I stopped by the NWS office recently to ask about wx balloon launches and the guy said they don't follow the standard. Instead they launch at 11:00 UTC and 23:00 UTC. I just checked the CalSky site and saw those are the times they use for their predictions. So once again Utah is the odd ball. :) patrick On 18 Aug 2014, at 10:52, daniel turner via Utah-Astronomy <utah-astronomy@mailman.xmission.com> wrote:
Chuck: One of my "go to" websites for nighttime viewing conditions is the U of WYO site in the link below.
Click on the SLC link and you get data from the latest sounding balloon. Balloons go up twice a day at 0 and 12 Zulu time which is 6am and 6pm MDT. Of major interest is the
Precipitable water [mm] for entire sounding: 12.97
at the bottom of the page. At a half inch or less (12mm) the air column is dry enough for some deep sky viewing of external galaxies.
8mm is rare during our monsoon but it happens and it's spectacular.
at an inch (25mm) the air is so full of water that we will be dodging thunderstorms and the viewing is poor.
I also look for layer in the sounding that have RELH% of 50 or more. even in an otherwise dry sky this layer is moist enough for the hygroscopic dust to start picking up water, forming droplets, and degrading the viewing. This usually manifests as hazy rings around brighter stars. People often mistake this for dew on their optics but if you look through a warm pair of 10x50s you will see the same rings. That tells you the stuff is in an air layer above you and not on your secondary mirror.
DT