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ARRL Propagation Bulletin ARLP019 (2016)

ARLP019 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 19  ARLP019
From Tad Cook, K7RA
Seattle, WA  May 6, 2016
To all radio amateurs 

ARLP019 Propagation de K7RA

Solar activity increased last week, making one of those occasional
upticks on the way down from the peak of the solar cycle.

Average daily sunspot numbers increased from 43.3 to 74.7, and
average daily solar flux increased by 10 points to 91.9. Average
planetary A index went from 9.4 to 11.3 and average mid-latitude A
index went from 11.6 to 10.7.

At 0415 UTC on May 2 the Australian Space Forecast Centre issued a
geomagnetic disturbance warning. At the end of the day, the
planetary A index was 31, indicating a geomagnetic storm.

The latest forecast has solar flux at 90 on May 6, 85 on May 7-12,
90 on May 13, 95 on May 14-15, 90 on May 16, 82 on May 17-22 and 85
on May 23, 90 on May 24, 95 on May 25-28, then 90, 95 and 105 on May
29-31, 110 on June 1-2, 105 on June 3, 100 on June 4-6, and 95 on
June 7-11. Solar flux is forecast to drop below 90 on June 12 and

Predicted planetary A index is 8 on May 6, 12 and 18 on May 7-8, 25
on May 9-10, then 20 on May 11, 8 on May 12-13, 12 on May 14 and 5
on May 15-18, and 12, 15, 12, 8, 5 and 10 on May 19-24, and 5 on May
25-27. The next active days are June 6-8, when the planetary A index
is expected to be 18, 25 and 20.

The OK1HH geomagnetic activity forecast for the period May 6-June 1,
2016.  The geomagnetic field will be:

Quiet on May 7-8, 16-17, 26-28, June 1
Mostly Quiet on May 9, 14, 18, 22, 29, 31
Quiet to Unsettled on May 6, 13, 21, 23-25
Quiet to Active on May 12, 15, 19-20
Active to Disturbed on May 10-11, 30

Increases in the solar wind from coronal holes are expected on May
7, 12-14, (17,) 22-26, 31, and June 1.

Parenthesis means lower probability of activity enhancement.

David Moore sent a link to an article titled, "Spectacular Solar
Flare Captured in New NASA Video." The link is, .  The flare occurred on April 17. That day,
the high latitude College A index (measured at Fairbanks, Alaska)
was 33. But a few days earlier the index was higher, at 45 and 47 on
April 13-14.

As the season shifts toward Summer, you may notice some changes in
HF propagation. For instance, on 15 meters from California to Japan,
back at the Vernal Equinox you would see good strong signals, with
openings beginning around 2100 UTC and fading out around 0430 UTC.
The path should be open 75-100% of the time from 2130-0300 UTC. But
by the middle of this month you might see signals several dB lower
and the path not as robust, with the probability of openings being
more toward the 50-75% range. Openings would begin around 2000 UTC
and signals should start getting weaker after 0300 UTC.

On 40 meters over the same path at the Vernal Equinox (around March
23) we would see the band start to open after 0630 UTC with strong
signals through the night until around 1530 UTC. But by the middle
of May, the period that this path is open is much shorter, starting
around 0830 UTC and fading out after 1400 UTC.

Looking the other direction, from California to Atlanta, Georgia
during the Spring, the strongest 40 meter signals over that path
would be between 0230-1200 UTC. But by the middle of May that
opening would shift to 0300-1030 UTC.

You can play with these numbers yourself, varying seasons, locations
and frequencies by using a propagation prediction program. A free
one, W6ELprop, is available from K9LA. His web site is and he has lots of useful information on radio
propagation. The link to propagation programs is at .  An alternate source is at .

If you would like to make a comment or have a tip for our readers,
email the author at

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at, For an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at More good
information and tutorials on propagation are at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for April 28 through May 4 were 84, 82, 82, 76, 75,
57, and 67, with a mean of 74.7. 10.7 cm flux was 94.9, 92.4, 94,
92.2, 89.8, 90, and 90.1, with a mean of 91.9. Estimated planetary A
indices were 5, 4, 7, 16, 31, 11, and 5, with a mean of 11.3.
Estimated mid-latitude A indices were 6, 3, 9, 16, 26, 11, and 4,
with a mean of 10.7.