textproduct: Burlington

WHAT HAS CHANGED

As of 236 AM EDT Tuesday...

Winds were increased for today and tonight as warmer temperatures help mix stronger winds aloft to the surface.

KEY MESSAGES

As of 236 AM EDT Tuesday...

1. Well above normal temperatures expected on Tuesday with much cooler weather expected on Wednesday and Thursday.

2. Strong to locally severe thunderstorms possible Tuesday afternoon and evening.

3. Cooler and drier conditions are favored Thursday and Friday before a transition back to seasonable temperatures and a wetter pattern.

4. Seasonable temperatures and increasing chances of precipitation expected for the weekend into early next week.

DISCUSSION

As of 236 AM EDT Tuesday...

KEY MESSAGE 1: Continued warm air advection will set the stage for unseasonably warm temperatures on Tuesday. The latest NBM shows high potential for 90 degree weather, however, much of the other guidance and MOS is showing temperatures likely plateauing in the mid to upper 80s. Cloud cover and convection will be a huge factor in determining how warm we get as a lot of guidance suggests partly to mostly cloudy skies. Any convection would increase cloud cover and any precipitation would drop temperatures significantly. Still, there is overwhelmingly high confidence in high temperatures being 15 to 20 degrees above normal. On Wednesday, a cold front will likely push through the region during the morning hours which will limit daytime heading with strong cold advection expected to follow in the wake of the front. We could still warm into the 80s across eastern Vermont but will likely be in the 70s for most of Vermont and New York based on the timing of the frontal passage. Thursday will be 10-20 degrees colder than Wednesday as we will see temperatures struggle to climb into the mid 50s to lower 60s. North winds in the 10-20 mph range will help make it feel a bit blustery, especially after the recent warmth. Most clear skies should help it feel a little warmer given the late May sun angle.

KEY MESSAGE 2: The convective potential for Tuesday continues to remain very conditional. A lot of the machine learning and AI tools are showing modest probabilities (15-30%) for severe weather Tuesday afternoon and evening while the latest deterministic guidance shows rather lackluster instability. There is high confidence in around 50 knots of deep-layer shear as we have a strong 500 jet move overhead but the thermodynamic profiles keep fluctuating from model run to model run. Even though temperatures are expected to warm into the mid to upper 80s and dewpoints rising in the lower to mid 60s, the mid-level lapse rates between 850 mb and 500 mb aren't exactly what you want to see to maximize severe potential. In addition, no notable surface convergence outside of orographic lifting is expected with the cold front not expected to come through until Wednesday morning. There will be some weak height falls under anticyclonic flow aloft and a weak shortwave trough pushing through which will give up some deep layer support but getting storms to initially develop will be difficult. The main focus, initially, will be across the higher terrain and along lake breezes as this could create some surface convergence and the upper level support could take over from there.

There may be residual cloud cover from overnight convection across western New York which may stunt surface heating. Should this occur, instability values may underperform further and lead to little to no thunderstorm activity. Hence the condition potential. Largely unidirectional wind profiles with slight curvature in the Champlain Valley is expected which likely makes Tuesday a wind threat. High LCLs will strongly inhibit tornado potential with high freezing levels also making severe potential very difficult to come by. The main window for convection will be between 4 and 8 PM with instability waning rapidly following sunset.

KEY MESSAGE 3: Winds weaken Thursday night with skies clearing; this may be a period of concern for some frost outside the Champlain Valley with lows in the mid/upper 30s for many locations, and low 40s for the Champlain Valley. Temperatures begin to warm up on Friday with northwest flow weakening, high temperatures will reach the 60s areawide. A slow warming trend is then expected through the weekend into Monday.

Models begin to split on precipitation timing heading into the weekend. Consensus maintains some chances of showers increasing Saturday with more widespread rain Sunday. However, a number of models are beginning to hold onto the ridge longer delaying precipitation onset until the late weekend. Either way, a pattern shift to deep return flow from the Gulf Coast northeastward into the Northeast is appearing probable. This flow pattern would result in multiple days of rain potential once it sets up.

KEY MESSAGE 4: There continues to be considerable differences in both ensembles and deterministic models in how shower chances play out for the upcoming holiday weekend. Ensemble members of both the GEFS and ECMWF are roughly split equally on whether waves of precipitation will cross the area Saturday into Sunday. The deterministic ECMWF also favors a wetter solution. Meanwhile, the remaining ensemble members along with the GFS and CMC keep ridging more firmly in place, with the axis running just to our east. This would keep rain shunted to our south and west through the day Saturday and most of Sunday, then trending rainy for Memorial Day. With this much uncertainty, have stayed with the NBM solution for now. Either way, temperatures will be seasonable with highs mainly in the 60s and lows in the 40s.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday...VFR conditions will prevail through the TAF period. SKC conditions this evening will see gradually increasing clouds overnight, though expect ceilings to remain AOA 10 kft through 12z Tue, and likely AOA 4000 ft through the remainder of the TAF period. Isolated to scattered showers/thunderstorms are possible Tuesday afternoon, some of which may be strong to perhaps severe. Coverage/timing is too uncertain at this point to include any mention in the TAF, but MVFR/IFR conditions will be possible in any thunderstorms. Surface winds become light and variable around 5 kt this evening. However, a LLJ moving overhead will allow for periods of LLWS at all terminals overnight. Surface winds increase out of the S/SW after 14z Tue, gradually shifting toward the W/SW with gusts of 18-25 kt expected.

Outlook...

Wednesday: VFR. Chance SHRA, Slight chance TSRA. Wednesday Night: VFR. NO SIG WX. Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. Chance SHRA. Saturday: VFR. Chance SHRA.

MARINE

As of 236 AM EDT Tuesday...

A Lake Wind Advisory remains in effect for the Broad Waters of Lake Champlain. Winds are expected to increase this morning out of the south with sustained speeds 15 to 20kts and gusts around 25kts. These stronger winds will continue through 8 AM and will diminish to 15 knots or less until the early afternoon; winds then increase again as faster winds aloft mix to the surface. Gusts in excess of 20kts are probable before flow turns more southwesterly. South winds return tonight with stronger gusts possible. A front will pass through the region Wednesday resulting in a wind shift out of the north with gusts up to 30kts.

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...None.