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Lab 8: Mid-Latitude Cyclones

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Jen Bell

on 30 March 2014

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Transcript of Lab 8: Mid-Latitude Cyclones

Lab 8: Mid-Latitude Cyclones
Mid-latitude cyclones are huge weather systems that form from a low pressure system and cover a wide area with precipitation.
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.
: the formation of a mid-latitude cyclone
Why do we care?
"Storm of the Century" Blizzard Conditions in Asheville, NC (1993)
What are they?
Cyclones are important!
They travel far
(thousands of miles),
they travel big
(hundreds of miles wide),
they travel tough
(precipitation, winds,
severe weather)...

1. Polar front separates cold polar easterlies from warm westerlies
2. Frontal boundary initially stationary

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
Mature Stage
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
Occluded State
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
Norwegian Polar Front Theory
*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

Most intense stage (maximum cloud cover and precipitation, and steepest pressure gradient).

Jacob Bjerknes (1897-1975): attributed with Polar Front Theory
*Suffered from lack of knowledge of upper atmospheric patterns
*Provided a good description of how surface patterns evolve, but couldn't explain why

Final Recap
A little help to get started...
Page 88, Tuesday Map
*Answer Questions #1-23 (#24, 25, and Review Questions are optional)

*Next week: Lab 9-Severe Weather Workshop

Full transcript