textproduct: Burlington

WHAT HAS CHANGED

As of 317 PM EDT Wednesday...

Confidence has increased in an impactful storm system for early next week.

KEY MESSAGES

As of 317 PM EDT Wednesday...

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

2. Aside from localized cold areas where freezing rain lingers, much warmer and more humid air has arrived with numerous showers falling through tonight, with heaviest rainfall expected from the Adirondacks and points west. A cold front will sweep through the area tomorrow morning, bringing gusty winds and much colder air.

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

4. Active weather is expected from Sunday night through Monday night, with a range of precip types and gusty winds anticipated.

DISCUSSION

As of 836 PM EDT Wednesday...

KEY MESSAGE 1: The latest forecast from the Northeast River Forecast Center indicates the Ausable River and Otter Creek are expected to reach minor flood stage on Thursday with Action Stage possible on the Lamoille, Winooski, and Missisquoi Rivers.

Additional rainfall tonight will be highly variable based on embedded heavier showers with values ranging from 0.25" to localized over 1.0" possible. The heaviest rainfall is expected over portions of northern NY with secondary axis possible across central VT. HEFS based simulation for Ausable River indicates median value of 6.2 feet, but mostly likely 25% to 75% range in the 5.0' to 8.0' range with a peak anticipated on Thursday morning. The HEFS shows a similar type profile for Otter Creek with median just above action stage of 6.0 feet with slightly less potential for reaching flood stage.

Meanwhile, 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 as we head into Thursday with additional snow melt and rainfall expected.

KEY MESSAGE 2: UPDATE...Through late this evening into the overnight hours, very localized freezing rain continues in the far northern St. Lawrence Valley. Cold air remains firmly entrenched north of a quasi-stationary boundary with moderate northeasterly winds channeling down the St Lawrence Valley. Until rain ceases or southerly flow develops, freezing rain will continue to be the primary precipitation type at Massena and nearby locations.

Previous Message...Through early this evening, very localized freezing rain continues in the far northern St. Lawrence Valley where temperatures will stubbornly stay near 31 or 32 degrees for at least a few hours longer. As of 2 PM, Massena ASOS had measured 0.06" of flat ice with steadier rain entering the area; potential to approach 0.25" in this area exists as rainfall rates increase closer to 0.1"/hour.

Overall, showers have become more widespread this afternoon following more isolated activity this morning, especially over northern New York but also in a corridor stretching northeastward across central Vermont. Increasing water vapor transport, with some input from the Gulf, has been streaming northeastward from western New York while southerly low level moisture transport has been aimed at Vermont. While we did have a few rumbles of thunder in the Adirondacks and south central Vermont this morning, additional thunderstorms are unexpected. Model guidance MUCAPE is progged to remain low, under 100 J/kg, through the remainder of the event.

Rainfall rates with the most widespread shower activity in western New York as been producing 0.1 to 0.4" per hour, with the high end roughly matching the 90th percentile HREF guidance. This ensemble guidance and radar trends suggest this heavier rain will into northern New York, especially the western foothills of the Adirondacks and points west, this evening. Additional clusters of heavier rain will then be possible farther east and overnight as more clusters of showers ride northeastward out of central New York. As expected, things are looking rather scattered with regards to footprints of heavier rainfall amounts, but because we are lacking deep warm clouds, rainfall does not look impactful with regards to flash flooding. River flooding, as discussed in Key Message 1, will be somewhat impacted by the footprint of the highest rainfall amounts as the specific basins may see highly variable amounts of rain tonight.

With regards to winds, while there will be a powerful jet moving through the region this evening, saturated and stable air should limit mixing. Overall, the trend from the 00Z guidance has continued with lower impacts behind the cold front, although rapid pressure rises and associated isallobaric wind will result in gusty winds. Current expectations are for localized and brief wind gusts mainly 40-45 MPH, especially in northern New York in typical areas in the lee of the Adirondack High Peaks. The slightly limited wind potential seems tied to relatively weak cold air advection, with a trend towards the surface low looking elongated as it moves near and then just northeast of the area overnight into the morning hours. Also, the orientation of the winds out of the west-southwest limits downslope potential in most of the Vermont terrain.

The potential for any meaningful post-frontal snow is limited, although higher elevations should pick up at least a coating of new snow before clouds scatter out during the day on Thursday. Temperatures will tend to stabilize after falling in the morning hours in the low to mid 30s in most locations across Vermont and upper 20s to low 30s in northern New York. Overnight temperatures will fall back below freezing areawide, putting an end to an extended thaw and likely producing some slippery conditions where standing water remains.

KEY MESSAGE 3: A clipper low will move through our forecast area from west to east late Friday into Friday night. This will bring a quick round of snow to northern NY and Vermont. The northern Adirondacks and northern Green Mountains will see the most snow out of the system and can expect a general 3-6 inches. Elsewhere, accumulations will range from 1-3 inches. Confidence in this general range is fairly high, as a look at probabilistic snowfall suggests reasonable high end amounts for our forecast area only between 3 and 8 inches, and reasonable low end amounts between 0 and 3 inches. Our deterministic forecast falls around the 50th percentile of ensemble solutions.

Given temperatures ranging from the low to mid 30s, some rain may mix in over lower elevations of the Saint Lawrence Valley and the Champlain Valley. Breezy south winds will also ramp up during the day Friday, and become southwest/west overnight. Strongest wind gusts (25 to 35 mph) can be expected over the northern Adirondacks and over the Champlain Valley on Saturday. These winds will have an impact on snow amounts, favoring higher snow totals in upslope locations and resulting in some shadowing downwind of mountains. 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.

KEY MESSAGE 4: The pattern amplifies significantly Sunday, setting the stage for a rapidly deepening low to lift northeastward out of the central US and up through southeastern Ontario and then Quebec. There are multiple potential hazards associated with the system, and it's just too early now to pin them down with details. However, the big picture is taking shape. A warm front will lift through our forecast area Sunday or Sunday night. Initially, this could bring some brief snow and possibly some very brief mixed precipitation to our area. Once the warm front moves through, strong southerly flow will develop with a direct Gulf and Atlantic connection. Precipitable water values will rise to 0.8 to 1.0 inch, which is 2 to 3 standard deviations and about 300% above normal for this time of year. Probabilities from NBM ensemble solutions of dewpoints rising above 45 degrees F are around 50 percent on Monday in our southern counties. This signals another period of effective snowmelt is possible (although this one will be brief). The event will finish off with a period of steady rain as the cold front moves through, followed perhaps by some brief snow on the back end.

Expect some rises on rivers with snowmelt and rainfall early next week, which also should flush out ice from some rivers. We will be watching the hydro aspects of this system particularly closely. In addition to hydro concerns, there will be a periods of windy south winds, particularly within the warm sector of the system.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Through 00Z Friday...Primary aviation threats continue to be LLWS and widespread MVFR/IFR CIGs. A strong LLjet is traversing the region with 60kts at/slightly below 5000ft. As the core passes by 06Z for most terminals, LLWS will diminish. Winds remain breezy as flow turns westerly overnight 06-10Z, then northwesterly by 18Z. Initial CIG improvement will generally be tied more to the end of rain before drier air and northwest flow helps lift CIGs. There are some questions at MPV where NW flow tends to maintain a wave cloud, so MVFR may linger beyond forecast there.

At MSS, fzra/severe clear icing will continue to be an acute hazard through about 04-06Z when winds finally change direction.

Outlook...

Thursday Night: VFR. NO SIG WX. Friday: VFR. Chance SN, Likely RA. Friday Night: Mainly VFR, with local MVFR and IFR possible. Likely SN, Definite RA. Saturday: Mainly VFR, with areas MVFR possible. Chance SN. Saturday Night: Mainly VFR, with local MVFR possible. 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.

CLIMATE

As of 317 PM EDT Wednesday...

More records will be threatened today.

Record High Temperatures:

March 11: KSLK: 60/1977

Record Precipitation:

March 11: KPBG: 0.50/1964

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 through Thursday afternoon for VTZ001>011-016>021. NY...Flood Watch through Thursday afternoon for NYZ026>031-034-035- 087.