Area Forecast Discussion

WHAT HAS CHANGED

As of 236 PM EDT Sunday...

No significant changes to the forecast at this time. Still anticipating daily scattered to numerous showers and possible sub severe embedded thunderstorms through Thursday.

KEY MESSAGES

As of 236 PM EDT Sunday...

1. Isolated to scattered showers and embedded thunderstorms are expected this afternoon and tomorrow afternoon, mainly across the Adirondacks, with isolated to scattered heavy downpours.

2. More widespread showers and thunderstorms are expected by Tuesday, with the best chance for widespread precipitation expected Wednesday as a slow moving system tracks through the region.

3. Trending drier heading into the first half of the weekend before showers return for Sunday.

DISCUSSION

As of 236 PM EDT Sunday...

KEY MESSAGE 1: High pressure will continue to drift northeast of the Canadian Maritimes, putting the region in a col (or area between 2 lows and 2 highs), with little flow aloft or wind direction. To the west, a weak shortwave will attempt to push east, but will encounter lingering surface dry air, and thus will be shunted west of the Champlain Valley. As this boundary works into northern New York however, there will be enough forcing off the terrain to sustain some isolated to scattered showers and embedded thunderstorms across the Adirondacks and perhaps the St. Lawrence Valley. PWATS are about 0.5" above normal, and with little steering flow aloft, brief heavy downpours will be possible. Increasing surface instability to 1500J/kg based on the current SPC Mesoanalysis across northern New York bodes some confidence in scattered convection. These showers and thunderstorms will be mainly pulse like storms, that bubble up, but dont last long and come back down. There is a lack of any shear or strong dynamics so no severe storms are expected, but any collapsing shower could innately bring some breezes to the surface. With decent PWATs to around an inch to an inch a quarter, briefly heavy rain is possible. However, given the recent dry stretch rainfall amounts will only be around a quarter to locally half an inch.

Showers will wane with the loss of diurnally heating tonight. Should a location in the Adirondacks get rain today, chances for localized patchy fog will increase. A repeat of today is expected tomorrow, though the shower and thunderstorm chances slide a but to the east with dry air retreating. Pulse showers and thunderstorms will develop in the early to mid afternoon across the terrain of the Adirondacks and Green Mountains, and by and large should be contained to the higher terrain. However, these showers could drift east into the Champlain Valley or eastern Vermont by the mid to late afternoon Monday, though chances are only 20-30%. Showers will once again wane towards sunset Monday. Should across northern New York receive multiple rounds of showers Sunday and then Monday, we'll need to monitor these areas for potential of flash flooding, but this threat is highly conditional. The Weather Prediction Center currently has most of northern New York, outside of the Champlain Valley, under a Marginal Risk (Risk level 1 out of 4; 5% chance for rainfall exceeding flash flood guidance) for Monday. Northern New York rivers could see some small rises, but nothing near bankfull with the recent dryness we have had. Better, more widespread rain chances are expected by mid week.

KEY MESSAGE 2: A slow moving upper low is still expected to track through the region by mid week with chances for persistent showery weather into Thursday. The main long wave trough over the Great Lakes will shift east into northern New York and Vermont by Tuesday with a more established system. A nearly cut-off vertically stacked surface low will move into the region with widespread showers increasing from west to east Tuesday late morning. Trends have continued to favor the center, and subsequently better forcing, staying to our south over Long Island and southern New England which places our region in the northern periphery overrunning portion of the system. Tuesday will see continued diurnally driven showers and thunderstorms with more widespread coverage than Monday. Pwats look to increase towards 1.5-1.75 inches with around 500-1000J/kg of SBCAPE. These ingredients could be supportive of heavy downpours, mainly across the St. Lawrence Valley in New York and Rutland and Windsor Counties in Vermont, though antecedent dry conditions may continue to limit these pwat realizations. It is still uncertain how far north the more widespread precipitation shield extends, but right now it is likely that the best precipitation chances and amounts will favor southern Vermont. Any areas that see heavier downpours on Sunday or Monday will need to be watched. By Tuesday, the WPC has the Marginal (at least 5%) Risk of excessive rainfall over the entire forecast area. Because of all these additional showers, thunderstorms, and general moisture/clouds around, highs Tuesday will come back down just a couple degrees, in the upper 70s to mid 80s.

The best chance for widespread showers will be Wednesday. The low over southern New England looks to occlude with good wrap around moisture transport off the Atlantic along the northern edge of the system. Rain on Wednesday is not expected to be as convective as previous days. By Wednesday, chances for an inch of rain over 48 hours increase from 50-80% from south to north across the entire region. Chances for 2 inches in 48 hours by Wednesday night are generally under 20% for the area, outside of southern Windsor County which is at 55% based on the latest NBM. Southern Windsor County will have the best chance for any higher rainfall amounts due to easterly flow. The current rainfall forecast highlights these target areas with up to an inch and three quarters locally possible in southeastern Vermont, and around an inch to an inch and a quarter for the rest of southern Vermont and northern New York Tuesday through Wednesday. Half and inch to to an inch is expected from the Northeast Kingdom to central Vermont and the northern Champlain Valley. Wednesday is another period that the WPC has our entire area under Marginal Risk of excessive rainfall. River rises will be expected by Wednesday night following the bulk of the precipitation, though current forecasts keep area waterways below bankfull. Precipitation should limit temperatures on Wednesday, reaching widespread 70s.

KEY MESSAGE 3: Lingering showers are likely on Thursday as the upper level trough slowly exits the region and the occluded surface low remains nearby. As they push to the east for Friday and Saturday, conditions will trend mostly dry. While an isolated shower cannot be ruled out, conditions will be almost completely dry. A cold front attempts to push south into the region on Sunday, likely bringing another rounds of showers with the potential for embedded thunderstorms. Temperatures will be mostly seasonable during this time, though likely trending slightly above average heading into the weekend. No major heat is expected going into next week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18Z Monday...VFR conditions will mostly prevail for the next 24 hours. The one exception will be at SLK where scattered showers and thunderstorms are possible this afternoon. A brief reduction to MVFR or IFR visibility is possible. The thunderstorm chance ends by 00Z. Winds will be generally light and southerly today, going light and variable tonight, and returning to light and southerly tomorrow. Gusts up to 15 KT are possible at PBG and BTV today and tomorrow.

Outlook...

Monday Night: VFR. Slight chance SHRA, Slight chance TSRA. Tuesday: VFR. Likely SHRA, Chance TSRA. Tuesday Night: Mainly VFR, with local IFR possible. Likely SHRA, Slight chance TSRA. Wednesday: MVFR/IFR conditions possible. Definite SHRA, Chance TSRA. Wednesday Night: Mainly VFR, with local IFR possible. Chance SHRA, Slight chance TSRA. Thursday: MVFR/IFR conditions possible. Chance SHRA, Chance TSRA. Thursday Night: Mainly VFR, with areas MVFR possible. Slight chance SHRA. Friday: Mainly VFR, with local MVFR possible. Slight chance SHRA, Slight chance TSRA.

BTV WATCHES / WARNINGS / ADVISORIES

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