G4 (Severe) Geomagnetic Storm of April 25, 1984

Name: G4 (Severe) Geomagnetic Storm of April 25, 1984
Start: 1984-04-25T12:00:00.000Z
End: 1984-04-27T03:00:00.000Z
Location: Earth

April 25 to 27, 1984 · 39 hours

A G4 (severe) geomagnetic storm began April 25, 1984, reached Kp 8- and lasted 39 hours, with a daily Ap as high as 103; at that Kp the aurora may be seen from about 47 degrees geomagnetic latitude.

The Kp through the storm

Began Apr 25, 12:00 UTC, peaked in the block from Apr 26, 18:00 UTC, ended Apr 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: 8- (7.67)
NOAA level: G4 Severe
Duration: 39 hours
Highest daily Ap: 103
Highest 3-hour ap: 179
Rank since 1932: 218 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 47 degrees geomagnetic latitude: 38°N in the central US, 37°N in the eastern US, 41°N in the western US and 47°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

Richmond, VA 46.7° geomag.
Lexington, KY 47.0° geomag.
Lexington-Fayette, KY 47.0° geomag.
Louisville, KY 47.2° geomag.
Lakewood, CO 47.3° geomag.
Denver, CO 47.3° geomag.
Aurora, CO 47.3° geomag.
St. Louis, MO 47.3° geomag.
Overland Park, KS 47.4° geomag.
Meads, KY 47.5° geomag.

71 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
April 25, 1984	33	6
April 26, 1984	103	8-
April 27, 1984	26	5+

Flares before it

Peak (UTC)	Class	Region	Before the storm began
Apr 25, 00:01 UTC	X13.0	NOAA 4474	12 hours
Apr 21, 20:17 UTC	X1.7	NOAA 4474	88 hours
Apr 24, 04:20 UTC	X1.0	NOAA 4474	32 hours
Apr 23, 16:40 UTC	M7.2	NOAA 4474	43 hours
Apr 22, 22:58 UTC	M5.0	NOAA 4474	61 hours
Apr 23, 02:01 UTC	M3.6	NOAA 4474	58 hours

The strongest M and X class flares GOES recorded from four days before the storm began to its end, the window in which a coronal mass ejection launched with a flare usually arrives. A flare in this list is context, not proof of the cause: many storms come from coronal holes, and many flares launch nothing toward Earth.

The storm before, Apr 20 The storm after, May 5 Every storm of 1984 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. Flares from NOAA NCEI’s GOES X-ray flare reports (1975 to 2017) and SWPC’s edited solar event lists, public domain; classes as NOAA recorded them at the time.