G5 (Extreme) Geomagnetic Storm of October 29, 2003

Name: G5 (Extreme) Geomagnetic Storm of October 29, 2003
Start: 2003-10-29T06:00:00.000Z
End: 2003-11-01T03:00:00.000Z
Location: Earth

October 29 to November 1, 2003 · 69 hours · known as the Halloween storms

A G5 (extreme) geomagnetic storm began October 29, 2003, reached Kp 9 and lasted 69 hours, with a daily Ap as high as 204; at that Kp the aurora may be seen from about 40 degrees geomagnetic latitude.

The Kp through the storm

Began Oct 29, 06:00 UTC, peaked in the block from Oct 29, 06:00 UTC, ended Nov 1, 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 (9.00)
NOAA level: G5 Extreme
Duration: 69 hours
Highest daily Ap: 204
Highest 3-hour ap: 400
Rank since 1932: 2 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 40 degrees geomagnetic latitude: 32°N in the central US, 31°N in the eastern US, 34°N in the western US and 40°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

Anaheim, CA 40.0° geomag.
Corona, CA 40.1° geomag.
Los Angeles, CA 40.2° geomag.
Riverside, CA 40.2° geomag.
Moreno Valley, CA 40.2° geomag.
Chandler, AZ 40.2° geomag.
Oxnard, CA 40.2° geomag.
Hollywood, CA 40.2° geomag.
Pomona, CA 40.3° geomag.
Gilbert, AZ 40.3° geomag.

164 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
October 29, 2003	204	9
October 30, 2003	191	9
October 31, 2003	117	8+
November 1, 2003	26	5

Flares before it

Peak (UTC)	Class	Region	Before the storm began
Oct 28, 11:10 UTC	X17.2	NOAA 10486	19 hours
Oct 29, 20:49 UTC	X10.0	NOAA 10486	during it
Oct 26, 06:54 UTC	X1.2	NOAA 10486	71 hours
Oct 26, 18:19 UTC	X1.2	NOAA 10484	60 hours
Oct 26, 21:40 UTC	M7.6	NOAA 10484	56 hours
Oct 27, 12:43 UTC	M6.7	NOAA 10486	41 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, Oct 24 The storm after, Nov 4 Every storm of 2003 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. 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.