DMA is the designated market area, used only for TV/radio so don't confuse it for the CWAs of the NWS or even just the general 'viewing area' of each TV station. Here is one for Memphis...
http://cctvimedia.clearchannel.com/cctvi_dma/10.gif The counties in Gray (outlined in red) mark the DMA, not the white-shaded counties.
The DMA basically lines out viewer habits. In a nutshell, whatever city the majority of viewers watch TV from, that county goes to that DMA. In example, for Dyer County TN, the majority of people in Dyer County watch TV stations out Memphis, though they have stations out Paducah and Cape Girardeau to watch as well, so Dyer County is part of the Memphis DMA. In Craighead County AR, most people watch TV out of Jonesboro AR though Memphis and Little Rock stations are available, so they are assigned to the Jonesboro DMA. KAIT is the major station in Jonesboro, an ABC station, and is quite excellent in severe weather coverage. They cover all of East Arkansas and the MO Bootheel, and can overlap the Memphis stations sometimes.
The surrounding DMAs are Little Rock, Jackson TN, Jonesboro, Paducah/Cape Girardeau (one DMA), Nashville, Greenwood MS, and Columbus/Tupelo MS (also one DMA). Each of those cities has at least one major network affiliated station operating from there.
In a news station's view, DMA will rule in most situations. If a storm is in the DMA, coverage is considered high priority, and most times a tornado warning will get wall to wall coverage by all stations in the DMA city. If a storm is occurring outside the DMA but inside the viewing area, its handled with a crawl or cut ins, but in serious situations can get wall to wall coverage, especially if a DMA county is also under a threat.
Now, your first sentence. Yes, it is hard to put the coverage of April 2 up to the standard of those like January 1999, where it was top notch and probably the best it could get. Because it was well forecasted is certainly a major factor. April 2 jumped on us, NWS Memphis was pretty concerned initially, then toned down a bit that afteroon, only for things to get way out of hand just shortly after beyond anybody and everybody's expectations.
I hope that help clears things up, don't be afraid to ask more questions or make other points, lol! Enjoy your time here and welcome to the board.
