The National Weather Service, in cooperation with the Arkansas Department of Emergency Management (ADEM), has proclaimed February 24 through March 2, 2019 as Severe Weather Awareness Week in Arkansas.
Citizens are urged to prepare for the severe weather season. People are encouraged to use the week to review severe weather safety rules, and to understand the hazards associated with severe thunderstorms.
The year began with a weak tornado (rated EF1) about 7.5 miles south-southeast of Yellville (Marion County) during the early morning hours of February 7. There has been an awful lot of rain lately as cold and warm air masses collide over the region (departure of winter and the emergence of spring). Several rounds of severe storms are almost certain to follow. It it gets active again this year, we need to be ready.
Below are the weather topics for the week:
February 25 – Flooding
High water usually comes in two phases: flash flooding and river flooding.
Flash floods usually occur within six hours. The rate of rainfall exceeds the rate of runoff; that is, rain falls faster than it can be carried away. Because water has nowhere to go, it covers roads and fills small streams and creeks.
Flash flooding is usually caused by very slow-moving thunderstorms, or thunderstorms that repeatedly move over the same areas.
Urban settings are especially prone to flash floods due to large amounts of concrete and asphalt surfaces that do not allow water to penetrate into the soil.
Places surrounded by steep, hilly terrain are also susceptible to flash floods due to rapid runoff /water moving downhill at elevated speeds/into streams and creeks.
In the last 30 years, flash flooding was the deadliest thunderstorm hazard, and caused more fatalities than tornadoes and lightning. There are an average of 80 to 90 fatalities annually due to flash floods across the country.
Roughly half of flash flood deaths occur when people try to drive through flooded areas. Moving water two feet deep is sufficient to carry away most vehicles, even pickup trucks and sport utility vehicles.
In 2018, there were two such fatalities in late November. The victims were in a vehicle in the Harrison (Boone County) area, and got swept into a drainage ditch. The incident occurred at night when it is difficult to recognize the dangers of flash flooding.
The most deadly flash flood event in recorded state history also occurred after dark. In 2010, the Little Missouri River, a flashy tributary, rose more than 20 feet during the predawn hours of June 11. This was after more than half a foot of rain. Campers at the Albert Pike Recreation Area (Montgomery County) were awakened to raging water, and 20 people drowned.
River flooding is a longer term event than flash flooding, and can last for several days or even weeks. Water from flash flooding eventually makes its way into rivers, with excess liquid flowing into nearby towns, fields, etc.
Rivers are most likely to overflow when the soil is saturated, and runoff rates are high, and/or water levels are elevated prior to a heavy rain event.
When rivers spill over, it can be devastating. Water can overtake homes, businesses, and thousands of acres of cropland.
In 2017, a heavy rain event in late April filled rivers in early May, and water engulfed more than 950,000 acres of cropland in eastern Arkansas, in 21 of 75 counties.
Tributaries such as the Black, White, and Cache Rivers were mostly responsible for the high water. According to the the University of Arkansas System Division of Agriculture, flooding resulted in over $175 million in losses, especially to rice, soybeans, and corn.
Flood Safety Rules:
• You should know which places in your area are prone to flooding, and avoid these places in times of rising water.
• Do not attempt to cross flowing streams while driving or on foot.
• If flood waters are between you and your destination, the National Weather Service wants you to remember a simple slogan: Turn Around – Dont Drown.
• Outdoor activities are very popular in Arkansas. If you enjoy camping or similar recreation, be especially careful if you spend the night near streams. A thunderstorm miles upstream from your location could produce enough rain to cause flooding, even if it is not raining much where you are.
• Never allow children to play around high water, storm drains, and culverts.
February 26 – Lightning
Lightning is a hazard in all thunderstorms, whether they are severe or not. In the last 30 years, lightning was the third deadliest thunderstorm hazard behind flash floods and tornadoes. There are an average of 45 to 50 fatalities a year due to lightning across the country.
In Arkansas in 2018, there were two lightning fatalities reported. A 27-year-old man was struck by lightning while doing construction work on June 8. Lightning struck a 67-year-old man on July 6 while he was in his yard.
Most lightning deaths and injuries occur in the summer when people are outdoors. Eight out of ten victims of lightning are male.
If a person is struck by lightning, that persons body will not retain any electrical charge. Thus, the injured person can and should be cared for immediately.
Lightning can strike as much as 10 miles away from a thunderstorm cloud. Given this, it is no surprise that most lightning deaths occur as a thunderstorm is approaching or moving away, and not necessarily overhead.
Lightning tends to strike tall objects, but not always. The air is a poor conductor of electricity, so lightning will often go the shortest distance to make a connection from cloud to ground.
Statistics show that Arkansas is a top 10 state as far as lightning activity in the last ten years. The state experiences more than 850,000 cloud-to-ground lightning flashes per year, over 15 lightning flashes per square mile.
Lightning Safety Rules
• Remember, it is lightning that causes thunder. If you can hear thunder, you are in danger from lightning. When thunder roars, go indoors. The safest place is a fully-enclosed building that is grounded. A hard-top car is also a safe location. Keep the windows rolled up and do not touch metal inside the vehicle.
• Do not take shelter in small sheds, pavilions, or tents, or under trees. Stay away from higher elevations spots such as hilltops, and avoid nearby poles and towers.
• Move away from chain-link fences and other metal fences such as those around ballparks and playgrounds.
• Motorcycles, scooters, bicycles, and farm tractors are not safe places.
• If you are in the water, get out immediately. If you are in a boat, head toward safe harbor.
• Organizers of events/activities are advised to designate a weather watcher. Assign an official who will stop the events/activities when lightning becomes imminent. Have
specific evacuation instructions in place so people know where to go.
• Telephone lines and metal pipes can conduct electricity, so do not use electrical appliances or corded phones. Computers and other expensive electronic equipment may be damaged by power surges. You may consider unplugging these items.
• Stay out of the bathtub or shower.
• Get off the golf course.
February 27 – Tornadoes
In 2018, 34 tornadoes were counted in Arkansas. In an average year, 33 tornadoes are expected in the state.
The peak seasons for tornadoes are spring and fall. This is when warm and cold air masses collide most often. In 2018, the busiest month was April with 13 tornadoes counted.
The strongest tornado of 2018, rated EF2 and maximum winds around 120 mph, tracked almost 12 miles from near Rudy to southeast of Chester, both in Crawford County on April 13.
There were no high end (at least EF4) tornadoes documented. The last one of these cut a 41 mile swath through Pulaski, Faulkner, and White Counties on April 27 2014. This tornado killed 16 people.
Monster tornadoes like this are rare. From 2000 through 2018, only two other tornadoes were rated as high as the one on April 27. During this 19-year time frame, 739 tornadoes were spawned locally, and 83 percent of them (614 tornadoes) were weak, rated EF0 or EF1. These weak twisters accounted for three fatalities.
Outdoor Tornado Sirens
Many towns and counties in Arkansas have acquired outdoor warning sirens to alert the public when tornadoes threaten. When these sirens are kept in proper working order, they do their job as expected and help warn the public. While Tornado Warnings often cause the sirens to blow, the National Weather Service does not have any control over the sirens.
In Little Rock, North Little Rock, and Pulaski County, the National Weather Service has an advisory role as to when the sirens should be sounded, but this does not prevent these jurisdictions from blowing their sirens if they deem it necessary. Elsewhere in Arkansas, the decision to blow the sirens is made by designated city or county officials.
Tornado Safety Rules
• One of the newer safety rules is to avoid taking shelter under a highway overpass. Rotating winds surrounding a tornado can hit you with a lot of debris, and blow you out from beneath the bridge.
• Be sure you know the difference between a watch and a warning. The National Weather Service issues a Tornado Watch when tornadoes are possible. A Tornado Warning is issued when a tornado has been indicated on Doppler Weather Radar or has been sighted.
• Counties and cities are mentioned in Tornado Warnings. If you are new to the area, keep a map handy for reference.
• Make sure that you have a reliable way to receive weather information. Battery-powered NOAA Weather Radios are an excellent way to keep up with the weather, even if your power has gone out.
• If you are going to be at a large gathering, such as at a school, stadium or place of worship, make sure that someone is keeping an eye on the weather.
• A tornado shelter, tornado cellar, or a safe room is the safest place to be, but these are not found in most homes. The next safest place is usually a basement, but these are not common in Arkansas. If you do not have any of these, go to an interior room on the lowest floor of a house or building. Put as many walls between you and the outdoors as possible.
• Many businesses, such as large stores, shopping malls, hospitals, nursing homes, and schools have pre-arranged safety plans and designated safe areas. If you are in one of these places, follow the instructions given inside these buildings.
• If you are in a vehicle, your best option is to move to a sturdy building.
• Mobile homes, even if tied down, offer little protection during a tornado, and should be abandoned.
• Keep in mind that the elderly, the very young, and people with physical or mental challenges will often need more time to get to safety. Make special provisions if you are a care-giver for these people.
February 28 – Severe Thunderstorms
At any given moment around the world, approximately 1800 thunderstorms are occurring. Although thunderstorms are relatively small, when considered on a global scale of weather, all thunderstorms are dangerous. Lightning, flash floods, hail,
straight-line winds, and tornadoes all result from thunderstorms.
A thunderstorm is considered severe when it produces winds of at least 58 mph, hail at least 1 inch in diameter (the size of a quarter) and/or a tornado.
Hail forms in storm clouds where the air is subfreezing. Updrafts which feed storm clouds drive raindrops skyward, and liquid turns to ice. Quite often, hailstones will fall through the cloud, collect water, and updrafts will force them aloft. The stones
refreeze and get larger.
In 2017, one of the big days for hail was March 10th. Initially, stones were as large as golf balls and hen eggs between Little Rock and Fort Smith. In southeast sections of the state, hail reached baseball to almost softball size at White Hall and Pine Bluff. There were 31 reports of large hail, a quarter size or larger. This was one of only 28 events with at least 25 instances of large hail since 1980.
Large hail, on average, causes over one billion dollars in damage to property and crops in the United States each year. Some injuries due to large hail occur in this country each year, but deaths from hail are relatively rare. Animals fare far worse than humans.
When updrafts are overcome by rain and hail in storms, air from a loft can descend in a hurry. When these downdrafts hit the ground and spread out in all directions, damaging straight-line wind gusts sometimes result.
In 2018, gusts reached 90 mph at the Shady Lake Recreation Area in Polk County on April 13, between Colt and Forrest City, both in St. Francis County, on June 2, and from Whitener to Clifty, both in Madison County, on November 30. Altogether, there were over two dozen instances of thunderstorm gusts of at least 70 mph.
Occasionally, thunderstorms spawn tornadoes. Most of these are produced in the spring and fall during the afternoon and evening.
There are 33 tornadoes in a typical year. There were 34 tornadoes locally in 2018, and these resulted in no fatalities.
Two other hazards associated with thunderstorms are lightning and flash floods. However, these are not considered severe.
Whenever thunder is heard, there is lightning nearby. Lightning is deadly, especially in the summer when people are outdoors.
Flash floods are another thunderstorm hazard. Vehicles driven into flooded areas result in the greatest number of flash flood deaths.
Across the country, the top three deadliest thunderstorm hazards in the last 30 years years were flash floods, tornadoes, and lightning, in that order.
Severe Weather Safety Rules
• Know the difference between a watch and a warning. The National Weather Service issues watches when conditions are favorable for the development of severe weather. Warnings are reserved for cases where severe weather is imminent or occurring.
• If a Severe Thunderstorm Warning or Tornado Warning is issued for your area, do not hesitate to find a place of safety. If a safe room is not available, the next best location is the lowest floor of a permanent structure in an interior room away from windows. Put as many walls between you and the outdoors as you can.
• Make sure that you have a source to receive the latest information, such as NOAA Weather Radio All Hazards, commercial radio, TV stations or cable TV. Other sources of warning information can include telephone notification services to which people subscribe, pagers and cell phones.
March 1 – Watches and Warnings
Surrounding an event featuring severe thunderstorms, watches and warnings are issued to help you prepare for the elements.
Severe thunderstorms produce damaging straight-line wind gusts of 58 mph or greater, quarter size hail or larger, and/or tornadoes.
When conditions are favorable for severe storms, a watch is issued by the Storm Prediction Center (SPC) in Norman, Oklahoma. SPC is a part of the National Weather Service.
Watches often encompass a large area, sometimes several states, and are valid for roughly six hours. When storms develop and are classified as severe, warnings are issued by your local National Weather Service office.
Warnings are posted for one or more counties and are valid for an hour or less.
With a watch in place, severe storms might happen. When warnings are in place, severe storms are happening.
Watch and Warning Rules
• You should be ready to go to a safe place when a watch is in effect. Monitor conditions for several hours or until the watch expires or is cancelled.
• You should go to your safe place when a warning is in effect. Stay put until storms pass and/or the warning expires or is cancelled.
• The safest place to be is a safe room or a basement. If these are not available, go to an interior room on the lowest floor of a house or building. Put as many walls between you and the outdoors as possible.
March 2 – Social Media Communication
It is no secret that Arkansas gets its share of deadly weather episodes. We remember the destructive tornadoes that tracked from Arkadelphia to Little Rock in March of 1997. Then there was the Super Tuesday twister that cut a 122 mile swath through seven counties in February of 2008. Five years ago, a monster tornado tore through Mayflower and Vilonia in April of 2014.
The devastation in the wake of these episodes reminds us of how important it is to be prepared for volatile conditions. While you cannot stop storms from developing, you can try to figure out what to do before severe weather arrives. It is about being
proactive instead of reactive. This can be accomplished through social media.
Social media platforms such as Facebook and Twitter are powerful tools used by the National Weather Service to spread the word about an upcoming high impact weather event, or to continuously update people of how an event is unfolding. It is a great way to retrieve reports from the public via photos and videos. This can help forecasters determine exactly what is happening, and provide more effective warnings for people upstream of the reports.
Even when it is quiet, social media is used daily to raise awareness of life-threatening weather, and for distribution of forecast and climate information, education, and outreach.
You can follow the National Weather Service in Little Rock online at the following addresses:
via Facebook facebook.com/NWSLittleRock
via Twitter twitter.com/NWSLittleRock