GRAND JUNCTION - Chance of rain...storm warning...storm watch...what does all that stuff mean, anyway? And who says we have that chance of rain this weekend?
Other than sticking your head out of the window to check the sky, our official source of weather forecasts is the National Weather Service, which is part of the National Oceanic and Atmospheric Administration, an operating unit of the U.S. Department of Commerce.
In other words, they are a group of scientists with specialties in hydrology, meteorology, and information technology. They use a lot of computer data, models, and good old-fashioned experience to predict our weather. Most of the time, they're pretty accurate. Sometimes, well, just like the rest of us, they can be wrong. While weather forecasting is part science, it also can be considered an art, as well.
The Grand Junction location is our closest weather service office, and is one of 120 across the U.S. The Grand Junction office provides forecasts for the Western Slope of Colorado along with parts of Utah, covering 50,000 square miles. Its Dopplar radar sits at 10,000 feet of elevation on the Grand Mesa, making it the highest radar of any weather service office in the country. While that high-altitude radar is good for covering a large area, it also means that radar misses some low-lying storms. That's why even with all of the satellites, radars and computers, an important component of the weather service is still just having people telephone in weather reports.
The weather service office itself is in a non-descript federal brick building near the airport in Grand Junction.
During a recent tour of the Grand Junction office, a flood watch was in effect for parts of the area, meaning conditions were good for flash flooding to take place that day. A flood warning means it's raining and somewhere, "and here it comes," explained Aldis Strautins, a hydrologist and forecaster in the Grand Junction office.
And an advisory? That's somewhere in-between.
A flood advisory, watch or warning means six inches of water or more is possible.
So how do they know that water might be coming?
Sitting at a bank of computers, Strautins looks at different versions of satellite images that he and his co-workers use for their forecasts.
One shows the visible images in the sky, such as clouds; infrared, shows storm activity, or a lack thereof; and water vapor.
While we might think of flooding rivers as more of a mountain or Utah thing, the Animas and Pine rivers did flood in the early 1900s when the remnants of a tropical storm parked in the area. And Vallecito suffered flash flooding in 2002 after the Missionary Ridge fire.
Along with the ever-faster computers, weather data also comes from weather balloons. Even in today's era of satellites, weather balloons provide data that still can't be obtained any other way, explained John Kyle, a meteorological technician in Grand Junction.
Weather balloons are released at the same time at 92 National Weather Service centers in North America and the Pacific, which is 5 a.m. and 5 p.m. in Grand Junction. The helium-filled balloon rises 1,000 feet per minute, carrying a little over three pounds of weather-sensing equipment called a radiosonde, which measures temperature, wind, humidity and pressure. When it lifts off the ground in Grand Junction, the balloon is about six feet in diameter. By the time it's 19 miles, or 100,000 feet in the air, it has expanded to the size of a one-car garage, and bursts. An antenna inside the domed building where weather balloons are launched tracks the signal. The data from this and the other weather balloons across the country are transmitted to a NOAA supercomputer on the East Coast that makes 213 trillion calculations per second, and that data goes into tomorrow's forecast.
The Grand Junction balloons tend to float east across the mesa to the Uncompaghre Plateau, Kyle explained. About 5 to 10 percent are recovered, and if you find one, the NWS asks you to mail it back.
Members of the public are welcome to watch a weather balloon launch. They're also asked to call whenever a large amount of rain, hail, or snow occurs. In the spring, NOAA staffers offer weather observation classes around the Western slope, and classes are usually offered in Durango, Pagosa Springs and Cortez.
Observations can be called in at (970) 243-7077. Weather forecasts are available at www.crh.noaa.gov/gjt/, and daily forecasts for the region from Grand Junction are available on facebook, as well.
