textproduct: Burlington

WHAT HAS CHANGED

As of 247 PM EDT Friday...

Wind gusts have been increased for the northern St. Lawrence Valley with recent guidance denoting stronger gusts near Massena, NY. Rainfall amounts areawide have also been increased slightly with recent trends.

KEY MESSAGES

As of 247 PM EDT Friday...

1. Rounds of showers and mountain snow are expected through the rest of today and into the weekend.

2. Gusty Winds are expected through the rest of the day today into tomorrow, especially in the northern St. Lawrence Valley and near mountain summits.

3. After some lingering shower potential Tuesday night, drier conditions return with a warming trend from mid to late next week.

DISCUSSION

As of 247 PM EDT Friday...

KEY MESSAGE 1: Widespread precipitation is beginning to overspread the region this afternoon from the north as a surface low shifts south. Upper level cyclonic flow associated with a blocked upper trough over the Canadian Maritimes will to increased moisture with upper level northwest flow. Surface precipitation today will come in two waves with the initial wave currently along the International Border. This initial round will be light with perhaps some virga as surface relative humidities remain low. However, this round will help saturate our air columns in time for the next convectively driven round of showers. The second round will be diurnally driven under the core of the low, and may contain some isolated rumbles of thunder as steep lapse rates with strong cooling aloft lead to modest instability. Some small graupel and perhaps small hail are possible, but impacts will be minimal if any. This more convective round will be closer to 6-8 PM this afternoon. Beyond sunset, temperatures will fall to 10 degrees below normal with overnight lows in the valleys near 40. More significant cold will be present across the higher terrain of the Greens and Adirondacks with lows falling to near freezing. With any shower activity, precipitation above 4000 ft will see all snow with light accumulations to an inch or two on the mountain summits. Wet bulbing and dynamic cooling could bring a few flakes as far as elevations at 2000 to 2500 ft in the Adirondacks and eastern Greens. Any hikers or recreators should use extra caution if heading to the mountains as conditions will rapidly deteriorate with elevation for those unprepared for winter conditions.

More steady rain will follow behind for tonight as the surface low becomes occluded and stalls over the region. Along the triple point of the occlusion a coastal low will develop near Cape Cod with reinforcing moisture and precipitation, focused in the Northeast Kingdom and near the Connecticut River Valley. Steady light to moderate rain will result through early tomorrow morning. The bulk of the rain will taper off around sunrise to mid morning tomorrow. Total rainfall amounts have increased with around an inch to an inch and a quarter in the Northeast Kingdom, and a quarter to half an inch elsewhere. Lesser amounts may be possible in the southern Champlain Valley and St. Lawrence Valley due to shadowing and further distance from the core of the moisture axis, respectively. As the system departs, lingering moisture and cool air may lead to patchy frost and some patchy fog primarily Saturday night in the Northeast Kingdom and areas of the Connecticut River Valley.

Additional shower activity is expected Sunday as cyclonic flow keeps the region moist with embedded shortwaves. Additional rainfall amounts will be a few tenths. Temperatures however will begin to moderate beginning Sunday as wider valleys will see mid to upper 60s, with some lingering low 60s for the higher terrain.

KEY MESSAGE 2: As a surface low begins to pass directly over the region, a strengthening low level jet to 50 knots at 2000 ft will shift south towards the St. Lawrence Valley this evening into tonight. Geostrophic northeasterly winds aloft will be aligned with the orientation of the St. Lawrence Valley which will enhance the strength of any associated surface gusts. However, surface winds will be more north to northwesterly, and not fully unidirectional with the strongest gusts. This will help limit the full mixing of the low level jet, though winds will still be gusty. Gusts near Massena, NY are forecast to be around 40 to 45 MPH, with the strongest winds occurring between Midnight and 5 AM tonight. Elsewhere, winds are expected to be between 15 to 25 MPH. Higher elevations above 2500 ft will also see stronger winds to 30 to 40 MPH which coupled with near freezing temperatures will lead to wind chills in the Adirondacks and Greens in the teens to low 20s. Hikers and recreators should plan for winter conditions if planning to be in the higher terrain tonight or tomorrow. Winds will turn to the north by tomorrow morning with channeled flow likely in the Champlain Valley. A Lake Wind Advisory is likely to be needed by sunrise tomorrow with winds gusting to 25 to 35 MPH on Lake Champlain and the surrounding areas. As the system shifts out late tomorrow afternoon, gusts and winds will trend towards calm for Saturday night.

KEY MESSAGE 3: Model guidance is somewhat split on how much moisture will wrap northwestward from an offshore low, but consensus favors some isolated to scattered showers progressing into eastern Vermont again by Tuesday night. Otherwise, ridging is favored to build Wednesday through the end of the week promoting highs back around 80 degrees for many places by Thursday and Friday. The big questions for next week into next weekend will be: how fast will the blocking high actually move, and if it does, how much will the ridge axis flatten? Blocking features usually move slower than model projections, so we could see some showers potentially linger into Wednesday, especially with warmth otherwise beginning to build. Current guidance also points to an approaching wave on Friday, but models tend to break down ridges too quickly while being too progressive with migratory features at this time scale. It's possible that the ridge axis will hold into the beginning of next weekend at least.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...VFR conditions will continue through the afternoon until the next wave rolls into northern New York and Vermont 00-06Z. Likely see CIGs dip to MVFR, then IFR for most terminals after 06Z. LLWS will also be a concern for aviators with a low level jet moving through this evening, then as more pronounced backside northwesterly flow increases aloft with the passage of the upper low and surface cold front. Conditions favored to slowly improve after 12Z with northerly winds increasing; gusts in excess of 25kts will be possible 12-18Z on Saturday.

Outlook...

Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA, Slight chance TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Monday: Mainly VFR, with local MVFR possible. Likely SHRA, Slight chance TSRA. Monday Night: VFR. Slight chance SHRA. Tuesday: VFR. Chance SHRA. Tuesday Night: VFR. Slight chance SHRA. Wednesday: VFR. Slight chance SHRA.

MARINE

A Lake Wind Advisory is in effect for all Lake Champlain. A band of showers and storms is approaching, and winds ahead and behind this convection will likely drive winds upwards to 15 to 25 knots, with gusts 30 knots likely. After activity has moved south, winds may briefly calm, but then are expected to increase after midnight as north winds begin channeling down the valley. Waves 1-2 feet will increase towards 2-4 feet, especially when more sustained flow is established overnight into Saturday morning.

BTV WATCHES/WARNINGS/ADVISORIES

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