At 0121 UTC on April 29 the Australian Space Forecast Centre released a geomagnetic disturbance warning for April 30 and May 1. Increased geomagnetic activity is predicted due to high speed solar wind coming from a coronal hole. There is a chance of minor storm levels.

Over the past reporting week (April 21-27), average daily sunspot numbers rose from 40 to 43.3, and average daily solar flux declined from 100.8 to 81.9. This is compared to the previous seven days.

Average planetary A index went from 10.9 to 9.4, and average mid-latitude A index rose from 8.9 to 11.6.

Predicted solar flux (from the Thursday April 28 forecast) is 95 on April 29-30, 92 on May 1-2, 90 on May 3-4, 95 on May 5-10, 100 on May 11, 95 on May 12-15, 82 on May 16-24, 80 on May 25, 82 on May 26-29, and 95 on May 30 through June 6.

Predicted planetary A index (also from April 28) is 14, 26, 20, 8 and 5 on April 29 through May 3, then 12 on May 4-5, 10 on May 6, then 5 on May 7-8, then 18, 25 and 20 on May 9-11, and 8, 5 and 12 on May 12-14, 5 on May 15-18, then 12, 15 and 12 on May 19-21, 8 on May 22-23, 5 on May 24-25, then 10, 18 and 12 on May 26-28, and 5 on May 29-30, 12 on May 31, and 5 again on June 1-4.

Petr Kolman, OK1MGW, of the Czech Propagation Interest Group sends the following geomagnetic activity forecast for the period April 29-May 25, 2016.

Geomagnetic field will be:
Quiet on May 6-7, 16-17
Mostly Quiet on May 1-3, 8, 15, 22-25
Quiet to Unsettled on May 12-13, 18, 21
Quiet to Active on April 29, May 4-5, 9-11, 14, 19-20
Active to Disturbed on April 30, May (9-10) [Parenthesis means lower probability of activity enhancement]

Increases in solar wind from coronal holes are expected on April 29-30, May 4-5, 8-11, 19-21



NASA released a video of an April 17 solar flare: http://bit.ly/1WU1nOO
 Ted Leaf, K6HI, of Kona sent this similar item: http://earthsky.org/space/stunning-view-of-solar-flare-april17-2016?


Spaceweather.com reports Earth will cross a fold in the heliospheric current sheet on April 29 or 30.

http://wso.stanford.edu/gifs/HCS.html

They go on to report, “This is called a 'solar sector boundary crossing,' and it could trigger geomagnetic activity around Earth's poles. NOAA forecasters estimate a 60 percent chance of G1-class geomagnetic storms on April 29.”

We see there were multiple sunspots in evidence in this view of April 28, although none have much magnetic strength: http://bit.ly/21gMPsW

Now on April 29, you can see the sunspots have moved in one day: http://bit.ly/1SCKUt1

Sharp-eyed reader Red Willoughby, KC4LE, of Birmingham, Alabama noticed some averages that didn’t look right in the ARRL Letter released yesterday, April 28. He may have wondered why the average daily solar flux was over 100, when all of the daily flux values for the week were under one-hundred.

I goofed. The numbers were all correct, but the averages were from last week. Those averages have been corrected in today’s bulletin.


For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of the numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation. More good information and tutorials on propagation are at http://k9la.us/.

Monthly propagation charts between four USA regions and twelve overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins.

Sunspot numbers for April 21 through 27 were 35, 22, 11, 46, 38, 65, and 86, with a mean of 43.3. 10.7 cm flux was 76.8, 76.6, 78.7, 81.8, 81.9, 85.2, and 92.6, with a mean of 81.9. Estimated planetary A indices were 5, 13, 12, 11, 8, 7, and 10, with a mean of 9.4. Estimated mid-latitude A indices were 23, 13, 11, 11, 6, 6, and 11, with a mean of 11.6.