SB PROP @ ARL $ARLP017
ARLP017 The ARRL Solar Report

ZCZC AP17
QST de W1AW
Propagation Forecast Bulletin 17 ARLP017

From ARRL Headquarters

Newington CT May 9, 2025
To all radio amateurs

SB PROP ARL ARLP017
ARLP017 The ARRL Solar Report

The Solar Geophysical Activity Report and Forecast from the USAF/NOAA
indicates that solar activity has been at low levels for the past 24 hours.


There are currently four numbered sunspot regions on the solar disk. Solar activity is expected to be low with a chance for M-class flares on May 10 and 11.


A simultaneous filament eruption produced a narrow Coronal Mass Ejection
(CME) signature that was first observed on May 6, and an additional slower filament eruption was also observed. Analysis of the events is ongoing and there was no significant growth or decay observed in the spotted regions on
the visible Sun.


The geomagnetic field is likely to experience periods of active conditions on May 10 and 11 due to continued Coronal Hole High-Speed Stream influences (CH HSS).


Geomagnetic field activity is likely to reach G1 (Minor) storm levels on May 18, and May 29 to 31 due to negative polarity coronal hole influences.
Periods of active conditions are likely on May 16 and 17, and on May 19 to 21 in response to CH HSS influences.


On Spaceweather.com [ http://Spaceweather.com ] for May 9, there is a video
of a "Solar Tornado" occurring on the Sun's surface.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, May 8, 2025, from F. K. Janda, OK1HH:


"Although we were expecting more activity in the relatively large sunspot
group AR4079 that crossed the central meridian on May 4, it did not happen. Indeed, its magnetic configuration did not promise it. Instead, a
sufficiently fast and proton - and especially free-electron-rich solar wind blew from the edges of the coronal holes, which for most of the past days
since the beginning of May caused not only increased geomagnetic activity,
but also increased attenuation and scattering of radio waves in the
ionosphere.


"Only a slight improvement in the situation can be predicted. In a few days, the only one major active region that we know about thanks to helioseismology should appear on the eastern limb of the solar disk. Again, it is likely to
be the only one in the disk, while the small number of remaining ones will
more or less not contribute to the overall level of solar activity.


"It remains the case that solar activity is likely to shift from the southern hemisphere to the northern hemisphere this year, but this will probably not
yet happen in May."


The latest video report from Dr. Tamitha Skov, WX6SWW, can be found on
YouTube at www.youtube.com/watch?v=XZ7C6ja3ZmE [ https://www.youtube.com/watch?v=XZ7C6ja3ZmE ] .


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 10 to 16 is 12, 10, 5, 5, 5, 5, and
12, with a mean of 7.7. The Predicted Planetary K Index for the same period
is 4, 3, 2, 2, 2, 2, and 4, with a mean of 2.7. Predicted 10.7 centimeter
flux is 165, 165, 160, 155, 155, 155, and 155, with a mean of 158.6.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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SB PROP @ ARL $ARLP017
ARLP017 Propagation Forecast

ZCZC AP17
QST de W1AW
Propagation Forecast Bulletin 17 ARLP017

From ARRL Headquarters

Newington, CT April 24, 2026
To all radio amateurs

SB PROP ARL ARLP017
ARLP017 The ARRL Solar Report

Solar activity remained at low levels this past week with numerous C1 flares from Region 4420, which exhibited growth during the period. Region 4419
showed minor decay, particularly in its trailing spots, while producing a
lone C1.0 flare. Region 4422 was numbered during the period but remained inactive. No Earth-directed CMEs were observed in coronagraph imagery.


Solar activity is expected to continue at low levels, with a slight chance
for isolated M-class activity, through April 24, primarily due to the flare potential from Region 4420 and limb activity.


Solar wind parameters reflected waning coronal hole high speed stream (CH
HSS) influences. The wind speed maintained an average of 525 km/s, and Phi
was predominantly in a negative orientation towards the Sun.


Region 4419 was the most active region of the period, responsible for 5 out
of the 7 C-class flares observed during the week, including the largest one:
a C4.1. The remainder 2 C-class flares of the period were a C1.1 from Region 4414 and a C1.6 from Region 4416. Coronal activity was observed during the
week with some filament eruptions and few CMEs without Earth-directed components.


Spaceweather.com [ http://Spaceweather.com ] reports the sun has been quiet
for weeks. That ended today with two powerful X-class solar flares. In quick succession, sunspot 4419 unleashed X2.4 (0107 UT) and X2.5 (0813 UT) explosions.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 23, 2026, by F. K. Janda, OK1HH:


Although solar activity during the first four months of this year was lower than in the previous two years of the 11-year solar maximum (2024-2025), this was anything but a continuing decline.

Periods of low solar activity gradually tended to lengthen and were interspersed with sudden increases in both overall and eruptive activity.

This trend is very clearly evident in the solar flux, which was very low
during the penultimate solar cycle (March 14-21), followed by a further and longer decline shortly after the beginning of April and particularly between April 9 and 13.


Moreover, during the long period of low solar activity (April 5-22), geomagnetic field activity increased (April 18-21), further diminishing hopes for the usual seasonal improvement in shortwave propagation conditions.

However, two sunspot groups then emerged on the eastern limb of the solar
disk, bringing their total number to four.

Then came Thursday, April 23, with several moderately powerful solar flares, alternating between the east and west of the solar disk, preceded by rapid changes in magnetic configuration where the eruptions were soon observed.


Therefore, in the coming days, we will continue to observe increased solar activity and the potential effects of fast solar wind on Earth. Shortwave propagation conditions will vary irregularly, while during the ongoing bursts of intense solar wind, ionospheric attenuation will increase at higher latitudes.


The Predicted Planetary A Index for April 25 to May 1 is 8, 5, 5, 5, 20, 18, and 12 with a mean of 10.4. The Predicted Planetary K Index is 3, 2, 2, 2, 5, 5, and 4 with a mean of 3.3. 10.7 centimeter flux is 115, 120, 125, 125, 125, 125, and 125 with a mean of 122.9.


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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