Arkansas and F5 Tornadoes. Is Time Running Out?

Is time running out on Arkansas?  Did you know it has been 84 years since Arkansas has experienced an F5 tornado?  According to the National Weather Service office in North Little Rock, on April 10th, 1929, the only documented F5 tornado in state history destroyed communities around Pleasant Valley, Possum Trot, and Sneed in Jackson county.  These locations are just a couple of miles away from Swifton.  Research from the NWS office indicates the tornado was .5 mile wide.  It began just south of Batesville in Independence county, then tracked into northern Jackson county and ended in far southern Lawrence county.  23 died that day and 59 were injured.

Of all the tornadoes across the United States, since 1950, only .1% are rated F5.  

Take a look at the map below courtesy of the Storm Prediction Center.  Arkansas is the ONLY state in the central U.S that has NOT had an F5 tornado since 1950.  There have been 59 of them in the last 63 years.  The first F5 tornado since 1950 was recorded near Waco, TX on May 11, 1953.  and the 59th was on Monday in Moore, OK.

Look how close some of these F5's have been to our state.

Number 25 is Delhi, LA on February 21, 1971
Number 34 is Sprio, OK on March 26,1976
Number 38 is Broken Bow, OK on April 2, 1982
Number 57 is Joplin, MO on May 22, 2011

What about F4 tornadoes since 1950?  While rare, those do occur in Arkansas.  There have been 27 of these since 1950.  The most well known F4 in Arkansas occurred on February 5th, 2008, when one tracked from Yell to Sharp county.  That's 122 miles long!  It killed 13 Arkansans and injured 139.  You probably remember that occurred on Super Tuesday.

Check out this map from the Tornado History Project of all the F4 tracks in Arkansas since 1950.

Here's a list of all the F4 tornadoes in Arkansas since 1950

In summary, I think it's just a matter of time before this happens.  I REALLY HOPE I'M WRONG!!!!!! I REALLY DO!  However, you must ask how long this streak can continue looking at all the F5's that have hit around us.  We need to think about this! What would you do?  Do you have a plan?  Schools MUST take a hard look NOW at where to put the kids.  This is the time to do it.  Don't wait!

Tracking Tuesday Trouble

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9:30 AM Tuesday Video Update....

 

I have been reviewing the data this Tuesday morning and I still think severe weather will be possible this afternoon with southwest Arkansas seeing the worst of it.  That does NOT mean the rest of the state is in the clear.    As I always say, we can look at the data over and over and over.  Mother Nature will do what she wants to do.  As much as we educate ourselves and study this stuff, there's someone else in control!

The morning rain and thunderstorm activity is a good thing and hopefully clouds will stick around.  This will limit the instability needed for big time thunderstorms.  However, if sun breaks out, things could get rough.  The focus for much of the thunderstorm activity later in the morning will be out in Oklahoma, then it should shift into Arkansas this afternoon.  It will form into a clusters of storms and move to the east-southeast and affect western, portions of central, and southwestern Arkansas.  Again, that's where I think the worst of this will be, but other areas will need to keep an eye to the sky as well.  We will all need to watch for the potential for some heavy rain as well.  2-4 inches will be quite possible.

Here are a few maps from the Storm Prediction Center.  Later this morning, I'll post some hi res data for you.  This is my day off from work and I have a ton of stuff going on this morning so check back and I'll have more.

Most of the state is under a slight risk for severe weather, but the moderate risk is for southwest Arkansas into TX and LA.

Most of the state has at least a 5% chance for seeing a tornado within 25 miles of any given point.  The highest threat is across the moderate risk area in the southwest with a 10% chance for a tornado within 25 miles of any given point.

There's a 30% chance for severe winds within 25 miles of any given point with a 45% chance across the southwest.

As far as severe hail (1'' or greater).  There's a 30% chance within 25 miles of any given point for much of AR with a 45% chance across the southwest and west.

Severe Weather Possible In Arkansas and Chasing In The Plains

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We're watching the possibility for some severe weather here in Arkansas late Monday into Tuesday morning and again Tuesday afternoon and evening.  The video below will go over hi res simulated radar and it should give you a good general idea as to how this could unfold.  Remember, models are rarely perfect so things can still change.

Everything You Wanted To Know About The Heat Index, But Were Afraid To Ask

It's not the heat, it's the humidity.  At least that's what we tell ourselves during the long, hot summer months. 

Because the body can't cool itself efficiently with moisture in the air, you feel hotter than the actual temperature.  The equation which is used to come up with the heat index temperature is complex and assumes specific variables.  I thought it would be fun to take a look! It's important to remember that while we use the heat index, it's different for each individual person as the formula assumes everyone is 5'7'' tall,  weighs 147 pounds, etc.  Read all the variables below.

 Heat Index =    -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10-3T2 - 5.481717x10-2R2 + 1.22874x10-3T2R + 8.5282x10-4TR2 - 1.99x10-6T2R2


where T = ambient dry bulb temperature (°F) R = relative humidity (integer percentage).


Here are just a few of the variables involved.  This is good water cooler chat!

* Vapor pressure . Ambient vapor pressure of the atmosphere. (1.6 kPa)
* Dimensions of a human. Determines the skin's surface area. (5' 7" tall, 147 pounds)
* Effective radiation area of skin. A ratio that depends upon skin surface area. (0.80)
* Significant diameter of a human. Based on the body's volume and density. (15.3 cm)
* Clothing cover. Long trousers and short-sleeved shirt is assumed. (84% coverage)
* Core temperature . Internal body temperature. (98.6°F)
* Core vapor pressure . Depends upon body's core temperature and salinity. (5.65 kPa)
* Activity. Determines metabolic output. (180 W m-2 of skin area for the model person walking outdoors at a speed of 3.1 mph)
* Effective wind speed. Vector sum of the body's movement and an average wind speed. Angle between vectors influences convection from skin surface (below). (5 kts)
* Clothing resistance to heat transfer. The magnitude of this value is based on the assumption that the clothing is 20% fiber and 80% air.
* Sweating rate. Assumes that sweat is uniform and not dripping from the body.
* Ventilation rate. The amount of heat lost via exhaling. (2-12%, depending upon humidity) * Skin resistance to heat transfer. A function of activity, skin temperature, among others.
* Skin resistance to moisture transfer. A function of the vapor-pressure difference across the skin (and, therefore, relative humidity). It decreases with increasing activity.
* Surface resistance to moisture transfer. Similar to heat transfer resistance but also depends upon conditions in the boundary layer just above skin's surface.