[tz] Yukon to move to year-round PDT

[Chris Walton]

> From: tz <tz-bounces at iana.org> On Behalf Of Brian Inglis
> Sent: March 6, 2020 5:07 PM
> To: tz at iana.org
> Subject: Re: [tz] Yukon to move to year-round PDT
> 
> On 2020-03-05 16:10, Chris Walton wrote:
> >>>> I agree with Michael D.
> >>>>
> >>>> There are four existing zones that are already on permanent UTC-7:
> >>>> 	America/Dawson_Creek
> >>>> 	America/Creston
> >>>> 	America/Fort_Nelson
> >>>> 	America/Phoenix
> >>>> None of these zones makes use the DST bit.  The time zone is displayed
> year round as MST instead of PDT.  I don't think anybody complains about it.
> >>>>
> >>>> I don't see any compelling reason to treat the two Yukon zones
> (America/Whitehorse & America/Dawson) any differently than the four
> existing UTC-7 zones.
> >>>>
> >>> Historic timestamps?
> >> Historic timestamps and their time zone abbreviations do not change.
> Nobody is suggesting that they should be changed.
> >> e.g. America/Dawson already supports all the historical time zone
> abbreviations that have been used in Yukon Territory since 1900:
> >>      PDT, PST, YDDT, YDT, YPT, YST , & YWT.
> >> The proposed change would force all dates that occur after March
> 14/2021 to have an MST time zone abbreviation.
> >> All dates that occur before March 14/2021 would continue to be displayed
> with the correct historical time zone abbreviations.
> > Correction: the change takes place this upcoming weekend (March 8/2020).
> It is not March 14/2021 as I indicated in my previous e-mail.
> 
> The change takes place in November; this weekend proceeds as normal.
OK.  The wording in the new release says "The spring 2020 seasonal time change will go ahead as planned this Sunday, March 8.  After that, Yukon will remain on Pacific Daylight Saving Time."
Thus any new time zone rules don't technically need to take effect until Nov 1/2020.
A change in November could be handled similarly to the America/Grand_Turk change that took place on Nov 1 2015 in which:
  a) the time of day did not change (i.e. nobody had to reset their clocks or watches). 
  b) time zone abbreviation flipped from EDT to AST.
$ zdump -v America/Grand_Turk | grep '2015 UTC = Sun Nov  1'
America/Grand_Turk  Sun Nov  1 05:59:59 2015 UTC = Sun Nov  1 01:59:59 2015 EDT isdst=1 gmtoff=-14400
America/Grand_Turk  Sun Nov  1 06:00:00 2015 UTC = Sun Nov  1 02:00:00 2015 AST isdst=0 gmtoff=-14400
-chris