G4 (Severe) Geomagnetic Storm of January 21, 2005

Name: G4 (Severe) Geomagnetic Storm of January 21, 2005
Start: 2005-01-21T15:00:00.000Z
End: 2005-01-22T06:00:00.000Z
Location: Earth

January 21 to 22, 2005 · 15 hours

A G4 (severe) geomagnetic storm began January 21, 2005, reached Kp 8 and lasted 15 hours, with a daily Ap as high as 66; at that Kp the aurora may be seen from about 45 degrees geomagnetic latitude.

The Kp through the storm

Began Jan 21, 15:00 UTC, peaked in the block from Jan 21, 18:00 UTC, ended Jan 22, 06:00 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 (8.00)
NOAA level: G4 Severe
Duration: 15 hours
Highest daily Ap: 66
Highest 3-hour ap: 207
Rank since 1932: 178 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 45 degrees geomagnetic latitude: 37°N in the central US, 36°N in the eastern US, 39°N in the western US and 45°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

Nashville, TN 45.1° geomag.
Durham, NC 45.1° geomag.
Greensboro, NC 45.2° geomag.
Winston-Salem, NC 45.2° geomag.
Clarksville, TN 45.4° geomag.
Reno, NV 45.4° geomag.
Springfield, MO 45.7° geomag.
Wichita, KS 45.9° geomag.
Chesapeake, VA 46.0° geomag.
Norfolk, VA 46.0° geomag.

84 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
January 21, 2005	66	8
January 22, 2005	33	6

Flares before it

Peak (UTC)	Class	Region	Before the storm began
Jan 20, 07:01 UTC	X7.1	NOAA 10720	32 hours
Jan 19, 08:22 UTC	X1.3	NOAA 10720	55 hours
Jan 19, 07:31 UTC	M6.7	NOAA 10720	55 hours
Jan 18, 15:51 UTC	M4.6	NOAA 10720	71 hours
Jan 19, 10:24 UTC	M2.7	NOAA 10720	53 hours
Jan 21, 10:16 UTC	M1.7	NOAA 10720	5 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, Jan 17 The storm after, Feb 7 Every storm of 2005 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.