Flash Flood and Severe Weather Potential from Harvey in West Tennessee

NOTE: This blog post is pertaining to a chance for flash flooding and severe weather that is forecast 

to occur between tonight, Wednesday, August 30th, 2017 and Friday, September 1st, 2017.

Over the next 48 hours, an historically unique amount of rainfall is expected to fall in West Tennessee. The showers will be moving in waves as rain bands associated with now Tropical Storm Harvey, soon to be come Tropical Depression Harvey, approaches the area. The forecast continues to evolve based on the new incoming model data and changes will likely be made depending on the path and speed Harvey takes through West Tennessee.




Harvey is now forecast to weaken to a Tropical Depression (maximum sustained winds less than 39 mph) by 7 a.m. Thursday. From there, the storm will move northeast toward West Tennessee, with the storm right overhead late Thursday night and early Friday morning. By 7 a.m. Saturday, the start of Labor Day weekend, the storm will be near Cincinatti, Ohio, far away from our area.



GOES-16 Satellite imagery shows where Harvey is now. Meteorologist Moe Shamell pointed out to me this morning that satellite is starting to show a lot of dry air on the eastern flank of the storm. Not only will this have an impact on rainfall amounts for the eastern portions of our viewing area near the Tennessee River, but it may enhance the potential for tornadoes during the day on Thursday. In the image below, moisture-filled air is shown in blue and green while dry air is shown in orange and yellow.

Regarding the risk for severe weather, out of the threat for tornadoes, damaging winds, or large hail, the main concern will be for a few tornadoes to develop during the day on Thursday. A Tornado Watch may be issued from the National Weather Service sometime Thursday morning. This is not uncommon with a tropical system. On the northeast flank of a cyclone, there is a very high amount of turning of the winds with height that allow for strong rotating updrafts to form brief, but usually weak, tornadoes. Keep an eye out for that Watch to be posted tomorrow.



Of course, beyond a tornado developing, the greatest and most serious concern for our weather over the next 48 hours is the threat of flash flooding. I do not want anyone to think this storm is going to be a repeat of what happened in early May of 2010 nor do I want anyone to think that exactly what happened in Texas or Louisiana is going to happen here in Tennessee, though I know that as hard as I try to dispel that idea, there will still be some who bring it up. Every storm is different, and Harvey will bring its own unique placement and intensity of rainfall.



That said, the totals could break records for daily total rainfall and 3-day total rainfall in the area. Right now, the latest computer model data is putting forecast rainfall totals all over the place in the 21 county area of West Tennessee. Some totals are less than 2" and others are between 6 and 10" for rain falling from now through Saturday morning.



A Flash Flood Watch has been issued for most of West Tennessee (Benton, Carroll, Chester, Crockett, Decatur, Dyer, Fayette, Gibson, Hardeman, Haywood, Henderson, Henry, Lauderdale, Madison, Obion, Shelby, Tipton, and Weakley counties) from 7 p.m. Wednesday through 7 p.m. Friday. 2″-6″ of rain are forecast for most of West Tennessee but with isolated totals of 6″-10″ possible in localized areas. The heaviest rain is forecast to fall from Thursday through early Friday morning.



I think the Madison County Fire Rescue squad said it best on their Facebook page this morning. "...we prepare for the worst and praying for the best."




Prepare now with your family, and have a plan in case flooding or severe weather impacts your day tomorrow. The likelihood of that happening is increasing. There are a TON of resources online freely available to tell you how to start preparations. One of those is the Red Cross.

Power outages, flooded roads, school closures are all on the table tomorrow and Friday. Plan ahead! Lastly here's a simulation for what the storm may look like on radar over the next 48 hours. It begins Wednesday morning and ends Friday evening.




Summary

• Flash flooding is the main concern. A Flash Flood Watch goes into effect Wednesday night and lasts until Friday night. Most of the area will see 2-6" fall with isolated totals of 6-10" possible. Most of the rain will fall on Thursday.
• A few tornadoes are possible on Thursday in the Mid-South, mainly near the Tennessee River. A Tornado Watch may be issued tomorrow.
• Rain will begin to leave the area on Friday before the Labor Day weekend.

We'll be updating our rainfall total forecast tonight, adjusting the time-frame for this event, as well as revising the risk for severe weather. Tune in to WBBJ 7 Eyewitness News tonight for the latest forecast!

Risk for Severe Weather Tonight (5/11/17)

NOTE: This blog post is pertaining to a chance for severe weather that is forecast 

for tonight, Thursday, May 11th, 2017.

So far so good! Temperatures are in the upper 70s to lower 80s under partly to mostly clear  skies for now. We’ve had a few isolated showers this morning but nothing terribly heavy yet. The main points of discussion in this post are the risk for severe weather later today and tonight, and the chance for scattered showers and thunderstorms on Friday.

Lets talk data…

At the moment, some of the more reliable models still have considerable differences within them, so even though we’re within 24 hours of seeing thunderstorms in West Tennessee, there’s still considerable difficulty pinning down where exactly those storms will be and when.

Here’s a look at the NAM 3km at 10pm…

…and here’s a look at the HRRR at 10pm.

Both models usually perform well, but they disagree on the placement for incoming showers and thunderstorms.  To be a little more specific, some models are allowing the rain to start between 8 and 10 PM but others suggest it could start earlier between 6 and 8 PM.

All of West Tennessee is either under a marginal risk (1 out of 5) or a slight risk (2 out of 5) for severe weather. This is a relatively low risk, but one or two thunderstorms that develop in West Tennessee tonight may become severe. If any thunderstorms do become severe, then we’ll need to be on the lookout for damaging winds and large hail. The chance for a tornado is low tonight.

After this system moves in this evening, the rest of the night and day tomorrow will have scattered showers and thunderstorms into Friday afternoon.

There’s no way to know for sure if it will rain during the West Tennessee Strawberry Festival Grand Floats Parade until tomorrow morning so we’ll prepare for the worst but hope for the best.

Best case scenario: we catch a break in the showers and get through the parade rain-free. Worst case scenario: we have a thunderstorm at 10:00am. Severe weather is even more unlikely tomorrow, so I’m not expecting that. 

So to summarize: 

• We have a chance for showers and thunderstorms tonight and tomorrow
• Some thunderstorms could become strong or severe tonight
• Damaging winds and large hail are possible if any thunderstorms become severe but the tornado threat is low
• Rain will continue to come and go Friday morning and afternoon, tapering off by sunset
  

Scattered Thunderstorms This Afternoon and Evening

NOTE: This blog post is pertaining to a chance for severe weather that is forecast 

for today, Friday, April 28th, 2017.

Showers have already begun in northwest Tennessee but as of this morning, West Tennessee is in an area that could see severe thunderstorms develop later on today. If you saw any of my weathercasts or posts yesterday, you know that there was still some uncertainty with this forecast. Today, the area that could see these thunderstorms is still uncertain but there are a few things we've learned from the weather data this morning.

West Tennessee is split between having no risk for severe weather at all and an enhanced risk (3 out of 5) which is largely placed north of I-40. If thunderstorms develop there today, that is where they could become severe.

To help convey the uncertainty with today's forecast, let me show you some of the latest weather data.

This computer model shows heavy showers and thunderstorms in northwest Tennessee at 4pm.

For the exact same time frame, another model shows no rain in West Tennessee at all and all of the activity north of the Tennessee-Kentucky state line.

Most of the models side with the data that shows very little rain in West Tennessee but I'm not convinced that we'll get completely out of this one unscathed. What you need to do is stay weather aware! Those that live near the Tennessee-Kentucky border need to be especially vigilant today. I'll post radar updates throughout the afternoon to keep you posted on which route our weather decided to take.

So to summarize:

• Severe weather potential exists for northwest Tennessee this afternoon and evening
• Large hail and flash flooding will be possible if thunderstorms become severe but a large portion of West Tennessee may not see any rain at all today
• Thunderstorms will exit West Tennessee completely as they continue to move north after midnight

Tune in to WBBJ 7 Eyewitness News tonight for the latest forecast!