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Bedtime Ice Update

Bedtime Update (12:25 a.m.)

Regional Radar:

As you can see, there’s plenty of rain moving through Middle Tennessee. It’s rain because the air the rain is falling through is above freezing.

However, surface temps remain just below freezing. Most ASOS/CWOP stations in Davidson and Williamson Counties reported temps between 29 and 31 (higher temps south, lower temps north).

Ice will be a problem on the roads — especially on bridges/overpasses/at elevation — as long as these temps remain at/under freezing. We’ve had reports of wrecks and ice on bridges, where the temps are well under freezing.

The freezing line will lift NW (see below), and it appears at 11 p.m. the freezing line is just to our SE. That an encouraging sign; the line does not have far to go:

The above freezing line has hardly moved over the past 4 hours.

The issue is: When will the freezing line arrive and stop the icing?

Officially, the NWS forecasts 32 by 6 a.m., and 36 by 9 a.m. They think South Williamson County will go above freezing first. The freezing line will lift north through the morning.

The NWS statement from 10:30 p.m. tonight (“Areas closer to Spring Hill will likely be above freezing well before 6 a.m., but later further north. I think 6 a.m. to 9 a.m. is about the best we can do now, and urge folks to check conditions before heading out.”) still makes sense.

The models say:

1.  32 and 33 degrees (it goes back and forth) from 4 a.m. to 9 a.m. (HRRR 4z).

2.  Above freezing at 5 a.m. (RAP — see below)

3.  The Hi-Res NAM (0z) model pulls us out of the freezing temps around 6 a.m.:

Rain is expected to continue through most, if not all, of the morning.

See y’all in the morning a few hours.

11:00 p.m. Update

A lot more sleet and freezing rain will be here around midnight. Do not be on the road when this comes through (Radar from 10:58 p.m.). Remember: it’ll fall as rain, then freeze.

10:30 p.m. Update

I asked the NWS about church to tomorrow for Davidson & Williamson Counties: when will temps rise above freezing? The response:

“It will vary from northwest to southeast. Areas closer to Spring Hill will likely be above freezing well before 6 a.m., but later further north. I think 6 a.m. to 9 a.m. is about the best we can do now, and urge folks to check conditions before heading out.”

Also, Nashville OEM measured bridge at OHB and 65 at 28 degrees! Travel quickly becoming hazardous!

 

9:18 a.m. Update

We are below freezing at the surface (officially 31 right now):

At 5,000 feet, the winds were continuing to shift (to blow out of the SW) so it can push all that elevated precip into Middle TN:

Data from tonight’s weather balloon suggests the initial round of precip will arrive as sleet or snow, then, as the warm (see above) SW winds at 5,000 feet continue to blow, it’ll ensure the precip falls as rain . . . then freeze when it hits the ground.

Models suggest precip will be light and sporadic before midnight, which is good news if you’ve got to get home:

9 p.m. (HRRR model):

11 p.m. (HRRR model):

But overnight, the precip will really start to increase.

2 p.m. to 8 a.m. (HRRR)

Temps should remain below freezing until sunrise. During this time, travel is a bad idea. Also, wind chills will be in the low 20s, so if you’re crazy enough to drive in the ice, don’t leave the ragtop down so your hair can blow.

Temps are forecast to warm beyond freezing after sunrise, and start to melt the ice. That’ll take a few hours. Ice on bridges, overpasses, and areas at elevation will be the last to melt.

More/Updated information can be found on Twitter @NashSevereWx.

5 pm Update

Tonight – *Winter Weather Advisory* – COLD; Freezing Rain Overnight Low 29

A Winter Weather Advisory is in effect from 9 p.m. tonight until 9 a.m. Sunday:

image_full7

Temperatures

We were supposed to reach the mid-to-upper 30s today. We never even made it past freezing. We maxed out at 32 at 1 p.m.

Temps tonight and into Sunday morning will stay below freezing:

6p 32 . 9p 29 . 12a 30 . 3a 31 . 6a 32 . 9a 36

This is a “shallow” layer of freezing air. The air about 2,500+ ft up will be warmer.

Precipitation

Meanwhile, at the upper levels of the atmosphere, moisture is streaming in from Mexico, Texas, Louisiana, Mississippi, and Arkansas.

This is our rainmaker. The rain will start slowly, then increase in intensity, especially after midnight.

Here’s the hour-by-hour “movie” from the Hi-Res NAM model, from Saturday 8 p.m. – Sunday 5 a.m. If you look closely, you’ll see a thin blue line drawn across Middle Tennessee. Freezing temps are north of the line. Notice it moves further north later in the morning:

The first precip that falls will be light snow and sleet. By midnight, it will be replaced by freezing rain and sleet because temps between 2,500 and 10,000 feet will be above freezing. However, under 2,500 feet, we’ll still be freezing, and ice will form.

Any precip that makes it to ground before 6 a.m. will freeze. It’ll stick to power lines, trees, garden gnomes, bridges, soccer balls left in the yard, overpasses, and, most importantly, roads.

Do not think “I’m fine, it’s just rain.” The rain will fall, hit the ground, and freeze.

Travel Impacts:

Expect:

  • .10″ to .20″ of ice for Davidson County
  • .10″ or less for Williamson County
  • A possible, additional half-inch or less of snow/sleet (for both counties)
  • Travel is not advised between the onset of the first precip tonight and when we get above freezing around 6 a.m.
  • Some minor, brief power outages are possible

Melting

By 6 a.m., we think the freezing line will lift north of both counties. This is when the melting process will begin.

This is subject to change, but we think mid-and-late-morning church services should be fine; however, travel may be hazardous for early morning.

Sunday – Above Freezing & Rain – Morning Low 32, High 41

6a 32 . 9a 36 . Noon 40 . 3p 42 . 6p 39 . 9p 36

Rain will continue through the morning, taper off during the middle of the day, then resume at night. Evening and overnight temps are not expected to be any lower than the upper 30s, so your Monday morning commute should be fine.

This blog is a supplement to more frequent updates and additional details provided on Twitter @NashSevereWx.

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