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Hydrologic CycleHydrologic Cycle

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HumidityHumidity Refers to the amount of water vapor in the airRefers to the amount of water vapor in the air

SpecificSpecific Ratio of water vapor to air (dry air + water vapor) for a Ratio of water vapor to air (dry air + water vapor) for a

given parcelgiven parcel Does not change with expansion or compressionDoes not change with expansion or compression

RelativeRelative Ratio of amount of water vapor for a given parcel to Ratio of amount of water vapor for a given parcel to

amount of water vapor if air was saturatedamount of water vapor if air was saturated AbsoluteAbsolute

Density of water in a given parcel of airDensity of water in a given parcel of air Subjected to volume changesSubjected to volume changes

Warm air has greater capacity to hold Warm air has greater capacity to hold moisture than cool airmoisture than cool air

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Relative HumidityRelative Humidity A ratio of the amount of water vapor in the air, A ratio of the amount of water vapor in the air,

relative to how much water vapor that air can relative to how much water vapor that air can hold……hold……

WHAT IS THE PROBLEM WITH USING RELATIVE WHAT IS THE PROBLEM WITH USING RELATIVE HUMIDITY TO SEE IF THE AIR IS HUMID?HUMIDITY TO SEE IF THE AIR IS HUMID?

Relative humidity =

Actual water vapor content of the air

Maximum water vapor capacity of the air at that temperature

X 100

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Specific HumiditySpecific Humidity

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Air Saturation and Dew Air Saturation and Dew PointPoint

= 100% relative humidity; that is the air is = 100% relative humidity; that is the air is holding as much moisture as it can at its holding as much moisture as it can at its temperature temperature = saturation and dew point= saturation and dew point

Dew Point is temperature to which air Dew Point is temperature to which air would have to be cooled to achieve would have to be cooled to achieve saturation assuming there is no change in saturation assuming there is no change in pressure or moisture contentpressure or moisture content

DEW POINT IS A GOOD INDICATOR OF DEW POINT IS A GOOD INDICATOR OF HOW MUCH MOISTURE IS IN THE AIR. HOW MUCH MOISTURE IS IN THE AIR.

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General Dewpoint General Dewpoint ThresholdsThresholds

Dew Point

Temp. °F (°C)

Human Perception

Relative Humidity

Air Temp 90°F

75°F(24°C)+ Extremely uncomfortable, oppressive 62%

70°F(21°C) - 74°F

Very Humid, quite uncomfortable 52% - 60%

65°F(18°C) - 69°F

Somewhat uncomfortable for most people

at upper limit 44% - 52%

60°F(16°C) - 64°F

OK for most, but everyone perceives the humidity

at upper limit

37% - 46%

55°F(13°C) - 59°F

Comfortable 31% - 41%

50°F(10°C) - 54°F

Very comfortable 31% - 37%

49°F(10°C)

or lower

Feels like the western US

a bit dry to some

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Fun with the Heat Index Fun with the Heat Index CalculatorCalculator

http://www.easysurf.cc/cnver16.htmhttp://www.easysurf.cc/cnver16.htm

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FogFog Fog is a cloud at ground levelFog is a cloud at ground level Indicates saturated conditions at ground Indicates saturated conditions at ground

levellevel Fog typesFog types

Advection fog- warm moist air moves over a Advection fog- warm moist air moves over a cold surfacecold surface

Evaporation or steam fog- cold air moves over Evaporation or steam fog- cold air moves over warm waterwarm water

Radiation fog- air layer in contact with the Radiation fog- air layer in contact with the ground cools to dew point…..creates shallow ground cools to dew point…..creates shallow fog on calm clear nightsfog on calm clear nights

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WHAT KIND IS THIS?

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WHAT KIND????

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Heavy Fog Days

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