A storm system will track to the west of the region, leading to rain and relatively warm temperatures today, according to the NWS Burlington Meteorologist Eric Myskowski.

“We have a pretty low pressure (system) that’s going to track up from the Great Lakes through the upper St. Lawrence Valley and into eastern Canada,” he said. “That puts us on the warm side of the storm.”

The steadiest rain is expected this afternoon and early evening before tapering to scattered showers later. Between a quarter to three-quarters of an inch of rain is predicted by the time precipitation comes to an end tonight across the Tri-Lakes, according to Myskowski.

Temperatures are not forecasted to fall back below freezing until Thursday evening, with high temperatures today expected to reach the mid-40s. As a result of the balmy weather and rain, Myskowski said that between 1 and 1.5 inches of liquid water are predicted to melt out of the snowpack during that time.

A largely ice-covered AuSable River is seen in Wilmington on Tuesday at a seasonably normal flow. River levels are expected to rise today and tonight in response to warm temperatures and rainfall, peaking sometime around the middle of the daytime on Thursday. (Enterprise photo — Chris Gaige)

“That will lead to 1.5 to maybe 2 inches of liquid entering area rivers,” he said.

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Flood risks

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NWS Burlington currently forecasts the AuSable River at its AuSable Forks gauge to reach “action stage,” a term that designates a river is reaching its bankfull capacity but is expected to peak beneath flood stage. This designation leads authorities to monitor it closely in case the river rises higher than predicted, resulting in potential flooding.

River levels are expected to rise throughout today and continue doing so throughout the overnight hours. They are generally expected to peak around the middle of the day on Thursday. However, Myskowski emphasized that there will likely be some variability to this timing, with larger rivers tending to peak later than smaller streams and tributaries, which will in turn rise and fall sooner.

There are two types of flooding that meteologists and hydrologists are keeping an eye on today and tomorrow. The first of which is “open-water,” or conventional flooding that can happen any time of the year when excessive amounts of water cause a river to meet or run over its bank capacity. Myskowski said impacts from open-water flooding are consistent and tend to occur down the entire stretch of the river.

He said that current forecasts point to action stage in the AuSable River from open-water, but flood stage is not expected. He added that no other local rivers across the Tri-Lakes are forecasted to reach flood stage as a result of today’s thaw.

The second type of flooding is from ice jams, which Myskowski said is much more localized and unpredictable than open-water flooding. He said conditions today and Thursday could lead to ice jams, but that NWS Burlington expects them to be isolated as of press time Tuesday evening.

“The rain and the warmer conditions will break up some ice in some area rivers,” he said. “But thankfully, that still looks like an isolated threat and not a widespread threat.”

Ice jam flooding occurs when ice frozen over a river breaks up and is pushed downstream but gets caught up on something. Myskowski said this often occurs along sharp bends or areas where a river is narrow — naturally or by a manmade structure, such as a bridge or overpass.

The chunks of ice form a dam, further obstructing chunks flowing in from further upriver, creating a self-enforcing feedback loop: the more ice that comes through, the thicker the wall gets. This also blocks some of the water flowing through, causing river levels to rise behind the ice dam, potentially creating flood in certain areas upstream of the jam.

Generally, warming water temperatures will eventually cause the ice chunks to melt and break up. However, in certain extreme circumstances in which catastrophic impacts to human life and property are possible, human intervention may be used to break up the ice jam using controlled explosives or specialized machinery.

Myskowski said that while certain stretches of river are historically more prone to ice jams, and meteorologists can predict the conditions that put the potential in place for them, it is impossible to know in advance if and just where exactly they will form.

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Taking action

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Myskowski said it was important for people to report ice jams if they see them occurring. While river gauges can sometimes detect ice jams occurring, he said they are usually too sporadically placed, especially in rural areas like the Tri-Lakes, to serve as a reliable indicator.

By learning of ice jams as soon as possible, emergency management personnel can move resources into place to potentially save people and property. People can call the NWS Burlington office to report an ice jam at 802-862-2475. They can also report an ice jam by email at btv.webmaster@noaa.gov on social media. People should call 911 first to report the situation if they are in an emergency.

Myskowski said that if a flood is occurring, whether from an ice jam or open water, people should seek higher ground if they are in a low-lying area near a river. Having an evacuation plan in advance can save crucial time during an emergency, and cut down on panic in the moment.

He reminded people to never drive through flooded roadways, as it is often difficult to tell just how deep the water is, and cars may get swept away by the force of the moving water.

Cooler temperatures are expected to move in throughout the day on Thursday, with the risk of flooding decreasing throughout Thursday evening and overnight. The cold is expected to remain in place throughout the weekend, with daytime high temperatures in the low 20s and overnight lows in the single digits. No significant snowfall is expected during that time.