A patch of the Sun that solar forecasters had effectively written off produced the strongest flare of its reporting period and a burst of high-energy protons strong enough to leave visible specks across a spacecraft camera. The region, catalogued as Plage Region 4520, had decayed to plage roughly two days earlier, meaning it had lost the dark sunspots that normally mark a region capable of significant eruptions.

The timing matters because a separate set of ejections is arriving now. NOAA's Space Weather Prediction Center has issued a G1 (Minor) geomagnetic storm watch for today, and its most recent three-day outlook adds a slight chance of reaching G2 (Moderate) levels if the ejections launched over the preceding days arrive as modeled. Confidence in the exact timing and strength of those arrivals is low, and forecasters have said so plainly.

For most households, a G1 storm is close to a non-event. It sits at the bottom of NOAA's five-step geomagnetic scale, and the listed effects are weak power grid fluctuations, minor satellite operations issues, and aurora that becomes visible farther from the poles than usual. Nobody needs to prepare anything. The reason to pay attention is different: the flare's origin is a reminder that forecasters cannot fully rule out eruptions from regions that look finished.

A Region That Should Have Been Finished

Solar physicists track active regions partly by their sunspots. A region bristling with dark, magnetically complex spots is the one to watch. When those spots fade and the area decays to plage, a bright patch of hotter gas where a sunspot group used to be, it usually signals a region winding down.

Region 4520 did not follow that script. It fired an M1.0 flare at 15:04 UTC on September 5 from a position near the Sun's southwest limb, and that flare turned out to be the strongest event of the 24-hour reporting period despite the region's decayed state. The M-class designation places it in the moderate tier of NOAA's flare scale, well below the X-class events that drive major disruptions. The flare also triggered a brief R1 (Minor) radio blackout affecting high-frequency communications over the northeastern part of South America.

EarthSky's daily sun coverage, written by a team that includes solar astrophysicist C. Alex Young, described the spike in protons above 100 MeV as relatively uncommon and noted that it points to real eruptive power despite the flare's modest class. Young is Associate Director for Science in the Heliophysics Science Division at NASA Goddard Space Flight Center.

The Proton Numbers Behind the Radiation Storm

NOAA measures solar radiation storms by counting energetic protons striking detectors aboard the GOES satellites. According to the agency's forecast discussion, the greater than 10 MeV proton flux began climbing at 15:30 UTC on September 5 and crossed the 10 particle flux unit event threshold at 16:15 UTC, peaking at 17.8 pfu at 16:45 UTC before the event ended at 21:35 UTC. That crossing put conditions at S1 (Minor) on NOAA's solar radiation storm scale. The event summary NOAA issued afterward rounded the peak to 18 pfu.

The more unusual measurement came at higher energy. The greater than 100 MeV flux also began rising at 15:30 UTC, crossed its 1 pfu threshold at 15:45 UTC, and reached a maximum of 1.16 pfu at 15:50 UTC. It fell back below threshold by 16:15 UTC. That is roughly half an hour above the mark, a brief excursion rather than a sustained event, but higher-energy protons penetrate more shielding and are less commonly produced by a flare of this size.

Those protons left a visible signature. As the ejection expanded outward, imagery from the SOHO LASCO C2 coronagraph showed flickering white specks scattered across the frame. Each speck is an energetic proton striking the camera detector directly, a phenomenon operators sometimes call snow.

Separating the Radiation Event From the Storm Forecast

Here is where the story splits, and where readers following aurora coverage should be careful. The ejection that accompanied the M1.0 flare from Region 4520 is not the one driving the current forecast. Modeling indicates that the ejection will sweep ahead of Earth in its orbit rather than striking the planet.

The geomagnetic activity in the forecast comes from active region AR4524, which remained the most magnetically complex region on the visible disk even as it slowly decayed. That region produced a C8.5 flare with an associated ejection estimated at 1,110 kilometers per second and a slower C6.5 event at roughly 873 kilometers per second. SWPC modeling put a possible combined arrival for those and other recent ejections early on September 8, with a halo ejection tied to a later C5.0 flare potentially arriving late on September 8 into September 9.

A high-speed stream from a coronal hole and a solar sector boundary crossing are converging on the same window, which is why forecasters expect disturbed conditions to persist rather than pass in a single sharp jolt.

Where the Aurora Might Reach and What Stays Uncertain

NOAA's watch describes G1 impacts as reaching primarily poleward of 60 degrees geomagnetic latitude, with aurora possible at high latitudes including the northern tier of the United States, in states such as northern Michigan and Maine. If conditions strengthen toward the G2 range that the three-day forecast flags as a slight possibility, viewing chances improve farther south. Whether that happens depends heavily on the orientation of the magnetic field embedded in the arriving ejections. A sustained southward field couples energy into Earth's magnetosphere efficiently; a northward orientation largely deflects it. Forecasters cannot measure that orientation until the material is roughly an hour from Earth.

Two limitations deserve emphasis. First, SWPC stated directly that confidence is low on both the timing and the magnitude of these arrivals, so any specific viewing hour circulating online is an estimate rather than a schedule. Second, storm levels are assigned after conditions are observed, not before. A watch is a forecast, while an alert means a threshold has actually been crossed. Understanding that difference is most of what the NOAA space weather scales are for.

Readers who want to track this themselves should watch SWPC's alerts, watches and warnings page, which posts observed threshold crossings before they appear in news coverage. Aurora photographers in the northern states should treat the next two nights as a possibility rather than a plan, and check the 30-minute aurora forecast before driving anywhere. The next scheduled forecast discussion and three-day forecast are issued at 00:30 and 12:30 UTC daily. Radio operators and anyone relying on high-frequency communication should expect occasional degradation, with the most recent forecast putting the chance of R1 to R2 radio blackouts at 15 percent through the period.

The practical bottom line is modest. A minor geomagnetic storm poses no risk to household electronics, health, or air travel. The genuinely interesting element is scientific: a solar region that had shed its sunspots still had enough stored magnetic energy to accelerate protons past 100 MeV, which is a useful caution against reading a quiet-looking Sun as a settled one.

What Readers Want to Know

What actually happened on the Sun? A solar region that had already decayed to plage, meaning it had lost its sunspots, produced an M1.0 flare at 15:04 UTC on September 5. The eruption accelerated protons toward Earth strongly enough to cross both the 10 MeV and 100 MeV measurement thresholds, triggering an S1 (Minor) solar radiation storm.

Is a G1 storm dangerous? No. G1 is the lowest level on NOAA's five-step geomagnetic storm scale. The listed effects are weak power grid fluctuations, minor satellite operations issues, and aurora visible farther from the poles. It poses no risk to household electronics or personal health.

Will the flare's coronal mass ejection hit Earth? No. Modeling indicates the ejection associated with the M1.0 flare will pass ahead of Earth in its orbit. The geomagnetic activity in the current forecast comes from separate ejections launched by active region AR4524.

Where might the aurora be visible? NOAA's G1 watch describes aurora as possible at high latitudes, including the northern tier of the United States in states such as northern Michigan and Maine. If activity reaches the G2 range that forecasters flagged as a slight possibility, chances improve farther south. Visibility depends on the magnetic orientation of the arriving material, which cannot be measured far in advance.

What are the specks visible in the spacecraft imagery? They are energetic protons striking the SOHO LASCO camera detector directly. Operators sometimes describe the effect as snow. It is a visible sign that a solar radiation storm is underway.

When is the next official update? NOAA's Space Weather Prediction Center issues its three-day forecast and forecast discussion twice daily, at 00:30 and 12:30 UTC. Observed threshold crossings appear on the agency's alerts, watches and warnings page before they reach news coverage.

How much confidence do forecasters have in the timing? Low, and they have said so explicitly. SWPC noted that confidence remains low on both the timing and the magnitude of the coronal mass ejection arrivals, so specific hours circulating online should be treated as estimates.