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 zero 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 zero 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.


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

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

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

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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.