A decaying sunspot nearing the Sun's western edge produced the strongest flare of the day, but the aurora chance for northern-tier states hinges on a separate stream of fast solar wind.

Sunspot region AR4551 fired a moderate M-class solar flare early Monday, Oct. 19, the strongest eruption on the Sun in the past day, according to NOAA's Space Weather Prediction Center (SWPC). The flare peaked at 09:03 UTC (5:03 a.m. EDT) and caused a minor R1 radio blackout on the sunlit side of Earth, which at that hour was centered over southern Africa, EarthSky reported.

The flare is not what drives the geomagnetic storm watch posted for Tuesday, Oct. 20. SWPC's G1 (Minor) watch, issued at 17:24 UTC Oct. 18 (1:24 p.m. EDT), is tied to a high-speed stream of solar wind flowing from a coronal hole, an open region in the Sun's outer atmosphere. Forecasters found no Earth-directed coronal mass ejection (CME) linked to the flare.

For most households, that adds up to a modest event — G1 is the lowest step on NOAA's five-level geomagnetic scale. NOAA's watch text says a G1 storm can bring weak power grid fluctuations and minor satellite effects, with aurora possible at high latitudes such as northern Michigan and Maine. The practical question for people who saw last weekend's display is whether AR4551 still has a larger eruption in it, and forecasters put those odds as limited but real.

AR4551 Is Turning Away, but Its Flare Risk Lingers

SWPC classified the event as an M1.6 flare in its forecast discussion issued 00:30 UTC Oct. 20, while EarthSky's preliminary tally listed it as M1.7. The region sat at S15W59, well into the Sun's western hemisphere, with a beta-gamma magnetic layout that can store energy for moderate flares.

SWPC also noted that the region "began to show signs of decay" as it moved toward the western edge of the solar disk, losing many of its intermediate spots. Because AR4551 is rotating away from the center of the Earth-facing side, any CME it launches from here is less likely to strike Earth head-on.

Flares are ranked A, B, C, M, and X, with each letter marking a tenfold jump in X-ray output. NOAA translates its radio effects onto its space weather scales, where an R1 event means weak or brief degradation of high-frequency radio on the daylit side of the planet.

SWPC gave a 25% chance of M-class flares through Oct. 22, mostly from AR4551 and a second region, AR4557. Its 3-day forecast issued at 12:30 UTC on Oct. 19 put the daily chance of R1 to R2 radio blackouts at 30% and of R3 or stronger blackouts at 10% through Oct. 21.

A Coronal Hole Stream Drives the Oct. 20 Watch

The same 3-day forecast said the greatest expected planetary K-index (Kp) for Oct. 19 to Oct. 21 is 4.67, which falls in the G1 range. Forecasters wrote that "G1 (Minor) geomagnetic storms are likely late 19 Oct and early 20 Oct" as the coronal hole stream arrives. The highest forecast window on Oct. 20 was 03:00 to 06:00 UTC (11 p.m. EDT Oct. 19 to 2 a.m. EDT Oct. 20).

As of 00:00 UTC Oct. 20, the stream had not yet taken hold. NOAA's planetary K-index readings through that time stayed at Kp 1 or lower, and the overnight discussion described the geomagnetic field as quiet over the prior 24 hours. Solar wind speeds averaged about 350 to 400 kilometers per second (roughly 780,000 to 895,000 miles per hour), near background levels.

SWPC expects weak enhancements on Oct. 20, active conditions on Oct. 21 and mostly unsettled conditions on Oct. 22 as the stream fades. Coronal hole streams usually build gradually, so storm levels can arrive late, run weaker than forecast, or not materialize. EarthSky also flagged a slow CME from Oct. 16 that may brush Earth, though its arrival remains uncertain.

Last Weekend's G3 Storm Set a Higher Bar

Nature World News previously reported that a suspected cannibal CME pushed the Oct. 10 storm to G3, a level above NOAA's G2 watch at the time. SWPC said in a G3 storm notice that G3 conditions began at 17:58 UTC Oct. 10 (1:58 p.m. EDT) after a CME from Oct. 8 reached Earth. That eruption followed an M6.7 flare on Oct. 8, according to SWPC's alert log.

A G3 storm corresponds to Kp 7, while G1 corresponds to Kp 5. The Oct. 10 storm pushed aurora well beyond the usual zone across Europe and parts of North America; a G1 stream generally keeps it near the Canadian border.

Aurora Odds and Practical Checks for Northern-Tier States

The best chances fall in Alaska and along the northern tier, including Washington, Montana, North Dakota, Minnesota, northern Michigan and Maine, from dark sites with a clear view north. Residents of Chicago, New York, Denver, or Seattle's light-polluted core should not expect a visible display at G1 levels. Phone cameras often record faint color low on the horizon that the eye misses.

Before heading out, check SWPC's alerts page for any K-index warning or alert, the Kp index and the 30-minute aurora forecast, along with cloud cover from the local National Weather Service office. A waxing Moon, about 10 days past the Oct. 10 new Moon, will add sky glow. Ham radio operators and pilots on polar routes may notice brief high-frequency radio fading if another M-class flare erupts.

No household action is needed — grid operators routinely manage G1 conditions, and GPS and phone service are not expected to be affected in any noticeable way. The main unknowns are whether the stream reaches G1 at all and whether AR4551 produces a larger flare before it rotates out of view.

SWPC issues forecast updates at 00:30 and 12:30 UTC (8:30 p.m. and 8:30 a.m. EDT), with the next scheduled discussion at 12:30 UTC Oct. 20. Nature World News will report any upgrade, cancellation, or new Earth-directed CME.

What Readers Want to Know

What happened on the Sun on Oct. 19? Sunspot region AR4551 produced an M1.6 flare, per SWPC, that peaked at 09:03 UTC (5:03 a.m. EDT). It caused a minor R1 radio blackout on Earth's sunlit side and did not launch an Earth-directed CME.

Is a geomagnetic storm forecast? Yes, a minor one. SWPC has a G1 watch for Oct. 20 tied to a coronal hole solar wind stream, not to the flare. As of 00:00 UTC Oct. 20, storm levels had not been reached.

Where could the northern lights appear? At G1 levels, NOAA says aurora may be visible at high latitudes, such as northern Michigan and Maine. Alaska and states along the Canadian border have the best odds under clear, dark skies.

Is this storm a risk to the power grid or my phone? Not in any meaningful way for households. G1 storms can cause weak grid fluctuations that operators routinely handle.

Could AR4551 still produce a big flare? It is possible. SWPC gives a 25% chance of M-class flares through Oct. 22, and a 10% daily chance of R3 or stronger radio blackouts through Oct. 21.

When is the next official update? SWPC updates its forecasts at 00:30 and 12:30 UTC daily. The next scheduled discussion is at 12:30 UTC on Oct. 20 (8:30 a.m. EDT).