Air Masses, Fronts and Weather Systems

 Movements of Air Masses and Fronts are vital to our understanding and prediction of Weather Systems  Weather Forecasting requires that we understand:  Cyclones (L=Lows) and Anticyclones (H=Highs)  Air Masses and Fronts Again, Let’s Recall the 5+ Basic Elements of the Atmosphere -- Also called Elements of Weather and Climate Solar Energy ▪ Temperature ▪ Pressure ▪ Wind ▪ Precipitation In this segment, we’ll discuss the last of these elements: + Air Masses (and Fronts)

What is an air mass? An air mass is a large body of air with same temperature and humidity Occupies thousands of square miles of the Earth’s surface, and it can be several miles high Air masses are born in a source region where they acquire their temperature and moisture characteristics Source Regions Areas dominated by high pressure serve as good source regions. High pressure also enables the air to move outward from the source region Source regions are often regions of low relief and calm wind that prevent turbulent mixing

Air Masses are Classified According to: 1. Surface of source region with associated Moisture characteristics  Continental (c)  Forms over land  dry  Maritime (m)  Forms over ocean  moist 2. Latitudinal extent of source region [Capital letters, T, P and A] with associated Temperature characteristics  Tropical (T)  Low latitudes  warm  Polar (P)  High latitudes  cold  Cold Arctic (A)  Poles  very cold

Air Masses are identified by letter codes – m for maritime (originate over ocean; moist), and c for continental (originate over land; dry). The second letter is a capital letter (A, E, P, T), to identify the latitude of the source region. Continental Arctic (cA) air mass is typically described as extremely cold and dry. Continental Antarctic (cAA) air mass is also exceedingly cold and is drier than its arctic counterpart as the source region is the continent of Antarctica. Continental Polar (cP) air mass is considered cold and dry but warmer than the arctic air mass located to its north. Continental Tropical (cT) air masses originate in the great desert areas of Earth (e.g., Sahara, Arabian, and Australian). The extremely low humidity is due to the lack of available water for evaporation.

Maritime Polar (mP) air mass is cool and moist, and it brings mild weather to coastal locations. Maritime Tropical (mT) air masses are warm and moist, and they are responsible for much of the precipitation east of the Rocky Mountains in the United States. Maritime Equatorial (mE) air masses form near the equator and are exceedingly warm and humid. Convection and convergence of these air masses in the Intertropical Convergence Zone (ITCZ) are the main reasons for the heavy rainfalls in the rainforests of this region.

FRONT Where air masses meet and do not mix. Fronts are boundaries that separate air masses

4 Types of Fronts: Cold Front Occluded Front Stationary Front Warm Front

Cold Front When a fast moving cold air mass runs into a slow moving warm air mass and the thicker cold air slides under the lighter warmer air.

A cold front symbol – the direction that the teeth point indicate the direction the front is moving. COLD FRONT  Cold air replaces warm  Much steeper than warm fronts  Advances faster than warm front  More violent weather – cumulonimbus clouds Short, sharp showers

Warm Front When a moving warm air mass collides with a slowly moving cold air mass and the warm air moves over the cold air.

Warm Front symbol – The directions that the bumps face is the direction the front is moving. WARM FRONT  Warm air replaces cold  Gentle slope (1:200)  Covers a wide area with its weather  Stratus clouds get lower as front approaches – Drizzle or steady rain

Stationary Front When a cold air mass and warm air mass meet, but neither air mass has enough force to move the other air mass.

Stationary Front Symbol

Occluded Front When a warm air mass is caught between two cooler air masses and the thicker cold air masses move underneath the thinner warm air mass and push it upward.

Occluded front symbol – The directions that the bumps face is the direction the front is moving.

Which types of fronts can you find on this map?