textproduct: Burlington

WHAT HAS CHANGED

As of 151 PM EST Monday...

No significant changes were made this forecast cycle. A few snow showers are expected in cyclonic flow through Thursday before a consolidated cold front swings through late week bringing some light accumulations of snow, gusty winds, and some potential for dangerously cold wind chill values over the weekend.

KEY MESSAGES

As of 151 PM EST Monday...

1. Dangerously cold weather due to combination of gusty winds and low temperatures is anticipated for much of the weekend. The cold will gradually ease early next week.

2. Some difficult travel is possible late Friday and Friday night as snow showers are expected associated with a strong Arctic cold front.

3. Below average temperatures continue with isolated to scattered snow showers expected Tuesday through Thursday.

DISCUSSION

As of 151 PM EST Monday...

KEY MESSAGE 1: Bottom line: Expect another period with temperatures below zero and wind chills at times reaching Cold Weather Advisory (- 20) criteria over the weekend. A sharp and strong cold front will bring another surge of bitter cold air along with gusty northwest winds into northern New York and Vermont Friday night through Saturday. There is pretty impressive ensemble agreement on the strength and track of surface trough with MSLP falling into the 990- 999 millibar range and rapid and strong pressure rises behind the front. That being said, there are substantial timing differences, reflected in the 925 millibar temperature spread in the AIGEFS. This spread peaks early Saturday morning, but overall there is good agreement that the leading edge of the front pushes through the region Friday night. As a result, the coldest air mass will settle into the region during the day on Saturday. These timing differences have implications for maximum temperatures on Saturday, with greatest uncertainty as one goes eastward. For instance, the latest probabilistic temperature data for St. Johnsbury shows a distribution with a long right tail, such that while the most likely high is only 6 degrees, there is a reasonable possibility highs could be in the teens. In that event, would expect temperatures to be steady or falling during the day while winds remain an important factor.

NAEFS 700 millibar and 850 millibar ensemble mean temperatures reflect strong mixing potential with anomalous cold aloft, especially so over northern New York. As such, blustery northwest winds will be ongoing through the period making the air feel even colder. The latest forecast shows minimum wind chills during this period in the -20 to -29 range across nearly all of northern New York and most of Vermont except for the Upper Valley. With colder air expected for Saturday night with winds becoming lighter, even light wind will support dangerously low wind chills, and aside from localized spots, the entire region is likely to see wind chills reaching Cold Weather Advisory criteria. The ECMWF-Extreme Forecast Index is highlighting noteworthy wind gusts during this period, especially in the typical downslope areas in the western Champlain Valley such as Ticonderoga, and east of the Greens. Maximum wind gusts on Saturday for much of the region look to be in the 30 to 40 MPH range, with a few gusts closer to 45 MPH favored in the localized areas previously mentioned. As winds decrease, potential for low temperatures Saturday night to fall below -20 increase into the 10-20% range in much of north central Vermont and 20-60% in much of northern New York away from the Champlain Valley. All model clusters of 500 millibar heights show the upper level low on Sunday parked to our east/northeast, supporting continued reinforcement of Arctic air and high confidence of very cold weather continuing through the weekend. Noting that as we move through February temperatures tend to warm, Sunday's maximum temperatures look particularly extreme relative to climatology (along the lines of 25 degrees below normal). Subtle differences in the pattern exist, which leads to varied snow shower/upslope snow chances Sunday into Monday.

KEY MESSAGE 2: While some light and relatively localized snow showers are possible on Thursday associated with a weak cold front and associated instability/upslope northwesterly flow, much more widespread snow shower activity is expected Friday afternoon, and especially the nighttime hours, as a strong Arctic cold front moves through the area. In addition to scattered snow showers during the day associated with height falls and cyclonic flow out ahead of the front, organized snow showers with possible embedded snow squalls will form along the front. Limiting This idea is shown in deterministic model guidance depicting a sharp wind shift/low level convergence helping produce briefly heavy snow shower activity before the air mass quickly becomes too dry and cold for additional precipitation. Low level lapse rates and the resulting instability (even 90th percentile SBCAPE is only reaches 5-15 J/kg) look minimal, associated with relatively cool pre-frontal air at the surface and poor (nighttime) timing of the front, so at this point the risk of heavy snow showers looks limited until the more dynamically driven precipitation arrives. An early estimate of total snowfall for this event will be in the range of a few tenths to locally a couple of inches, supported by high snow ratios

KEY MESSAGE 3: Weak migratory high pressure will break down tonight with clouds increasing overnight ahead of a weakening clipper-type low. Skies will remain clear through the evening allowing for temperatures to drop sharply after sunset. As a result, utilized last night's low temperatures and a blend of guidance to get a curve for tonight. Lows should be in the single digits slightly below zero for most locations with typically colder hollows ranging from 8 to 15 degrees below zero.

Decreasing supportive dynamics aloft will result in weakening of the clipper type low supporting the surface circulation opening into a trough as it moves into the region. This favors more isolated to scattered coverage of showers except of directly down wind of Lake Ontario into portions of St Lawrence County where showers will be more numerous. Cyclonic curvature aloft settles over the region through Thursday under a northwest surface flow pattern. Continued intermittent snow showers are likely especially along the western slopes of the northern Greens. Snow totals will be meager due to very limited atmospheric moisture likely ranging from a dusting to around 1 inch across the 48hr period. On the flip side, temperatures be warmer with southwest flow Tuesday/Wednesday - feeling almost balmy with highs in the low/mid 20s rather than single digits and teens of recent.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Through 00Z Wednesday...VFR conditions prevail for the next 6 to 12 hours across our 7 taf sites. Still some lingering low level moisture trapped below sharp/shallow thermal inversion which could produce some low clouds/IFR at SLK/MSS, but given lack of development last night, feel probability is low tonight. Winds are terrain driven under 5 knots tonight, becoming south/southwest 4 to 8 knots on Tues with increasing mid to high level clouds. Some light snow shower activity is possible over northern NY taf sites after 18z, but given dry low levels precip might have difficulties reaching the ground.

Outlook...

Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Wednesday: Mainly VFR, with local MVFR possible. Slight chance SHSN. Wednesday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: MVFR. Chance SHSN. Friday Night: Mainly MVFR, with areas VFR possible. Chance SHSN. Saturday: VFR. Slight chance SHSN.

BTV WATCHES/WARNINGS/ADVISORIES

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