National Weather Service Hazardous Weather and Flooding Preparedness Weather Overview

National Weather Service Elements of Weather

National Weather Service Temperature Represents heat energy or the speed of motion of molecules. Absorption of heat and temperature change vary by substance. The sun heats land more quickly than water. The sun supplies most of the energy that keeps our earth warm. The atmosphere is transparent to the suns heat. Most of the suns energy passes through the air and heats the land and water.

National Weather Service Temperature (Continued) Most of the heat supplied to the air comes from the earth radiating heat, from heat released by water, and from air movement. The amount of solar energy striking the earth depends on the earths rotation and orbit. Molecules will move to equalize temperatures where possible.

National Weather Service Temperature (Continued) Why is it colder at the north and south poles? The sun must pass through a larger section of the atmosphere to warm the earth surface. The weather on our planet is created by sun heating areas of the planet unequally. This occurs because: 1. The sun's radiation reaches only half the planet at any one time. 2. The amount of radiation reaching the surface varies at different places. 3. The planet tilts as it revolves around the sun.

National Weather Service Seasons The earth revolves around the sun every 365 days. Different parts of the planet tilt toward the sun and receive more radiation. June 21 (the summer solstice), the North Pole is tilted toward the sun and has continuous day. December 21, the North Pole is tilted away from the sun. In April, the planet has relatively little tilt, meaning that day and night are about equal length in most places.

National Weather Service Seasons Why is it warmer in July then January? The earth is actually closer to the sun in January (3%) It is the tilt of the earth!!!!!!!!!!!!! The earth is tilted toward the sun in the Summer (North Hemisphere). This is a larger factor then proximity to sun.

National Weather Service Daily Temperature Variations

National Weather Service Hadley Cells

National Weather Service Hadley Cell

National Weather Service Climate Regions

National Weather Service

Pressure A measure of the weight of the atmosphere on top of us. Pressure decreases with height. As you go higher in the atmosphere, there are fewer molecules to exert pressure. Molecules in the atmosphere move to equalize pressure, moving from high pressure to low pressure areas. The flow of molecules from areas of high pressure to low pressure produces wind.

National Weather Service Pressure (Continued) Low pressure is usually associated with rising (warm) air and stormy weather. Air moves counter clockwise around Lows (Coriolis Effect due to earths rotation).

National Weather Service Pressure (Continued) High pressure is usually associated with sinking (cool) air and nice weather. Air moves clockwise around Highs (Coriolis Effect). Pressure lines on weather maps are called isobars.

National Weather Service Some Definitions Isobars – lines on a weather map which connect points of equal pressure High Pressure – areas of sinking air Low Pressure – areas of rising air

National Weather Service Surface Pressure Map HIGH HIGH HIGH LOW LOW ISOBAR What is the wind direction over Ohio?

National Weather Service

Elements of Weather Moisture Dew Point – Temperature to which air must be cooled to be saturated Used by Meteorologists – gives a more accurate picture of amount of moisture in atmosphere Relative Humidity – Percentage of water vapor in the air

National Weather Service

Moisture Source Regions

National Weather Service Air Masses

National Weather Service Wind Wind is the horizontal flow of air caused by differences in Temperature and Pressure. Winds tend to flow around areas of high and low pressure rather than directly from high to low pressure. Winds tend to flow parallel to isobars. This is caused by the earths rotation which turns winds to the right (Coriolis Effect). The more isobars, the stronger the wind.

National Weather Service Wind (Continued) Winds are a primary contributor to severe weather. Why? They move moisture, as well as warm and cool air. They provide shear for tornadoes to form. Strong winds not only increase the strength of thunderstorms, but contribute to damage from downbursts.

National Weather Service Whats Happening? Temperature Pressure Visibility/Weather Pressure Change Dewpoint Wind Precipitation Blizzard of 78 Jan 26, 1978

National Weather Service Ohio Surface Map

National Weather Service Basic Surface Station Model Temperature (F) Dewpoint (F) Simple Station Model Common on Many Maps Major Weather Elements Covered Temperature and Dew point Left Hand Side of Model Temperatures in Fahrenheit

National Weather Service Basic Surface Station Model Basic Weather Symbols

National Weather Service Basic Surface Station Model Interpreting Pressure Reports: (Millibars) If reported value greater than 500: Initial 9 is missing. Place it on left, then divide by 10. For example: 827 becomes mb. If reported value less than 500: Initial 10 is missing. Place it on left, then divide by 10. For example (as in above diagram): 027 becomes mb

National Weather Service Basic Surface Station Model Wind Speed (Knots) and Direction:

National Weather Service Basic Surface Station Model Cloud Cover (Percent):

National Weather Service Basic Surface Station Model Exercise 1

National Weather Service Basic Surface Station Model Exercise 2

National Weather Service Basic Surface Station Model Exercise 3

National Weather Service Front Types and Characteristics Elements of Weather Cold FrontThunderstorms, severe weather Stationary Front Warm Front Steady precipitation Potential for long term precipitation ranging from benign to severe weather and flooding

National Weather Service Surface Features

National Weather Service

How Low Pressure Systems Develop

National Weather Service LOW PRESSURE DEVELOPMENT In the area of the front, temperature, moisture, pressure and wind are out of balance.

National Weather Service Low Pressure Development (Continued) The front begins to move as winds change from along the front to across the front.

National Weather Service Low Pressure Development (Continued) A frontal wave forms. One portion of the front has now changed to a warm front as winds push warm air northward. Western parts of the front become a cold front and cold air begins to move southward. Rotation has begun.

National Weather Service Low Pressure Development (Continued) Winds are increasing and warmer air is now helping to intensify the system. Precipitation has probably already begun ahead of the warm front.

National Weather Service Low Pressure Development (Continued) The system strengthens. A closed low forms. Winds are even stronger. Rain falls east of the warm front. Thunderstorms will probably form out ahead of the cold front.

National Weather Service Low Pressure Development (Continued) The system has mixed the cold and warm air, into a cool mixture. Most of the energy is now gone.

National Weather Service Low Pressure Development (Continued) Finally, the low pressure system has nearly disappeared, and a new stationary front is ready to begin the process again.

National Weather Service Low Pressure Development (Continued) Now, lets put it all together and into motion.

National Weather Service Severe Weather Outbreak

National Weather Service Jet Streams and Storm Tracks

National Weather Service Jet Stream

National Weather Service Prevailing Westerlies

National Weather Service

Jet Streams

National Weather Service Prevailing Westerlies Affected by the Jet Stream

National Weather Service Shift in the Jet Stream

National Weather Service Jet Streams (Continued) A Winter Storm forms in Oklahoma, who will get heavy snow? Kansas, Iowa into Wisconsin and Michigan. What type of weather might be expected across Ohio and PA? Warm weather, with a chance of rain.

National Weather Service Jet Streams (Continued) Low pressure forms off the South Carolina Coast the 15th of January. A coastal (Noreaster) snowstorm?

National Weather Service

End of Weather Overview