Update 5:30 p.m. May 11: PJM Extends GMD Warning through May 12

No Significant Impacts to Grid Operations Expected


PJM has extended a Geomagnetic Disturbance Warning through the end of Sunday, May 12.

PJM initially issued a warning on May 10 to its generation and transmission companies that a possible geomagnetic disturbance (GMD) could affect the PJM system between 1:48 p.m. and 9 p.m. on May 10.

With an extended period of heightened solar activity, PJM observed persistent geomagnetically induced current (GIC) at multiple stations and upgraded the warning to a Geomagnetic Disturbance Action at 10:15 p.m. on May 10. The GMD Action was canceled at noon on May 11 but the GMD Warning remained in effect , and the warning has been extended through the end of Sunday, May 12.

No major impacts to grid operations have been reported.

The extended warning through May 12 is for a possible disturbance of K-7 through 11:59 p.m. The National Oceanic and Atmospheric Administration (NOAA) classifies level K-7 as “strong.”

PJM does not anticipate any significant impacts or emergency conditions at this time. PJM is monitoring GMD activity closely and is in close coordination with generation and transmission owners and neighboring grid operators.  

How Do Geomagnetic Disturbances Affect the Grid?

Geomagnetic disturbances, also known as solar magnetic disturbances, are caused by activity on the sun’s surface.  During solar storms, sunspots, solar flares or other phenomena may produce large clouds of plasma, known as coronal mass ejections. These may induce powerful electric currents from above or within the earth that may travel through high-voltage transmission facilities. These currents may flow through grounded grid equipment, usually transformers. High current levels have potential to disrupt or damage transmission facilities.

For example, in March 1989 a major disturbance caused a nine-hour blackout in Quebec and severely damaged a Salem Nuclear Power Plant transformer in Salem County, New Jersey.

Solar activity and the earth’s magnetic field is monitored by NOAA’s Space Weather Prediction Center. Alerts and warnings are issued to grid operators so they may prepare for possible impacts of space weather.  NOAA’s alerts prompted PJM’s Emergency Procedures notice.

How Does PJM Help Protect Against Geomagnetic Disturbances?

PJM responds to NOAA alerts rated above a certain threshold by issuing a warning to generation and transmission operators to prepare.

To increase awareness of possible issues, PJM members have installed special equipment to detect and measure ground-induced currents. When a geomagnetic disturbance is forecast, PJM monitors these installed detectors at various locations. Should sustained ground currents at a certain level be detected, the PJM Manual for Emergency Operations details actions PJM and its members take in response. Read more about geomagnetic storms and their impacts on the NOAA website.