One of the tools that is in every meteorologists’ tool belt is what are called “atmospheric soundings” or “Skew-T diagrams”. There show how the atmosphere is behaving as you go up. We can look at how the temperature and humidity levels change, how the wind speed and direction changes, how “unstable” the atmosphere is…and many other things.
One of the primary reasons for looking at these in the cold season is to see what type of precipitation is likely to occur.
Here is the forecast sounding early Saturday afternoon: The temperature is the red line. Ground level, where we are, is the bottom of the graph. The top of the graph is 30-40,000 feet, near where commercial jets fly. The numbers at the bottom are the temperatures in Celsius. Temperatures increase from left to right. The “0” or freezing line, is what we want to pay attention to. Notice the temperature is to the right, or warmer, than that freezing line from the ground up to several thousand feet. That means that whatever precipitation is falling is in the form of rain. because any precipitation that forms in the frozen air above that level will melt on the way down.
To get snow, we need much more of the atmosphere to cool below freezing (O degrees Celsius). That’s what will happen Saturday afternoon and evening. Watch what happens to the temperature in this animation (the clock is in the lower right):
The temperature, the red line, keeps moving left until the entire atmosphere above our heads is below freezing by 6-7:00pm. So, there will likely be some snow toward the end of the day Saturday. Looks like a coating to an inch or two.
We are starting a warming trend this morning that will take us into the day Friday. AND, it will probably be in the 60s Monday. So it is with great regret that I must blog about the possibility of snow Saturday into Saturday night.
Here’s the bottom line right up front: This forecast is very tricky right now and confidence is not high. I can see where we get no accumulating snow and I can see where we get a few inches. It’s just too early, with too many variables, to have a higher degree of confidence this morning. Confidence in the forecast will grow this afternoon and tomorrow.
So, here’s a peek “behind the curtain”. Here’s why confidence is low.
But what TYPE of precipitation? Probably a cold rain, but snow and/or mixed precipitation may be nearby to the west. Here’s the NAM model precipitation snapshot in the afternoon: Notice the snow is pretty close by.
As precipitation starts falling and the atmosphere cools, I think the odds of seeing snow go up as the day wears on. So, while it probably will not START as snow, a changeover to snow seems likely at some point. But, the system will be pulling away. How much moisture will be left when it is cold enough to snow?? That’s a big question, and one I am not sure of the answer of.
A look at some of the snow accumulation forecast on the most recent models:
In these tough forecast situations, “ensemble” models can be of great help. The “initial conditions” (temperature, wind, etc.) are tweaked many times and with each tweak the model is run again. If the tweaks result in very different outcomes, the forecast confidence is lower. If the outcomes are similar, you tend to be more confident.
Anyway, here’s the SREF ensemble model’s snow forecast: There are a couple of “stragglers” that give us 3-4″, but most of the members of this model give us less than an inch. Many of the lines are clustered at ZERO. The average of all 21 members is a bit less than an inch.
My suspicion is that these odds are too high. BUT, I am not ready to discount those ideas yet. We will see what this afternoon’s models have to say. Right now I lean toward a minor snow accumulation, maybe a coating to an inch or two (still too much for late March!!), but as I said at the top….confidence is not high.
Who wants to be a meteorologist??? Haha.
Thanks for reading.