SB PROP @ ARL $ARLP045
ARLP045 The ARRL Solar Report

ZCZC AP45
QST de W1AW
Propagation Forecast Bulletin 45 ARLP045

From ARRL Headquarters

Newington CT, December 5, 2025
To all radio amateurs

SB PROP ARL ARLP045
ARLP045 The ARRL Solar Report

Solar activity was at low levels this past week, with only C-class flares. Region 4294 remains the largest region on the disk, but is appearing to be simplifying magnetically.

Region 4296, on the other hand, gained a delta region in its intermediary region, though with no corresponding increase in flare activity as of yet.

New flux emerged along the eastern side of Region 4298, resulting in several
C flares throughout the reporting period.

Region 4299 also developed a delta region in its primary spot, but no appreciable shear was observed.

Region 4301 developed, was numbered, but was otherwise unremarkable.
No Earth-directed CMEs were observed in available coronagraph imagery.

Isolated to occasional M-class flares are expected through December 6, with a chance for X-class flares, given past flare history, and the potential of current active regions on the disk.


The environment will likely remain enhanced due to fast solar wind conditions through December 6.


M class flares (R1 to R2/Minor to Moderate) are likely, with slight chance
for X flares (R3 Strong or greater), through 12 Dec due primarily to the
flare potential of Region 4294.


Geomagnetic activity is likely to reach active levels on December 3 and 6,
and G1 (Minor) storm levels on December 4 and 5, driven by influences from a negative polarity CH HSS.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, December 4, 2025, by F. K. Janda, OK1HH:


The significant increase in solar activity since the beginning of December
has finally confirmed the original assumption that the current 25th
eleven-year solar cycle will have two peaks.

The first occurred last October, while we have been eagerly awaiting the
second this year (especially in the fall). The increase in activity at the
end of this summer started promisingly, but it was only the first of several.

It was only after the large solar flare on November 11, 2025, which was the largest since October 3, 2024, that it was possible to estimate that the
second maximum was approaching.


High solar activity period can be expected during the first half of December, while it is a bit of a shame that it did not occur a week or two earlier.
This would have been particularly appreciated by shortwave radio amateurs, as the telegraph part of the largest competition, the CW WW DX Contest, traditionally takes place during the last weekend of November.


Although the current parameters of high-speed solar wind do not create
exactly the structure of the Earth's ionosphere that we would like, at least the highest usable frequencies allow connections to be established on all shortwave bands. During December, we are likely to experience another
increase in solar activity in the last third of the month, preceded by
several days of increased geomagnetic activity.


The latest video report from Dr. Tamitha Skov, WX1SWW, can be found on
YouTube at https://www.youtube.com/watch?v=s3_mnw1MPoA [ https://www.youtube.com/watch?v=s3_mnw1MPoA ]


The Predicted Planetary A Index for December 6 to 12 is 12, 10, 8, 5, 5, 5, 8 with a mean of 7.5. Predicted Planetary K Index is 4, 3, 3, 2, 2, 2, and 3, with a mean of 2.7. 10.7 centimeter flux is 190, 190, 190, 190, 185, 180, and 180, with a mean of 186.4.


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 ]

NNNN
/EX

ARRL The National Association for Amateur Radio(R)


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