  The Ngari (Ali) prefecture of Tibet, one of the highest areas in the world,
has recently emerged as a promising site for future astronomical observation.
Here we use 31 years of reanalysis data from the Climate Forecast System
Reanalysis (CFSR) to examine the astroclimatology of Ngari, using the
recently-erected Ali Observatory at Shiquanhe (5~047~m above mean sea level) as
the representative site. We find the percentage of photometric night, median
atmospheric seeing and median precipitable water vapor (PWV) of the Shiquanhe
site to be $57\%$, $0.8"$ and 2.5~mm, comparable some of the world's best
astronomical observatories. Additional calculation supports the Shiquanhe
region as one of the better sites for astronomical observations over the
Tibetan Plateau. Based on the studies taken at comparable environment at
Atacama, extraordinary observing condition may be possible at the few
vehicle-accessible 6~000~m heights in the Shiquanhe region. Such possibility
should be thoroughly investigated in future.
