textproduct: Burlington

WHAT HAS CHANGED

As of 215 PM EST Wednesday...

A Winter Weather Advisory has been issued for portions of northern New York and the southern Champlain Valley of Vermont.

KEY MESSAGES

As of 215 PM EST Wednesday...

1. A wintry mix is expected Thursday night into Friday with impacts likely to the morning commute.

2. Weekend warmup with showers likely Saturday.

3. The potential for ice jams and hydrological related issues will need to be monitored early next week due to much above normal temperatures and significant snow melt.

DISCUSSION

As of 215 PM EST Wednesday...

KEY MESSAGE 1: Confidence has increased enough to issue a Winter Weather Advisory for a period freezing rain and snow/sleet mix across much of northern New York and portions of the southern Champlain Valley of Vermont Thursday night into Friday. Synoptically, not much changed with todays NWP guidance which features a potent shortwave traversing the central CONUS along a stalled frontal boundary tonight into Wednesday, tracking just south of the forecast area Thursday night into Friday morning. To the north, high pressure builds southward from Canada with low-level cold air undercutting warmer air aloft pushing northward from the south. This scenario creates a mess of weather types with much of Vermont outside of the southern Champlain Valley seeing a mix of snow and sleet, while elsewhere freezing rain is likely the more dominant ptype Thursday night before precipitation tapers off Friday morning and surface temps slowly rise above freezing. Snow and sleet accumulations will be minimal in the dusting to 1 inch range, but ice accumulations could be up to 2 tenths of an inch for some areas. This ice accretion shoudln't be enough to create any widespread power issues, but the Friday morning commute could be treacherous for some locales.

KEY MESSAGE 2: Low pressure tracking through the Great Lakes combined with high pressure off the Atlantic seaboard will produce strong southwesterly warm air and moisture advection across the Northeast on Saturday with temperatures pushing well above seasonal normals. Southeasterly flow east of the Green Mountains will limit heating a bit with upper 40s to around 50 expected, while westward widespread 50s to potential low 60s are likely. Much of the day looks to be dry until the late afternoon and evening when a cold front will bring a round of rain showers and potentially a few rumbles of thunder to the region through Saturday night.

KEY MESSAGE 3:

The forecast for next week continues to indicate the potential for well above normal temperatures from early to mid next week. A summer like Bermuda high pressure ridge will remain anchored to the southeast coast, extending north towards the International Border. South/southwest flow will result in temperatures 20-30 degrees above normal for early March, with 850 and 500mb temperatures in the 97- 99th percentiles based on the NAEFS. Highs will push the upper 50s, with perhaps some localized low 60s across the southern St. Lawrence Valley, southern Vermont, and eastern downslope regions of the Adirondacks and Greens.

There will be several weak boundaries that will travel along the St. Lawrence Valley and International Border, attempting to suppress the warm temperatures at times, with the best organized boundary looking to move through mid week. Better chances for shower activity next week will be across northern New York on the western periphery of the thermal ridge. Ensemble PWATs both in the Euro and GEFS are denote a likely probability exceeding 0.5", with a good amount of members up to 0.75-1". Overall, current moisture totals doesn't look overly concerning, however, there are some signals of some more convective type showers by mid week, which could become concerning in the coming days. There is still some uncertainty with how organized these boundaries will be and how much associated QPF falls with any shower activity.

Regardless of the above uncertainty, warm temperatures and dewpoints above freezing will lead to widespread snow melt across the area. The prolonged warm spell will surge 72hr Mon-Wed thawing degree hours to 650-900, with some localized areas pushing 1000 in the southern St. Lawrence Valley, southern Vermont, and Champlain Valley. These values suggest enough melting for widespread ice break up, which could lead to or increase the risk of ice jam related flooding. Current NAEFS and GEFS snow melt liquid equivalent loss ranges from 2-4". Combined with the ensemble QPF possibilities, total liquid additions to rivers varies from 2.5-5" which would support at least Action to Minor river flood potential. GEFS and NAEFS still indicate many rivers will experience sharp rises with a 60-80% probability of the Mad River, Ausable River, Otter Creek, and possible the Winooski River near Essex, reaching at least Action Stage. There is slightly more confidence that the Ausable, Otter Creek, and Mad could reach at least Minor Flood Stage with over a 75% probability in the NAEFS and GEFS. Typically to reach Moderate or Major flood stage with ice jams, a significant rain event with convective elements is needed, which appears unlikely at this point. Given the uncertainty with the increasing hydrological concerns next week, please pay close attention to the forecast as we move closer to early to mid next week.

AVIATION /19Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...VFR conditions are expected to continue through the next 6-12 hours. Brief high pressure will break down into this evening as a moisture starved cold front shifts south from Canada overnight. The region will become sandwiched between a stationary boundary to the south and the approaching cold front to the north which will help winds trend towards calm. This convergence will also lead to moisture becoming trapped under an inversion with warmer air aloft and the colder Canadian air sinking under. This trapped moisture could lead to the development of some low surface fog, particularly in the wider valleys impacting MSS/BTV/PBG, especially if skies become clear. The best chances for fog will be closer towards sunrise as the cold front enters the region. Associated with the cold front, ceilings will trend towards MVFR 1000-2000ft agl north of RUT, with perhaps some intermittent MVFR at RUT between 2000-3000ft agl which will increase from the south. The cold front will wash out as it reaches central Vermont, but winds will shift to the north by tomorrow morning becoming breezy with winds around 10 knots. Any fog should mix out by 14-15Z, with continued MVFR ceilings towards the end of the TAF period.

Outlook...

Thursday Night: Mainly MVFR, with areas VFR possible. Chance FZRA, Chance SN, Chance PL. Friday: Mainly MVFR, with local VFR possible. Chance SN, Slight chance FZRA. Friday Night: Mainly MVFR, with local IFR possible. Windy with gusts to 30 kt. Chance RA. Saturday: Mainly MVFR, with areas IFR possible. Windy with gusts to 30 kt. Chance RA. Saturday Night: MVFR/IFR conditions possible. Chance RA. Sunday: Mainly VFR, with local MVFR possible. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX.

EQUIPMENT

The KBTV ASOS has suffered a communications failure. The issue has been diagnosed, but there is currently no estimated time of return to service. The affected communications line is not serviced by the NWS. Terminal Aerodrome Forecasts will continue, but regular observations may not be available.

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...Winter Weather Advisory from 7 PM Thursday to 1 PM EST Friday for VTZ009-011-018-019. NY...Winter Weather Advisory from 7 PM Thursday to 1 PM EST Friday for NYZ029-030-034-087.