textproduct: Burlington

WHAT HAS CHANGED

As of 250 AM EDT Monday...

No significant changes.

KEY MESSAGES

As of 250 AM EDT Monday...

1. Rounds of scattered showers today, with a few thunderstorms possible especially mid afternoon through early evening.

2. Another weak frontal system will bring shower and thunderstorm chances Wednesday, with mostly dry and seasonable weather otherwise midweek.

3. A quiet second half of the week.

DISCUSSION

As of 250 AM EDT Monday...

KEY MESSAGE 1: Rain overnight/early this morning has proven to be on the light side of possible outcomes, with most of the heavier showers staying in southern Quebec closer to where a subtle trough has been draped. As a result, much of Vermont and northern New York has seen little or no rain with only spotty showers moving across northern areas. The situation will change during the day as the weak frontal system gradually approaches and passes through our region. The primary surface trough/wind shift line will be oriented from northeast to southwest, and showers will tend to organize along it. Poor upper level forcing and abundant dry air aloft nosing in from the west, evident in water vapor satellite imagery, will minimize the potential for showers and thunderstorms in most of northern New York. Farther east, diurnal heating ahead of the boundary will occur with breaks in cloud cover allowing temperatures to rise into the 75 to 80 range with dew points in the middle 60s. This heat will overlap sufficiently deep moisture and instability to support a low risk of a thunderstorm in a swath from eastern Essex County New York northeastward across much of northeastern Vermont and points south. The CAPE and shear balance for thunderstorms with a minimal severe threat remains evident in the HRRR/RAP/RRFS guidance, particularly in southern Champlain Valley in the 4 to 6 PM window when mean mixed layer CAPE reaches the 500-800 J/kg range with effective shear of about 25 knots (0-6 km shear only about 30 knots). Compared to convective guidance 24 hours ago, surface based instability has only ticked up very slightly, and model output statistics driving the NBM are less bullish than the dynamical models for the thunderstorm probabilities today, suggesting most showers will not produce thunder. Given the relatively small footprint of heavier showers, rainfall amounts should be highly variable with localized footprints of upwards of 1" while many areas miss out on substantial rain (0.25") through this event.

KEY MESSAGE 2: Aside from a low chance of a few terrain driven showers on Tuesday, the next chance of rain continues to be on Wednesday. Broad consensus remains that a weak cold front will pass through the Northeast during the day and washout somewhere in our vicinity. This scenario leads to much higher chances of showers and thunderstorms in northern New York than Vermont, especially eastern Vermont. The probabilities of thunderstorms remain low with most guidance rather limited in instability consistent poor lapse rates amidst a thick overcast along the frontal zone. Have maintained slight chances of thunder in the St. Lawrence Valley for the afternoon hours per model consensus and no mention of thunder elsewhere. Overall, this event remains unlikely to be impactful. Note timing/location of the front and associated cloud cover will affect forecast temperatures, which currently may be a few degrees too high (upper 70s to low 80s) in western Vermont and points west if clouds overspread our region on the earlier side. Shower chances could linger into Thursday, although chances are much lower than on Wednesday, per ensemble guidance; some deterministic guidance suggests at least some hit or miss showers will develop in cyclonic flow.

KEY MESSAGE 3: Broad cyclonic flow slowly migrates eastward during the second half of the week, bringing near normal temperatures and dry conditions through Saturday. Sunday's forecast hasn't fully come into focus at this time, but we have potential for a system to bring in widespread shower activity throughout the day. A consensus forecast will likely emerge over the next few days and we'll be able to hone in on the specifics.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Through 12Z Tuesday...Widespread shower activity and MVFR CIGs will persist across northern Vermont for much of the day. Overcast skies will tamp down surface instability and limit development of thunderstorm activity. Locations that receive heavy showers could see temporary reduction to IFR, but anticipate this will be the exception rather than the rule.

Outlook...

Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Likely SHRA. Wednesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX.

MARINE

As of 230 AM EDT Monday... A Lake Wind Advisory remains in effect for this morning for Lake Champlain as steady south/southeast winds persist. Observed winds overnight have been 20-30kt with gusts as high as 35 knots over the broad lake and northern waters. Observed significant wave heights have averaged in excess of 2 feet in the vicinity of Valcour Island, suggesting wave heights of 3-5 ft have been occurring nearer to Colchester Point. Winds and waves will begin to slacken after sunrise, although they will linger in the 15 to 20 knot range throughout the morning prior to a cold front moving through and winds turn northerly.

BTV WATCHES/WARNINGS/ADVISORIES

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