Doppler radar is a tremendously powerful tool in modern-day weather analysis and forecasting. Recently, the National Weather Service completed the upgrade to dual-polarization on 122 of it’s radars across the country. This new technology allows meteorologists to get a better feel for what the radar is ‘seeing’ as it scans our skies.
Massive Santa Ana-fueled fires are burning in Ventura County, California. The defining characteristic of Santa Ana winds is dry, moisture-starved air. These winds blow into SoCal from the Great Basin and fuel the flames.
The SoCal wildfires are being monitored and fought by crews in the air and on the ground. But weather satellites and radars can even pick up on what is going on!
The plumes of smoke from the fires rise thousands of feet into the air.
The most interesting images to me are those from the KVTX Los Angeles Doppler radar. The actual radar is situated about 25 miles to the northwest of the fire site. The beam is scanning at about 1,500 feet above the ground over the fire – in other words, right through the smoke plume.
The first radar image is a reflectivity scan. This is simply a measure of how much energy is reflected back to the radar dish. The radar isn’t smart enough to know that it’s beam is hitting smoke particles and not rain. Don’t focus on the random blue specs – that is neither smoke nor rain. Rather, keep your eyes on the area just off the coast where the brighter greens and yellows are located.
The second radar image is the velocity scan. This is frequently used to assist in issuing Tornado Warnings because the colors indicate which way the winds are blowing – either towards or away from the radar site. In this case, however, the red color just off the coast indicates that the smoke plume was moving in a general direction away from the radar. By cross-examining the reflectivity image, I am able to determine that the smoke plume was moving to the southwest.
The third radar image is a new product called correlation coefficient – something that wasn’t available before the dual-polarization upgrade. This product allows meteorologists to gauge the similarity of the vertical and horizontal returned-energy in a small volume of air. Wait, what? Keep reading…
Essentially, pure rain shows up as being very similar because all the radar energy hits is rain drops. When the radar beam hits smoke, as in this case, the “cc” values are very low (indicated by the grey colors just off the coast). After all, a plume of smoke contains all sorts of particles. This provides solid confirmation that the reflectivity (greens and yellows) in the first radar image is smoke and not rain.
The image below is from KNBC-TV NewsChopper 4. We’re lucky that we rarely, if ever, see wildfires of this magnitude in New England.