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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.
Spaceweather.com
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 www.arrl.org/propagation
and the ARRL
Technical
Information
Service 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.
NNNN
/EX
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