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Lab 8: Mid-Latitude Cyclones
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Lab 8: Mid-Latitude Cyclones
Mature Stage
What are they?
Norwegian Polar Front Theory
6. Perturbation continues to grow as cold front advances
7. Warm air lifted by convergence in low, temperature contrasts along fronts
8. Precipitation produced in zones of uplift
9. Passage of fronts produces distinct shifts in wind directions
*Polar front theory developed in Norway after World War I
*Explained evolution of mid-latitude cyclones in terms of surface patterns *Employed analogy of battle fronts to describe clash of air masses
*Suffered from lack of knowledge of upper atmospheric patterns
*Provided a good description of how surface patterns evolve, but couldn't explain why
Jacob Bjerknes (1897-1975): attributed with Polar Front Theory
Mid-latitude cyclones are huge weather systems that form from a low pressure system and cover a wide area with precipitation.
Cycolgenesis
: the formation of a mid-latitude cyclone
Why do we care?
1. Polar front separates cold polar easterlies from warm westerlies
2. Frontal boundary initially stationary
A little help to get started...
3. Small perturbation forms in frontal boundary, incipient wave develops
4. Central low develops due to convergence and uplift, along with cyclonic circulation
5. Perturbation amplifies, warm and cold fronts develop and start advancing
"Storm of the Century" Blizzard Conditions in Asheville, NC (1993)
Cyclones are important!
They travel far
(thousands of miles),
they travel big
(hundreds of miles wide),
they travel tough
(precipitation, winds,
severe weather)...
Page 88, Tuesday Map
Occluded State
Final Recap
These cyclones can bring continuous precipitation for many days covering a large area of the US and during the winter, especially, wintry conditions can spread across much of the US with one storm system, even in the southern regions.
Most intense stage (maximum cloud cover and precipitation, and steepest pressure gradient).
*Answer Questions #1-23 (#24, 25, and Review Questions are optional)
*Next week: Lab 9-Severe Weather Workshop
10. Advancing cold front begins to overtake warm front
11. Warm sector gets lifted off the surface
12. Storm begins to weaken
Evolution typically occurs over a few days, and storms can re-intensify and repeat cycle