Message:21758 In: PROP.ARL
From: NC8QDate: Sat, 02 May 26 09:46:00 Z
Newsgroups: PROP.ARL
Subject: ARLP018 Propagation Forecast
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R:260502/1001Z 76908@VE3CGR.#SCON.ON.CAN.NOAM LinBPQ6.0.25
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ZCZC AP18
QST de W1AW
Propagation Forecast Bulletin 18 ARLP018
>From ARRL Headquarters
Newington, CT, May 1, 2026
To all radio amateurs
SB PROP ARL ARLP018
ARLP018 The ARRL Solar Report
Solar activity has been at low levels with frequent C-class flaring observed primarily from Regions 4420 and 4425.
The largest flare of the period was a C5.1/Sf on April 29 from Region 4420. Region 4420 showed some slight decline in areal ext
ent with flux submergence noted in the trailing spots, though rotation and consolidation in the leading spots persist, and the
region retains its delta configuration. Region 4425 showed some movement in the trailer spots with overall simplification, incl
uding loss of a delta spot. Slight growth was observed in Regions 4423 and 4424, with new flux emergence noted in both. Region
4428 exhibited growth with the separation of the bipoles. Region 4427 remained an unremarkable unipolar spot in decay.
No Earth-directed coronal mass ejections (CMEs) were observed in available coronagraph imagery.
Solar activity is likely to reach moderate levels (R1-R2, minor-moderate) through May 2, with a slight chance for X-class flare
s (R3-strong or greater) due primarily to the flare potential of regions 4420 and 4425.
Solar wind parameters were at near background levels throughout the period. Solar wind speeds steadily declined from around 355
km/s early in the period to near 310 km/s, with a slight recovery to around 320 km/s by end of period.
Enhanced conditions are expected to persist through May 1, though confidence is moderate given the relatively small source coro
nal hole. A return to near nominal levels is expected by May 2.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, April 30, 2026, by F. K. Janda, OK1HH:
Following a surprisingly low level of solar activity between April 9 and 13, when the solar flux fell below 100 s.f.u., there w
as a surprising reversal in the form of a significant increase in both overall and flare activity during the last third of Apri
l. On April 24, two X-class flares were observed, and on April 26, the solar flux exceeded 150 s.f.u.
The last day with high geomagnetic activity was April 21. The rest of the month was mostly quiet. This was consistent with a re
duction in the area of coronal holes, none of which were adjacent to active regions. Consequently, conditions for shortwave ion
ospheric propagation gradually improved, particularly in the final days of April.
A decline in solar activity is expected in the first third of May, while if the configuration of active regions and coronal hol
es resembles that observed in April, geomagnetically quiet conditions could continue until May 5. In the coming days, a deterio
ration in ionospheric shortwave propagation can be expected as a result of low solar activity and increased geomagnetic activit
y.
The Predicted Planetary A Index for May 2 to May 8 is 5, 8, 8, 5, 5, 20, and 15 with a mean of 9.4. The Predicted Planetary K I
ndex is 2, 3, 3, 2, 2, 5, and 4 with a mean of 3.0. 10.7 centimeter flux is 148, 142, 140, 140, 135, 135, and 135 with a mean o
f 139.3.
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Se
rvice web page at www.arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see www.arrl.org
/the-sun-the-earth-the-ionosphere. Information and tutorials on propagation can be found at http://k9la.us.
Also, check this: "Understanding Solar Indices" from September 2002, QST. https://bit.ly/3Rc8Njt
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