textproduct: Burlington

WHAT HAS CHANGED

As of 223 AM EDT Tuesday...

No significant changes. It is looking increasing likely that the cold front comes through Saturday to end the heat event.

KEY MESSAGES

As of 223 AM EDT Tuesday...

1. Major to localized extreme heat risk expected Wednesday thru Friday 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 increase today and continue through Friday, with some localized strong to severe storms possible.

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

DISCUSSION

As of 223 AM EDT Tuesday...

KEY MESSAGE 1: Ridging builds into the region from the west for middle and late week, with surface high pressure centering over the mid- south. This will cause multiple days of southwest flow and allow an area of significant heat to become established in the region. This will be aided by an unseasonably strong area of low pressure across the Great Plains. The ridge looks to remain in place at least through Friday, before it finally looks to get shunted to the south on Saturday. The peak of the highest heat indices looks to be on Wednesday and Thursday, with the former having the highest dew points and the latter likely having the highest temperatures. There will be a couple factors that could potentially mitigate the worst of the heat, but despite those, there is high confidence of impactful heat from Wednesday through Friday. The first factor is the potential for showers and thunderstorms each day, which would drop temperatures and provide clouds to minimize solar heating. Daily ridge runners look to pass around the periphery of the high, and even if they remain to the north over Quebec or to the west over western New York, there will still be convective debris carried into the region by the upper level westerly flow. The other is the exact placement of the high, mostly affecting Friday. Guidance is still split on the exact end of this heat event, and there is still a low possibility that the high retreats to the southwest enough during the day that the worst of the heat remains to the south, though well above average conditions would prevail. Overall, heat indices in the 95-100 range are forecast for most places, with heat indices to around 105 in the Champlain and Lower Connecticut River valleys. Overnight lows around and above 70 will provide minimal relief and the duration will cause cumulative effects.

KEY MESSAGE 2: The region will be on the northeastern extent of a large ridge of high pressure, with the surface high centered well to the south over the middle south. This puts us in the prime area for ridge runners as they round the top of the high over the Great Lakes and begin to dive southeast. An elevated mixed layer will become established on Wednesday and continue into Thursday, but as is typical, despite a few thousand joules of CAPE, capping will try to prevent any convection from forming. However, the shortwaves should provide enough forcing to overcome this and set off some thunderstorms. The first MCS is currently over Lake Huron and will move southeast today, though guidance has thankfully been trending toward sending the strongest convection south too quickly and keeping it to the west. The main area to watch for strong to severe storms looks to be St. Lawrence County. There is no model consistency for Wednesday through Friday, but there are also no signals of continuous convection. Even after the current MCS formed, most model guidance was not even initializing it for a couple runs. Additional synoptic forcing from a cold front on Saturday could lead to the most widespread showers and storms. Overall, adequate 0-6 KM shear and CAPE will be present all week, but the cap and placement of the ridge will be acting against the severe potential. Isolated to scattered strong to severe storms will be possible any day due to the environment, but they will be very conditional. The biggest hazard with any of these storms would be damaging winds.

KEY MESSAGE 3: Heading into the weekend, warm weather looks to linger although temperatures and heat indices will not be as warm as the week above. Current forecast shows temperatures generally in the 80s areawide, with temperatures gradually trending cooler heading into the start of next week. Overnight lows look to remain on the w armer side, generally in the 60s, which may lead to accumulating heat impacts. Although it looks like it won't be quite as hot as earlier in the week, it is important to remember to drink water and take frequent breaks if working outside, especially with such an extended period of warmer weather. There looks to be 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 at this time.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday...VFR conditions continue to prevail at all terminals, and will continue through much of the forecast period with a few high clouds overhead. Winds continue to remain light and variable overnight, trending more southerly after 12Z. There continues to be some uncertainty in regards to convective development and possible showers and thunderstorms after 18Z, but given the uncertainty they have been left out of the forecast for now. If any showers and thunderstorms do develop late in the forecast, brief periods of MVFR and possibly IFR would be possible if overhead, but VFR will generally prevail.

Outlook...

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

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:

June 30: KBTV: 93/2018

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...Extreme Heat Watch from Wednesday afternoon through Friday evening for VTZ001-002-005-009-011-021. NY...Extreme Heat Watch from Wednesday afternoon through Friday evening for NYZ028-035.