:Product: Forecast Discussion
:Issued: 2026 Apr 18 0030 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
Solar Activity

.24 hr Summary...
Solar activity was at low levels. The largest event of the period was a
C4.1/Sf flare from Region 4419 (N13E15, Eki/beta-gamma). Slight growth
in area and magnetic complexity was observed in the regions. Slight
growth was observed in the intermediate area of Region 4416 (N20W78,
Dso/beta). This region produced numerous B-class flares.

No Earth directed CMEs were observed in coronagraph imagery. 

.Forecast...
Solar activity is expected to be low with a chance for M-class (R1-R2,
Minor-Moderate) flare on 18-20 Apr primarily due to the flare potential
of Region 4419.

Energetic Particle

.24 hr Summary...
Electrons greater than 2 MeV at geosynchronous orbit reached high levels
with a peak of 2,441 pfu observed at 17/1650 UTC. The greater than 10
MeV proton flux was at background levels.

.Forecast...
The greater than 2 MeV electron flux is expected to briefly drop to
normal to moderate levels on 18 Apr with the arrival of a negative
polarity CH HSS. Flux levels are expected to increase back to high
levels on 19-20 Apr. The greater than 10 MeV proton flux is expected to
continue at background levels on 18-20 Apr.

Solar Wind

.24 hr Summary...
Solar wind parameters continued at nominal levels through about 17/1750
UTC. Total field ranged from 4-12 nT, while the Bz component was between
+/- 5 nT. Solar wind speeds varied between approximately 280-360 km/s.
After 17/1750 UTC, phi angle became variable between positive and
negative orientations through the end of the period.

.Forecast...
Solar wind parameters are expected to become more enhanced early on 18
Apr with the arrival of a CIR followed by negative polarity CH HSS
activity. Solar wind speeds ranging from 600-700 km/s are likely based
onrecurrent values. Enhanced conditions are expected to persist through
21 Apr.

Geospace

.24 hr Summary...
The geomagnetic field was at quiet levels.

.Forecast...
The geomagnetic field is expected to be at quiet to active levels
through early on 18 Apr. For the remainder of 18 Apr, CH HSS geomagnetic
conditions are expected to increase to G1-G2 (Minor-Moderate)
geomagnetic storming levels. Active to G1 (Minor) levels are expected to
continue through 19 Apr followed by unsettled to active conditions on 20
Apr as HSS effects persist.