The NEXRAD Doppler Radar and Bats…

doppler-1-640x380The great joys of new observational tools include unintended consequences. I can relay a story about the WSR-88D (NEXRAD) Radar to illustrate this.

As a new Warning Coordination Meteorologist at the National Weather Service in 1991 in Norman, Oklahoma, a group of us were the first to be allowed to use the new radar. We knew it would be a great tool to observe and warn for thunderstorms, tornadoes and heavy rain. The contractor turned the radar over to us on March 20, 1991, and we had our first severe weather outbreak the next day, as severe thunderstorms producing tornadoes moved across the Ada, Oklahoma area.

We were amazed at what we could see, but as with most new observational tools, as many or more questions were raised as answered. As we got into the summer, we noticed that around sunset, in locations in both southwest and northwest Oklahoma, a “dot” would appear on the radar in particular locations. The dots would grow into an open circle and disappear. A few curious NWS forecasters decided to make a trip to southwest Oklahoma to check out what was happening.

Their findings were astonishing. They found thousands of bats leaving a cave at sunset, and this was detected by the new radar! The findings were written up, and bat enthusiasts, as well as people who studied bird migrations and even butterflys, had a new tool to use.

Here is a recent example of what the “bat” image looks like. The image is from the Austin-San Antonio radar at New Braunfels, Texas. You’ll notice the Severe Thunderstorm Warning (yellow polygon), and the Flash Flood Warning (green polygon) first. But a look at the areas circled in white show the bats headed out from their caves as night approaches. Central Texas is well known for being “bat-friendly” with the Hill Country caves providing a suitable habitat for the bats.

Jim Purpura
Certified Consulting Meteorologist
Director, Weather Forecasting

July Rain

It’s a strange day in Southern California today. I have lived in California my entire life (both northern and southern) and can’t remember the last time I felt raindrops July. Besides monsoon thunderstorm activity in the mountains, it’s typically a dry tinder box around here this time of year. This shot of moisture wasn’t anything in the ballpark of a drought-buster, but it was nice to see some green on the radar.

From last night through this morning, most locations in San Diego County have only reported a trace of rain, with a few (mostly in the higher elevation) reporting up to 0.05″ of rain so far. Subtropical moisture will continue flowing into Southern California from the southeast through tonight, so showers should linger for a while, and then mostly hug the mountains and deserts as the day progresses. After that, these rather humid and “muggy” conditions (for our standards) should deteriorate starting tomorrow as the subtropical connection is cut, and the pattern transitions back to normal for this time of year. It looks like there is hope for the end of the marine layer mornings along the coast in the near future as well!

Radar composite at 08:50 PDT showing a rare (and nice) plume of subtropical moisture in the southwest.
(The Weather Channel)

Stephen Bone