Mid-South placed in a Slight Risk for severe weather today

2:00pm Update: A Severe Thunderstorm Watch has been issued for the entire metro until 9pm. The mentioned MCS (area of storms) has moved into northeast AR and will move into northern Tipton Co by 3pm and into the city of Memphis by 4pm, continuing through northwest MS, including DeSoto Co, by 5pm. Damaging wind of 60 mph+ and hail are the main severe weather threats.  Heavy rain will also affect the afternoon commute with areas of standing water likely. Plan additional time during your drive home this afternoon and exercise caution on area roadways.

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At 11:30am, the Storm Prediction Center expanded the Slight Risk zone to encompass all of west TN and north MS, adding to the previous area that included all of AR. This places the entire metro area in the middle of a chance of severe weather.

The Mid-South was placed in a Slight Risk of severe weather for today by SPC

The reason for the expansion has to do with the formation of an MCS (mesoscale convective system) in southern MO that is propagating east-southeast into an unstable atmosphere over the Mid-South.  If it holds together, it could bring a squall line with damaging wind (or a #memstorm as it's come to be known on Twitter).

MCS moving east-southeast out of southern MO at 12:15pm CDT. Click for larger image 

Timing for this line initially appears to be late afternoon, possibly during the afternoon rush hour. As we know, MCS's typically bring straight-line wind of 50-60+ mph, torrential rain that can produce localized flash flooding, and even some hail to a large area, which could include the entire metro area.  Any wind damage could cause power outages in this type of storm as well. The chance of severe (58 mph or greater) wind with this slight risk of 30%, which is fairly significant.

Wind and hail probabilities for today (chance of 58+ mph wind and 1"+ hail within 25 miles of any location).

Though we are not certain that this storm system will make it all the way to the metro, the likelihood is increasing. In fact, with a cold front approaching the region, computer models are beginning to hint at another one of these storm systems forming over the AR Ozarks late this afternoon and moving southeast behind this system. Chances are this one would miss the metro to our south, but we'll need to be prepared for the possibility of more storms during the early overnight hours.

MemphisWeather.net will be monitoring the developing weather scenario throughout the day and will be nowcasting any strong to severe storms as they happen on our social media channels listed below. Now is also a great time to pick up the MemphisWeather.net mobile app for Android or iPhone and activate StormWatch+, which will alert you via push notification if your location of interest is placed under a watch or warning.  Get it at the link below!

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For weather information for Memphis and the Mid-South, where and when you need it, visit MemphisWeather.net on the web, m.memphisweather.net on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Slight risk for severe weather again on Thursday (updated)

Wednesday, 8:15pm update:

It appears computer models are holding off on any early morning precipitation for the Mid-South. Given the information provided in the blog post immediately below, our confidence is increasing we will see some severe thunderstorms in and around the area beginning anytime after late morning.  The most likely time will be during the afternoon and early evening hours.  Though a tornado threat can't be completely ruled out, the primary threats with tomorrow's storms will be large hail and high wind.  Storms should form into clusters or lines, which could heighten the straight-line wind threat.

MWN will provide nowcasting via social media throughout the event tomorrow.  Now is a good time to arm yourself for the potential of severe weather with the MemphisWeather.net app with StormWatch+.  StormWatch+ is our personalized severe weather notification tool that will warn the locations you input when severe weather threatens.  Check it out now on iTunes/App Store or Google Play for Android.

Previous blog entry:

The Mid-South is under a Slight Risk of severe weather for Thursday. How the scenario plays out is the subject of this blog.

Another day has brought little clarification in exactly how tomorrow's weather scenario will unfold as the biggest factor in possible severe weather appears to be how overnight convection (storms) plays out to our west.  What appears certain is that at least part of Arkansas will experience one or more mesoscale convective systems (MCS's) overnight that will move generally east and weaken as they approach the metro around dawn.  These types of systems can have several effects on the weather downstream, both positive and negative, depending on their ultimate evolution.  Some of this was hashed out in last evening's blog on the topic.

Multiple mesoscale convective systems (MCSs) traverse the Plains and Midwest (June 27, 2011)

Upstream MCS activity can bring extensive cloud cover or rain to an area as they fall apart during the early morning hours, thus providing a stabilizing influence and limiting renewed thunderstorms later in the day. The atmospheric disturbances (mesoscale convective vortices - MCV's) that linger following the demise of these systems also can bring a source of lift to a region that can reinvigorate storms when combined with sufficient heating and instability.  Generally areas under the "fallout" of one of these MCS's as it weakens ends up with a greatly reduced chance of storms later in the day, while areas downstream of the "fallout zone" get the benefit of daytime heating (providing instability) and lift from the disturbance left behind by the decaying storm system upstream.

Satellite imagery at time of above radar image. Extensive cloud cover accompanies MCSs. After the MCS falls apart, the lingering cloud cover can hinder further convection later in the day.

We've seen both cases play out in the area, as well as the unmentioned case where the overnight convective system never weakens and comes through in a strong to severe state in the early morning hours.  Right now, I don't really see that happening.

So, will the overnight storms die off over AR, leaving us with an unaffected "juicy" airmass capable of generating afternoon/evening severe thunderstorms?  Or do we get the "fallout zone" - with morning clouds/showers and afternoon storms that fire off to our east?  Time will tell...  Either way, I think this will be our best chance for meaningful rain in some time.

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For weather information for Memphis and the Mid-South, where and when you need it, visit MemphisWeather.net on the web, m.memphisweather.net on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.