Warm Up January 25, 2011

Weather Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy.

Weather Maps Surface maps depict the large-scale elements of the weather. http://www.weather.com/maps/maptype/currentweatherusnational/uscurrentweather_large.html

Symbols- What do they mean? Cold front- blue triangles in the direction of the movement of the front Warm front- red half-circles in the direction of the movement of the front Stationary front- alternating blue triangles and red half-circles in both directions Occluded front- alternating triangles and half-circles usually in purple High pressure systems- H Low pressure systems- L

Fronts- The Battle of Air Masses Air masses of different temperatures and densities meet and try to move each other out. The area where air masses meet is called a “front” (just as the the area where soldiers fight is called the frontlines). Often along “fronts” we have weather events and/or precipitation.

Fronts meeting creating hail

Cold front A cold front is a moving cold air mass that displaces the warmer air in its path. Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere). Precipitation is generally at and/or behind the front. Tornados, hail and thunderstorms may occur along these fronts.

Warm Front A warm front is a moving warm air mass that replaces a colder air mass. Generally, with the passage of a warm front, the temperature and humidity increase, the pressure rises, and although the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere), it is not as pronounced as with a cold frontal passage. Precipitation, in the form of rain, snow, or drizzle, is generally found ahead of the surface front, as well as convective showers and thunderstorms. Fog is common in the cold air ahead of the front. Clearing usually occurs as the front passes.

Stationary Front The battle of the air masses is at a standstill. This often means there will be clouds, and rain until the front dissipates (scatters, disperses, is driven away).

Occluded Front Where cold, warm or cool air come together. Shown here in purple. Often associated with drying air masses.

High Pressure Happens where the atmospheric pressure is greater than that of the surrounding area. Dense air sinks making it hard for clouds to form and so fair weather is typically associated with high pressure.

Low pressure This is an area where the atmospheric pressure is lower than that of the area surrounding it. Lows are usually associated with high winds, warm air, and atmospheric lifting. Because of this, lows normally produce clouds, precipitation, and other bad weather such as tropical storms and cyclones.

Websites to Visit http://passporttoknowledge.com/storm/