:Product: Forecast Discussion
:Issued: 2026 May 26 1230 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
Solar Activity

.24 hr Summary...
Solar activity remained at low levels, with the largest event of the
reporting period being a C2.4/sf at 26/0717 UTC from Region 4448
(S08E42, Cao/beta).

As the sunspot complex in the southeast rotated further onto the visible
disk and away from the limb foreshortening affects, it was determined
that old Regions 4451 and 4446 were the same sunspot group and have been
grouped under Region 4446 (S16E43, Cko/beta-gamma), to make a total of
eight numbered regions on the visible disk. The only region to show
appreciable flux emergence and magnetic shearing was Region 4447
(S16W02, Dai/beta). All other regions were either largely stable or in
very gradual decay.

Additional activity included a partial halo CME from beyond the
Northwest limb that was observed in LASCO C2 beginning at 25/2212 UTC.
Due to the location of origin (suspected activity from old Region 4436,
L=330), no geoeffective impact is anticipated.

No Earth-directed CMEs were observed in coronagraph imagery.

.Forecast...
Solar activity is expected to be at low to moderate levels through 28
May, with a chance for isolated M-class flares (R1-R2/Minor-Moderate)
due to the flare potential of the visible disk.

Energetic Particle

.24 hr Summary...
The greater than 2 MeV electron flux at geosynchronous orbit was at low
to moderate levels. The greater than 10 MeV proton flux and the 100 MeV
flux became elevated late on 25 May, with the 10 MeV flux crossing the
S1 (Minor) threshold at 26/0010 UTC and reaching a peak flux of 2,380
pfu at 26/0110 UTC. The 100 MeV flux did not cross the alert threshold
of 1 pfu and had returned to near background levels by the end of the
reporting period.

.Forecast...
The greater than 2 MeV electron flux is expected to remain at low to
moderate levels through 28 May. There is a chance (50%) for the greater
than 10 MeV proton flux to return to S1 levels, and a slight chance
(20%) for the 100 MeV flux to reach 1 pfu, on 26 May. A return to
background values is expected for 27-28 May.

Solar Wind

.24 hr Summary...
Solar wind parameters reflected near-background conditions. The phi
angle had a distinct solar sector boundary crossing to the negative
(towards the Sun) sector at approximately 25/1400 UTC. This boundary
transition lead to a drop in density and changes in the components of
the interplanetary magnetic field. Total magnetic field (Bt) was
variable across the period, ranging from a peak of 9.5 nT down to 2 nT.
The north-south (Bz) component reached a maximum southward deflection of
-7 nT at approximately 25/1610 UTC and spent the remainder of the
reporting period gradually increasing to a maximum of 6 nT at ~26/1110
UTC. Solar wind speeds started the period around 350 km/s before rising
slightly following the SSBC to finish the period near 400 km/s.

.Forecast...
Solar wind parameters are anticipated to be at or around ambient levels
through 26 May. Enhancements are anticipated on 27 May ahead of the
arrival of a relatively weak negative polarity coronal hole high-speed
stream (-CH HSS), likely persisting through 28 May.

Geospace

.24 hr Summary...
The geomagnetic field was at quiet to unsettled levels throughout the
reporting period.

.Forecast...
The geomagnetic field is anticipated to be at mostly quiet levels on 26
May as near-background solar wind conditions persist. An increase to
unsettled to active levels is likely on 27-28 May due to the anticipated
onset and influence of a -CH HSS.