SB PROP @ ARL $ARLP015 ARLP015 Propagation Forecast ZCZC AP15 QST de W1AW Propagation Forecast Bulletin 15 ARLP015 From ARRL Headquarters Newington, CT April 10, 2026 To all radio amateurs SB PROP ARL ARLP015 ARLP015 The ARRL Solar Report Solar activity remained at low levels this week. Most of the C-class activity came from either Region 4414 or Region 4409, which has developed a delta spot in its intermediary area. All remaining spots were either stable or in slight decay, with Region 4406 rotating over the west limb by the end of the reporting period. Coronal activity was observed in CCOR-1, LASCO, and STEREO available imagery during the period. Of the four eruptions, one was far-sided, one was too narrow plus too far north of the ecliptic to have any Earth-directed component, and two had the potential for Earth-directed components. The first was associated with a C2.4 flare from Region 4414, while there was no clear source for the second. Modeling indicates these eruptions will pass behind Earth's orbit, and no impact is anticipated. Eruptions potentially associated with the C8.9 are currently being analyzed. Radio blackouts reaching the R1 levels were observed over the past 24 hours. The largest was on Apr 9th 2026, at 08:45 UTC. Solar activity is expected to be at low levels over April 9 to 11, with a chance for M-class (R1-R2/minor-moderate) flares and a slight chance for X-class (R3/strong or greater) flares, driven primarily by the flare potential of Regions 4409 and 4414. A brief description of Sunspots can be found on the Space Weather Prediction Center website at www.swpc.noaa.gov/phenomena/sunspotssolar-cycle. Solar wind parameters reflected the transition out of a waning negative polarity coronal hole high-speed stream (CH HSS) into nominal conditions. Wind speeds continued to decline from a peak of ~500 km/s to near 400 km/s by the end of the period. Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 9, 2026, by F. K. Janda, OK1HH: Perhaps the biggest surprise in recent days was that, following the geomagnetic disturbance of April 2 3 (which had been expected, albeit a day earlier and with lower intensity), there were no further major surprises. Solar activity declined as predicted, whereas because it declined over a relatively long period, there was a greater-than-expected drop in critical frequencies in the F2 ionospheric region at mid-latitudes. For forecasting developments in the second third of April, the 27-day cycle could serve as a relatively reliable guide this time. First of all, one might expect a one- to two-day increase in geomagnetic activity (which is also indicated by the presence of solar coronal holes near the central meridian), followed by relative calm. This is despite the short time that has elapsed since the eleven-year peak of solar activity. The Predicted Planetary A Index for April 4 to April 10 is 5, 4, 3, 2, 2, 2, and 2 with a mean of 2.8. The Predicted Planetary K Index is 18, 10, 8, 7, 5, 4, and 7 with a mean of 8.4. 10.7 centimeter flux is 106, 105, 108, 110, 115, 115, and 120 with a mean of 111.2. For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Service web page at www.arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere. Information and tutorials on propagation can be found at http://k9la.us. Also, check this: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt NNNN /EX | 
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