textproduct: Burlington

WHAT HAS CHANGED

As of 331 PM EDT Monday...

A Fire Weather Watch has been issued for western portions of Vermont and all of northern New York for Tuesday.

KEY MESSAGES

As of 331 PM EDT Monday...

1. Critical fire weather conditions are expected Tuesday in much of northern New York and parts of Vermont.

2. A welcomed wet period with a long duration, moderate rainfall is expected later this week, primarily on Thursday.

3. Unsettled conditions are expected to linger through the weekend into early next week.

DISCUSSION

As of 331 PM EDT Monday...

KEY MESSAGE 1: Over a week of dry weather and lack of greenup is supporting fire weather concerns tomorrow when gusty south winds are expected to develop. Driving our consistent dry and sunny weather has been a narrow ridge of high pressure stuck over us and currently overhead. It will shift just east of us tomorrow, sandwiched in between an approaching trough of low pressure from the west and a slow moving low over the western Atlantic. In the upper levels, ridging will stay strong over Vermont, while cyclonic flow moves into New York. This pattern sets the stage for Red Flag conditions over northern New York and western Vermont where a Fire Weather Watch is in effect. Plentiful dry air will be present while a belt of stronger winds aloft gets tapped into such that frequent gusts over 25 MPH are likely. In fact, momentum transfer with such a dry air mass could be efficient enough to see a few gusts as high as 40 MPH in northern New York especially towards the International Border, but have held off on making this into the official forecast.

In Vermont, particularly central and eastern areas, there is a more limited concern of such strong winds with a weaker gradient and less favorable southeasterly trajectories of near surface air. That being said, these winds should gust upwards of 20-25 MPH throughout the afternoon concurrent with RH values below 30%. Note that each day during the current dry spell we are cumulatively drying out our land surfaces such that it is easier to see lower RH values than modeled. This afternoon, for example, RH values as of 2 PM were largely down into the 25 to 30% range, near or below minimum forecasted values from the National Blend of Models. The breeziest conditions in northern New York will also lead to some enhanced humidity drops as drier air aloft mixes down in the northernmost valleys where the latest relative humidity (RH) forecasts are down to about 20%. A similar scenario on April 9th with southerly winds led to afternoon RH values dropping into the upper teens to twenties in much of our region.

KEY MESSAGE 2: A flip from dry to wet weather is on track for midweek. A double barreled low scenario, with an initial low pressure system passing from northern New York into southern Canada Wednesday night and secondary low forming to our south and east along a slow moving front during the day Thursday, is moving into further focus. With this scenario, a widespread soaking rain will occur areawide but with heaviest amounts favored into two zones west and east, with less rain in northwestern Vermont/northeastern New York. The latest precipitation forecast shows rainfall totals exceeding 1" being likely in the St. Lawrence Valley and portions of central/eastern Vermont. Generally, expect a large area of rain, with embedded heavier showers associated with some elevated instability, will gradually translate eastward along the front Wednesday night through Thursday evening. The back edge of rain should be last to exit northeastern Vermont Thursday night as the secondary low slowly passes to our north and east and becomes the dominant player, while the trough takes on a slightly negative tilt. Cooler air will filter in from the north and west through this period as a trough becomes fully established over the region.

KEY MESSAGE 3: There is little change in the overall synoptic pattern in the long term through the weekend into next week. Strong ridging across the North Atlantic will stagnate an upper low across Quebec and the Canadian Maritimes with daily shower chances resulting across the area looking increasingly likely. Best chances for any showers look to be across near the International Border, though the specific timing of any shower activity still remains uncertain. Under the core of the upper low, temperatures will be unseasonably cool with snow showers reasonably possible for elevations above 2000ft. Lower elevations should remain closer to seasonable norms, though still slightly below, with mainly rain with any shower activity. Highs are favored to be in the upper 40s to mid 50s, and lows in the 30s.

One thing to note is that the climatological start to the growing season in the Champlain Valley begins May 1st (this Friday) when we expect overnight lows to be near Frost Advisory criteria (32-36F) both Friday night and lesser so Saturday night. Cloud cover may limit the overall cooling that takes place, but conditions may be favorable for frost development. We will monitor this in the coming days.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Through 00Z Wednesday...The primary aviation concern will be developing gusty winds on Tuesday and associated areas of wind shear and turbulence. VFR conditions prevail at all sites for the next 12 to 24 hours with light terrain driven winds under 5 knots tonight. Winds increase from the south at 5 to 15 knots with localized gusts 15 to 25 knots expected after 15z Tuesday.

Outlook...

Tuesday Night: VFR. Slight chance SHRA. Wednesday: Mainly VFR, with local MVFR possible. Slight chance SHRA. Wednesday Night: Mainly VFR, with areas MVFR possible. Definite SHRA. Thursday: Mainly MVFR, with local IFR possible. Definite SHRA. Thursday Night: Mainly MVFR, with local IFR possible. Chance SHRA. Friday: Mainly MVFR, with areas VFR possible. Chance SHRA. Friday Night: VFR. Slight chance SHRA. Saturday: VFR. Chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Fire Weather Watch from Tuesday morning through Tuesday evening for VTZ030-033. NY...Fire Weather Watch from Tuesday morning through Tuesday evening for NYZ202>205.