What are ARTCC, RCO and FSS and what are differences?
ARTCC or Air Route Traffic Control Center: 


Does control traffic, generally in larger areas and above FL180 (Class A airspace) 
Will broadcast some weather info and provide advisories 



  ARTCCs broadcast a Severe Weather Forecast Alert (AWW), Convective
  SIGMET, SIGMET, or CWA alert once on all frequencies, except
  emergency, when any part of the area described is within 150 miles of
  the airspace under their jurisdiction




RCO or Remote Communication Outlets: 


Extends the range of FSS broadcasting ability 
Many are being shut down



  The remaining RCOs are of two types: 1,223 RCOs that allow pilots to
  contact flight service and receive transmissions over a common
  frequency; and 398 RCOs over which pilots can transmit—usually on
  122.1 MHz—and monitor flight service’s response on the frequency of a co-located VOR.




FSS or Flight Service Stations: 


  Flight Service Stations (FSS) are air traffic facilities that
  communicate directly with pilots to conduct preflight briefings,
  flight plan processing, inflight advisory services, search and rescue
  initiation, and assistance to aircraft in emergencies. FSS also relay
  Air Traffic Control clearances, process Notices to Airmen (NOTAMs) and
  provide updates on aviation meteorological and aeronautical
  information.


Provides inflight weather, preflight planning and clearances and takes NOTAMS. Does not control traffic in the air but is involved in dispatching instructions (clearances) prior to takeoff. 

Offering weather is a bit tricky. Controllers and those on the other end of the radio all have access to different levels of weather information and weather radar. Many will provide some level of information if asked. What they will provide is perhaps worthy of its own question here.