Here are my early thoughts about Tuesday’s winter event. It’s looking like warm, dry air aloft will conspire to keep our snow totals down and bring the chances for icy precipitation up.
This has been a challenging winter. Some of that is inherent with winter forecasting, some of it is related to the inherent uncertainty that comes with using weather models as a forecast tool, and some of it is related to the fact that weather forecasting is rooted in uncertainty.
However, I can say with fairly high confidence that this system will not be as significant as the Christmas Night storm last month. That’s about the only thing I can say with much confidence at this point.
Unlike the last system, where I had no doubt beforehand that it would be all snow, there is a bit more doubt about precipitation type with this system.
In order to get snow, the atmosphere must meet two temperature requirements in order for snow to make it all the way to the surface. First, the temperature near the surface must be at or below 32 degrees. Second, the atmosphere must remain below 32 degrees up to between 10,000 and 15,000 feet – the region where snow growth occurs. If the temperature creeps above 32 in either of these regions, we would see is ice or liquid precipitation instead of snow.
Also working against us is the fact that the air aloft when the event starts is going to be VERY dry. Before the precipitation can start reaching the ground, the entire column of air below the region where snow is forming (that area between 10,000 and 15,000 feet I mentioned earlier) has to become saturated with water vapor. As snow develops, it will fall and then evaporate again, saturating the lower levels of the atmosphere. Only after the entire column to the surface is saturated will we see precipitation of any form.
The models over the last 12 hours have been supporting this trend. Precipitation should begin overnight Monday night into early Tuesday morning, possibly starting out as snow. However, once the sun comes up Tuesday, we should see a switch over to a mix of sleet and freezing rain with some snowflakes mixed in, and possibly even a switch to all rain during the warmest part of the afternoon. Significant snow isn’t looking like a very good possibility at this point; however, Tuesday morning especially will be a rather rough travel period. If you have travel plans that have you leaving town Tuesday morning, I suggest you look into alternate possibilities at this point.
The one bit of saving grace in all this is if you look at the predicted precipitation amounts, subtract out the amount of liquid that will be lost to evaporation in the atmosphere, it doesn’t leave much left to leave the ground. Right now, I’d set an upper bound at around 3” of snow and/or 0.25” of ice. What we’ll likely see is a combination of the two, in the form of an inch or two of slush, by the time it’s all over.
The next 12-24 hours will be very telling about what we’re going to expect with this event. For the snow lovers, it’s not looking very good.