textproduct: Burlington

WHAT HAS CHANGED

As of 248 AM EDT Wednesday...

A Heat Advisory has been issued for heat indices in the low to mid 90s in the Champlain Valley on Friday.

KEY MESSAGES

As of 248 AM EDT Wednesday...

1. Scattered showers and thunderstorms each day through Friday.

2. Building heat and humidity through Friday. Heat Advisory in effect for the Champlain Valley 12-8 PM Friday.

3. Chances for showers and a few thunderstorms are expected Sunday with temperatures cooling towards normal early next week.

DISCUSSION

As of 248 AM EDT Wednesday...

KEY MESSAGE 1: After a few dry days with ridging in control, a northern stream shortwave will move into our area from the west today. This will dampen the ridge and bring a return to unsettled and showery conditions that will last through Friday. At least chances of showers are possible each day, especially in the afternoons when instability will be the greatest. The two windows of greatest coverage of showers/thunderstorms will be this afternoon (Wednesday afternoon) and again on Friday afternoon/evening. Gulf moisture wrapping up and around western Atlantic high pressure will bring PWats to near 2.0 inch and dewpoints near 70 today. The resultant building instability will support the development of scattered showers and thunderstorms this afternoon as the shortwave moves in. Lack of deep shear and relatively weak wind fields will limit severe potential today, though locally moderate to briefly heavy downpours are possible today in any thunderstorms that do materialize.

More widespread showers and thunderstorms are possible Friday as a front sweeps through from west to east during the late afternoon/evening hours. Ahead of the front, temperatures in the upper 80s to low 90s with dewpoints upper 60s/low 70s will result in impressive instability of potentially over 2500 J/kg. Given this environment, some thunderstorms are likely to materialize as the front sweeps through. However, better shear will be displaced to the west, so at this point things don't look to be fully ideally lined up for severe storms.

KEY MESSAGE 2: Seasonal temperatures today will warm through the end of the work week, with heat and humidity becoming a concern especially on Friday. 925 mb temps will warm to 20-25 deg C each afternoon, which suggests surface temps in the upper 80s to near 90 Thursday and Friday. Given the unsettled pattern however, with numerous shortwaves moving through and the potential for clouds and showers, have continued the trend of a more conservative high temperature forecast than suggested by the NBM. Our forecast high temperatures for Thursday range through the 80s...warmest in the Champlain and Connecticut River Valleys. Though these temps are just slightly higher than seasonal norms, building humidity with dewpoints approaching 70 will increase heat impacts. Heat indices Thursday will be in the mid 80s to low 90s. Overnight temperatures Thursday night into Friday will be quite warm as well, with lows in the mid 60s to around 70.

Friday will be the warmest day of the week, and a Heat Advisory is in effect for Friday from 12-8 PM for much of the Champlain Valley, where heat indices will be in the low to mid 90s. Just how warm temperatures will get on Friday will depend on timing of the front later in the day and the evolution of associated cloud cover and showers/thunderstorms. There is the potential heat indices could cap just below Advisory criteria if showers/tstorms start earlier, but NWS HeatRisk suggests at least a moderate to potentially major risk of heat-related impacts. Given the warm low temperatures from Thursday night, Friday will already start off on the warmer side. This will in turn increase heat impacts for vulnerable populations, and those sensitive to heat along with anyone with outdoor plans on Friday should take precautions for the heat.

Temperatures Saturday will be in the mid 70s to mid 80s, but dewpoints will be much lower and thus conditions will feel much less muggy over the weekend.

KEY MESSAGE 3: Mean longwave troughing is highly favored to become established across east-central Canada by Sunday with upper level flow over Vermont and northern New York becoming increasingly zonal. Model consensus shows a front moving rapidly through Sunday bringing showers and the potential for a few thunderstorms. While cold air advection will be limited, temperatures will cool early next week behind the wave. Highs for Sunday are expected to range from the upper 70s to lower 80s for most locations, but will not feel as oppressive with dew points in the 50s. Broad cyclonic flow aloft will keep shower chances ongoing Tuesday through mid week as another trough moves towards the region late in the week. The silver lining will be that temperatures continue their cooling trend back into the 70s.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Through 12Z Thursday...Chances for showers increase as low pressure tracks through southern Canada pushing a weak front through the region. While the front is not supported by a strong thermal gradient, height falls will be sufficient to increase chances of thunderstorms for the afternoon and evening hours. Given forecast atmospheric soundings show instability extending the depth of the troposphere, some showers/thunderstorms may produce locally heavy rainfall. Should a thunderstorm move directly over a terminal, IFR VIS/CIGs will be possible. Moisture lingers after 00Z supporting lowering CIGs with potential for widespread IFR after 03-06Z. Some LLWS will be possible late in the forecast period but more localized to MSS and SLK from 00-06Z.

Outlook...

Thursday: Mainly VFR, with local IFR possible. Chance SHRA, Slight chance TSRA. Thursday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Friday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Friday Night: VFR. Definite SHRA, Chance TSRA. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA, Slight chance TSRA.

CLIMATE

Record High Temperatures:

June 12: KMPV: 88/2017 KMSS: 89/2005

Record High Minimum Temperatures:

June 12: KBTV: 71/2017 KPBG: 67/2017 KSLK: 62/1996

BTV WATCHES/WARNINGS/ADVISORIES

VT...Heat Advisory from noon to 8 PM EDT Friday for VTZ001-002-005- 009-011. NY...Heat Advisory from noon to 8 PM EDT Friday for NYZ028-035.