Message:21024 In: PROP.ARL
From: NC8QDate: Sat, 18 Apr 26 11:04:00 Z
Newsgroups: PROP.ARL
Subject: ARLP016 Propagation Forecast
Message-ID:
Path: N2MH4|NC8Q
R:260418/1105Z 30357@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260418/1104Z 48686@NC8Q.#DAY.OH.USA.NOAM LinBPQ6.0.25
ZCZC AP16
QST de W1AW
Propagation Forecast Bulletin 16 ARLP016
From ARRL Headquarters
Newington, CT April 17, 2026
To all radio amateurs
SB PROP ARL ARLP016
ARLP016 The ARRL Solar Report
Solar activity was at very low levels with only isolated B-class flaring, mostly from Region 4416.
There are currently four numbered regions on the visible disk. Region 4416 remains the largest group by area but exhibited signs of structural weakening, including flux submergence and a slight decay of its intermediary pores. Region 4419 was the most complex group on the disk and showed flux emergence, growth, and divergence within its intermediary spots, leading to the development of a mixed-polarity gamma configuration. Region 4418 is trending toward plage with only two small bipolar pores remaining, and Region 4415 remained stable. CMEs observed in coronagraph imagery were determined to be directed away from Earth.
Solar wind parameters reflected waning coronal hole high-speed stream influences toward a nominal regime. Solar wind speeds underwent a gradual, albeit erratic, decline from early-period highs near 420 km/s to stabilize around 375 km/s by the end of the reporting period. The phi angle was predominantly oriented in a positive (away from the Sun) direction.
Solar wind parameters are expected to remain primarily near nominal levels through April 16. Significant enhancements are anticipated on April 17 with the onset of a co-rotating interaction region (CIR) that will precede the arrival of a negative polarity high-speed stream (-CH HSS).
Spaceweather.com reports a large hole has opened in the sun's atmosphere, and it is directly facing Earth. High-speed solar wind flowing from this coronal hole should arrive on April 18th, potentially sparking G2-class geomagnetic storms.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 16, 2026, by F. K. Janda, OK1HH:
It is as if we were not just past the 11-year solar activity maximum; the solar flux fell and remained below 100 s,f,u for five days (April 9-13), while the number of sunspot groups dropped to just three. Flare activity declined similarly. However, more significant for the future development of solar activity and especially for its impact on Earth is the large coronal hole No. 42, which is approaching the central meridian from the northeast. Its western border can be considered a potential source of solar wind that will reach Earth in the coming days.
Initially, it seemed that this would not happen until April 19, but closer observation of its development shows that the Earth will be hit by a fast solar wind as early as April 18 during the day. Or perhaps as early as the late afternoon of April 17, in which case the disturbance could begin with a positive phase (with an increase in MUF), which should continue through the negative phase for much of the weekend.
The latest solar report from Dr. Tamitha Skov, WX6SWW, can be found on YouTube at https://www.youtube.com/watch?v=cOcV9xp8qU8&pp=0gcJCdMKAYcqIYzv
The Predicted Planetary A Index for April 18 to April 24 is 15, 20, 12, 10, 8, 5, and 8 with a mean of 11.1. The Predicted Planetary K Index is 3, 4, 4, 3, 3, 2, and 3 with a mean of 3.1. 10.7 centimeter flux is 110, 110, 120, 130, 140, 145, and 145 with a mean of 128.5.
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
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