There has been considerable information disseminated in recent days in regards to Atmospheric Rivers; some of it factual and some so much so. Here are a couple pretty good resources:
NOAA ESRL Atmospheric River (AR) Info page
http://www.esrl.noaa.gov/psd/atmrivers/
ESRL Real-time AR Modeling
http://www.esrl.noaa.gov/psd/psd2/coastal/satres/data/html/ar_detect_gfs.php
Dettinger - Scripps Presentation on Atmospheric Rivers in California
http://www.scwa.ca.gov/files/docs/outreach/calendar/extreme-events/Atmosperic%20Rivers%20Dettinger%20EE%203-14-12.pdf