Scintillation - The apparent twinkling of a star due to its light passing through regions of differing air densities in the atmosphere. This results in the light being refracted and scattered before it reaches the viewer.

Astronomical Twilight - Is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, scattered light from the Sun is less than that from starlight and other natural sources. Before and after astronomical twilight, the sky is absolutely dark.

NAM (North American Mesoscale) - This is one of the preferred short range forecast models that are run in the US at the National Centers for Environmental Prediction in College Park, MD. The model runs four times per day, with each cycle running out to 84 hours.

Ceiling - A term that is commonly used in aviation. Ceiling is the height of the lowest layer of broken or overcast skies. This lets pilots know how far above the surface they will be once they get below the cloud layer.

Drizzle - A type of precipitation consisting of numerous tiny droplets of water less than 0.5 mm in diameter. Drizzle typically falls when there is fog or low stratus cloud cover over an area.

Parhelion (Sun dog) - The scientific name for sun dogs. This phenomenon is seen as two colored luminous spots that appear at roughly 22 degrees on both sides of the sun at the same elevation. They are caused by the refraction of sunlight passing through ice crystals. They are most commonly seen during winter in the middle latitudes and are exclusively associated with cirriform clouds. They are also known as mock suns.

Snow roller - A phenomenon that can occur when there is a wet snow on the ground combined with strong winds. Snow rollers look like the beginnings of the snowballs that humans roll when constructing a snowman.