There are a lot of interesting anomalies that you may see on displays that show NEXRAD (or any kind of) weather radar data. Some are caused by software, some are caused by the radar misinterpreting what it sees. None are worth some of the conspiracy theories that non-scientists have come up with.
Last month, blog reader Mike asked what is responsible for the radar "bloom" (or "radar blobs") that occurs nationwide, but especially in the Southeast U.S. in Spring and Fall. What he is referring to is the gradual growth of non-precipitation objects on radar after sunset (and the data fades after sunrise). During the night, this causes a large blob around each radar site. I have uploaded some examples from that night.
|EXAMPLES OF RADAR BLOOM: In the Huge AccuWeather Raw U.S. Loop and the Huge NWS Raw U.S. Loop, you are seeing the raw data from each NEXRAD radar plotted on a U.S. map. But in the Small AccuWeather Processed Northeast Loop, AccuWeather's computer algorithms and meteorologists have attempted to "clean up" the radar by taking out areas of data that they thought were invalid. This caused the "cookie cutter" hole around Indianapolis and the lack of clutter in the Southeast. The "C"-shaped object over the Great Lakes is rain from a low pressure system, though you can still see the "blooms" around and inside it. There are also a couple things of note in the Indianapolis Radar Site Raw Loop - the "spike" in the first frame is a "sunset spike" and is caused by the radar being temporarily "bllinded" by the setting sun. The blobs of blue and brown in the Northeast quadrant are areas of rain moving south from the aforementioned low pressure system.|
|EXAMPLES OF HIGH-DBZ AP: Notice on this example, a Northeast Still Image, how the high dBZ AP in Canada and New York looks a lot like the thunderstorms off the coast of the Carolinas. If you Download* This Northeast Loop then you can see that, while the thunderstorms move, the AP stays still. On the |
Binghamton Radar Site Raw Loop, notice how the AP mimicks the mountain tops, because the beam won't make it to the valleys once it hits the mountains. Notice also in the northwest part of the image how there are no echoes over the lake, because the surface is too flat to reflect back to the radar.
When the sun goes down and the surface begins to cool, the change in refractive index in the lowest few (to several) hundred feet of the atmosphere tend to bend the radar beam toward the surface. This bending holds the radar beam near the surface for extended distances, where it encounters scatterers that would not normally be available above the boundary layer. These scatterers include insects, bats, aerosols, particulate matter, etc., and account for the increased radar return referred to as "radar bloom."
The models continue to show a very deep low pressure system approaching the United Kingdom & Ireland near Christmas Day.
The historic Mideast snowstorm and upcoming U.K. Christmas storm observed through computer forecast model images.
A pair of mesoscale vortexes formed over Lake Superior yesterday. I pulled up 3-D radar data just before the storms made "landfall."
A major snowstorm is headed to the Northeast U.S. -- including AccuWeather HQ.
The lake-effect snow machine is cranking out some incredible amounts during the first 24 hours of this major outbreak. Here are top amounts, webcams and 3D radars:
The coldest air of the season plagued Montana and surrounding Canada last night, knocking temperatures well into the -40s F, with wind chills in the -60s!