CH HSS Windows: G1/G2 watch, then active days
Fast conclusion: the strongest near-term operations signal is NOAA’s forecast for G1–G2 geomagnetic storm conditions on May 15–16 from coronal-hole high-speed-stream influences, followed by additional active windows later in the issue period.
What changed
NOAA’s May 14 3-day forecast gives a greatest expected 3-hour Kp of 5.67, corresponding to G2, and says G1–G2 storms are likely on May 15–16 due to CH HSS influences. NOAA’s weekly outlook extends the broader watch: G1 levels are likely over May 15–17, active conditions are likely on May 18, May 23, and May 27, and unsettled conditions are likely on May 21–22 and May 28–31.
Plain-language orientation
Bz is the magnetic-field component that helps determine whether solar-wind energy couples into Earth’s environment. Southward and sustained Bz is more important than a brief dip. Kp tells how disturbed the geomagnetic field became; Bz and solar-wind speed help explain whether the disturbance is likely to build or fade.
Why it matters
For grid and operations readers, this is a monitoring posture rather than an emergency posture. G1–G2 windows can matter for aurora visibility, GNSS tolerance, HF communications, satellite drag awareness, and grid situational awareness, but the practical action is to keep the relevant dashboards visible and avoid confusing a short Kp rise with a durable infrastructure event.
Watch first
Kp trend, sustained southward Bz, solar-wind speed, and whether conditions last across multiple 3-hour periods.
Do not overread
A recurrent high-speed stream can raise activity without implying severe geomagnetic storming.
Action framework
- May 15–17: keep geomagnetic dashboards visible and treat G1/G2 alerts as the live decision layer.
- May 18, 23, 27: keep a lighter active-condition check, especially for GNSS-sensitive field work, HF communications, satellite operations, and aurora-facing public interpretation.
- May 21–22 and May 28: log unsettled periods but do not promote them as storm windows unless real-time solar-wind conditions strengthen.
Uncertainty line
CH HSS timing and geoeffectiveness can shift. The forecast gives the window; the real-time solar wind decides whether the window becomes operationally meaningful.
Public sources used
Sources are linked directly so readers can verify timing, forecast language, and limits.
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