To complement the Daily Summary for Wednesday, 14 April 1999
TRACKING WEATHER SYSTEMS
The low and high pressure systems of mid-latitude surface weather
maps are migratory. Often these systems appear to take preferred,
seasonal tracks across the country. As an exercise, we can track
these systems over several days or a week.
Movement of these systems can be monitored on a tracking
chart. Positions of systems from surface weather maps
are plotted on the tracking chart at regular intervals to give
a picture of their progression.
WHAT IS NEEDED
Using a blank US base map such
as that found on the Online Weather Homepage, you can:
- Locate the centers of the lows (cyclones) and highs (anticyclones)
on the 0Z and 12Z surface maps from the Online Weather Homepage.
You should select only those well-defined cyclones or anticyclones
that have at least one closed isobar and that can be found twelve
hours later. Plot the location of the centers of cyclones and
anticyclones at 12 hour intervals (00 and 12 Z) from the surface
analyses onto your base map. For clarity, you may want to use
separate base maps for cyclones and anticyclones.
- Mark the position of the pressure center (H or L) on the tracking
chart with a circle and neatly plot the time above that location.
- Connect the location circles for the same cyclone/anticyclone
with a black line.
As an additional feature, you could also inspect the upper air
charts for the same time interval. Often times, the surface weather
systems are steered by the mid tropospheric winds. Therefore,
inspect the 500 mb analysis charts for 0Z and 12Z from the Online
Weather Homepage. Look at the direction of the 500 mb flow
above the particular surface weather feature.
WHAT INFORMATION CAN BE DETERMINED
While you are monitoring the movement of weather systems, you
may want to consider and identify:
- In what direction(s) did the cyclones move? Did you detect
any preferential tracks? If so, where were these tracks located?
- In what direction(s) did the anticyclones move? Did you detect
any preferential tracks? If so, where were the tracks?
- How do these surface pressure features move with respect to
the upper level flow patterns?
- Did you find that any systems formed in the region during
the interval? If so, where did these systems appear?
- Did any systems decay? If so, where did they finally disappear?
- What happened when a system moving east from the Pacific approaches
the Western states? Could you track these systems across the mountains
and into the Plains states?
Return to the Wednesday Daily Weather Summary
Return to Online Weather Homepage
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological
Society.
