textproduct: Burlington

WHAT HAS CHANGED

As of 332 PM EDT Sunday...

Winds have increased for Tuesday, along with chances for thunderstorms.

KEY MESSAGES

As of 332 PM EDT Sunday...

1. Some light rain associated with the remnants of Isaias will spread across the region tonight, most persistent in southern Vermont.

2. An active period of weather is expected Monday night through Wednesday, including changeable temperatures, periods of rain, and some rumbles of thunder associated a frontal system crossing the area.

3. Lingering mountain rain showers Wednesday will give way to drier and briefly mostly clear conditions for Thursday.

4. A strong low pressure system sweeping through the St. Lawrence Valley will likely bring widespread rainfall and breezy conditions Friday into Friday night, followed by a sharp cooldown.

DISCUSSION

As of 332 PM EDT Sunday...

KEY MESSAGE 1: The former tropical cyclone Isaias is spinning over eastern Kentucky this afternoon, moving towards the east- northeast at about 22 MPH. Counterintuitively, there is very little rain around its circulation; instead, the bulk of the rain associated with its remnants is well to its northeast across the Mid-Atlantic region and southern New England, where a plethora of moisture transport from the Caribbean and Gulf is being drawn northward out ahead of the system, as evident in advective layer precipitable water satellite products today. This advection should support further northward push of rain, eventually overspreading our region late this afternoon, gradually filling in towards northern Vermont and northeastern New York tonight before retreating to the east as favorable lift and moisture quickly departs as low pressure likewise exits.

The details on the start time of rain and how far north precipitation reaches before spreading more towards the east remains difficult to pin down. High confidence of rain remains across southern areas, and observational trends have actually been a touch faster than the consensus with rain already reaching southern counties in Vermont early this afternoon. Therefore, think the reversal of the trend from last night looks reasonable, in which some rain will probably reach all of the way to the International Border, with generally increasing amounts as you go southward. Potential of seeing high end amounts from 24 hours ago in our southern areas in the 1 to 1.5" range has decreased, with the latest 90th percentile values mainly in the 0.5" to 1" range. The expected storm track is far enough south that the better frontogenesis, even in the mid- levels, will remain outside of our region to reduce chances of heavier rainfall rates. Rain will gradually taper off and pull away after midnight, with northern/western areas only seeing up to a couple hours of rain.

KEY MESSAGE 2: As high pressure builds southward over eastern Canada tomorrow night, shallow cold and dry air will seep in from eastern New England and dam up against the Green Mountains and spill down the St. Lawrence and Champlain valleys. Meanwhile, strong warm air advection above that layer will surge in from the southwest out ahead of a wave of low pressure moving eastward across the Great Lakes. The resulting inversion will be quite robust and serve to produce typically substantial temperature variations in our region, and with frontally forced rain showers, elevated convection will be capable of producing thunder. The latest calibrated REFS thunder probabilities are an impressive 70-80% in western portions of St. Lawrence County, tapering off to around 50% near the Vermont/New York border, and further dropping to about 20% by the New Hampshire border. As we get into the HRRR window, these numbers may fall, but the general idea is that signals for showers with embedded thunder during the day on Tuesday continue. Along with the thunder is the expected swath of moderate rainfall and near certain rain chances through the day. A rare washout type of scenario is likely, although a window of drying during the afternoon is possible if the surface boundary was to wobble farther north.

Meanwhile, with near-surface winds out of the south/southeast and an impressive east-west pressure gradient, winds may become marginally strong, including in the eastern Champlain Valley where an easterly component to the wind could help boost temperatures as well. For now with some uncertainties in the magnitude, have stayed shy of the highest wind potential in the deterministic forecast, but expect a windy day in the mountains and lakes, especially in northern Vermont. The mean REFS wind gusts show potential for near Wind Advisory (46 MPH gusts) criteria downwind of the western slopes of the Greens in particular, along with near 35 knot winds on the broad waters of Lake Champlain.

It remains a challenging temperature forecast. The AIGEFS has trended towards the latest run of the GFS with regards to maintaining northeasterly flow in the northern St. Lawrence Valley. Temperatures here are incredibly difficult to forecast with this type of system, as a northeast drainage wind would hold temperatures in the 40s while a flip to the southwest would allow temperatures to surge through the 60s. As consensus improves, would expect future forecast high temperatures may become much cooler, but we have continued to lower highs most appreciably in eastern Vermont where hourly temperatures only gradually warm through the upper 40s to low 50s.

KEY MESSAGE 3: The long term period begins on Wednesday with a moderately strong WNW mid-level flow regime in place across the North Country. The period will generally feature mostly cloudy conditions with some lingering rain showers possible, especially focused across the higher terrain. By Thursday, sfc high pressure is forecast to build in from the Ottawa Valley. Increasing subsidence associated with this feature will help dry out the trapped cloud/moisture layer at 4-6kft, allowing for some partial clearing. Valley high temperatures for both Wednesday and Thursday will generally run in the 50s, which is near to perhaps a degree or two below seasonal levels for mid-October. The quiet weather will be short-lived, however, as the sfc anticyclone translates eastward into the Gulf of Maine by Thursday night, setting up a return S-SE flow and increasing clouds ahead of our next frontal system. We may see Lake Wind Advisory criteria with developing southerly winds on Lake Champlain for Thursday night into Friday morning.

KEY MESSAGE 4: The main highlight for the long term period arrives Friday into Friday night as a vigorous H5 trough and strong low pressure system sweep through the St. Lawrence Valley. This system will likely bring widespread rainfall and breezy conditions to Vermont and Northern New York. Widespread rainfall amounts between 0.5 and one inch appear likely based on latest NWP consensus, and PoPs for late Friday are in the 70-90% range.

As the trailing cold front sweeps through, the potential exists for much cooler conditions for next weekend. The 12Z GFS depicts a particularly deep trough, consistent with previous runs. The 850mb temperatures on the GFS drop to -7C to -8C by 18Z Saturday, and then down to -8C to -9C by 18Z Sunday. While it is worth noting that the GFS tends to have a cold bias in these setups, the current forecast confidently reflects the potential for below-normal temperatures based on the broader 12Z NWP model suite. Expect highs generally in the mid-upr 40s for both Saturday and Sunday.

With a northwesterly flow and sufficient moisture in place, we cannot rule out upslope/mountain snow showers or flurries next weekend, with some minor summit-level accumulations possible. Once the system exits and skies finally clear, this autumn snow against the remaining fall foliage at low elevations could make for a highly picturesque and contrasting view across the high peaks of the Adirondacks and Vermont's Green Mountains.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Through 06Z Tuesday...Light rain is ongoing at SLK, PBG, BTV, MPV, EFK and RUT. A period of IFR cigs expected at KSLK between through 14Z, otherwise mainly MVFR-VFR. In general, TRRN OBSCD across nrn NY and VT during the pre-dawn hours and early morning hours on Monday. Lgt/vrbl winds with a shift to the NNW aft 12z Mon and remain less than 10 kts.

Outlook...

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

MARINE

As of 332 PM EDT Sunday...Southerly winds in the 20-25 kt range will continue through this evening before tapering off overnight. These winds will likely produce waves in the 3-4 feet in portions of the broad waters and Inland Sea, before likewise tapering off to under 1 foot towards daybreak.

A period of stronger wind and wave action is expected for Tuesday, with a south-southeast channeled wind event expected along with gusty showers.

BTV WATCHES/WARNINGS/ADVISORIES

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