I am not 100% sure on the cause, but it is very possible that it is related to the already reported bug that the NWS servers will supply stale data possibly for several days at a time for certain endpoints on the API. You could be seeing data from a few hours before, say in the early morning hours.
I implemented logic to go around this issue on the forecasts, but I can’t remember if this also occurs for the observations. If you see this again, you can retrieve the API response from https://api.weather.gov/stations/KDAL/observations. The tricky part is that when you do this, you won’t be requesting the data using the exact user key that home assistant uses when it requests. So, you may get up to date information when you do this even though home assistant is getting stale data. But, you can look at the previous time points in the response and see if a previous timepoint matches your HA data. If so, that would further confirm this behavior.