SB PROP @ ARL $ARLP015
ARLP015 The ARRL Solar Report

ZCZC AP15
QST de W1AW
Propagation Forecast Bulletin 15 ARLP015

From ARRL Headquarters

Newington CT April 25, 2025
To all radio amateurs

SB PROP ARL ARLP015
ARLP015 The ARRL Solar Report

Solar activity has been at low levels with only minor C-class flaring through April 24, 2025, and is expected to be moderate with a chance of M-class
flares (R1-R2, Minor-Moderate) through April 26. No Earth-directed Coronal
Mass Ejections (CMEs) have been observed. A southwest CME was observed on
April 23 and is considered to be far-side due to the lack of any on-disk
plasma motion/flare activity.


Solar wind parameters continued to be slightly enhanced due to the Coronal
Hole High-Speed Streams (CH HSS) associated with the positive polarity
coronal holes in the southern hemisphere. Solar wind parameters are expected
to continue to be influenced by positive polarity, with CH HSS conditions through April 26. Nominal conditions are expected thereafter.


On April 25, Spaceweather.com [ http://Spaceweather.com ] reported the Earth was struck by an interplanetary shockwave on April 24 around 0700 UTC. An interplanetary shock wave is an abrupt change in the solar wind - probably caused by the Coronal Mass Ejection.


Overall, solar activity remained at low levels. Region AR4064 remained the largest sunspot group on the disk. The regions intermediate spots grew in penumbral area over the past 24 hours.


The geomagnetic field is expected to remain at mostly quiet to unsettled levels, with active conditions likely on April 27 due to the influence from multiple positive polarity CH HSS.


There are currently 11 numbered sunspot regions on the solar disk.

Solar activity is expected to be low with a chance for M-class flares on
April 26 and 27.


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://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 [ http://arrl.org/the-sun-the-earth-the-ionosphere ] . 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 ]

The Predicted Planetary A Index for April 26 to May 2 is 8, 8, 6, 6, 6, 25,
and 35, with a mean of 13.4. The Predicted Planetary K Index is 3, 3, 2, 2,
2, 5, and 6, with a mean of 3.3. Predicted 10.7 centimeter flux is 165, 165, 170, 170, 170, 170, and 175, with a mean of 169.3.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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SB PROP @ ARL $ARLP015
ARLP015 Propagation Forecast

ZCZC AP15
QST de W1AW
Propagation Forecast Bulletin 15 ARLP015

From ARRL Headquarters

Newington, CT April 10, 2026
To all radio amateurs

SB PROP ARL ARLP015
ARLP015 The ARRL Solar Report

Solar activity remained at low levels this week. Most of the C-class activity came from either Region 4414 or Region 4409, which has developed a delta spot in its intermediary area. All remaining spots were either stable or in slight decay, with Region 4406 rotating over the west limb by the end of the
reporting period.


Coronal activity was observed in CCOR-1, LASCO, and STEREO available imagery during the period.

Of the four eruptions, one was far-sided, one was too narrow plus too far
north of the ecliptic to have any Earth-directed component, and two had the potential for Earth-directed components. The first was associated with a C2.4 flare from Region 4414, while there was no clear source for the second.

Modeling indicates these eruptions will pass behind Earth's orbit, and no impact is anticipated.

Eruptions potentially associated with the C8.9 are currently being analyzed. Radio blackouts reaching the R1 levels were observed over the past 24 hours. The largest was on Apr 9th 2026, at 08:45 UTC.


Solar activity is expected to be at low levels over April 9 to 11, with a chance for M-class (R1-R2/minor-moderate) flares and a slight chance for X-class (R3/strong or greater) flares, driven primarily by the flare
potential of Regions 4409 and 4414.


A brief description of Sunspots can be found on the Space Weather Prediction Center website at www.swpc.noaa.gov/phenomena/sunspotssolar-cycle [ https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle ] .


Solar wind parameters reflected the transition out of a waning negative polarity coronal hole high-speed stream (CH HSS) into nominal conditions.
Wind speeds continued to decline from a peak of ~500 km/s to near 400 km/s by the end of the period.


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


Perhaps the biggest surprise in recent days was that, following the
geomagnetic disturbance of April 2 3 (which had been expected, albeit a day earlier and with lower intensity), there were no further major surprises.
Solar activity declined as predicted, whereas because it declined over a relatively long period, there was a greater-than-expected drop in critical frequencies in the F2 ionospheric region at mid-latitudes.


For forecasting developments in the second third of April, the 27-day cycle could serve as a relatively reliable guide this time. First of all, one might expect a one- to two-day increase in geomagnetic activity (which is also indicated by the presence of solar coronal holes near the central meridian), followed by relative calm. This is despite the short time that has elapsed since the eleven-year peak of solar activity.


The Predicted Planetary A Index for April 4 to April 10 is 5, 4, 3, 2, 2, 2, and 2 with a mean of 2.8. The Predicted Planetary K Index is 18, 10, 8, 7, 5, 4, and 7 with a mean of 8.4. 10.7 centimeter flux is 106, 105, 108, 110, 115, 115, and 120 with a mean of 111.2.


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 v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)