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Areal Flood Advisory + Winter Storm Watch

Current Temps and Radar

Behold the lack of our usual unfunny jokes and amusing GIFs in this edition. I am not amused by this forecast.

As I write this, the sun is shining.

Approaching quickly from the west is a storm system, which will start spreading clouds, and then rain showers, across the region overnight. Rain is likely by the morning commute Tuesday, and should continue off and on until 6 PM Tuesday. By then, only 0.25″ of rain is forecast to have fallen.

Meanwhile, a warm front will have lifted north and in Middle Tennessee. Tuesday’s temps will climb through the 40°s and 50°s, before topping out in the low-to-mid 60°s. Dewpoints will also rise, but with meager instability values, only a few scattered thunderstorms are possible. None are expected to be severe.

By 6 PM Tuesday, a steady, soaking, heavy rain should be ongoing. Thunderstorms remain possible Tuesday night. Again, not expecting anything severe.

To account for all this rain, NWS-Nashville has issued an Areal Flood Watch beginning Tuesday at 6 PM.

Rainfall amounts of 1″ to 3″, combined with a saturated ground layer from previous winter storm events, will increase the risk for flooding across the area. As you can see from the above graphic, we are expecting up to 2″ of rain.

It’s important that we not let the approaching winter weather overshadow the flooding potential.

Shortly after midnight Tuesday night, and moving into the wee hours of Wednesday morning, temperatures will start to drop from the 60°s. We expect 40°s by 6 AM, and below freezing by noon.

NWS has issued a Winter Storm Watch beginning noon Wednesday through noon Thursday as a dynamic and unusually powerful winter system rolls in.

Rain will transition to freezing rain, then sleet, then snow. The sequence of these events is pretty certain, but the exact transition times are uncertain. For now it is generally expected that sleet then snow will begin sometime Wednesday afternoon.

Here’s a rough ETA of the transition timeline. It’ll change. Don’t memorize it:

Snow and sleet accumulation from 3″ to 6″, in addition to 0.10″ of ice, is expected. Exact accumulations will depend on the timing, which remains fuzzy. These ranges are intentionally broad, and reflect forecast uncertainty. We could go higher or lower than these totals.

However, it is a safe assumption to expect rapidly deteriorating travel conditions shortly after noon, and continuing into and through the evening hours Wednesday. Note that one model, the NAM, wants to hold off on the changeover to sleet/snow until Wednesday night. That would be lovely. This will be very closely watched and scrutinized.

The good news is that the high temperatures from Tuesday and Tuesday night will help prevent a lot of the ice from developing before we change over to sleet. The bad news is that the sleet accumulation is expected to be ongoing, and accumulating, for several hours. Sleet is especially hazardous to travel.

Low temperatures late Thursday night into Friday morning will bottom out in the teens, and perhaps go as low as 10°, before rebounding to 39° Friday afternoon. This should extend hazardous travel conditions through the remainder of the work week.

“Major travel impacts are expected Wednesday afternoon through at least Friday afternoon.” (That’s from the next of the Winter Storm Watch itself).

If you see the weather models floating around with estimates of 6″ to 1 foot of snow, you should know that those are being widely discredited. But, half that amount is possible.

Consult multiple reliable sources for weather information multiple times as the weather community continues to ingest fresh model data to define and refine ETAs and accumulations. 

This website supplements @NashSevereWx on Twitter, which you can find here. Updated information is often posted there and is not reflected on this website.

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