CWS 1B - 1
AIR PRESSURE AND WIND
Note: This Activity is the same as AMS Weather Studies Current Weather Studies 1B from
Preview Week. Students only need to complete the Activity once.
1. If directed by your instructor, print this file.
2. Print the associated Current Weather Studies B Image 1 File.
3. Print the Daily Summary and/or Supplemental Information Files, if directed by your
instructor.
To Complete Investigation:
1. Reference: Chapter 1 in the Weather Studies textbook.
2. Complete Investigation 1B in the Weather Studies Investigations Manual as directed by
your instructor.
3. Complete this Monday online-delivered Current Weather Studies 1B activity if directed
by your instructor.
While summer-season weather across the “lower 48” states may bring severe thunderstorms
and even tropical systems, there are usually few strong extra-tropical low-pressure systems.
Strong temperature contrasts that fuel major low-pressure systems are often confined to
higher latitudes in summertime, i.e. Canada. Near the end of August 2014, one moderate
low-pressure system did form in the north-central Plains States and move northeastward into
southern Canada.
Image 1 is the “U.S. - Data” map from the RealTime Weather Portal for 18Z 21 AUG 2014.
It depicts weather conditions at individual locations across the contiguous U.S. plotted using
a coded format called the “station model”. The station model will be explained in more
detail in Investigation 2A.
1. Selected weather-reporting stations are shown on the map as circles. The wind directions
at those reporting stations are shown by the line (which can be thought of as an arrow
shaft) depicting the air flow into each circle. In meteorology, wind at a station is
identified by the direction from which the air is flowing, i.e., air arriving at the station
from the north is called a north wind. This helps to identify the atmospheric conditions
of the arriving air. Therefore the wind direction at San Antonio, in south-central Texas,
at map time was generally from the [(west)(north)(east)(south)].
2. Given the direction the wind at San Antonio was from, it would be reported as a
[(west)(north)(east)(south)] wind.
CWS 1B - 2
The wind speed is reported by a combination of long (10 knots) and short (5 knots)
“feathers” attached to the direction shaft. At map time, San Antonio had a 15-knot wind (one
long and one short feather). [A double circle without a direction shaft signifies calm
conditions, such as Grand Junction, in western Colorado, whereas a shaft without feathers
would denote 1-2 knots. One knot (1 nautical mile per hour) is about 1.2 land (statute) miles
per hour.]
3. A bold red “L” has already been marked on the map along the eastern portion of the
border between North and South Dakota to denote the general center of low pressure in
that area. Compare the hand-twist model of a Low to the wind directions at stations
surrounding the low-pressure center. Wind directions at these stations suggest that, as
seen from above, the air spiraled generally [(clockwise)(counterclockwise)] around this
Northern Hemisphere low-pressure center.
4. The winds at stations near the low-pressure center indicated that the air also was directed
generally [(inward toward)(outward from)] the low-pressure center.
5. This wind flow pattern about the Low is therefore [(consistent with)(contrary to)] the
hand-twist model of a Low.
6. A bold blue “H” has been marked on the map in central Alabama to denote the general
center of high pressure in that area. Compare the hand-twist model of a High to the wind
directions at stations in the several-state area surrounding the high-pressure center. Wind
directions at these stations suggest that, as seen from above, the air spiraled generally
[(clockwise)(counterclockwise)] around this Northern Hemisphere high-pressure center.
7. The air also spiraled generally [(inward toward)(outward from)] the high-pressure
center.
8. This wind flow pattern about the High is [(consistent with)(contrary to)] the hand-twist
model of a High.
9. The surface weather map from the Monday Current Weather Studies A (Image 2) on the
course website was for the same time as this activity’s Image 1. The Monday Image 2
weather map shows the pressure analysis using isobars. The isobar pattern on the
Monday Image 2 map [(did)(did not)] generally depict the positions of the L and the H
found on this CWS Image 1 map. (Also, if you look at the isobar pattern you drew on
Monday’s Image 1 map; it should also reveal these same pressure centers.)
When the current weather map available on the RealTime Weather Portal shows centers of
Lows or Highs near your location, you might consider your local wind direction (as reported
on weathercasts or shown by a nearby flag flapping in the wind, for example) with map
circulations and the hand-twist model of weather systems. The typical designation of the Ls
and Hs as centers of stormy and fair weather systems, respectively, can be compared to
satellite views showing clouds across the U.S. Check to see if the region immediately around
a Low is generally cloudy or the broad area centered on a High as mostly clear.
CWS 1B - 3
A website that dynamically displays the forecast wind flow at the time shown in both
direction and speed at locations across the U.S. can be found at: http://hint.fm/wind/.
Moving your cursor across the map will give the wind speeds at specific locations. You
might compare the wind flow patterns seen at this site to those of the latest surface weather
map’s positioning of Highs and Lows. Another interactive map showing winds across the
globe is: http://earth.nullschool.net/.
Further details for deciphering station data can be found in your User’s Guide (linked from
the RealTime Weather Portal). The reporting surface weather stations plotted on course
maps can be identified from the “Available Surface Stations” link on the course website’s
Surface data section and identities given in the “User’s Guide”. Also a map of National
Weather Service offices can be found at:
http://www.wrh.noaa.gov/wrh/forecastoffice_tab.php.
One tool for wind speed conversions between miles per hour and knots (as well as other
quantities) and their formulae can be found at: http://www.srh.noaa.gov/epz/?n=wxcalc.
If directed by your instructor, place the answers to Investigation 1B and Current Weather
Studies 1B on the B Answer Form linked from the RealTime Weather Portal.
Return to AMS Weather Studies RealTime Weather Portal
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