Geomagnetic storm in progress


A geomagnetic storm reaching G1 – Minor levels is currently in progress following the early arrival of July 17th Coronal Mass Ejection (CME).

The interplanetary shockwave produced by the long duration C1 flare on July 17, initially expected to arrive early on July 21, reached the ACE spacecraft at 23:10 UTC on July 19 with an approximate speed of 450 km/s. Magnetometers around the globe registered the CME arrival at 23:55 UTC.

Total IMF strength ranged from 2 to 5 nT until the shock arrival when it reached 17 nT. The Bz component reached a maximum southward deviation of -12 nT upon shock arrival.

Geomagnetic K-index of 5 (G1 – Minor) threshold was first reached at 23:59 UTC, and then at 01:20 UTC and 04:55 UTC. Weak power grid fluctuations can occur under those conditions, minor impact on satellite operations is possible; aurora may be visible at high latitudes.

Image credit: NOAA/SWPC

G2 – Moderate geomagnetic storm levels are expected through 12:00 UTC.


Enhanced solar wind parameters are expected to continue into July 21 due to a negative polarity coronal hole high speed stream (CH HSS) becoming geoeffective.

The greater than 2 MeV electron flux is expected to be at moderate to high levels on July 20 and 21 in response to elevated wind speeds from CH HSS activity. Electron flux is expected to decrease to normal to moderate levels by 12:00 UTC on July 21, continuing into July 22, due to a redistribution of particles in response to the arrival of the anticipated CME and CH HSS. The greater than 10 MeV proton flux is expected to continue at background levels.

SWPC alerts, watches and warnings

Space Weather Message Code: SUMSUD
Serial Number: 218
Issue Time: 2016 Jul 20 0019 UTC

SUMMARY: Geomagnetic Sudden Impulse
Observed: 2016 Jul
19 2355 UTC
Deviation: 64 nT
Station: BOU

NOAA Space Weather Scale descriptions can be found at


Space Weather Message Code: ALTK05
Serial Number: 981
Issue Time: 2016 Jul 19 2358 UTC

ALERT: Geomagnetic K-index of 5
Threshold Reached: 2016 Jul
19 2359 UTC
Synoptic Period: 2100-2400 UTC

Active Warning: Yes
NOAA Scale: G1 – Minor

NOAA Space Weather Scale descriptions can be found at

Potential Impacts: Area of impact primarily poleward of 60 degrees Geomagnetic Latitude.
Induced Currents – Weak power grid fluctuations can occur.
Spacecraft – Minor impact on satellite operations possible.
Aurora – Aurora may be visible at high latitudes, i.e., northern tier of the U.S. such as northern Michigan and Maine.


Space Weather Message Code: WARK06
Serial Number: 339
Issue Time: 2016 Jul 20 0528 UTC

EXTENDED WARNING: Geomagnetic K-Index of 6 expected
Extension to Serial Number: 338
Valid From: 2016 Jul 20 0030 UTC
Now Valid Until: 2016 Jul 20 1200 UTC
Warning Condition: Persistence

NOAA Space Weather Scale descriptions can be found at

Potential Impacts: Area of impact primarily poleward of 55 degrees Geomagnetic Latitude.
Induced Currents – Power grid fluctuations can occur. High-latitude power systems may experience voltage alarms.
Spacecraft – Satellite orientation irregularities may occur; increased drag on low Earth-orbit satellites is possible.
Radio – HF (high frequency) radio propagation can fade at higher latitudes.
Aurora – Aurora may be seen as low as New York to Wisconsin to Washington state.

Featured image: Aurora forecast at 07:55 UTC on July 20, 2016. Credit: NOAA/SWPC

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