On Our Radar: Water and Weather Tools February 2018

Throughout history, people have stared up at the sky trying to convince the weather to work in their favor. While still an option for hopeful Texans, nowadays we have technology and tools that forecast long- and short-term weather patterns. When it comes to our water supply, weather—in particular, precipitation—plays a critical role. The TWDB uses several weather resources and forecasting tools that are available to all Texans, whether you’re planning a weekend at the lake, preparing to plant a garden, or just plain interested in weather.

One of these tools is the TexMesonet, a network of weather stations that track and measure atmospheric conditions, rainfall, temperature, soil moisture, and temperature. Current weather conditions and forecasts are provided by the National Weather Service, and historical weather data are also available. There are more than 2,000 stations displayed in the TexMesonet viewer, some of which are designed, built, and maintained by the TWDB. Other locations will be added in the future.

The interactive Flood Viewer map features a weather radar. Regional weather alerts issued by the National Weather Service can be viewed for the whole country and are color-coded with text explanation to represent severe weather warnings such as winter weather, high wind, flood and coastal flood, and much more. The Flood Viewer also tracks flood conditions by monitoring streamgages and lake conditions throughout the state so Texans can take action to stay safe if nearby flooding is imminent.

Like flood, drought also has significant effects on Texas, most especially on its water supply. The TWDB’s Forecast of Average May–July Rainfall tool provides county-level information on whether the average rainfall for the May through July season will be above normal, near normal, or below normal. The term normal refers to the season’s long-term historical average. May and June are the wettest months across much of Texas, and July is the start of the rainfall season for the western part of the state. If the May through July rains fail, we can be pretty sure that Texas is in the throes of a summer drought. Such a drought could worsen as we head into August, which is one of the driest and hottest months of the year over much of the state.

The forecasts, issued from January 16 through May 1, are updated every two weeks and are based on predicted large-scale weather patterns and soil moisture between January and March that are known to influence May through July rainfall. The forecasts issued in April are based on actual large-scale weather patterns and soil moisture. Soil moisture is important because wetter soil typically leads to wetter water conditions and more evaporation and moisture in the air. It’s the water cycle in action!

By using a statistical forecast technique similar to that used to forecast May‒July rainfall, we are able to forecast estimates of cumulative reservoir evaporation during the May through July season. The TWDB’s reservoir evaporation forecast map features the amount of evaporation in inches for each major reservoir (i.e., reservoirs with capacity greater than 5,000 acre-feet) in Texas. This tells us how much water could be lost from storage due to evaporation and gives water planners an idea of how water supply may be affected during those critical months.

Weather conditions during other seasons can also affect drought in the summer. For example, when a phenomenon known as a La Niña event is in place in the fall and winter seasons, the southern U.S. tends to experience warmer- and drier-than-normal conditions in the winter and sometimes into spring. The 2011 drought was preceded by a La Niña event in the winter of 2010 that continued into the spring of 2011. A La Niña event and rainfall and temperature patterns typically associated with such conditions have been observed this winter, too, making spring rainfall even more necessary to offset potential summer drought.

An easy way to keep a pulse on conditions in Texas is by checking out the Water Weekly, a one-page update available on our website each week. This short summary highlights statewide reservoir statistics, current drought conditions, and other timely information—complete with maps.

While we can’t control the weather (as much as we’d like to), we can do everything in our power to responsibly prepare for weather conditions that can affect our water supply. Being informed is a key step, and all of us are empowered to use these weather-related resources and tools throughout the year.

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