Space Weather Forecast Discussion
Forecast Discussion
Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
Issued: 2017 Sep 21 0030 UTC

Solar Activity
.24 hr Summary...
Solar activity was very low with a few B-class flares observed. NOAA/SWPC Region 2681 (S12E73, Hsx/alpha) was assigned, but despite production of several B-class flares the region appeared magnetically simple, although foreshortening effects prevented a better analysis. Region 2680 (N08W67, Hsx/alpha) was little changed, but produced the largest B-class flare of the period - a B8 flare at 20/1932 UTC. No Earth-directed CMEs were observed in available coronagraph imagery.
Solar activity is expected to be very low, with a slight chance for C-class flares all three days (21-23 Sep) due to the combined flare potential of Regions 2681 and 2680 and based primarily off their activity trends. Although region 2680 is anticipated to rotate off the visible disk by the end of day two (22 Sep), some increased probability of C-class flares is possible by day three (23 Sep) as former Region 2673 (S09, L=119) nears closer to its return to the east limb.

Energetic Particle
.24 hr Summary...
The greater than 2 MeV electron flux was at moderate to high levels with a max flux of 33,761 pfu at 20/1840 UTC. The greater than 10 MeV proton flux continued at background values.
The greater than 2 MeV electron flux is expected to continue at high levels all three days (21-23 Sep) and the greater than 10 MeV proton flux is expected to remain at background levels.

Solar Wind
.24 hr Summary...
Solar wind parameters were indicative of continuing, but waning CH HSS influences. Total IMF strength ranged primarily from 3 to 5 nT, and the Bz component was variable between +/- 5 nT. Solar wind speed decreased from 525 km/s to start the period, down to speeds of around 450 km/s by the periods end. The phi angle remained in a positive (away from Sun) sector.
Solar wind speed is anticipated to decline unsteadily towards ambient background conditions as the influence of the positive polarity CH HSS continues to wane on days one and two (21-22 Sep). The IMF may become slightly disturbed on day three (Sep 23) due a possible solar sector boundary crossing (SSBC).

.24 hr Summary...
The geomagnetic field was quiet to unsettled in reaction to waning CH HSS influences.
The geomagnetic field is expected to be quiet to unsettled on day one (21 Sep) under waning CH HSS influences. Day two (22 Sep) is expected to be primarily quiet as the CH HSS rotates away from geoeffective position. Day three (23 Sep) is expected to be quiet to unsettled in response to a slightly disturbed IMF associated with a possible SSBC.
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