Tropical Cyclone - It's the generic term for a non-frontal large scale low-pressure system over tropical or sub-tropical waters. These systems have organized convection (i.e. thunderstorm activity) as well as a definite cyclonic surface wind circulation. When the cyclonic winds become sustained at 40 mph they are called tropical storms. They become hurricanes when sustained winds reach 74 mph or greater.

Psychrometer - An instrument used to measure the water vapor content of the air. The first pantented instrument that was coined a "psychrometer" was invented in 1818 by a German inventor named Ernst Ferdinand August.

Derecho - A widespread and usually fast-moving complex of thunderstorms that produce damaging straight-line winds. These systems are long lived, as the swath of wind damage associated with them extends for hundreds of miles. Wind gusts can range from 60 to over 100 mph in a derecho.

GFS (Global Forecast System) - One of the American operational forecast models run at the National Centers for Environmental Prediction. GFS stands for Global Forecast System. The GFS model is run 4 times a day and it covers the entire globe. GFS forecast output can extend up to 384 hours from when it is run.

Rime Ice - A white, granular, and opaque deposit of ice formed by the rapid freezing of supercooled water droplets onto a surface. Rime ice can accumulate to a few inches on trees and other objects when subfreezing air and fog lingers over a region for an extended period of time. A type off precipitation known as graupel is created by the accumulation of rime ice on ice crystals.

Glory - An optical phenomena that consists of colorful rings that appear around the shadow of an object when the shadow is cast onto a cloud deck below the objects elevation. A glory consists of violet coloring on the inner portion, while a reddish tint is seen on the outer edge. An airplane that casts a shadow on a cloud deck below it can create a glory that can be seen by passengers in the plane.

Upslope Fog - A type of fog forms when light winds push moist air up a hillside or mountainside to a level where the air cools adiabatically to the point that it reaches saturation. At this point water vapor condenses into water droplets, thereby forming a layer of fog.