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Introduction 7

Chapter 1

From the Rocky Mountains to the Pacific Ocean

8

Early September snowstorms

Thunderstorms

Canyon winds

Beautiful fall weather

Wind and rain

Chapter 2

Along the Pacific Coast 20

Rain, rain, and more rain

Storminess

Lightning, thunder and hail

Freezing weather for two weeks

A touch of spring

Chapter 3

From the Pacific Ocean to the Rocky Mountains

43

Gusty winds

More rain

Warm temperatures

High water

Deep snow

Epilogue 70

Bibliography 72

Glossary 74

Index 76

Table of Contents

City of Portland HYDRA Network

USGS Rainfall Network

Oregon Hydrometeorological Networks

USA Annual Average = 29 inches◦ Oregon Average = 27 inches◦ Pennsylvania = 40 inches◦ Texas = 30 inches◦ Nevada = 8.8 inches

Coast - up to 70 inches or more◦ (as much as 168 inches in Coast Range)

Eastern Oregon - 8 to 10 inches

So: A Statistical Abstraction

Global Climate AnimationsDepartment of GeographyUniversity of Oregon

Concepts of atmosperic moisture Processes - precipitation Variability over space and distance – maps Variability in time – graphs

◦ Seasonal cycles◦ Interannual cycles◦ Glacial cycles

Rain Snow Sleet Hail Fog Drip ……and everything else wet

Measures of Atmospheric Moisture

•absolute humidity•specific humidity•vapor pressure•saturation vapor pressure•relative humidity•mixing ratio•saturation mixing ratio•wet-bulb temperature•dew-point temperature

 

   

Adiabatic temperature change and stability 

In "The Atmosphere" we discovered that air temperature usually decreases with an increase in elevation through the troposphere. The decrease in temperature with elevation is called the environmental lapse rate of temperature or normal lapse rate of temperature. Recall that  the normal lapse rate of temperature is the average lapse rate of temperature of .65o C / 100 meters. The environmental lapse rate of temperature is the actual vertical change in temperature on any given day and can be greater or less than .65o C / 100 meters.  Also recall that the decrease in temperature with height is caused by increasing distance from the source of energy that heats the air, the Earth's surface. Air is warmer near the surface because it's closer to its source of heat. The further away from the surface, the cooler the air will be. It's like standing next to a fire, the closer you are the warmer you'll feel. Temperature change caused by an exchange of heat between two bodies is called diabatic temperature change. There is another very important way to change the temperature of air called adiabatic temperature change.Adiabatic temperature change of air occurs without the addition or removal of energy. That is, there is no exchange of heat with the surrounding environment to cause the cooling or heating of the air. The temperature change is due to work done on a parcel of air by the external environment, or work done by a parcel of air on the air that surrounds it. What kind of work can be done? The work that is done is the expansion or compression of air. Imagine an isolated parcel of air that is moving vertically through the troposphere. We know that air pressure decreases with increasing elevation. As the parcel of air moves upward the pressure exerted on the parcel decreases and the parcel expands in volume as a result. In order to expand (i.e.. do work), the parcel must use its internal energy to do so. As the air expands, the molecules spread out and ultimately collide less with one another. The work of expansion causes the air's temperature to decrease. You might have had personal experience with this kind of cooling if you've let the air out of an automobile or bicycle tire. Air inside the tire is under a great deal of pressure, and as it rushes outside it moves into a lower pressure environment. In so doing, the parcel quickly expands against the outside environment air. By placing your hand in front of the valve stem, you can feel the air cool as it expands. This is called adiabatic cooling.As air descends through the troposphere it experiences increasing atmospheric pressure. This causes the parcel volume to decrease in size, squeezing the air molecules closer together. In this case, work is being done on the parcel. As the volume shrinks, air molecules bounce off one another more often ricocheting with greater speed. The increase in molecular movement causes an increase in the temperature of the parcel. This process is referred to as adiabatic warming. The rate at which air cools or warms depends on the moisture status of the air. If the air is dry, the rate of temperature change is 1oC/100 meters and is called the dry adiabatic rate (DAR). If the air is saturated, the rate of temperature change is .6oC/100 meters and is called the saturated adiabatic rate (SAR). The  DAR is a constant value, that is, it's always 1oC/100 meters. The SAR varies somewhat with how much moisture is in the air, but we'll assume it to be a constant value here. The reason for the difference in the two rates is due to the liberation of latent heat as a result of condensation. As saturated air rises and cools, condensation takes place. Recall that as water vapor condenses, latent heat is released. This heat is transferred into the other molecules of air inside the parcel causing a reduction in the rate of cooling.

Nature Notes – 1937 Climate of Crater Lake National

Park Annual Snowfall

SNOTEL – Data and Products SNOTEL Climate Anomaly Maps Water Supply Outlook for the western U.S.

Long –Term RecordsPrecipitationTemperature