textproduct: Burlington

WHAT HAS CHANGED

As of 254 PM EDT Friday...

Isolated to scattered rain/snow shower chances possible Saturday across the higher terrain.

KEY MESSAGES

As of 254 PM EDT Friday...

1. A frontal system is beginning to move into the region this afternoon with widespread wetting rain expected through tonight. Lingering isolated upslope showers will be possible Saturday across the higher terrain with cooler, breezy conditions.

2. A warming trend will start late this weekend with another round of widespread rain Sunday into Monday. Gusty winds are possible.

3. Unsettled with above normal temperatures expected through the middle of next week.

DISCUSSION

As of 254 PM EDT Friday...

KEY MESSAGE 1: A cold front is currently pushing into the region from eastern Ontario, as the frontal axis stretches from Montreal to Ottawa, and southwest to Buffalo. This front will continue to push east through this afternoon/evening reaching Vermont between 6-8 PM. This system is NOT expected to be a soaker, but the forecast does denote some beneficial wetting rainfall between 0.1-0.3" across the region, helping to alleviate dry fine fuels, and reducing fire weather concerns into the weekend. Higher amounts between 0.25-0.4" are expected near the International Border with some mountain summits approaching 0.5". Hi-Res CAMs (like the HRRR) denote an area of enhanced precipitation potential across the southern Champlain Valley and western Rutland County. SBCAPE will only be around 150- 200J/kg, but with the presence of the front, this may be enough to support isolated convective elements with some locally higher precipitation amounts. This system track does favor potential shadowing in the northern Champlain Valley and Windsor County where only 0.1-0.2" of rain is expected, less than surrounding areas.

The front continues to move east tonight with precipitation tapering off for most after midnight tonight as colder drier air from the northwest filters in. Across the Northeast Kingdom early Saturday morning, northwest flow may keep some low level moisture around as the mid level dry out, leading to some low-topped rain/snow showers. Snow accumulations will be minimal if any with ground temperatures above freezing. Otherwise, Saturday will be on the chilly side, but mainly sunny side, with northwest caa and breezy conditions with highs in the low to mid 40s. Some diurnally driven isolated rain/snow showers aided by northwest flow will be possible in the higher terrain Saturday afternoon, but impacts will be minimal if any. High pressure builds in Saturday night with overnight lows in the mid to upper 20s in the higher terrain, and low 30s in the wider valleys.

KEY MESSAGE 2: Temperatures will begin a warming trend heading into next week as our flow becomes south dominant with our high sliding east. A digging long wave trough will set the stage for unsettled weather heading into next week, with the first of several rounds of precipitation arriving late Sunday into Monday. A warm front will lift north late Sunday with increasing precipitation chances across northern New York and into Vermont by Sunday night. A few tenths of inch of rain will be possible Sunday afternoon into Sunday night, with higher amounts in the northern St. Lawrence Valley and northern Greens. The associated surface low looks to slide east, with some continued uncertainty in its exact track. Models continue to wobble between a center track over Montreal and a track along the northern fringes of the North Country. This has large implications for Monday. Expectations are that a sharp temperature and precipitation cutoff will be associated with the system, as it will follow a positive tilted axis as the departing weekend high will stall to the southeast. Areas across the International Border could see rounds of showers through the day Monday in the upper 50s to low 60s, whereas areas south Chittenden County in Vermont could see less rain overall and temperatures into the mid to upper 60s. The position of the system track will be key for this. The current forecast calls for half an inch across much of northern New York and northern Vermont, with 0.1 to a quarter inch of rain for the rest of Vermont and the Champlain Valley through Monday afternoon.

The main impact from this system will a strong 60-80 mph 850mb low level jet. It is uncertain how the mixing profiles will set up with the system, as the core of the jet will be colocated with the main precipitation shield along the International Border. A low level inversion should allow for at least some gusty winds up to 25-35 mph in the northern Champlain Valley and northern downslope regions of the Adirondacks along the US-11 corridor. This will be closely watched as stronger winds near Wind Advisory levels cannot be ruled out should the mixing potential increase, especially if the precipitation shield trends north, or areas see breaks in the rain. For now, mixing is thought to be tempered with the ongoing precipitation with lower winds.

KEY MESSAGE 3: The large scale pattern indicates building mid/upper lvl heights acrs the Eastern CONUS, while low level boundary remains draped near the International Border. Fast westerly flow aloft prevails acrs our central/northern cwa for most of next week, with warm air to our south and cooler air north. Position and movement of this boundary wl have significant impacts on temps and precip fields through the middle of next week. ECMWF/GFS and CMC show the warmest 925mb to 850mb temps on Weds with progged 925mb temps btwn 15-18C, which support highs well into the 70s with maybe a few valley locations near 80F. NBM still suggests a large spread on Weds with 25th percentile high temp of 65F and 75th percentile of 79F, while the mean is 71F for BTV.

Next question wl be areal coverage of clouds and potential for precip, as latest GFS shows building sfc based CAPE values in the 250-700 J/kg range. The highest probability of thunder currently looks to be on Weds aftn, given sfc heating and moisture. The latest WPC forecast does indicate chc to likely pops everyday in the extended forecast, but not expecting a complete washout as precip looks to be convective and scattered in nature. In addition to the very warm temps on Weds, gusty south/southwest winds develop as 925mb to 850mb jet increases to 35 to 50 knots. Warmer temps should result in deeper mixing profiles on Weds. Slightly cooler and drier wx returns for Thurs, behind weak boundary.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...A cold front with a line of showers is approaching the St Lawrence Valley at this time. Currently VFR conditions prevail at all TAF sites, but conditions will change rapidly this afternoon/evening as CIGS quickly lower behind the initial boundary. Expecting VFR to trend toward MVFR by 21z-00z with IFR by 00z at SLK/MSS. I have a tempo to cover the uncertainty on timing of IFR at MSS between 21z-01z. Otherwise, CIGS should trend toward MVFR by 00z at PBG/BTV/MPV and EFK with some intervals of IFR conditions likely between 02z-08z tonight. The IFR cigs should be only 2 to 6 hours at most sites with conditions improving by sunrise on Saturday to MVFR and mostly VFR by 15z. South winds become north/northwest 5 to 15 knots with some localized higher gusts on Saturday morning expected. Visibilities stay mostly in the VFR category but fall into MVFR in the heavier shower activity this aftn/evening.

Outlook...

Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA. Sunday Night: MVFR. Definite SHRA. Monday: Mainly VFR, with areas MVFR possible. Likely SHRA. Monday Night: Mainly MVFR, with local IFR possible. Chance SHRA. Tuesday: Mainly MVFR, with local IFR possible. Chance SHRA. Tuesday Night: MVFR/IFR conditions possible. Likely SHRA. Wednesday: MVFR/IFR conditions possible. Likely SHRA, Slight chance TSRA.

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...None. NY...None.