[SFDX] ARLP029 The ARRL Solar Report

[Bill]

ARLP029 The ARRL Solar Report

	

SB PROP @ ARL $ARLP029

ARLP029 Propagation Forecast

ZCZC AP29

QST de W1AW

Propagation Forecast Bulletin 29 ARLP029

 From ARRL Headquarters

Newington, CT July 17, 2026

To all radio amateurs

SB PROP ARL ARLP029

ARLP029 The ARRL Solar Report

Solar activity has remained at low levels, with an occasional low-level 
C-class flaring observed, including a C3.3/Sf flare on July 15 from 
Region 4489. The largest event of the period, a long-duration C8.9 flare 
that peaked on July 15, originated from a returning region on the 
eastern limb. This region is not yet numbered and will be assessed once 
it has become visible from Earthís perspective, but the latest imagery 
from Solar Orbiter suggested only a simple and rather average bipolar 
group with a relatively small penumbra.

There are two numbered sunspot regions on the visible disk. Region 4482 
showed minor new flux emergence behind its mature primary spot, 
developing a bipolar configuration. As Region 4489 rotated further into 
view and limb foreshortening effects decreased, very small 
opposite-polarity trailing spots became visible, making it a stable 
bipolar group. Additionally, a small, magnetically simple, region 
tracked in Solar Orbiter imagery has begun to rotate over the east limb 
near S10. No Earth-directed CMEs were observed in available coronagraph 
imagery.

Solar activity is expected to remain at low levels through July 18, with 
a slight chance for M-class (R1-R2/minor-moderate) flares, primarily 
driven by active regions anticipated to rotate onto the visible disk 
over the next few days.

Solar wind parameters reflected possible combined glancing coronal mass 
ejection (CME) effects and subsequent weak positive polarity coronal 
hole high-speed stream (+CH HSS) influences.

A return to more ambient-like conditions is expected over the next three 
days.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's 
Ionosphere, July 16, 2026, by F. K. Janda, OK1HH:

The significant decline in solar activity throughout the first half of 
July is clearly illustrated by the solar flux values, which fell from 
203 s.f.u. (July 2) to 100 s.f.u. (July 14ñ15), as well as by the number 
of sunspot groups, which dropped from five to two. A significant drop in 
the critical frequencies of the F2 layer began as early as July 4 during 
the geomagnetic disturbance of July 4ñ5, and due to the sharp decline in 
solar activity, these values returned to average levels only very slowly 
in the following days. Consequently, the sporadic E layer had an even 
greater impact on shortwave propagation (particularly in the 
mid-latitudes of Europe on July 14 and 16).

The increase in solar activity, which is expected to begin as early as 
the end of this week and should last nearly until the end of the month, 
will result in significantly better shortwave propagation conditions 
than those experienced in the first half of the month. More significant 
changes (possibly an initial rise, but then very likely a temporary drop 
in MUF) will likely be caused by a geomagnetic disturbance, which is 
tentatively expected on July 21 and 22.

The predicted Planetary A Index for July 18 to 24 is 5, 5, 5, 5, 12, 10, 
and 7, with a mean of 7.0. The predicted Planetary K Index is 2, 2, 2, 
2, 4, 3, and 2, with a mean of 2.4. Predicted 10.7 centimeter flux is 
135, 135, 135, 135, 135, 135, and 135, with a mean of 135.0.

For more information concerning shortwave radio propagation, see 
www.arrl.org/propagation 
<https://arrl.informz.net/z/cjUucD9taT0zNjgxOTk1JnA9MSZ1PTUyNTQ3MzY2NCZsaT00Mzg5OTg1Mg/index.html> 
and the ARRL Technical Information Service web page at 
www.arrl.org/propagation-of-rf-signals 
<https://arrl.informz.net/z/cjUucD9taT0zNjgxOTk1JnA9MSZ1PTUyNTQ3MzY2NCZsaT00Mzg5OTg1Mw/index.html>. 
For an explanation of numbers used in this bulletin, see 
www.arrl.org/the-sun-the-earth-the-ionosphere 
<https://arrl.informz.net/z/cjUucD9taT0zNjgxOTk1JnA9MSZ1PTUyNTQ3MzY2NCZsaT00Mzg5OTg1NA/index.html>. 
Information and tutorials on propagation can be found at http://k9la.us 
<https://arrl.informz.net/z/cjUucD9taT0zNjgxOTk1JnA9MSZ1PTUyNTQ3MzY2NCZsaT00Mzg5OTg1NQ/index.html>.

NNNN

/EX

	

	

ARRL The National Association for Amateur Radio®

	

<https://arrl.informz.net/InformzDataService/mailing/bcd/bWFpbGluZ0luc3RhbmNlSWQ9MzY4MTk5NSZzdWJzY3JpYmVySWQ9NTI1NDczNjY0> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/sfdxa/attachments/20260717/d92708a2/attachment-0001.html>