with a brief reduction below Wind Advisory thresholds for an hour or two. However, as they become more southwesterly, channeling in the St. Lawrence Valley will lead to a resurgence of stronger winds, once again along the US-11 corridor. Winds may gust again up to 55 MPH at times. Winds in Vermont tomorrow afternoon will likely hover around Wind Advisory thresholds, but not be as strong as in the morning, though some stronger gusts may still be possible as mixing becomes stronger with some breaks in precipitation. Winds will weaken back towards 25 to 35 MPH by tomorrow night, though they will remain breezy from the west around 25 to 35 MPH through Friday and Saturday as an upper low remains just north of the International Border and a jet streak at 250mb lingers.

KEY MESSAGE 2: A strong sub-985mb low will bring widespread precipitation tomorrow with chances for strong to severe thunderstorms tomorrow afternoon. Isentropic lift associated with a lifting warm front will allow widespread light to moderate rain to increase from southwest to northeast by early tomorrow morning. Good frontogenesis at 850 and 700mb will allow for a solid swath of rainfall within a 4-8 hour window around sunrise tomorrow morning where a majority of the rainfall for the system will fall. A strong LLJ associated with the system will likely lead to some shadowing across the Champlain valley and northern slopes of the Adirondacks as rain becomes shredded by the strong winds. Furthermore, southeasterly surface flow initially will lead to downsloping on the western facing slopes of the Greens and Adirondacks which will likely lead to pockets of reduced rainfall totals in the aforementioned areas as well. As the warm front lifts late tomorrow morning, and we get into a pseudo warm sector, instability will begin to increase. However, soundings show a stout warm layer aloft, with likely convective debris with mid to high level clouds which will help to lower the equilibrium level and reduce the realized total CAPE. However, with models denoting some stronger mixing potential by tomorrow afternoon, some wider CAPE profiles may be possible. In this low CAPE, high Shear environment, some limitations and concerns will be possible. If mixing becomes too strong, with increased surface dry air, in tandem with the strong shear, dry air entrainment will kill off any convective initiation, with more gusty shower type activity. However, should mixing be just enough to sustain wider CAPE, while mitigating dry air entrainment, the strong shear profiles could lead to some embedded rotation. The Storm Prediction Center has put areas along the Connecticut River in a 2% tornado risk for tomorrow. This is very conditional on the instability levels, and if we can get a long enough break between the morning warm frontal rain and thunderstorm activity in the afternoon. Regardless, should any storms grow, regardless of entrainment, gusty winds will be likely. It will not take much to mix down the stronger LLJ winds within the shower or thunderstorm activity. The best chances for any strong to severe weather will be likely south of a line from Saranac Lake, NY to Montpelier, VT. Any chances for severe weather will decreased after 8 PM with some lingering light showers into the evening. Shower chances continue into Friday and Saturday as an upper trough lingers around the International Border.

Pwats will be around 1.5 inches by tomorrow morning, with around an inch by the afternoon. Some locally good downpours will be possible with the decent pwats, but flooding risks will be low with the quick progression of the system as a whole. A few pockets of quarter to half an inch per hour rates may be possible in the afternoon across the Adirondacks and eastern Greens, as denoted on the latest 12Z HREF run. Right now current thinking is that widespread quarter to half an inch rainfall amounts are likely everywhere, with areas east of the Greens and the Adirondacks potentially seeing up to an inch. Areas that receive any thunderstorms, mainly in southern Vermont could see between 1-2 inches. Anything above 2 inches looks unlikely due to the lower confidence in stronger convective elements and the quick progressive nature of the system.

KEY MESSAGE 3: Cyclonic flow remains aloft in the wake of The Thursday system keeping conditions unsettled through Saturday with breezy northwesterly winds likely. Gusts in excess of 20 mph are probable and will keep wave action high on Lake Champlain. Terrain focused showers chances will continue with upsloping along the Adirondacks and Greens. Temperatures will trend noticeable cooler under sustained cold air advection, but not remarkably colder due to eastern Canadian maritime source region. Highs will decrease into the upper 60s and low 70s by Saturday.

Monday, low pressure troughing will track move offshore and develop into a closed system resulting in increased winds and shower chances again. Current model consensus keeps the track close enough to the shore to allow for deformation and orographic precipitation to blossom across northern New York and Vermont. However, a few models are splitting from consensus suggesting that the track of the system isn't a foregone conclusion. These models are suggesting a flatter trajectory that would result in a sharper moisture gradient across the region that could preclude rain for portions of northern New York and potentially northern Vermont. Temperatures are favored to warm beyond Monday as ridging returns.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...VFR conditions will persist through 12Z before CIGs lower as widespread showers spread over northern New York and Vermont. 18-23Z showers and isolated thunderstorms are favored with highest chances of TSRA over northern New York as a trough swings through.

Largest threat to aviators 12-18Z Thursday will be strong SFC gusts associated with a tight pressure gradient and LLWS ahead of and along a front moving through the region. Can't rule out some strong convection either along the front, but will wait to include in TAFs until they are closer. CIGs lower at least to MVFR as gusts increase in excess of 30kts for most terminals.

Outlook...

Thursday Night: VFR. Slight chance SHRA. Friday: VFR. Slight chance SHRA, Slight chance TSRA. Friday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Likely SHRA, Slight chance TSRA. Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA. Sunday: Mainly VFR, with areas MVFR possible. Chance SHRA, Slight chance TSRA. Sunday Night: VFR. Slight chance SHRA. Monday: Mainly VFR, with local IFR possible. Chance SHRA, Slight chance TSRA.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Wind Advisory from 8 AM to 8 PM EDT Thursday for VTZ001>009- 011-016>020. NY...Wind Advisory from 8 AM to 8 PM EDT Thursday for NYZ026>031- 034-035-087.