After weeks of calm, solar activity is suddenly high again, with two
strong solar flares erupting from opposite sides of the Sun. A
Coronal Mass Ejection (CME) was associated with a strong solar flare
on May 12, but modeling shows the ejection passing behind Earth. The
geomagnetic field has been at unsettled to active conditions.

A CME associated with a filament eruption in the northern hemisphere
is expected to pass above Earth on May 17, glancing influences will
likely enhance the solar wind field during this time. The
co-rotating interacting region (CIR) associated with the large,
positive polarity Coronal Hole (CH) in the southern hemisphere is
expected to become geoeffective on May 18 which will further enhance
the field.

There remains a 65% chance that M-Class (R1-R2, Minor-Moderate)
level flare activity will occur through May 18 with a 30% chance for
X-Class (R3-Strong) levels during the same time due to the complex
magnetic field within Region AR4087.
 
The solar wind reflected influences from the Coronal Hole High-Speed
Stream (CH HSS) originating from the negative polarity coronal hole
in the southwest part of the sun.
 
The forecast of Solar and Geomagnetic Activity for May 17 to June 2,
2025:

Solar activity is expected to be predominantly low through the
outlook period, with varying chances for M-class flare activity.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at moderate levels until May 28, and again on June 6
and 7.  High levels are expected from May 29 to June 5 as CH HSS
influences increase during this time.

Geomagnetic field activity is anticipated to reach minor storm
levels on May 28 to June 1 under negative polarity CH HSS
influences.

Active levels are likely June 2 and 6.  Mostly unsettled levels are
likely on May 18 to 21, as well as June 2 and 5.  Quiet levels are
expected on May 22 to 26.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - May 15, 2025, from F. K. Janda, OK1HH:

"The level of solar activity in the first half of May mostly did not
resemble the current peak of the 25th 11-year cycle. The total
number of sunspot groups across the disk ranged from two (May 2) to
six (May 11), with no more than one larger group - first the
relatively quiet AR4079 and then the eruptively very active AR4086
(whose growth could already be tracked prior to disk rise on the
http://jsoc.stanford.edu/ - 'Helioseismic Far-Side Imaging'
website).

"Ionospheric shortwave propagation conditions were mostly poor to
below average. The main culprit was not the slightly lower level of
solar radiation, but was mainly the solar wind. The Earth's
ionosphere was under the influence of elevated free electron
concentrations on most days, while was later bombarded by protons
following the increase in flare activity in AR4086 with subsequent
CMEs.

"The consequence was not so much lower MUF values as increased
attenuation and scattering in the ionosphere. This was all the more
advantageous for stations with higher powers and, in particular,
with antenna systems with low radiation angles.

"Further increases in solar activity in the northern half of the
solar disk are still expected in the coming months but cannot be
predicted more accurately. In modern times, however, we can monitor
it closely - and prepare for it all the better and in good time."

On May 16, Spaceweather.com reports that an Aurora warning is issued
for the planet Mars!

The latest solar report from Dr. Tamitha Skov, WX6SWW, can be found
on YouTube at: https://youtu.be/5hRRuaP-bT0?si=bQr5hSz0vc8WPepn .

For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .

Also, check this:

https://bit.ly/3Rc8Njt

"Understanding Solar Indices" from September 2002 QST.

The Predicted Planetary A Index for May 17 to 23 is 5, 8, 10, 8, 8,
6, and 6, with a mean of 7.3.  The Predicted Planetary K Index is 2,
3, 4, 3, 3, 2, and 2, with a mean of 2.7.  10.7 centimeter flux is
115, 115, 120, 125, 125, 125, and 130, with a mean of 122.1.