G4 (Severe) Geomagnetic Storm of July 24, 2004

Name: G4 (Severe) Geomagnetic Storm of July 24, 2004
Start: 2004-07-24T12:00:00.000Z
End: 2004-07-26T03:00:00.000Z
Location: Earth

July 24 to 26, 2004 · 39 hours

A G4 (severe) geomagnetic storm began July 24, 2004, reached Kp 8 and lasted 39 hours, with a daily Ap as high as 154; at that Kp the aurora may be seen from about 45 degrees geomagnetic latitude.

The Kp through the storm

Began Jul 24, 12:00 UTC, peaked in the block from Jul 25, 15:00 UTC, ended Jul 26, 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 (8.00)
NOAA level: G4 Severe
Duration: 39 hours
Highest daily Ap: 154
Highest 3-hour ap: 207
Rank since 1932: 138 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
July 24, 2004	37	6
July 25, 2004	154	8
July 26, 2004	47	7+

Flares before it

Peak (UTC)	Class	Region	Before the storm began
Jul 22, 00:32 UTC	M9.1	NOAA 10652	59 hours
Jul 20, 12:32 UTC	M8.6	NOAA 10652	95 hours
Jul 25, 05:51 UTC	M7.1	NOAA 10652	during it
Jul 24, 18:50 UTC	M2.5	NOAA 10652	during it
Jul 23, 17:28 UTC	M2.2	NOAA 10652	19 hours
Jul 25, 13:49 UTC	M2.2	NOAA 10652	during it

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, Jul 22 The storm after, Jul 26 Every storm of 2004 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.