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ARRL Propagation Bulletin ARLP033 (2020)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 14, 2020
To all radio amateurs 

ARLP033 Propagation de K7RA

New sunspot cycle 25 continues to make a strong showing.  Sunspots
appeared on every day for over three weeks, beginning on July 21.

Average daily sunspot numbers for the week slipped a bit from 19.6
to 14.3 this week, but average daily solar flux increased from 72.8
to 73.8.

Geomagnetic indicators remain quiet.  Both the average daily
planetary and mid-latitude A index were 3.7.

Predicted solar flux for the next month and a half is 72 on August
14 and 15, 70 on August 16 to 21, 72 on August 22 to 27, 73 on
August 28 and 29, 75 on August 30 to September 9, 73 on September 10
and 11, 72 on September 12 to 23, 73 on September 24 and 25, and 75
on September 26 and 27.  This is a welcome change from recent
forecasts which saw predicted solar flux consistently below 70.

Predicted planetary A index forecasts continued quiet geomagnetic
conditions, at 5 on August 14 to 23, 8 on August 24 and 25, 5 on
August 26 to 28, then 8, 16 and 8 on August 29 to 31, 5 on September
1 to 19, 8 on September 20 and 21, 5 on September 22 to 24, then 8,
16 and 8 on September 25 to 27.

Geomagnetic activity forecast for the period August 14 til September
9, 2020 from F. K. Janda, OK1HH.
"Geomagnetic field will be 
Quiet on: August 15 and 16, September 5 to 7 
Quiet to unsettled on: August 14, 17 to 19, 22, (23,) 24 and 25, (26
to 29,)
September 2 to 4, 8 and 9
Quiet to active on: (August 20 and 21, 30 and 31, September 1) 
Unsettled to active is not expected 
Active to disturbed is not expected 

Solar wind will intensify on: August (22 and 23,) 24 and 25,
September 1 and 2, (4 to 6)

Parenthesis means lower probability of activity enhancement."

Jon Jones, N0JK (EM28 in Kansas) had this comment about the mention
of 6 meter sporadic-e in last week's bulletin.  "Many of the reports
I have received for July (including long time 6M op N0LL) reported
great conditions on 50 MHz Es.  On July 13 N0LL had his FT8 screen
full of stations from Japan calling him on 50.313 MHz.  Today August
9 I had sporadic-E on 6 Meters to Florida, Texas, Mexico, and
Arizona from Kansas."

Jon is editor of the monthly "World Above 50 MHz" column in QST.

A recent video from WX6SWW, Tamitha Skov:

K9LA recently posted a survey of various solar cycle 25 predictions.
Read it at .  He also
did a presentation at on the same
subject.  The material from that event will be up for a limited
time, so catch it before it is gone on September 9.  And Carl's
Basic Concepts resource is always good for a review at .

Personally I like the prediction that promises a repeat of the epic
Cycle 19 of the late 1950s.  I was a small child then, but my father
had a low-band FM 2-way radio mounted in his company car, probably
operating somewhere between 30-40 MHz judging from my hazy memory of
the length of the bumper mounted whip antenna.

We were in Reedley, California in the San Joaquin Valley, and he
sold agricultural chemicals to farmers.  He would use the radio to
contact the office in Fresno, but at the peak of Cycle 19 local
communications were often interrupted by skip from Texas and various
states in the Midwest.

From correspondence I've received from readers, I know there were
many new teen aged hams at that time, and many just assumed that the
fantastic propagation of the day was normal.  Many were disappointed
by Cycle 20, which was when I got my Novice ticket.

So I think we are due for another big cycle, although this is purely
emotional, and I try to avoid the Gambler's Fallacy.  That is the
name of the logical fallacy in which when observing a random series
of events such as when spinning a roulette wheel, if we keep seeing
the ball land on red over and over, then we are due for black to
come up.  But with independent random events, one result cannot
predict the next.

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

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

Sunspot numbers for August 6 through 12, 2020 were 14, 14, 11, 13,
12, 12, and 24, with a mean of 14.3.  10.7 cm flux was 73.1, 74,
74.7, 73.9, 74.2, 73.5, and 73.1, with a mean of 73.8.  Estimated
planetary A indices were 5, 4, 5, 3, 3, 3, and 3, with a mean of
3.7.  Middle latitude A index was 4, 5, 5, 3, 3, 3, and 3, with a
mean of 3.7.


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