QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
>From Tad Cook, K7RA
Seattle, WA  May 19, 2017
To all radio amateurs 

SB PROP ARL ARLP020
ARLP020 Propagation de K7RA

The Australian Space Weather Forecast Centre issued a geomagnetic
warning at 0301 UTC on May 19:

'Geomagnetic conditions may rise to minor storm levels late on 19
May. Geomagnetic activity is expected to remain enhanced to active
to minor storm levels with some major storm periods on 20 May.
Mostly unsettled to active levels of geomagnetic activity may be
expected on 21 May with the possibility of some minor storm periods
on this day.

'INCREASED GEOMAGNETIC ACTIVITY EXPECTED DUE TO CORONAL HOLE HIGH
SPEED WIND STREAM FROM 19-21 MAY 2017.

'GEOMAGNETIC ACTIVITY FORECAST:

'19 May:  Quiet to unsettled during first half, and active to minor
storm during second half of the day

'20 May:  Active to minor storm, some major storm periods possible

'21 May:  Unsettled to active, minor storm periods possible'

We saw seven consecutive days with 0 sunspots recently on May
9-15. This overlapped the recent reporting week (May 11-17) with the
previous week. The spotless period ended on May 16 when two sunspot
groups appeared, 2656 and 2657, with sunspot numbers of 11 and 13 on
May 16-17.

Average daily sunspot numbers reported in last week's bulletin were
17.1, and the average in the current reporting week was only 3.4.
This is because last week's report covered two consecutive days with
0 sunspots, this week covered five days with no activity.

Average daily solar flux declined from 71.5 to 70.5, the average
estimated daily planetary A index rose from 6.3 to 8.3, while the
mid-latitude A index rose from 5.9 to 9.4.

Predicted solar flux (from Thursday's NOAA and USAF 45-day forecast)
is 72 on May 19-21, 74 on May 22-25, 76 on May 26-29, 74 on May 30
thru June 3, 72 on June 4, 70 on June 5-10, 72 on June 11-12, 74 on
June 13-17, 76 on June 18-25, and 74 on June 26-30.

Predicted planetary A index is 45, 30, 20 and 12 on May 19-22, 8 on
May 23-24, 5 on May 25 thru June 3, 8 on June 4, 5 on June 5-9, then
8, 12, 22, 32 and 20 on June 10-14, then 48, 36, 20, 12 and 8 on
June 15-19, and 5 on June 20 thru the end of the month.

Geomagnetic activity forecast for the period May 19-June 14, 2017
from F.K. Janda, OK1HH:

'Geomagnetic field will be
Quiet on June 1, 8
Mostly quiet on May 29, June 4, 9, 12
Quiet to unsettled May 23-28, June 5-6, 10
Quiet to active on May 21-22, June 3, 7, 11, 13
Active to disturbed on May 19 (- 20, 30-31,) June 2, 14

'Amplifications of the solar wind from coronal holes are expected on
May 19 (20-21, 31,) June (5-6,) 9 (- 14)

'Remark: - Parenthesis means lower probability of activity
enhancement and/or lower reliability of prediction.'

If you would like to make a comment or have a tip for our readers,
email the author at [email protected].

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at,
arrl.org/propagation-of-rf-signals. For an explanation of
numbers used in this bulletin, see
arrl.org/the-sun-the-earth-the-ionosphere.

An archive of past propagation bulletins is at
arrl.org/w1aw-bulletins-archive-propagation. More good
information and tutorials on propagation are at k9la.us/.

Monthly propagation charts between four USA regions and twelve
overseas locations are at arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL
bulletins are at arrl.org/bulletins.

Sunspot numbers for May 11 through 17, 2017 were 0, 0, 0, 0, 0, 11,
and 13, with a mean of 3.4. 10.7 cm flux was 69.1, 68.9, 70.4, 71.2,
70.6, 71.9, and 71.4, with a mean of 70.5. Estimated planetary A
indices were 6, 7, 4, 10, 14, 9, and 8, with a mean of 8.3.
Estimated mid-latitude A indices were 8, 6, 5, 11, 17, 10, and 9,
with a mean of 9.4.