METEOROLOGIST JEFF HABY
The Skew-T Log-P offers an almost instantaneous snapshot of the atmosphere from the surface
to about the 100 millibar level. The advantages and disadvantages of the Skew-T are given below:
What are some disadvantages of Skew-T's?
- Only available twice a day (00Z and 12Z)
- Character of weather can change dramatically between soundings
- Sounding does not give a true vertical dimension since wind blows balloon downstream
- Sounding does not give true instantaneous measurements since it takes several minutes to travel
from the surface to the upper troposphere
Below are all the basics lines that make up the Skew-T
Isobars-- Lines of equal pressure. They run horizontally from
left to right and are labeled on the left side of the diagram. Pressure is given in increments of 100
mb and ranges from 1050 to 100 mb. Notice the spacing between isobars increases in the vertical (thus
the name Log P).
Isotherms- Lines of equal temperature. They run from the
southwest to the northeast (thus the name skew) across the diagram and are SOLID. Increment are
given for every 10 degrees in units of Celsius. They are labeled at the bottom of the diagram.
Saturation mixing ratio lines- Lines of equal mixing ratio (mass
of water vapor divided by mass of
dry air -- grams per kilogram) These lines run from the southwest
to the northeast and are DASHED. They are labeled on the bottom of the diagram.
Wind speed and direction given for each plotted barb.
Plotted on the right of the diagram.
Dry adiabatic lapse rate- Rate of cooling (10 degrees Celsius per
kilometer) of a
rising unsaturated parcel of air. These lines slope from the southeast to the northwest
and are SOLID. Lines gradually arc to the North with height.
Moist adiabatic lapse rate-- Rate of cooling (depends on moisture
content of air) of a
rising saturated parcel of air. These lines slope from the south toward the northwest.
The MALR increases with height since
cold air has less moisture content than warm air.
Environmental sounding-- Same as the actual measured temperatures
in the atmosphere. This is the jagged line running south to north on the diagram. This line is always
to the right of the dewpoint plot.
Dewpoint plot- This is the jagged line running south to north.
It is the vertical plot of
dewpoint temperature. This line is always to the left of the environmental
Parcel lapse rate-- The temperature path a parcel would take if
raised from the
Planetary Boundary Layer. The lapse rate follows the DALR until saturation, then follows
the MALR. This line is used to calculate the
CINH, and other
Below is an example diagram showing the lines of the Skew-T Log-P diagram