Because in reality, when you go much past 12 degrees per second, the antenna probably does not have enough time to receive a return echo from a distant storm (laws of physics I'm guessing) before the dish turns away from the storm. This also can be a processor burden issue as well. You'll notice when the "fastest radar in the world" turns at 20-30 degrees per second, storms in western Oklahoma start looking elongated (smeared). Even they discovered I was right when I emailed them about this exact thing and have been slowing it down when storms are far away from the radar.
Actually, this is not true... the speed of light is some 186,282 miles per second. Even if the radar beam is going out 100 miles before echoing, that's only a 200-mile round trip. Total time for this round trip would be around a thousandth of a second. In that time, a radar beam translating at 30 degrees per second (12-second full sweep) would have moved only approximately 0.030 degrees, or at the distance of 100 miles, only 276 feet. At 100 miles, 276 feet is much smaller than the measurable interval of the radar. So, that means that a 30-degree per second angular velocity really does nothing to affect the performance of the radar getting accurate data back.
This, of course, is assuming that the radar can even get out that far. I doubt that because of the nominal tilt of the radar to allow it to get above ground clutter, the data this radar receives from echoes 100 miles distant will not be representative of surface conditions, because even at 0.5 degrees above horizontal at the antenna (a fairly low base tilt), the radar beam will be over 9000 feet above the surface (the result of beam height AND surface of the earth dropping away due to the planet's curvature). The stuff that's real dangerous to us is happening in the lowest 1000-2000 feet of the atmosphere... so a radar scan of stuff that much higher than that isn't going to help us much. That's why the NWS depends on a network of these radars as opposed to the TV stations' stand-alone units or pairs of units (as is the case for KFOR).
12 degree/second or 30 seconds to do a complete sweep. How far is a storm going to move in 30 seconds? Actually that is pretty fast. The NWS radars are typically 6 minutes between scans during storms.
The reason that the TV radar can complete a sweep in 30 seconds and the NWS radar can complete a sweep in 6 minutes (or 5 minutes if they really want to beat the crap out of the radar) is that the TV radar is not doing a volume scan... it scans at only one level. The NWS radar completes a scan at it's lowest level, and then it tilts the antenna up a degree or two and sweeps again, and then it tilts the antenna up a couple more degrees or two and sweeps again, and so forth, until it has completed what's called a "volume scan". There are two preciptiation mode sweep patterns, one that does 9 tilt levels in 6 minutes, and another that does 14 tilt levels in 5 minutes. If you want to work it out, the sweep speed of the former works out to be 9 degrees/second and the latter is almost 17 degrees/second.
But then again, it's not all about speed of sweep. A faster sweep speed will return data faster, but it makes the radar less sensitive. A slower sweep speed, like that which the NWS radars run at when there is no precipitation ("clear-air mode") allows the radar to scan a certain area for a longer time and therefore be more sensitive.
So, the TV radars return data at one level. That's what the OLD NWS radars used to do... single-level return. No volume-scanning. Or maybe a second tilt at best. Getting data back for one level is certainly faster, but it really isn't any better than the radar of the 70's and 80's (except maybe that's it's Doppler radar as opposed to reflectivity-only conventional radar). I understand that the weather wars mean that faster is more important, and that's why you'll hear the TV stations tout their Whopper Doppler 1,000,000 radar's scan speed to be so fast... because they want you to come to them for you will believe to be the fastest updates. I'll guarantee you, though, that any real meteorologist on TV is using the NWS radar data to make their forecasts.
I believe its on highway 277 south of newcastle....
I believe that's correct... I pass it on the way to work everyday... it's just north of Highway 9.
Me? I don't watch TV for weather information. The weather wars have degenerated the genre of public notification in times of bad weather to one of greed and snake oil while trying to make you believe they are passing quality data. I'd rather be informed than entertained and misled when my life is threatened. But hey... at least they got flashy computer animations and pretty colors.
