textproduct: Burlington

WHAT HAS CHANGED

As of 227 PM EDT Friday...

No significant changes.

KEY MESSAGES

As of 227 PM EDT Friday...

1. Seasonable and dry weather this weekend before temperatures and humidity increase early next week.

2. A brief burst of heat will give way to a steadier period of more seasonable weather following a risk of nocturnal severe thunderstorms.

DISCUSSION

As of 227 PM EDT Friday...

KEY MESSAGE 1: A cold front passed through this morning, causing a cooler and significantly drier airmass to enter the region straight down from Quebec. Dew points have been gradually falling during the day and that trend will accelerate this afternoon as the core of the drier air makes its way south, aided by diurnal mixing. By evening, dew points should be in the 50s throughout the region, with some upper 40s in the higher terrain and Northeast Kingdom. Canaan has already has seen its dew point drop to 49! Highs in the upper 70s and 80s will be in store for this weekend, with lows in the 50s away from the immediate shore of Lake Champlain. The colder hollows should see lows drop into the 40s. Increased heat and humidity will enter the region to start next week, with highs rising into the 80s and low 90s and dew points rising into the 60s. The first chance of showers does not appear to be until Tuesday at the earliest.

KEY MESSAGE 2: Signals for a brief, "jailbreak" style extreme heat event on Tuesday have only increased with the latest ensemble data. Based on the full 00Z suite and much of the 12Z data today, there is excellent multi-model support for either low level temperatures near the 98-99 percentile, or slightly less extreme temperatures near the 95th percentile, by Tuesday afternoon. Therefore, there is high certainty that anomalous warmth associated with the eastward expansion of a prominent deep layer ridge, or heat dome, centered over the Midwest makes its way into the area on Tuesday. As previously noted, this heat will should not be particularly humid as it will be displaced from the typical sources (eg. southern Pacific or Gulf moisture). That being said, low level flow out of the southwest should still advect in higher dew points with uncomfortable heat lingering past sunset. The latest thinking is that marginal Heat Advisory criteria will be reached; maximum heat index values could be in the middle 90s in the Champlain Valley and Lower Connecticut Valley with lower 90s in most other valley locations. Also it appears higher dewpoints will be favored towards the northwest such that the St. Lawrence Valley may be on the humid side. Will note the current NBM temperatures peaking as high as the upper 90s are running a little hot compared to the consensus, so anticipate forecast temperatures and resulting heat index values to trend closer to those mentioned. Since this is a single hot day, heat-health impacts aren't anticipated to be as significant as a longer duration event but will be meaningful for vulnerable populations.

Much cooler and dry air will return on Wednesday behind a strong cold front. Said front will act as a trigger for thunderstorms late Tuesday in southern Canada as moisture pools ahead of this boundary, producing a highly unstable environment favorable for supercells or even derecho-like linear storms given very high deep layer shear (60- 70 knots favored). Impacts for our area, with expected timing centered around the overnight hours and long lead time with formation of storms favored much to our north, are questionable (15% risk of severe thunderstorms currently noted by the Storm Prediction Center), but will be worth keeping an eye on as we get closer, especially in northern and northeastern Vermont. Largely seasonably and comfortable weather will follow, with perhaps a weaker cold front coming through to reinforce cooler air by the end of the week.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...Seasonable Canadian high pressure will be settling into the airspace during the next 24 hours, leading to decreasing cloudiness and lightening winds. The only hazardous flight conditions will be around the formation of fog overnight. It's a somewhat tricky forecast given advection of drier air ongoing, making crossover temperatures uncertain. Current thinking is that some fog will develop at MPV, SLK, and EFK. Duration of fog at MPV, between fog climatology, the recent heavy rainfall and relatively high probabilities of visibilities under 1 mile through local aviation model products, will be prolonged. Have cut back a little bit from the previous forecast but this can be fine tuned; generally anywhere in the 06Z to 12Z period LIFR conditions are possible with IFR conditions generally likely. Based on climatology SLK should also see at least intermittent dense fog through this period, but noted probabilities are lower for a given hour compared to MPV. This site missed out on significant rain yesterday, limiting the available moisture for fog formation. Finally, expectations for fog duration at EFK falls somewhere in the middle of the MPV and SLK. Elsewhere, sites like MSS may have enough low level northeasterly flow to point towards little fog, but cannot rule it out.

Outlook...

Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. Chance SHRA, Slight chance TSRA. Wednesday: VFR. Slight chance SHRA, Slight chance TSRA.

BTV WATCHES/WARNINGS/ADVISORIES

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