textproduct: Burlington

WHAT HAS CHANGED

As of 128 PM EST Wednesday...Upgraded the immediate St Lawrence Valley to Winter Storm Warning for 5 to 9 inches of snow, otherwise rest of the forecast remains unchanged.

KEY MESSAGES

As of 128 PM EST Wednesday...

1. Rain changes to snow across northern New York tonight and across most of Vermont on Thursday morning, producing a slick and hazardous Thursday morning and evening commute. A sharp and elevation dependent snowfall is expected, especially across Vermont.

2. Cold temperatures will lead to bitterly wind chills Thursday night into Friday.

3. A brief warmup Saturday will be short lived with a return to normal to below normal conditions and showery weather by the end of the weekend and into next week.

DISCUSSION

As of 128 PM EST Wednesday...

.Key Message 1: Rain changes to snow across northern New York tonight and across most of Vermont by Thursday morning, producing a slick and hazardous Thursday morning and evening commute. A sharp and elevation dependent snowfall is expected, especially across Vermont.

Lets start with what we know, its currently 26F at Whiteface, 28F Mt Mansfield, 30F at Little Whiteface, SLK 39F and 45F here at BTV, indicating elevations above 3000 feet should see an all snow event, producing a sharp elevation dependent snowfall from valley floors to summits, especially in VT.

Sfc analysis shows a broad area of low pres with sharp cold front extending from north of Maniwaki to central Ohio with temps in the upper 30s to mid 40s acrs most valley locations, but single digits and teens behind arctic boundary. GOES 19 Water vapor imagery shows board moisture advection in deep sw flow, while potent s/w energy associated with digging mid/upper lvl trof is located near Chicago, along with developing dry slot. This potent energy, combined with a tightening thermal gradient wl help to enhance sfc low pres development over western PA by 00z this evening. Low pres is expected to deepen as it slowly tracks northeast toward the northern CPV by 12z Thurs, along a sharpening 925mb to 850mb thermal boundary. Little change in thermal profiles have been noted in the latest guidance, which shows 925mb temps hovering near 0C, while progged 850mb temps are btwn 0 and -3C during initial surge of moisture tonight, with slightly warmer values over southern VT. These thermal profiles support snow levels near 3000 feet initially, but as better dynamics/lift arrive thinking levels fall between 1800 and 2200 feet by 03z NY and by 06z acrs the northern/central Green Mtns of VT.

Given the primary closed 925mb and 850mb circulation is progged to move acrs northern NY, this results in limited cooling under southerly flow in VT, while much colder profiles advect into the SLV/northern Dacks quicker. This advection on developing northerly flow will help to quickly change rain to snow acrs the valleys of northern NY btwn 06z-09z, with a period of moderate to heavy snowfall expected, especially SLV on Thurs morning. As sfc low pres and closed 925-850mb circulations pass to our north on Thurs, much colder air wl quickly overspread VT btwn 15-21z Thurs, resulting in quickly falling temps and rain changing to snow. This changeover scenario has been delayed again by another 2 to 4 hours, so most of the Thursday morning commute in the CPV should feature a cold rain with a few wet snowflakes as temps hold in the mid 30s.

Exact snowfall amounts continue to be very challenging with this system, given changing thermal profiles and potential for well defined dry slot to develop per latest GOES-19 water vapor imagery. Greatest confidence of 7" or more based on the latest from WPC and NBM probs is acrs SLV, where an upgrade to a Winter Storm Warning has occurred. Elsewhere a sharp elevation dependent snowfall is expected with a dusting to 3 inches Champlain Valley 8 to 10 inches atop Mt Mansfield to Jay Peak and similar amounts over the northern Dacks. Very minor snowfall accumulations are expected acrs the CT River Valley and southern CPV, with a general 1 to 4 inches over the NEK of VT. A secondary window of light accumulating snowfall is likely late Thurs night into Friday morning as mid lvl moisture axis and favorable upslope flow impact our region. A few fluffy additional inches in the mtns will be possible.

13Z NBM shows a 40 to 60% prob of 24 hour snowfall > 7" acrs the SLV, while probs of >4" is 60 to 100% over most of northern NY. HREF mean 24 hour snowfall has increased over the SLV with values in the 8-10" range and 2-4" in the northern CPV. HREF does indicate the potential for hourly snowfall rates in the 0.5" to 1.0" for a period of time on Thurs AM, where WPC indicates a 50% to 80% prob of exceeding winter storm warning criteria. Furthermore, NBM 25th percentile is 5" and 75th is 10", with a mean value of 7-8" for the SLV and 3 to 7" for northern Dacks and mostly in the 1 to 4 inch range for the northern CPV. Lows by Thurs AM range from mid teens SLV to mid 30s lower CT River Valley with highs on Thurs falling into the single digits and teens by sunset.

.Key Message 2: Cold temperatures will lead to bitterly wind chills Thursday night into Friday.

As sub 990mb low pres lifts away from northern VT on Thurs night, brisk westerly winds wl advect a pocket of very cold temps acrs our region. Latest guidances shows 850mb temps in the -19C to -22C, while 925mb temps are in the -14C to -18C. These values have modified by several degrees over the past couple of days, but expect bitterly cold wind chills on Thurs night into Friday with values -5F to -15F, with -20F to -30F at summits. Temps modify quickly back toward normal on Friday with developing southwest flow on backside of high pres.

.Key Message 3: A brief warmup Saturday will be short lived with a return to normal to below normal conditions and showery weather by the end of the weekend and into next week.

A large scale upper level gyre across the Hudson Bay in Canada will be responsible for our weather in the extended for the weekend and next week. Several shortwaves will eject off a broad longwave trough that will slowly slide eastward over the course of several days. As a result we will be under prevailing southwesterly flow as these shortwaves ride from southwest to northeast along the trough through the St. Lawrence Valley. Brief warming Saturday under fairly uniform southwest flow will allow temperatures to rise into the low to mid 30s, with perhaps some subtle cad across the eastern Greens as a weak surface low rides up the New England Coast early Saturday. Associated with these shortwaves this weekend, continued showery weather will bring prolonged chances (30-50%) for showers, mainly in the St. Lawrence Valley and along the spine of the Greens. Although temperatures will be in the mid 30s for the wider valleys, we likely we see some dynamic cooling aloft and wet-bulbing at the surface leading to precipitation in the form of snow. A lake effect band off Lake Ontario cannot be ruled out with southwest flow. Snow amounts through Monday will be marginal at only a few inches, however, driven by meager forcing. Any system that moves through will be un- phased and not timed well between areas of forcing and moisture. It should be noted that there is an outside chance for some snow showers in the eastern Greens potentially Sunday night into Monday with some model solutions, namely the GFS, that have depicted a stronger developing coastal low Sunday which could bring some synoptically driven snow chances. However, the number of ensembles depicting this solution are low. Beyond the weekend, continued cold and showery conditions persist, though little accumulating snow is expected through midweek next week.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...A developing surface low will trend ceilings towards MVFR by 21-00Z this afternoon, with SLK and MSS already at MVFR cigs 2000-3000ft agl. Ceilings will continue to lower with the onset of precipitation in the form of rain after 00Z, with cigs trending towards IFR 600-1000ft agl. by 06Z at all sites; SLK and MSS will trend towards IFR by as early as 22-00Z. Winds will become calm overnight with steadier rain which will drop vsbys to IFR levels by 06Z. Colder air will wrap around the system into MSS/SLK between 00-06Z with -rasn, and prevailing -sn by 06Z. Snow may be heavy at times with vsbys as low as 1/2SM. The transition to snow will take longer across the Vermont sites and PBG as the low moves directly overhead. Vermont sites will trend towards snow between 10- 13Z, starting at MPV/EFK with BTV changing to snow last by 13Z. Temperatures will quickly fall below freezing with the potential for a flash freeze at all terminals as precipitation changes to snow. Best chances for a flash freeze will be at the northern New York terminals. There is chance (30-40%) of LIFR ceilings to 400ft at SLK/PBG/EFK during some of the heavier precipitation between 06-12Z, and non-zero chance of LIFR at all other terminals. Snow will continue at least through 15Z, with some tapering off at PBG/BTV near the end of this TAF period. Winds will switch to the northwest by 12Z Thursday and become breezy with gusts up to 20 kts, mainly at MSS/PBG/BTV. Ceilings will see a slow improvement back to MVFR from IFR near the end of this TAF period from west to east.

Outlook...

Thursday Night: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Friday: VFR. NO SIG WX. Friday Night: VFR. Slight chance SHSN. Saturday: VFR. Chance SHSN. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHSN. Sunday: MVFR. Chance SHSN. Sunday Night: Mainly MVFR, with areas VFR possible. Slight chance SHSN. Martin Luther King Jr Day: Mainly VFR, with areas MVFR possible. Chance SHSN.

EQUIPMENT

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. Use extra caution when navigating the broad waters of Lake Champlain. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...Winter Storm Warning from 7 PM this evening to 7 PM EST Thursday for NYZ026-027-087. Winter Weather Advisory from 7 PM this evening to 7 PM EST Thursday for NYZ029>031-034.