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.