Coronal Mass Ejections (CMEs) are large expulsions of plasma and magnetic field from the Sun’s corona. When geoeffective (directed toward earth), aurora is likely.

The OVATION (Oval Variation, Assessment, Tracking, Intensity, and Online Nowcasting) model is an empirical model of the intensity of the aurora developed at the Johns Hopkins University, Applied Physics Laboratory by Patrick Newell and co-workers1.   The model uses the solar wind velocity and interplanetary magnetic field measured at the L1 orbit position at 1.6 million km (1 million miles) upstream from earth as input and calculates three types of electron precipitation and the proton precipitation which strongly correlate with the aurora. An estimate of aurora viewing probability can be derived by assuming a linear relationship to the intensity of the aurora.

Source: NOAA Space Weather, AGU Pubs

Green.

The Aurora Chasers explain it with a video.

https://youtu.be/1GFmuuKePpw

And the National Park Service explains it in an article.

https://www.nps.gov/articles/-articles-aps-v8-i1-c9.htm

A forecast is a description of the space environment at a future date based on actual data, proxies and models.

Forecasts are the predictions of future events, based on analysis and modeling of the past and present conditions of the environment. Space weather forecasts are typically for conditions 1-3 days in advance.

In Space Weather, persistence and recurrence of active regions on the sun over the 27-day solar rotational period play an important role in accurately forecasting the space environment.

Source: NOAA Space Weather

The 27-day Space Weather Outlook Table, issued Mondays by 1500 UTC, is a numerical forecast of three key solar-geophysical indices.

Source: NOAA Space Weather

interplanetary magnetic field (IMF)

The Kp-index The strongest observed geomagnetic activity over a 3 hour period, from ground-based magnetometers around the world. The Kp level does not tell you that the aurora is out.

Sources: NOAA Space Weather,  Space Weather Live

Bz is the measure of the North/South orientation of the interplanetary magnetic field measured perpendicular to the ecliptic plane.  When Bz is southward, or antiparallel to the Earth’s magnetic field, geomagnetic disturbances become much more severe than when Bz is northward. In the graph, sun is on the left, and earth is on the right. Bz is seen in the north/south direction over the earth graphic.

Source: NOAA Space Weather

An intense burst of radiation coming from the release of magnetic energy associated with sunspots.

This is a little hard to explain in written word for the basic science class, or new aurora watcher, so here is a video that explains it with animation.

https://youtu.be/g9owdmL2UWQ

Zenith is the point of the celestial sphere directly overhead at a given place on Earth from the observer. These two graphs explain visually.

Sources: Support to Aviation Control Service and NASA

A & B-class are the lowest class of solar flares.

C-class solar flares are minor solar flares.

M-class solar flares are what we call the medium large solar flares.

X-class solar flares are the biggest and strongest and may result in a great aurora display. When you hear about an X-class solar flare, watch the aurora forecast and data over the next few days.

Further reading: SpaceWeatherLive and Wikipedia

A G5 storm is equivalent to Kp 9.

G1 – Kp 5

G2 – Kp 6

G3 – Kp 7

G4 – Kp 8

G5 – Kp 9

Here is a link with an explanation of the G scales (Geomagnetic Storms):

https://www.swpc.noaa.gov/noaa-scales-explanation

The Deep Space Climate Observatory, or DSCOVR, gives real-time solar wind observations so that forecasters can provide early warnings about geomagnetic storms. It acts like a sensor buoy at sea that warns of an oncoming tsunami—DSCOVR can warn forecasters 15 to 60 minutes before solar storms reach Earth.

DSCOVR is a joint mission between NASA, NOAA, and the USAF and was designed as a successor to NASA’s Advanced Composition Explorer (ACE).

Source: https://solarsystem.nasa.gov/missions/DSCOVR/in-depth/