Severe Weather Concerns Wednesday

Current Radar 

Monday – Rain Increasing – High 61°

South winds blowing 13-16 MPH (gusting close to 30 MPH) are efficiently transporting a lot of moisture into Middle Tennessee, setting the stage for a good rain even this afternoon and tonight.

Here’s the HRRR model:

We may even see a few innocent thunderstorms tonight, when rain should be heavy at times. Over 0.5″ of rain is expected through sunrise tomorrow.

Tuesday – Only a Few Showers – Early 56° High 67°

The rain we’ll get late Monday night into Tuesday morning represents a shortwave that’ll have exited the area during the day on Tuesday. So, only a few showers are expected. Better chance of rain returns late Tuesday night.

If you need to do last minute shopping, or if you’re planning to travel, Tuesday is better than Wednesday.

Wednesday – Natchez Trace Severe Weather Concerns – Early 60° High 73°

Yesterday, this was the Storm Prediction Center’s severe weather outlook for Wednesday:

Here’s today’s outlook for Wednesday:

We sit right on the line of #2 (Slight); in fact, if you really drill down to it, Williamson County is inside the yellow area. Don’t read anything into that.

This has me a little concerned.

In this yellow area, the Storm Prediction Center wrote this morning of “organized severe storm development…including supercells…appears possible. Large hail…locally damaging wind gusts and a couple of tornadoes all appear possible…with activity spreading east-northeastward…perhaps into and through portions of the Tennessee Valley by late Wednesday afternoon.”

This has our attention.

Now, for all that to happen, there would need to be a dry slot at mid levels of the atmosphere and at least some insolation – good old fashioned sunshine – to kick all this off.  That’s what the models appear to be showing. The SPC doesn’t say, but I’ll bet they rounded off the yellow risk area right at our doorstep thinking all those ingredients may not come together where we are.

Other uncertainties exist, one we talked about last month — the location of the surface low pressure center. It’s forecast to pass pretty far north:

If it was closer, there would be real alarm.

The models, however, like our severe weather chances.

For one, there should be plenty of CAPE (convective available potential energy), the fuel storms need. This had been missing in our storm set ups in November:

Forecast soundings also continue, even today, to paint a severe picture. These are pretty technical and difficult to explain, but the parameters you need to make severe weather appear to be there. I’ve drawn yellow boxes around them.

GFS forecast sounding for Wednesday night.

NAM model, same time:

With apologies to also-included Louisiana and Arkansas, note how the Natchez Trace defines the area of severe weather concern Wednesday:

Any storms, or, God-forbid, supercells that develop will move NE, along or near the path of the Trace. If you’re travelling that way on Wednesday, consider either going super early, or leaving Tuesday or Thursday.

Severe weather, including tornadoes, can and do occur near Christmas. We had a F-4 tornado hit Cool Springs Christmas Eve morning in 1988.

How concerned am I? A little concerned. This is not a stormageddon; I think the term “outbreak” for this event would be exaggeration.

If the models continue to deliver the same information tomorrow, that concern will be raised a little more.

Note: there will be a NWS conference call with media and emergency management to discuss this risk at 11 AM today. We’ll tweet it out on Twitter @NashSevereWx, where you can always find updated info. This website is only a supplement to our Twitter feed. Consult multiple reliable sources for your weather information.

What About Christmas Eve & Christmas?

Warm. We should hit 70° both days.

We still think we’ll see a decline in rain chances on Christmas Eve night and into Christmas morning, only for rain and thunderstorm chances (severe unlikely) to return after noon Christmas Day.

This website supplements @NashSevereWx on Twitter, which you can find here.