I mostly hear whiskey but have heard other phonetic letters as well. What does this indicate/mean?
The weather and operating conditions at an airport can and do change. So the recording that pilots listen to have a validation code at the end, which changes on a regular basis over a 24 hour cycle.
When the pilot requests taxi or instrument flight clearance, they have to provide the right time related code to prove they listened to and have the most up to date weather and field conditions before flying.
Ref:
https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap2_section_9.html
Generally, ATIS is updated hourly, sometime close to the top of the hour. Every now and then, officials will issue an off-schedule update if conditions change enough to warrant it, like a sudden change in temperature/pressure after a front moves through.
It is to tell what version of the weather report you have. They are frequently updated. First is called alpha next is bravo then charlie and so on…
Typically the ATIS (Automated Terminal Information System) or ASOS (for non towered airports) provides prevailing weather conditions as well as procedures affecting airport operations (ie runway/ taxiway closures, TFR’s etc) and is usually updated approximately five minutes ahead of the hour
IRL, the ATIS is typically voiced by DecTalk Huge Harry and at times it does become slightly humorous at how the program interprets dashes and pauses (i.e. “Dewpoint OneOne” instead of Dewpoint One One" or “You have information (pregnant pause) Bravo”
Thanks all. There is so much going on in ATC communications. Going to take more than a month to pick up on it all. 
Every 30 minutes that is and whenever significant changes occur.
Are you in FAA-land or elsewhere? I releases a 100+ radiotelephony manual I wrote when I was a radiotelephony instructor together with my ATC Mod. but its ICAO phraseology added with some Eurocontrol recommendations.
A controller once tried to catch me out. Current info was Foxtrot but I forgot to say that I had it. He said “Have you got information Echo?”. I’d been warned about him so I said “Affirm, I do have Echo. I also have Foxtrot. Try and keep up”.
Got bought a drink in the café later…
2 Likes
HaHaHa. Good on Ya!