textproduct: Burlington

WHAT HAS CHANGED

As of 759 AM EST Tuesday...

Have issued a quick morning update to increase PoPs (several mountain sites continue to report snow and resulting visibilities under 3 miles this morning, temperatures/dew points (observations running a touch cooler than forecast), and cloud cover (valleys are clearer than mountain sites).

KEY MESSAGES

As of 136 AM EST Tuesday...

1. Blustery and cold today.

2. Snow will cause hazardous travel on Wednesday, first with widespread light snow in the morning and then scattered snow showers with localized snow squalls during the afternoon and evening.

3. Seasonable and mostly dry weather is expected for the end of the week. A warm up is expected for Saturday, with sharply colder temperatures returning Saturday night into early next week.

DISCUSSION

As of 136 AM EST Tuesday...

KEY MESSAGE 1:

A polar high pressure area will continue to build southeastward from eastern Ontario this morning, where observed temperatures are below zero. Substantial low level cold air advection is occurring between this system and the departing Nor'easter, and mesoanalysis shows an impressive gradient in 925 millibar temperatures with a nose of relatively warm air ahead of this thermal boundary in Vermont. Hence, temperatures have dropped off first in the St. Lawrence Valley where wind chills as of this writing are as low 5 below zero. Expect the colder and drier air will continue to make inroads farther east through the morning, although the most anomalous cold remains in our western areas. HREF mean 925 millibar temperatures bottom out at -23 Celsius in Adirondack western slopes, near the 1st percentile; normally this would lead to highs struggling to rise above 0F, but low level flow in this area will shift southwesterly during the day to modify the air mass somewhat. As such, even in the coldest areas highs will likely top out in the 10-15 range in New York, and in Vermont highs will mainly be in the mid teens to low 20s. These temperatures are about 15 degrees below normal in much of Vermont and closer to 20 degrees below normal in much of northern New York.. Aside from some shallow moisture this morning supporting flurries in the Adirondacks, northern Green Mountains, highlands of the Northeast Kingdom, no precipitation is anticipated. The cold and dry air will support temperatures falling off quickly tonight until winds pick up, which as typical when high pressure passes to our east will be primarily at high elevation and in the wide valleys with most other spots seeing temperatures reach their bottom for the night only when clouds arrive from the west. Lowest wind chills through the period will continue to be in the higher summits where dangerously low wind chills below -20 will be likely through midday with minor improvement through tonight.

KEY MESSAGE 2: A clipper system will approach our region tomorrow night with its warm front providing forcing for a widespread light snowfall. Onset for snow appears to be in the predawn hours which will cause slippery travel and low visibility (likely between 1/2 mile and 1 mile) for the morning commute. Highest confidence of impacts based on expected timing of steadier snow appears to be in the St. Lawrence Valley, Adirondacks, and western/southern portions of Vermont, including Addison, Orange, Rutland, and Windsor counties. Snow during this event will be brief, generally between 2 and 3 hours, with snowfall rates near a 1/2 inch per hour.

Have tried to indicate a break in snow for most locations, especially away from the mountains and influence of Lake Ontario, during the late morning hours before snow showers develop in the "warm sector" of the clipper. Convective allowing models generally show scattered to numerous snow showers developing out ahead of the cold front; a paintball chart of reflectivity greater than 25 dbZ shows modest agreement in timing of potential heavy snow showers and squalls during the mid-afternoon to early evening hours, tied to an upper level shortwave and some surface convergence. The snow squall parameter values of 2 to 4 amidst 20 to 60 J/kg SBCAPE are ample to at least have embedded snow squalls within clusters of snow showers. Some models show some organization of linear development that would be more significant for travel, with intensification in the Champlain Valley during the evening commute time. While greatest instability and frontal timing generally supports highest likelihood of snow squalls in northern New York, it appears favorable convergence and a pre- frontal trough might compensate for less moisture and instability farther east. Temperatures in the valleys will likely be near freezing while road temperatures, given late February solar angle, rise above freezing ahead of these snow showers. Therefore, some snow squalls could have a flash freeze potential in addition to gusty winds and low visibility. Motorists planning travel Wednesday afternoon should keep an eye on the forecast and prepare for rapidly changing weather conditions if the ingredients come together.

Regardless of the convective activity, the cold front will pass Wednesday night into Thursday morning with modest pressure rises of about 1 millibar/hour as cooler air swings in from the west. Without a northerly component to the wind, the air mass won't change too much behind the system as temperatures remain seasonably cool into Thursday morning. Low temperatures will mainly be in the teens following a day with highs in the low to mid 30s.

KEY MESSAGE 3: A period of seasonable and mostly dry weather is expected late this week as the region remains under the influence of surface high pressure. High temperatures look to climb into the low to mid 30s areawide. Model guidance continues to trend towards a drier forecast Thursday night into Friday compared to previous runs, with surface high pressure overhead, keeping most precipitation to our south. As high pressure shifts eastward, strong southerly flow across the region will bring much warmer temperatures to the region for Saturday, with the current forecast showing high temperatures climbing well above normal into the 40s. This warm up will be short- lived, as a cold front looks to push across the region Saturday night into Sunday, bringing some sharply colder temperatures and scattered snow showers.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Through 12Z Wednesday...A mix of VFR and MVFR conditions currently prevail across terminals, and will continue throughout the morning. Ceilings have generally been between 2000 and 3500 ft AGL, with cloud cover expected to become more scattered towards the afternoon, especially in valley locations. Winds will be north to northwesterly throughout the forecast period, generally 5 to 10 knots with occasional gusts up to 20 knots, gradually abating through the day. Some light snow showers will be possible for a few hours this morning, before quickly dwindling, with minimal impacts expected to terminals. Otherwise, mostly dry conditions will prevail through the forecast period.

Outlook...

Wednesday: Mainly MVFR, with areas VFR possible. Chance SN, Chance SHSN. Wednesday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Thursday: VFR. NO SIG WX. Thursday Night: VFR. Slight chance SN. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with areas MVFR possible. NO SIG WX.

EQUIPMENT

The KMPV ASOS has suffered a communications failure. The issue has been diagnosed, but there is currently no estimated time of return to service. Terminal Aerodrome Forecasts will continue, but amendments to those forecasts will be suspended.

NOAA Weather Radio station WXM-44, transmitting from Mt. Ascutney, Vermont, on frequency 162.475 MHz is non- operational at this time. NWS technicians have diagnosed the problem, but repairs will likely not be able to occur for quite some time due to circumstances beyond our control. Therefore, the time of return to service is currently unknown. The following NOAA Weather Radio transmitters may be able to provide service during this outage: WWG 50 from Burke Mtn, VT at 162.425 MHz and WNG 546 from Hanover, NH at 162.525 MHz.

The Colchester Reef meteorological station is out of service. This site is not serviced by the NWS and there isn't an estimated return to service at present. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

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