textproduct: Burlington

WHAT HAS CHANGED

As of 228 AM EDT Tuesday...

Smoke has been added to parts of northern New York and Vermont based on wildfire smoke developing across Canada. The potential for high heat and widespread strong to severe thunderstorms, especially along the international border, remains on track.

KEY MESSAGES

As of 228 AM EDT Tuesday...

1. A Heat Advisory is in effect for Vermont and much of northern New York today, along with some wildfire smoke moving into the region. Some localized fire weather concerns are possible 2. An Enhanced risk of severe thunderstorms remains for northeastern New York and northern Vermont tonight when significant severe weather and isolated flash flooding is possible. A more typical potential for showers and perhaps some thunderstorms returns for Thursday.

3. Relatively seasonable weekend and start to next week with shower chances.

DISCUSSION

As of 228 AM EDT Tuesday...

KEY MESSAGE 1: Hot weather is expected today as a brief surge of heat breaking out of the expansive upper high in the Central US will bring 90s across the region. A humid air mass will build, but not reaching the heights of the heat at the end of June into early July. Heat indices of 93-103 will be common through the region. There are a few caveats to make note of. One will be gusty winds. That can be a double-edged sword, allowing downslope regions to warm, but also resulting in turbulent mixing that can allow some of the cooler air aloft to filter to the ground not completely washed out by adiabatic compression. There's also cloud cover associated with the convective mass in northern Quebec Province, and some of the wildfire smoke due to fires initiated as a result of thunderstorms rounding the ring of fire across central Canada. HRRR and Canadian smoke forecasts depict increasing smoke aloft, and even some near the surface as well propagating east this morning and afternoon. On one hand, this might slightly reduce temperatures at the surface, but wildfire smoke can exacerbate heat-health hazards. Regardless if this causes us to come up short on the heat index forecast, the impacts will be the same. Avoid prolonged exposure outdoors and drink plenty of water. Seek shade often and take frequent breaks. Finally, the combination of breezy conditions with gusts 20-35 mph and relative humidity values of 35-45 percent in south-central Vermont could produce localized fire weather concerns where less precipitation has been observed.

KEY MESSAGE 2: There has been little change regarding the severe threat along the international border. Some variations in the coverage of storms remains, but the intensity will not be in question as 2000- 3000 J/kg of CAPE will be present along northern Vermont and northern New York as a sharp frontal boundary initiates thunderstorms north of the international border. Ample shear will provide the potential for organization of storms into bowing segments and significant downburst winds. One potential consideration will be the smoke aloft and how that will effect the removal of the capping inversion in place. Mid-level smoke can absorb solar radiation that can stabilize conditions in the low- level, but on the other hand, this could maintain mid-level lapse rates until the height falls and precipitation begin to erode the cap. Based on soundings, it still seems to be about 6PM or 7PM that the cap erodes, and then the convection already ongoing across Canada, and the sharp boundary they are associated with allows the development of strong updrafts in our region. Storms will be in a bit of a race against the clock. Decreasing CAPE, storm-relative helicity, and eroding/translating EML are expected after 8-9 PM. So storms have a 2-3 hour window to become intense, and then gradually weaken as they pass south. If initial convection heads east early, this could also stabilize our area, and smoke is always a wild card with these features. Some isolated flash flooding will be possible if thunderstorms redevelop on the western periphery of any bowing segments, with the greatest chances for such a feature across the northern half of Vermont. Guidance remains more stayed with the hydro potential, but we will monitor closely.

Thus, risk timing is greatest between 7 PM and midnight. All hazards are possible, including low probabilities of wind gusts greater than 70 MPH and a tornado risk, although we emphasize straight line winds are much more likely to be the hazard in this environment given fairly straight hodographs in the low levels. The risk dwindles heading south and west due; however, a long tracked, well-developed line or supercell poses some risk across our region, consistent with the Slight (Level 2 of 5) risk of severe thunderstorms south of the Enhanced area (Level 3 of 5).

Following any additional showers ahead of the cold front early Wednesday morning, the next chance for showers and thunderstorms comes on Thursday ahead of a weaker variety cold front. Gradual cooling will take place as an upper low spirals to our northeast. The Thursday evening/Thursday night front will also come from the north, but with much less heat and humidity to work with and more limited wind shear, expect much less impact with perhaps a couple of afternoon/evening thunderstorms depending on the timing of convection.

KEY MESSAGE 3: A somewhat strong area of low pressure for the time of year will make a run at the region for the latter part of the weekend and the beginning of next week, and it will likely bring multiple rounds of showers. Ensemble consensus brings the pressure just under 1000 MB. GEFS/EPS/CMCE combined ensemble probabilities of the region receiving more than 0.5 inches of rain are between 30-60 percent and they fall to below 15 percent for receiving more than an inch. Temperatures will stay around seasonable normals, with highs generally in the 70s to mid 80s, and lows generally in the 50s and low 60s. Depending on the storm track and timing of any associated frontal passages, the threat of strong to severe storms will be watched, but the threat should remain on the lower side due to a cooler and less humid airmass.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Through 12Z Wednesday...Conditions are currently all VFR and that will be the case through the afternoon. A broken line of showers and storms will move down from the north this evening and overnight. It will cause frequent lightning, a period of MVFR to IFR visibility and gusty/erratic winds at any terminal it reaches. The storms should exit northern areas by 6Z. Winds will be relatively light and variable for the rest of the night, except at PBG and MSS where gusts out of the west to southwest up to 15 KT are possible. Winds become stronger and southwesterly at the rest of the terminal today, with gusts in the 15-25 KT range. Winds slowly diminish this evening. A round of LLWS is possible this evening at all terminals.

Outlook...

Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. NO SIG WX. Thursday: VFR. Chance SHRA, Chance TSRA. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

CLIMATE

High temperatures on Tuesday will be hot, but we are at the climatological warmest part of the year. Therefore, it is far from a certainty that any records will occur.

MSS looks most likely to set a new record. PBG also is currently forecast to set a new record. MPV, and especially BTV and SLK, are unlikely to do so. See below for current records:

Max Temp Records Date BTV MPV MSS PBG SLK 07-14 100|1995 94|1952 92|2012 95|1952 95|1934

High Min Temp Records DatePBG 07-14 70|1974

BTV WATCHES/WARNINGS/ADVISORIES

VT...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for VTZ001>011-016>021. NY...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NYZ026>029-031-035-087.