NOAA’s Space Weather Prediction Center (SWPC) issued a G2 – Moderate geomagnetic storm watch for April 17 and 18, due to an approaching negative polarity coronal hole high-speed stream (CH HSS) expected to disturb Earth’s magnetic field late on April 17 and through April 18.
The highest expected storm level is below G1 – Minor on April 16, rising to G2 – Moderate on both April 17 and April 18.
G2 storms can produce voltage alarms in high-latitude power systems and may affect transformer operations during prolonged disturbances. Satellite operators can experience orientation irregularities and increased drag on low Earth orbit spacecraft, while high-frequency radio communications may degrade at higher latitudes.
The primary impact area under G2 storms is poleward of 55° geomagnetic latitude, placing the highest infrastructure and communications sensitivity across northern Canada, Alaska, and other high-latitude regions.
Aurora may become visible as far as New York, Wisconsin, and Washington state, depending on local weather, cloud cover, light pollution, and whether geomagnetic activity reaches forecast peak levels during nighttime hours.
The strongest geomagnetic response often depends on how efficiently the solar wind couples with Earth’s magnetosphere, including the orientation of the interplanetary magnetic field. A sustained southward Bz component can increase storm intensity, while weaker coupling can keep activity below forecast thresholds.
Forecasters expect solar wind conditions to become enhanced by mid to late April 17 as a co-rotating interaction region arrives ahead of the high-speed stream. SWPC said solar wind speeds of 600-700 km/s (373-435 mph) are likely during the event based on recurrent values, with elevated conditions expected to persist through April 18.
Solar activity remained low in 24 hours to 12:30 UTC on April 16, with only B- and C-class flares observed from active Region 4419. Two CMEs observed off the northeast and southeast limbs on April 15 were assessed as having no Earth-directed component, while additional CMEs observed off the northwest and west limbs were identified as backside events.
Solar activity is expected to remain low overall through April 18, although Region 4419 retains a chance of producing isolated M-class flares capable of minor to moderate radio blackouts.
References:
1 Forecast Discussion – NOAA/SWPC – Issued at 12:30 UTC on April 16, 2026