ARLP029 The ARRL Solar Report undefined

 

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 and the ARRL Technical Information Service web page at . For an explanation of numbers used in this bulletin, see . Information and tutorials on propagation can be found at .

 

Also, check this: "Understanding Solar Indices" from September 2002 QST.

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/EX

 

 

 

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