textproduct: Burlington

WHAT HAS CHANGED

As of 242 AM EDT Thursday...

While high-res modeled ingredients for severe storms look more favorable today, the stationary frontal boundary is located farther south than anticipated, which could make it difficult for the expected instability and warmth to materialize this afternoon for central Vermont. Based on this, no major changes to the thunderstorm forecast this afternoon, but have included the mention of gusty winds in the forecast with stronger storms. Confidence has also increased for some fog, mist, and/or drizzle tonight, similar to last night.

KEY MESSAGES

As of 242 AM EDT Thursday...

1. Rounds of showers expected today after fog and low clouds lift this morning, with heightened thunderstorm chances across southern Vermont this afternoon and evening. Please stay weather- aware and have a method of receiving Watches and Warnings.

2. Additional showers, mist, drizzle, and fog may make for hazardous travel again tonight, then the boundary finally clears out of our area Friday. Please use caution when driving in low visibilities.

3. Rainy and windy weather is expected for the latter half of the weekend as another frontal system impacts the region. Brief mountain snow is possible late Sunday into Sunday night with a cold frontal passage.

4. Much colder but dry to start next week, though trending warmer with chances of rain by mid week.

DISCUSSION

As of 242 AM EDT Thursday...

KEY MESSAGE 1: A stalled frontal boundary located across the southern portion of our forecast area this morning is bringing light showers, mist, drizzle, low clouds, and patchy dense fog this morning in light winds and abundant moisture. Visibilities are poorest (1/4 to 2 miles) across the northern tier of our forecast area, north of the boundary. Later this morning, after showers move out of the region and fog gradually mixes out, we anticipate a dry period ahead of our next low pressure system, and the stationary boundary is expected to shift northward, drawing warmer air into the northern New York and Vermont. in southern and central Vermont, as well as portions of the Adirondacks and southern Champlain Valley, there should be some areas of clearing, allowing temperatures to rise into the 70s (well above seasonal averages), with highs in the 60s remaining closer to the international border and on mountains. An area of low pressure will ride along the frontal boundary this afternoon and evening, bringing multiple rounds of showers. The HREF continues to be aggressive with instability in the southern Champlain Valley and southern Vermont with about 65-85% chance of 500+ J/kg CAPE and 45- 65% chance of 1000+ J/kg CAPE as dew points are expected to rise to around 60 F. NAM3K also shows most unstable CAPE/MUCAPE at around 1600-1800 J/kg, which could assist in the production of hail. One fly in the ointment for severe development is that the stationary boundary may not make it very far north in time for the main forcing to come through this afternoon, which could have us underperform in warmth and instability. However, HREF mean 0-6 KM shear continues to look dynamic with 45-60 knots, and 0-1 KM SRH between 70-220 m2/s2 and 0-3 KM SRH between 180-310 m2/s2 also support this. NAM3K suggests Effective Bulk Wind Difference around 55-60 knots. Due to the favorable ingredients, isolated to scattered severe storms are possible across southern Vermont. The main threat would be damaging winds, though large hail is possible as well. Due to the relatively fast motion of the storms, flash flooding is not expected despite modest projected precipitable water values around 1.20-1.40".

KEY MESSAGE 2: Another night of showers, mist, drizzle, and fog is likely tonight as the front sinks back southward across the forecast area. One thing we're not seeing as much of tonight is a strong atmospheric inversion trapping moisture that was present this morning. However, the moisture (precipitable water values 1.00- 1.50") looks to linger, and models continue to suggest at least a minor inversion setting up for a portion of tonight. Temperatures tonight will also be largely similar to last night, with lows in the upper 40s and 50s, fairly mild for this time of year. On Friday, the frontal boundary haunting the region with moisture looks to finally shift southwards and into the Atlantic Ocean by the end of the day. This means dramatically decreasing chances of showers and temperatures remaining above normal with highs in the 60s and lower 70s.

KEY MESSAGE 3: Low pressure will slide by well to our north Saturday and Saturday night, dragging a cold front along in its wake. Temperatures will warm on a 50-55 knot southerly 850 mb jet ahead of the front, allowing highs to rise into the 60s and lower 70s. Efficient mixing will bring windy conditions Saturday afternoon into the overnight as the core of the jet moves overhead. Southerly gusts of 20 to 30 mph are likely Saturday and Saturday night, with locally higher gusts possible in the Champlain Valley due to channeling and along the northern slopes of the Adirondacks due to downsloping. The cold front is expected to move through late Saturday night into early Sunday, resulting in temperatures at their warmest Saturday evening, then falling slowly throughout the day Sunday in brisk westerly winds after the frontal passage. Rain showers are most likely Saturday evening through Sunday morning, coming to an end from west to east Sunday evening and night as drier air flows in following the frontal passage. As the showers end, they may change over briefly to snow showers as temperatures fall into the 20s and lower 30s Sunday night. Little to no snow accumulation is expected, particularly below summit levels, as the atmosphere should dry out quickly before temperatures fall too low.

KEY MESSAGE 4: Following a cold front on Sunday, a cooler and drier air mass will filter into the region for the start of next week with perhaps some snow shower chances on Monday. Brisk northwest flow will draw cooler and drier Canadian air as high pressure begins to shift east out of the Great Lakes. A trailing shortwave on the backside of a departing trough will shift south on the leading edge of the high with a few chances for snow showers in the higher terrain. With 925mb temperatures Monday to -5C to -9C, sfc highs will struggle to reach 40 areawide, with the higher terrain hugging the freezing mark. The GFS model progs the 520dam line to sag south into the Mohawk Valley of New York and southern Vermont further supporting cold surface temperatures and cool enough mid level atmospheric profiles to support a saturated thin DGZ. Snow growth will be limited, however, due to a low equilibrium level to 700mb and a significantly dry low level. Any snow showers that do form will likely fall as virga for most of the region, outside of the higher summits.

Towards mid week, model agreement decreases rapidly with the placement of several troughs associated with an upper low. Though, do anticipate some increasing precipitation chances as moisture returns to the area with temperatures on the cool side.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Through 06Z Friday...Changeable conditions will continue tonight with winds light and variable with a stationary boundary just to the south of the region. Areas of low clouds north of the boundary are leading to pockets of IFR to LIFR with some light showers moving eastward. Visibilities are not quite as low as last night varying at times between 1/2SM to 4SM. To the south and east, low clouds have not materialized at RUT/MPV, but are expected to trend towards MVFR, with perhaps some brief IFR closer to sunrise. All in all, confidence is highest in IFR closer to the International Border where detachment from the boundary is largest with saturated low levels. MSS/EFK/BTV will be the most likely to see periods of IFR/LIFR tonight, however, current observations denote an area of VFR across the Adirondacks and CPV. While the GLAMP denotes prolonged IFR, trends upstream show increasing ceiling from the southwest in the aforementioned areas. Once the drizzle and rain clears closer to sunrise between 10-13Z, the expectation remains for most terminals to return to at least MVFR with brief IFR, before trending back to VFR between 14-16Z. Similar to yesterday, south/southwest winds will develop late this morning with improving aviation conditions. Some light showers may be possible closer to 16-18Z across northern New York, but the main terminal impacts this afternoon will be possible thunderstorms, timing details for these storms will become better for the 12Z TAF package.

Outlook...

Friday: MVFR/IFR conditions possible. Chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: VFR. Windy with gusts to 30 kt. NO SIG WX. Saturday Night: Mainly VFR, with areas MVFR possible. Likely SHRA. Sunday: Mainly MVFR, with local IFR possible. Likely SHRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance SHSN. Monday: VFR. Slight chance SHRA, Slight chance SHSN.

BTV WATCHES/WARNINGS/ADVISORIES

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