Investigation SURFACE AIR PRESSURE PATTERNS

Investigation 1A: Applications
SURFACE AIR PRESSURE PATTERNS
Weather Studies: Investigations Manual 2012-2013 & Summer 2013
1A - 7
Figure 2 (“Pressures” map) was acquired from the course website and reports surface air
pressures (corrected to sea level) rounded to the nearest whole millibar at 12Z 29 NOV 2011.
[12Z is numerically four hours “ahead” of Eastern Standard Time (EST), so the 12Z map
depicts conditions at local times of 7 AM EST (6 AM CST, 5 AM MST and 4 AM PST).]
5. The highest reported pressure on the map was at Valentine, Nebraska, Pocatello, Idaho
and Elko, Nevada. It is [(1028)(1031)(1036)] mb.
6. The lowest plotted air pressure on the map was 1003 mb at [(Atlanta, Georgia)
(Columbus, Ohio)(Amarillo, Texas)].
7. The isobars in the conventional series that will be needed to complete the pressure
analysis between the lowest and highest values on this map are:
[(1002, 1006, 1010, 1014, 1018, 1022)(1003, 1007, 1011, 1015, 1019, 1023)
(1004, 1008, 1012, 1016, 1020, 1024, 1028)]. When an isobar value of pressure occurs
at a single point and surrounding pressures are either all less than or all greater than that
value, that isobar need not be drawn.
More than one isobar of the same value may need to be drawn on the map if pressure values
located in separate sections of the map area require it. Several isobars have already been
drawn in the western U.S. The 1020- and 1024-mb isobars in the southwestern U.S. have
been started and need to be completed.
To complete the pressure analysis of the map, refer to the Tips on Drawing Isobars in the
first portion of the Investigation. Using a pencil, follow the steps below to complete the
pressure analysis for the rest of the map area to determine the pressure pattern that existed at
the time the observations were made. Consider each pressure value to be located at the center
of the reported number.
8. While any isobar value of the set may be chosen to be drawn, let us finish the 1024-mb
isobar already begun. From northern New Mexico bend the isobar east and northeastward
to the Great Lakes region. Continue generally northeastward fitting it between numbers
where lower values are to the right and higher to the left while passing through the
middle of 1024 values until reaching the edge of the plotted map area – at Lake Superior.
Label this isobar with its value, 1024, at the end of the isobar line where it leaves the map
field similar to its beginning. The pressure values across the northwestern U.S. north and
west of the 1024-mb isobar are [(less than)(equal to)(greater than)] 1024 mb.