SSB PROP @ ARL $ARLP028
ARLP028 Propagation Forecast

ZCZC AP28
QST de W1AW
Propagation Forecast Bulletin 28 ARLP028

From ARRL Headquarters

Newington, CT July 10, 2026
To all radio amateurs

SB PROP ARL ARLP028
ARLP028 The ARRL Solar Report

Solar activity reached moderate levels with an M1.5/1N flare on July 8 from Region 4482. There are currently five numbered regions on the visible disk. Region 4482 demonstrated continued growth and developed a delta spot within
its trailing spot group. Region 4485 displayed new flux emergence. Regions
4486 and 4487 were newly numbered during the period. Region 4481 was stable
and remained an unremarkable unipolar group. No Earth-directed CMEs were observed in available coronagraph imagery.


Solar activity is expected to remain at low levels through July 11, with a
high chance for M-class (R1-R2/minor-moderate) flares and a slight chance for X-class (R3/strong and greater) events. This flare probability is almost entirely due to the complexity and potential of Region 4482.


Solar wind parameters reflected near ambient background conditions. Solar
wind speeds were generally near 400 km/s. The phi angle was predominantly in the positive sector.


Enhancements are anticipated to begin on July 9 and continue through July 11 with the arrival of a co-rotating interaction region (CIR) ahead of a
negative polarity coronal hole high-speed stream (-CH

HSS).

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, July 9, 2026, by F. K. Janda, OK1HH:


The power flux of solar radio noise at a frequency of 2800 MHz (at a
wavelength of 10.7 cm), which is measured precisely every day at noon local time in Penticton, Canada, and is referred to as the solar flux, remains at
a relatively low level.

The reason is that the number of observed sunspot groups on the solar disk dropped to just three on July 7, the lowest number recorded during a single solar rotation (the following day, their number increased to five). The
largest active region, NOAA 4482, which we observe in the southeast of the solar disk, has not changed significantly in size and continues to produce moderate-intensity flares on a regular basis.

All three coronal holes are currently relatively far from it.
The intensity of the solar wind is changing only slightly; periods of
increased geomagnetic activity alternate with quiet days, making it
impossible to accurately predict future developments.


A more pronounced increase in solar activity is expected in the second half
of July (with a gradual increase in solar flux up to 180 s.f.u.). More significant geomagnetic activity can be expected if major solar flares occur, especially if they occur near or west of

the central meridian. This is likely to happen sometime in the second half of July.


The predicted Planetary A Index for July 11 to 17 is 12, 8, 5, 5, 5, 10, and
8, with a mean of 7.6. The predicted Planetary K Index is 4, 3, 2, 2, 2, 3,
and 3, with a mean of 2.7. 10.7 centimeter flux is 125, 120, 125, 130, 135, 135, and 135, with a mean of 129.3.


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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