SB PROP @ ARL $ARLP018
ARLP018 Propagation Forecast

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 extent 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, including 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 flares (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 coronal 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 was a surprising reversal in the form of a significant increase in both overall and flare activity during the last third of April. 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 reduction in the area of coronal holes, none of which were adjacent to active regions. Consequently, conditions for shortwave ionospheric 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 holes resembles that observed in April, geomagnetically quiet conditions could continue until May 5. In the coming days, a deterioration in ionospheric shortwave propagation can be expected as a result of low solar activity and increased geomagnetic
activity.


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 Index 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 of 139.3.


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)


--- PyGate Linux v1.5.14
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)