textproduct: Burlington

WHAT HAS CHANGED

As of 231 AM EDT Tuesday...

Have increased winds on western and northern slopes of Vermont mountains today due to potential for downsloping southeasterly winds 30-40 mph. A Lake Wind Advisory has been issued for Lake Champlain as winds become southeast and increase to 15-25 knots this afternoon.

KEY MESSAGES

As of 231 AM EDT Tuesday...

1. Widespread moderate, but beneficial, rainfall will occur across the region today and tonight as a frontal boundary stalls over the region.

2. Periods of breezy winds are expected over the next couple of days, resulting in apparent temperatures as low as the mid 20s and 30s by late week.

3. A strong low pressure system will bring gusty winds and widespread rain on Friday, then turning much colder and blustery with scattered snow showers for the weekend. Anyone with outdoor plans for this upcoming weekend should monitor the forecast closely.

DISCUSSION

As of 231 AM EDT Tuesday...

KEY MESSAGE 1: A cold front is crossing New York and Vermont from north to south early this morning, producing widespread showers and drizzle as the parent low pressure ejects off eastern Canada into the northern Atlantic Ocean. The boundary is expected to stall out across the northeastern U.S. today and tonight as another fast moving clipper style system approaches from the west. This wave will increase southerly flow across the boundary as well as trigger moisture advection and increasing isentropic lift. This will result in an extended period of wet conditions for the forecast area. Southerly flow will be on the increase today, resulting in widespread rainfall amounts 1.00-1.50 inches, with lowest amounts occurring in southern Vermont and highest amounts likely on summits. A few thunderstorms will be possible, especially this afternoon as the low pressure approaches and moves overhead this evening. This setup may promote some cold air damming east of the Greens, with highs today below 50 degrees in eastern Vermont. Elsewhere, we should have typical mid October highs reaching the 50s and lower 60s. Rain chances will be on the decrease tonight as the low pressure moves away, but enough moisture lingers to keep lows on the milder side in the 40s to mid 50s.

KEY MESSAGE 2: A cold front is crossing New York and Vermont from north to south early this morning, then it is expected to stall out across the northeastern U.S. today and tonight. A low level jet that will amplify moisture across this stationary boundary will move through today, increasing southerly flow for the northern Champlain Valley. Mixing over the lake may be sufficient to intermittently bring some of these moderate gusts to around 30-40 mph down to the lake surface today. Southeasterly winds should also downslope across the northern and western slopes of the northern Greens and Northeast Kingdom today, producing gusts 30-40 mph in parts of Franklin, Orleans, Lamoille, Chittenden, Washington, and Orange counties of Vermont. Finally, a stronger push Wednesday will shunt the stationary boundary southward with northerly breezes developing behind a reinforcing boundary. Gusts 20 to 35 mph will be possible Wednesday night, with stronger ridge level winds expected. This will make for a chilly night as apparent temperatures fall into the mid 20s and 30s. Conditions likely won't improve much Thursday either, with temperatures only reaching the 50s.

KEY MESSAGE 3: A very dynamic pattern is expected to bring changeable weather to the region for late week and over the weekend. An upper trough will dig into the Great Lakes early Friday, deepening as it swings eastward and eventually forming a closed low somewhere between Hudson Bay and the Gaspe Peninsula on Saturday. Meanwhile, a weak northern stream low over the northern Great Lakes will phase with another low located in the Midwest, allowing for an intensifying surface low lifting up somewhere in the vicinity of the St Lawrence Valley on Friday and eventually into the Canadian Maritimes on Saturday. Widespread rain will spread over our region on Friday on strong isentropic lift and the nose of a 55+ kt 850 mb jet. At the least this jet will make for windy conditions across the higher summits, but even lower elevations could be breezy even if mixing won't be optimal under steady rainfall. However, a strong cold front will quickly cross the region later Friday into Friday night, and the influx of colder air and associated steepening lapse rates will amplify mixing stronger winds down to the surface. South winds of 15 to 25 mph with gusts to 30 mph are likely on Friday, potentially stronger in the Champlain Valley and over the higher summits. These winds will turn to the west/northwest after the frontal passage Friday night and Saturday; note the mean gusts off of the long-range ensembles are 35-40 mph, with a 30-50% chance of exceeding 40 mph over the Adirondacks, along/east of the spine of the Greens, and over Lake Champlain. While we don't anticipate needing a Wind Advisory (for gusts greater than 46 mph), trends will need to be watched closely going forward.

The other impact with this system and its strong cold front will be rapidly falling temperatures, allowing rain to turn to snow. Precipitation will linger longest in the higher terrain, especially the favored western slopes as we'll see wrap-around upslope northwest flow. Even the wider valleys could see a bit of the white stuff Friday night/early Saturday as snow levels look to fall below 500 ft, particularly in the St Lawrence and northern Champlain Valleys. Snow showers will persist over the higher terrain through the day on Saturday, then taper to an end Saturday night. While it's still too early to talk about specific snow amounts, note that the latest GEFS has a 60-90% chance of more than 1 inch of accumulation over the Adirondacks and northern Greens/Northeast Kingdom. After daytime highs in the 50s on Friday, Saturday will only top out in the 30s in most areas. Combined with the brisk winds, wind chills will remain in the single digits over the higher summits much of the day. Elsewhere, many spots will start out in teens and 20s Saturday morning, only improving toward 30F by the afternoon.

Sunday will see cool but improving conditions as high pressure builds over the region. Ridging will keep us dry through mid week, with high temperatures warming from the 40s on Sunday to close to 60F by Tuesday.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday...IFR/LIFR conditions will prevail through a good part of the first 6- 8 hours of the TAF period as abundant low- level moisture keeps low ceilings and areas of mist/drizzle through early this morning. Expect ceilings to generally remain AOB 800 ft and visibilities 3- 6SM with locally lower conditions at times. Ceilings will lift very slowly after 10z Tue as winds turn to the S/SE (ENE at MSS) and become gusty as low pressure moves along the international border. Areas of drizzle/mist will become widespread showers at this time, as well, and expect visibilities 3-5SM while ceilings lift toward 1200-2500 ft. Winds gusty to 25+ kt by this afternoon, especially at BTV due to funneling. Winds will start to abate late in the day, but a LLJ will keep LLWS of 35-45 kt at most terminals this afternoon into the evening hours.

Outlook...

Wednesday: Mainly MVFR, with local IFR possible. Slight chance SHRA. Wednesday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Thursday: VFR. NO SIG WX. Thursday Night: VFR. Chance SHRA. Friday: Mainly MVFR, with local IFR possible. Definite SHRA. Friday Night: MVFR. Windy with gusts to 30 kt. Definite SHRA. Saturday: Mainly VFR, with areas MVFR possible. Windy with gusts to 30 kt. Chance SHSN, Slight chance SHRA.

MARINE

Periods of rough lake conditions are anticipated this week into the weekend. Today, a low level jet is moving across the region, bringing the potential for periods of rough lake conditions. A Lake Wind Advisory has been issued for Lake Champlain due to winds becoming southeast and increasing to 15 to 25 knots this afternoon, with gusts up to 30-40 knots. Waves are expected to build to 3 to 6 feet as well. Winds will diminish to 10 to 15 knots later tonight or Wednesday morning. Additional periods of concern will be Wednesday night and again Friday into Saturday as a couple of fronts move through the region. Overall, it will not be a pleasant week to venture out on Lake Champlain, especially in smaller watercraft.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...None.