G4 (Severe) Geomagnetic Storm of July 14, 1960

July 14 to 17, 1960 · 60 hours

A G4 (severe) geomagnetic storm began July 14, 1960, reached Kp 8+ and lasted 60 hours, with a daily Ap as high as 93; at that Kp the aurora may be seen from about 43 degrees geomagnetic latitude.

The Kp through the storm

Began Jul 14, 15:00 UTC, peaked in the block from Jul 16, 00:00 UTC, ended Jul 17, 03:00 UTC.

From 00 UT the day before to the end of the day after. Blocks in the storm are colored by level; the rest are gray.

The storm

Peak Kp: 8+ (8.33)
NOAA level: G4 Severe
Duration: 60 hours
Highest daily Ap: 93
Highest 3-hour ap: 236
Rank since 1932: 90 of 4,139

How far south the aurora could have been seen

At Kp 8+ NOAA’s scales put the aurora’s reach at about 43 degrees geomagnetic latitude: 35°N in the central US, 34°N in the eastern US, 37°N in the western US and 44°N in northern Europe.

NOAA says a G4 storm’s aurora has been seen as low as Alabama and northern California.

US cities within reach, the southernmost first

San Francisco, CA 43.3° geomag.
Little Rock, AR 43.3° geomag.
Oakland, CA 43.4° geomag.
Modesto, CA 43.4° geomag.
Huntsville, AL 43.6° geomag.
Stockton, CA 43.7° geomag.
Oklahoma City, OK 43.7° geomag.
New South Memphis, TN 43.8° geomag.
Memphis, TN 43.9° geomag.
Santa Rosa, CA 44.0° geomag.

106 US cities of 150,000 people or more sit at or poleward of that line. Low on the northern horizon under a dark, clear sky; not a record of sightings.

Tonight’s aurora forecast

Day by day

The daily Ap is the mean of the day’s eight three-hour ap values.

UT day	Daily Ap	Highest Kp that day
July 14, 1960	40	6+
July 15, 1960	93	8
July 16, 1960	77	8+
July 17, 1960	24	5+

The storm before, Jun 29 The storm after, Jul 19 Every storm of 1960 The strongest on record This day in weather history Tonight’s aurora forecast

Sources

Kp and ap from GFZ Helmholtz Centre for Geosciences, Geomagnetic Observatory Niemegk, licensed CC BY 4.0: Matzka, J., Stolle, C., Yamazaki, Y., Bronkalla, O. and Morschhauser, A., 2021, The geomagnetic Kp index and derived indices of geomagnetic activity, Space Weather, doi:10.1029/2020SW002641; data doi:10.5880/Kp.0001. Storms, levels and aurora reach worked out by WeatherOverTime from those values and NOAA’s space weather scales. Definitive through August 31, 2026; later values are preliminary. Rebuilt 2026-09-24.