Moisture and Clouds Current Weather Humidity Clouds Adiabatic Processes Return Exam 1 For Next Class: Read Chapter 5 (pp. 151-167)

Yes, it does snow in North Carolina! February 2009 Bethel, NC 100” mean annual snowfall at highest elevations and >24” from big storms at middle elevations January 1977 Matney, NC Johnson, Southern Snow

Humidity What is humidity and what are the different ways to measure humidity in the atmosphere?

Water Vapor in the Atmosphere Humidity: any one of many ways of describing the amount of water vapor in the air Varies with the season, from one day to the next, within a single day, and from one place to another © AMS

Water Vapor in the Atmosphere Relative Humidity Compares the actual amount of water vapor in the air with the amount of water vapor that would be present if that same air were saturated Expressed as a percentage When air is saturated, relative humidity is 100% Varies inversely with temperature © AMS

Relative Humidity Figure 7.8

Water Vapor in the Atmosphere Vapor Pressure Pressure produced by the gas molecules composing air depends on mass of the molecules kinetic molecular activity © AMS

Water Vapor in the Atmosphere Saturated Air Raising the air temperature increases saturation vapor pressure Lowering the air temperature reduces saturation vapor pressure © AMS

Saturation Vapor Pressure Figure 7.12

Specific humidity: grams of water vapor per kilogram of air (g/kg) Absolute humidity: grams of water vapor per cubic meter of air (g/m3) Source: Wikipedia

Maximum Specific Humidity Figure 7.13

Humidity Patterns Figure 7.11

Precipitable Water Depth of water that would be produced if all the water vapor in a vertical column of air were condensed into liquid water © AMS

Dewpoint The dewpoint is the temperature at which dew forms and is a measure of atmospheric moisture. It is the temperature to which air must be cooled at constant pressure and water content to reach saturation. Source: Wikipedia

Wet Bulb Temperature The wet-bulb temperature is the temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel. Critical temperature for snowmaking at ski resorts Source: Wikipedia

Cloud Types and Identification Clouds that produce precipitation are called nimbostratus and cumulonimbus. Figure 7.22

Adiabatic Processes Figure 7.17

Adiabatic Cooling Figure 7.17

Adiabatic Heating Figure 7.17

Atmospheric Lifting Mechanisms Figure 8.6

Orographic Precipitation Figure 8.9

Orographic Patterns Figure 8.10

NC Precipitation Where is the wettest place in North Carolina? Driest?

Asheville Lake Toxaway Driest Weather Station 37.32 inches (annual average) Lake Toxaway Wettest Weather Station 91.72 inches (annual avg.) EPA-NIEHS Climate Change Workshop, June 17, 2011

Average Annual Precipitation