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WEATHER
Seasons
Global Circulations Global circulations explain how air and storm
systems move over the earth’s surface The circulation patterns are complicated by 3
factors: Earth’s rotation Tilted axis Uneven distribution of land in Northern and
Southern Hemisperes This complicated circulation patterns are
broken into 3 “cells”: Hadley – around equator, blows toward equator Ferrel – mid-latitude, blows toward poles Polar – around poles, blows easterly
The Jet Stream
Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere.
The winds blows from west to east Jet streams are the strongest for both the
northern and southern hemisphere winters
Jet Stream (cont.)
The Jet stream follows the sun’s angle in the sky, southerly in the summer and northerly in the winter.
Jet streams are typically wide and not distinct, but a region where the wind increase toward a core of strongest wind.
One way of visualizing this is consider a river. The river's current is generally the strongest in
the center with decreasing strength as one approaches the river's bank. It can be said that jet streams are "rivers of air.“
Climates The reoccurring "average weather" found in
any particular place German climatologist Wladimir Köppen divided
the world's climates into categories based on general temperature profile related to latitude
A. Tropical, B. Dry, C. Moist Sub-tropical, D. Moist Continental, E. Polar, and F. Highlands
Heat Index
Heat waves kill more people in the United States than all of the other weather related disasters combined
Humans perspire to cool themselves, therefore the higher the humidity, the harder it is for humans to cool themselves
Heat index is a function of humidity and temperature
Remember, these values are in the SHADE You can add up to 15°F (8°C) to these values if
you are in direct sunlight
Wind Chill
The effect of the wind on people and animals
As the wind increases, it removes heat from the body, driving down skin temperature
inanimate objects will not cool below the actual air temperature
Wind
(mph)
Temperature (°F)
40 35 30 25 20 15 10 5 0 -5 -10
-15
-20
-25
-30
-35
-40
-45
-50
-55
-60
0 40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50 -55 -60
5 37 31 25 19 13 7 1 -5 -11 -16 -22 -28 -34 -40 -46 -52 -58 -63 -69 -75 -81
10 34 27 21 15 11 3 -4 -10 -16 -22 -28 -35 -41 -47 -53 -59 -66 -72 -78 -84 -90
15 32 25 19 13 6 0 -7 -13 -19 -26 -32 -39 -45 -51 -58 -64 -71 -77 -83 -90 -96
20 30 24 17 11 4 -2 -9 -15 -22 -29 -35 -42 -48 -55 -61 -68 -74 -81 -88 -94-
101
25 29 23 16 9 3 -4 -11 -17 -24 -31 -38 -44 -51 -58 -64 -71 -78 -84 -91 -98-
104
30 28 22 15 8 1 -6 -12 -19 -26 -33 -39 -46 -53 -60 -67 -73 -80 -87 -94-
101
-107
35 28 21 14 7 0 -7 -14 -21 -27 -34 -41 -48 -55 -62 -69 -76 -83 -89 -96-
103
-110
40 27 20 13 6 -1 -8 -15 -22 -29 -36 -43 -50 -57 -64 -71 -78 -84 -91 -98-
105
-112
45 26 19 12 5 -2 -9 -16 -23 -30 -37 -44 -51 -58 -65 -72 -79 -86 -93-
100
-107
-114
50 26 19 12 4 -3 -10 -17 -24 -31 -38 -45 -52 -60 -67 -74 -81 -88 -95-
102
-109
-116
Z-Time
All aspects of meteorology are based upon a world-wide 24-hour clock called Zulu time
more commonly called Universal Time Coordinate
With the 360° daily rotation of the earth, the sun is moving 15° each hour which leads to the formation of 24 time zones
Based on the time in Greenwich, England. 00Z (midnight zulu) is 6 pm Central
Standard
Clouds
Clouds form when air is cooled to its dewpoint the temperature the air reaches saturation
As air rises, it expands due to less pressure, and cools do to expansion Called the Adiabatic Process
The rate of this cooling and expanding with elevation is called lapse rate
the dry lapse rate is a constant for each 1000 feet increase in elevation, the air
temperature will decrease 5.4°F
Cloud Categories
Cirro form – high level clouds composed mostly of ice crystals, denote fair weather
Nimbo form – mid-level clouds that are very heavy with moisture and bring steady rain
Cumulo form – fluffy midlevel clouds that have a flat base and are very tall
Strato form – low level clouds that form a blanket over the sky and bring dizzily weather
Wind
Air in motion A wind vane measures the wind direction An anemometer measures the wind speed Isobars on a weather map denote areas of
equal pressure The closer the isobars, the greater the pressure
gradient Wind speed is directly proportional to pressure
gradient Wind speed and direction are also impacted by
the coriolis force – the earth’s rotation
Coriolis Force
Wind
Winds spiral out of high pressure regions and into low pressure regions because of friction.
Fronts Fronts are the boundaries between two air
masses The front is classified by what type of air is
moving into the region (warm/cold) Warm fronts typically have a gentle slope so
the air rising along the frontal surface is gradual stratiform cloudiness and precipitation along and to
the north of the front The slope of cold fronts are more steep and air
is forced upward more abruptly narrow band of showers and thunderstorms along or
just ahead of the front
Frontal Boundaries
Precipitation
Needs ingredients to create A source of moisture Typically a large body of water like oceans
Lifting of moist air must occur Mountains, pressure gradients, frontal
boundaries Ice crystals or water droplets need to
grow large enough to fall Collision and coalescence or ice crystal
method
Types of Precipitation
Rain – liquid water droplets Snow – Crystallized frozen water Sleet – frozen water droplets Freezing Rain – Water droplets that freeze
when they land on objects Hail – Larger balls of ice that have formed
from repeated lifting and falling through the atmosphere adding layers of ice each time
Thunderstorms
Ingredients Moisture, instability, uplift
Life Cycle – lasts about 30 min Towering Cumulus (strong updrafts) Mature Cumulus (updrafts and down
drafts) Dissipating Stage (downdrafts)
Multi-cell cluster
Multi-cell line
Super Cell Thunderstorm
Tornadoes
Tornadoes come from super cells with strong wind sheers.
The greatest chance for tornado comes from the mesocyclone area.
Enhanced F-Scale: EF0 (65-85 mph) – EF5
(over 200 mph)
Lightning
Giant spark of static electricity Largely a mystery to scientists 1 billion volts, 300,000 amps, and 10 miles away Thunder is the acoustic shock wave resulting
from the extreme heat generated by a lightning flash
For every second between the flash of lightning and the clap of thunder, you can estimate 1 mile until the storm is directly over you
Doppler Radar
Stands for RAdio Detection And Ranging WSR-88D
Weather Surveillance Radar - 1988 Doppler Gives the ability to detect motion Bounces radio waves off of water droplets
in clouds. The larger or denser the droplets, the stronger
the reflected signal, and the more severe the storm.
Weather Station Reports
Temperature
Cloud Types
Cloud TypesCloud ceiling
Pressure in mb (999.8)
Visibility (mi)
Current weather Change in
pressure (mb)
Wind Speed & Direction
Cloud Types
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