Into each life some rain must fall …and fall …and fall …and fall
January 23, 2020 12:40 PM   Subscribe

10 years of US weather radar in two hours [YouTube]. This time-lapse movie, starting from January 2010, shows ten years of precipitation in a mosaic of all the NEXRAD radar sites in the contiguous states. NEXRAD is a network of 159 high-resolution Doppler radars maintained by the National Weather Service. Besides precipitation intensity, Doppler radar can also detect the direction and velocity of wind inside a thunderstorm, making it invaluable for tracking tornadoes and detecting straight-line winds caused by downbursts. Many commenters on the YouTube page have identified specific timecodes in the movie where you can see noteworthy instances of severe weather such as tornado swarms, derechos, hurricanes, and nor’easters [see the end of this post for a partial list].

Precipitation intensity is represented by a color scale, with green indicating the lightest rain, yellow as moderate rain, and orange and red representing the most intense rains falling at rates of up to 2 inches per hour. Magenta can be absurdly intense rainfall of up to 16 inches per hour, but usually it means hail. In the movie you may notice in early 2011 additional colors are added to represent wintry precipitation (blue & white for snow and pink for sleet or mixed rain/snow). This was due to an upgrade for NEXRAD, which added vertical polarization to the previous horizontal radar waves, allowing radars to better distinguish between rain and snow. The yellow and red outlines that keep popping up are severe thunderstorm watches and tornado watches, respectively (not to be confused with warnings!).

Doppler radar does have limitations. A radar beam spreads out with distance - becoming approximately 1000 feet wider for every ten miles of distance - resulting in decreased resolution when detecting distant precipitation. This is why a solid line of thunderstorms sometimes appears to break apart as it approaches a radar site: the line was never solid in the first place, but lack of resolution at a distance obscured that fact. Beam spreading can also make distant storms appear weaker than nearby storms because they return less of the radar beam’s energy. Another limitation stems from the fact that, due to the Earth’s curvature, a radar beam scans higher altitudes the farther it travels from the radar site, sometimes completely missing rain below it.

These limitations give NEXRAD radar an effective range of about 140 miles, so gaps in coverage are a problem. Some gaps are filled by privately-owned radars, but there are many remote areas that will never be fully covered, and there are even some heavily populated areas have a dangerous lack of radar coverage.

As you watch the time-lapse, you may sometimes notice what appear to be stationary blobs of rain centered on some radar sites. These blobs are not actually precipitation, but are instead caused by temporary atmospheric conditions like temperature inversions, fog, and variations in air density. This is an example of anomalous propagation. The aforementioned conditions can cause a radar beam to superrefract or duct through the atmosphere. When this happens, the beam will sometimes bend downward causing some of the radar energy to hit the ground and return energy back to the radar, which shows up as a false echo.

There are lots of other things that can show up on Doppler radar, some as real echoes, and some as false echoes. Here are a few:

bird roost rings:
These are common on late summer and autumn mornings where birds flock in and around bodies of water. Just before sunrise there is often a coordinated lift-off and dispersion of the birds into surrounding areas for feeding during the day. A similar phenomenon can be seen at dusk when large bat colonies take flight. Many other kinds of airborne objects can reflect radar energy and show up as echoes on your screen, including insect swarms, other kinds of insect swarms, and plumes of smoke from buildings on fire.

wind farm interference:
If wind turbines are within line-of-sight of a Doppler radar and the blades are rotating, they can show up as a false precipitation signature. Algorithms are usually able to filter out many echoes caused by physical obstacles like hills and buildings because the energy reflected by them has no motion. But since turbines are moving, their reflected energy is interpreted as weather. This can even be caused by chairlifts in motion at ski areas.

sunrise & sunset spikes:
Twice a day, at sunrise and sunset, radar experiences interference from the electromagnetic energy emitted by the sun. NEXRAD operates in the microwave part of the spectrum (S band, to be specific) and some amount of the sun’s energy arrives in microwave wavelengths. When a radar dish points directly at the sun at sunrise and sunset, it’s hit by this microwave radiation. This is then displayed as a brief spike of (falsely) returned energy.

some significant timecodes in the movie:
0:01:07 - 2010 early February blizzard 'Snowmageddon' (the first of three major winter storms to hit the East that month)
0:04:00 - 2010 May floods in Appalachia
0:11:54 - 2010 December blizzard
0:15:55 - 2011 April 25-26 Tornado Super Outbreak
0:16:51 - 2011 May 21-26 tornado outbreak sequence (including the Joplin, MO tornado)
0:30:20 - 2012 June 29-30 derecho
0:34:15 - 2012 Hurricane Sandy
0:37:45 - 2013 early February nor'easter
1:13:43 - 2016 January blizzard
1:22:21 - 2016 Hurricane Matthew
1:33:06 - 2017 Hurricane Harvey
1:33:36 - 2017 Hurricane Irma
1:45:55 - 2018 Hurricane Florence
1:46:46 - 2018 Hurricane Michael
1:57:43 - 2019 Hurricane Dorian
posted by theory (11 comments total) 49 users marked this as a favorite
Holy cow this is neat! Already sent it to the weather nerds I follow on Twitter.
posted by jquinby at 1:01 PM on January 23

The wind farm thing is real: oh so many hours spent with Environment Canada and Nav Canada. At the time, Nav Canada were still struggling along with '90s era digital radar. This identified a wind turbine blade on the upstroke as a small plane taking off (creating a "track this" object) on their screens, which immediately appeared to CFIT a couple of seconds later as the blade was on the downstroke. This of course raised an alarm for every turbine, so a wind farm looked a bit like a Royal Flying Corps training aerodrome circa 1916.
posted by scruss at 1:26 PM on January 23 [2 favorites]

Fantastic post, thanks!
posted by TigerMoth at 1:35 PM on January 23

This is really cool!!!

0:30:00 - 2012 June 19th flood in Duluth, MN. Somewhere around 0:30:00.01 I looked out my window and thought "Damn, I don't think I've ever seen a thunderstorm last for six hours before."
posted by Gray Duck at 2:03 PM on January 23

I love this. I wish it showed more ocean, Mexico, and Canada, because it can look as if weather appears from nowhere/ vanishes off the borders, but it's so cool to watch. Will be playing it on the TV shortly. Also, anice break from news in the US. Thanks
posted by theora55 at 3:00 PM on January 23 [1 favorite]

I like the summertime weather over the SW/Colorado with thunderstorms like a pulse.
posted by Pembquist at 9:19 PM on January 23

Another interesting phenomenon one can observe on NEXRAD images, which just so happens to look a lot like the "rays" seen at local sunrise or sunset, is people operating WiFi networks in certain parts of the 5GHz band in a manner not allowed here in the US. This is the reason many 5GHz channels are restricted to indoor use only and why DFS, along with its annoying but necessary radar detection algorithm, is a thing.

Unfortunately, many people import equipment from overseas that allows them to use those channels at power levels greater than allowed in the US and/or allows the user to disable DFS on those channels.

There are days here in Miami that rain showers coming in off the Atlantic are significantly obscured by this interference. If it annoys me, I can only imagine what the NWS people think.

On a positive note, if you are interested by thunderstorms and radar, GRLevel3 (you've probably seen it on TV at some point) provides excellent visualization. If you can justify the expense, GR2Analyst is crazy awesome, as it uses the higher resolution NEXRAD Level 2 products to create a full 3D visualization of storms. On several occasions when I was living in Oklahoma it was possible for me to see tornadoes develop in near real time, in one particularly sad instance including the trees, cars, and bits of houses lofted hundreds of feet up in the air by the storm. It provokes quite a sense of awe. If you time your trial period right, you too can "enjoy" the experience without having to pay for the software.

Sadly, all the really nice Android NEXRAD software that is still being maintained requires a subscription. BRB, gotta go pour one out for PYKL3 and get wX configured in a way that makes it less obtuse to use.
posted by wierdo at 10:37 PM on January 23 [5 favorites]

I have read that there are concerns that upcoming 5G cellphone networks will severely interfere with weather radar as well.
posted by sjswitzer at 7:30 AM on January 24

The issue with 5G is not weather radar, but weather satellites. One of the bands that 5G can use is close enough to a frequency emitted by water vapor (IIRC, it could be a different channel) in the atmosphere and the spectrum mask required by the FCC sufficiently lax that the very weak signal picked up by the satellites will likely be overwhelmed by "unintended" interference from 5G equipment operating in that band.

Unlike with Sprint's interference with public safety communications after deciding they ought to be able to deploy LTE in the two way radio band they got when they acquired Nextel, it isn't possible for the satellites to use a different frequency since the signal in question is of natural origin.

It's such an own goal it is completely embarrassing.
posted by wierdo at 8:28 AM on January 24 [5 favorites]

This is fascinating, and the music is so ominous! Thanks for posting.
posted by sundrop at 7:15 AM on January 25

The reentry of space shuttle Columbia was visible on doppler radar.
posted by the Real Dan at 11:29 AM on January 25

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