textproduct: Burlington

WHAT HAS CHANGED

As of 249 PM EDT Sunday...

No significant changes at this time.

KEY MESSAGES

As of 249 PM EDT Sunday...

1. Rounds of showers and some thunderstorms are expected later Tuesday (especially northern New York) and Wednesday (especially Vermont) associated with a fairly slow moving frontal system.

2. No significant impacts through the extended forecast.

DISCUSSION

As of 249 PM EDT Sunday...

KEY MESSAGE 1:

Breezy northwest winds will diminish tonight, supporting a chilly night, as high pressure centered to our south approaches and then shifts east into the western Atlantic Ocean tomorrow night. Meanwhile, near surface smoke today is lingering across the Ohio Valley into the Mid-Atlantic region, and is being well captured by the RRFS-Smoke model. As winds turn southerly on Tuesday, we'll likely see some smoke return; forecast concentrations currently are indicated to be in the "unhealthy for sensitive groups" range. Some haze associated with smoke aloft will also likely filter in from the north tonight into Monday. Vertically integrated smoke may not become thick enough to reduce air temperature substantially on Tuesday, with progged values approaching 100 mg/m2, but it's something to monitor. Think the combination of increasing clouds and smoke will lead to another day with daytime temperatures underachieving, although unlikely as significantly so as yesterday; this will have implications for the thunderstorm potential discussed below.

The main weather impacts for the midweek timeframe continue to be on track with another seasonally potent low pressure system passing to our west bringing widespread showers and thunderstorm chances. It continues to not look particularly impactful for our area, but there are some things to watch for given another potent/dynamic low pressure system coming through. A primary low should pass through northern Quebec on Tuesday, with an additional wave of low pressure developing along the surface boundary closer to northern New York and Vermont Tuesday night into Wednesday. While the area of greatest instability is favored to our south/west over central New York and points south, thunderstorm probabilities for Tuesday afternoon/evening have increased slightly into the 35-40% range for most locations in west- central Vermont and southwestern portions of the Adirondacks and St. Lawrence Valley, dwindling eastward slightly where potential for thunderstorms increases after sunset. Lowest chances of thunderstorms through Tuesday night are across the Northeast Kingdom. The general west-east gradient is consistent with thunderstorm probabilities in machine learning data, which also greatly favors stronger variety of thunderstorms staying away from our forecast area given limited instability (possibly remaining under 250 J/kg) associated with moist adiabatic lapse rates and limited surface heating. With substantial height falls occurring overnight, instability may actually increase overnight shifting eastward; the best combination of ingredients for heavy rain may be in the early morning hours, but concerns for excessive rainfall at this time are low. Streamflow and soil moisture are near normal currently and will trend below normal following a couple of dry and sunny days. As such, impactful rainfall would tend to be very isolated and reliant on deep convection and training of thunderstorm cells, which at this time is unlikely for any of our region. Late Tuesday perhaps western portions of northern New York will have enough instability for heavy rainfall rates, but convection during this period is likely to be progressing eastward.

The somewhat more interesting forecast scenario appears on Wednesday in Vermont. Probabilistic data is fairly bullish on thunderstorm potential (6 hour chances increase to around 30% after 2 PM) across northern Vermont, greatest in central to northeastern areas. Compared to 24 hours ago, these probabilities are fairly similar but the maximum area shifted northward. Will note that while the upper level forcing for precipitation will be supportive of widespread showers, the severe weather potential is questionable and may favor areas to our south and east; mid-level cooling and drying aloft may inhibit thunderstorm development. However, if there is enough low level moisture and diurnal heating, ingredients for thunderstorms will be present in Vermont given the obvious triggering mechanism. The current projected location of surface fronts puts a triple point near the northern Champlain Valley Wednesday morning. Therefore, the wind fields could be conducive to rotating storms if other required ingredients come together including sufficient low level moisture and instability. Some data shows a surge of instability in the relatively modest 1000- 1500 J/kg range overlapping 30-35 knots of deep layer shear in eastern Vermont Wednesday afternoon just ahead of the cold front, but even less CAPE is shown in other guidance which further reduces the risk of stronger storms. Overall, if the timing of the frontal passage is on the later side, both the thunder and severe risks would increase across Vermont; generally New England will have this stormy potential on Wednesday. Localized heavy rain is possible conditional on the thunderstorm development, and the Excessive Rainfall Outlook marginal risk across Vermont reasonable at this point.

KEY MESSAGE 2: Precipitation associated with a departing trough of low pressure will come to an end by Thursday morning. High pressure will move in during the day Thursday allowing temperatures to climb into the mid 80s by Friday for the warmer valley locations. A weak front could reach unto our area late Friday or Saturday bringing a scattered chance of thunderstorms briefly. Outside of the scattered showers, the weekend will be dry with near normal temperatures.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18Z Monday...VFR expected through the period with FEW/SCT cloud bases mainly 040-070 AGL at most terminals. Northwest winds moderately gusty to 25 kt through 00Z, abating thereafter. No precipitation expected.

Outlook...

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

MARINE

Gusty northwest winds 15 to 25 knots will continue into early evening before diminishing tonight. Waves should be mainly around 1 to 2 feet with some localized higher waves favored on the Vermont side of the lake towards Shelburne Bay given the 310 degree wind direction. Winds will drop below 10 kts overnight and waves will drop below 1 foot accordingly.

After a quiet period, another southerly wind event will likely occur during the day on Tuesday.

BTV WATCHES/WARNINGS/ADVISORIES

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