textproduct: Burlington

WHAT HAS CHANGED

As of 455 AM EDT Tuesday...

Quick update to increase pops this morning, adjust temps, and winds grids. Radar imagery showing greater areal coverage of showers/embedded rumbles than original expected over northern NY.

Issued Wind Advisory for portions of northern NY. Also, added gusty wind wording associated with thunderstorm potential this afternoon.

KEY MESSAGES

As of 254 AM EDT Tuesday...

1. Gusty southwest winds expected today, especially across northern NY. A few stronger thunderstorms possible this afternoon with localized gusty winds as the primary threat, along with frequent lightning.

2. A widespread 1 to 2 inches of rain expected between today and Wednesday evening across our region, but threat for flooding is low.

3. Unsettled weather with cooler temperatures this weekend into early next week.

DISCUSSION

As of 254 AM EDT Tuesday...

KEY MESSAGE 1: A Wind Advisory has been issued from 15Z to 00Z today for gusty southwest winds 15 to 30 mph with gusts up to 50 mph for portions of northern NY. Latest 00z NAM/HRRR and RAP sounding data all suggests very favorable mixing profiles up to 750mb today, resulting in localized gusty southwest winds, especially across portions of northern NY, where progged 925mb to 700mb winds are the strongest. NAM12KM and NAM3KM soundings show favorable mixing under warming bl temps, with top of the mixed layer winds of 45 to 55 knots, while bottom values are in the 35 to 45 knot range, supporting localized gusts 40 to 50 mph possible. The core of strongest winds wl be from OGS to MSS, then angling along the northern downslope areas of the Dacks from Malone to Altona from roughly noon to 5 PM. Soundings suggest favorable dry adiabatic mixing profiles with 0-3km lapse rates in the 8-9 C/km range. Also, the timing of clouds/precip is important toward the amount of llvl instability/mixing, as earlier arrival limits sfc heating and depth of mixing and would support lighter winds per GFS solution. Elsewhere, winds 10 to 25 mph with gusts 25 to 40 mph is expected over the CPV and parts of central/eastern VT.

Have coordinated with SPC this morning with regards to maintaining the new Day 1 Marginal Risk (1 out of 5) acrs our cwa this aftn. Little has changed with regards to our thinking, as latest GOES-19 mid lvl water vapor imagery shows a rather messy upstream scenario. Mid/upper lvl trof conts to deepen over the northern Great Lakes, while modest heights falls are occurring over the eastern Great Lakes associated with initial 700-500mb embedded vort and pre- frontal sfc trof. Meanwhile, have noted multiple pockets of convection and plenty of clouds/moisture in the developing warm sector under deep southwest flow from the SLV into the northern Ohio Valley. The challenging aspect with regards to convection this aftn is how much does the upstream convective debris cloud canopy hinder bl layer heating/instability from developing. Latest 00z CAMs suggest ML CAPE values in the 500-1000 J/kg range, but as mixing improves during the early aftn hours, sfc dwpts could drop back into the upper 40s. Sounding profiles are very impressive with steep sfc to 3km lapse rates in the 8-9 C/km range, supporting higher based convective capable of localized gusty winds within mini bowing line segments. Also, noted unidirectional wind profiles through 500mb and more straight lined hodographs today, which is confirmed with area VAD profiles, suggesting bowing line segments as primary convective mode. Still concerned developing deep layer shear near 50 knots and modest CAPE profiles may shear higher/stronger convective tops apart, minimizing severe potential. If greater clearing develops and instability can approach 1500-1800 J/kg, the probability of stronger/more robust updrafts and severe threat increases acrs our cwa this aftn. Its pretty much a nowcasting scenario, in monitoring latest clearing/heating/instability trends and evolution of upstream convection today.

KEY MESSAGE 2: Numerous showers and embedded thunderstorms this aftn evolve into a widespread stratiform rain event late tonight into Weds acrs our cwa. 00z guidance continues to support a widespread 1 to 2 inches of rainfall by Weds evening acrs our cwa. This wl be driven off synoptic scale lift, from tightening low level thermal boundary and developing weak area of low pres lifting along boundary on Weds. Most of our cwa is progged to be on the cool/north side of this system, with limited instability and rainfall rates in the 0.10 to 0.25 inch per hour range. The strong llvl convergence, combined with a sw to ne axis of enhanced 850mb to 700mb fgen forcing, should produce enough synoptic ascent to support this moderate rainfall event. Current guidance suggests heaviest axis of rainfall wl be from the central Dacks into central VT, where some localized values in the mountains could exceed 2.0". Given the anticipated rates and long duration event, no river or flash flooding is expected with this event. A cold raw and wet Wednesday is predicted with highs only in the mid 40s to mid 50s, maybe lower 60s near VSF. Steadier rainfall slowly tapers off by late Weds night with some areas of fog/low clouds likely into Thurs morning.

KEY MESSAGE 3: The general unsettled weather pattern will continue into the long term. This is due to broad troughing/cyclonic flow that will remain anchored over eastern Canada. As multiple shortwaves round the base of the trough and transit over our forecast area, we can expect off and on periods of rain over the weekend and into early next week. Temperatures will stay slightly below seasonal norms, but will be warm enough to support rain as the dominant precipitation type in all but the highest elevations. Overnight low temperatures may support some frost development this weekend (depending on evolution of cloud cover and overnight winds), especially Saturday morning in the northern Adirondacks and eastern Vermont. However, the Champlain Valley is the only area within our forecast area of responsibility that has started the "growing season" as per our frost-freeze program, and conditions there will remain warm enough to preclude a frost threat. Thus at this point headlines are not anticipated, but keep an extra eye on the late week/weekend forecast if you have sensitive vegetation.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday...The most impactful weather over the next 24 hours will be the development of gusty south/southwest winds through the day today. Winds will start off light from the south (except already locally gusty in the Champlain Valley), increasing to 10-20 knots after 12Z with gusts 25-35 knots between 14Z and 22Z. Strongest surface gusts are expected at KMSS, where gusts will locally reach the 35 to 40+ knot range mainly between 17Z and 21Z. Have put LLWS in all TAF sites this morning, then ended the LLWS at some TAF sites after 15Z as the boundary layer mixes out and surface gusts increase. More localized LLWS redevelops after 21Z. In addition to winds, rain showers will move in from west to east, arriving mainly between 13Z and 21Z (although some brief scattered showers are possible before 13Z). Though widespread thunderstorms are not expected, some isolated embedded thunderstorms may develop during the daytime hours. Given lack of any strong boundary, the timing of thunderstorms today is lower confidence, so have left mention of thunderstorms out of TAFs at this point. Will add mention in later issuances if confidence increases and timing is able to be narrowed down. For now, a broad window of 18Z to 00Z looks to be the general timeframe of more supportive conditions for some isolated thunderstorms. Within any showers or heavier thunderstorms today, a brief and localized increase in wind gusts is possible given the strength of the low-level jet. Rain intensities will mainly be light today with visibilities mainly expected to stay in the 5-6+ SM range. However, during any heavier showers or thunderstorms, some brief moderate rainfall is possible which would reduce visibilities briefly to the 2-5 SM range. Ceilings will lower today as rain approaches, but are expected to remain mainly at VFR levels at all except KSLK and KMSS. These two TAF sites may have a period of up and down cigs around 2500-3500 feet between 12Z and 20Z, with a mix of SCT and BKN at times skycover.

Outlook...

Wednesday: Mainly MVFR, with local IFR possible. Definite RA. Wednesday Night: Mainly VFR, with areas MVFR possible. Likely RA, Chance SHRA. Thursday: VFR. Slight chance SHRA. Thursday Night: VFR. Slight chance SHRA. Friday: VFR. Chance SHRA. Friday Night: VFR. Slight chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

MARINE

Southerly winds 10 to 15 knots are slowly increasing this morning and should be 15 to 25 knots by sunrise with a few higher gusts possible this morning, before subsiding back into the 10 to 20 knot range by this afternoon. Wave 1 to 2 feet build 2 to 4 feet this morning, before decreasing by sunset this evening.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...Wind Advisory from 11 AM this morning to 8 PM EDT this evening for NYZ026>028-030-031-034-087.