textproduct: Burlington

WHAT HAS CHANGED

As of 252 PM EDT Monday...

Precipitation amounts were increased by around 50% across northern Vermont and the Adirondacks for Tuesday and Tuesday night. The potential for gusty winds is continued to be watched closely Friday into Saturday.

KEY MESSAGES

As of 252 PM EDT Monday...

1. Widespread moderate, but beneficial, rainfall will fall across the region Tuesday and Tuesday night as a frontal boundary stalls over the region.

2. Periods of breezy winds are expected through early Thursday.

3. A strong low pressure system will pass through the St. Lawrence Valley and will bring widespread rainfall and even some mountain snow Friday into Saturday with sharply cooler temperatures into the weekend.

4. Gusty winds will accompany the late week system Friday into Saturday, slowly relaxing by Saturday night.

DISCUSSION

As of 252 PM EDT Monday...

KEY MESSAGE 1: A cold front will be dropping southward this evening with rain chances increasing overnight as the parent low ejects into the northern Atlantic off eastern Canada. The result will be for the boundary to stall out over the region for Tuesday through Tuesday night as another fast moving clipper style system approaches from the west. This wave will increase southerly flow across the quasi-stationary boundary deepening moisture advection and increasing isentropic lift across the boundary. This will result in an extended period of wet conditions for the Adirondacks and north/central Vermont. Initial rainfall will favor upslope areas of the Adirondacks and the northern Greens with westerly flow aloft. However, overnight into Tuesday, flow turns more southerly and deepens promoting strong moisture advection across the stalled boundary. This flow direction will result in increased precipitation amounts with a lack of shadowing. As such, precipitation amounts were increased area wide, with lowest totals around 0.5" towards southern Vermont to 1-2 inches tonight through Tuesday night from central Vermont northward. Highest amounts will be over the northern Greens and Adirondacks, but 1-1.75" is possible even for lower elevations in northern Vermont and northern New York. A few thunderstorms will be possible, especially Tuesday morning with a trough sweeping through and again Tuesday afternoon with the low approaching. This setup may promote some cold air damming east of the Greens, with highs Tuesday below 50 degrees in northeastern Vermont.

KEY MESSAGE 2: As the boundary drops southward this evening winds in the northern Champlain Valley will briefly increase with northerly winds of 15 to 25 mph and some gusts to around 30 mph across Lake Champlain. These winds will drop after midnight. Next, a low level jet that will amplify the moisture across the stationary boundary will move through Tuesday increasing southerly flow mainly for the northern Champlain Valley since moisture will dampen wind potential. Mixing over the lake may be sufficient to intermittently bring some of these moderate gusts to around 30 mph down to the lake surface. 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 with stronger ridge level winds expected.

KEY MESSAGE 3: A northern stream Alberta clipper will phase with a southern stream closed low leading to an amplifying strong shortwave by early Friday. Widespread rain is expected Friday before temperatures sharply cool Friday night with the potential to see a switch to terrain snow showers Friday night into Saturday. Widespread rainfall amounts above half an inch are likely with 80-100% ensemble probabilities of 0.5 inches or more on Friday before any precipitation transitions to a rain snow mix in the terrain. Trends continue to denote likely probabilities of an inch or more with 60- 90% chances across the Adirondacks, and much of central and northern Vermont as well. Consensus favors our northern zones as the focus of the highest precipitation amounts with this system.

A cold front will sweep through the area Friday night sharply lowering temperatures 10 to 15 degrees from Friday evening to Saturday morning. Temperatures will likely dip below freezing for most if not all locations across the area with only those near Lake Champlain and immediately near the St. Lawrence River staying above freezing. As temperatures fall, snow levels during the day Saturday will also lower to 500-1000ft agl, with a transition to snow above 1500ft agl, and a rain, wet snow mix, in elevations between 1000- 1500ft agl. A few mixed in flurries cannot be ruled our even in the Champlain Valley, though temperatures will be marginal in the mid to upper 30s. Some snowliage appears likely with ensembles denoting nearly 100% chances for purely snowfall in the Adirondacks and Northeast Kingdom. Snowfall impacts will be minimal with road temperatures well above freezing, and with only marginal surface temperatures, snow will likely be of a wet character, with minor accumulation only on the highest elevations and mainly on vegetation only. Most locations will not see any accumulations at this point.

Rain and snow showers will taper off Saturday evening as the system pulls away to the northeast. 850 mb temperatures Saturday night will be remarkably cold for this time of year in the -9 to -11C range Saturday night supporting temperatures in the 20s for most of the area, including the entire Champlain Valley. Pockets of teens will be possible in the coldest hollows of the Adirondacks and Northeast Kingdom as surface temperatures anomalies will be 10 degrees below normal. Temperatures will slowly moderate back towards seasonable normals to start next week.

KEY MESSAGE 4: The dynamic end of week system will deepen as it approaches the St. Lawrence Valley Friday with a strengthening pressure and thermal gradient. While there are slight differences to the overall track of the center of the system, strong gusty south winds are expected Friday, followed by strong cold advective northwesterly winds by Saturday. The GFS favors a more northward low center track which would enhance the southerly flow Friday after in the Champlain and the St. Lawrence Valley, whereas the Euro favors a low center directly over the Champlain Valley Friday with slight weaker southerly flow. Regardless of track, gusts Friday are favored to be upwards of 35 MPH for the Champlain Valley, with a 50-70% chance for high end values up to 40 MPH in the ensemblistic guidance. Slightly weaker winds to 20-30 MPH elsewhere Friday. Winds will turn to the northwest Friday night with better confidence in stronger winds Saturday due to a lack of precipitation limitations that exist Friday. Sustained winds will increase to 20 to 25 MPH, with 55-80% chance for gusts over 40 MPH from the Adirondacks eastward on Saturday. Recreators should also plan for mountain summit gusts as high as 40-55 MPH, especially in the Adirondacks. Surface winds will slowly weaken back towards 10 MPH or less Saturday night with gusts and mountain winds following suit by Sunday.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Through 18Z Tuesday...A complex TAF forecast is expected through the next 24 hours for all terminals. A dynamic weather system will approach the region this evening into tomorrow with deteriorating conditions overnight tonight. Widespread variable cigs from IFR to high MVFR will continue towards sunset before probabilities of IFR cigs increasing from 10-20% to around 30-50% for many terminals between 22-24Z. Blocked flow will increase after 22Z, with low level moisture likely resulting in BKN006-BKN009 cigs for BTV/EFK/MPV/RUT. IFR cigs for the aforementioned locations is low to moderate, with expectations that there will be bouncing conditions for a while after sunset. SLK is expected to remain IFR through the TAF period. Light showers and mist return this evening as well beyond 22Z with winds turning more northwesterly for all terminals, outside of MSS which will see northeast channeled flow, and increasing to around 10 knots for MSS/BTV/PBG. Variable cigs between high IFR and low MVFR is expected for all terminals between 00-07Z. Confidence in IFR cigs beyond 07Z for all terminals will be high beyond 07Z as a sharp inversion develops across the area with ongoing light showers and mist. Blocked flow will also strengthen resulting in IFR cig probabilities even at BTV between 50-60% beyond 07Z.

The most impactful portion of this period will be after daybreak tomorrow when light to moderate rain will move from west to east. Visibilities will lower towards 2 to 4SM after 10Z with slight cig improvements to 1000-1500ft agl, outside of SLK which will remain IFR. LLWS will develop at mountain terminals with a strong low level jet to 40 knots at 2000ft agl. Winds concurrently will increase to 10 to 15 knots with gusts as high as 25 knots by 18Z tomorrow from the southwest, especially at BTV/MPV. MSS will see continued channeled flow from the northeast through the TAF period.

Outlook...

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

MARINE

Periods of rough lake conditions are anticipated this week into the weekend. This evening, a brief period of breezy conditions are anticipated as flow turns out of the north. Flow flips Tuesday with a low level jet moving across the region with southerly breezes developing and potential resulting in periods of rough lake conditions. Additional periods of concern will be later Wednesday 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.