textproduct: Burlington

WHAT HAS CHANGED

As of 346 AM EDT Thursday...

A Winter Weather Advisory is now in effect for areas along and east of the Green Mountains, particularly above 1000 feet elevation, where a minor ice event is expected tonight.

KEY MESSAGES

As of 346 AM EDT Thursday...

1. Light wintry precipitation and light icing are likely in the mountains and much of Vermont east of the Green Mountains, mainly during the nighttime hours. Slick travel conditions are possible which could impact the Friday morning commute.

2. Unseasonably warm conditions expected Friday and again Saturday night into Sunday, with showers and gusty winds but no significant impacts.

3. Light snow showers expected Monday into Tuesday as upper trough crosses the north country. Cooler than normal temperatures are expected through Wednesday night.

DISCUSSION

As of 346 AM EDT Thursday...

KEY MESSAGE 1: A mid-level wave riding along a persistent front to our south is producing light rain early this morning in southern Vermont. With messy thermal profiles near the ground, some sleet and snow may mix in with the rain but no impacts are expected given the very light intensity and sub-freezing temperatures only in the mountains through this period. Once this wave exits, there will still be a lot of low level moisture around and terrain driven, easterly upslope type of very light rain will be possible primarily in southern portions of the Adirondacks and Greens, but overall things look quiet during most of the day.

A polar high pressure area to our north will settle into the Canadian maritimes through the day, promoting an increasing southeasterly flow with colder air damming up against the Green Mountains. As a result, as light precipitation spreads northeastward this evening, we'll see a minor freezing rain event develop in portions of central and eastern Vermont. The degree of cold air will be fairly marginal such that it'll take time for temperatures to fall below freezing and this sub- freezing air will tend to settle in the mid-slopes. Lower elevations, such as in the Upper Valley and in the vicinity of Lake Memphremagog, will likely stay just above freezing tonight.

All together, it's a challenging forecast for ice amounts even without factoring in the orientation and strength of the frontogenesis that will focus the bulk of the rain. The consensus in model guidance is for the steadier rain to spread into northern portions of the area tonight with precipitation more showery and lighter in southern areas. So the PoPs are relatively low in southern portions of the Winter Weather Advisory area but the flow pattern favors sub-freezing temperatures more to the south than northern portions of Vermont. There also is uncertainty in the exact timing of the steadier precipitation, ranging up to several hours but generally falling within the nighttime period.

There are a couple of competing factors for ice accumulation. Wet-bulb temperatures will likely be only as low as 31 degrees for most of the event, suggesting ice to liquid ratios will tend to be on the low side. However, winds will be fairly strong, especially after midnight as a low level jet ramps up, which helps water freeze more quickly. Would expect as a result some highly variable ice accumulations, and unfortunately a lot of these locations will not have a lot of ground truth unless members of the public measure ice early Friday morning.

Temperatures will tend to warm fairly quickly compared to many of these types of events as low level flow trends due southerly, so while the Winter Weather Advisory extends beyond the morning commute, expect many areas that see freezing rain could have temperatures rise well above freezing by mid-morning.

KEY MESSAGE 2: Friday looks rather windy, although shy of Wind Advisory criteria. In particular, southerly/southwesterly valley channeling and 50-55 knot 925 millibar winds supports peak gusts above 40 MPH at times in the northern Champlain and St. Lawrence Valleys. It appears cloud cover and showers will be prevalent enough to keep temperatures from being particularly extreme, but it will be quite the turnaround from the recent cool conditions with highs largely in the 60s.

Cooler and drier northwesterly winds will filter in for Saturday, which has trended cooler but pleasant with high pressure briefly building in. The next storm quickly will follow as the next low pressure system again tracks to our west. A narrow plume of deep moisture riding out ahead of cold front will ensure widespread rainfall that could be briefly heavy, although the potential for significant rain still looks low with 90th percentile 24 hour rainfall amounts per the National Blend only as high as 1.33" at this time. These higher end amounts actually only between 0.6" and 1.0" in most of southern and eastern Vermont where risk of heavy rain is lowest. The combination of this widespread rainfall and additional higher elevation snowmelt continues to bring the expectation of sharp river rises with low risk of reaching bankful.

Winds currently look slightly less impressive compared to Friday, but overall similar within the St. Lawrence Valley in particular. This area is favored for a period of stronger southwesterly winds on Sunday after the cold front passes. More widespread windy conditions will tend to be muted, as the primary period of stronger winds aloft elsewhere still looks aligned with the rain and with a southwesterly orientation that doesn't result in much downsloping or mixing potential.

KEY MESSAGE 3: An upper level trough along with several lobes of embedded shortwave energy will bring upslope snow showers to our area from Sunday night through Tuesday. Cold air will sink down over the north country from Canada during this timeframe, and cooler than normal temperatures will remain through Wednesday night. Trough pushes east of our area on Tuesday night into Wednesday bringing upslope showers to an end and a return to more seasonable temperatures.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...MVFR conditions only remain at MPV because of lower ceilings. After 15Z, increased moisture across the region will likely lead to another period of MVFR ceilings through the daylight hours, along with increased chances for precipitation late in the day, generally after 20z. Light and variable winds this morning, then increase again out of the S/SE during the daytime. The exception will be KMSS which will hold onto a NE wind through the period. Winds will become strong and gusty on Friday.

Outlook...

Friday: Mainly VFR, with areas MVFR possible. Windy with gusts to 35 kt. Chance SHRA, Slight chance TSRA. Friday Night: MVFR. Slight chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday Night: Mainly MVFR, with areas VFR possible. Windy with gusts to 30 kt. Definite SHRA. Sunday: Mainly MVFR, with local IFR possible. Definite SHRA. Sunday Night: Mainly VFR, with areas MVFR possible. Slight chance SHRA, Slight chance SHSN. Monday: 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 from 7 PM this evening to 10 AM EDT Friday for VTZ003-004-006>008-010-018>021. NY...None.