Geomagnetic storm watch in effect for May 18

Geomagnetic storm watch in effect for May 18

NOAA SWPC forecasters have issued a geomagnetic storm watch for May 18, 2021, after a pair of coronal mass ejections (CMEs) launched from the Sun on May 13 and 14.

Enhanced solar wind parameters are expected on May 17  due to the influence of a negative polarity Coronal Hole High Speed Stream (CH HSS), followed by further enhancements on May 18 and 19 due to the anticipated arrival of the periphery of a CME that left the Sun on May 13 and a second CME that left the Sun early May 14.

Active to G1 - Minor geomagnetic field conditions are expected, with a chance for isolated G1 storm levels on May 19 due to lingering influences from the May 13 CME, as well as the possible passage of the aforementioned May 14 CME.

While individually those CMEs appear to be weak and insubstantial, they could add up to a geomagnetic storm when they arrive in quick succession this Tuesday, May 18, Dr. Tony Phillips of said.

Space Weather Message Code: WATA20
Serial Number: 895
Issue Time: 2021 May 16 0037 UTC

WATCH: Geomagnetic Storm Category G1 Predicted

Highest Storm Level Predicted by Day:
May 17:  None (Below G1)   May 18:  G1 (Minor)   May 19:  None (Below G1)


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.

Featured image credit: NASA SDO/AIA 131


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