Ham Radio Solar Storm Impact. May 2025: HF Blackouts & VHF Propagation SurgesThe Sun’s recent uptick in activity, marked by a powerful M8.1 flare on May 31, 2025, and ensuing geomagnetic disturbances, has had measurable impacts on ham radio communications. As solar cycle 25 peaked into its maximum phase in late May, high‐energy particles and enhanced solar wind streams altered ionospheric conditions, leading to diminished high‐frequency (HF) performance, elevated noise floors, and sporadic absorption events. Let’s examine the specifics of these disturbances, their effects across amateur bands, and how operators have observed and adapted to the volatile space weather over the past week. The Washington PostWatchers News

M8.1 Solar Flare and S1 Radiation Storm
On May 31, an M8.1‐class solar flare erupted from Active Region 4100 at approximately 00:05 UTC. This event propelled a coronal mass ejection (CME) toward Earth at nearly 1,000 km/s, triggering an S1 (Minor) solar radiation storm by 17:00 UTC the same day. Watchers NewsWatchers News The Space Weather Prediction Center (SWPC) immediately raised alerts, indicating that protons and electrons injected into the magnetosphere would elevate ionospheric ionization levels—particularly in the D-layer—causing increased HF absorption on the sunlit side of Earth. NOAA Space Weather Prediction CenterNOAA Space Weather Prediction Center In practical terms, amateurs witnessed elevated noise floors (S3–S4) on 20 m and 40 m, along with sporadic S1–S2 absorption blackouts during peak sunlit hours in mid‐latitude regions. solar.w5mmw.netNOAA Space Weather Prediction Center

Geomagnetic Storm Watch and G4 Potential
Following the flare, SWPC issued a G4 (Severe) geomagnetic storm watch for June 2, anticipating that the arriving CME shock front would compress Earth’s magnetosphere and spike the planetary K‐index above 8. Watchers NewsNOAA Space Weather Prediction Center G4‐level storms are known to cause “HF radio propagation sporadic,” meaning widespread and sometimes prolonged disruptions to HF links, particularly at mid to high latitudes. WikipediaNOAA Space Weather Prediction Center Reports from late May confirm that as K_p climbed to 8–9 in the early hours of June 1, MUF (Maximum Usable Frequency) values on 14 MHz dropped by as much as 50%, forcing many operators to seek lower bands (e.g., 7 MHz and below) to maintain contacts. Wikipediasolar.w5mmw.net Additionally, aurora borealis sightings extended as far south as Alabama and Georgia, indicating a strongly disturbed geomagnetic field. The Washington PostWatchers News

Ionospheric Absorption and MUF Depression
Geomagnetic storms primarily disturb the F-layer, reducing electron density and lowering the MUF. For example, pre‐storm solar flux values hovered around 150, but during the geomagnetic peak, operators noted effective flux‐equivalent conditions closer to 80–90 on certain HF bands. solar.w5mmw.netWikipedia The D-layer absorption—heightened by energetic protons—caused pronounced attenuation on 10 m through 40 m, with some links completely dropping (i.e., sudden ionospheric disturbances). NOAA Space Weather Prediction CenterWikipedia A typical mid‐latitude station in Ohio reported that 14.250 MHz signals that were normally S9 during midday plummeted to noise or below S1, rendering SSB and digital modes like FT8 nearly unusable from 1400–1700 UTC on May 31. solar.w5mmw.netNOAA Space Weather Prediction Center

Elevated Noise Floors and Auroral Enhancements
Accompanying absorption, the spacecraft‐monitored solar wind speed exceeded 780 km/s by June 1, driving geomagnetic indices to G3–G4 levels. solar.w5mmw.netWatchers News Under these conditions, HF noise floors increased to S3–S4 on most amateur bands, effectively reducing receiver sensitivity by 20–25 dB. solar.w5mmw.netWikipedia Conversely, auroral propagation on 6 m (50 MHz) spiked dramatically. Numerous DX clusters logged sporadic E and auroral reflections on 50 MHz between 0200–0500 UTC on June 1, with a dozen European stations reporting signals from North American beacon stations well outside normal line‐of‐sight ranges (e.g., 3,000 km+ openings). The Washington PostNOAA Space Weather Prediction Center However, these sporadic E enhancements were intermittent, collapsing as K_p began to subside near local sunrise. NOAA Space Weather Prediction Center

VHF/UHF Impacts and Polarization Effects
While HF bands bore the brunt of ionospheric absorption, VHF (144 MHz) and 70 cm (432 MHz) links also experienced sporadic disruptions. During the peak of the storm, geomagnetic‐induced scintillation caused rapid amplitude and phase fluctuations on UHF satellite uplinks, adversely affecting telemetry decoding rates. Watchers NewsNOAA Space Weather Prediction Center Ground‐to‐space links, such as AO-91 (UO-91) U/V transponder QSOs, witnessed brief fadeouts when the K_p index surpassed 7. Watchers NewsWikipedia Notably, a portable station in Michigan reported a sudden drop in AO-91 downlink strength by 8 dB for roughly 20 minutes starting at 0300 UTC on June 1, demonstrating that even UHF traffic is not immune during severe geomagnetic conditions. solar.w5mmw.netWatchers News Polarization purity also degraded—whisper‐quiet circular‐polarized LEO satellite QSOs experienced cross‐polarization noise as the ionospheric plasma rotated signal polarization unexpectedly. WikipediaNOAA Space Weather Prediction Center

Digital Modes and Contesting Performance
Digital modes proved especially vulnerable. During the afternoon of May 31, a cluster of digital operators reported that FT8 decodes fell by 30–40% on 20 m and 40 m. solar.w5mmw.netNOAA Space Weather Prediction Center In several round‐table nets, digital operators shifted rapidly to lower frequencies (e.g., PSK31 on 7.070 MHz) to maintain reliability. solar.w5mmw.netNOAA Space Weather Prediction Center Meanwhile, contesters preparing for the CQ WW WPX Contest (June 1–2) faced frustrating QSO losses, with many participants logging “dropouts” of multi‐multiplier stations that would momentarily vanish mid‐QSO. NOAA Space Weather Prediction CenterWikipedia On the positive side, WSPR and JS8Call users noted some long‐path openings to Oceania on 30 m during local nighttime (when the storm’s D-layer absorption diminished), enabling low‐power transoceanic tests that would not have been possible under quieter conditions. solar.w5mmw.netdx.qsl.net

Mitigation Strategies and Operator Recommendations
To navigate these conditions, operators should monitor NOAA SWPC bulletins and real‐time K-index plots (e.g., www.swpc.noaa.gov/products/planetary-k-index). NOAA Space Weather Prediction CenterWikipedia Adjusting operating plans to focus on lower HF bands (80 m/40 m) during daytime absorption and exploiting auroral/VHF openings at night can salvage contacts. solar.w5mmw.netNOAA Space Weather Prediction Center Additionally, turning down receiver bandwidths and raising thresholds (e.g., moving from 2.7 kHz to 500 Hz filters for SSB) reduces impact from elevated noise levels. solar.w5mmw.netNOAA Space Weather Prediction Center Satellite operators should schedule passes to avoid local geomagnetic peak times or switch to FM/TDMA modes, which are more robust to short‐term scintillation. Watchers NewsWikipedia For those running digital experiments (FT8, WSPR), decreasing transmit power and extending transmission sequences can improve decode probability under high absorption. NOAA Space Weather Prediction Centersolar.w5mmw.net

Looking Forward: Solar Cycle 25 Trends
This week’s storm activity is emblematic of the broader peak in solar cycle 25, which began its ascent in 2023 and now exhibits frequent M-class and occasional X-class flares. Moonraker OnlineNOAA Space Weather Prediction Center According to NOAA’s “Solar Cycle Progression” page, sunspot numbers have remained above 90 since April 2025, with solar flux consistently above 140—conditions conducive to both improved long-distance MUF propagation and heightened storm risk. solar.w5mmw.netNOAA Space Weather Prediction Center As we transition into summer, the frequency of active regions crossing the solar disk will likely keep HF conditions volatile, alternating between excellent “sunspot-enhanced” propagation and abrupt absorption events. Moonraker OnlineWikipedia

Conclusion
Recent solar activity, highlighted by the M8.1 flare and ensuing G4‐watch conditions, has demonstrably altered ham radio performance: HF bands have experienced absorption and MUF depression, noise floors have surged, and digital mode reliability has suffered. Yet, operators have also witnessed improved VHF auroral openings and low-power digital paths during nighttime. By staying attuned to space weather forecasts, adjusting band plans, and employing narrower filters, hams can both mitigate disruptions and capitalize on unique propagation phenomena. As solar cycle 25 advances past its zenith, ongoing vigilance and adaptive strategies will be essential for maximizing station performance under an ever-changing Sun. The Washington PostNOAA Space Weather Prediction Center

73 for now, and be Safe!…from the Higginsreport.