Flash Flood Emergency in effect for the entire Shoals area

Flood Watch: multiple rounds of rain likely through Friday

The National Weather Service issued an Areal Flood Watch  for North Alabama and Southern Tennessee from Tuesday morning to early Friday morning.

Image generated at 3 PM on 2/18/2019

What is the difference between an Areal Flood and a Flash Flood?  Via NWS Birmingham:

“These two types of flooding may be confusing, so we thought we would take a minute to try and clarify the difference between them.

A Flash Flood Warning is issued for flooding that normally occurs within six hours of heavy or intense rainfall.  This results in small creeks and streams quickly rising out of their  banks.   Dangerous flooding in areas near these creeks and streams, as well as low-lying flood prone areas, develops very quickly and is a significant threat to life and/or property.

An Areal Flood Warning is normally issued for flooding that develops more gradually, usually from prolonged and persistent moderate to heavy rainfall.  This results in a gradual ponding or buildup of water in low-lying, flood prone areas, as well as small creeks and streams. The flooding normally occurs more than six hours after the rainfall begins, and may cover a large area.  However, even though this type of flooding develops more slowly than flash flooding, it can still be a threat to life and property.”

Forecasts for heavy rain over a seven-day period can be a little hard to handle, but so far things are on track. In the past week, we have had 4.11” of rain in Pisgah, 3.76” in Fort Payne, 2.82” in Huntsville and 1.60” in Florence. There’s still more rain to come: another 4” to 6” possible through this Saturday.

We’re dry for the rest of Monday; the next batch of showers cranks up early Tuesday morning. Most of Tuesday looks wet and chilly: highs in the 40s to around 50ºF. Tuesday rainfall looks small in comparison to the whole forecast; it’s still healthy, though! Expect around around 1/2” to 1” of rainfall through Tuesday night. That rain continues into Wednesday, and it gets heavier: another 1-3” of rain through Wednesday night.

Flooding potential: NOAA’s Weather Prediction Center uses flood outlook terminology that is similar to the Storm Prediction Center’s severe weather outlooks: slight, marginal, moderate, and high.

Tuesday’s outlook indicates a higher flood threat northwest of the Tennessee Valley region on Tuesday, but that threat increases for North Alabama and Southern Tennessee on Wednesday.

Current ‘flash flood guidance’ for North Alabama shows that rainfall rates greater than 1.7” per hour would cause flash flooding; it would also take about 2.5” to 3.0” in a six-hour period to cause flash flooding. That’s not looking extremely likely on Tuesday and Wednesday.

This rainy period is slowly building some river flooding issues, though. The Tennessee River at Whitesburg and Florence will be in minor flood by Thursday; the Paint Rock River should be in flood as early as Monday evening and continue rising through Thursday. Flooding like this is relatively slow and manageable, but it is a major problem if you’re not ready for it or not aware of it. If you live near, work near or plan recreation along the water this week or next, pay close attention to flood warnings!

Wet through the weekend: Rain tapers off Wednesday evening, and we only see a few showers around for Thursday. It picks up again on Friday with widespread showers, then we may get yet another semi-break on Saturday before a wave of heavy rain – and potentially a few severe storms – blow through along a cold front Saturday night. The severe weather threat is not concrete, so we will keep you posted on how that pans out through the next few days.

Forecast daily rainfall (data using WPC forecast numbers for Huntsville)

Total rainfall through the next seven days likely comes in under last week’s eye popping projections; however, it’s still a very wet week ahead!

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