textproduct: Burlington

WHAT HAS CHANGED

As of 338 AM EDT Wednesday...

Confidence in potentially severe weather has increased across portions of southern Vermont for Thursday. Fog is also likely tonight as a boundary remains over the region.

KEY MESSAGES

As of 338 AM EDT Wednesday...

1. Light showers and isolated rumbles of thunder expected today trending towards more drizzle and fog by tonight with a boundary remaining draped over the region.

2. Additional rounds of showers with heightened thunderstorm chances expected Thursday into Friday across southern Vermont as a stronger frontal system rides along our quasi stationary boundary.

3. Another storm system is expected to bring rainy and windy weather to the region Saturday evening through Sunday, with showers potentially switching over to snow on Monday as cold air briefly returns.

DISCUSSION

As of 338 AM EDT Wednesday...

KEY MESSAGE 1: Widespread low clouds and patchy fog remain across most of the region with pooling moisture along a quasi stationary boundary draped across our region. Any fog is expected to lift with sunrise as light southerly flow nudges the boundary slightly north for this afternoon. Satellite shows widespread convection associated with merging MCSs in the Upper Midwest to the eastern Great Lakes, as thunderstorms continue to move east along a quasi stationary boundary draped across the Great Lakes into the Northeast. Our shortwave today is currently positioned across the lower Michigan peninsula with an MCS moving east into Lake Erie. CAMs show this area of convection weakening as it approaches the St. Lawrence Valley this morning. What remains of the MCS as it enters our region will likely just be some light to moderate showers with an isolated rumble of thunder, mainly in the St. Lawrence Valley this morning, with shower activity diminishing as it moves east and becomes cutoff by its cold pool. Cooler air from this cold pool near the International Border will keep the northern areas of the region cooler today with highs in the low to mid 50s, where locations south like Springfield and Rutland, Vermont may warm into the 70s. Unlike yesterday, there is better confidence in cloud cover and convective inhibition lingering through most of the day from this approaching MCS. The cold pool should remain over the region today limiting the potential for severe weather or any widespread thunderstorms. However, south of the boundary into Rutland/Windsor Counties, any clearing today may allow for some isolated thunderstorm development, though these storms should remain sub severe and weak, with better instability south of our region. Light showers will continue into this evening with weak forcing, with perhaps some mid level drying from upper level divergence associated with an approaching low level jet for Thursday. This drying will be associated with a strong inversion tonight which will likely lead to widespread drizzle and some patchy fog as temperatures cool, but surface moisture remains ample. Lows tonight will be similar to last night with values in the mid 40s to mid 50s.

KEY MESSAGE 2: A shortwave currently over the Central Plains will track across the Great Lakes into our region Thursday with increasing showers and embedded thunderstorms. This area of energy will ride along our nearly stationary boundary that will remain parked over the region through the end of the week. The latest SPC day2 outlook shows a Slight Risk (2 out of 5) for western Rutland County in Vermont, and southern Essex County in NY, with a Marginal Risk (1 out of 5) for portions of the northern Adirondacks and central and southern Vermont on Thursday. The main threat with any thunderstorms Thursday look to be damaging wind gusts and some isolated large hail.

As with the recent days, there is little change in the overall synoptic pattern with a strong ridge across the southeast leading to several rounds of showers and thunderstorms into the weekend. A shortwave on Thursday will likely be preceded by a decaying MCS as has been the theme the last few days. Convective blowoff through the day will help to keep instability at bay for the better part of Thursday before some clearing can work in for the afternoon/evening. A weak sfc low will track northeast along the St. Lawrence Valley with a lifting warm front during Thursday morning. It will be difficult to determine how much cloud cover remains into the afternoon as to how much instability can develop. The HRRR and HREF appear to be the most aggressive across southern Vermont with the HREF denoting 50-70% chance for > 500 J/kg of sfc CAPE, and 30-40% for > 1000 J/kg, which for mid April is pretty good. Additionally, the low level jet associated with the sfc low will be better located with the highest CAPE as compared to Tuesday with a colocated maximum of 0 to 6 km shear up to 50 kts, which would support thunderstorm activity. The NAM3 is more muddy with broken cells and stratiform mixed in which would limit any discrete cell potential, which does exist in the HRRR 00Z run. Given the presence of the boundary, the best chances for any severe weather would be across Rutland/Windsor counties with temperatures potentially into the mid 70s. Areas north of the boundary could remain in the low to mid 60s depending on the precipitation shield and cloud cover, which will be hard to determine as the boundary fluctuates. Pwat values will be near 1 to 1.3" which would support some localized heavy downpours, and combined with elevation snowmelt, some sharp rises on central/northern waterways are likely through Friday. However, no flooding is expected, but high flows will need to be watched depending on any repeated thunderstorm activity. The main threat with any storms would be damaging winds and isolated large hail, though, some rotating storms cannot be ruled out with curved hodographs and > 250 m2/s2 0 to 3 SRH values in southern Vermont.

A similar pattern setup on Friday will lead to additional shower and thunderstorm chances. A sfc low will track across the region, with some better forcing underneath the center of the low across the Adirondacks and central and southern Vermont. Thunderstorm chances will be maximized in the late morning and early afternoon with surface instability likely from another decaying MCS. However, the instability will be competing with a drying mid to upper level as a nose of high pressure will try to work in for Friday afternoon. There is still some timing differences between global models which will play a role in where any thunderstorm activity will setup. CAMs will be in range in the next forecast package to provide some better guidance.

KEY MESSAGE 3: Surface low pressure is expected to cross Ontario into Quebec on Saturday, with an upper level trough trailing slightly behind it. Southerly winds will increase as gradients tighten over northern New York and Vermont and as a strong low level jet streak approaches the area from the west. This southerly flow will advect in plenty of warmth by Saturday afternoon with highs reaching into the upper 60s and lower 70s, which is 10-15 degrees above seasonal normals for this time of year. The south/southwest orientation of the low level jet will favor gusty winds over the St. Lawrence Valley, off the northern slopes of the Adirondacks, and channeled up the northern Champlain Valley, where gusts in the range of 20 to 30+ knots are possible late Saturday afternoon and into the overnight. Precipitation chances will also increase late Saturday afternoon and evening, with widespread soaking rainfall likely lingering into Sunday afternoon and evening as well. An associated cold frontal boundary is forecast to cross the forecast area early enough Sunday morning to limit destabilization and thunderstorm potential. Model blend precipitation projections continue indicate we could get around a quarter of an inch of precip in 24 hours, but not likely much more than that. Colder air rushing in behind the front Sunday will make it tough for most spots to reach above the 50 during the afternoon before falling into the 20s and lower 30s Sunday night. Due to this dramatic temperature drop towards freezing, there is the potential for lingering rain showers to change over to snow showers Sunday night, starting first on mountaintops and lowering in elevation from there. By the time the cold air reaches the wider valley floors early Monday morning, probability of precipitation will be only about 20-40%. Highs Monday will likely only reach the mid 30s to lower 40s. High pressure takes over early next week to recover temperatures slightly, then model consensus dwindles beyond that.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Through 12Z Thursday...Widespread low clouds (cigs 200-1400 feet above ground level) and patchy fog (visibilities 1/4 to 6 miles) remain across most of the region with pooling moisture along a stationary frontal boundary draped across our region. Fog and low clouds are expected to lift following sunrise as light southerly flow nudges the boundary slightly north for this afternoon. Widespread MVFR or VFR conditions are anticipated by around 15Z-16Z Wednesday. Light showers and isolated rumbles of thunder are expected today trending towards more drizzle and fog by tonight with a boundary remaining draped over the region. Most likely time period of showers will be 15Z through 21Z Wednesday. Visibilities may briefly lower to below 4 miles in these showers/storms, but confidence is not high on the exact timing and location of this lower vis today. By 00Z-06Z (MSS a little earlier) Thursday, we should see a return to widespread IFR ceilings and potentially IFR visibilities tonight, similar to what was observed last night as mist and drizzle get trapped under an atmospheric inversion. Surface winds over the next 24 hours will be light and highly variable, with some southwesterly to southerly component this afternoon. MSS could have an overall northeasterly flow instead, at times 10-15 knots this afternoon. Some LLWS is also expected over the Adirondacks as southwest to west winds at 2000 feet increase around 15Z Wednesday through 02Z Thursday at SLK.

Outlook...

Thursday: MVFR/IFR conditions possible. Likely SHRA, Slight chance TSRA. Thursday Night: MVFR/IFR conditions possible. Likely SHRA, Slight chance TSRA. Friday: Mainly MVFR, with local IFR possible. Chance SHRA, Slight chance TSRA. Friday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Saturday: VFR. NO SIG WX. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Sunday: Mainly MVFR, with local IFR possible. Likely SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

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