textproduct: Burlington

WHAT HAS CHANGED

As of 234 PM EDT Saturday...

Frost Advisory has been issued from 2 AM to 8 AM tonight for eastern Essex and eastern Clinton County in New York, and western Addison County in Vermont.

KEY MESSAGES

As of 234 PM EDT Saturday...

1. Below normal temperatures will remain into tomorrow with the potential for Frost tonight as showers taper off this evening.

2. Temperatures will quickly rebound to at or above normal for the start of next week as our pattern turns more active.

3. Generally unsettled weather is expected mid next week into the weekend.

DISCUSSION

As of 234 PM EDT Saturday...

KEY MESSAGE 1: Diurnally enhanced cold advection showers will continue into the mid afternoon, before tapering off this evening as diurnal heating wanes. Some of these showers may contain some small graupel with cooling temperatures aloft that will support some small graupel/hail growth. A few hundreths of precipitation is expected within any showers today. Subtle ridging will begin to build in tonight which will provide a reprieve from shower activity into tomorrow, but will also allow for the potential for patchy fog tonight. With the Climatological growing season in the Champlain Valley underway, given the potential for temperatures to drop below the Frost threshold of 36F, a Frost Advisory has been issued for western Addison County in Vermont, and eastern Clinton and eastern Essex County in New York form 2 AM to 8 AM tonight.

There is still some uncertainty in the overall cloud coverage based on the HREF and observed broken to overcast skies across eastern Ontario. However, as already evident, some downsloping off the eastern Adirondacks has allowed for some daytime breaks in the clouds across the eastern Adirondacks. This clearing, albeit conditional, bodes some confidence in at least some patchy fog in the sheltered locations of the western Champlain Valley. Moreover, some weak radiative cooling in western Addison County from blocking by the Adirondacks will also lead to some potential patchy Frost. Confidence outside the aforementioned areas in the Champlain Valley is much lower for frost development due to some waa from Lake Champlain under northwest flow, in addition to some confidence in more cloud coverage from a developing coastal off the New England Coast. While temperatures will also be conducive for Frost outside the Champlain Valley, we will not issue headlines as the climatological growing season outside the CPV has not begun yet.

Sunday will remain chilly with highs 5-10 degrees below normal into the upper 40s to low 50s. Moisture should clear out with a much drier day as relative humidities fall into the 30-40% range. Wester/northwest winds will become breezy into the afternoon as subtle ridging crests over northern New York. Temperature Sunday night will be in the upper 30s to low 40s, with little concern for any Frost.

KEY MESSAGE 2: Our pattern will turn more active beginning early next week. Mid/upper troughing will become dominant across northern New York as our flow becomes oriented southwest to northeast along a stretched long wave trough across the western US. This troughing will advect both warmer temperatures and continued moisture into the entire region for early next week. Temperatures will climb into the 60s on Monday and to near 70 Tuesday. Consequently with the sudden rise in temperatures, both precipitation chances and windy conditions will increase. The first of several shortwaves will ride along this elongated trough Monday morning into Monday afternoon. A few hundreths of rainfall is expected, mainly in the Adirondacks and locations near the International Border. Weekend dryness, in addition to an approaching 40-50 knot low level jet likely will lead to some virga initially with any precipitation associated with this shortwave. Furthermore, virga may also allow some gusty winds up to 25 to 30 MPH, particularly across the northern fringes of the Adirondacks, to mix to the surface.

The better setup, with overall better forcing, and dynamics will be Tuesday into Tuesday night. A frontal system will draw upon strong upper level flow from a 250mb jet streak advecting Pacific moisture well into the interior of the country and even perhaps into our region. This streak will also be the cause of continued gusty winds into Tuesday ahead of widespread wetting rain into Tuesday night. DESI NBM probabilistic guidance shows around a 50% of reaching a quarter inch or more, with 40% of half an inch or more of rain across the St. Lawrence Valley. The winners from these early week systems will likely be the St. Lawrence Valley where the axis of the trough is expected to setup. The GFS does show a narrow ribbon of instability associated with the showers Tuesday night, but the rainfall appears to be more post frontal, so not anticipating much in the way of thunder, but will lead mention of thunder in the grids. These early week showers will set the stage for more active and wet conditions into mid to late next week.

KEY MESSAGE 3: A large-scale trough gradually builds into the region during Tuesday through the end of the week. It will be slow enough that a few different shortwaves will pass through and surface lows will develop along those. The first one passes well to the northwest on Tuesday. An associated cold front will move into the region Tuesday and bring a round of rain, particularly to northern New York. The next low passes through Wednesday with the center looking to track over or slightly west of the region. A rumble of thunder is possible as the cold front pushes through in the afternoon. The final low looks to track through Thursday into Friday, with the center passing to the east of the region. There will be enough cold air on the backside of it that it could end as a few snow showers in the mountains. Through Friday, GEFS/EPS/CMCE combined ensemble probabilities of receiving 1 or more inches of rain are 85-100 percent, 2 or more inches are 35-55 percent, and 3 or more are 0-20 percent. Most of the precipitation will be stratiform and limit flooding concerns, but the effects of potentially three storm systems in a row will still be watched.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through 00Z Monday...Showers taper off this evening, resulting in widespread VFR conditions across all TAF sites. As atmospheric mixing comes to an end tonight, high pressure nosing in from the Plains will assist with some subsidence and sinking air as an inversion makes to trap moisture at the surface. This will likely mean slightly lowering ceilings (2000-3000 feet above ground level) throughout the night, though any clearer spots could see temperatures fall below threshold levels and produce some patchy fog and near-surface clouds. Timing for this will be sometime between 05Z and 13Z Sunday, with highest potential for MVFR or lower conditions occurring at SLK, MPV, EFK, and RUT. While not out of the question at BTV, PBG, and MSS, the St. Lawrence Valley should keep a west-southwesterly wind 5-10 knots overnight, and the Champlain Valley will likely be influenced by the lake and keep conditions VFR throughout the night. Sunday morning, we'll see winds pick up out of the west and northwest, quickly scouring out any low clouds and/or fog, likely gusting 15-25 knots by the afternoon.

Outlook...

Sunday Night: VFR. Chance SHRA. Monday: Mainly VFR, with local MVFR possible. Chance SHRA. Monday Night: VFR. Slight chance SHRA. Tuesday: VFR. Likely SHRA, Slight chance TSRA. Tuesday Night: Mainly VFR, with local IFR possible. Likely SHRA. Wednesday: MVFR/IFR conditions possible. Definite SHRA. Wednesday Night: Mainly VFR, with local IFR possible. Likely SHRA. Thursday: Mainly MVFR, with areas IFR possible. Likely SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Frost Advisory from 2 AM to 8 AM EDT Sunday for VTZ009. NY...Frost Advisory from 2 AM to 8 AM EDT Sunday for NYZ028-035.