Messy Weekend Coming Up

There's no technical way to say this. Simply, it will get messy this weekend.

After a harsh, deep freeze event preceded by more insulting, accumulating snows on top of an already deep snowpack, we look to the weekend and sigh, "What next?"

I hate to say it. But, a period of freezing rain appears likely. I'm not looking at the models yet to determine precipitation type. Just from watching similar setups, I am convinced that as warmer air aloft attempts to scour out the impressive cold at the surface, we will witness how stubborn cold air can be as the precipitation breaks out.

A best case scenario for surface temperatures at or below freezing, as absurd as it may sound, is for heavy rain to fall on the frozen surface. This will produce a two-fold result.

First, the heavy rain does not allow for ice to accumulate efficiently on limbs and power lines or even the pavement. True, some ice accretion will occur but would be preferred as to a lighter rain event over a long period of time that would allow for more efficient ice accretion on tree limbs and power lines, causing some potential issues.

Next, the heavier rain will bring down the warmer air from aloft more quickly to the surface thereby warming the surface. This works just the opposite when you can have sleet and snowflakes when the temperature at the surface is in the 40's, because the temperature above is so much colder thereby transferring the cold to the surface and dropping the temperatures.

The problem is...more than likely, it will not work out that way.

Therefore, it would be better for the precipitation to remain sleet for an extended period of time before transitioning to rain, perhaps freezing initially, then switching to good ole-fashioned liquid.

Well Mike, why not just to keep it all snow before changeover? The warmer air aloft will not allow the precipitation to remain as snow unless the cold air above is so dense that it resides well above 5,000 feet.

This does not mean we will not have a prolonged period of snow. Since the Arctic air in place has a lot of dry air, any moisture will cool the column of air all the way to the surface as it evaporates, slowly saturating the column. So, snow could be around a while for some of us.

Lastly, let me say I do have concerns about sheltered areas like valleys, especially toward Eastern Kentucky. Cold air has a propensity to become trapped in these areas making it difficult for warm air to scour out the cold air. Ice accumulations could become a major problem in these areas as the air warms all the way down to 2,000 feet but the cold air at the surface just cannot escape unless you have heavy rain, which does not appear likely as the temperatures are below freezing. The heavier rain should arrive mainly after we reach above 32 degrees. Ice accretion could become substantial in these areas, at least 0.25 to 0.50" and maybe more depending on how long it takes for the cold air to succumb to the warmer air.

MS