Solar activity reached moderate levels due to an isolated M1.5/1n
flare on March 19 at 2040 UTC from Region AR4031.  Regions AR4028,
AR4034, and AR4035 exhibited slight growth.

Region AR4026 re-emerged in the Southwest quadrant. Regions in the
Northwest quadrant, including AR4020, AR4022, AR4025, and AR4031 all
appeared to be in a decay phase.

No Earth-directed CMEs were detected in available coronagraph
imagery.

No S1 (Minor) or greater solar radiation storms are expected through
March 23.

No significant active region activity favorable for radiation storm
production is forecast.

C-class flares are expected to continue to March 22, with a chance
for isolated M-class (R1-Minor) flares.

A chance for R1-R2 (Minor to Moderate) radio blackouts due to
M-class flares will persist through March 23.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - March 20, 2025, by F. K. Janda, OK1HH:

"While the current solar activity is a bit lower than we would like
and then would be consistent with the current phase of the solar
cycle, it may be a prelude to another peak within the current
11-year cycle maximum.

"This hypothesis is supported by the starting shift of the sunspot
activity from the southern hemisphere of the Sun to the northern
hemisphere (see also the M-class flares in AR4031 and the following
filament flare, i.e., in the northwest quadrant of the solar disc).

"At the same time, the presently forecasted period is likely to
begin with a transient decrease in geomagnetic activity. But this
may be interrupted as early as March 23 if an enhanced solar wind
blowing from Solar Coronal Hole 24 hits Earth.

"If this happens in the daytime, a so-called positive phase of the
disturbance could follow with an increase in MUF and a general
improvement in ionospheric shortwave propagation conditions."

Spaceweather.com has a link to an article that discusses new
evidence that cosmic rays spark lightning.

Weak disturbances in the solar wind are anticipated through March 20
in response to persistent transient/High-Speed Stream (HSS) effects
as well as possible flanking influences of a nearby CME passage that
departed the Sun on March 17. Solar wind parameters are expected to
slowly diminish on March 21.  Another enhancement is expected late
on March 22 due to the arrival of a CIR preceding a negative
polarity Coronal Hole HSS.

A CIR - or Corotating Interaction Region - is a recurring plasma
structure in the heliosphere formed when fast solar wind streams
interact with slower solar wind ahead of them.

Quiet to unsettled levels are expected on March 21. By late on March
22, unsettled to active levels are likely due to the aforementioned
CIR arrival.

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 10.7 centimeter flux for March 21 to 27 is 195, 200,
195, 190, 180, 165, and 160, with a mean of for a mean of 183.6  The
Predicted Planetary A Index is 8, 5, 5, 5, 15, 25, and 25, with a
mean of 12.6.  The Predicted Planetary K Index is 3, 2, 2, 2, 4, 5,
and 5, with a mean of 3.3.