geology-As directed by your instructor, complete

CWS 8B – 1


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1. As directed by your instructor, complete this activity with its associated images. Also
print any other Summary or Supplemental files designated.
2. Reference: Chapter 8 in the Weather Studies textbook. Complete the Investigations in the
Weather Studies Investigations Manual as directed by your instructor.

We are aware from Stüve diagrams that weather is a 3D phenomenon; conditions extend
upward through the atmosphere. The Monday Current Weather Studies 8A examined forces
arising from horizontal pressure differences that put air into motion. Once in motion,
Coriolis and friction forces emerge, and the combination leads to the spiraling circulations
around Lows and Highs as seen on surface weather maps. Here we extend our examination
of weather systems into that third dimension by including upper air maps. We will compare
the surface weather map to the display of atmospheric conditions on a mid-tropospheric map.
Image 1 is the surface weather map for 12Z 28 OCT 2014, Tuesday morning. A welldeveloped storm system was swirling as it crossed the north-central U.S. The low-pressure
center of the system was located over the upper peninsula of Michigan. A short warm front
that became stationary extended to the southeast from the Low center. A cold front curved
south and southwestward to Texas to reach another pair of local low-pressure points along
the front that then became stationary before dissipating across Arizona and southern
California. Another storm system could be seen off the Pacific Northwest coast. A High was
located over the Atlantic extending into the Southeast with another in the northern
Intermountain West.
1. It can be seen in Image 1 that Chicago, in northeast Illinois behind the cold front, was
cooler and less humid than stations in the warm sector ahead of the cold front. Chicago’s
station model showed one of the highest surface wind speeds at map time. The wind
speed was about [(15)(25)(45)] knots.
2. Chicago’s wind direction was oriented [(parallel)(at an angle)] to the nearby 1008-mb
isobar. This wind pattern was a result of the combination of horizontal forces acting on
air near the surface, including the pressure gradient force directed generally toward the
3. The overall circulation pattern of surface winds about the Low center was counterclockwise, and its [(inward)(outward)] motion was a result of the friction force near the
surface. The circulation about the High off the East coast was clockwise but also across
isobars due to friction.

CWS 8B – 2

Image 2 is the 500-mb constant-pressure map for 12Z 28 OCT 2014, the upper-air conditions
over the coterminous U.S. and adjacent areas of Canada and Mexico at the same time as the
conditions shown on the Image 1 surface weather map.
Conditions at 500-mb are those in the middle troposphere associated with the surface
conditions shown on a surface map at the same time. Weather systems extend well into the
troposphere and a three-dimensional understanding of them is necessary for making accurate
weather forecasts.
Maps of upper-atmospheric conditions are made twice each day at 00Z and 12Z from data
gathered by rawinsonde (radiosondes tracked for wind information) soundings. Those upper
air maps and Stüve diagrams displayed on the course website are created from the radiosonde
instruments launched from about 70 stations across the continental U.S. and Canada/Mexico.
On an upper-air map, the temperature, dewpoint, height and wind data from a station’s
rawinsonde report at a specific pressure are plotted around each station location (at the
forward end of the wind arrow) in an upper-air station model format, as discussed earlier in
Investigation 8B and the User’s Guide, linked from the Extras section of the course website.
4. On the 500-mb map, the plotted report for Detroit/Pontiac, in southeastern Michigan,
shows that, at the 500-mb pressure level over the station, the temperature was
[(–8)(–13)(–23)] °C.
5. The dewpoint at 500 mb over Detroit was [(–11)(–27)(–42)] °C.
6. Recalling that the heights plotted at individual stations on 500-mb maps are in tens of
meters (add a 0 to the three plotted digits), the coded height at Detroit (“568”) indicated
500 mb occurred at [(5820)(5720)(5680)] meters above sea level.
7. The wind at Detroit was generally from the southwest at about [(20)(35)(65)] knots.
[Note: When winds of 50 knots or greater are reported, a pennant is used on the station’s
wind shaft for a 50-kt increment along with the appropriate number of long and short
The following data were from a rawinsonde report at another station’s 500-mb level at
12Z 28 OCT 2014 (note that temperature, dewpoint and wind speed values are rounded for
plotting) –
Height (m): 5540, temperature (°C): –21.7, dewpoint (°C): –41.7,
wind direction (deg. clockwise from N): 320 (i.e. W is 270°),
wind speed (kts): 39.
8. Examining the stations plotted on the 500-mb map in Image 2 shows this station to be
[(Glasgow, MT)(Pittsburgh, PA)]. Current rawinsonde reports of upper air data can be
found from the Upper Air section, “Upper Air Data – Text” on the course website.
The pattern of 500-mb heights (heights above sea level where the air pressure is 500 mb as
found by radiosondes at that time) can be shown by contour lines. To better visualize the

CWS 8B – 3

contour pattern plotted by the computer on the Image 2 map, highlight the blue 5580-m
contour by tracing over it. [The 5580-m contour is labeled in southern Iowa. It enters across
northwestern Washington State to Canada and back into the U.S. curving over Iowa before
moving northeastward exiting into Canada.]
9. The contour pattern of the 500-mb map has [(only a trough in the central U.S.)
(only ridges in the eastern and western U.S.)(both a central trough and adjacent
10. Comparing the wind speeds in general for the 500-mb level with those at similar
locations for the surface at 12Z 28 OCT 2014, shows that, as altitude in the atmosphere
increases, wind speeds generally [(decrease)(remain the same)(increase)]. This
relationship results partially from the absence of friction in the middle and upper
11. The 500-mb map also shows that, where contour lines are relatively close, such as across
the north-central portion of the country, wind speeds are relatively [(low)(high)]
compared to where contour lines are more widely spaced. This principle corresponds to
that of the spacing of isobars and wind speeds on surface maps.
12. At upper levels, the wind directions are also related to the contours. That is, especially
where winds are relatively fast, the winds are generally [(“parallel” to the contours)
(directed across the contours at large angles)].
The absence of friction at upper levels means that flow is controlled mainly by the pressure
gradient and Coriolis forces. Therefore, winds are generally along the contours on upper
level maps as opposed to the inward circulations with Lows and outward with Highs seen on
surface maps. Compare these 500-mb flows to those seen on the Image 1 surface map.
13. Using the 500-mb station values as well as the contour pattern, compare the heights at
International Falls, in northern Minnesota, with those at Caribou, in northern Maine, and
Quillayute, in western Washington State, stations at approximately equal latitudes. The
500-mb height was [(lower)(higher)] over International Falls compared to those over
Caribou and Quillayute.
14. Also compare the temperatures for International Falls and Caribou/Quillayute. The 500mb temperature at International Falls was ‒28 °C. The 500-mb temperature over
International Falls is [(lower)(higher)] compared to Caribou/Quillayute 500-mb
temperatures. As you recall, the relation of column temperatures to heights of pressure
surfaces was examined using conceptual “pressure blocks” in Investigation 5B.
Image 3 is the twenty-four hour water vapor animation from 11Z 27 OCT to 10Z 28 OCT
2014. The geostationary satellite water vapor sensor detects extensive water vapor at middle
levels of the troposphere (typically 700 to 400 mb) as gray shades, with clouds as bright
white and relatively dry regions as dark. The animation displays atmospheric flows that
begin with the time of the 500-mb map. Observe several cycles of the animation.

CWS 8B – 4

15. The bright white areas on the water vapor loop show the clouds associated with the storm
system and its fronts on the Image 1 surface map. The loop shows the general west to
east flow of atmospheric systems. The circulation of the weather system was centered
over the Great Lakes region rotating in a [(clockwise)(counterclockwise)] direction. This
flow pattern is consistent with the Low shown on the Image 1 map.
Middle and upper tropospheric conditions are inextricably linked with surface weather
features. They are involved in the development and movement of weather systems over the
Earth. We will consider these relationships along with upper tropospheric maps and
conditions in Current Weather Studies 9A.

If directed by your instructor, place the answers to Investigation 8B and Current Weather
Studies 8B on the B Answer Form linked from the AMS Weather Studies website.
Return to AMS RealTime Weather Portal
©Copyright 2014, American Meteorological Society

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