textproduct: Burlington

WHAT HAS CHANGED

As of 334 PM EDT Tuesday...

Ice amounts/duration of freezing rain increased in northern St. Lawrence Valley for tomorrow. Winds and wind gusts have increased for early Thursday, with potential for a short period of strong winds.

KEY MESSAGES

As of 334 PM EDT Tuesday...

1. The threat of ice jam flooding will continue through Wednesday night as mild temperatures keep snowmelt runoff flowing into rivers. Open water flooding is also possible later Wednesday through Thursday.

2. A temperature battleground will develop tonight as much colder air infiltrates northern valleys, especially the St. Lawrence and Champlain Valley. Greatest likelihood of accumulating freezing rain remains near and north of the Route 11 corridor in northern New York, although patchy freezing rain will be possible farther south tomorrow morning.

3. Westerly winds will usher in much colder weather Thursday morning areawide as a cold front passes through. Difficult travel, especially during the morning commute, could result from a combination of gusty and locally strong west winds, snow showers, and sharply falling temperatures that could freeze standing water.

4. An active weather pattern will bring multiple rounds of precipitation Saturday onward.

DISCUSSION

As of 334 PM EDT Tuesday...

KEY MESSAGE 1: No significant changes in thinking for the overall flood threat for the next 24-48 hours. After one Flash Flood Warning for the Saranac Lake in Morrisonville and a couple of extensions of other warnings for ice jam flooding earlier today, things are currently quiet early this afternoon. However, very mild temperatures (72F here at BTV!) are likely contributing to ample snowmelt, which will continue to flow into area rivers and streams. Therefore, we would expect rivers to start rising again soon if they are not already, and likely continue into at least the first part of the overnight. Temperatures will fall to near or below freezing later tonight in the northern Champlain and St Lawrence Valleys and northern Adirondacks though, which will help slow melt by Wednesday morning. Still, wouldn't be surprised to see further ice movement and possible ice jams/flooding overnight.

While the bulk of the area will then warm back up into the 50s and 60s tomorrow, the St Lawrence Valley and eastern VT will likely remain in the 30s due to east/northeast winds keeping the cold air wedged in. This too will limit snowmelt during the day tomorrow. So flows on northern and eastern rivers may recede somewhat, while central/southern waterways will continue to have snowmelt across their basins. In addition, showers will develop tonight and become fairly widespread Wednesday into Wednesday night, and this too will add to the runoff. So further rises and ice movement/jams are possible. In fact, wouldn't be surprised to see ice flush out completely of some rivers and smaller streams. For some of those waterways, such as Otter Creek, open water flooding will still be possible even once the ice is gone. Should this occur, peak flows should occur sometime Thursday, depending on the waterway.

Whether it's ice jam flooding or open water flooding, we strongly urge everyone to remain cautious along area waterways. River ice can break up very suddenly, and water can rise rapidly if jams do occur. River ice is very unstable and it is absolutely not safe to approach ice jams or walk on the ice. And even if rivers and streams remain within their banks, the water will be running high and fast and it will be very cold, so please stay well away from river banks.

KEY MESSAGE 2: Following record setting warmth at Vermont climate sites (see Climate section of AFD), a dramatic change will occur as a backdoor cold front opens the door for polar air to funnel southward, with most marked cooling down our valleys compared to mid- slopes and high terrain. The shallow cold air advection still looks to bring temperatures below freezing during the overnight hours, with greatest confidence where Winter Weather Advisories are in place. That being said, farther south and east, such as in eastern Clinton County and western portions of the northern Champlain Valley, a few hours around daybreak we may see temperatures also fall below freezing. Precipitation chances are relatively low and duration of sub-freezing temperatures short enough to leave these areas out of the Winter Weather Advisory, but be aware of possible freezing rain in these areas as well.

The precipitation expected late tonight through the day Wednesday will be in the form of scattered rain showers, as thunderstorms in the warm sector of a quasi-stationary front overrun the boundary racing to the northeast. This makes forecasting precipitation amounts and timing of rain rather difficult; much of the day will likely be dry across Vermont and southern/eastern parts of northern New York. Over our western/northern areas, given the development of a pressure trough over the vicinity of Route 11 in St. Lawrence County, rain will be more significant. Enhanced surface convergence should support steadier rain across the St. Lawrence Valley. This area will also stay very cold (low to mid 30s) compared to the foothills of the Adirondacks (50s) with continuous feed of northeasterly winds. This is the area of most concern, and due to combination of heavier precipitation and localized sub- freezing temperatures, have increased the most likely ice amounts near the International Border near Massena above 0.25". There is about a 10% chance of approaching 0.5", which would potentially create power outage issues in a localized area. Note recent warmth does make it difficult to see widespread road/travel impacts with any freezing rain, but it could happen if temperatures spend enough time below freezing late tonight into the morning hours.

KEY MESSAGE 3: No significant changes with an expected powerful cold front that will zoom eastward Thursday morning. That being said, confidence has increased that a Wind Advisory will be needed for portions of the region for a period of time late tomorrow night into Thursday morning; some model guidance shows mean mixed layer winds near 50 MPH for up to several hours with an impressive cold air advection scenario. Precipitation type will switch from rain to snow as snow levels rapidly fall with cooling thermal profiles, with perhaps an hour or two of potential snow showers before enough dry air works in. Have a broad area of a coating to a half inch of snow. Some of the snow accumulations may be a little generous, especially in lower elevations downwind of the mountain slopes, where unblocked flow and associated gusty westerly winds scatter out moisture quickly once temperatures become cold enough for accumulating snow. Seasonably cold conditions will then persist into Friday, with temperatures largely at or below 40 degrees through this period.

KEY MESSAGE 4: The weather pattern in the longer term remains active, with a few systems to note. The first will be a clipper, which will bring some snow to the area Friday night into Saturday. While it's too early to pin down snowfall amounts, an initial look at ensembles within the National Blend of Models suggests a 1-4 inch event is the most likely scenario for much of our forecast area.

After a brief break from precipitation on Sunday, an amplifying upper- air pattern will allow for a deepening low to lift northeastward near or directly through our forecast area early next week. The amplified flow will support strong southerly flow ahead of the system, followed by a sharp frontal passage marking the transition to much colder air behind. This overall setup would support varying precipitation types throughout the event, with periods of mixed precipitation, rain, and snow all possible.

In addition to precipitation, the amplified pattern will mean our roller coaster of temperatures will continue. Near to above normal temperatures are expected for the weekend, followed by a sharp fall of temperatures sometime in the Monday-Tuesday timeframe, depending on timing of the front. Finally, expect windy conditions within the warm sector, likely Sunday night into Monday. Probabilities of wind gusts exceeding 30 mph according to the NBM peak early Monday morning in the 50 to 80 percent range over the Champlain Valley and northern Adirondacks.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...Initially quiet weather is expected, with VFR conditions prevailing into this evening. Overnight, ceilings will lower to MVFR levels as rain showers move into the area. NY TAF sites will see some freezing rain Wednesday morning, especially at KMSS and KPBG, where freezing rain will be the predominant precip type by 12Z before changing back to rain before 18Z. Precipitation at KSLK is forecast to be primarily rain, but some freezing rain is possible between 05Z and 11Z. KBTV has a lower, but non-zero, chance of some brief freezing rain around 11Z. Have left this out of the KBTV TAF at this point given low certainty. Precipitation at KMPV, KEFK, and KRUT will be in the form of rain.

Initial southwest/west winds will switch to north this evening, locally northeast in KMSS and KSLK. KMSS will gust 15 to 25 knots after 07Z. Winds elsewhere will switch to south after 15Z, becoming gusty 15 to 25 knots from the south/southeast especially at KRUT and KMPV after 15Z.

Outlook...

Wednesday Night: Mainly MVFR, with local IFR possible. Definite RA, Likely SHRA, Slight chance TSRA. Thursday: VFR. Chance SHRA, Slight chance SHSN. Thursday Night: VFR. NO SIG WX. Friday: VFR. Chance SHSN, Chance SHRA. Friday Night: MVFR/IFR conditions possible. Chance SHSN. Saturday: Mainly MVFR, with areas VFR possible. Slight chance SHSN. Saturday Night: Mainly VFR, with local MVFR possible. Chance SHSN. Sunday: Mainly VFR, with local MVFR and IFR possible. Likely SHRA, Likely SHSN.

CLIMATE

As of 334 PM EDT Tuesday...

Temperatures soared above daily records today. Unofficial record highs were set as of 3 PM, including 61 degrees at MSS (Massena), 63 degrees at PBG (Plattsburgh), 66 degrees at MPV (Montpelier), and 71 degrees at 1V4 (St. Johnsbury).

The high of 72 degrees at BTV (Burlington) was not only a daily record but also ties the warmest temperature this early in the winter/spring (January 1st through March 10th).

EQUIPMENT

NOAA Weather Radio station WXM-44, transmitting from Mt. Ascutney, Vermont, on frequency 162.475 MHz is non-operational at this time. NWS technicians plan to restore its functionality tomorrow, March 10th. The following NOAA Weather Radio transmitters may be able to provide service during the outage: WWG 50 from Burke Mtn, VT at 162.425 MHz and WNG 546 from Hanover, NH at 162.525 MHz.

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. Winter Weather Advisory from 11 PM this evening to 2 PM EDT Wednesday for VTZ001. NY...Flood Watch through Thursday afternoon for NYZ026>031-034-035- 087. Winter Weather Advisory from 11 PM this evening to 2 PM EDT Wednesday for NYZ026>028-030-031-087.