Chapter 8: Air Masses, Fronts, and Middle-Latitude Cyclones Air masses Air masses Fronts Fronts Middle-latitude cyclones Middle-latitude cyclones

Air Mass Source Regions air mass: an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any altitude air mass: an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any altitude source regions: regions dominated by surface high pressure source regions: regions dominated by surface high pressure Because air sinks in high pressure systems, air stays in contact with the surface and acquires its temperature and moisture characteristics.Because air sinks in high pressure systems, air stays in contact with the surface and acquires its temperature and moisture characteristics.

Table 8-1, p. 205 Classification: Temperature and humidity Naming conventions

Fig. 8-2, p. 206

cP (Continental Polar) and cA (Continental Arctic) Air Masses Continental polar Continental polar continental Arctic continental Arctic lake effect snows lake effect snows In the continental US, the coldest winter air is associated with cA air masses.

mP (Maritime polar) Air Masses Pacific air Pacific air mP air often brings rain to the west coast of the US. mP air often brings rain to the west coast of the US.

mT (Maritime Tropical Air Masses) subtropical air subtropical air Bermuda high Bermuda high mT air brings hot, muggymT air brings hot, muggy air to the eastern US in air to the eastern US in summer. summer.

cT (Continental Tropical Air Masses) Northern Mexico Northern Mexico and southwestern U.S. and southwestern U.S. Summer Summer

Fronts Fronts A transition zone between two air masses of different temperature and/or humidity

Stationary Fronts Has essentially no movement, and wind is usually parallel with the stationary front Has essentially no movement, and wind is usually parallel with the stationary front Light precipitation may or may not appear Light precipitation may or may not appear This terminology was developed by Norwegian meteorologists shortly after World War I.This terminology was developed by Norwegian meteorologists shortly after World War I.

Cold Fronts cold front: Temperature, humidity, wind direction differences cold front: Temperature, humidity, wind direction differences clouds and precipitation clouds and precipitation vertical cross section: vertical cross section: slope of 1:50 slope of 1:50

Warm Fronts overrunning: slope of 1:300 overrunning: slope of 1:300 weather changes weather changes precipitation patterns precipitation patterns vertical cross section vertical cross section

Fig. 8-19, p. 220 Dryline

Occluded Fronts cold occlusion cold occlusion warm occlusion warm occlusion Occluded fronts have characteristics of both warm and cold fronts.Occluded fronts have characteristics of both warm and cold fronts.

Polar Front Theory wave cyclone wave cyclone frontal wave frontal wave open wave open wave warm sector warm sector mature cyclone mature cyclone

Where Do Mid-Latitude Cyclones Tend to Form? cyclogenesis cyclogenesis lee-side low lee-side low Alberta Clipper Alberta Clipper Mid-latitude cyclones specific to certain areas get interesting names: Panhandle hook, nor’easter, Hatteras Low.Mid-latitude cyclones specific to certain areas get interesting names: Panhandle hook, nor’easter, Hatteras Low.

Figure 4, p. 226 Northeasters (or nor’easters): develops or intensified off the eastern seaboard of North America then move northeastward along the coast

Developing Mid-Latitude Cyclones and Anticyclones convergence and divergence convergence and divergence convergence and divergence patterns aloft are extremely important to the development of mid-latitude cyclones convergence and divergence patterns aloft are extremely important to the development of mid-latitude cyclones

Jet Streams and Developing Mid-Latitude Cyclones jet stream jet stream jet streak: jet stream core jet streak: jet stream core upper-air support upper-air support During World War II, the jet stream was used by the Japanese to carry balloon bombs across the Pacific Ocean to North America.During World War II, the jet stream was used by the Japanese to carry balloon bombs across the Pacific Ocean to North America.

Fig. 8-30, p. 231