textproduct: Burlington

WHAT HAS CHANGED

As of 301 PM EDT Friday...

No significant changes were made.

KEY MESSAGES

As of 301 PM EDT Friday...

1. Seasonable weather will continue through tomorrow. Aside from a few showers through this evening, the period looks dry.

2. Unsettled, showery weather is expected Sunday into Monday as waves of low pressure pass near our region. Risk of impactful weather has decreased somewhat.

3. Daily chances of showers and potential for a few thunderstorms are expected mid to late next week as temperatures warm above seasonal averages.

DISCUSSION

As of 301 PM EDT Friday...

KEY MESSAGE 1: Localized showers and a thunderstorm or two remain on track today and tomorrow, with typical summertime weather anticipated. Through the rest of today, narrow strips stretching from north-northwest to south-southeast of regionally higher instability will continue to support scattered showers. Coverage is relatively high in northeastern New York, particularly in southern Franklin and Essex counties, with more isolated showers near and just east of the Green Mountain spine. There are also some cells west of Montreal moving towards the International Border that we will be watching. Overall, the pattern supports showers potentially pulsing up to produce a rare instance of lightning but little sustained thunderstorm activity, and diminishing past peak heating/by sunset. Temperatures tonight and tomorrow should be on the warm side but within 5 degrees of normal; lows will mainly be in the mid 50s to low 60s and highs in the upper 70s to mid 80s.

Chances for showers and thunderstorms are very low tomorrow with limited instability (CAPE peaking near 500 J/kg) and upper level ridging moving across our region. A rare shower could occur over the mountains, but it looks like a dry day. Late in the day into the nighttime hours, we will begin to see some large scale ascent with some cyclonic flow aloft and a developing surface front that will be largely stationary just to our west (near Ottawa stretching southwestward towards Lake Erie).

KEY MESSAGE 2: Chances for showers will increase gradually from Sunday into Monday, although we are becoming more confident that this will not be a significant event. It appears deeper convection capable of producing flash flooding will be to our southeast, not lining up with the pooling moisture over northern New York on Sunday/Sunday night. The latest global ensemble run shows a lower potential for extreme rainfall, with the 90th percentile rainfall amounts below 2". That being said, a combination of increasing low level heat and humidity and cooling aloft will yield enough CAPE for at least occasional heavy downpours but low chance of thunderstorms. The higher risk of an isolated storm would be out ahead of where the bulk of shower activity will be (such as from the Adirondacks into northernmost Vermont), and then possibly shifting into central Vermont on Monday depending on timing of the system's cold front passing through.

The position of the upper level trough on Sunday across the central Great Lakes region and surface reflection tracking northeastward into the eastern Great Lakes through the day supports a preference for most of the precipitation to stream northeastward across northern New York and far northwestern Vermont with much of our area mostly dry until Sunday night. The latest run of the NAEFS shows the axis of greatest PWAT, with an ensemble mean greater than 1.75", across the St. Lawrence Valley Sunday evening, shifting into Vermont and diminishing in magnitude overnight. While the corridor of deep moisture supports efficient rainfall especially with any training of showers, at this time it appears the bulk of the heaviest rainfall is targeted towards southern Canada. The expected axis of persistent cloudiness and showers leads to high temperatures on Sunday forecast to be fairly similar to Saturday in Vermont while several degrees lower in much of northern New York. Per upper air temperature climatology, portions of eastern Vermont, especially southern areas, are favored to be hottest although nothing particularly extreme; highs in the upper 80s are possible.

Rainfall amounts through Sunday night remain uncertain but currently favored to be highest in the St. Lawrence Valley, averaging about 0.75" to 1", where a slight risk (>15% and < 40%) of excessive rainfall exists. To the east, average amounts of 0.3" to 0.5" are indicated in far northwestern Vermont southwestward across the Adirondacks region, 0.1" to 0.25" in the Champlain Valley and north central Vermont, and under 0.1" in eastern Vermont. While the latest QPF is fairly bullish in a deterministic sense on Monday in Vermont (indicating amounts in the 0.5" to 1" in much of central and eastern Vermont), trends towards a faster progression of the northern stream trough and associated influx of drier air aloft point to lesser, widespread rainfall. So while precipitation chances on Monday have as anticipated increased, heavy rain is looking unlikely. Instead, it is more likely to be a beneficial rainfall, as much of northern Vermont is running at least a little below normal on precipitation over the last month or so.

KEY MESSAGE 3: Mean 500mb ridging is expected to shift slowly eastward with a nearly 600dm high anchored off the mid-Atlantic states and its axis just east of Vermont. This position favors unsettled conditions with weak cyclonic curvature aloft and flow out of the west to southwest as well as increasing temperatures with a building low to mid level ridging. With absence of strong capping in the 850-700mb levels, heating may be self-limiting as dew points rise promoting the formation of instability showers and potentially a few terrain initiated thunderstorms. Still high temperatures in the mid/upper 80s will feel uncomfortable with heat indices possibly exceeding 90 Thursday. Some models point to a passing trough Thursday as well, so diurnal instability and this trigger mechanism could combine to produce a few stronger variety thunderstorms in this scenario. However, timing and strength of the trough is suspect this far out and may not be coincident with maximum heating.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...Aside from a few showers in eastern Vermont and near the Adirondacks, conditions will remain quiet today. A stray shower may occur at EFK/MPV/SLK through 20Z with best chances of occurrence at EFK where showers are ongoing. By 20Z the wave responsible will be shift southeastward drier air, evident on water vapor imagery, working into the region. Otherwise, the main forecast concern will be for overnight fog. MPV and EFK are most likely to see IFR or lower CIG/VIS restrictions given clearing skies and a solid radiational cooling set up 02-14Z. SLK still appears likely to be affected by fog, but could have a lingering low/mid CIG that may delay onset of fog.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

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