Weather and Climate

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Weather and Climate

• Clouds

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Dew and Frost

• Where does dew and frost form? Why?

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Frozen Dew vs. Frost

• Are frozen dew and frost the same thing?
• Frozen dew forms when the air temperature gets
  below freezing after dew forms.
• Frost occurs when the dew point temperature is at
  or below freezing.
• Water vapor goes directly from vapor to solid.

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When the dew is on the grass,rain will never
come to pass.When grass is dry at morning
light,look for rain before the night!
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Good Conditions for Dew Formation

• Clear, calm nights ? good for dew
• Cloudy, windy night ? dew not likely
• Calm clear nights are usually associated with a
  high pressure fair weather system.
• Cloudy and windy weather is usually associated
  with an approaching storm system.

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What is black frost?

• Sometimes the air temperature may go below
  freezing but no frost forms.
• The air is very dry
• The dew point temperature is never reached.
• This is also called simply a freeze.
• This type of event is very damaging to crops.

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Clouds Condensation Nuclei

• Sources
• Dust
• Volcanoes
• Factory smoke
• Forest fires
• Salt from ocean spray
• Sulfate particles emitted by phytoplankton

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Hygroscopic vs. Hydrophobic

• Some particulates attract water and are called
  hygroscopic.
• Such as ocean salt, sulfuric acid, nitric acid
• Water can condense in less than 100 relative
  humidity.
• Some particulates repel water and are called
  hydrophobic.
• Such as oils, gasoline, paraffin waxes, Teflon
• Water vapor will resist condensing even when
  relative humidity is greater than 100.
• At any given time there are usually enough
  condensation nuclei for clouds to form near 100
  relative humidity.

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Haze
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Fog

• Fog is not the same as haze, but can often
  develop from haze.
• Fog has a visibility less than 1km (0.62miles).
• There are different mechanisms for fog formation.

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Radiation Fog
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Valley Fog

• Valley fog is a type of radiation fog.
• Cold, heavy air drains down mountains and
  collects in the valleys.
• Rivers running through valleys, helps make them
  very susceptible to fog.

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Advection Fog
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Upslope Fog
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Evaporation (Mixing)Fog

• This fog is formed by the same process that
  allows you to see your breath on a cold winter
  day.
• This fog is formed by two unsaturated parcels of
  air mixing.

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Steam Fog
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Frontal Fog

• Type of evaporation (mixing) fog.
• Warm rain falling through a layer of cold moist
  air can produce fog.
• This is commonly observed before a warm front, or
  behind a cold front, hence the name
• Also called precipitation fog.

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Foggy Weather

• The three regions of the US with the most number
  of heavy fog days are
• The Pacific Coast States
• The Appalachian highland region
• New England

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Is fog good or bad?
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Cloud Types
1.
2.


3.

4.
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Howards System

• Wispy clouds were named cirrus, which means
  curl of hair in Latin.
• Puffy clouds were named cumulus, which means
  heap in Latin.
• Sheet like clouds were named stratus which
  means layer in Latin.
• Rain clouds were named nimbus, which means
  violent rain in Latin.
• By combining these basic types different clouds
  could be described.

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Combining Names

• Cumulonimbus ?
• Nimbostratus ?
• Stratocumulus ?

• Rain and puffylook
• Rain and layer look
• Layer and puffy look

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Cloud Types

• In 1887, Abercromby and Hildebrandsson expanded
  Howards classification.
• Clouds were divided into four groups
• High clouds
• Middle clouds
• Low clouds
• Clouds with vertical development

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High Clouds (Cirrus)

• In the middle and low latitudes, high clouds
  generally form above 20, 000ft.
• These clouds are mostly ice crystals and are very
  thin. Why?.
• Higher up it is cold! Cold air has less of a
  capacity for water vapor.
• These clouds appear white in color.

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High Clouds
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Cirrocumulus
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Cirrostratus
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Cirrostratus
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Cirrostratus
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Middle Clouds (Alto)

• Cloud base begins 6,500ft-23,000ft, in middle
  latitudes.
• Composed of water droplets, except when cold
  enough for ice crystals.

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Altocumulus
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Altostratus

• Often cover the entire sky, extending over
  hundreds of square kilometers.
• Sometimes the sun can be seen through these
  blue-gray clouds, appearing as a watery sun.

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Low clouds

• Base of clouds is below 2000m (6,500 ft.)
• Almost always composed entirely of water
  droplets.
• In extremely cold weather may contain ice
  particles and snow.

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Nimbostratus
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Stratocumulus
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Stratus
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Cumulus
Clouds with Vertical Development
Cumulus Congestus
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Cumulus Humilis

• Cumulus Congestus

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Cumulonimbus

• These are thunderstorm clouds.
• These clouds may extend from 600m into the
  tropopause.
• Often characterized by an anvil top.
• Produce lightning, hail, and thunder.

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Lenticular Clouds
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Pileus
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Mammatus Clouds

• For formation Sinking air must be colder than
  surrounding air and have a high liquid water or
  ice content.
• The sinking air warms, but not very quickly
  because of the latent heat taken from the air to
  evaporate the liquid, or melt the ice.
• If the sinking air remains saturated and cooler
  than the surrounding air, the sinking occurs
  beyond the base of the cloud.

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Mammatus Clouds
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Nacreous Clouds
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Noctilucent Clouds