82 NC counties and 1 VA county are under alert, including Wake, Cumberland, Durham, Johnston, and Orange counties. Details
Published: 2007-10-07 12:55:18
Updated: 2007-10-07 12:55:18
Posted October 7, 2007
By Don Egan
MIKE MOSS SAYS: Don, The difficulty in performing an adequate radar detection/analysis of a storm that is very near the radar site itself is not unique to the new radar system, but is a characteristic of all weather radars that derives from two problem areas. The lesser of the two issues is that of a "recovery period" required between transmission of a very powerful radar pulse through the waveguide and out via the antenna and switching to a receive mode to "listen" for a very weak return signal to be picked up by that same antenna. There is a very brief delay interval between the two that is required to prevent the transmitted signal from damaging the receiver, and this interval separating transmission from reception results in a circular area just a couple hundred meters around the radar site in which no targets can be detected. A larger issue is that storms very near the radar may have many of their important structural clues located at altitudes above the radar beam, which hasn't risen very far above the ground that close in. This issue is often referred to in weather radar circles as the "cone of silence" above and in the immediate vicinity of a radar. How large this cone is depends on the particulars of a given storm as well as on the scan strategy being used by the radar. Both of these limitations are simply unavoidable results of the physics of radar surveillance.
In the case of the storm you were referring to, the reason for checking the Morehead City radar at times was to utilize a radar outside the "cone of silence" area. Note that if this was a problem unique to our new radar, Greg would have switched to the Raleigh NWS (NEXRAD) radar instead - however, that radar is located very close to ours and was simultaneously in a poor position relative to the storm, making Morehead City the next closest system with a view of the storm (not an ideal view, because of the degree of beam spreading and altitude gained by that beam from so far away). Of course, as the storm moved on a little ways to the east it became fully observable again with both Dual Doppler 5000 and the Raleigh NEXRAD.