G 5 Extreme
HF radio propagation may be impossible in many areasfor one to two days, satellite navigation may be degraded for days,low-frequency radio navigation can be out for hours, and aurora hasbeen seen as low as Florida and southern Texas.
G 4 Severe
HF radio propagation sporadic, satellite navigationdegraded for hours, low-frequency radio navigation disrupted, andaurora has been seen as low as Alabama and northern California.
G 3 Strong
HF radio may be intermittent, and aurora has beenseen as low as Illinois and Oregon.
G 2 Moderate
HF radio propagation can fade at higher latitudes,and aurora has been seen as low as New York and Idaho.
G 1 Minor
Migratory animals are affected at this and higherlevels; aurora is commonly visible at high latitudes (northernMichigan and Maine).
S 5 Extreme
Complete blackout of HF communications possiblethrough the polar regions, and position errors make navigationoperations extremely difficult.
S 4 Severe
Blackout of HF radio communications through the polarregions and increased navigation errors over several days are likely.
S 3 Strong
Degraded HF radio propagation through the polarregions and navigation position errors likely.
S 2 Moderate
Small effects on HF propagation through the polarregions and navigation at polar cap locations possiblyaffected.
S 1 Minor
Minor impacts on HF radio in the polar regions.
R 5 Extreme
Complete HF radio blackout on the entire sunlit sideof the Earth lasting for a number of hours. This results in no HFradio contacts.
R 4 Severe
HF radio communication blackout on most of the sunlitside of Earth for one to two hours. HF radio contact lost during thistime.
R 3 Strong
Wide area blackout of HF radio communication, loss ofradio contact for about an hour on sunlit side of Earth.
R 2 Moderate
Limited blackout of HF radio communication on sunlitside, loss of radio contact for tens of minutes.
R 1 Minor
Weak or minor degradation of HF radio communicationon sunlit side, occasional loss of radio contact.