textproduct: Burlington

WHAT HAS CHANGED

As of 237 AM EDT Thursday...

Confidence has increased in possible advisory snow amounts for a clipper system Friday into Saturday, as well as for an impactful storm system for early next week.

KEY MESSAGES

As of 237 AM EDT Thursday...

1. The potential for localized and minor ice jam related flooding continues through Today, along with minor open water flooding forecasted for the Ausable River and Otter Creek.

2. A strong cold front will sweep through the area this morning, bringing gusty winds and much colder air.

3. A clipper system will bring a few inches of snow and some gusty winds Friday into early Saturday.

4. High amplitude pattern will set the stage for an event with several weather hazards early next week.

DISCUSSION

As of 237 AM EDT Thursday...

KEY MESSAGE 1: The latest forecast from the Northeast River Forecast Center still indicates the Ausable River and Otter Creek are expected to reach minor flood stage today with Action Stage possible on the Lamoille, Winooski, Mad, Barton, Oswegatchie, St. Regis, and Missisquoi Rivers. Open water flooding will be the main concern on the Ausable River and Otter Creek from snow melt, as most of the river ice has cleaned out.

Additional rainfall this morning will be variable with values ranging from 0.1" to 0.3" as a corridor of heavier showers ahead of a cold front slides east. These rainfall amounts will cause additional rises on rivers and streams, this combined with numerous ice jams in place, could cause renewed localized ice jam flooding. The greatest potential for additional ice jam flooding based on current ice jam locations would be the St Regis River at Hogansburg and Brasher Falls, Saranac and Great Chazy. Still think we have to watch the Passumpsic River near Lyndonville closely with additional snow melt and rainfall expected today; ice movement is already present on the Sleepers River.

Temperatures will return to normal levels with reduced flooding concerns through the weekend, but slow river falls will keep river levels elevated through today and tomorrow.

KEY MESSAGE 2: A strong cold front is beginning to push into the region this morning trailing a band of locally higher rain showers. Shower activity is mainly scattered as the boundary shifts east, and should exit the region just after sunrise this morning. Column moisture content should dry our in the mid levels reducing the chances for any post frontal snow showers. River flooding, as discussed in Key Message 1, will be somewhat impacted by the footprint of the highest rainfall amounts as the specific basins have seen highly variable amounts of rain.

Temperatures will fall rapidly behind the rain this morning, with some locations falling 20-30 degrees within a few hours, namely the Champlain Valley. Temperatures will ultimately level off in the upper 20s to low 30s by this afternoon, aided by weak caa with gusty west to northwest winds this morning. These morning gusty winds are associated with a low level jet of 45-55kts, with the overall expectation that as the low to mid levels cool aloft, lapse rates will steepen as surface temperatures lag in total cooling. These lapse rates will support mixing with gusts mainly 30-40 MPH in Vermont and the St. Lawrence Valley, with occasional 40-45 MPH gusts along the northern fringe of the Adirondacks and northern St. Lawrence Valley, north of US Route 11. Winds will peak around sunrise this morning, remain breezy through today, and weaken by this evening. Higher, prolonged gust potential looks to reduced as the orientation of the winds at peak mixing is not supportive of downsloping, in addition to the peak low level jet ahead of the boundary.

KEY MESSAGE 3: A clipper type system will move through the region from west to east Friday into Saturday morning. A few inches of snow are expected across northern New York and Vermont. A retreating high early Friday may lead to slightly reduced amounts if dry air lingers, but a quick burst of snow is increasingly likely Friday afternoon across the area. The current timing of the snow onset could effect the Friday evening commute.

The track of the system does not bode confidence in high snowfall amounts. These clipper system typically do not yield enough time for enhanced snow rates, nor carry the moisture needed for higher snow totals. Furthermore, the track of this system in the hi-res guidance depicts the surface low to move over the St. Lawrence Valley and northern Vermont. This would support shadowing across the Champlain Valley and eastern Vermont, with the higher amounts in the higher terrain, mainly the western facing slopes of the northern Adirondacks. The current forecast shows generally 2-3 inches across the St. Lawrence Valley, 3-6" across the western Adirondacks and a dusting to an inch or two across Vermont. Probabilities of exceeding 4" is mainly maximized over the Adirondacks at 60-70%. If trends continue, a Winter Weather Advisory may be needed for portions of St. Lawrence and Franklin Counties in New York. Given marginal temperatures in the low to mid 30s, even with some wet bulbing, some areas of rain are possible across the St. Lawrence and Champlain Valleys as well as across southern Vermont. It's overall not a great setup for the Champlain Valley or much of eastern Vermont to pickup much snow, but the higher elevations of northern New York and northern Vermont will get a nice coating of snow.

In addition to the snow potential, winds will also be a concern. A deepening surface low riding behind a departing high will add the influence of the isallobaric wind. Coupled with a 50-60kt LLJ, winds may become gusty at times. Concerningly, the hi res guidance is beginning to depict some downsloping potential across northern New York with NAM3 soundings showing top of the mixed layer winds around 50kts, and bottom of the mixed layer winds to near 40kts. Ensembles show these features, but not as high in magnitude, owing to a difference in surface low centers among the hi res models which resides more north than the global models. Have trended towards the NBM90th given the increased model trends towards higher gusts, but trends will need to be closely monitored, such that if realized, a wind advisory could be needed.

KEY MESSAGE 4: The contrast of deep high pressure across the Atlantic and intensifying low pressure across the Plains will result in deep southerly flow. A 1035mb surface high will amble into the Canadian Maritimes and send a warm front north on Sunday. The transition of high pressure after a surge of cooler air is usually favorable for mixed precipitation. The speed of incoming warm air and initial dry air will likely make this a fast transition from snow to rain, and then the front itself moves out quickly. Given the limited precipitation and quickly increasing temperature Sunday night, there may not be much impact. Behind the front, one will likely notice an immediate surge of wind by Monday morning. Increasing surface temperatures will allow better mixing as pressure gradients also tighten. Temperatures will go from seasonable 40s on Sunday, to mid 50s and to lower 60s in Monday. A wave of moisture from the Atlantic will lift north during the day. It could compete with terrain shadowing, but a few showers will be possible throughout the day due to lift from warm, moist advection. Some instability will also be present. Winds will peak Monday afternoon, ahead of powerful frontal boundary. Global guidance already depicts a linear type feature that rushes east with a sharp thermal gradient. Behind the front, temperatures will sink back into the 20s, and a few teens in northern New York on Monday morning. Temperatures will gradually moderate to seasonal norms behind the system as high pressure becomes established.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Through 06Z Friday...A frontal boundary is shifting east, and has past KMSS, and is approaching KSLK/KPBG/KBTV. This will quickly push east over the next couple hours. A brief dip to IFR ceilings or visibility will be possible at KMSS, and then appears more likely for KSLK and KEFK, 06z-08z and 08z-10z respectively. Until the front exits east of Vermont around 12z, pockets of LLWS will remain across several terminals. Behind the front, south to southwest winds around 5-10 knots will shift to west to northwest and increase to 9-16 knots sustained with gusts 18-28 knots, locally up to 30-33 knots possible at KMSS. Ceilings may be slow to improve, but after 19z-22z, conditions will trend VFR as lingering moisture exits the region. Based on shallow moisture in northwest flow, cannot discount some flurries at areas like KSLK, but it seems unlikely.

Outlook...

Friday: VFR. Chance SN, Likely RA. Friday Night: Mainly MVFR and IFR, with areas VFR possible. Likely SN, Definite RA. Saturday: Mainly VFR, with areas MVFR possible. Chance SN. Saturday Night: VFR. NO SIG WX. Sunday: Mainly VFR, with local MVFR possible. Chance SN, Chance RA. Sunday Night: MVFR. Windy with gusts to 30 kt. Likely RA, Chance SN, Likely FZRA. Monday: Mainly MVFR, with local IFR possible. Windy with gusts to 30 kt. Definite RA.

EQUIPMENT

The Colchester Reef meteorological station is out of service. This site is not serviced by the NWS and there isn't an estimated return to service at present. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Flood Watch until 2 PM EDT this afternoon for VTZ001>011- 016>021. NY...Flood Watch until 2 PM EDT this afternoon for NYZ026>031-034- 035-087.