SAN ANTONIO — Weather radar picked up what initially looked like scattered rain showers near San Antonio on Thursday evening, but a closer look revealed the returns were actually large groups of bats emerging for the night rather than precipitation. The tricky radar signature appeared just north of the city near Boerne, Helotes, and New Braunfels, illustrating how easily bat emergences can be mistaken for light rain on standard radar imagery during the early evening hours when many colonies typically leave their roosts in search of food.
Two Distinct Signatures Stood Out on Base Reflectivity
On the initial Super-Res Reflectivity image captured at 7:09 PM, two isolated areas of returns appeared north of San Antonio, one near Boerne and another closer to Helotes, both resembling small pockets of light to moderate rainfall on the standard reflectivity display. At first glance, these signatures looked entirely consistent with typical scattered shower activity common across the Texas Hill Country region during the warmer months of the year.
However, meteorologists noted that actual rain was present elsewhere on the radar during this same time period, meaning the two highlighted spots stood out as somewhat inconsistent with the broader precipitation pattern visible across the rest of the display. This inconsistency was the first clue that something other than rainfall might be responsible for the two isolated returns showing up on the screen.
Dual-Pol Radar Confirmed the Signatures Were Not Rainfall
To determine the true nature of the returns, forecasters turned to Dual-Pol radar using Correlation Coefficient, or CC mode, a tool specifically useful for distinguishing raindrops from non-raindrop targets such as birds, insects, or bats. This mode allows meteorologists to see beyond simple reflectivity values and assess what is actually producing the radar return based on the shape and consistency of the reflected signal being received.
The CC mode imagery showed the true rainfall clearly displayed in reddish tones across the bottom half of the radar display, representing consistent, well-organized raindrop returns typical of genuine precipitation. Meanwhile, the areas near Boerne and New Braunfels showed a distinctly different, more chaotic and scattered signature consistent with biological targets rather than falling precipitation, effectively confirming the bat theory for forecasters watching the display.
Bat Emergences Are a Known Source of Radar Confusion
Bat emergences from caves and roosting sites are a well-documented cause of confusing radar signatures across Texas, particularly during the warmer months when large colonies leave their roosts around sunset in search of insects to feed on throughout the overnight hours. The Texas Hill Country region surrounding San Antonio is home to numerous large bat colonies capable of producing exactly this kind of radar signature on a fairly regular basis each evening…