NOAA’s Space Weather Prediction Center posted a geomagnetic storm watch at 17:45 UTC on Nov. 5 that calls for minor, G1-level storming on each of three days, Nov. 6, 7 and 8. The notice lists weak power grid fluctuations among the possible effects, along with minor impacts on satellite operations and aurora at high latitudes. It is a watch, not a report that a storm has begun.
Save more, waste less: The Cool Down’s newsletter sends smart, simple changes that help you and the planet in your everyday life.
We may earn a commission if you sign up.
The product is coded A20F and carries serial number 1136. It supersedes serial 1135 from a day earlier, which had called for G1 only on Nov. 6 and 7 and left Nov. 5 below storm level, so the newest version adds one more day to the window.
The G1 call for Nov. 6, 7 and 8, day by day
The alert feed entry for the watch reads “Geomagnetic storm watch, G1 (Minor) predicted for Nov 6, 7, and 8,” and lists the highest expected storm level for each date. It says the impact area is primarily poleward of 60 degrees geomagnetic latitude, which keeps the most noticeable effects near the polar regions. The message carries no extra comment from the forecaster on duty.
The listed effects are weak power grid fluctuations, a minor effect on satellite operations, and aurora visible at high latitudes, with northern Michigan and Maine named as the example locations.
The feed shows the watch arriving amid a run of related alerts. A warning of Kp 4 conditions, serial 5447, was issued on Nov. 4 at 08:19 UTC and has since expired. An electron-flux alert, serial 3767, followed on Nov. 5 at 12:54 UTC, noting that flux above 2 MeV had exceeded 1,000 pfu after a prior-day maximum of 1,477 pfu on Nov. 4. A Type II radio emission alert, serial 1533, logged the flare-related shock beginning at 18:28 UTC the same day.
Coronal hole wind, not a coronal mass ejection, drives the G1 call
The center’s three-day forecast issued at 12:30 UTC on Nov. 5 gives the reasoning. Forecasters wrote that “G1 (Minor) or greater geomagnetic storms are likely on 06-07 Nov due to CH HSS influences,” shorthand for a high-speed stream of solar wind flowing from a coronal hole, an open region of the Sun’s magnetic field. The forecast table builds Kp, the three-hour index that measures geomagnetic disturbance, to 4.00 in the 18-21 UT block on Nov. 6, then 4.67 at 21-00 UT, and reaches 5.00 at 00-03 UT on Nov. 7 before easing to between 3.33 and 3.67 for the rest of that day.
Kp 5 is the threshold for a G1 storm. The forecast peak sits right on it, which is why the call is “minor” and why the margin for a miss in either direction is small.
The forecast discussion issued at 00:30 UTC on Nov. 6 kept the same reasoning. Disturbances are likely on Nov. 6 through 8 from a negative-polarity coronal hole stream, it says, with solar wind speeds having slipped from about 380 to 320 km/s over the previous day and no sustained southward magnetic field yet. G1 storms are likely on all three dates, the discussion adds, with a chance of G2, or moderate, storms on Nov. 7 and 8.
An M3.5 flare and a possible CME on the Sun
The Sun added a second variable on Nov. 5. Sunspot Region 4566 produced an M3.5 flare at 18:33 UTC, and an accompanying Type II radio sweep pointed to a shock moving at roughly 609 km/s. Forecasters noted a possible CME signature in the coronagraph imagery but said more imagery was needed to judge it, so the watch itself does not depend on any ejection. For Nov. 6 through 8, the discussion expects low solar activity overall, with a chance of M-class flares and a slight chance of X-class flares from Regions 4565 and 4566.
Energetic particles were elevated too. The same discussion reports that electron flux above 2 MeV reached high levels, peaking at 2,197 pfu at 17:00 UTC on Nov. 5, and should stay high on Nov. 6 before dropping to moderate on Nov. 7 and 8. Proton levels stayed at background.
G1 in the NOAA scales, and the rest of November
NOAA’s space weather scales page describes a G1 storm as one that can bring weak power grid fluctuations and minor satellite effects, with aurora commonly visible at high latitudes such as northern Michigan and Maine. It puts the Kp level at 5 and estimates about 1,700 G1 events per 11-year solar cycle, or roughly 900 days per cycle. By that count G1 is the most common rung of a scale that runs to G5, and the scale is the framework the watch cites for its grid and satellite language.
Longer-range guidance is calmer. The 27-day outlook issued Nov. 2 predicted mostly quiet to unsettled conditions for the month, with Kp 4 on Nov. 9 and its highest planetary A index, 24 at Kp 5, on Nov. 27. The next three-day forecast arrives at 12:30 UTC on Nov. 6, and it will show whether the Nov. 7 chance of G2 storms was kept or dropped.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
Save more, waste less: Subscribe to The Cool Down →
We may earn a commission if you sign up.
More from Morning Overview
- Tropical Storm Rachel is dumping up to 12 inches on four Mexican states on its way to major hurricane strength
- The FTC says Lens.com doubled the price shoppers saw in Google ads
- Common allergy, bladder and sleep pills tied to sharply higher dementia odds
- NOAA now gives this winter a 75% chance of the strongest El Nino since 1950
