Bat Signal Caught on Radar…and no it isn’t Batman (Photo Credit: NWS Austin/San Antonio and Radarscope)
DISCUSSION: Earlier this month, the National Weather Service in Austin/San Antonio tweeted a radar image of a colony of bats outside of the cities of Concan and Knippa in Texas. Where did these bats come from and how can we see them on radar?
Texas is home to some of the largest bat colonies in world. This includes the largest known bat colony at the Bracken Cave Preserve and the largest urban bat colony at the Congress Avenue Bridge in Austin. Just a few hours away from these two colonies is the Frio Bat Cave, which is where the bat colony shown in the above radar imagery resides. In April and May, it is common to see swarms of hungry pregnant mother bats leaving their caves looking for food just after sunset with waves of bats leaving for 2-3 hours. In early June, the baby bats are born, meaning that the swarms of bats leave their caves later in the evening. In late July/early August, bat season reaches its peak and these bat swarms will continue to be seen until as late as November. How exactly can these bats be seen from weather radar?
Radar sends out signal that hits an object and is then reflected back to the radar at varying strengths depending on the size of the object. Usually, the signal received back is reflected from precipitation. However, other objects such as smoke plumes, insects, birds, and bats, can also reflect signal back to the radar. This is why you can get what looks like precipitation showing up on the radar even when there is none occurring in that area. How do we know a radar signature is bats and not actually rain or another source? A bat signature on radar will show up first as a sudden circle that quickly spreads outwards in subsequent frames of the radar until the bats have all dispersed. These signatures are also typically found in the evening when bats leave their caves to find food. If you live in an area with an active bat colony, you may just be able to spot these animals leaving their caves on radar!
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©2018 Meteorologist Stephanie Edwards
A Blast to Tropical Cyclone Intensity Forecasts Past (Photo Credit: NOAA Hurricane Research Division)
Discussion: An important technique to estimate the strength of tropical cyclones is known as the Dvorak technique. The Dvorak technique, developed by Vernon Dvorak is a satellite-derived system to estimate storm strength solely based on visible and infrared satellite imagery. The system uses cloud patterns visualized through satellite imagery and can then be used to indirectly measure wind speed and central pressure. Today the Dvorak method is used mainly as verification to measure wind and pressure. This important technique is even used by the National Hurricane Center. What makes this system useful and accurate is because storms with approximately similar intensities were found to contain similar cloud pattern identified on satellite imagery.