Could be either a real SAR event or an exercise. You might want to try the CAP freqs or the other National/VA SAR channels (155.205, 155.895, and others listed under VDEM and SAR on the main page.) I'm in Fairfax County now, but I'll put my radio on those and see if I hear anything.
Edit: at 11:35, hearing encrypted P25 on 171.7 and 172.675 as well.
Edit again: 11:36, 155.1600 CSQ: "could you please ask team echo to standby" (female)
followed by "base copies"
11:41 "team echo, we need you to proceed south to 85 10 75 60, search the drainage downhill, towards the blue trail""proceed south, to 85-10-75-60 search to the intersection of the blue trail...copy echo, base out"
11:43, base talking to "relay 1" talking about repeating team echo's radio traffic, so far haven't heard any callsigns These coordinates are Virginia Search and Rescue coordinates, now hearing another person talking on 155.160, but too weak to understand...seems like Base is the only station I can hear
11:46 "should be 85-10-73-60, with IC's apologies"
11:51: - more encrypted traffic on 171.7, nothing on the other SNP P25 channels this time (usually when I hear one, I hear two or three repeating the same traffic, however, it could be a propagation thing, considering how far away from this whole thing I am)
11:54: 148.150 PL 100.0 (CAP channel 1) key-up, followed by a repeater key on 148.125 PL 167.9...don't know if this is related or not.
11:56: "relay 1 please instruct alpha to the blue trail to 85-60-73-50 and then call in for further instructions"
12:01: base starting to come in really weak, no longer hearing SNP traffic whatsoever...I'm wondering if the conditions are changing...hmm, I guess not, for what its worth, I tuned in 152.7125 with my HT (fork mountain STARS CC) and its still VERY loud so I think I should be able to hear SNP (I can nearly always hear SNP VHF and Fork Mountain at the same time, and vise-versa)
12:14: missed the first part of this but heard "return to base for debrief" followed by "copy, base out"
12:16: encrypted P25 on 171.7, 172.675 and 173.675 all at once. 166.9 remains silent.
12:18: "med 84 (or net 84?) this is base"...followed by "relay 1 this is base, can you copy charlie?"...immediately following this, I heard encrypted P25 on 171.7/172.675/173.675 and "Secure the net, secure the net." on 155.160.
12:21: base talking to team india, signal getting progressively stronger to my location
12:23: mobiles talking, "left a bag about one hour's walk from where he started". Simultaneous encrypted traffic on the SNP channels.
12:25: "return to base using the best method, and bring Kyle(?) with you"
12:26 to 12:28, base talking to multiple teams, Golf, Charlie and India mentioned.
12:34: Hearing clear P25 traffic on 171.7 now, talking about license registration information
12:35: mission base talking to relay 1, giving coordinates to team golf...
