And this sort of water retension bounce is exactly why folks
who freak out at frequent weighing should not do that.

Completely predictable and expected.

When a new exercise program starts the muscles initially
hoard glycogen carbs to handle the changed short term
load.  Since glycogen is stored dissolved in water that
means there is extra water retention in the muscles.

After a while the muscles adjust to the program as their
long term load and their no longer hoard glycogen for it.
At that point the water used to disolve the glycogen is no
longer retained.  How long it takes for the muscles to
adjust depends on the level of fitness prior to starting
the new program and on the rate of fitness improvement
during the program.  Somewhere between a couple of
weeks and a couple of months.

This reminds of what folks want to lose - Want to lose
fat, work to lose fat, need to focus on the trend not on
the daily water retention bounce.  Want to lose water,
work to lose water, set yourself up for eternal frustration
as fighting water retention is like fighting the tides.  No
matter how much effect you put into it the water comes
back when the tides come back.

The problem with weighing too often - Folks who do not
know about water retnetion issues like muscles hoarding
glycogen freak out.  The problem with NOT weighing
often - Fail to learn what your water retention swing is
and you don't know the size of your no-change range
during maintenance.  If you have a 6 pound water
retention swing (that's the size of mine) and you target
a 4 pound range during maintenance it is physically
impossible to stay in your maintenance range.  There
is no right answer for how often to weigh, just a range of
tradeoffs based on a long list of issues.