Winter Storm Warning - It is issued by the National Weather Service when severe and life threatening winter weather conditions are occurring or are imminent. Most are issued for heavy snow and wind, but may also be issued for ice and sleet storms. The amount of snowfall needed to warrant a winter storm warning varies around the country.

Frontogenesis - The creation and amplification of a temperature gradient in a frontal zone. Fronto-genesis is essentially the process that occurs when a front is born and becoming more defined. A strengthening temperature gradient means that the temperature change from one side of the front to the other is intensifying and becoming more focused.

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.

Squall Line - A line of intense thunderstorms that are accompanied by high winds and heavy rain. Squall lines typically move through quickly and oftentimes occur along or ahead of a fast moving cold front. These lines can sometimes extend for hundreds of miles.

Haboob - An intense sand or dust storm that is driven by strong winds. Sand and dust can be driven to heights as high as 5000 feet during a particularly strong haboob. They are most common in arid regions, but can occur elsewhere during severe droughts. During the dust bowl years of the 1930's, haboobs were common across the Great Plains.

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.

Seiches - Standing waves that oscillate back and forth over an open body of water. They are most common in large bodies of water such as bays or lakes. The impetus for a seiche to occur is persistent strong winds that push water from one end of the body of water to the other. When the winds let up, the water that has been pushed to one side of the bay or lake starts to oscillate to the opposite shore and then back again. Anyone who sloshes water from one side of a bathtub to the other side has witnessed a small-scale seiche. The Great Lakes occasionally see seiche events that are noted by a rhythmic rise and fall of water levels.