Subject: Weekly Highlights of Solar and Geomagnetic Activity, 26 May - 01 June 2025

:Product: Weekly Highlights and Forecasts
:Issued: 2025 Jun 02 0216 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
26 May - 01 June 2025

Solar activity ranged from low to high levels. Regions 4098 (S04,
L=021, class/area Dai/180 on 26 May), 4100 (N08, L=244, class/area
Eki/440 on 30 May) and 4104 (N06, L=216, class/area Dso/080 on 30
May) all produced M-class flare activity this period. A majority of
the activity originated from Region 4100 to include the largest
event of the period, a long duration M8.1 flare observed at 31/0005
UTC. Associated with this event was a 1,938 km/s Type II sweep, a
Type IV sweep, a 1,000 sfu Tenflare and a Castelli-U radio
signature. Wide-spread coronal dimming in EUV imagery was followed
by a full-halo CME signature, first identified in GOES-19 CCOR-1
imagery at 31/0030 UTC. Model and analysis of this event suggested
the CME's estimated time of arrival at Earth to be early to
midday on 01 Jun.

A 10 MeV proton event occured during the period associated with the
CME event. 10 MeV protons first exceed the 10 pfu threshold at
31/1710 UTC, peaked at 666 pfu at 01/0915 UTC and was still in
progress as of this writing.

The greater than 2 MeV electron flux at geosynchronous orbit was at
high levels on 26, 29-31 May and 01 Jun with a maximum flux of 9,160
pfu reached at 31/1620 UTC. Normal to moderate levels occured on
27-28 May.

Geomagnetic field activity was at quiet to severe (G4-Severe) storm
levels during the period. Unsettled to active levels were observed
on 26-28 May due to negative polarity CH HSS influence. Minor (G1)
to Strong (G3) storm conditions were observed on 29 May due to CIR
effects in advance of a new negative polarity CH HSS. Quiet to
isolated G1 (Minor) readings were observed on 30-31 May under
continued negative polarity CH HSS influence. On 01 Jun, activity
increased to G4 (Severe) storm levels as CME effects from the early
31 May flare reached Earth. During the 01 Jun activity, Bt reached
27 nT, Bz reached as far south as -24 nT and wind speeds exceeded
1100 km/s.

Forecast of Solar and Geomagnetic Activity
02 June - 28 June 2025

Solar activity is likely to reach moderate levels
(R1-R2/Minor-Moderate), with a chance for R3 (Strong), through 06
Jun as Region 4100 makes it to the west limb. A chance for M-class
(R1-R2) X-ray activity will persist throughout the outlook period
due to multiple regions on the visible as well as multiple active
regions scheduled to return from the farside of the Sun.

The current proton event in progress is expected to end on 02 Jun
with no additional events expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at high levels on 03-05, 14-22 and 26-28 Jun
following recurrent coronal hole influence. The remainder of the
period is expected to be at normal to moderate levels.

Geomagnetic field activity is expected to be at mostly elevated
levels due to anticipated influence from miltiple, recurrent coronal
holes. G1 (Minor) to G2 (Moderate) geomagnetic storms are likely on
02-03 Jun due to waning CME effects. Unsettled to active conditions
are likely on 04-07 and 10-12 Jun due to recurrent negative polarity
CH HSS influence. Unsettled to G1 (Minor) conditions are likely on
13-22 Jun due to positive polarity CH HSS influence. Unsettled to G1
(Minor) conditions are likely on 23-28 Jun due to negative polarity
CH HSS influence.



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* Origin: NOAA Space Weather Prediction Center (3:633/280.2@fidonet)