ARLP017 The ARRL Solar Report undefined

 

SB PROP @ ARL $ARLP017

ARLP017 Propagation Forecast

 

ZCZC AP17

QST de W1AW

Propagation Forecast Bulletin 17 ARLP017

From ARRL Headquarters

Newington, CT April 24, 2026

To all radio amateurs

 

SB PROP ARL ARLP017

ARLP017 The ARRL Solar Report

 

Solar activity remained at low levels this past week with numerous C1 flares from Region 4420, which exhibited growth during the period. Region 4419 showed minor decay, particularly in its trailing spots, while producing a lone C1.0 flare. Region 4422 was numbered during the period but remained inactive. No Earth-directed CMEs were observed in coronagraph imagery.

 

Solar activity is expected to continue at low levels, with a slight chance for isolated M-class activity, through April 24, primarily due to the flare potential from Region 4420 and limb activity.

 

Solar wind parameters reflected waning coronal hole high speed stream (CH HSS) influences. The wind speed maintained an average of 525 km/s, and Phi was predominantly in a negative orientation towards the Sun.

 

Region 4419 was the most active region of the period, responsible for 5 out of the 7 C-class flares observed during the week, including the largest one: a C4.1. The remainder 2 C-class flares of the period were a C1.1 from Region 4414 and a C1.6 from Region 4416. Coronal activity was observed during the week with some filament eruptions and few CMEs without Earth-directed components.

 

reports the sun has been quiet for weeks. That ended today with two powerful X-class solar flares. In quick succession, sunspot 4419 unleashed X2.4 (0107 UT) and X2.5 (0813 UT) explosions.

 

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 23, 2026, by F. K. Janda, OK1HH:

 

Although solar activity during the first four months of this year was lower than in the previous two years of the 11-year solar maximum (2024-2025), this was anything but a continuing decline. Periods of low solar activity gradually tended to lengthen and were interspersed with sudden increases in both overall and eruptive activity. This trend is very clearly evident in the solar flux, which was very low during the penultimate solar cycle (March 14-21), followed by a further and longer decline shortly after the beginning of April and particularly between April 9 and 13.

 

Moreover, during the long period of low solar activity (April 5-22), geomagnetic field activity increased (April 18-21), further diminishing hopes for the usual seasonal improvement in shortwave propagation conditions. However, two sunspot groups then emerged on the eastern limb of the solar disk, bringing their total number to four. Then came Thursday, April 23, with several moderately powerful solar flares, alternating between the east and west of the solar disk, preceded by rapid changes in magnetic configuration where the eruptions were soon observed.

 

Therefore, in the coming days, we will continue to observe increased solar activity and the potential effects of fast solar wind on Earth. Shortwave propagation conditions will vary irregularly, while during the ongoing bursts of intense solar wind, ionospheric attenuation will increase at higher latitudes.

 

The Predicted Planetary A Index for April 25 to May 1 is 8, 5, 5, 5, 20, 18, and 12 with a mean of 10.4. The Predicted Planetary K Index is 3, 2, 2, 2, 5, 5, and 4 with a mean of 3.3. 10.7 centimeter flux is 115, 120, 125, 125, 125, 125, and 125 with a mean of 122.9.

 

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.

NNNN

/EX

 

 

ARRL The National Association for Amateur Radio®