The solar flare on 12/13 produced an X3 flare with the following risks associated to this type of event.
S 3 Strong
Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in high-flying aircraft at high latitudes may be exposed to radiation risk.***
Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar panel are likely.
Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely.
*** High energy particle measurements (>100 MeV) are a better indicator of radiation risk to passenger and crews. Pregnant women are particularly susceptible.
The following would be a -worst case- scenario once the flare interacts with the Earth's geomagnetic field. A few years ago a geomagnetic storm did over $15 million (Candian) damge to Ontario's power companies.
G 5 Extreme
Power systems: : widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts. Transformers may experience damage.
Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites.
Other systems: pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40° geomagnetic lat.)**.
** For specific locations around the globe, use geomagnetic latitude to determine likely sightings (Tips on Viewing the Aurora)