G2 (Moderate) Geomagnetic Storm of May 20, 1984

Name: G2 (Moderate) Geomagnetic Storm of May 20, 1984
Start: 1984-05-20T15:00:00.000Z
End: 1984-05-23T03:00:00.000Z
Location: Earth

May 20 to 23, 1984 · 60 hours

A G2 (moderate) geomagnetic storm began May 20, 1984, reached Kp 6 and lasted 60 hours, with a daily Ap as high as 45; at that Kp the aurora may be seen from about 55 degrees geomagnetic latitude.

The Kp through the storm

Began May 20, 15:00 UTC, peaked in the block from May 21, 00:00 UTC, ended May 23, 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: 6 (6.00)
NOAA level: G2 Moderate
Duration: 60 hours
Highest daily Ap: 45
Highest 3-hour ap: 80
Rank since 1932: 1,114 of 4,139

How far south the aurora could have been seen

At Kp 6 NOAA’s scales put the aurora’s reach at about 55 degrees geomagnetic latitude: 47°N in the central US, 46°N in the eastern US, 49°N in the western US and 56°N in northern Europe.

NOAA says a G2 storm’s aurora has been seen as low as New York and Idaho.

US cities within reach, the southernmost first

Anchorage, AK 61.9° geomag.

1 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
May 20, 1984	30	5
May 21, 1984	45	6
May 22, 1984	32	5+
May 23, 1984	30	6-

Flares before it

Peak (UTC)	Class	Region	Before the storm began
May 20, 22:41 UTC	X10.1	NOAA 4492	during it
May 19, 22:00 UTC	X4.1	NOAA 4492	17 hours
May 21, 20:27 UTC	X2.7	NOAA 4492	during it
May 22, 15:01 UTC	M6.3	NOAA 4492	during it
May 21, 03:26 UTC	M5.7		during it
May 20, 05:43 UTC	M5.4	NOAA 4492	9 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, May 19 The storm after, May 24 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.