textproduct: Burlington

WHAT HAS CHANGED

As of 252 PM EDT Friday...

Increased confidence in rain next Thursday.

KEY MESSAGES

As of 252 PM EDT Friday...

1. Intervals of scattered showers and thunderstorms with warm, humid conditions will continue through much of the weekend.

2. A brief period of lower humidity and dry conditions later Sunday into Monday morning will end with increasing chances of showers and thunderstorms later Monday.

3. Seasonable conditions are anticipated next week with additional chances for showers and thunderstorms as well as gradually decreasing temperatures.

DISCUSSION

As of 252 PM EDT Friday...

KEY MESSAGE 1: Isolated to scattered showers with a couple of thunderstorms remain on track for this evening into the overnight hours. For late this afternoon and evening, it appears our setup is reminiscent of yesterday with pulse storm potential. However, subtle differences will limit the thunderstorm threat. Instability over the Adirondack region is less robust, and so the ability for stronger convection will be limited by these initial weaker updrafts. However, increasing cyclonic flow as an upper level wave over the eastern Great Lakes gets slowly pushed towards our region will help generate more showers with time, peaking during the early morning hours and across northern portions of Vermont. With such weak forcing including lack of a well defined front or low pressure system, precipitation amounts will continue to be quite spatially variable. Activity will generally shift to the northeast with time, and pockets of heavier rainfall (~0.25 - 0.5" with localized 1" amounts) will tend occur through tomorrow morning. Some locations, probably in southern portions of Vermont, again should see little or no rain.

For Saturday, there are again some mixed signals in terms of the convective evolution. Each of the last couple of cycles, machine learning guidance has been somewhat bullish on potential for some stronger thunderstorms. Consensus shows higher probabilities both south and east of our region; the latest Day 2 Storm Prediction Center severe risk does highlight the mid-Atlantic region again following today's stronger storms in that area as well. That being said, generally thunderstorm probabilities are roughly as high in our region as towards the south, with regionally greatest chances in northeastern Vermont and lowest chances in the southern St. Lawrence Valley and southern Vermont. Representative forecast soundings in St. Johnsbury during the early evening show MLCAPE of around 1500 J/kg (moderately high CAPE) and effective shear of 10-15 knots (low wind shear), so the environment looks marginally supportive of pulse thunderstorms with mainly typical thunderstorms and a rare stronger wind gust possible.

Following yesterday's anomalous moisture, precipitable water will be a bit lower tonight when it surges with the wave coming through (about 1.7" to 1.9"), and fall further tomorrow (about 1.5" to 1.7"). So while a marginal (level 1 out of 5) risk of flash flooding continues associated with heavy rainfall rates in thunderstorms, think the footprints of 2" + that we saw yesterday are less likely. With meager instability available ahead of a final round of scattered showers moving through overnight Saturday into the day on Sunday, risk of impactful weather diminishes further as the weekend wears on. As the associated weak surface front passes to our east, sharply drier, refreshing air will return during the second part of the day.

KEY MESSAGE 2: Tranquil, seasonably warm conditions from late Sunday into Monday will prevail as a narrow axis of deep layer ridging zips into and then out of our region to be replaced by a prefrontal trough Monday evening. Most of the impacts from this trough and the following cold front will follow Monday night, but overall the threat of showers and thunderstorms will ramp up towards evening, particularly in northernmost portions of New York where both rain and thunder chances are highest through the afternoon hours. Stronger storms currently look unlikely with only modest instability and shear, but we'll have to monitor any trends in the data if they deviate from the current thinking.

KEY MESSAGE 3: A cold front is expected to cross the region Monday night, bringing an increased chance (45-85%) of precipitation to northern New York and Vermont, including some overnight embedded thunder. Temperatures will be on the milder side throughout the night, remaining at or above the mid 50s to mid 60s. Tuesday could also be a showery day with embedded thunder (precip chances 15-55%) under modest cold air advection and seasonable temperatures in the mid 70s to mid 80s. Mid week will feature a period of 15-55% chance of precipitation and seasonable temperatures (highs mid 70s to lower 80s, lows 50s and lower 60s). Then, longwave troughing returns late week, bringing a resurgence of higher shower and thunderstorm chances on Thursday afternoon plus highs falling into the 70s for most both Thursday and Friday.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Through 00Z Sunday...Isolated to scattered showers will continue through 08z Sat, mainly from KSLK eastward. VFR conditions should prevail during that time, but brief reductions of both visibility and ceilings to MVFR are possible with any precipitation. Precipitation will exit after 08z, with perhaps some partial clearing through early Saturday morning. Those locations that receive rain this evening could see fog develop, with the most likely timing 08z-12z. At this time, have the most confidence in IFR conditions in fog at SLK/MPV, but it can't be totally ruled out anywhere, though MSS has the lowest chances. Otherwise, patchy MVFR ceilings/visibility in fog through 12z, then conditions quickly improve to VFR for the remainder of the day. Scattered showers and thunderstorms will redevelop after 16z, with MPV and EFK having the best chance of seeing precipitation. Winds light and variable to calm overnight tonight, trending toward S/SW 5-8 kt after 13z Sat.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

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