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