METEOROLOGY FOR EVERYONE

Prepared by: Dr. Ahmet KILIÇ

WEATHER PHENOMENON

 
HAZE  
FOG  

 

 

 

Weather has fascinated people for centuries. Ever since the beginning of time, the lives of every species on this planet have been affected by weather. Only during the past few decades have we really begun to understand how the weather works with the inventions of satellites, reliable doppler radar, and other instruments used to gather data. Now we can accurately predict what the weather will be like a day from now, or a week from now.

PRECIPITATION
RAIN
DRIZZLE
SHOWERS
FREEZING RAIN OR DRIZZLE
SLEET
SNOW
 

HAZE

Suspension in the atmosphere of minute dust or salt particles that are not individually seen but that nevertheless reduce visibility.There are two types of haze.

Dry haze - large/giant particles in the air (smoke, smog, dust)

 

 

 

 

 

 Wet haze - Water condenses onto hydroscopic cloud condensation nuclei when relative humidity (RH) is as low as 75%. Wet haze has a dull gray, white color.

 

 

FOG

Fog, forms as the RH increases to 100% - haze particles grow into fog (cloud) particles near the ground is really a cloud near the ground. Visibility is less than 1 km. 

Radiation fog forms when shallow air near surface is moist, nights are clear and calm. Although light winds will bring more air in contact with ground. Radiational cooling allows the temperature to drop to the dew point. Once the temperature reaches the dew point, radiation fog begins to develop.

Valley fog.Common in the fall - especially when our weather is dominated by high pressure often forms in valleys first since this is where the coldest air is  called valley fog.

 

 
 
Advection fog forms when warm and moist air travels over a cold surface and condensation in the form of fog occurs.

 

1. Southerly winds bring warm, moist air over cold ground or snow and,

2. Moisture condenses into fog as air cooled below.

 

Steam fog forms when heat and moisture are transferred from the warm water to the cooler, drier air near the lakes surface. It is seen seen over lakes in winter.

Upslope fog forms when the parcel ascends up the slope, it expands and cools to the dew point. It is Need winds to move air up the slope.

 
PRECIPITATION

Any liquid or solid form of water particles that falls from the atmosphere and reaches the Earth's surface is known as precipitation. Precipitation can occurs in a variety of forms such as drizzle, hail, rain, sleet or snow.  

Rain: Falling drops of water larger than 0.02 inches in diameter. In forecasts, "rain" usually implies that the rain will fall steadily over a period of time. See "showers" below.

Light rain: Falls at the rate of 0.1 inch or less an hour.

Moderate rain: Falls at the rate of 0.11 to 0.30 inches an hour.

Heavy rain: Falls at the rate of 0.30 inches an hour or more.

Drizzle: Falling drops of water smaller than 0.02 inch in diameter. They appear to float in air currents, but unlike fog, do fall to the ground.

Light drizzle: Drizzle with visibility of more than 5/8 of a mile.

Moderate drizzle: Drizzle with visibility from 5/16 to 5/8 of a mile.

Heavy drizzle: Drizzle with visibility of less than 5/16 of a mile.

Showers: Rain that falls intermittently over a small area. The rain from an individual shower can be heavy or light, but doesn't cover a large area or last more than an hour or so.

Snow: Falling ice composed of crystals in complex hexagonal forms. Snow forms mainly when water vapor turns directly to ice without going through the liquid stage, a process called sublimation.

Snowflakes: Aggregations of snow crystals.

Snow flurries: Light showers of snow that do not cover large areas and do not fall steadily for long periods of time.

Snow grains: Very small snow crystals. The ice equivalent of drizzle.

Snow pellets: White, opaque ice particles that form as ice crystals fall through cloud droplets that are below freezing but still liquid (supercooled). The cloud droplets freeze to the crystals forming a lumpy mass. Scientists call snow pellets "graupel." Such pellets falling from thunderstorms are often called "soft hail."

Sleet: Drops of rain or drizzle that freeze into ice as they fall. They are usually smaller than 0.3 inches in diameter. Official weather observations list sleet as "ice pellets." In some parts of the country "sleet" refers to a mixture of ice pellets and freezing rain.

Freezing rain or drizzle: Falling rain or drizzle that cools below 32 degrees F, but does not turn to ice in the air. The water is "supercooled." When the drops hit anything they instantly turn into ice.

Ice storm: A storm with large amounts of freezing rain that coats trees, power lines and roadways with ice. Often the ice is heavy enough to pull down trees and power lines.

Hail: Falling ice in roughly round shapes at least 0.2 of an inch in diameter. Hail comes from thunderstorms and is larger than sleet. Hailstones form when upward moving air -- updrafts -- in a thunderstorm keep pieces of graupel from falling. Drops of supercooled water hit and freeze to the graupel, causing it to grow. When the balls of ice become too heavy for the updrafts to continue supporting them, they fall as hailstones. Sleet, in contrast, consists of raindrops that freeze on the way down.

Thunderstorm: A rain or snow shower in which there is lightning. Thunder is always caused by lightning. In general, the upward and downward winds, updrafts and downdrafts, in thunderstorms are more violent than those in ordinary showers.

Thundersnow: A thunderstorm with snow instead of rain falling on the ground.

Severe thunderstorm: A thunderstorm with winds of 57 mph or faster or hail more than 3/4 inch in diameter reaching the ground. Severe thunderstorms can also produce tornadoes.

RAIN

Rain develops when growing water droplets become too heavy to remain in the cloud and as a result, fall toward the surface as rain. Rain can also begin as ice crystals that collect each other to form large snowflakes. As the falling snow passes through the freezing level into warmer air, the flakes melt and collapse into raindrops. Rain, which is composed of widely separated drops with diameters usually greater than 0.02 inches, generally falls from towering cumulus clouds. The cumulus clouds, with fast, upward moving air currents, allow cloud droplets to combine and grow. Raindrops can reach sizes up to 0.25 inches before falling to the ground. The intensity of rain is based on the amount that falls in one hour.
 

DRIZZLE

Drizzle, which is defined as drops with diameters less than 0.02 inches falling close together, usually falls from stratus clouds. The relatively thin stratus clouds have slow, upward moving air currents. In these conditions, cloud droplets have little time to grow before they become too heavy for the air currents to support.

 
SLEET

Sleet forms when a partially melted snowflake or raindrop turns back into ice as it is falling through the air.  Sleet, precipitation of small, partially melted grains of ice. As raindrops fall from clouds, they pass through layers of air at different temperatures. If they pass through a layer with a temperature below the freezing point, they turn into sleet. Snowflakes that have melted by passing through a warm layer will turn into sleet if they then pass through a freezing layer. Sleet often falls together with snow and rain, and may deposit an icy coating on exposed surfaces. Sleet occurs only during the winter, while hail, a different form of icy precipitation, may fall at any time of the year.
 

SHOWERS

 

 

Rain that falls intermittently over a small area. The rain from an individual shower can be heavy or light, but doesn't cover a large area or last more than an hour or so.

FREEZING RAIN OR DRIZZLE

 

Rain or drizzle  becomes supercooled and freezes upon impact with cold surfaces. Freezing rain is most commonly found in a narrow band on the cold side of a warm front,  where surface temperatures are at or just below freezing.

 

SNOW

When small ice crystals inside the clouds collide and stick together they form Snowflakes. Most snowflakes melt on their way to the ground and fall as rain. But only when the air near the ground is cold enough snowflakes fall as snow.

Precipitation formed by the sublimation of water vapor into solid crystals at temperatures below freezing. Some samples of ice crystls.