At 0631 UTC on April 20 the Australian Space Forecast Centre issued a Geomagnetic Disturbance Warning.

“Earth is currently under the influence of a high-speed stream from a negative polarity equatorial coronal hole. Geomagnetic activity at Quiet to Active levels is expected and at times may reach up to Minor Storm levels if there are notable southward Bz periods.

INCREASED GEOMAGNETIC ACTIVITY EXPECTED DUE TO CORONAL HOLE HIGH SPEED WIND STREAM FROM 20-21 APRIL 2018

GEOMAGNETIC ACTIVITY FORECAST

20 Apr:  Quiet to Active

21 Apr:  Quiet to Active”

This link to Space Weather Live explains the reference to “southward Bz periods” above: https://bit.ly/1S6H68D

Average daily sunspot number over the recent reporting week (April 12-18) rose from 0 to 5.4. Of course, any non-zero sunspot number lower than 11 is imaginary, because of the arcane method used for calculating sunspot numbers.

Every sunspot group counts for 10 points, and each sunspot within that group counts as one point. So, one sunspot in one group yields a sunspot number of 11. Three sunspots in two groups yields a daily sunspot number of 23. The last time we saw a sunspot number greater than 22 was February 9-12 when the numbers were 23, 35, 24 and 26.

So, an average daily sunspot number lower than 11 must include at least one zero-sunspot day. In the past reporting week, only three days had any sunspots.

Average daily solar flux rose from 67.7 to 69.9. Average daily planetary A index declined from 9.4 to 6.1, while average mid-latitude A index went from 8.1 to 5.6.

Predicted solar flux for the next 45 days is 72 on April 20-26, 71 on April 27, 69 on April 28 through May 5, 70 on May 6-12, 72 on May 13-19, 69 on May 20 through June 1, and 70 on June 2-3.

Predicted planetary A index is 15, 12 and 8 on April 20-22, 5 on April 23-25, 8 on April 26, 5 on April 27 through May 5, 10 on May 6, 15 on May 7-8, 10 on May 9-10, 5 on May 11-15, 12 and 10 on May 16-17, 5 on May 18 through June 1, then 10 and 12 on June 2-3.

F.K. Janda, OK1HH of the Czech Propagation Interest Group brings us his weekly geomagnetic activity forecast for the period April 20 to May 15, 2018.

“Geomagnetic field will be:

Quiet on April 24-25, 27-28, May 13-14 

Mostly quiet on April 22-23, May 15

Quiet to unsettled on April 26, 29-30, May 1, 3-5, 9, 12

Quiet to active on April (21,) May 2, 7-8, 10-11 

Active to disturbed on April (20,) May 6 

Solar wind will intensify on April (24)-25, May (2-3,) 5-6, (7-11) 

Remark:

- Parenthesis means lower probability of activity enhancement.

- With regard to ongoing changes, current forecasts are less reliable again.”

From SolarHam, which presents a weekly Monday observation: https://www.youtube.com/watch?v=TW8EXYUPcz4

Dr. Skov reports from a scientific conference in Switzerland this week: https://youtu.be/9MEEzyxJ_cw

She also corresponded directly with me . . .

“Dear Tad,

“I'm writing you while sitting in the ISSI meeting room in Bern, Switzerland listening to twelve fascinating scientists argue about solar observations. The discussion is quite lively as we learn how we can work together to detect and forecast an invisible kind of solar storm. These storms are called ‘stealth CMEs’ and they used to be rare events. But with our quiet Sun, all that is changing. There is a very good chance that these near invisible events will continue to cause surprise storms at Earth over the next decade, disrupting amateur radio, GPS, and causing issues for power grids with little or no warning of their impact. Solving this significant problem is exactly why we have assembled here in Bern.

“This week I highlight this amazing team of solar and space physicists, who are helping shape the future of Space Weather prediction. The forecast is shot in my hotel room so it has more of a ‘live’ feel than my usual studio productions. Hopefully, it not only gives you a look into the new activity our Sun brings this week, but also gives you a glimpse into the important part of my world that is Space Weather research. 

Cheers,

Tamitha"

A look at the STEREO image on Friday morning shows an active region just beyond the horizon: https://stereo.gsfc.nasa.gov/

For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of 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 12 through 18, 2018 were 13, 14, 11, 0, 0, 0, and 0, with a mean of 5.4. 10.7 cm flux was 70, 69.7, 69.5, 70.6, 69.2, 69.3, and 70.8, with a mean of 69.9. Estimated planetary A indices were 9, 9, 6, 6, 3, 4, and 6, with a mean of 6.1. Estimated mid-latitude A indices were 8, 8, 6, 5, 3, 3, and 6, with a mean of 5.6.