:Product: Forecast Discussion
:Issued: 2021 Sep 18 0030 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
Solar Activity

.24 hr Summary...
Solar activity reached low levels due to an impulsive C3 x-ray event on
the SE limb observed at 17/0420 UTC. Associated with this event were
lower frequency radio emissions including a Type II radio sweep observed
at 17/0417 UTC as well as a CME just beyond the East limb beginning at
17/0428 UTC in coronagraph imagery. Bright surging on the SE limb, along
with B and C-class activity, portends the possible return of old Rgn
2860 (S29, L=002). 

No Earth-directed CMEs were observed.

.Forecast...
Solar activity is expected to be very low, with a chance for C-class
activity on 18-20 Sep due to potential flare activity on the SE limb.

Energetic Particle

.24 hr Summary...
The greater than 2 MeV electron flux reached moderate levels and the
greater than 10 MeV proton flux was steady at background levels.

.Forecast...
The greater than 2 MeV electron flux is expected to be moderate to high
on 18-20 Sep due to recent CME activity combined with possible CH HSS
activity. The greater than 10 MeV proton flux is expected to continue at
background levels.

Solar Wind

.24 hr Summary...
Solar wind parameters indicated the onset of the 13 Sep CME at 17/0130
UTC. Solar wind speed ranged from 290-421 km/s. Total field reached a
maximum of 15 nT at 17/1809 UTC while the Bz component was between
+11/-13 nT. Phi angle was mostly positive.

.Forecast...
Moderate enhancements in the solar wind parameters are expected to
continue due to CME effects coupled with the likely onset of a negative
polarity CH HSS. Enhanced conditions should persist through 19 Sep.

Geospace

.24 hr Summary...
The geomagnetic field was at quiet to G1 (minor) storm levels due to CME
effects.

.Forecast...
The geomagnetic field is expected to be at unsettled to G2 (Moderate)
geomagnetic storm levels on 18 Sep as CME effects persist followed by
the onset of a negative polarity CH HSS. Quiet to unsettled levels are
expected on 19 Sep followed by mostly quiet conditions on 20 Sep as
effects wane.