Tigfisher, I had that exact same thing happen with my Tigershark 1000, back around 2007 or 2008. Went out early one morning, the low was about 20 degrees (yep, here in coastal SC, it does get that cold) I didn't realize my lines were frozen from the boat sitting on the trailer in the yard, and I ended up running hot.
One thing you can do to make sure this doesn't happen is to make a blowout tool. Get a brass ball valve, a male air hose QC fitting, and a male garden hose fitting, and the fittings to connect the 2 ends to the ball valve.
To use it, thread the male GH end to your flush fitting. Close the ball valve, and connect the QC to an air hose. SLOWLY open the ball valve. The air pressure will purge any remaining water in the lines, and it only takes a few PSI to do it. You don't want to open the valve WAO at 125 PSI to start with. Once you see/hear the water blasting out the jet pump, you can open the ball valve a little more until you only hear air blowing out of the jet unit.
At this point, the water cooling/discharge lines are purged, and will be much less prone to freezing.
BTW, the blowout tool works great for quickly draining the hoses around the yard, to prevent them from freezing, as well.