In the San Antonio, Texas region, the climatological average rainfall peaks in May and September (Figure 1), with a rainfall amount between 90 – 100 mm (~3.5 – 4 inches). In May, when cold and dry air masses stemming from the Northwest collide with warm moist air masses from the Gulf of Mexico, convective storms form and can produce heavy rains and flooding, which results in the May peak shown in Figure 1.
During May 24-25, 2013, severe storms hit the San Antonio area and dumped nearly 10 inches of rain
(Figure 2), more than twice the amount of the monthly climatological average and the 2nd
highest rainfall total in the city’s history, according to the National Weather Service. Figure 2 indicates the heaviest rain area was located in the northeast of the city. Figure 3 is a time series of this storm sequence, showing that there were two rain events that passed through the region during the two-day period.
Figure 2. Rainfall amount (in mm) accumulated between 0Z May 24 and 23 Z May 25 2013, from North American Land Data Assimilation System (NLDAS) data in Giovanni. (http://gdata1.sci.gsfc.nasa.gov/daac-bin/G3/gui.cgi?instance_id=NLDAS0125_H). “+” marks the city of San Antonio. (Click for full-size.)
Figure 3. Rainfall time series (derived from NLDAS) for the San Antonio area, showing two heavy rainfall events between 0Z May 24 and 23Z May 25, 2013. (Click for full-size.)
Precipitation products archived at the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) are available for further investigation of this record flooding event in San Antonio. Figure 4 shows the city’s record rainfall event, which occurred on October 17, 1998. Figures 2 and 4 show that the heaviest rain areas for these two record flooding events are both located in the Texas Hill Country to the north and northeast of the city, indicating that orographic lifting might have affected the rainfall amounts and locations of the events (Figure 5).
Figure 4. Rainfall amount (in mm) accumulated between 0Z October 17 and 21 Z October 17, 1998, from the TRMM Multi-Satellite Precipitation Analysis (TMPA) data in Giovanni (http://gdata1.sci.gsfc.nasa.gov/daac-bin/G3/gui.cgi?instance_id=TRMM_3-Hourly). “+” marks the city of San Antonio. (Click for full-size.)
Figure 5. The heavy rain centers for the two record flooding events in the San Antonio region are located in the Texas Hill Country to the north and northeast of the city, indicating that orographic lifting might have affected the rainfall amounts. (Map generated from Google Maps; click for full-size.) The small map shows the location of the Texas Hill Country (brown area) in relation to San Antonio. (Click for full-size.)
Figure 6 shows two animations for this flooding event, created from the NCEP/CPC 4-km Global (60 deg N - 60 deg S) Merged IR Brightness Temperature data set accessible on the Hurricane Data Analysis Tool
page. The top image is an animation of brightness temperatures in grayscale (similar to those commonly shown on TV weather forecasts), showing the cloud evolution of the severe storms. The bottom image shows the evolution of the severe storms in false color; the cold cloud tops of the storms are clearly visible.
Figure 6. Animations of brightness temperatures (equivalent blackbody temperatures, in degrees Celsius) in grayscale (top) and false color (bottom), showing the evolution of the convective storms that caused the flooding in San Antonio May 24-25, 2013. While the rain on May 24 was widespread over Texas, the storms on May 25 (commencing about 10Z) were more localized to the San Antonio and Hill Country region. Both of these animations are shown full-size.
Credits: Hualan Rui generated Figures 2 and 3. Article and text by Zhong Liu.
Questions or comments? Email the NASA GES DISC Help Desk: firstname.lastname@example.org .