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Winter Weather Advisory, Ice 0.1″ to 0.2″, Snow Up To 1″ to 2″, Watching Those Jerk HRRR Model Runs

First let me acknowledge and thank our Intern, Brendan Schaper, for his help with this update.

Winter Weather Advisory – 8 AM Friday through Midnight Friday Night

We remain under a Winter Weather Advisory, beginning Friday at 8 AM, ending midnight Friday night.

Rain will transition to freezing rain and sleet in the morning, then to snow late morning or early afternoon. Ice accumulation of one to two tenths of an inch will occur along with the possibility for 1-2 inches of snow.

Timing

  • Morning Commute – Rain is here…transitioning to a freezing rain between 6-9 AM.

However . . . 

. . . what I’m about to say is not the forecast, but we need to mention one model, the HRRR. It thinks there may be a break in the precip around 7 AM lasting to 9 AM, maybe longer.

Other models disagree, such as the NAM3 model:

I don’t know which will turn out to be right. This possibility of a break in the precip will have be closely watched tonight and overnight; if the HRRR ends up being the only “right” model, the impacts described below will be much less.

This is why we recommend staying informed of actual observations, rather than make inflexible plans based on model data. We will update everyone about this tonight, overnight, and in the morning on Twitter @NashSevereWx.

We now return you to the regularly scheduled forecast:

  • Lunchtime – Freezing Rain and sleet as we drop below freezing. Road conditions increasingly becoming a concern.

  • PM Commute – Icy roads in full swing. Driving conditions hazardous. Note “dangerous” and “hazardous” should be interpreted interchangeably.

Everything tapers off Friday night. Temps plunge into the 20°s and stay there all weekend.

Ice

Ice happens two ways.

Freezing rain is regular rain that falls, then freezes. That should happen first, in the morning.

Sleet is the stuff that goes pitter patter on windows. To avoid ice accumulation, we want freezing rain to quickly turn to sleet, and sleet to fast turn into snow.

Ice Accumulation from the latest NAM3 Model:

Ice Accumulations from the latest GFS model:

Take these latest model images with a grain of salt. The GFS model has been pretty consistent on 0.15-0.30″ of ice. The Euro model has predicted more than 0.2″ of freezing rain for us. But, as you read above, if the HRRR model is right, ice accumulations will be much less.

No Ice Storm Warning, for us; instead, ours is a Winter Weather Advisory for up to 0.20″ of ice.

Ice is the worst form of precipitation. Obviously, ice makes travel nearly impossible. Ice accumulation weighs down trees and power lines. 13-14 MPH winds forecasted tomorrow can cause them to fall. However, we should be able to mostly tolerate 0.20″, though travel will be a no-go.

The ground is still very warm; however, a warm ground may soon be a distant memory. The forecast for 0.1″ to 0.2″ takes the “warm ground” into account. If the snow transition doesn’t happen quickly, we’ll quickly turn into a skating rink.

Snow

Latest runs of the models think we’ll see just a little snow, averaging around 1.5″. Personally, I think it’ll be less than that. Officially, NWS calls for “up to” 1″ to 2″.

Sled Index remains: “I put my sled back where I found it. At least I know where it is.”

A snow jackpot appears increasingly unlikely, no matter how many ice cubes you flush. But remember, observations are key, we’ll update this information tonight, overnight, and through the morning.

Your Plans

Road conditions: TDOT Smartway

Flights: Fly Nashville.

Remember, on January 22, 2016, there was an event similar to this. The consensus model opinion was that rain would change to snow around noon, and we’d end up with a modest snowfall. Instead it changed to snow around 7 AM and Nashville got 8″.

If possible, make flexible plans. Your decision to do X or Y activity will depend on your risk tolerance, the need to be doing X or Y, and your specific ability to react. Do not think “I’m safe early morning” and make inflexible plans that will leave you trapped or gridlocked if these ETAs are wrong.

We’ll be “wall to wall” on this event on Twitter, watching temps very closely. I hope we will be able to see the freezing temps coming and advise you whether the below ETA is looking good or not. I say “I hope” because there are too few resources to access sufficient, reliable, timely weather observations; tomorrow, we are going to feel the uncertainty this creates. We will use what we have: a network of surface temps from mainly personal weather stations, twice-daily balloon launches, dual-pol radar data, and models built on assumptions that may be just a bit off.

If the HRRR model is right, we’ll only get a fraction of what has been forecast. Prepare yourself emotionally by understanding we have not promised you results; you’ve been promised our best information about predicting the future.

Keep in mind we cover just two counties, Davidson and Williamson. We cannot and should not forecast beyond that area. So, your trip to Atlanta or Cincinnati or Dallas — I haven’t studied the weather conditions along that entire route, and I don’t really know what to expect there. I certainly don’t want to give you bad information.

It Will Be Cold!

When the temps crash, they will crash hard. Gonna be windy! Expect wind chills in the teens late tomorrow.

Bridges and Overpasses, Areas at Elevation

Bridges and overpasses always freeze first. Everything can be fine . . . until you hit an overpass and you start to slide. The “flash freezing” of bridges and overpasses is a real thing. It won’t happen to you without warning, though, because you’ve just been warned.

Joelton, you’re usually the canary in the mine, it happens to you first. Also, that section of 840 near Fairview is both at elevation and full of bridges and overpasses. It’s a treacherous stretch of highway.

Clear Ice & Snow From the Top of Your Car

At least once per snow, we get a note from a police department asking people to remove the ice and snow atop your cars and trucks before driving. At 50 MPH, ice can slide off and penetrate the window of the car behind you. It’s dangerous.

Yeah yeah yeah, if it happens, maybe the person behind you was following too close. If that’s your response to this situation, be the bigger person! Maybe you can agree no one deserves an ice missile through the windshield at 50 MPH, even if they were following too close. Be considerate of the bad drivers and jerks tailgating you, Mr. and Ms. Perfect Driver.

Also if your brake lights are covered, maybe dust them off so we can see you stop.

We may not get much of this, but in case we do, be considerate.

Expect Changes to the Forecast!!

Consult multiple, reliable sources for all your weather information. Check back with them frequently. Avoid confirmation bias — hearing a forecast you like, then ignoring contrary information. (We hope we’ve avoiding our own confirmation bias with updates about the HRRR model).

Keep in mind the weather is not beholden to the forecast and the models. Observations defeat forecasts every time, and we’ll be Tweeting observations like crazy today, tonight, tomorrow, through the entire event. You can find radar, tweets, and cameras here. Or, just follow us on Twitter.

More info tonight and tomorrow, and as usual on Twitter @NashSevereWx.

Will, Andrew, the Interns, and I volunteer our time to this site and at Twitter @NashSevereWx. The stuff we use to bring you all this info — data, computers, software, subscriptions, IT — costs money. If you like what we do and you’d like to support us financially, hit the link below. Yesterday, we had to commit another $40/month “to up our resources” to (cough) hopefully prevent this site from crashing due to high demand.  However, if you can’t help or don’t want to help, it’s cool, feel no guilt trip. We want this to be free to everyone.


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