NEXRAD: base reflectivity or composite?


New Member
When looking at NEXRAD imagery to analyze wx conditions, which option is more useful: base reflectivity or composite? Why?
I guess it depends what you're looking for? I mean the way I understand it...the composite shows the worst precip at any altitude-good for if you are going to be blundering around in the clouds and want to know which stuff is really nasty. The base would show you what's actually falling, good if you're VFR and want to know where the areas of reduced visibility are, or just how much you'll have to dodge around to stay clear of the nasty stuff.
Both have their niche.

Base reflectivity depicts the location and intensity and location of precipitation reaching the ground. For practical purposes, base reflectivity is ideal for identifying where the snow, rain, or hail is actually reaching the ground and at what intensity. It also can provide a purposeful overview of storm cycles from a precipitation point of view as well (during convective activity). Ultimately, the further you look from the radar site, the higher the angles are and precipitation may be depicted as well. If you were landing at SLC with convective activity reported in the area and you were within the terminal range (< 30), I would use base reflectivity.

Composite reflectivity is best used for analyzing the moisture in the air (prior to falling to the ground) as it's a compilation of the radar sweeps. It is best used to analyze long distances or en route weather since it will show the amount of moisture or instability the air contains. Think of composite reflectivity as a forecast per se. It simply depicts the *potential* precipitation that *may* occur.

In essence, one shows what is capable of happening (composite) and one shows what is happening (base). I always taught and used one as more of an en route product and one as a terminal product.
When looking at NEXRAD imagery to analyze wx conditions, which option is more useful: base reflectivity or composite? Why?

Composite is as stated above, but Base Reflectivity is a single "shot" of radar that is taken at a 3˚ angle from the station. Close to the station it might be the base, but it is simply whatever lies in the path of that 3˚ angle radar shot. Take a look at 00-45F and read about how it works. One thing you can use it for certain is to see that a heavy radar return 100 miles from the station guarantees a very tall storm with nasty stuff up high. I used to remember the actual distance/altitude amounts, but I can't now. 00-45F will clear it up for you.