SC.912.E.7.5

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SC.912.E.7.5

• Predict future weather conditions based on
  present observations and conceptual models and
  recognize limitations and uncertainties of such
  predictions.

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Earth Systems and Patterns

• The scientific theory of the evolution of Earth
  states that changes in our planet are driven by
  the flow of energy and the cycling of matter
  through dynamic interactions among the
  atmosphere, hydrosphere, cryosphere, geosphere,
  and biosphere, and the resources used to sustain
  human civilization on Earth.  

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questions

• Some thunderstorms are caused by convection
  resulting from the collision of two air masses.
  Which describes the collision involved in this
  type of thunderstorm?
• A. Two cold fronts collide.
• B. Two warm fronts collide.
• C. A cold front moves into an area with warm air.
  
• D. A warm front moves into an area with cold air.
  

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20.5 Forecasting Weather
CHAPTER
20
CHAPTER HOME
Weather
VOCABULARY
Meteorologists must gather huge amounts of data
in order to make their predictions. They rely on
sensing instruments and on computer models to
provide the information they need.
station model
SECTION OUTLINE
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station model
CHAPTER
20
Weather
VOCABULARY
station model
A compact expression of weather information for
an area, including temperature, dew point,
weather conditions, wind speed and direction,
barometric pressure, and cloud cover.
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20.5 Forecasting Weather
CHAPTER
20
CHAPTER HOME
Weather
VOCABULARY
Meteorologists use the data to make surface
weather maps and forecasts.
station model
SECTION OUTLINE
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Surface Air Pressure Map
Lightly draw lines connecting identical values of
sea level pressure. Remember, these lines, called
isobars, do not cross each other.
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Isobars can be used to identify "Highs" and
"Lows". The pressure in a high is greater than
the surrounding air. The pressure in a low is
lower than the surrounding air.

• Label the center of the high pressure area with a
  large blue "H".
• Label the center of the high pressure area with a
  large red "L".

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High pressure regions are usually associated with
dry weather because as the air sinks it warms and
the moisture evaporates.
Low pressure regions usually bring precipitation
because when the air rises it cools and the water
vapor condenses.
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Where should we expect rain or snow? Where
should we expect dry weather?
How could we tell if it was rain or snow
expectations?
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Surface Temperature Map
You will draw lines connecting the temperatures,
much like you did with the sea-level pressure
map. However, you will also need to interpolate
between values. Interpolation involves estimating
values between stations which will enable you to
properly analyze a map.
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Isotherms are used to identify warm and cold air
masses. Where is the region with the lowest
temperatures? Where is the region with the
warmest air?
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Dewpoint Temperature Map
This map shows the dewpoint temperature for
various locations over the conterminous U.S. The
values are in F. Recall, dewpoint is the
temperature to which, if the air cooled to this
value, then the air would be completely
saturated.
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Isodrosotherms are used to identify surface
moisture. The closer the temperature and dewpoint
are together, the greater the moisture in the
atmosphere. As the moisture increases so does the
chance of rain. Also, since moist air is lighter
than dry air, the greater the moisture, the
easier for the moist air to lift into the
atmosphere resulting in a better chance for
thunderstorms. Typically, dewpoint 70F or
greater have the potential energy needed to
produce severe weather.
What will this information, combined with our
previous data sea pressures and temperatures,
tell us? Can we predict the actual temperature
and precipatation in all areas exactly?
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Surface Pressure Change Map
This map shows change in surface pressure (in
whole millibars) during the past three hours at
various locations.
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Draw lines connecting equal values of pressure
change for every two millibars. These lines are
drawn for the -8, -6, -4, -2, 0, 2, 4, 6, 8,
etc. values. Remember, like isobars, these lines
(called isallobars) are smooth and do not cross
each other.
Using a blue colored pencil, beginning at any 2
value, lightly draw lines connecting equal values
of the 2 millibars pressure change. Remember,
you will need to interpolate between values to
draw your lines correctly. Draw the remaining
"positive" pressure change value(s) at two
millibars intervals. Using red colored pencils
lightly draw a line connecting equal pressure
change values of less than zero (0). Finally,
using black, draw a line connecting the zero (0)
line.
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Cold fronts are often located in areas where the
pressure change is the greatest. The front
represents the boundary of different air masses.
Cold air is more dense than warm air so when a
cold front pass your location, the pressure
increases. We analyze for pressure change to look
for these boundaries. We can also tell where high
pressure and low pressure systems are moving by
looking where the greatest change is occurring.
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Analyzing maps with the current weather
conditions is an essential part of the entire
forecast process. Basically, if we do not know
what is currently occuring, it is near impossible
to predict what will happen in the
future. Computers have been able to analyze maps
for over 20 years. However, computers cannot
interpret what they analyze. There is no
substitute for the hand analysis. Analyzing maps
by hand causes the forecaster to study every
detail in the weather and enables him/her to
discern the continuity or "flow" of the weather.
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Great forecasts, the ones that save lives and
property, begin with the careful analysis of the
current conditions. Conversely, based upon
post-analysis, "bad" (or busted) forecasts, the
ones most remembered by the public, could have
been improved if one did a careful analysis in
the beginning. Map analysis is not too unlike
drawing in a dot-to-dot coloring book. Just as
one would draw a line from one dot to the next,
analyzing maps is similar in that we will draw
lines of equal values between dots representing
various elements of the atmosphere.
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compare, and comment on, the direction the wind
blows around high and low pressure (based upon
the arrows they drew) compared to the direction
of the staffs on the surface map.
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compare, and comment on, the cloud cover under
the areas of high and low pressure.
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what type of present weather they see plotted on
this map. What type of past weather do the
students see?
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