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Evening Update. Word To Your Mother.

I apologize* for the titles of the last two posts. (*not really. And while we’re here, you should tell your mother about the ice potential Friday and Saturday nights).

Evening updates in red. Everything else, you read earlier this afternoon.

Tonight – Rain – Overnight Low 37

At 6 pm, we officially reached 2.07″ in rainfall since 12:01 a.m., breaking the daily (December 5) record of 1.97″ set in 1954. It’s still raining.

Long Term Flooding Concerns

Rainfall through Tuesday night will approach 5″ total. This may cause flooding, mainly along creeks, streams, and tributaries.

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More rain is expected tonight, overnight, and all day Friday. As you’ll read below, rain takes a break Saturday, resumes Saturday night, and continues all day Sunday and into Monday.

I’m sure you noticed this morning’s rain signaled the arrival of the polar cold front, which slashed temps from 69 at 10 a.m. to 51 by 11 a.m.

Below is the “sounding.” This is merely a way to display data from the weather balloon our NWS launched at 6 p.m. tonight.

Don’t worry about understanding it. The point is it shows temps are:

(a)   Above freezing at the surface (39),

(b)  Reaches the freezing level at around 2,500 feet or so,

(c)  Climbs back above — in fact well above — freezing between 2,500 feet and 12,380 feet, and finally

(d)  Dips well below freezing at 12,381 feet and above.

This proves there is warm air overhead. The frigid air exists only close to the ground. We expect a similar atmospheric profile to remain all weekend. Thus, any precip that falls will remain as rain (or maybe sleet if it gets cold enough up there), and if/when ground temps reach freezing, all that rain will freeze.

Science!

Rainfall tonight is not expected to freeze or cause travel concerns, however, temps have tumbled into the upper and mid 30s, under (by 3 or 4 degrees) what was forecast. However, our NWS, having noted this, still thinks we will not reach freezing tonight.

Weather models suggest freezing rain may surprise areas to our NW (Clarksville & surrounding areas) tonight, so they got a brand new Winter Weather Advisory out of it. But, for us, we think it’ll be close, but just a cold rain.

Also, thunderstorms. It’s very unusual to see thunderstorms in 40 degree weather. Radar as of 8:54 p.m.:

Here’s the updated NWS graphic:

Friday*WINTER WEATHER ADVISORY* – Cold Rain; Freezing Rain Afternoon/Evening – Early Morning: 37 & Steadily Declining 

6am 37 . 9am 37 . Noon 37 . 3pm 35 . 6pm 33 . 9pm 32

Around sundown Friday, temps will approach – or even arrive – at freezing.

Winter Weather, Round 1 – Friday Night

Our Winter Weather Advisory (issued this morning, and “continued” by our NWS at 3:46 p.m.) goes into effect 4 p.m. Friday, and expires at midnight.

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It’s all about when the 32 degree freezing line arrives. If the freezing line arrives faster than expected, the afternoon precip we think will fall as rain will turn into a wintry, icy mess.  Conversely, if the line slows down, we may only see a cold rain all day and most (or all) of the night.

The current thinking from this morning remains unchanged this afternoon: the freezing line will arrive here around dark, before the precip leaves.

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We may see a few hours of freezing rain and sleet, causing:

  • 0.1″ of accumulating ice.
  • 1/2″ of snow and sleet gathering on top of the ice.
  • NWS: “there could be some hazardous travel across the metro Nashville area.” It’s safe to say this includes everyone in Williamson County.

A few other points:

  • The further NW you live, the more likely you’ll see icing Friday night.
  • Snow is not expected.
  • Don’t mistake rain as a sign roads are safe. The opposite is true when it’s 32 degrees at the surface. Freezing rain falls as rain, hits the ground, and freezes.
  • Ice laughs at tough, all terrain, git-R-dun, manly trucks.

It’s been a while since we’ve had a bad ice storm. A primer:

Screen Shot 2013-12-05 at 2.17.55 PM

The 0.1″ of ice in our forecast is not likely to cause anything beyond a few sporadic power outages, but, again, that assumes this forecast is accurate. It may not be.

Bridges, overpasses, those at elevation (Joelton, NW Williamson County, those living atop hills) are likely to see much more ice than the rest of us. Y’all need to pay particular attention.

Saturday – Cold & Sunny; More Freezing Rain Overnight – Morning Low 29, High 35

6am 29 . 9am 30 . Noon 34 . 3pm 35 . 6pm 32 . 9pm 30

We still think we will see a break in the rain from the wee early morning hours until around 6 p.m. Saturday.

Winter Weather, Round 2 – Saturday Night / Overnight / Sunday Morning

Around sundown, the rain will return, and temps are forecast to drop to, then below, freezing.

Another Advisory (Winter Weather, Ice Storm, etc.) may be necessary.

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The updated Scaled Predictive Ice Storm Aftermath (SPIA) Index, which speaks only to the impact of ice on the power grid. This grid represents less impact than it did this morning.

Power outages are expected. Most of us remain in the Yellow (1), but those on the west side of Davidson & Williamson Counties are in the Orange (2):

Screen Shot 2013-12-05 at 3.44.29 PM

Travel is expected to be more difficult, if not impossible, Saturday night vs. Friday night.

We still think those going to church Sunday morning will have a difficult time getting there.

Sunday – Still Raining, But Above Freezing – Morning Low 32, High 43

The rain continues. Southern winds return, bringing well-above-freezing temps, hopefully clearing away any accumulating ice.

The next weather briefing will be at 4:30 a.m. Friday. I’ll blog it, so read the post when you get up. I may include another update tonight if there are any big changes to the forecast.

Most of our weather information is posted to our Twitter account, where you can also ask questions: @NashSevereWx.

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