SB PROP @ ARL $ARLP020
ARLP020 The ARRL Solar Report

ZCZC AP20
QST de W1AW
Propagation Forecast Bulletin 20 ARLP020

From ARRL Headquarters

Newington CT May 30, 2025
To all radio amateurs

SB PROP ARL ARLP020
ARLP020 The ARRL Solar Report

Solar activity reached moderate levels early this past week with several flares. An X1-class flare erupted mid-week, but activity has slowed down with the majority of the low-level C-class flares. A coronal mass ejection (CME)
was observed on May 27 with a flare from Region AR4100.


Modelling determined the CME to be well behind Earth's orbit. No other potentially Earth-directed CMEs were detected in available coronagraph
imagery. M-class flare activity, minor - moderate, is likely, with a slight chance for X-class flare events, strong or greater, through May 30.


The forecast of Solar and Geomagnetic Activity to June 21, 2025

Solar activity is likely to reach moderate levels
(R1-R2/Minor-Moderate), with a chance for R3 (Strong), over the next three
days as Region AR4098, the most productive region on the visible disk, makes its way to the west limb of the Sun. A chance for M-class X-ray activity (R1-R2) will persist throughout the outlook period due to multiple regions on the visible as well as multiple active regions scheduled to return from the
far side of the Sun.


No proton events are expected at geosynchronous orbit.

The Geomagnetic field activity is expected to be at a mostly elevated level
due to anticipated influence from multiple, recurrent coronal holes. G1
(minor) geomagnetic storms are likely on June 13-14; active conditions are likely over June 2, June 5, June 10 and 11, and June 15 to 17.


Unsettled conditions are likely over June 3 and 4, June 6 and 7, and June 18
to 21. Quiet conditions are only expected on June 8 and 9.


On May 30, Spaceweather.com reports on a Super-Fast Solar Wind, and a 24-hour Geomagnetic Storm.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - May 29, 2025, from F. K, Janda, OK1HH:


"On May 29, geomagnetic activity reached the level of a strong storm (Kp 7) worldwide, which came as no surprise to those who had been monitoring the recurring disturbances during the last four solar rotations, and especially
the developments on the Sun over the last five days or so.


"Solar flares were observed, only occasionally with coronal mass ejections (CMEs).

Although the large coronal hole in the southwest of the solar disk
disappeared, other coronal holes appeared across the solar disk in the meantime.

The largest of these extends from the southwest to the northeast and has been crossing the central meridian since May 26.

It has negative polarity and is associated with the arrival of a high-speed stream (up to about 730 km/s).

Even in the coming days, after the current disturbance subsides, mild active storm conditions (Kp 4) will continue.


"Overall solar activity will increase slightly in the coming days, and geomagnetically active days will alternate irregularly with calmer ones. Ionospheric conditions for shortwave propagation will improve, but at best
only to average levels."


For more information concerning shortwave radio propagation, see www.arrl.org/propagation [ http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] and the ARRL Technical Information Service web page at, www.arrl.org/propagation-of-rf-signals [ http://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 [ http://arrl.org/the-sun-the-earth-the-ionosphere ] .

Information and tutorials on propagation can be found at: http://k9la.us [ http://k9la.us/ ] .


Also, check this: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

The Predicted Planetary A Index for May 31 to June 6 is 8, 10, 12, 8, 10, 12, and 10, with a mean of 10. The Predicted Planetary K Index is 3, 3, 4, 3, 3,
4, and 3, with a mean of 3.3. Predicted 10.7 centimeter flux is 125, 120,
115, 110, 110, 115, and 120, with a mean of 116.4.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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