textproduct: Burlington

WHAT HAS CHANGED

As of 254 PM EDT Saturday...

No significant changes have been made to the forecast. The SPC Severe Weather Outlook for tomorrow shows the region in a Marginal Risk (Level 1 of 5) with the potential for isolated strong to severe thunderstorms.

KEY MESSAGES

As of 254 PM EDT Saturday...

1. After a dry and seasonable afternoon, precipitation chances will increase across the region tonight through the start of the week.

2. Following a dry midweek period, the next chance for scattered showers and thunderstorms arrives in the late Thursday to Friday timeframe.

DISCUSSION

As of 254 PM EDT Saturday...

KEY MESSAGE 1: After a stretch of dry and seasonable weather the last few days, shower chances will return later tonight through the weekend. The main feature driving precipitation chances is a large upper level trough approaching from the Great Lakes. A frontal boundary associated with the parent low will move through tomorrow afternoon, driving the chances for scattered showers and thunderstorms through the afternoon. Model guidance shows modest instability tomorrow afternoon, with CAPE values of 500 J/kg or so depending on the location, although there is some uncertainty as to how much cloud cover lingers through the morning and inhibits afternoon heating. While it's not the most impressive environment, there should be enough instability, shear, and forcing to drive thunderstorm development tomorrow afternoon. SPC currently shows nearly all of the forecast area in a Marginal Risk for severe weather tomorrow, meaning that a few isolated strong to severe thunderstorms are possible, with possible hail and strong winds as the primary threats. The most likely time frame for thunderstorms will be from noon through about 7PM, so be sure to monitor the forecast if you have any outdoor plans. Storms looks to be progressive, limiting any hydro concerns at this time, especially given the dry weather the last few days. Current rainfall forecasts generally show about 0.25 to 0.50 inches of rain across the area, with lower amounts near the International Border and higher amounts possible within any thunderstorms.

For the start of the week, the region will remain in broad cyclonic flow, will will allow for linger showers on Monday and Tuesday, especially across the higher terrain. This cyclonic flow will also lead to some lake effect showers off Lake Ontario, with increased shower chances expected across northern New York during this time period. Temperatures will be on the cool side, with highs only climbing into the 70s, with some locations in the Adirondacks struggling to climb out of the upper 60s.

KEY MESSAGE 2: Long wave troughing appears to remain over the eastern US later next week, with the base of the trough to our west. As such, the pattern will be somewhat unsettled with chances for showers returning late in the week. The low pressure track is strongly favored to be well to our north into central or northern Quebec, so widespread heavy rain or strong wind is not on the table, and deep layer shear appears limited for severe storms at this time. Of the latest ensemble scenarios, ones with a bit more amplified trough than the mean upper level heights show 0-500 millibar shear probabilities exceeding 30 knots at a greater than 30% chance (rather than close to 0%).

Probable hazards for this system would be fairly widespread, general thunderstorm potential associated with the system's cold front, which may be thermodynamically strong. Machine learning and other ensemble guidance does suggest seasonably high instability for late August could be present, with a slight preference for stronger variety thunderstorms as you go southward (roughly 5% chance of severe weather per GEFS). With a faster timing of an incoming cold front, this threat may be limited to Thursday, and a slower timing would suggest Friday would be a day to watch for thunderstorms, especially in Vermont. The latest guidance has trended perhaps a little more towards the later timing, consistent with an occluding low pressure system and associated slowing eastward progress of a cold front. For now, a slight chance of thunderstorms Thursday evening, and slight chance to chance Friday afternoon in most of the region, seems reasonable at this point. Given the amount of outdoor activities anticipated on Friday and large scale setup for thunderstorm potential, this will be a period to keep a close eye.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18Z Sunday...VFR conditions will prevail through at least 06Z at all sites. Thereafter, a low stratus layer may develop at MPV; confidence on its development is relatively low, so have indicated a trend towards MVFR ceilings during the early morning hours with consensus on lowest ceilings around 12Z or soon after. Meanwhile shower chances will be increasing generally from west to east, with temporary MVFR conditions due to a combination of visibility and ceilings favored at all sites. Timing of showers looks late enough to leave out of this TAF cycle at EFK and MPV. Along with the showers, a belt of slightly stronger south-southeast winds aloft will move overhead, which should be enough for LLWS at MSS. Otherwise, occasionally gusty winds in the 15 to 20 knot range are favored this afternoon into the evening at BTV, RUT, and MPV; south to southeast winds will tend to diminish after 00Z and pick back up in the 10-14Z period.

Outlook...

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

BTV WATCHES/WARNINGS/ADVISORIES

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