Hey Edward, I think you may have a great situation with tuning.
I live in New England, where as the saying goes, if you don't like the weather, wait a minute.
Over the past couple of weeks my outdoor temp / indoor RH went from 15 degrees / 17% to 40 degrees / 33% with a high bump of 72 degrees /39% just last Thursday. Right now (Sunday), after a wind driven snow squall, it is 28 degrees / 23% RH with an average wind chill factor (35 mph wind plus gusts) pushing that 28 degrees down to 13 degrees, and a potential single digit overnight temp forecast. * Living in a old wooden house with not so great insulation, the lower temps kick up the dryness due to radiator heating system working harder. And the thermostat is set to a constant 62 degrees.
OK, enough weather. Bottom line is there is little stability to the weather here. Net effect on guitars (which live in their cases year round, and in winter with Oasis humidifiers and hygrometers) is that while the guitars do maintain their tuning overall, for each guitar that is a relative tuning with itself, and I cannot count on the tuning being 'standard' across the board. This does not matter much as long as I am just playing without other people / instruments. So while there are seasonal weather swings, there can also be daily and weekly ones too. As Paul mentioned, a couple of cowboy strums will tell me if I really need to check the tuning.
So I am happy when my instruments do stay in relative tuning, and I have few complaints since I have long ago reconciled to the bit of extra work humidifying them and keeping them in tune when needed. Best I can do. So if anyone else has this RH variability, don't give up hope.
* Edit > 3/15/21: Actual wind chill at 1 degree at 6:30 AM this morning. Above text written last night. More dry heat.
Don