textproduct: Burlington

WHAT HAS CHANGED

As of 242 PM EDT Saturday...

Increased the winds tomorrow afternoon with better mixing potential. Have also kept gusty winds and heavy rain wording within any thunderstorm chances tomorrow afternoon.

KEY MESSAGES

As of 242 PM EDT Saturday...

1. Strong to potentially severe thunderstorms and localized flash flooding possible tomorrow.

2. A return to more seasonable temperatures and a brief break in unsettled conditions is expected to start off next week.

3. Cooler with some showers next week and a larger storm system Thursday.

DISCUSSION

As of 242 PM EDT Saturday...

KEY MESSAGE 1: Behind our quiet weather today, shower chances will increase near the International Border tonight into tomorrow morning ahead of a strong cold front. There is a bit of lower confidence in severe weather tomorrow, though the potential for some stronger storms remains unchanged. A weaker shortwave will traverse just north of the International Border beginning tonight with a slight chance to chance PoPs near Massena as some showers may graze the northern St. Lawrence Valley. Into the daytime, mixing will increase into the late morning with a drying of the low levels across central and southern Vermont. Into northern New York, proximity to the front should keep mixing tempered with precipitation ongoing. The exact depth of the mixing layer remains somewhat uncertain, with the HRRR mixing nearly to 600mb, whereas the NAM3 mixes lower, closer to 850mb. A blend of the two seems reasonable, with a combination of dry low level air, but increased mid level moisture advected north from the Gulf. This results in a shallow inverted V type sounding for the southern Champlain Valley and southern Vermont, with a saturated mid level. While inverted V soundings usually indicate the potential for isolated microbursts, the modeled DCAPE is around 700- 800J/kg, given the shallowness of the LCL. Furthermore, this DCAPE will likely not be fully realized as overall instability will be muddied with convective debris and moist mid layers, resulting in a mid level inversion and little MLCAPE. This inversion will likely help cap the vertical extend of many showers and embedded thunderstorms. Regardless, there may be some synoptically driven gusty winds tomorrow given stronger mixing around 30 to 35 MPH, with top of the mixed layer winds around 50 kts. Additionally with the inverted V profiles, stronger downdrafts may be possible with embedded gusty winds under any thunderstorms. Have added gusty winds to the forecast.

The more concerning aspect to the forecast will be widely scattered to isolated hydro concerns. Guidance continues to show good pwats across the region to 1.5 inches with several CAMS denoting streaks of 3-6 hr QPF around 1-2 inches. Tall skinny CAPE profiles with a deep warm cloud depth to around 10,000 ft are favorable for heavy precipitation. Have continued with enhanced heavy rain wording tomorrow for localized flooding concerns. The NAM3 and HRRR highlight the potential for three rounds of showers with embedded thunderstorms, thus should an area see some training cells, some localized flooding is possible. The Weather Prediction Center has placed the entire region in a Marginal Risk for Flooding potential tomorrow. Current guidance points to the central Greens, and potentially southern Vermont as areas we will continue to monitor for the better chances for hydro concerns. Total rainfall tomorrow ranges between near an inch in the St. Lawrence Valley to a quarter inch in the Connecticut River Valley in Windsor County. Rain will be persistent across the St. Lawrence Valley and more showery elsewhere tomorrow. Rainfall amounts may be locally higher under any thunderstorm activity.

KEY MESSAGE 2: Behind the cold front on Sunday, a much cooler air mass will usher in a return to seasonable temperatures for Monday and Tuesday. Highs will be near 70 to the mid 70s with overnight lows in the upper 40s to mid 50s. These cooler temperatures however, will be associated an upper trough and weak instability which could bring some daily chances for showers, especially across the higher terrain. These showers will be light in nature as they lack any meaningful moisture or instability profiles. Best chances will be Monday morning, particularly across the Adirondacks.

KEY MESSAGE 3: Large scale troughing will be established for much of next week, bringing seasonably cool temperatures and several rounds of shower chances as shortwaves pivot around the longwave. Diurnal heating will help increase the shower chances in the afternoon a bit due to the cool air aloft. However, most of the time it will be dry. It is increasingly likely that a more organized area of low pressure will move through Thursday into Thursday night, bringing widespread rainfall. With the current favored track to the north, it will likely bring gusty synoptic winds. A low level jet of 40 to 60 KTs looks increasingly possible, as long as the low track continues to be to the north. GEFS, EPS and CMCE combined ensemble probabilities of more than an inch and two inches of total rain are 70-90 percent and 20-50 percent respectively. The rounds of precipitation currently look to be light enough and moving quick enough to prevent much of a flooding threat.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through 00Z Monday...VFR conds expected through the forecast period, except late in the period at KMSS. Mainly expecting light winds less than 10 kts overnight with just some passing scattered mid and high cloudiness, most prevalent across the SLV and far northern counties. Decaying convection across the Ottawa Valley may produce a dying light shower or brief sprinkle at KMSS through 02Z, but low confidence suggests omission of this possibilty at this point. LLWS also noted at KMSS and KSLK in the 01-08Z time frame, generally 240/250 @ 35-40kt w/assoc. modest turbulence. After 12Z, cold front begins to approach from the northwest with increasing chance of showers and a few stronger storms across northern counties, then progressively south into central VT by early evening. Mixed signals in the models on the strength of storms so confidence in widespread storms is on the lower side of moderate, but be aware a stronger line of convection is plausible in these areas from noon/early afternoon onward into early evening with gusty winds and turbulence. Winds generally south to southwesterly 08-12 kts with gusts to 20 kts, though variable and erratic near any convection.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

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