textproduct: Burlington

WHAT HAS CHANGED

As of 308 AM EDT Monday...

Increased winds across the St Lawrence Valley on Tuesday and tweaked arrival timing of showers and embedded thunderstorms on Tuesday afternoon/evening.

KEY MESSAGES

As of 308 AM EDT Monday...

1. Periods of breezy southwest winds expected at times today through Tuesday, along with temperatures climbing into the 70s by Tuesday.

2. Occasional showers with embedded thunderstorms are expected on Tuesday afternoon and evening, with additional showers anticipated into Weds. Storm total rainfall amounts of 0.50 to 1.50 inches possible, but threat for flooding is low.

3. No major impacts or significant weather expected late week into the weekend, as the pattern continues to support unsettled conditions with below normal temperatures.

DISCUSSION

As of 308 AM EDT Monday...

KEY MESSAGE 1: Upper air analysis and latest GOES-19 mid level water vapor imagery shows weak embedded s/w with pocket of mid lvl moisture associated with waa lifting acrs northern NY this morning. This energy and dynamics wl continue to produce a few scattered showers this morning, mostly near the International Border. Developing southwest flow at all levels of the atmosphere wl occur with moderately strong llvl waa. Progged 925mb temps climb btwn 9- 11C by 21z this aftn, with some partly sunny skies should support highs well into the 60s most locations. Tonight 925mb to 850mb jet of 35 to 50 knots strengthens acrs our cwa ahead of approaching mid/upper lvl trof and associated cold frnt. This increasing pres gradient should result in a very mild night, especially wider valleys, where winds wl stay mixed and limit temps from falling. Have trended toward the 75th NBM for lows, which supports values in the mid 40s east of the Greens to mid/upper 50s SLV and CPV. Localized areas near PBG could decouple and drop into the upper 40s. Expect light winds in the deeper/protected valleys of central/eastern VT, while exposed summits and wider valleys see localized gusts 25 to 35 knots tonight.

Gusty south/southwest winds are expected on Tuesday, especially northern NY, including the SLV where progged 850mb jet of 55 to 60 knots is anticipated. NAM12KM and NAM3KM soundings show favorable mixing under warming bl temps on Tues, with top of the mixed layer winds of 45 to 55 knots, while bottom values are in the 35 to 40 knot range, supporting localized gusts up to 45 mph possible. NAM solutions seem to be the most aggressive with channeled southwest flow and favorable mixing profiles, while GFS and HRRR are slightly weaker. If trends continue a low end wind advisory could be needed for the SLV and portions of the northern Dacks on Tues for localized gusts 45 to 50 mph. 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 20 mph with gusts 20 to 35 mph is expected over the CPV and parts of central/eastern VT. Given llvl wind profiles our first Lake Wind Advisory of the season is likely late tonight into Tues. Still have to watch how the cooler lake water can stabilize bl and limit mixing.

KEY MESSAGE 2: SPC has upgraded the Day 2 outlook to place a marginal (1 out of 5) risk of severe storms acrs our cwa for Tues. From my perspective the potential for strong to severe storms is not ideal, given bl dwpts only in the upper 40s to lower 50s, limited or delayed height falls associated with approaching mid/upper lvl trof and weak convergence with pre-frontal trof/differential heating boundary. Crnt thinking some modest instability develops btwn 15z- 18z Tues with ML CAPE values in the 500-1000 J/kg range, while low to mid lvl wind fields strengthens, increasing favorable deep layer shear in the 35 to 50 knot range. As showers with embedded rumbles of thunder develop by 18z, expanding cloud canopy under less than ideal southwest flow wl help to stabilize environmental conditions. This combined with strengthen wind fields wl shear off vertical development of convection and could limit strong/severe potential. Given pre-storm thermo-dynamics and vertical wind profiles, feel probability of any severe development is <5% attm. Localized hodographs in the CPV are impressive, showing large cyclonic curvature, supporting potential supercells, but instability parameters are marginal. Temps under southwest waa should warm well into the 70s before the rain arrives.

Showers with embedded rumbles of thunder on Tues evolves into a widespread cold stratiform rainfall on Tues night into Weds, as weak sfc low pres develops along a slow moving boundary. MBE vector analysis shows progressive individual elements moving southwest to northeast, but eastward progression of line is very slow at 4 to 8 knots, given deep unidirectional flow paralleling boundary. This wl result in slow moving rain elements on Tues night into Weds, with the potential of 1 to 2 inches of rainfall from the eastern Dacks into most of VT. The probability of flooding is low, given recent dry weather and modest rainfall rates. Lows wl drop back into the 40s on Tues night and only warm into the 50s on Weds. A cold, raw and wet Weds is anticipated.

KEY MESSAGE 3: Aside from Friday night when consensus is strong on dry weather, some chances for showers will persist through the weekend with another longwave trough parked over the area. These showers should tend to be scattered rather than widespread, and mostly diurnally-driven as steep low level lapse rates lead to shallow instability. Note that while the large scale pattern is similar to what we saw this past weekend, the airmass doesn't look quite as chilly. A low level southwesterly wind is indicated among all model clusters through most of the weekend across the region. In relation, AI-GEFS 850 millibar anomalies bottom out near the 25th percentile Friday evening with gradual improvement after that point, reaching near normal on Sunday. These low level temperatures support highs that are currently forecast in the low to mid 60s in the lowest elevations, and mid to upper 50s elsewhere, during the weekend. Relatively light winds aloft and breaks in cloudiness, dependent on timing of shortwave troughs passing through, could support frost and freeze conditions each weekend morning.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Through 12Z Tuesday...Across a relatively compact area showers continue to push eastward across the airspace this morning. They should mainly affect northern terminals and are exiting from west to east in the 12Z to 15Z period. Brief MVFR visibilities and/or ceilings during these showers are possible, but based on observations so far today most sites will remain VFR with EFK and SLK most likely to see some MVFR conditions.

Otherwise, ceilings should be generally 3 to 7 thousand feet agl, and clouds are expected to trend scattered this afternoon. Mixing of southwesterly boundary layer winds will result in some low level turbulence during the afternoon with gusts in the 20 to 29 knot range. The low level jet will strengthen after 00Z leading to resumption of LLWS late in the period. Flight conditions will remain VFR, although lower ceilings are possible towards the end of the TAF period at MSS.

Outlook...

Tuesday: VFR. Windy with gusts to 30 kt. Chance SHRA, Slight chance TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Definite SHRA. Wednesday: Mainly MVFR, with local IFR possible. Definite SHRA. Wednesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Thursday: VFR. Slight chance SHRA. Thursday Night: VFR. Chance SHRA. Friday: Mainly VFR, with local MVFR possible. Chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

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