G5 (Extreme) Geomagnetic Storm of March 23, 1946

March 23 to 27, 1946 · 78 hours

A G5 (extreme) geomagnetic storm began March 23, 1946, reached Kp 9- and lasted 78 hours, with a daily Ap as high as 195; at that Kp the aurora may be seen from about 42 degrees geomagnetic latitude.

The Kp through the storm

Began Mar 23, 21:00 UTC, peaked in the block from Mar 25, 15:00 UTC, ended Mar 27, 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: 9- (8.67)
NOAA level: G5 Extreme
Duration: 78 hours
Highest daily Ap: 195
Highest 3-hour ap: 300
Rank since 1932: 28 of 4,139

How far south the aurora could have been seen

At Kp 9- NOAA’s scales put the aurora’s reach at about 42 degrees geomagnetic latitude: 33°N in the central US, 32°N in the eastern US, 36°N in the western US and 42°N in northern Europe.

NOAA says a G5 storm’s aurora has been seen as low as Florida and southern Texas.

US cities within reach, the southernmost first

Salinas, CA 42.4° geomag.
Birmingham, AL 42.4° geomag.
Albuquerque, NM 42.5° geomag.
Henderson, NV 42.6° geomag.
Spring Valley, NV 42.6° geomag.
Paradise, NV 42.6° geomag.
Fresno, CA 42.7° geomag.
Las Vegas, NV 42.7° geomag.
North Las Vegas, NV 42.7° geomag.
Sunrise Manor, NV 42.7° geomag.

122 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
March 23, 1946	23	6+
March 24, 1946	117	8
March 25, 1946	195	9-
March 26, 1946	51	6+
March 27, 1946	30	5

The storm before, Mar 22 The storm after, Mar 27 Every storm of 1946 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 2026-09-25.