Gulfstream IV First Officer reported rapid loss of altitude while traversing weather conditions that included static discharges and turbulence. The flight then experienced loss of cabin pressurization prompting them to request an immediate descent.

Narrative

I was the SIC on this flight; PIC was Pilot flying. We were at 45;000 feet when we saw lightning about 50 miles ahead; below us. PIC decided to deviate right since that area looked clearer. The radar showed only that nearby cell; so we continued. A few minutes later; we began seeing heavy static discharges and entered moderate turbulence. We lost about 3;000 feet; and our speed dropped from Mach .78 to .72. Both the autothrottle and autopilot disconnected. PIC managed the speed manually and began climbing back toward 45;000 feet while still in turbulence.During this time; the ice detector light came on; followed by a Cabin Pressure Low CAS message and its checklist. We ran the associated checklist. We also heard a hissing sound. We immediately donned my oxygen mask and requested a descent. We descended steadily at about 2;500 feet per minute. I informed ATC that we had lost pressurization and needed to descend; and they cleared us to 11;000 feet. We landed safely without declaring an emergency.