Propagation Forecast Bulletin 41

ARLP041 Propagation de K7RA

Sunspot numbers and solar flux softened over the past week, with average daily sunspot numbers declining from 120.9 to just 37, and daily solar flux down from 122.7 to 93.8. These numbers the October 1-7 activity against the previous seven days.

Average planetary A index was way up, from 5.1 to 24.3. The A index reading of 77 on Wednesday was a big factor in the
high average. That is a huge number, indicating a strong geomagnetic.

Predicted solar flux for the near term is 80 on October 9-10, 85 on 11, 90 on October 12, 95 on October 13-14, 100 on October-16, 130 on October 17-18, 125 on October 19, 120 on October-25, 115 on October 26, 110 on October 27 and 100 on October-29.

Solar flux is predicted to decline to 85 on November 1-3, then rise 130 on November 12-14.

Predicted planetary A index is 27 on October 9, 12 on October 10-11, and 15 on October 12-13, 12 on October 14-15, then 10, 12, 8, 10 12 on October 16-20, followed by 8 on October 21-27, then 10, 12and 10 on October 28-30, 12 on October 31 to November 1, then 8, 12and 15 on November 2-4, then 20, 18 and 12 on November 5-7, and 8 on November 8-11.

A geomagnetic forecast comes to us from Tomas Bayer of the BudkovGeomagnetic Observatory in South Bohemia (Czech Republic):

“Currently, active conditions should continue after the storm yesterday (at the Budkov observatory, the seventh K-index reading on October 8 has reached 6). The first three days of the forecast week (October 10-12), we expect at the Budkov observatory at most unsettled conditions. After day 4 (October 13), geomagnetic conditions should turn to quiet, nevertheless, an isolated active episode is possible. Day 5 (October 14), we expect at most unsettled conditions, the rest of forecast week should be at most quiet with a short active episode.”

We also have a weekly geomagnetic forecast from F.K. Janda, OK1HH of the Czech Propagation Interest Group. He expects the geomagnetic field will be active to disturbed October 9-10, quiet to active October 11, quiet to unsettled October 12, quiet to active October 13, quiet to unsettled October 14-15, quiet to active October 16-17, mostly quiet October 18-19, quiet to active October 20, mostly quiet October 21, quiet to unsettled October 22, quiet on October 23-24,
quiet to unsettled October 25, quiet on October 26, mostly quiet October 27, quiet to unsettled October 28-29, quiet to active October 30, quiet to unsettled October 31, quiet to active November 1, and active to disturbed on November 2-4.

He expects increased solar wind on October 9-10, 16-17, 19-20 and November 2-4.

John Van Dalen, N7AME of Everett, Washington wrote, “My read of the last week have been disgusting to say the least. The East Coast seems to be enjoying some propagation as does South America and the lower 48. But it appears that Washington State is in a real slump unless I have a radio problems or all three antenna have gone bad.”

Yes, the high levels of geomagnetic disturbance this week have had a disruptive effect on HF propagation. John reminds us of a useful tool for propagation work, the online version of VOACAP:

It’s easy to use and works great. The predicted mean sunspot number for the month is already entered, so all you need are the two endpoints of the path you want to look at.

Jon Jones, N0JK in Kansas reports a nice 6 meter opening during all the geomagnetic upset:

“A surprise 6 meter F2 opening occurred the afternoon of October 7 between the Caribbean, Central America and Gulf Coast and Midwest states.

“The solar flux was only 83, but the Boulder K index went to 7 causing a class G3 geomagnetic storm.

“Aurora was spotted in northern W9 and W0 at 1900z.

“Around 1925z FG8OJ was spotted to south Texas along with VP2ETE.

“I was on the radio at 1940z. TI3/W7RI popped up 59++ on 50.110 MHz and in my log at 1941z. Scott, TI3/W7RI worked many stations over the next 25 minutes. Other TI stations active included TI5XP and WA8NJR/TI5. The TI stations worked W8, W9 and W0 along with the Gulf Coast states. This was one hop F2. By 2005z the TI – Midwest opening
was over. A brief but intense opening. Stations further south heard the OA4TT/b for another hour or so.”

Thanks, Jon!

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

My own archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format at and .

Click on “Download this file” to download the archive, and ignore the security warning about file format. Pop-up blockers may suppress the download.

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 October 1 through 7 were 73, 58, 47, 18, 15, 24, and 24, with a mean of 37. 10.7 cm flux was 119.7, 107.4, 96.9, 88.3, 82.6, 81.4, and 80.5, with a mean of 93.8. Estimated planetary A indices were 11, 14, 11, 20, 18, 19, and 77, with a mean of 24.3. Estimated mid-latitude A indices were 8, 9, 10, 16, 12, 11, and 44, with a mean of 15.7.

From K7RA Solar Update


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