Uncategorized

More Snow Talk

Quick Summary: Next 48 Hours

Temps

Rain

Tonight – Cloudy

We don’t expect any rain. Just a lot of clouds.

Monday – Afternoon/Evening Rain – Wake Up 36°, High 59°

After a cloudy morning, scattered light to moderate rain showers will approach west-to-east after lunch.

Rain should begin around lunch. Models haven’t moved much since I wrote this morning, so I will use the same images posted this morning.

Here’s the NAM model at 1 PM:

These off-and-on showers should continue through the afternoon and evening.

Around midnight, the end of the rain will be in sight:

Rain totals should be less than a quarter-inch.

Tuesday – Drizzle Early, then Mostly Cloudy – Wake Up 46°, High 52°

Mid-Week

End of the Week/Weekend

Ok, well, it’s now time to start talking about snow potential. (Note: if you read the below this morning, scroll down for the afternoon data, in blue).

Let’s start with the most important sentence from today’s NWS-Nashville forecast discussion. If you remember anything from this, please remember:

“…[A]ny mention of any type of frozen accumulation as of this point would be significantly premature with all this model timing discrepancy differences.” Translation: trying to determine how much of anything we may get is a ridiculously too-soon exercise. To that point, again from our NWS: “quandaries of uncertainties are running wild in the extended portion of the forecast package when it comes to timing details and actual temps in relationship to dealing with the system expected to approach and move across the midstate late in the work week and into next weekend.”

1.  Thursday Night / Friday Morning

A little precipitation is expected to slide into Middle Tennessee from the W/SW Thursday night. Early Friday morning, there’s a possibility some of this precipitation could transition to a rain/snow mix, but the latest look at the models suggests it will be just a little too warm aloft and at the surface to cause any problems, or even snow at all. But, it’s a close call, and the models have been all over the place, so this is something to watch closely.

This remains a pretty close call, but for now the models are such disagreement it’s impossible to draw any conclusions. One of the models thinks we won’t have much precipitation to work with, and any precip we do get will be just rain. The other thinks we may see some snow north of I-40.

2.  Friday Night / Saturday Morning

Of the two chances for snow, this one is the best. This was the snow potential we discussed yesterday, and it’s still “there” in the models today.

Well, it’s kind of there.

It’s mostly about the track of a surface low (L) pressure center. If you want snow, you want it to pass to the southeast of us. Unfortunately for snow fans, the 0z run of the GFS passes the L straight over us Friday at midnight. This track puts freezing temps far off to our northwest, giving us a cold, miserable rain:

The good news is the European model does take a better track … if you want snow. I can’t post the data verbatim, but I can illustrate, in red, below, what it looks like, so you can compare and contrast it to the above image.

Snow fans will want that surface low pressure to track closer to Atlanta than it does Chattanooga, and if it does, we might have some excitement Saturday.

Afternoon Update: Our NWS office has been in “group think” mode with other NWS offices this afternoon. Everyone’s talking about the location and track of the L.

They think the latest run of the GFS model puts the L (seen below):

too far north. If that happened, it would only be rain Friday night and Saturday. This is similar to the track we described in this morning’s update. That is only the most recent run of that model. If you take the group of model runs and average them together (the “ensemble mean”), you get a track similar to the European model. See the red box:

That would favor snow.

The latest run of the European model puts the low in an ideal position for snow in Middle Tennessee overnight Friday and into Saturday morning. It also wraps a lot of moisture in here which would, if this model verifies (and it’s impossible to say it will), be a good amount of snow. However, because of the model discrepancies, any mention of any type of frozen precipitation accumulation remains significantly premature. I’m sure some idiot will post a map from the European model suggesting a foot of snow, and pass it around Twitter and Facebook. Please ignore it. As usual, it’s not hard to find a weather model to predict snowmageddon 5 days away. I saw several of these maps passed around social media last year, and we all know how much snow we got.

Finally, a terrific graphic presentation of the model discrepancies:

IMG_0239-1.JPG

Uncertainty reflects understanding, not ignorance.

Remember, “…any mention of any type of frozen accumulation as of this point would be significantly premature with all this model timing discrepancy differences.”

This website is only a part of the ongoing weather conversation on Twitter @NashSevereWx, which you can find here.

Categories: Uncategorized