weather 2013. part 1. station model 15 /.5 986 21 1.5 24 * air temp (°f) visibility (miles) dew...

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