The National Weather Service in Houston/Galveston has issued a Flash Flood Watch for Fort Bend County from noon Tuesday through Wednesday afternoon. Periods of showers and thunderstorms associated with a slow moving storm system should move across Southeast Texas Tuesday afternoon through Wednesday afternoon. The heaviest rains may come Tuesday night into Wednesday morning.
The National Weather Service expects widespread rainfall amounts of 3 to 7 inches with locally higher amounts possibly approaching 10 to 12 inches.
Flash flooding of low-lying locations is possible, especially in urban areas with poor drainage or rural roads. Flooding of streams, creeks, and bayous is likely through Wednesday. Heavy rainfall may cause significant travel impacts during the Wednesday morning commute.
A flash flood watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation.
Fort Bend County visitors and residents should monitor later forecasts and be prepared to take action the National Weather Service issue subsequent Flash Flood Warnings.
What is the danger?
Storms passing through Harris County beginning Tuesday afternoon could bring the threat of tornadoes and high winds. Heavy rainfall will also be a factor with most of the area receiving 3-4 inches of precipitation and isolated areas receiving 6-8 inches. Rainfall in these amounts will cause street flooding.
What you need to do:
Residents are urged to monitor local media and the National Weather Service (NWS) forecasts over the next several days for weather information. In the event of severe weather, particularly tornadoes, warnings may be issued with only a short period to take protective actions.
The NWS Storm Prediction Center provides these excellent tornado safety tips:
• In a house with no basement, a dorm, or an apartment: Avoid windows. Go to the lowest floor, small center room (like a bathroom or closet), under a stairwell, or in an interior hallway with no windows. Crouch as low as possible to the floor, facing down; and cover your head with your hands. A bath tub may offer a shell of partial protection. Even in an interior room, you should cover yourself with some sort of thick padding (mattress, blankets, etc.), to protect against falling debris in case the roof and ceiling fail. A helmet can offer some protection against head injury.
• In an office building, hospital, nursing home or skyscraper: Go directly to an enclosed, windowless area in the center of the building — away from glass and on the lowest floor possible. Then, crouch down and cover your head. Interior stairwells are usually good places to take shelter, and if not crowded, allow you to get to a lower level quickly. Stay off the elevators; you could be trapped in them if the power is lost.
• In a mobile home: Get out! Even if your home is tied down, it is not as safe as an underground shelter or permanent, sturdy building. Go to one of those shelters, or to a nearby permanent structure, using your tornado evacuation plan. Most tornadoes can destroy even tied-down mobile homes; and it is best not to play the low odds that yours will make it. This mobile-home safety video from the State of Missouri may be useful in developing your plan.
• At school: Follow the drill! Go to the interior hall or windowless room in an orderly way as you are told. Crouch low, head down, and protect the back of your head with your arms. Stay away from windows and large open rooms like gyms and auditoriums.
• In a car or truck: Vehicles are extremely risky in a tornado. There is no safe option when caught in a tornado in a car, just slightly less-dangerous ones. If the tornado is visible, far away, and the traffic is light, you may be able to drive out of its path by moving at right angles to the tornado. Seek shelter in a sturdy building, or underground if possible. If you are caught by extreme winds or flying debris, park the car as quickly and safely as possible — out of the traffic lanes. Stay in the car with the seat belt on. Put your head down below the windows; cover your head with your hands and a blanket, coat, or other cushion if possible. If you can safely get noticeably lower than the level of the roadway, leave your car and lie in that area, covering your head with your hands. Avoid seeking shelter under bridges, which can create deadly traffic hazards while offering little protection against flying debris.
• In the open outdoors: If possible, seek shelter in a sturdy building. If not, lie flat and face-down on low ground, protecting the back of your head with your arms. Get as far away from trees and cars as you can; they may be blown onto you in a tornado.
More tornado safety information is available here.
In the event of road flooding, the most important thing to remember is Turn Around, Don’t Drown! More deaths occur due to flooding than any other hazard and most of those occur when motorists ignore warnings and attempt to drive through flooded roadways. Additional flood safety information available here.
Where you can learn more:
Forecasts: National Weather Service
Local Traffic: Houston TranStar
Preparedness & Emergency Information: www.readyharris.org
For more information visit the Regional Joint Information Center website at www.readyharris.org
Q: Why do some clouds seem to have striped patterns?
A: Clouds that form in long linear stripes are fairly common, and they are formed by a phenomena known as gravity waves, explains Brent McRoberts of Texas A&M’s Department of Atmospheric Sciences. “Air generally flows along a horizontal path, but sometimes imbalances in the density of the air cause it to oscillate up and down as it moves along,” he notes. “In striped cloud patterns, the air is flowing perpendicular to the cloud lines. When the air is moving up, the moisture within it condenses, and while the air is descending, the moisture evaporates leading to clear skies. Not all gravity waves, however, lead to these striped cloud patterns. If the air is very moist, there will be full ripple clouds with no clear sky slots in between, and if the air is too dry, there will be no clouds at all. But in all cases, the air is moving in a wavelike pattern.”
Q: What can gravity waves tell us about the weather?
A: Not much, McRoberts adds, because gravity waves can form during fair and stormy conditions. “Most often, they form in the wakes behind mountaintops, but they can also form from daytime heating or from lifting along storm fronts,” he says. “These gravity waves are like ripples that form when you drop a pebble into a stream. A small disturbance will cause the air to ripple, but eventually the large-scale flow of the atmosphere will overpower and diminish the small-scale waves. Weather prediction computer models deal with a balanced atmosphere, so they have special equations that filter out the observed deviations caused by gravity waves that would otherwise lead to a chaotic forecast.”
Q: You hear a lot about El Niño and La Niña. What’s the difference?
A: The main difference between the two involves water temperature, explains Brent McRoberts at Texas A&M University. El Niño and La Niña – Spanish for “the child” – both occur in the central Pacific Ocean. “During an El Niño event, which can last almost a year, the waters in that region are warmer than usual,” he says. “The opposite occurs during a La Niña – the waters tend to be cooler than usual. But the important thing is that both events can affect weather patterns in the United States and around the world.”
Q: How do they change our weather?
A: In years when a La Niña occurs, there tends to be warmer and drier conditions in many areas, including Texas, McRoberts says. “In general terms, a La Niña period means drier weather patterns for Texas. There are been numerous studies done on how El Niño and La Niña affect weather patterns, and specifically, hurricanes and their intensity. Some research indicates that the sorts of hurricanes that affect Texas are more common during La Niña periods than during a neutral or El Niño year.”
Q: You sometimes hear the term “Alberta Clipper.” What is it?
A: An Alberta Clipper is a winter storm that forms over regions of Canada near the province of Alberta and sweeps in a southeastern direction over the northern United States, says Brent McRoberts of Texas A&M University. “It is believed the name comes from the big sailing ships of the 1800s, the ones with the huge sails that could travel quite quickly for vessels of that time period and were among the fastest ships on the seas. An Alberta Clipper storm moves quickly once it forms and brings cold temperatures, strong winds, and snowfall to the northern Great Plains and Great Lakes regions,” McRoberts explains.
Q: Are the storms considered blizzards?
A: No, says McRoberts. “An Alberta Clipper usually has very cold temperatures and gusty winds, but because of its quick movement, tends to produce small snow totals,” McRoberts explains. “If snow does occur, it’s usually just a light dusting to a few inches. However, if a Clipper moves over the Great Lakes region, it can produce lake-effect snowfall in those areas that are on the downwind of a lake. But generally, an Alberta Clipper produces gusty winds and very cold air over the areas in moves into and very rarely is categorized as a blizzard.”
A: For certain people, the answer is definitely yes, says Brent McRoberts of Texas A&M University. “Many people have said they can tell a change in the weather is about to happen because their joints or muscles start to ache,” says McRoberts. “This is likely due to a change in the barometric pressure, which often happens before a thunderstorm or in advance of a cold front. Damp weather is often associated with a low pressure system. A decrease in the air pressure decreases the tension in some large blood vessels, meaning they tend to expand. When this happens, it tends to lead to increased discomfort in joints and muscles. Also, we know that very rapid changes in temperature and humidity can make some people say they feel ‘stiff and achy.’ Many people who have arthritis say their joints are definitely affected by weather changes.”
Q: So can any weather change be a health problem?
A: Probably so, he adds. Some people like rainy days, which can bring muscle misery to others and even breathing trouble, and some people may enjoy cool, dry days, which can also bring aches and pains for some people, including increased sniffing. Since it appears almost certain that weather has an affect how we feel, there has been a dramatic increase in interest in the field of biometeorology – the study of how weather affects our bodies. One German study shows that as much as 25 percent of the human population is ‘weather sensitive,’ meaning weather changes tend to worsen some pre-existing health conditions. Even headaches are being investigated – some researchers say migraine headaches are linked to sudden weather changes.”
Q: How strong does a snowstorm have to be before it’s called a blizzard?
A: There are some specifics regarding blizzards, says Brent McRoberts of Texas A&M University. “In meteorological terms, a blizzard is a severe storm that has below-freezing temperatures, winds of at least 35 miles per hour and heavy snowfall, with visibility reduced to just 1/4 of a mile, and all of these conditions have to last at least three hours,” he explains. “So just a heavy snowfall is not always a blizzard. Blizzard conditions occur most often in the Great Plains, North Central United States and parts of the Northeast.”
Q: What are some of the country’s worst blizzards?
A: The blizzard that hit the Northeast in recent days may well wind up in the record books, he notes, as it shut down Washington, D.C., Baltimore and other cities, and final snow totals are still being recorded. In previous years, Buffalo had a blizzard that paralyzed the city for days in 1999, Colorado had a similar situation in 1997 and Boston suffered terrible blizzard conditions in 1978, McRoberts says. “Chicago had devastating blizzards in 1979 and one in 1967,” he adds. “The ’67 blizzard totaled 23 inches of snow with drifts up to 9 feet and the city was virtually shut down for days, with the Department of Streets and Sanitation estimating that about 75 million tons of snow fell. At least 60 people died, many of them from heart attacks while shoveling snow. Although records tend to be sketchy, perhaps the country’s worst blizzard occurred in 1888. In parts of the Midwest, the temperature fell from 74 degrees to minus 28 within hours, and the Colorado River froze solid throughout much of Texas. That blizzard claimed 235 lives.”
A: Frost forms when the temperature at the ground reaches freezing, says Brent McRoberts of Texas A&M University. “Very often on calm, clear nights, the temperature near the ground can be several degrees cooler than temperatures above the ground,” he explains. “The thermometer might read 34 degrees on top of a roof, but at the ground, it might read 32 degrees. This is because the ground loses heat quickly. So water vapor in the air, because it is so cool, condenses as supercooled dew and then turns to frost and maybe ice. Frost tends to form on glass, such as car windshields or windows, metal or rock surfaces first because these tend to lose more heat quicker. So usually, a car windshield will frost over before vegetation does.”
Q: Does frost form quicker in some areas than others?
A: Yes, McRoberts says. “Cold air is dense and it tends to sink,” he explains. “On a calm night, cold air will tend to sink into low spots. That’s why valleys can be much cooler than the surrounding area because the cold air from the hills sinks into the lower areas. So when the cold air starts sinking, frost will form quicker in the low spots than the high ones. It’s not uncommon for some valleys to be cooler by 10 degrees or more, thus more frost tends to form in these low areas. Also, some soil types, such as sand, retain less heat than others, and frost tends to form quicker on these.”