textproduct: Burlington

WHAT HAS CHANGED

As of 231 PM EDT Saturday...

No significant changes were made to the forecast.

KEY MESSAGES

As of 231 PM EDT Saturday...

1. Relative quiet through Sunday afternoon.

2. Swap to active pattern begins Sunday evening through early Monday with rain and embedded thunder, and then strong wind gusts outside precipitation on Monday.

3. A surface front will remain in our general region for the middle and later portions of next week with mild temperatures and periodic threats for showers and a few storms.

DISCUSSION

As of 231 PM EDT Saturday...

KEY MESSAGE 1: Two cool, mostly dry days are on tap. High res guidance depicts several pinpricks of shallow convection simmering in the Northeast Kingdom. Breezy northwest winds will also advect dry air, with low-level relative humidity dropping to 30-40%. Low-level dry air will prevent some precipitation from reaching the ground, but good mid-level lapse rates and sufficient moisture at 4000-5000 ft will be present. Shower activity will peak about 4-6 PM before settling after sunset with the loss of daytime heating. Our seasonably cool conditions in the mid 40s to lower 50s will translate to a seasonably cool night in the 20s to about 30. A seasonable Sunday will give way to cloudiness, and then precipitation chances increase Sunday evening. Before clouds and precipitation arrive, dry relative humidity values are expected across Vermont down to 30%, but with 5-10 mph.

KEY MESSAGE 2: The warm front Sunday afternoon/evening will be fairly pronounced, and the cross isobaric flow at 295K is strong. Analysis of model soundings suggest about 100-200 J/kg of elevated instability will be present with a strengthening 60-70kt 850mb southwesterly jet near the nose of the inversion. The timing of the jet during the nighttime and coincident with rain will likely prevent mixing winds to the surface, but any flights coming in will be rocky. Embedded convection could produce thunder and heavier rainfall rates. Where the heaviest rain will fall depends on where the nose of the incoming LLJ lands, and high res guidance is not in the greatest agreement. Some scenarios place the strip of heavier rain along and north of the international border while others place is squarely over the Adirondacks and central Vermont. The majority depicts activity north, but have tried to demonstrate a PoP max that travels northeast before settling north of the international border.

The question for Monday becomes whether we clear out during the day or when a subtle 500mb trough moves east. Depending on how much clearing we get, any lingering winds from the still 40-50kt southwesterly LLJ could mix to the ground, especially in eastern downslope regions and channeling in southwest to northeast valleys. So parts of northern New York and the northern Champlain Valley are presently forecast to observe 35-45 mph gusts beginning pre-dawn into Monday afternoon. Warming downslope flow will produce regions of localized heating. In general, temperatures will climb into the 60s, up to 70 in the Upper Valley. Although the interquartile range of the NBM is rather large (~10 degree spread between the 25th and 75th percentile), showing some of the differences in timing the subtle 500mb trough and exit of morning precipitation.

The slowest models push precipitation into the area by Monday evening, and so additional showers are expected, and that will begin to cap any potential wind gusts once rain returns. The late timing should limit any thunder from this. On Monday night, a small ridge will build in between with light west-northwest to northerly flow. It may not completely remove some of the moisture pooling in the region, though. So Monday night into Tuesday morning will remain on the warm side in the 40s to near 50.

KEY MESSAGE 3: Blended national solutions continue to support the idea that an east-west oriented frontal boundary will remain close to or atop our region from Tuesday through the end of next week. While there should be some dry periods, several surface waves riding along the boundary will bring the threat of showers, and a few non-severe storms as periodic steep lapse rates aloft traverse through the mean mid-level westerly flow. The best threat of wetting rainfall looks to occur by later Tuesday into Thursday with hints of some drying by week's end/Friday. Broad south/southwesterly boundary layer flow should be sufficient to push temperatures well above mid-April daily averages by some 10-20 degrees, or well into the 60s/lower 70s for afternoon highs, consistent with the current CPC 6-10 day outlook. With the front in proximity to our area for much of the period, variable clouds should also be the rule with some intermittent sunshine.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18Z Sunday...VFR conditions continue across the region with SCT-BKN045-060 through 00z Sun. Thereafter VFR conditions continue with clearing skies thru 12z then high-mid deck moves into area ard-aft 14z Sun.

Winds continue to be between 15 to 25 knots throughout the afternoon. Winds look to trend more light and variable after 00Z.

Outlook...

Sunday Night: Mainly VFR, with areas MVFR possible. Definite SHRA. Monday: Mainly MVFR, with areas VFR possible. Definite SHRA. Monday Night: Mainly MVFR, with local IFR possible. Chance SHRA. Tuesday: Mainly VFR, with local IFR possible. Chance SHRA, Slight chance TSRA. Tuesday Night: MVFR/IFR conditions possible. Chance SHRA, Slight chance TSRA. Wednesday: Mainly IFR, with local MVFR possible. Likely SHRA. Wednesday Night: Mainly IFR, with local MVFR possible. Likely SHRA, Slight chance TSRA. Thursday: Mainly MVFR, with local IFR possible. Chance SHRA, Slight chance TSRA.

EQUIPMENT

The Colchester Reef meteorological station is out of service. This site is not serviced by the NWS. An estimated return to service is May 1st. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

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