SB PROP @ ARL $ARLP035

ARLP035 Propagation Forecast

ZCZC AP35
QST de W1AW
Propagation Forecast Bulletin 35 ARLP035

From ARRL Headquarters

Newington, CT August 28, 2026
To all radio amateurs

SB PROP ARL ARLP035
ARLP035 The ARRL Solar Report

Solar activity reached moderate levels this week. Region 4513 was responsible for an M2.2/1B flare that reached its peak on August 26. This event was accompanied by a 10.7-centimeter radio burst that reached 140 solar flux
units (SFU) and a type II radio sweep with an estimated shock speed of 930
km/s despite its relatively impulsive nature. No resulting coronal mass ejection (CME) has been observed in available coronagraph imagery as of the time of this report.


Other activity of note since the last reporting period included an easterly
CME first seen in two LASCO C2 coronagraph imageries on August 25.


The first event likely originated from the vicinity of Region 4513 around August 25 while no definitive source could be identified with any confidence for the latter. Nevertheless, both of these events are currently being
modeled and assessed to determine the presence of an Earth-directed path.


Solar activity will likely remain at minor-moderate (R1-R2) levels, with a slight chance for strong (R3) activity, through August 28, mostly due to the flare history and potential of Region 4513.


Solar wind parameters were at undisturbed levels with solar wind speeds
between ~300-340 km/s, total field at or below 5 nT and Bz northward or near neutral. Phi angle was predominantly negative.


Nominal solar wind conditions are expected to continue until midday August
27, when the onset of a positive polarity coronal hole high speed stream (CH HSS) influence is anticipated. Additional solar wind disturbances, with increased solar wind densities and total IMF, are likely on August 28 due to the impact of the CMEs that left the Sun on August 25.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, August 27, 2026, by F. K. Janda, OK1HH:


More or less in line with expectations, total solar activity has been
slightly elevated during the last third of August, including flare activity
we have been observing moderate-sized flares since August 24, peaking on
August 25. Most sunspots and all larger groups are now located in the western half of the solar disk, which increases the likelihood of rising geomagnetic activity, which had been low for a relatively long period beginning on August 21. This resulted in above-average shortwave propagation conditions,
including propagation in the Earth s polar regions.


Solar activity is expected to remain elevated for the remainder of August and will drop significantly in early September.

Geomagnetic activity, however, will increase, whilst is likely to remain
higher for the rest of August.

Consequently, shortwave propagation conditions will no longer be as
consistent as in recent days; instead, there will be a decrease in usable frequencies and an increase in attenuation.

The beginning of September will be calmer, albeit with slightly lower
critical frequencies in the F2 layer of the ionosphere.


The Predicted Planetary A Index for August 28 to September 3 is 10, 8, 5, 5,
5, 5, and 5 with a mean of 6.9. The Predicted Planetary K Index is 3, 3, 2,
2, 2, 2, and 2 with a mean of 2.3. Predicted 10.7 centimeter flux is 120,
120, 120, 120, 120, 120, and 115 with a mean of 119.3.


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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