textproduct: Burlington

WHAT HAS CHANGED

As of 240 PM EDT Thursday...

Some storms this afternoon/evening could be strong, especially near the northern St. Lawrence Valley, and potentially near the Northeast Kingdom. Have added the potential for gusty winds, localized heavy rain, and frequent lightning to the weather through this afternoon/evening.

KEY MESSAGES

As of 240 PM EDT Thursday...

1. Our heat wave will continue through tomorrow across much of the Northeast with unusually hot and humid conditions causing a sharp increase in the risk for heat related illnesses.

2. The chances for thunderstorms and showers will continue into this weekend with potential for a few strong to severe storms.

3. Warm weather will linger into next week, along with daily chances of showers and thunderstorms.

DISCUSSION

As of 240 PM EDT Thursday...

KEY MESSAGE 1: Dangerous heat will continue to impact Vermont and northern New York today through Friday. Widespread temperatures in the upper 80s to mid 90s have already been observed with heat indices in the Champlain Valley already near 100F. The high heat index values will be present through tomorrow afternoon. Temperatures are currently in the upper 80s to low 90s. Today will be the hottest of the week as the ridge axis crests over the region. Contrary to yesterday however, dewpoints are not quite as high as yesterday as some drier air aloft and better mixing has lowered the low level moisture slightly. Regardless, dangerous heat index values exceeding 100F in places are still expected, with tonight remaining hot and muggy, limiting any relief from the hot and humid daytime hours. We'll see a bit of a respite from the humidity tomorrow and Saturday, but it will still be very warm and muggy. North wind advection will begin to slowly draw in some drier air tomorrow lowering dewpoints back into the upper 50s to mid 60s by Saturday. Subsequently, temperatures tomorrow will be a degree or two cooler than today, and on the 4th, around the low to mid 80s, with some locations in the upper 80s in the northern Champlain Valley and lower Connecticut Upper Valley. Heat Index values for holiday activities will be around the mid to upper 80s on Saturday. Sunday will be the pick of the weekend with temperatures only i the upper 70s to low to mid 80s, and afternoon dewpoints in the low to mid 50s.

Heat related impacts will increase through tomorrow due to the cumulative effects from the prolonged heat wave. Please make sure to take proper heat safety precautions, including limiting your time outdoors, drinking plenty of water, and seeking indoor shelter with air conditioning. Check on your relatives and neighbors, especially if they are elderly. And don't forget about your pets; bring them indoors or provide them with ample shade and fresh cool water.

KEY MESSAGE 2: Heat and humidity will combine to create impressive SB CAPE values today between 2500-3500 J/kg today. Shear will be slightly better today, up to 30-40 kts depending on the model, which may lead to some better organization with any storms that develop today. Satellite depicts an agitated cumulus field north of Lake Ontario along a lake breeze, in addition to another area of agitated cumulus north of Ottawa. Unlike yesterday, there are no pre-existing thunderstorms upstream, and most activity today may be strictly diurnally driven. Furthermore, shortwave upstream are not quite as deep as yesterday as well, which may limit the overall coverage of any showers. Given some persistence forecasting from yesterday, a similar setup as yesterday is possible. Expectations are for some clustering of storms to develop in eastern Ontario and southwestern Quebec this afternoon, generally between 4-6 PM. These storms as they become more organized will slide into the northern St. Lawrence Valley, with potentially some stronger storms with gusty winds, localized heavy rainfall, and frequent lightning. CAMs depict a linear feature moving southeast from Massena into the northern Adirondacks and becoming more broken and weakening southward between 6-8PM. Additionally, a weak shortwave Otherwise today, models show some shower activity trailing the initial convection across northern New York, making it into northern Vermont and the Northeast Kingdom. These showers have a lower confidence of developing. With our mid level flow generally easterly, anvils from Ontario may help stabilize convection downstream into northern Vermont. Furthermore, soundings still show an apparent EML remaining as a capping mechanism to more robust storms. Still, there is a secondary potential for some isolated to scattered showers and thunderstorms across northern Vermont, mainly between 8-11 PM, given the increasing instability across the region. Outside of the two potential thunderstorm areas, any showers today will be heavily tied to the higher terrain with no forcing mechanism present. Strong to severe thunderstorms can't be ruled out given the large CAPE values, thought coverage will be less widespread than yesterday given not as strong shortwaves. Still the SPC continues to encompass our entire forecast area in a Marginal Risk (level 1 out of 5) for Today. Model guidance during this Ring of Fire setup has been lackluster at best. Convection across Wisconsin will likely persist towards eastern Ontario close to sunset, based on persistence and upper flow patterns, which may become our focal point for any activity across Vermont later this evening. Any storms that pop up today would at the least produce heavy rainfall, though widespread flooding is not anticipated.

Additional storm chances exist tomorrow, mainly tied to the peak heating hours as the ridge slowly shifts south. Cells tomorrow will have similar shear profiles as the jet creeps southward, which will lead to more clustering of storms. However, the axis of better shower activity looks to shift more from Ogdensburg to Middlebury and points south. This region is where the SPC has a Day 2 Marginal Risk (level 1 out of 5) for the potential for some stronger storms. Of note, is that the NAM3/HRRR denote a line of showers and potential thunderstorms across the International Border, which tracks to the southeast through the region between 6-10 PM, though weakening as it moves through. Confidence in this feature is low at the moment. A backdoor cold front will pass through the region Friday night into Saturday night which will dramatically lower dewpoints from the upper 60s to the upper 50s by Saturday. Some shower activity with perhaps a rumble of thunder will be possible, mainly in the southern regions, due to the presence of a forcing mechanism. Shower activity will begin to taper off towards Saturday afternoon/evening. Sunday looks to be the pick of the weekend with a dry day expected.

KEY MESSAGE 3: Heading into next week, warm weather will linger, although temperatures and heat indices will not be as warm as currently. At this time, high temperatures are most likely to range in the 80s and lower 90s with chances for showers and thunderstorms each afternoon through midweek. Overnight lows remain on the warmer side, generally in the 60s, which may lead to accumulating heat impacts. The first part of the week won't be too hot though.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Through 00Z Saturday...The chances for thunderstorms and showers will continue into this weekend with potential for a few strong to severe storms. VFR conditions are expected to prevail through most of the next 24 hours. Additional chances for showers and thunderstorms will be possible this evening, with little confidence in areal coverage and intensity. Winds west to southwesterly this evening, trending light and variable overnight. There could be some fog formation overnight, but uncertainty remains on where this occurs and the exact extent of fog. Most likely spot looks like MPV for a couple hours 06Z-12Z, but it is also possible at EFK, and not out of the question at any site that received or receives rain today. Winds will increase Friday out of the west-northwest 5-15 knots with gusts as high as 15-25 knots possible.

Outlook...

Friday Night: VFR. Scattered SHRA. Independence Day: VFR. Scattered SHRA, Isolated TSRA. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. Chance SHRA. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Tuesday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

CLIMATE

Extreme heat and humidity will affect the region for the latter half of the week, 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 2: KBTV: 97/2018 KMPV: 90/2018 KMSS: 94/2018

July 3: KMPV: 91/2002

Record High Minimum Temperatures:

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

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

BTV WATCHES/WARNINGS/ADVISORIES

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