SB PROP @ ARL $ARLP042
ARLP042 Propagation Forecast
ZCZC AP42
QST de W1AW
Propagation Forecast Bulletin 42 ARLP042
From ARRL Headquarters
Newington, CT October 16, 2026
To all radio amateurs
SB PROP ARL ARLP042
ARLP042 The ARRL Solar Report
Look for improved propagation on the upper HF bands, as both the sunspot numbers and 10.7-centimeter radio flux remain near or above 100. According to NOAA's Space Weather Prediction Center (SWPC), the increase in activity is being fueled primarily by sunspot Region 4551, which is described as the largest and most complex of six sunspot regions currently visible on the surface of the Sun. Mostly quiet geomagnetic conditions are expected as well, with some disturbances possible late next week.
The Australian Space Weather Forecasting Centre predicts mostly normal HF propagation conditions worldwide.
The W3LPL Propagation Forecast from the Daily DX is predicting significantly improved DX conditions on 10 and 12 meters for as many as the next 10 days, with excellent conditions on 17, 15, and 20 meters as well. DX openings on 30 meters should begin in late afternoon each day, followed by 40 meters around an hour before sunset, and 80 meters just after sunset.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere, October 15, 2026, by F. K. Janda, OK1HH:
The so-called 27-day recurrence derived from the duration of one rotation of the Sun around its own axis is often a useful tool for forecasting fluctuations in solar activity. Although rare, there are instances when the trend is exactly the opposite, which can be directly misleading for predicting future developments. The most recent peak solar flux of 136 s.f.u. on October 13 was measured exactly 27 days after September 17, when the flux was 97 s.f.u. the first day of a relatively long interval with low values below 100 s.f.u. Consequently, the state of the Earth's ionosphere and thus shortwave propagation conditions was not as favorable as might be expected at this time of year.
Furthermore, solar activity will decline for the remainder of October. Although a disturbance in the Earth's geomagnetic field can be expected after October 20, it should be brief, and the rest of the month is expected to bring relatively calm and favorable conditions.
The Predicted Planetary A Index for October 16 to October 22 is 5, 5, 5, 5, 5, 15, and 20 with a mean of 8.6. The Predicted Planetary K Index is 2, 2, 2, 2, 2, 3, and 4 with a mean of 2.4. 10.7 centimeter flux is 100, 95, 95, 100, 100, 105, and 100 with a mean of 99.3.
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
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