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Module 7: Analyze This - Mid-Latitude Cyclone Case Study

Heng Jia Le, Benedict (2584017)

Embry-Riddle Aeronautical University Asia

WEAX 201: Meteorology 1

Mrs. Yvette Benavides

November 28, 2021

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1. Surface map with station model observations

Visual Indicator 1:

With Reference to the surface map (With station model observations) over the US
Great Lakes region, a mid-latitude cyclone is identified in the stage of advance occlusion.
This can be supported with the visual indicator of the presence of a counter-clockwise wind
flow around the low pressure area.

The station models located around the low pressure center denote that there is a
counter-clockwise wind flow around the low pressure area. The wind direction is shown on
the wind barb of the station model, evidently showing a counter-clockwise flow about the
low pressure center, circling the storm. The temperature around the low pressure center that is
denoted in red numbers on the top left of each station model shows that the air temperature is
low and cold air is present around the storm as well. Thus, the counter-clockwise wind flow
around the low pressure area is a visual indicator of a mid-latitude cyclone in an advance
occlusion stage.
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2. Surface map with IR satellite imagery

Visual Indicator 2:
With Reference from the surface map (IR satellite imagery) over the US Great Lakes
region, a mid-latitude cyclone is identified in the stage of advance occlusion.
This can be supported with the visual indicator of a occluded front seen from the surface
map.The colors on the IR satellite imagery of the surface map mark key temperature ranges
around the area. Located right of the low pressure areas, it can observe that the cold front
(Blue Triangles) catches up and overtakes the warm front (Red semi-circles), which forms an
occluded front (Purple triangles and semi-circles) near the state of Wisconsin. When this
happens, it indicates that the mid-latitude cyclone is in an advance occlusion stage. At the
advance occlusion stage, cold air now encircling the storm, and the warm sector reduced.
This is evident of the colours on the IR satellite imagery, showing the low temperature
present at the occluded front. Thus, the occluded front is a visual indicator of a mid-latitude
cyclone in an advance occlusion stage.
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Specific Visual Evidence

A specific visual evidence that was identified is on the surface map with IR satellite
imagery. An inverted C shape cloud that is flowing in a circular pattern can be observed on
the map, located on the east side of the United States, which is evident that there is an
advancing mid-latitude cyclone. The clouds illustrated on the surface map (IR satellite
imagery) also show how they are spread over a wide area in the surface warm front and
spread in a narrow band in the area of a surface cold front. The cold air is observed to be
encircling the storm, and the energy supply from the warm front sector is reduced, thus,
dissipating the weather system.
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3. 500 mb map

Visual Indicator 3:

With Reference from 500 mb map over the US Great Lakes region, the visual

indicator of a mid-latitude cyclone in an advance occlusion stage is the trough that can be

identified at the low pressure area denoted with a red letter “L”, located around the state of

Illinois. Upper-level atmospheric support is required for mid-latitude cyclone development, in

the form of net upper level divergence or convergence, in order to achieve a net removal of

air and lowering pressure, or a net addition of air and rising pressure. (Ahrens & Henson,

2021). In addition to generating upper level convergence and divergence, the deepening of

troughs and ridges by shortwaves creates temperature advection in the upper levels. Warm

Air Advection where the wind blows across isotherms from warmer air towards colder air can

be identified at the east side of the trough. The temperature range of the warm air advection is
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between -14 degrees Celsius to -16 degrees Celsius, as identified on the station model on the

500mb map. Cold Air Advection where wind blows across isotherms from colder air towards

warmer air can be identified at the west side of the trough. The temperature range of the cold

air advection is between -28 degrees Celsius to -24 degrees Celsius, as identified on the

station model on the 500mb map. The advection process is evident as seen from the 500mb

map’s isotherms (Red dashed lines) as wind is blowing across it.

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4. 300 mb map

Visual Indicator 4:

The visual indicator on 300 mb map is the presence of a strong upper-level divergence. The

300 mb map is primarily used to locate the jet stream. The jet stream is identified where the

wind speed is 70 kt (81 mph / 130 km/h) or greater (colored shading). Ideal position above

the surface low of the jet streak to enhance storm development if the divergent region of the

jet streak is positioned directly over the surface low, where upward vertical motion is

enhanced, and the surface low will deepen. This phenomenon can be observed in the state of

Michigan where a region of strong upper-level divergence is associated with a jet stream. The

jet stream can be seen traveling from the west to the east, located over the surface low

pressure area denoted as a red letter “L”. 

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References

Ahrens, C. D., & Henson, R. (2021). Meteorology today: an introduction to weather,

climate and the environment (13th ed). Cengage.