textproduct: Burlington

WHAT HAS CHANGED

As of 256 PM EDT Wednesday...

Heat Advisory was expanded to included eastern Windsor County.

KEY MESSAGES

As of 345 PM EDT Wednesday...

1. Scattered showers and thunderstorm chances continue through Friday. Risk of stronger thunderstorms is primarily Friday afternoon/evening.

2. Humid and increasingly hot through Friday, then dry and seasonably warm on Saturday. Impactful heat possible on Friday.

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

DISCUSSION

As of 345 PM EDT Wednesday...

KEY MESSAGE 1: A messy weather pattern, with subtle forcing for only somewhat organized showers and thunderstorms, will persist today and Thursday. The first of these systems, featuring a narrow upper level trough, is enough to spark increasingly numerous showers and thunderstorms late this afternoon through tonight. The near storm environment has plentiful instability, with near 2000 J/kg CAPE, but low shear (near or less than 20 knots of effective shear - this is leading to pulse type of thunderstorms with brief heavy rain and lightning as expected hazards. Deep layer shear will increase a bit tonight concurrent with a very weak trough passing through, so a period of more widespread showers with embedded thunderstorms is expected. These showers should generally progress west to east through most of northern New York and Vermont, clearing eastern Vermont after midnight.

For Thursday, the potential for more non-severe thunderstorms continues to be lower compared to today, but somewhat uncertain. Mid-level warming and some slight height rises during the day will reduce surface-based instability compared to today. Lingering troughiness in northeastern Vermont may support cloudier conditions compared to areas farther south and west. Differential heating related to this boundary or other boundaries that develop will help act as a trigger potentially for thunderstorms, especially later in the day and evening as the next weak trough moves in from the west. The greatest forcing and organized thunderstorm activity appears to be focused well to our south with this system, where much greater instability is expected. As such, chances for widespread thunderstorms appears low at this time.

The severe thunderstorm risk for Friday is very unclear at this time, with higher confidence in organized stronger storms capable of damaging winds farther south from central New York towards the Mid-Atlantic states. The Storm Prediction Center's slight risk was expanded eastward, likely be due to greater probabilities of severe wind. In northern New York and Vermont, relative to areas to the south, the signals are more mixed. Some machine learning guidance is very aggressive in the risk of severe thunderstorms associated with this system (such as the GEFS 30-45% chance across Vermont), but others focus.

KEY MESSAGE 2: A seasonably warm and humid air mass is present and will modify slightly until a cold front sweeps eastward across the eastern US Friday night. There has been about a 2 degree warm bias in the NBM maximum temperatures recently, with these biases decreasing with forecasting lead time. However, based on the observed temperatures this afternoon, this issue may be lessening as temperatures have managed to warm near or above this guidance. Therefore, confidence is relatively low on the degree of heat for tomorrow when much of the forecast data suggests temperatures should be a couple of degrees warmer. Cloud cover and lingering showers tomorrow are limiting factors to produce sub-Heat Advisory criteria. Partly sunny skies are generally expected, and if this winds up being on the sunnier side along with dew points remaining elevated again in the upper 60s to lower 70s in most locations, impactful heat will be possible as heat indices approach the low to mid 90s.

Greater confidence in these types of heat indices continue on Friday when Heat Advisories are in effect in portions of our region, as a more pronounced ridge aloft will support sunshine and warmer air aloft. Valley temperatures will more easily reach into the low to mid 90s with deeper mixing, such that even with slightly lowering dew points feel 95 or higher heat index values are more likely. Additionally, the cumulative effect of hot and humid conditions will make for more significant impacts than on Thursday. That being said, given early season heat, precautions should be taken with regards to proper hydration and clothing to stay safe each of the next couple of days.

KEY MESSAGE 3: Multi-layer low pressure will be swirling over Ontario and Quebec by the end of the weekend, swinging a cold front through the Northeast on Sunday. This will mean above normal temperatures Saturday night with lows in the mid 50s to lower 60s, then one more day of above normal temps on Sunday ahead of the frontal passage. Highs Sunday are expected to reach up to the mid 70s and 80s before falling with the frontal passage. Model consensus shows the cold front moving through rapidly on Sunday, bringing showers (up to 30- 60% chance of measurable precip in a given location) and the potential for a few thunderstorms Sunday afternoon. Following the front, we'll see temperatures return to near or below normal early next week with highs in the upper 60s and 70s, as well as lows in the upper 40s and 50s. Dew points will also be relatively low in the mid 40s to lower 50s each afternoon. Showers chances will remain a steady 20-50% throughout the early work week as cyclonic flow continues to throw shortwaves through the region.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Through 00Z Friday...Scattered showers and thunderstorms will continue through 04z tonight, with MVFR conditions likely in any precipitation. Rainfall has been quite heavy at times, with brief periods of IFR visibility noted. Heaviest showers/thunderstorms will exit by midnight, with a few scattered showers possible overnight. Ceilings will lower to 1500-2500 ft at all terminals after 04z, with IFR conditions likely at KMSS/KSLK/KMPV during that time. Ceilings start to lift after 14z Thu, and expect VFR/local MVFR for much of the period after 18z. However, additional showers/thunderstorms are expected on Thursday, though coverage is still uncertain, so have not included in the TAFs at this time. Light winds at 6 kt or less through the period.

Outlook...

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

CLIMATE

Record High Temperatures:

June 12: KBTV: 94/2017 KMPV: 88/2017 KMSS: 89/2005

Record High Minimum Temperatures:

June 11: KBTV: 71/2017

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- 009-011-021. NY...Heat Advisory from noon to 8 PM EDT Friday for NYZ028-035.