textproduct: Burlington

WHAT HAS CHANGED

As of 217 PM EDT Sunday...

Increased thunder chances during the midday and afternoon hours on Monday, but severe t-storm potential remains low.

KEY MESSAGES

As of 217 PM EDT Sunday...

1. Widespread showers overnight, with separate development of showers and some embedded thunderstorms midday/afternoon Monday.

2. Seasonable conditions persist through the second half of the week with mainly dry weather Thursday into Saturday.

DISCUSSION

As of 217 PM EDT Sunday...

KEY MESSAGE 1:

High clouds are in the process of increasing from west-to-east across northern New York and Vermont this afternoon, associated with mid-level trough extending from northern Ontario southward across Lake Huron, Lake Erie and into Ohio. PBL winds have turned southerly with 1022mb sfc anticyclone now east of Cape Cod. Southerly winds should remain moderate overnight with approaching frontal system and absence of much radiational cooling overnight. Overnight lows will generally range from the low-mid 60s. With the increasing southerly gradient flow, a Lake Wind Advisory has been posted (see Marine section below for tonight. The Lake Wind Advisory may be necessary through the morning hours on Monday as well.

Not much in the way of mid-tropospheric height falls overnight, but some low-level WAA in advance of the approaching front should be just enough to yield scattered rain showers overnight, especially after 03Z or so. There is some marginal elevated CAPE for parcels lifted from 850-775mb per HRRR and NAM3 forecast soundings. As such, kept with the idea that there could be a few embedded convective elements with a few overnight rumbles of thunder possible. PoPs are highest across central/nrn VT during the pre-dawn hours (70-80%) and generally 30-50% elsewhere.

Heading into Monday...surface boundary progresses through slowly from west to east. If we get some breaks in the cloud cover, there is a chance for modest PBL destabilization by late morning/early afternoon. Consistent with this, the 12Z HRRR developed 500-800 J/kg SBCAPE during the peak heating hours Monday, that is relatively uncapped. Anticipating a separate broken line of showers - and perhaps a few embedded thunderstorms - to develop during the midday hours while drifting slowly ewd across central/ern VT by mid-late afternoon. Weak mid-level lapse rates and modest sfc-6km shear suggest that if thunderstorms form, they are unlikely to become severe. However, have shown a separate period of 60-70% PoPs to account for this expected separate period of convective showers and storms during Monday afternoon. High temperatures on Monday will be seasonable to slightly below average for mid-August, in the mid- upper 70s.

KEY MESSAGE 2: Lingering showers will move out on Wednesday night and Thursday as broad cyclonic flow slowly migrates eastward. After the system moves off, a period of drier weather looks to return for the latter half of the week. Daytime temperatures increase towards climatological normals into next weekend with highs in the 70s and lower 80s as well as overnight lows falling into the 40s and 50s. There is the potential for another system to sweep through next weekend bringing some sustained showers. We'll continue to monitor this potential as the event approaches.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18Z Monday...Dry conditions through the daylight hours today with southeasterly winds 5-15 knots, more east-northeasterly 5-10 knots at site MSS. Widespread showers with beneficial rainfall tonight will be followed by scattered showers and localized thunderstorms Monday. As rain showers arrive this evening and tonight, we'll see a general trend towards MVFR or lower ceilings, reaching widespread MVFR cigs by 01Z-04Z Monday. Winds should persist out of the south, with sites MSS and SLK picking up a more southwesterly component around 05Z-08Z. Southerly flow will likely remain channeled and gusty through the Champlain Valley, gusting 20-25 knots at site BTV throughout the night tonight and early Monday morning. IFR ceilings are possible sometime tonight and into Monday morning as well, though some uncertainty remains. Most likely spots for IFR ceilings will be SLK and MSS with that southwesterly wind, though no site is out of the question. As of this afternoon, confidence is not high enough to include in the TAF. Most model soundings are not as saturated as probabilistic data might suggest. As the showers approach and we get additional observations from areas upstream, this may increase confidence in one direction or another. LLWS is also possible as a southwesterly low level jet crosses the region around 02Z-12Z Monday. Most likely spots for low level wind shear are BTV, SLK, MPV, EFK, and RUT, though brief LLWS may occur elsewhere as well.

Outlook...

Monday Night: Mainly VFR, with local IFR possible. Slight chance SHRA. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance TSRA. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Slight chance SHRA. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX.

MARINE

As of 217 PM EDT Sunday...

A Lake Wind Advisory has been posted for Lake Champlain tonight. A sharp increase in southerly gradient flow is expected this evening, with sustained winds 20-30kt over the broad lake through the majority of the overnight hours. The Great Lakes Wave Model indicates max wave heights of 3-4 ft between 06-14 UTC from near Colchester Point to east of Valcour Island, which appears reasonable based on expected southerly sustained wind speeds. Should see those wind speeds lessen after noon on Monday.

BTV WATCHES/WARNINGS/ADVISORIES

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