Download Lecture 4 METR 1111 - University of Oklahoma

Lecture 4 (9/30)
METR 1111
Station Plots
and Fronts
Station Plots
• Station plots are a quick and easy way to
view the current weather conditions
- Puts METAR data in graphical format
• There are different kinds of station plots
• We will be looking at surface plots today
Temperature
• The temperature is at the upper left side of
the station’s circle.
• Measured in degrees Fahrenheit
• Temperature here is 64°F
Weather Symbol
Located directly below the temperature
• Weather symbol is not included in the
station plot if nothing
interesting is happening.
Common Weather Symbols:
Dewpoint Temperature
• Dewpoint temperature is on the bottom left
side of the station.
• This is also in degrees Fahrenheit
Cloud Cover
• Cloud Cover is indicated by the amount of
shading in the station’s circle
• no shading = clear
• 1/4th shaded = few clouds
• half shaded = scattered clouds
• 3/4ths shaded* = broken clouds
• fully shaded = overcast conditions
Sea Level Pressure
• Sea Level Pressure is on the top right side
• Need to add a 9 or a 10 in front of numbers
on map and a decimal goes between the last
two numbers
• Typical values between
970mb and 1030mb
• Here, the SLP is 1002.7mb
Wind Barbs
• Wind barb indicates wind direction & speed
• The barb points in the direction FROM where the
wind is blowing.
• Our example = southeast wind, 15kts
• Wind speed is measured (in knots) by the number
and type of flags on the barb.
• Short flag=5kts, Long flag=10kts, Triangle=50kts
What is a front?
• At a frontal boundary, some or all of the
following changes occur:
• Temperature change
• Change in dewpoint
• Wind Shift
• Pressure trough
Cold Fronts
• A cold front is a boundary where cold, dry
air is sliding under warm, moist air.
• A typical temperature change with a cold
front is about 20°F but varies greatly
More on Cold Fronts
• Ahead of a cold front, winds are usually south to
southeastrly winds. Behind a cold front, winds
usually from the north or northwest.
• A cold front is denoted on a surface map like this
• Filled triangles point
towards direction
of movement
3-D Picture of Cold Front
• Notice the warm air is lifted up and over the
cold air and forms clouds. Warm air is less
dense than cold air so it rises where they
meet.
Warm Fronts
• A warm front is a boundary where warm,
moist air is advancing against cooler, drier
air.
• Temperature change averages 15°F but
varies.
More on warm fronts
• Ahead of a warm front, winds are usually
east or northeasterly winds. Behind it,
south to southwesterly winds prevail.
• A warm front looks like this where the half
circles point toward the direction it’s
moving.
Stationary Front
• Boundary between warm, moist air and cold
dry air in which neither air mass is
advancing.
• Indicated by alternating blue triangles and
red half circles.
• Often happens when front loses it’s “punch”
or is blocked by high pressure.
Occluded front
• A occluded front, or occlusion, occurs when
a warm air mass and a cool air mass come
in contact with each other, making
boundaries at both the ground as well as
aloft.
• Often associated with showers or snow(in
winter) and is the beginning of the end to a
storm.
• Indicated by triangles and half circles on the
same side.
For next time:
• Complete homework 4 (already posted)
• Read Chapter 5 What Makes Rain?
• Collect your assignments and quizzes at the
back of the room.
• Don’t forget I drop 1 homework and 1 quiz