SB PROP @ ARL $ARLP016
ARLP016 The ARRL Solar Report

ZCZC AP16
QST de W1AW
Propagation Forecast Bulletin 16 ARLP016

From ARRL Headquarters

Newington CT May 2, 2025
To all radio amateurs

SB PROP ARL ARLP016
ARLP016 The ARRL Solar Report

On May 2, Spaceweather.com reported: "Astronomers are monitoring a very large sunspot now turning toward Earth. Sunspot AR4079 stretches more than 140,000
km from end to end and has two dark cores each large enough to swallow Earth. Moreover, it is surrounded by a ring of Ellerman Bombs.


"Ellerman bombs are a sign of magnetic complexity in a sunspot. Opposite polarities bump together, reconnect, and--boom! A full-fledged flare may not
be far behind."


Solar activity increased to moderate levels this past week. The largest flare was on April 30 from an area where there was a major M-class flare producer
on its previous rotation last week.


No Earth-directed Coronal Mass Ejections (CMEs) were observed. Solar activity is expected to be low with a chance for M-class flares (R1-R2,
minor-moderate), and a slight chance for X-class flares (R3-strong) through
May 2.


Radio blackouts reaching the R1 levels were observed over the past 24 hours. The largest was on April 30.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - May 1, 2025, by F. K. Janda, OK1HH:


"In the past few weeks I have allowed myself to take a break because I have been under the care of excellent doctors and caring nurses in a top Prague hospital. Fortunately, I had a receiver available and could and did use it occasionally, but the computer was at home, QRB 53 km away. Now I'm back and continuing my usual activities: observing the events between the Sun and the Earth, analyzing the context and trying to predict the future developments (yes, I know that more accurate predictions are not possible, while I can
well justify why - but why not take science a bit as a sport too, right...?).


"In the last few days of April, AR4079 rose on the northeastern limb of the solar disk, while soon increased in area to over 1000 millionths. Already during the early months of this year, the Sun had subtly hinted that the
centre of gravity of activity might shift from its southern to its northern hemisphere, but only now can we see this trend more clearly. So, it's
possible that we're in for another upward swing within the current 11-year cycle, with active regions mostly north of the equator. This could hold the promise of improved ionospheric shortwave propagation conditions this Autumn.


"During this April, we experienced a really large number of geomagnetically disturbed days and mostly low MUF values. The calm and improvement occurred only in the last decade of April, when we witnessed all six geomagnetically quiet days of the whole April.


"Going forward, although we do not expect a major increase in solar activity for the time being, it will not be important during the Northern Hemisphere ionospheric Summer. Solar activity will more or less remain at the current level, the geomagnetic field will be calmer compared to the past weeks - and the situation in the ionosphere will be more favourable."


Solar wind parameters remained slightly enhanced due to waning positive polarity of the Coronal Hole High-Speed Stream (CH HSS) influences. A return
to a mostly ambient-like state is expected for May 1, but by May 2, an enhancement in solar wind parameters is likely with the arrival of a
recurrent, negative polarity CH HSS.


Unsettled to active levels will likely persist into May 4 as an additional negative polarity CH HSS moves into place.


Geomagnetic field activity is likely to reach G1 (Minor) storm levels on May
5 and 6 due to negative polarity CH HSS influences, and again on May 18 due
to positive polarity CH HSS influences.


Periods of active conditions are likely on May 07 to 10, and on May 16 and 17 in response to CH HSS influences. Quiet and quiet to unsettled levels are expected to prevail throughout the remainder of the period.


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 out: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]


The Predicted Planetary A Index for May 3 to 9 is 10, 8, 18, 18, 15, 15, and 15, with a mean of 14.1. Predicted Planetary K Index is 3, 3, 5, 5, 4, 4, and 4, with a mean of 4. Predicted 10.7 centimeter flux is 140, 140, 150, 160,
160, 165, and 165, with a mean of 154.3.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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SB PROP @ ARL $ARLP016
ARLP016 Propagation Forecast

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 [ http://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 [ 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 [ 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://www.arrl.org/propagation-of-rf-signals?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] . For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere [ http://www.arrl.org/the-sun-the-earth-the-ionosphere?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] . 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 ]

NNNN
/EX

ARRL The National Association for Amateur Radio(R)


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