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ARRL Propagation Bulletin ARLP017 (2020)

ARLP017 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 17  ARLP017
From Tad Cook, K7RA
Seattle, WA  April 24, 2020
To all radio amateurs 

ARLP017 Propagation de K7RA

The last day with a visible sunspot was April 4.
Over the past reporting week, April 16 to 22, average daily solar flux
was 69, down a half point from the previous week, when the average
was 69.5.
Average daily planetary A index was 7.3 while mid-latitude A index
was 7.  This was up from 6.1 and 5, mainly due to the first
geomagnetic storm of 2020, which pushed planetary A index to 18 on
April 19.  That event bumped up the average.
Solar flux numbers have been soft of late, with averages over recent
weeks of 71.1, 69.4, 70.2, 69.5 and now 69.  Lower solar flux
probably means less radiation that might excite the ionosphere.
Predicted solar flux is 71 on April 24 to 30 and 69 on May 1 through
June 7.  Actually, the April 23 forecast shows predicted solar flux
at 96 on May 12, but we've seen this error once in the past.  The 
digits were transposed.  
The predicted planetary A index is forecast at 5 on April 24 to 29, 8
on April 30, 5 on May 1 to 4, 12 on May 5, 5 on May 6 to 16, then 12, 10,
8 and 10 on May 17 to 20, 5 on May 21 to 23, then 10, 5, 5 and 8 on May
24 to 27, 5 on May 28 to 31, 12 on June 1, and 5 on June 2 to 7.
Geomagnetic activity forecast for the period April 24 to May 19, 2020
from F. K. Janda, OK1HH.
Geomagnetic field will be: 
Quiet on:  May 1 to 3, 6, 13 to 15, 19 
Quiet to unsettled on:  April 24, 28, 30.  May 18 
Quiet to active on:  (April 25, 27, May 5, 7 to 9, 12, 17) 
Unsettled to active on:  (April 26, 29, May 4, 10 and 11, 16) 
Active to disturbed:  nothing expected 
Solar wind will intensify on April 17 to 19, (20,) 26 to 28, May 4
to 6, 8 to 10
- Parenthesis means lower probability of activity enhancement. 
- The predictability of changes remains lower as there are no
Frank, W3LPL alerted us to an updated cycle 25 prediction:
"Early this month SWPC published their official updated prediction
of Solar Cycle 25 in a new user- interactive graph format.  Their
updated prediction is based on the results of NOAA's Solar Cycle 25
Prediction Panel.
SWPC forecasts a solar maximum between 105 and 125 with the peak
occurring between November 2024 and March 2026.  There is broad
consensus that Solar Minimum is ongoing this year -- or may have
already occurred -- and that Cycle 25 will have no major change in
the level of solar activity compared to Cycle 24.
For many years SWPC's solar cycle predictions have used the Royal
Observatory of Belgium's International Sunspot Number.  SWPC's 
official solar cycle prediction now uses the SWPC sunspot number. 
The International Sunspot Number is typically about one third lower
than the SWPC sunspot number.  
While this is SWPC's official Cycle 25 prediction, its important to
note there is still divergence among various forecasting methods and
members of the space weather forecasting community.  Most forecasts
and forecasters agree that the Cycle 25 peak is likely to be within
plus or minus 20 percent of Cycle 24 and is likely to occur between
2024 and 2027."
N0JK reported from Kansas: 
"I had sporadic-E on 50 MHz April 21.  From 1900 to 2100z stations in
Florida were coming in well.  Made about a dozen contacts on FT8.  
Also decoded CO8LY FL20 calling CQ.
Then saw on the PSK Reporter two Kansas stations copied HC5VF in
Ecuador on 6 Meter FT8 around 2310z.  This likely via multi-hop
Tamitha Skov, WX6SWW has a new report:
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 and the ARRL Technical Information
Service at  For an
explanation of 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 16 through 22, 2020 were 0, 0, 0, 0, 0, 0,
and 0, with a mean of 0. 10.7 cm flux was 68.5, 67.9, 69.8, 68.6,
68.2, 69.1, and 70.7, with a mean of 69.  Estimated planetary A
indices were 5, 4, 4, 3, 18, 9, and 8, with a mean of 7.3.  Middle
latitude A index was 5, 4, 4, 2, 16, 8, and 10, with a mean of 7.


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