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SB PROP @ ARL
$ARLP029
ARLP029
Propagation
Forecast
ZCZC AP29
QST de W1AW
Propagation
Forecast
Bulletin 29
ARLP029
From ARRL
Headquarters
Newington, CT
July 17, 2026
To all radio
amateurs
SB PROP ARL
ARLP029
ARLP029 The
ARRL Solar
Report
Solar activity
has remained
at low levels,
with an
occasional
low-level
C-class
flaring
observed,
including a
C3.3/Sf flare
on July 15
from Region
4489. The
largest event
of the period,
a
long-duration
C8.9 flare
that peaked on
July 15,
originated
from a
returning
region on the
eastern limb.
This region is
not yet
numbered and
will be
assessed once
it has become
visible from
Earthís
perspective,
but the latest
imagery from
Solar Orbiter
suggested only
a simple and
rather average
bipolar group
with a
relatively
small
penumbra.
There are two
numbered
sunspot
regions on the
visible disk.
Region 4482
showed minor
new flux
emergence
behind its
mature primary
spot,
developing a
bipolar
configuration.
As Region 4489
rotated
further into
view and limb
foreshortening
effects
decreased,
very small
opposite-polarity
trailing spots
became
visible,
making it a
stable bipolar
group.
Additionally,
a small,
magnetically
simple, region
tracked in
Solar Orbiter
imagery has
begun to
rotate over
the east limb
near S10. No
Earth-directed
CMEs were
observed in
available
coronagraph
imagery.
Solar activity
is expected to
remain at low
levels through
July 18, with
a slight
chance for
M-class
(R1-R2/minor-moderate)
flares,
primarily
driven by
active regions
anticipated to
rotate onto
the visible
disk over the
next few days.
Solar wind
parameters
reflected
possible
combined
glancing
coronal mass
ejection (CME)
effects and
subsequent
weak positive
polarity
coronal hole
high-speed
stream (+CH
HSS)
influences.
A return to
more
ambient-like
conditions is
expected over
the next three
days.
Weekly
Commentary on
the Sun, the
Magnetosphere,
and the
Earth's
Ionosphere,
July 16, 2026,
by F. K.
Janda, OK1HH:
The
significant
decline in
solar activity
throughout the
first half of
July is
clearly
illustrated by
the solar flux
values, which
fell from 203
s.f.u. (July
2) to 100
s.f.u. (July
14ñ15), as
well as by the
number of
sunspot
groups, which
dropped from
five to two.
A significant
drop in the
critical
frequencies of
the F2 layer
began as early
as July 4
during the
geomagnetic
disturbance of
July 4ñ5, and
due to the
sharp decline
in solar
activity,
these values
returned to
average levels
only very
slowly in the
following
days.
Consequently,
the sporadic E
layer had an
even greater
impact on
shortwave
propagation
(particularly
in the
mid-latitudes
of Europe on
July 14 and
16).
The increase
in solar
activity,
which is
expected to
begin as early
as the end of
this week and
should last
nearly until
the end of the
month, will
result in
significantly
better
shortwave
propagation
conditions
than those
experienced in
the first half
of the month.
More
significant
changes
(possibly an
initial rise,
but then very
likely a
temporary drop
in MUF) will
likely be
caused by a
geomagnetic
disturbance,
which is
tentatively
expected on
July 21 and
22.
The predicted
Planetary A
Index for July
18 to 24 is 5,
5, 5, 5, 12,
10, and 7,
with a mean of
7.0. The
predicted
Planetary K
Index is 2, 2,
2, 2, 4, 3,
and 2, with a
mean of 2.4.
Predicted 10.7
centimeter
flux is 135,
135, 135, 135,
135, 135, and
135, with a
mean of 135.0.
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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