textproduct: Burlington

WHAT HAS CHANGED

As of 305 PM EDT Monday...

A Freeze Warning has been issued for the St. Lawrence Valley in northern New York and in Vermont for areas outside the Champlain Valley and Northeast Kingdom from midnight tonight to 9 AM tomorrow morning. A Frost Advisory has been issued from 2 AM to 9 AM tonight for the Champlain Valley of northern New York and Vermont, except Grand Isle County in Vermont.

KEY MESSAGES

As of 305 PM EDT Monday...

1. Seasonably cool and mainly dry with frost and sub freezing conditions tonight.

2. Widespread rainfall expected Wednesday with unsettled weather continuing through the late week.

3. Cool, showery conditions will persist late this week into the weekend before warming up early next week.

DISCUSSION

As of 305 PM EDT Monday...

KEY MESSAGE 1: As isolated to scattered shower and clouds wain after the loss of diurnal heating this evening, skies are expected to clear out as an area of high pressure noses in from the west. Clearing is expected to be more widespread than last night, where many locations reached frost temperature thresholds, with better confidence in widespread frost and freeze conditions areawide tonight. Temperatures are expected to fall at or just below the freezing mark in the St. Lawrence Valley and areas in Vermont outside the Champlain Valley and Northeast Kingdom. Locations near the St. Lawrence and Connecticut Rivers may not quite reach the freezing mark, but are still expected to be within frost temperature thresholds, however, most of the aforementioned areas will be at risk of reaching freeze conditions. As such a Freeze Warning has been issued for the aforementioned locations from midnight tonight to 9 AM tomorrow morning. In the Champlain Valley of northern New York and Vermont, a Frost Advisory is in effect from midnight tonight to 9 AM tomorrow morning as temperatures are expected to reach 33 to 36 degrees. Similarly, locations near Lake Champlain, including the city of Burlington and Plattsburgh, may not necessarily reach frost advisory thresholds due to the proximity to the lake which will help moderate temperatures. Moreover, Grand Isle County in Vermont, due to the moderation of the lake is not expected to see frost tonight. However, further inland towards the mountains and cold hollows of the valley, it is expected that frost thresholds will be met.

Tuesday will be very similar to today, though with more clear skies as high pressure moves overhead. Relative humidities will once again lower towards the 30-40% range, perhaps 25-30% in the Upper Valley of the Connecticut River. However, fire weather concerns will be low due to a lack of prevailing winds aloft to mix down to the surface, with light winds expected tomorrow. Temperatures tomorrow will be into the low to mid 50s. As high pressure drifts east tomorrow night, additional frost is possible, though it will be tied to mainly eastern Vermont as cloud cover move sin from the west ahead of our next storm system mid week. How fast the cloud cover increase Tuesday night may limit frost development, but this will be more refined in the next one to two forecast packages.

KEY MESSAGE 2: Into Wednesday and Thursday, there is an increasing chance for widespread wetting rainfall. Strong ridging across the western CONUS will trend our flow pattern towards troughiness with an upper level low still in place across the Hudson Bay. A developing upper level trough will shift east displacing the early week ridging ushering in warmer and more moist air. Rainfall is expected to overspread the region Wednesday from southwest to northeast as a warm front lifts through. Good upper level diffluence associated with the trailing edge of a jet streak will help maximize precipitation rates with seasonable PWATs to 0.75-1 inch. Rainfall totals, at this time are forecast to be highest across southern Vermont and the St. Lawrence and Adirondacks in New York where a quarter to half an inch is possible. Further north into central and northern Vermont and near the International Border, lower rainfall amounts to a tenth to quarter is possible. A strengthening low level jet on the leading edge of the overarching long wave trough may allow for a faster frontal passage in addition to shredding of clouds which could limit the maximum possible rainfall from the system. Moreover, this jet may lead to a downsloping scenario for the western slopes of the Greens and northwestern slopes of the Adirondacks from southeasterly winds. Model soundings show a steep inversion near mountain summit levels with top of the mixed layer denoting the potential for 30 to 40 mph wind gusts along the western facing slopes of the Greens and northwestern slopes of the Adirondacks. The trouble with the mixing will be the ongoing precipitation and how much can actually mix down.

The precipitation shield associated with the warm front becomes more scattered into Wednesday evening as an associated cold front will move across the southern portions of our area. Depending on how much clearing from parcel stretching can occur, some instability may develop across St. Lawrence County before daytime heating ceases with the potential for a rumble of thunder or two. The overall system looks to evolve into an upper low as it becomes cutoff over eastern New England into Thursday. A resurgence of wrap around moisture as the system deepens and pivots about New England will lead to further rain chances through the day Thursday with an additional quarter to half an inch across southern and eastern Vermont. Trends in the hi res models that go out that far have been towards a deformation band that sets up somewhere across southeastern Vermont Thursday which could lead to some enhancement in rainfall amounts across the aforementioned region. No flooding concerns are expected at this time due to lower stream flows and recent detachment from previous rains. Unsettled weather looks to continue into the long term forecast.

KEY MESSAGE 3: Surface low pressure looks to linger on the New England Coast Thursday night as upper level low pressure rotates across southern New England. This will keep the potential for showers across much of Vermont and parts of northern New York overnight (65- 85% PoPs) and also during the day on Friday (50-70% PoPs) as the upper low drifts slightly east and the surface low lifts north into Maine. By Friday night, vertically stacked low pressure will finally make a bigger move into the Canadian maritimes and surface ridging will attempt to replace it, lowering PoPs to around 10-30%. The lingering moisture and showers will keep temperatures below seasonal averages with highs mid 50s to lower 60s and lows in the 40s. Another shortwave looks to speed into the region over the weekend, keeping precipitation potential around 20-40% into early next week with perhaps a brief drier period Sunday night into Monday morning. Overall any precip this weekend and early next week would be more on- and-off showery and no one day seems to be a total washout, though things could change as we get closer. This should allow temperatures to rise to near or above seasonal normals with highs in the mid 60s and 70s and lows in the 40s to mid 50s. Depending on how much warming we can get early next week, temperatures in southern Vermont could even approach 80 F.

AVIATION /19Z MONDAY THROUGH SATURDAY/

Through 18Z Tuesday...Mostly dry today and Tuesday. VFR conditions are expected to prevail over the next 24 hours with perhaps 20-40% chance of the odd shower now through 22Z Monday that could lower visibilities to 4-6 miles and/or lower ceilings to 2500-3000 feet above ground level. Breezy conditions are being observed this afternoon with winds out of the west-northwest and gusts 10-20 knots. PBG differs from the other sites with a more light and variable wind this afternoon, and MSS is seeing more of a valley- channeled southwesterly flow. Winds this evening will taper off towards 00Z Tuesday, with several sites expected to go calm and others maintaining a light (3-6 knots) northwesterly wind, except in RUT, where a light southeasterly drainage flow will reign. There remains some potential for SLK to get some fog tonight as winds go calm and skies clear, but it's still tricky to say for sure due to dry air (afternoon dew points observed in the lower 20s). If SLK gets a rain shower this afternoon/evening, this could increase their chances of fog tonight. Tuesday during the day, winds are expected to pick up again out of the northwest with isolated to scattered gusts 15-20 knots possible. The exception to this would be PBG, which may develop a northeasterly wind off Lake Champlain instead.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

VT...Freeze Warning from midnight tonight to 9 AM EDT Tuesday for VTZ006-008-010-011-016>021. Frost Advisory from midnight tonight to 9 AM EDT Tuesday for VTZ002-005-009. NY...Freeze Warning from midnight tonight to 9 AM EDT Tuesday for NYZ026-027-087. Frost Advisory from midnight tonight to 9 AM EDT Tuesday for NYZ028-035.