WX blog: It is NOT going to snow in Tampa Bay this week

By Josh Linker, Spectrum Bay News 9 Meteorologist
Last Updated: Saturday, December 30, 2017, 11:58 AM EST

It is Winter and now much of the country is freezing. 

So, why waste a good opportunity to hype something that won’t happen? 

That seems to be what has been flying around social media the last 2 or 3 days. "Here comes snow in Florida", "Could it snow in Tampa?", "Snow possible next week in Central Florida." 

Those are just a few of the silly headlines I saw floating around on Facebook and Twitter this past week. 

So, then you click on the articles and they offer a wide range of nonsense. From a complete lack of meteorological understanding to simply then announcing that it probably won’t happen anyway. But, now the hysteria has begun. 

Sure, no one reading those articles actually believes that if it snows here in Tampa Bay, it would be a lot, but I have taken calls, emails, messages and posts on social media asking me if it is really going to snow next week.

Ugh.  Now I have to undo someone else’s poor weather forecast. 

Let’s get into the nuts and bolts of it right now….I saw 2 different media outlets here in Tampa Bay showing one run of a computer model forecast from the 28th of December indicating the possibility of snow in Tampa on the 3rd or 4th of January. 

Before I delve into how they completely misinterpreted the data, let me first say this….forecasting anything off of one run of one computer model several days out is irresponsible, let alone forecasting something that hasn’t happened in almost 30 years. But, here is where the other folks really dropped the ball.

Both media outlets showed the model’s prediction of precipitation combined with where the “540 line” was going to be. Without getting too scientific, the “540 line” is one of a few guidelines used in forecasting a rain/snow line in climates that don’t have a significant maritime influence. Last I checked, the peninsula of Florida was surrounded by water. 


540 line with 6 hour past precip at 2 pm Jan 3

To give you an understanding without getting too detailed, the 540 line represents a “thickness” of the air between 2 pressure heights in the atmosphere. The lower the number, the shorter the distance between those 2 layers. 

This represents colder air. The higher the number, the greater the distance, the warmer the layer of air. 540 decameters is often used to make that distinction for precip type. 


540 line with 6 hour past precip at 8 pm Jan 3

But, in order for the precipitation to fall as snow, the atmosphere has to be below freeing for most of that layer. Snow can fall if the surface is above freezing if the precipitation is falling hard enough. 

So, on that same computer model for Jan 3rd, the temperature aloft in the middle of that layer described above is about 10 degrees too warm for frozen precipitation. 


850 mb temp at 2 pm Jan 3

This is represented by these images showing 850 mb temperature. You can notice in the images that that computer model has temperatures about 3 to 6 degrees Celsius. 


850 mb temp at 8 pm Jan 3

Any knowledgeable meteorologist should know that it can’t snow in that environment. Because it means, that if it was snowing several thousand feet in the air, it would melt long before it even comes close to the ground. Looking at these images, it seems like snow would be possible around Savannah, GA or maybe Jacksonville, FL but that would be about as close as it would come to Tampa Bay.

Then, issue number 2 is there is the understanding of what the computer model is showing from a precipitation standpoint. Both media outlets that I saw, showed an image that had the “thickness “ lines (that 540 line I was talking about) overlaid on top of the precip.

But, the problem is with that, is that the precipitation is a total 6 hour precipitation. Which when you dive deeper into the model actually ends BEFORE the colder air begins to come in. 

Next is the mere fact that the wind at that time will be west to northwest.

That means air will be moderating quickly over Gulf of Mexico water temps in the 60s. This isn’t Lake Erie folks! It is the Gulf of Mexico following a warm December. So, even if an Artic airmass was coming across the Gulf in this environment, it would certainly be falling as rain near the coast. Perhaps if the airmass were cold enough, it could support wintry precip on the East Coast of Florida.

Here is the bottom line, there is a reason why it can snow somewhat regularly (once every other year or so)  in North Florida and not in Central and South Florida. That is because in order for it to snow,m there must be moisture AND freezing air at the same time. 

Our coldest air occurs in the mornings of cold air masses, when there is dry air and the sky has cleared.  I know it is fun to think about the prospect of snow in the Tampa Bay Area, and believe me, I think it would be very cool and exciting to forecast, but conditions have to be just perfect for something to happen that hasn’t happened in 3 decades. 

And sadly for those of you that wanted snow, this week isn’t your time.

Happy New Year.