North Texas is known for its ever-changing weather conditions. Violent thunderstorms may strike in an instant. All thunderstorms should be considered dangerous and everyone in our community should understand, respect and know how to protect themselves from the effects of severe weather. Lightning, tornadoes, downbursts, hail, and flooding rainfall are all dangerous by-products of thunderstorms that pose a significant threat to Frisco.
It is important to understand the difference between a severe weather “watch” versus a “warning.” Either can be issued by the National Weather Service (NWS) for a specific amount of time and designated area when atmospheric conditions are ripe for the development of a possible thunderstorm and/or tornado.
A “watch” means "watch the sky" as conditions are right for possible development of severe weather. Keep an eye on developing weather and stay tuned to a local radio or television station in case conditions worsen.
A “warning” indicates a severe thunderstorm and/or tornado has been spotted or is indicated on the NWS radar. All those within the designated warning area should take cover immediately and remain there until the danger passes. The City of Frisco will activate the Outdoor Warning Sirens when severe weather, such as a tornado, threatens the community. If severe weather is approaching Frisco and the warning sirens are heard, seek shelter immediately and monitor TV and radio for further instructions.
A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud. It is spawned by a thunderstorm and typically produced when cool air overrides a layer of warm air, forcing the warm air to rise rapidly leading to rotational winds, and thus a tornado. The damage from a tornado is a result of high wind velocity and wind-blown debris. Tornadoes strike with incredible velocity with wind speeds approaching up to 300 miles per hour. These winds are capable of uprooting trees and structures, and turning harmless objects into deadly missiles.
When a tornado is approaching, there are only minutes to make life-and-death decisions. Advances in weather radar technology have improved forecasters' ability to identify storms likely to spawn tornados. The City of Frisco has 24 strategically placed Outdoor Warning Sirens throughout the city to alert citizens when severe weather threatens to strike Frisco.
If a tornado warning is issued, go to a predetermined area where family members can safely gather and take shelter. Such an area could be a center hallway, bathroom, basement or closet on the lowest floor of the home. If in a multi-story building or a shopping mall, there may not be time to get to the lowest floor. In that case, go to the center of the building and find an area in a hallway far away from windows. If outside, hurry to the lowest floor of a sturdy building or lie flat in a ditch or low-lying area. If inside a mobile home, get out immediately and head to one of the above-named areas. Turn on a TV or radio and listen for additional instructions. Frisco’s Cable Channels 12 (Grande), Channel 16 (Time-Warner), Channel 37 (Verizon FIOS), or Channel 99 (AT&T U-verse) as well as local TV and radio stations, will broadcast information updates as they become available. WBAP Radio, 820 AM, is the designated Emergency Alert System (EAS) station for this area.
Tornado Safety Actions:
- Monitor National Oceanic and Atmospheric Administration (NOAA) radio
or local media (TV, radio, internet) for information.
- Move to a small interior room away from windows when a tornado warning
is issued or a tornado is imminent.
- Have disaster supplies on hand (flashlight, food/water, battery-operated
radio, etc.) in an easily portable container, such as a backpack.
- Designate a safe shelter area if you live in a mobile or manufactured home.
Make the designation with help from your neighbors and the owner/manager
of the mobile home park or community.
- Lie flat in the nearest depression, ditch or culvert if outdoors and
unable to get to shelter. Cover your head with your arms to shield from
- Get out of vehicles immediately and seek shelter in a building, if time
permits, or move to a ditch or culvert away from the vehicle.
Never try to outrun a tornado.
- Take shelter in an interior hallway on a lower floor away from windows or
glass when you're in a large building, such as a mall or auditorium.
The National Weather Service issues Severe Thunderstorm Warnings for a particular county, or portions of it, when dangerous winds and damaging hail are likely to exceed the thresholds known to cause significant damage to well-built structures or cause bodily harm. These storms produce hail 3/4-inch or greater and have winds in excess of 58 miles per hour.
Large hail is created by strong rising wind currents (updrafts) that carry water droplets into the upper regions of a thunderstorm where they freeze. These frozen water droplets descend back down only to be carried back up high into the storm system where they refreeze into larger frozen drops. Finally, the cycle repeats itself enough times that the hail becomes so heavy it falls to the earth. Hail that is dime size or greater can produce dents in the tops of vehicles, damage roofs, break windows and cause significant bodily injury. Hailstones can form to softball size and fall at speeds in excess of 100 mph.
Damaging winds are another dangerous ingredient that make up the thunderstorm. Two types of dangerous winds are produced by thunderstorms: Tornadoes and Downbursts. Tornadoes, which have already been mentioned, are rotational winds. Downbursts, also known as straight-line winds, are more prominent in thunderstorms. Downburst (straight-line) winds can produce widespread damage similar to that of a tornado. In fact, downburst winds have been measured in excess of 120 miles per hour or equivalent to an F2 Tornado.
“The National Weather Service has modified the way it categorizes the anticipated risk of severe storms. There are now six classifications for severe weather and they are explained in the following chart:” Outlook-category-descriptions
Thunderstorm Safety Actions:
- Monitor NOAA Weather Radio for "Severe Thunderstorm Watches or
- Avoid driving into severe thunderstorms or consider delaying travel.
- Go to a small interior room on the lowest floor of your home, school, or
business when severe thunderstorms threaten our community.
- Have disaster supplies on hand (flashlight, food/water, battery-operated
- Move animals into shelter, and vehicles into garages to prevent damage, if
FLOODS & FLASH FLOODING
Most communities in the United States experience some form of flooding after spring rains or heavy thunderstorms. Frisco is no exception. Flood waters can rise quickly or slowly but typically develop over a period of days. Flash floods usually result from intense storms dropping large amounts of rain within a brief period.
Flood waters can be extremely dangerous. The force of just six inches of swiftly moving water can knock a person off their feet. The best protection during a flash flood is to leave the flooding area and move to higher ground.
Flash Flooding Safety Actions:
- Never drive through a flooded area. If you come upon a flooded road, turn
around and go another way.
- Abandon vehicles stalled in rapidly rising flood water and move to higher
- Avoid walking through flooded areas. Remember, as little as 6 inches of
swiftly moving water can sweep you off your feet.
- Watch for animals, especially snakes. Many animals lose their homes during
flooding and may seek shelter in yours.
Texas summers are hot. Heat is one of the leading weather-related killers in the United States, resulting in hundreds of fatalities each year and even more heat-related illnesses.
The National Weather Service has made changes in the excessive heat criteria, not only for us at NWS Dallas/Fort Worth, but across the region.
National Weather Service Weather Forecast Office for:
Excessive Heat Warning: Heat Index > 110 or Temperature >105 (F)
Heat Advisory: Heat Index > 105 or Temperature > 103 (F)
Note: These criteria will be met for a minimum of two consecutive days (forecast or observed) before we will issue any advisories or warnings for excessive heat.
The criteria we use as a guideline has not changed much, with one major exception. There is no longer an overnight low criteria for the National Weather Service Weather Forecast Office for Dallas/Fort Worth to meet before deciding on an advisory/warning.
Go to http://www.nws.noaa.gov/os/heat/index.shtml for additional information on heat safety.