Dreaming of a white Christmas along the Gulf Coast? Then you are really rooting for all of the following ensemble members of the 100-member VAREPS model guidance:
Member 16
Member 65
Member 67
Member 93
These are the only members that currently show temperatures cool enough for wintry weather while also holding any kind of chance that precip may fall (currently less than 10%).
Oh, and yes, Member 67.
Now that I have cool points with the Youts…. This next chart showing the probability of precip is a bit of a mess to read, but the data is in there.
The interesting thing is when you put it all together, you get this plot:
73 members show a snowfall total of 0.0135″ of snow on December 23rd!
You may be thinking, “BAM! We’z Gettin’ Snow!”
This cluster plot, at first glance, is a bit deceiving, though. With a 100-member ensemble, 73 members means it shows a 73% chance of a some sort of snowy precip falling for parts of the (inland) Gulf Coast near Christmas. That is a very, very high number. And while not technically a White Christmas, still that is wild!
When you see something wild, though, as a meteorologist, you have to question it — not just post it to facebook for clicks. So! let’s “pause for the cause” and think about how these clusters are created. And if that is actually true.
These are built by clustering together similarly-shaped outcomes across all 40 days of the forecast period. So, what this is saying isn’t that there is a 73% chance of a snow near christmas, but rather, that when you clusters all of these 100 members up, 73 end up looking similar and a certain number of those produce 0.0135″ of snow.
That is a really odd snow total, though. I wonder if it is just a single member in that cluster of 73 showing, say, 1″ of snow.
A quick way to check that is to simply run the math: What is 1 divided by 73?
Oh. Well lookie there! It is 0.0135.
So, that means that one of our original four members is THE member that is calling for a single inch of snow. Which member is it? Once I dug into the data, it was our friend, Member 67.
So it isn’t a 73% chance, but rather a 1% chance.
So, yeah, Lloyd, there’s a chance!
