In No. 22 I suggested that we might want to look at the barometer trends before we fly. That sent me back to the 2012 data I have (near DC which is why I am in here typing instead of outside flying). I picked out several of the trends in that data set and thought (hope) they might be of some interest WRT this question. A trend represents an appreciable period of time over which barometric pressure varies linearly with time (plots as a straight line on a curve). Each up trend is followed by downward pressure change (but it may be to jaggy for me to have considered it linear and, of course there are times when the pressure is stagnant or slowly changing too. Here are some of the data.
Trend 0.736 mB/hr ( 5.02 ft/15min); Duration of trend: 9.05 Hrs Starting at 2012-12-22 12:55:07
Trend -1.218 mB/hr (-8.32 ft/15min); Duration of trend: 3.47 Hrs Starting at 2012-12-23 10:13:28
Trend 0.306 mB/hr ( 2.09 ft/15min); Duration of trend: 15.10 Hrs Starting at 2012-12-23 17:32:58
Trend -1.081 mB/hr (-7.38 ft/15min); Duration of trend: 3.95 Hrs Starting at 2012-12-24 10:58:33
Trend 0.773 mB/hr ( 5.28 ft/15min); Duration of trend: 7.40 Hrs Starting at 2012-12-25 01:03:27
Trend 0.609 mB/hr ( 4.16 ft/15min); Duration of trend: 7.22 Hrs Starting at 2012-12-25 14:18:28
Trend -2.650 mB/hr (-18.09 ft/15min); Duration of trend: 6.56 Hrs Starting at 2012-12-26 09:51:36
Trend 1.217 mB/hr ( 8.31 ft/15min); Duration of trend: 7.54 Hrs Starting at 2012-12-27 02:24:49
Trend 0.990 mB/hr ( 6.76 ft/15min); Duration of trend: 10.46 Hrs Starting at 2012-12-27 13:44:36
Trend -1.496 mB/hr (-10.21 ft/15min); Duration of trend: 3.61 Hrs Starting at 2012-12-29 03:17:58
Trend -1.741 mB/hr (-11.89 ft/15min); Duration of trend: 3.32 Hrs Starting at 2012-12-29 10:11:23
Trend 1.325 mB/hr ( 9.05 ft/15min); Duration of trend: 3.61 Hrs Starting at 2012-12-29 17:29:37
Trend 0.901 mB/hr ( 6.15 ft/15min); Duration of trend: 5.63 Hrs Starting at 2012-12-29 21:32:43
Trend 1.385 mB/hr ( 9.46 ft/15min); Duration of trend: 4.48 Hrs Starting at 2012-12-30 05:21:15
Trend 1.057 mB/hr ( 7.22 ft/15min); Duration of trend: 2.82 Hrs Starting at 2012-12-30 14:31:58
Trend -1.321 mB/hr (-9.02 ft/15min); Duration of trend: 3.01 Hrs Starting at 2012-12-31 10:12:51
The message here is that there are fairly frequent windows of several hours duration in which we might expect a barometric altimeter reading to differ by as much as 18 feet from takeoff to landing in a 15 minute flight. But we wouldn't have been flying that day because it was pretty windy and there was some snow and rain (and there were no SOLOs).
I guess the other part of the message is that if you see or have seen inconsistent altitude between beginning and end of flight you can go to
Weather History & Data Archive | Weather Underground and check the barometer readings at the relevant time and place to estimate the trend and compare to the examples here.