As we’ve mentioned, even though the temp is just above freezing over most of Alabama except the higher elevations, be careful driving home this afternoon! It takes snow or sleet a minute or two to melt sometimes, and the roads can still be slippery in spots. Just leave plenty of distance between you and the car in front of you, and keep the speed down.
The next upgrade to NEXRAD, to be installed over the next few years, will be to make each one a “dual-polarization” radar. This way, the radar will send out microwaves oriented horizontally and vertically and be able to see the difference in reflectivity between each, helping to identify precipitation type (rain, snow, sleet, hail). The old measurements will all be there too. UAH and WHNT-TV in Huntsville share the ARMOR dual-polarization radar, researching what these radars can show.
Differential reflectivity (ZDR) measures the horizontal orientation of the precipitation falling. Raindrops tend to be flat (high ZDR), hailstones are more round (low ZDR). Snowflakes also tend to have lower ZDR.
When snow is wet, it tends to stick to other snowflakes more efficiently, forming big snowflakes. Some heavy snow moved through Trussville around 330 pm, with snow flakes near an inch across. These big snowflakes also tend to fall very horizontally.
Check out the ARMOR ZDR from 330 pm, and the very high values of ZDR over parts of Walker, Jefferson, and Blount Counties.
