I'm going to throw my 2 cents in and say it might be FEMA.
From my logs that have had the same NAC:
141.6125 Harris County, TX Sept 2013
170.6000 Port Lavaca, TX Aug 2010
162.5625 Milford, CT Nov 2010
166.2000
167.9375
170.4625
173.2000
173.5875
166.0875 Southeast FL Nov 2010
Reports of NAC FFF on the Kentucky EMA/National Guard Statewide VHF Network
KY EMA /KY National Guard Scanner Frequencies and Radio Frequency Reference
137.4375 Kennett, MO July 2010
137.6625
162.5875 Kansas City, MO February 2010
163.1500
164.6625
165.2625
165.2750
166.4000
168.5375
168.6500
168.8250
169.1000
169.1375
170.6125
172.9500