1	Chapter 10: Cyclones: East of the Rocky Mountain
2	Extratropical Cyclones Extratropical cyclones are large swirling storm systems that form along the jetstream between 30 and 70 latitude. The entire life cycle of an extratropical cyclone can span several days to well over a week. The storm covers areas ranging from several hundred to thousand miles across.
3	Mid-Latitude Cyclones Mid-latitude cyclones form along a boundary separating polar air from warmer air to the south. These cyclones are large-scale systems that typically travels eastward over great distance and bring precipitations over wide areas. Lasting a week or more.
4	Polar Front Theory Bjerknes, the founder of the Bergen school of meteorology, developed a polar front theory during WWI to describe the formation, growth, and dissipation of mid-latitude cyclones.
5	Life Cycle of Mid-Latitude Cyclone Cyclogenesis Mature Cyclone Occlusion
6	Life Cycle of Extratropical Cyclone Extratropical cyclones form and intensify quickly, typically reaching maximum intensity (lowest central pressure) within 36 to 48 hours of formation. è development (cyclogenesis) phase The storms can sometime maintain a peak intensity for one to two days. è mature phase Dissipation of a cyclone to a point where its clouds and circulations are no longer coherent can take several more days to over a week. è occlusion phase.
7	Extratropical Cyclones in North America
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9	Flows Cross Over a Mountain
10	Typical Environment Prior the Cyclone A cold, dry airmass over Canada and the northern US A warm, humid airmass over the southern and eastern US A warm, dry airmass over the higher elevations of the western US and Mexico A cool moist airmass over the noreastern US and Canada.
11	Initial Development of the Cyclone
12	Initial Movement of the Cyclone at Surface
13	Early Weather Along the Front
14	South of the Cyclone Center
15	Summary of Early Weather East of the Cyclone: widespread clouds and precipitations to the north of the warm front in the forms of rain, freezing rain, and/or snow. South of the Cyclone: a line of showers or thunderstorms forms along the leading eastern-most boundary, which could be the upper-level front, dry line, or a cold front. These two precipitation centers (east and south) form a “Comma” cloud. Northwest of the Cyclone: Snow forms along the up-slope side of the Rockies.
16	Cyclone Intensification A cyclone intensifies as its central pressure lowers and the pressure gradients surrounding the low-pressure center strengthen. Intensification of low-level pressure gradients causes an increase in wind speed throughout the cyclone, tightening the temperature and moisture gradients in the vicinity of the fronts, and creating heavier precipitation and more possibility for sever weather. The central low pressure within a cyclone will intensify if the divergence aloft (due to jetstreak and curvature) exceeds the convergence into the low in the boundary layer due to friction.
17	How to Produce Storm Intensification
18	The Mature Cyclone
19	The Dissipating Cyclone Dissipation of the cyclone can take several days to over a week depending on the maximum intensity of the storm. During this time, active weather still occurs along the frontal boundary. As cold air continues to move southeastward, the upper-level trough will continue to deepen and will eventually cut off from the main flow. This “cutoff low” aloft has cold air in the center. The low at the surface is directly underneath the cutoff low aloft, and the whole system slowly spin down as frictional convergence raises the pressure of the surface low.