textproduct: Burlington

WHAT HAS CHANGED

As of 439 PM EDT Tuesday...Updated to remove St Lawrence County from Severe Thunderstorm Watch.

The Excessive Heat Watch has been upgraded to an Excessive Heat Warning with a Heat Advisory being issued for the rest of the area from Noon on Weds to 7 PM on Friday for heat index values of 95 to 105 degrees with localized higher values likely in the Champlain Valley. Added enhanced gusty winds for thunderstorms tonight, as complex of severe storms are possible overnight.

KEY MESSAGES

As of 301 PM EDT Tuesday...

1. Major to localized extreme heat risk anticipated Wednesday and Thursday with heat index values near 105 degrees possible in the Champlain Valley/Eastern Windsor and 95 to 100 elsewhere.

2. Daily chances for showers and thunderstorms continue through Friday, some localized strong to severe storms possible, especially late tonight.

3. Dangerously hot and humid conditions will linger into the holiday weekend along with daily chances of showers and thunderstorms.

DISCUSSION

As of 301 PM EDT Tuesday...

KEY MESSAGE 1: A long and dangerous heat wave is expected to impact the fa from Weds into the upcoming holiday weekend, as a strong mid/upper lvl heat ridge builds acrs the central Appalachian Mountains. Progged 925mb temps are expected to be in the 26-28C range for Weds and 27-30C on Thurs, which is 99th-100th percentile for our cwa, indicating the significance of this upcoming heat wave. In addition, 2m dwpts wl continue to climb tonight as convection helps to saturate the bl, resulting in many areas seeing values in the 68-75F range by Weds. Little mixing out of drier air is expected during peak heating, so this wl create heat index values around 105F in the warning area and 95 to 100F in the advisory. The warmest day continues to be Thursday acrs our cwa with high temps in the lower 90s mtns to upper 90s to near 100F in the Champlain and Lower CT River Valleys. A few record high temps are likely to be broken during this heat wave. The boundary layer moisture wl result in very muggy conditions overnight with lows upper 60s to upper 70s most nights. These very warm and muggy conditions wl provide little relief at night, especially wider valleys.

KEY MESSAGE 2: Very challenging fcst with regards to thunderstorm potential and intensity tonight through Friday. SPC has upgraded most of our cwa to slight risk (2 out of 5) for severe on Thurs with 15% wind and marginal risk for excessive rainfall continues by WPC.

GOES-19 mid lvl water vapor imagery shows our next embedded s/w energy and moisture north of the Great Lakes, diving southeast toward the Ottawa Valley. This energy is expected to arrive around midnight for the SLV and into the CPV by early Weds morning. The elevated convective parameters are impressive with MU CAPE values btwn 1200-1800 J/kg, along with a very well defined EML moving directly overhead at 06z. This is associated with impressive waa and very sharp sw to ne instability gradient acrs our cwa tonight. The idea of a cluster of strong to locally severe thunderstorms are very much possible overnight with damaging winds the primary svr wx threat. We could see a very similar scenario to this aftn's convective that is occurring just south of our cwa overnight tonight acrs our cwa. Anybody camping outdoors overnight tonight should monitor the weather closely and be ready to take shelter if storms threaten.

The heat and humidity wl create daily CAPE values in the 2000-3000 J/kg acrs our cwa with 0 to 6 km deep layer shear around 30 knts. However, better shear in the 40 to 50 knt range arrives along the International Border area by Thurs aftn. Our thinking for Weds is more trrn showers and thunderstorms are likely with some localized threat for severe possible, given the large CAPE values. The synoptic scale ascent on Weds and Thurs is much less with weaker dynamics/short wave energy, but instability wl be greater. Thinking primary convective mode would be pulse-like, evolving into mini- bowing line segments with localized damaging winds as the main threat, followed by hail. SPC has upgraded our entire cwa to slight risk for severe (2 out of 5). Additional threat for strong to severe storms are possible on Thurs and Friday, but overall coverage and intensity is difficult to determine at this time.

KEY MESSAGE 3: Heading into the weekend, warm weather lingers although temperatures and heat indices will not be as warm as the previous days. Current forecast shows temperatures reaching the 80s areawide, with temperatures trending cooler heading into the start of next week. Overnight lows remain warm, generally in the 60s, which may lead to accumulating heat impacts. There are chances for showers and thunderstorms throughout the weekend with the proximity of the frontal boundary moving through the area, which may also help keep temperatures cooler. There continues to be a lot of uncertainty in this time range in regards to precipitation chances heading into next week, with a wide range of model solutions.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...VFR conditions continue to prevail at all terminals. Winds continue to remain light and mainly out of the south but also being influenced by upstream convection. An area of convection is tracking into northern New York from Ontario. Showers and thunderstorms may affect MSS and SLK associated with this area. Brief periods of MVFR and possibly IFR would be possible if overhead, but VFR will generally prevail. An additional area of convection is expected to pass through the region overnight, but timing and location is still a bit uncertain at this time.

Outlook...

Wednesday Night: VFR. Chance SHRA, Slight chance TSRA. Thursday: VFR. Chance SHRA, Chance TSRA. Thursday Night: VFR. Slight chance SHRA, Slight chance TSRA. Friday: VFR. Slight chance SHRA, Slight chance TSRA. Friday Night: VFR. Slight chance SHRA, Slight chance TSRA. Independence Day: VFR. Chance SHRA, Chance TSRA. Saturday Night: VFR. Slight chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

CLIMATE

Extreme heat and humidity is possible later this week, especially on Wednesday and Thursday, which could lead to some daily records. Below are the current daily high and low temperature records in jeopardy at our area climate sites.

Record High Temperatures:

July 1: KBTV: 96/2018 KMPV: 92/2018 KPBG: 94/1968 KMSS: 94/2018

July 2: KBTV: 97/2018 KMPV: 90/2018 KMSS: 94/2018

July 3: KMPV: 91/2002

Record High Minimum Temperatures:

July 1: KBTV: 76/2018 KPBG: 73/1971 KSLK: 69/2018

July 2: KPBG: 77/2002 KSLK: 68/2002

July 3: KBTV: 76/1911 KPBG: 73/2002

July 4: KPBG: 71/1973 KSLK: 67/1952

BTV WATCHES/WARNINGS/ADVISORIES

VT...Heat Advisory from noon Wednesday to 7 PM EDT Friday for VTZ003-004-006>008-010-016>020. Extreme Heat Warning from noon Wednesday to 7 PM EDT Friday for VTZ001-002-005-009-011-021. NY...Heat Advisory from noon Wednesday to 7 PM EDT Friday for NYZ026-027-029>031-034-087. Extreme Heat Warning from noon Wednesday to 7 PM EDT Friday for NYZ028-035.