textproduct: Burlington

WHAT HAS CHANGED

As of 335 AM EDT Friday...Many scattered showers are producing thunder this morning, so chances of thunderstorms has increased.

KEY MESSAGES

As of 335 AM EDT Friday...

1. A light wintry mix will continue this morning in the Green Mountains and points east, with slick travel likely mainly above 1000 feet elevation and secondary roads.

2. Unseasonably warm conditions expected this afternoon. As the warmup occurs, gusty south winds ranging from 30 to 45 MPH are expected in much of northern New York and northern Vermont along with scattered showers and a few thunderstorms.

3. Another storm system will bring widespread rain and localized strong winds Saturday night into Sunday. Much cooler conditions will filter into the region behind this system with a chance for elevationally dependent snow showers.

4. Cooler and quieter stretch of weather expected from Monday night through Wednesday night, then more showery with temperatures closer to seasonal normals towards the end of the week.

DISCUSSION

As of 411 AM EDT Friday...

KEY MESSAGE 1: A fascinating precipitation type conundrum occurred overnight with very moist and cold air near the ground supporting light snow across much of central and eastern Vermont. As clouds grow taller again with showers moving in from the west, precipitation type should return to rain and thereby produce pockets of freezing rain where temperatures are in the upper 20s to low 30s. It is a complex ice accretion scenario where convective precipitation does not lend itself to efficient icing with greater runoff, but temperatures early this morning have been on the low side of model guidance so there is some room for slight warming to still see at least a glaze of ice fall where these showers track. Radar trends put most of these showers from near Killington and points north. Temperatures have largely been elevationally dependent with almost all sub- freezing locations above 1000 feet, and especially 1500 feet, so risk of winter weather impacts in the valleys is minimal. Conditions should improve by 10 AM as the inversion height sharply lowers and near surface temperatures slowly rise.

KEY MESSAGE 2: Showers with embedded thunder have been racing east-northeastward on the nose of a strong 850 millibar jet, supporting elevated instability and deep moisture transport. The risk of thunder is expected to peter out as the morning progresses with reduced MUCAPE. Will note the SPC HREF- calibrated thunder risk was under 10% where we have seen thunder early today, so it would not be surprising if showers continue be capable of producing thunder through about 10 AM. After that time, a punch of drier mid-level air will work its way into the region taking a sledgehammer to the elevated CAPE. A few afternoon/evening showers ahead of the system's cold front will be possible but look less substantial than this morning's activity; PoPs are largely 15 to 30% for this timeframe.

The main story aside from the thunderstorm risk will be the gusty south winds. For the northern Champlain Valley these winds will probably peak this morning, while increasing this afternoon in the St. Lawrence Valley. While not particularly strong, gusts will probably reach the 40 to 45 MPH range with a few instances near 50 MPH near Lake Champlain. Other portions of northern Vermont and the Adirondacks could also see 35 to 40 MPH gusts through the afternoon ahead of the cold front, with post-frontal winds tonight out of the west not as strong as low pressure passing to our north is progged to weaken with time.

KEY MESSAGE 3: Forecast confidence remains high that widespread rain will fall Saturday night into Sunday morning along a stronger cold front. Less certain is the magnitude of winds with the associated low level jet. Model soundings show a stout inversion that would make it difficult to see much of the winds aloft make it to the surface aside from mountaintops during this period. Greatest risk for strong winds (some gusts near or above 50 MPH) would be in the north facing slopes of the Adirondacks such as near Malone and Ellenburg. Rainfall remains fairly moderate with only a narrow plume of anomalous moisture that moves steadily towards the east. Strong surface convergence and divergence aloft will promote a large area of rain that will keep chances of rain going for a fairly long time (roughly 12 to 18 hours), but most of the event will feature light rain.

Behind the cold front as it passes Sunday afternoon, a wintry pattern will set up with a deep upper trough building by Monday morning. There are somewhat mixed signals on forcing for precipitation so for now we are light on details. Overall, there is potential for a combination of lake-effect and upslope snow showers on Monday, which would mainly impact higher elevations with boundary layer temperatures still a bit warm for snow in the valleys.

KEY MESSAGE 4: High pressure will finally shift east from the Great Lakes bringing an end to any lingering snow showers from Monday night through Wednesday night. Temperatures will trend a bit cooler than seasonal normals during this timeframe. High temperatures will be in the 30s and 40s, with overnight lows dipping into the 20s. With the high pressure, temperatures will trend towards normal to above normal by mid to late week with some showers chances by later next week. Surface high will get suppressed to our south Thursday into Friday, and allowing next chance for showers as a low passes north of the Great Lakes. Maximum temperatures will be back up into the 50s on Thu and Fri of next week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through 12Z Saturday...LLWS and gusty surface winds will be the main aviation threat this forecast period with some IFR/MVFR CIGs being the secondary threat. We also have some areas of mixed precipitation this morning, but should change to all rain shortly. A low level jet slowly moves through the region with 60kts in the 2000-5000ft layer resulting in both speed and directional shear promoting hazardous flying conditions. Conditions range from VFR down to IFR currently with ceilings and visibilities varying from one site to another. SFC winds will continue to strengthen throughout the TAF period, with gusts of 20 to 40 knots possible before speeds begin to taper down after 22Z.

Outlook...

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday Night: Mainly VFR, with areas MVFR possible. Definite SHRA. Sunday: MVFR/IFR conditions possible. Definite SHRA. Sunday Night: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Monday: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Tuesday: Mainly VFR, with areas MVFR possible. Slight chance SHSN.

EQUIPMENT

The Colchester Reef meteorological station is out of service. This site is not serviced by the NWS. An estimated return to service is May 1st. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Winter Weather Advisory until 10 AM EDT this morning for VTZ003-004-006>008-010-018>021. NY...None.