Dynamic Cooling: What is it, and how can it affect our snow totals into the weekend?

Weather Blog

There’s a lot more that happens in the atmosphere that meets the eye, which is why the science of meteorology can be tricky. Certain processes that happen while precipitation falls can create fast changing conditions that are important to keep in mind while forecasting.

Breakdown

The storm system set to move into our region Friday night is an interesting one. It’s an area of low pressure consisting of a stacked low set to move across the Upper Mississippi valley beginning early Friday, and towards the Great Lakes by Saturday. 

While this low moves across the U.S. into Friday, it’s actually weakening. This is a common process that occurs with dynamic low pressure systems that move eastward as they appear to “jump” over the Appalachians, and transfer their energy back to the New England coast while strengthening in the process. When this happens, wrap around moisture from the low can give us changeable weather conditions and developing snow showers on the other side as it moves away. A lot of times these types of systems like to do what they want in the moment, and it will be a battle between warm and cold air; rain and snow.

The intensity of precipitation can impact the type of precipitation that falls, which only adds to the difficulty of winter weather forecasting. The main process at play that can impact how much rain and snow end up falling Friday into Saturday is known as dynamic cooling.

This process occurs when you have a strengthening low pressure system that creates enough vertical motion, or lift to produce heavy precipitation. As air rises, it cools within the atmosphere. With enough lift occurring in a column of air that induces enough cold air, especially in the absence of strong warm air advection, it can cause falling rain to change over to wet snow even with a decent amount of warm air in place aloft.

This looks to be a key player in the forecast over the next 48 hours…

A change from rain to snow can occur even in a relatively warmer air regime. The melting process also can give rise to situations where precip intensity determines what ends up falling to the ground. If precip is generally light, it most likely will fall as rain if temperatures are warm enough to support it. However, it the rain is falling hard enough where stronger cooling occurs, this can change rain to wet snow as noted above. Even if the ground temp is above freezing, the melting of snow can cool the top layers of the soil as it hits the ground. Pair that with heavy snow falling and you can get a quick burst of accumulating snow, despite the initially “warmer” surface. 

Forecast Points

  • The first wave of precipitation will arrive late Friday night, most likely between 6 PM and midnight. 
  • A layer of warm air moving in ahead of the system should make initial round of precip fall as rain for most, but areas of wet snow could begin to mix in overnight with everyone fair game to see this rain/snow mix. 
  • Accumulations by Saturday morning look to be between a half inch up to 2 inches for elevated areas, but slick spots remain possible for everyone. Higher terrain south of Rochester will likely see a changeover to snow first in the form of a clingy, wet snow.
  • Could be enough cold air as the low moves away to kick up decent snow showers especially through Saturday and into Sunday in the form of lake effect. Wind gusts up to ~40 mph Saturday night could create localized areas of blowing snow during the Bills game in Buffalo.

Questions Remaining: As colder air aloft is relatively weak, it depends on how much lift and dynamic cooling we get going to change rain to snow. Will it be enough to cool the atmosphere? All in all, there will be an element of snow being a factor here, especially from Saturday into Sunday as wrap around moisture pulls colder air overhead to spark up some lake effect snow to seal the deal, and it will definitely impact localized snow totals by Sunday evening.

You can get more details about the forecast HERE.

~Meteorologist Christine Gregory

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