Download Weather

Weather...
You can’t see me, but you feel me, you can’t touch
me, but I can touch you. I have been called the
“Breathe of the Gods”, or the killer and giver of
life, gentle and fierce, friendly and enemy, angry
and happy. The Native Americans called me
Moriah, and Snow Eater (Chinook). The Japanese
call me Kaze and in Russia I am called Veter. I can
shatter homes, or wake a child from a peaceful
sleep or bring relief in times of need. I can spread
the most dreaded diseases or bring a welcome
freshness. What am I?
Weather is....
The current state of the
atmosphere...what is happening right
now
 BUT… Climate is different
Climate – longer time scale (the average
conditions , temperature, humidity,
rainfall, winds, and other meteorological
elements over a long period of time

Main points to remember as we
learn about weather:
The sun warms the earth’s surface and
therefore all the air above the surface
 The earth is warmed most at the equator and
least at the poles---why?
 The air above land is warmed more quickly
than air above water.
 Warm air expands and rises, creating an area
of low pressure; cold air is dense and sinks,
creating an area of high pressure

What are weather variables?
Temperature
 Barometric (air) pressure
 Wind speed/ Wind Direction
 Humidity (Relative humidity)
 Precipitation


The Station Model
Weather Factors

Weather: The state of the atmosphere
at a specific time and place
TEMPERATURE=
the average motion of molecules
↑ TEMP= ↑movement of molecules= feels hot
↓ TEMP= ↓movement of molecules= feels cold
Instruments to measure
weather variables

Temperature

Measured with a
thermometer

2 common scales are
Farenheit*** and Celcius
Air Pressure- the force
exerted by a column of air
at a given point

Warm air= expanding or rising air=
leaves behind L pressure
Cold Air=sinking air= leaves an area of
H pressure
 The higher the altitude… the lower the
pressure

Air Pressure

Air pressure (H or L)
is measured with a
device called a
barometer
Units of pressure:
millibars and inches of
mercury
Air pressure rules
When air pressure is noted on station
model as greater than 500, we place a 9 in
front of the number and a decimal point at
the tenths place. Ex 506 = 950.6 mB of air
pressure
 When the air pressure is noted as less than
500, we place a 10 in front of the number
and a decimal at the tenths place Ex 467 =
1046.7 mB of air pressure

Trends in Atmospheric Pressure
If the pressure is falling… stormy
weather lies ahead
 If the pressure is rising… clear skies are
coming

Wind
-moving air
 Direction and speed are needed to
describe the wind
 Wind direction is the direction that wind
is blowing from
 Wind moves from High Pressure to Low
Pressure
 Large pressure gradient= strong winds
 The knot is a unit of speed equal to
one nautical mile per hour, which is
equal to exactly 1.852 km/h and
approximately 1.151 mph

What causes winds?
A wind is a
horizontal
movement of air
from a area of high
pressure to an area
of low pressure
 It is this difference
in pressure that
makes the air
move=wind

Winds are measured
by direction and
speed
 The anemometer is
the tool we use to
measure this
 Wind chill=↑ cooling
the wind causes

Wind speed
Wind speed is measured
using an anemometer.
Speed is measured in
mph or knots (1.15 mph
= 1 knot)
 Feathers are used to
show wind speed on a
station model

Wind direction
Wind direction is
found by using a
wind vane.
 Wind direction is
always described
as the direction
FROM which the
wind moved

Local Winds

The land cools and heats faster than the ocean.
Water holds heat longer than land, and takes longer
to heat or cool.
During the day, the land
SEA BREEZE
gets hotter faster than the
water. The heated air
rises, leaving behind an
area of low pressure.
Wind from the cooler sea
blows in to take the place
of that warmer air. These
happen during the day!
Land Breezes
At night the lands cools off faster than
the sea. Cool air sinks creating an area
of high pressure. Wind blows from the
land to the sea.
Wind Speed and Isobars
IsobarsIsolines of
equal pressure
The larger the
pressure
gradient the
faster the
The closer the
isobars the
faster the wind
Coriolis deflects winds to the right
in the northern hemisphere
Wind speed (con’t)
Draw the tail feather on a
station model
A. A 5 knot wind blows from the N
 B. A 10 knot wind blows from the N
 C. A 15 wind blows from the N
 D. A 20 knot wind blows from the N
 E. A 30 knot wind blows from the N
 F. A 35 Knot wind blows from the N
 G. Repeat A-F for a Southerly Wind, a North Easterly
Wind and a South Westerly Wind

Humidity

-the amount of water vapor in the air
(mass of water vapor/total mass of air)

The hotter the air… the more water
vapor it can hold
Relative Humidity
-the amount of water vapor in the air
compared to what the air can hold
(before the air is saturated)
 Relative humidity is defined as the ratio
of the water vapor compared to the
amount of water vapor that the water
could hold. Relative humidity is
expressed as a percentage
 High relative humidity= muggy feel or
rain

Relative Humidity
Relative humidity
is described as the
amount of water
vapor in the air
compared to the
total it can hold.
(ex. sponge)
 Measured with a
sling psychrometer

Relative Humidity

-the amount of water vapor in the air
compared to what it could hold
Dry air= 0%
 Saturated = 100%


The hotter the air… the more water
vapor it can hold
Dew Point
-the temperature at which water vapor
condenses out of the air
 - the temperature at which air is
saturated
 Dew in the moring


The hotter the air… the more water
vapor it can hold
Dry air is more dense than
moist air

Humid air is less dense than dry air
because a molecule of water (mass
=1+1+16 ≈ 18 ) is less massive than a
molecule of nitrogen (mass= 14 +14 ≈
28) and a molecule of oxygen (16+16 ≈
32).
Pressure and Moisture also have an inverse relationship
Review
As
altitude, temperature
and moisture increases,
density and pressure
decrease
Cloud Formation

Clouds form when water
vapor condenses on
aerosols (dust, salt
particles in the air)


Factors needed for cloud
formation…
The temperature in
which condensation
begins is called the dew
point
TYPES OF CLOUDS

Cirrus Clouds: wispy, feathery clouds
Form only at high levels,
therefore are made of ice
crystals
Types of Clouds

Cumulus Clouds: are puffy white cotton
ball looking clouds
Cumulonimbus Clouds

These are thunderstorm clouds
Types of Clouds

Stratus Clouds: clouds that form in flat
layers- cover all or most of the sky and
are low level clouds
Precipitation

FALLING
LIQUID OR
SOLID WATER
FROM CLOUDS
(RAIN,
DRIZZLE,
SNOW, SLEET
FREEZING
RAIN, HAIL)
Precipitation

A rain gauge is used
to measure the
amount of
precipitation over a
period of time
Types of precipitation






Rain- Falls from clouds above Freezing and
air above freezing
Drizzle- Small precipitation <0.5 mm
Snow- Falls from clouds below freezing and
air below freezing
Sleet- Falls from clouds above freezing but air
below freezing
Hail-up and down movement of rain in clouds
multiple freezing as altitude goes up and
down
Freezing Rain-Hail-Falls from clouds and air
above freezing but ground below freezing
Haze, Fog and Smog are NOT
forms of PRECIPICATION
Problem Set 3

Identify the forms of precipiation
Reading a weather map

ISOBAR= connects areas of equal
pressure BAR comes from BARometric
pressure
Reading a weather map...

Isotherm: Connects areas of equal
temperature; therm means temperature
Aim Masses & Source Regions
Air Mass is an
extremely large body
of air whose properties
of temperature and
moisture content
(humidity), at any
given altitude, are
fairly similar in any
horizontal direction.
Source Regions are
simply geographic
areas where an air mass
originates. Should be:
uniform surface
composition - flat
light surface winds
Air Mass Classification
4 general air mass classifications categorized
according to the source region.
polar latitudes P - located poleward of 60 degrees
north and south
tropical latitudes T - located within about 25 degrees
of the equator
continental c - located over large land masses--dry
marine m - located over the oceans----moist
Types of Air Masses
cP continental polar cold, dry, stable
cT continental tropical hot, dry, stable air
aloft--unstable surface air
mP maritime polar cool, moist, and
unstable
mT maritime tropical warm, moist, usually
unstable
Air Masses
Air masses are masses of air that have
the same characteristics of the surface
over which it develops
 Pressure Systems
descending (going down)=H pressure
ascending (going up)=L pressure

Fronts: Fronts: the boundary
between 2 air masses

Warm Front: warm air slides over
departing cold air- large bands of
precipitation form
This is
the
symbol
on a
map for
a warm
front
Cold Fronts

This is the symbol
for a cold front
Cold air pushes under a warm air mass.
Warm air rises quickly=narrow bands of
violent storms form
Occluded Front

This is the
weather map
symbol for an
occluded front
2 air masses merge and force warm air
between them to rise quickly. Strong
winds and heavy precipitation will occur
Stationary Front

This is the
weather map
symbol for a
stationary front
Warm or cold front stops moving. Light
wind and precipitation may occur across
the front boundary
Problem Set
What type of
weather is
associated with
each type of
front
 Draw the symbol
for each front

Wind blows from high pressure
areas to low pressure areas
The pressure gradient and coriolis force
cause low’s to spin counter clock-wise and
highs to spin clockwise