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ARRL Propagation Bulletin ARLP018 (2018)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 4, 2018
To all radio amateurs 

ARLP018 Propagation de K7RA

Sunspots disappeared again this week, with a blank Sun on April 28,
and continuing on every day since.

Average daily sunspot numbers dropped from 20 to 3.6, while average
daily solar flux decreased from 73.4 to 69.3.

Average daily planetary A index declined from 11.9 to 4.4 and
average mid-latitude A index went from 8.6 to 5.

Predicted solar flux is 67 on May 4-5, 68 on May 6, 69 on May 7-10,
68 on May 11-13, 70 on May 14-28, 68 on May 29 through June 9, and
70 on June 10-17.

Predicted planetary A index is 5 on May 4-5, then 18, 22, 16, 12 and
8 on May 6-10, 5 on May 11-16, then 42, 12 and 8 on May 17-19, 5 on
May 20 through June 1, then 8, 15, 12, 10 and 8 on June 2-6, 5 on
June 7-12, then 42, 12, and 8 on June 13-15 and 5 on June 16-17.

F.K. Janda, OK1HH of the Czech Propagation Interested Group has been
compiling this weekly forecast since 1978.

"Geomagnetic activity forecast for the period May 4-29, 2018

"Geomagnetic field will be: 
Quiet on May 23-26, 28-29 
Mostly quiet on May 14, 16, 21-22, 27
Quiet to unsettled on May 4, 11-13, 19-20 
Quiet to active on May 5, 8-10, 15, (18) 
Active to disturbed on May (6-7,) 17 

"Solar wind will intensify on May 5-7, (8-11,) 17-18, (19-20, 26-27) 

- Parenthesis means lower probability of activity enhancement. 
- With regard to ongoing changes, current forecasts are continuing
  to be less reliable."

Thanks to British ham Max White, M0VNG and others for alerting us to
the recent buzz about the current solar cycle perhaps reaching a
minimum sooner than predicted:

Consensus seemed to place the approaching solar minimum around two
years from now in 2020, but recent trends suggest the minimum may
appear sooner. Does this mean the turnaround and following increase
may also come sooner than previously anticipated?

K9LA has info on this:

New from Dr. Tamitha Skov: - On the
Ledge About Stealthy Solar Storms

"Dear Tad,

"Sometimes I wish I had started this Space Weather Woman thing a
decade ago. That way I would be able to do a direct comparison with
how things were during our last solar minimum in 2008. But then I
realize, I wouldn't have had the benefit of you giving me timely
reports from your local areas on social media. I wouldn't have heard
you talking about the impacts you were experiencing during these
solar events. This reminds me how grateful I am to all of you today.
If it weren't for you, I would never know the extent to which Space
Weather affects our everyday lives.

"This brings me to this week's forecast video. I am still shaking my
head that we managed to miss a stealthy solar storm that brought
aurora clear down to Illinois, USA. Guaranteed, national grids were
on high alert as we crossed through the G2-level storm threshold.
The irony that this stealthy solar storm occurred while we convened
a workshop on how to predict them is not lost on me. In fact, it's
kind of a cosmic cattle prod. If we can experience such a strong
solar storm that surprised us all--so near solar minimum--what does
that say about our forecasting ability?

"I hope events like these serve as a wakeup call to us scientists,
forecasters, and meteorologists alike. Although this week the
Earth-facing side of the Sun is reasonably quiet, I will take this
moment to reflect on all the work we have yet to do. In fact, that's
exactly what I was doing while sitting on my window ledge during my
last night in Switzerland (see the picture above). I was reflecting.
Thanks so much for reminding me how important all of this is.



Ever seen this?

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For more information concerning radio propagation, see the ARRL
Technical Information Service web page 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

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bulletins are at

Sunspot numbers for April 26 through May 2, 2018 were 14, 11, 0, 0,
0, 0, and 0, with a mean of 3.6. 10.7 cm flux was 69.4, 68.7, 70.2,
71.1, 70.2, 68.4, and 67.1, with a mean of 69.3. Estimated planetary
A indices were 4, 6, 4, 4, 6, 3, and 4, with a mean of 4.4.
Estimated mid-latitude A indices were 4, 5, 5, 3, 10, 3, and 5, with
a mean of 5.


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