|Rainfall Estimates at the Click of a Mouse
A number of inquiries have been received by our office asking how to get rainfall estimates from around Deep South Texas and the Lower Rio Grande Valley. On the left side of this page, you'll find a link to rainfall estimates. Clicking on this page will take you to the Advanced Hydologic Prediction Service Precipitation Analysis web page, from where you can produce any number of rainfall estimates, drilling down from the Conterminous U.S. and Puerto Rico, to NWS Administrative sectors and River Forecast Centers, down to the local Weather Forecast Office level. Current data are the default, but options exist for weekly, bi-weekly, monthly, bi-monthly, 90-day, 180-day, month-to-date, and calendar year-to-date. In addition, monthly archives exist back to 2005, and include observed data, as well as "normals" and variations from normal.
The rainfall estimator, in simple terms, compares rainfall calculations from local Doppler Radars with ground rainfall reports (gauges and other measuring sensors), develops a bias (correction factor), then applies that factor back to the radar calculation. The "corrected" radar rainfall data are combined into a "multi-sensor field" which is then quality controlled on an hourly basis. A significant drawback to this approach for Deep South Texas and the Lower Rio Grande Valley is the lack of wide coverage of ground sensors. Due to the combination of abundant rural land, a lack of gauges across the western Lower Rio Grande Valley, little or no input from northeast Mexico, and no input from nearly half the radar coverage area over the open Gulf of Mexico, rainfall estimates can be considerably undervalued, especially in sub-county or city scale events, such as the Starr County Flooding which occurred between August 17th and 25th, 2008. Widespread rainfall events, such as Hurricane Dolly or along a stationary front, show more accurate rainfall estimates. For significant rainfall events over small areas, locally crafted maps provide a more accurate assessment. See our Weather Events section for more. For a full description of the estimation process, click here.
The following is a quick list of instructions on how to create a rainfall estimate.
- Current Data. Initially shows entire U.S. and Puerto Rico, and defaults to Today. Use scroll bar to select time period desired.
- Archive: Month/Year. Defaults to the current month and year; national image will change automatically after radio button selected. Under 2. Product, options for Observed, Normal, Departure from Normal, and Percent of Normal appear.
- Location: NWS Brownsville. Clicking radio button for NWS WFOs under 3. Location, then scrolling down to Brownsville, TX and selecting, will zoom the image into Deep South Texas and the Lower Rio Grande Valley. For county maps, rivers, highways and cities, and River Forecast Center Boundaries, just "check" the appropriate box.
For any additional questions you may have about rainfall estimates, please send comments here. Thanks for your support.