textproduct: Burlington

WHAT HAS CHANGED

As of 218 AM EDT Saturday...

Isolated flash flood threat remains for late Sunday into early Monday with slow-moving showers and thunderstorms possible.

KEY MESSAGES

As of 218 AM EDT Saturday...

1. Very Warm Temperatures and Dry Conditions Saturday

2. Increasing chances for showers and embedded thunderstorms Sunday afternoon into Sunday night. Locally heavy rainfall possible.

3. Daily chances for showers and thunderstorms with temperature at or above seasonal normals.

DISCUSSION

As of 218 AM EDT Saturday...

KEY MESSAGE 1: No significant weather expected today or tonight. Patchy early AM fog may be locally dense in a few of the deeper river valleys, but will generally dissipate with PBL mixing between 12- 13Z. A narrow ridge of high pressure will bring mostly sunny and very warm conditions to the North Country today. Will see an increase in high cloud cover this afternoon associated with an upstream upper trough extending from northern Ontario southwestward to a closed 500mb low across Iowa. Even with filtered sunshine, 850mb temperatures of +15C to +16C will support valley highs in the mid to upper 80s. Surface winds will become southerly at 5-10 mph supported by weak southerly gradient flow. Modest low-level moisture advection will generally keep 2-m dewpoints in the mid-60s, resulting in humid conditions areawide.

For tonight...generally quiet and muggy conditions. Inverted sfc trough shifts ewd from the Ottawa Valley toward the St. Lawrence Valley during the pre-dawn hours on Sunday. This will bring a low chance (20-30%) of some rain showers into the St. Lawrence Valley before daybreak. Otherwise, looking for overnight lows in the mid- upper 60s, except locally in the lower 60s east of the Green Mountains.

KEY MESSAGE 2: We'll be monitoring the slow-moving upper flow pattern Sunday into Monday. Generally looking at a positive tilt mid-level trough across sern Ontario, which extends back southwestward to a closed low in the Ohio Valley region. Prevailing mid and upper level ridge over Eastern New England will result in very slow movement to this upstream system, but it appears that forcing will be sufficient for isolated to scattered showers by Sunday afternoon, especially across nrn NY. Weak mid-level lapse rates support limited instability, with narrow CAPE profiles. However, increasing PW values, approaching 1.7-1.9" and WBZ heights near 13kft will support locally heavy rain with any convective activity that does develop.

Support for showers and thunderstorms evolves ewd across the Champlain Valley and across central/nrn VT during Sunday night into Monday. Have indicated high PoPs (80-90%) with widespread showers and a few embedded thunderstorms with weak CAPE through the overnight hours. Again, thermodynamic conditions don't support a severe threat, but locally heavy rainfall is possible. Sfc boundary eventually settles south and east of our forecast area late Monday afternoon with generally drying conditions from NW-SE. At the current time, have indicated 0.5 to 1.0" rainfall with this system across most of the North Country, and some amounts locally exceeding 1.0" in the St. Lawrence Valley. Can't rule out a localized flash flood threat, especially given slow movement of inverted trough and very high PW values. However, not a strong consensus for heavy rain outside the St. Lawrence Valley at the present time, and amounts there are currently not expected to be significant enough to produce flooding over the prevailing flatter terrain of the St. Lawrence Valley. We will continue to monitor, but most sections of the North Country will see a period of wetting rainfall late Sunday into Sunday night and into the first half of Monday. Drier conditions generally return for Tuesday with highs in the low-mid 80s.

KEY MESSAGE 3: A typical late summer pattern looks to set up across the region for the second half of the upcoming week. Daily chances for showers, with some thunderstorms possible, seem likely as we see 250- 500 J/kg of CAPE each afternoon with weak shear. This should result in pulse like showers and thunderstorms that try to develop across the higher terrain and lake breezes. There is the potential for a round of organized convection towards the end of next week as a cut off low over the southeastern US phases with northern stream energy and ejects northward quickly ahead of a cold front. However, deterministic guidance is all over the place with trying to resolve how the southern stream and northern stream energy interact with one another. Temperatures each afternoon should easily warm into the lower to mid 80s but given persistent cloud cover and shower activity, it seems rather unlikely any location will hit 90 degrees this week.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Through 06Z Sunday...Patchy dense fog is expected through 12Z with localized visibilities as low as 1/4SM. Based on the position of mid-level clouds, it seems most likely that fog will develop across KMPV, KSLK, KEFK, and KRUT and IFR to VLIFR conditions have been added into the TAFs through 12Z. Thereafter, VFR conditions with light southerly winds will prevail through the remainder of the TAF period with just very high level clouds (at or above 20kft) moving overhead.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

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