weather 2013. part 1. station model 15 /.5 986 21 1.5 24 * air temp (°f) visibility (miles) dew...
TRANSCRIPT
Weather 2013
Part 1. Station Model
15 /
.5
986
21
1.5
24
*
Air Temp (°F)
Visibility (miles)
Dew Point (°F)
Barometric Pressure – millibars (mb)
1) If # > 500, move decimal 1 place to left and put a “9” in front. Ex. 998.6 mb
2) If # < 500, move decimal 1 place to left and put “10” in front. Ex. 232 = 1023.2 mb
Barometric Trend (change) during last 3 hours (move one decimal to left) = 1.5 mb
Amount of precipitation in last 6 hours (in)
Part 1. Station Model
15 /
.5
986
21
1.5
24
*
Present Weather
Wind Direction – like an arrow coming in from where the wind originated (ex. East)
Wind Speed
-------- = 10 knots
---- = 5 knots
= 50 knots
Part 1. Station Model
Part 2. Air MassesA. Characteristics of air masses
1. Determined by where they originate
2. Air over land = dry, water = humid
3. Air near poles = cold, equator = warm
B. Naming Air Masses1. Continental – form over land; dry air
2. Maritime – form over water; wet air
3. Polar – form near poles; colder air
4. Tropical – form near equator; warmer air
5. Arctic – form over poles; Very cold air
Part 3. Air Pressure Systems
A. LOW Pressure 1. Low density air (lighter),
rising aira. Usually warm, moist air
2. Has precipitation
3. Counter clockwise, into the center
Part 3. Air Pressure Systems
B. HIGH Pressure1. High density air
(heavier), sinking aira. Usually cooler, drier air
2. Fair, clear weather
3. Wind clockwise
AWAY from center
Part 3. Air Pressure Systems
C. Measurement of Air Pressure1. Barometer – measures air pressure
2. Unitsa. Inches of mercury
b. Millibars (mb)
3. Barometric Trendsa. Rising – clearing weather likely
b. Falling – increasing chance of precipitation
c. Steady - unchanging
Part 4. Fronts
A. Cold Front
Part 4. Fronts
1. Cold fronts move QUICKLY (less friction)2. Weather conditions
a. Cooler tempsb. Short period of precipitationc. As front passes, air becomes cooler and
drier (clearing skies)d. Wind shifts to north (cold air from north)e. Air pressure rises since cooler, drier air is
heavier than warm, moist air
Part 4. Fronts
B. Warm Front
Part 4. Fronts
1. Warm fronts move SLOWLY (more friction)
2. Weather conditionsa. Gradually warmer temps
b. Increased clouds
c. Steady precipitation for a longer time
d. Winds shift to a south direction
e. Air pressure decreases (warm, moist air weighs less)
Part 4. FrontsC. Stationary Front
Part 4. Fronts
D. Occluded Front1. Clouds and precipitation
Part 4. Fronts
E. Finding Fronts on Weather Maps1. Look for sudden changes in
a. Temperature
b. Air Pressure
c. Wind direction
Part 4. FrontsF. Development of Low Pressure Centers
(Cyclones)1. Form at interface between warm and
cold air masses
cP
mT
Part 5. Forecasting WeatherA. Weather patterns in US move from West to
East (or SW to NE)
B. Low pressure = cloudy and precipitation1. Rising, unstable air
2. Falling air pressure usually means the approach of stormy weather
C. High pressure = fair weather (cool, dry air)1. Rising air pressure usually means fair weather is
approaching
Part 5. Forecasting Weather
D. Fronts cause unsettled weather, rising air causes precipitation
E. Warm fronts have longer periods of precipitation since they move slower than cold fronts (cold fronts have short and heavy periods of precip)
Part 5. Forecasting Weather
F. Large pressure differences cause strong winds
1. Isobars are close together = greater wind speed
Part 6. Violent WeatherA. When very cool, dry air collides with
warm, humid air violent weather can occur (thunderstorms or tornadoes)
Tornadoes Hurricanes
Formation
Area Effected
Size
Duration
Wind Speed
Cloud Shape
Over land from collision of very different air masses (temp and moisture); spring - summer
Over tropical water (energy from warm water); summer – early fall; lose strength when go over land
Most common in mid-west states
100 meters (up to a mile wide)
Minutes
200+ miles/hr
Funnel
Coastal areas of SE and Eastern US
650 km (up to 400 miles)
Days
75 – 150+ miles/hr
Huge spiraling low pressure area
