It's cold out AND it's raining! Why not snow?

Finally! It's raining while it's cold out! Why no snow?


JACKSONVILLE, Fla. – Baby, it's cold outside! I mean it is a teeth chattering kind of morning and wouldn't ya know, it's raining out.

If you're like me the thought instantly comes to mind, "oh my, could it snow?" The answer is a resounding NO! Not even close.

Drats! Sorry kids, off to school with ya!

Don't kill the messenger. If I could change it, I would but my weather wand is in the shop. 

Okay, so here's the deal: the atmosphere is obviously 3 dimensional. There is atmosphere to your left and right, in front of you and up above you (X, Y and Z axis if you will). When the air is cold enough and you have moisture falling into it, it snows, right? Actually, not always.

As Paul Harvey would have said, "here's the rest of the story."

The chart you're looking at is called a Rawinsonde sounding. It's basically a vertical look at the atmosphere above your head. The red line is the temperature with height, the green line is the dew point with height and the big yellow diagonal line is the freeze line with height. Everywhere to the right of the yellow line is above freezing and everywhere to the left is below freezing.

You see where the red line and the green line come together at the bottom of the sounding? That's where the air is nearly or completely saturated and that's where the rain is falling from. 

Now remember that big yellow line that represents the freezing line? Well you see that that line falls to the left of where the precipitation is occurring, meaning the rain has formed and is falling in air above freezing at about 5,000 feet (850 millibars). 

That level is significantly lower than the freezing level which is at over 11,000 feet (669 mb - just follow the red line up to where it crosses the yellow line). Where the air is below freezing, you'll notice how the red line (temperature) and the green line (dew point) diverge significantly! That means the atmosphere is dry as a powder house higher up in the atmosphere where the air is below freezing.

Therefore, regardless of the surface being in the upper 30s and lower 40s, the air above the surface in the atmosphere is just way, way too warm to allow any precipitation to fall as snowflakes and where the air is cold enough to make snowflakes, there isn't any moisture. 

Unfortunately, we've been bamboozled again! 

Maybe next time.