National Weather Service Hazardous Weather and Flooding Preparedness Weather Overview.
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Transcript of National Weather Service Hazardous Weather and Flooding Preparedness Weather Overview.
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Hazardous Weather and Flooding Preparedness
Weather Overview
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Elements of Weather
Temperature
Pressure
Moisture
Wind
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TemperatureTemperature
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 sun’s heat. Most of the sun’s energy passes through the air and heats the land and water.
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Temperature (Continued)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 earth’s rotation and orbit.
Molecules will move to equalize temperatures where possible.
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Temperature (Continued)Temperature (Continued)
Why is it colder at thenorth 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.
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SeasonsSeasons
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.
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SeasonsSeasons
Why is it warmer in Why is it warmer in July then January?July then January?
The earth is actually closerto 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.
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DAY - Landwarms fasterthan water
NIGHT - Landcools fasterthan water
The varioussurfaces absorb,retain, andradiate heat anddetermine thedaily surface airtemperataure to4000 ft.
Practically nodaily temperaturevariance occurs inthe free air above4000 ft.
SOLARRADIATION
Daily Temperature Variations
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Hadley CellsHadley Cells
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Hadley CellHadley Cell
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Climate RegionsClimate Regions
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PressurePressure
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.
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Pressure (Continued)Pressure (Continued)
Low pressure is usually associated with rising (warm) air and stormy weather.
Air moves counter clockwise around Lows (Coriolis Effect due to earth’s rotation).
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Pressure (Continued)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.
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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
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Surface Pressure MapSurface Pressure Map
HIGHHIGH
HIGHHIGH
HIGHHIGH
LOWLOW
LOWLOW
10241024
10241024
10241024
10241024
10201020
10201020
10201020
10161016
10161016
10161016
10161016
10121012
10081008
10081008
10041004
10121012
ISOBARISOBAR
What is the wind direction over Ohio?
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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
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GreatLakes
Atlantic
GulfInflow
Pacific
How do you thinkthe Great Lakesimpact weather inwarm conditions?
Moisture Source Regions
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ContinentalPolar
MaritimePolar
ContinentalTropical
MaritimeTropical
MaritimePolar
MaritimeTropical
Air Masses
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WindWind
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 earth’s rotation which turns winds to the right (Coriolis Effect).
The more isobars, the stronger the wind.
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Wind (Continued)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.
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What’s Happening?What’s Happening?
Temperature PressureVisibility/Weather Pressure Change Dewpoint Wind Precipitation
Blizzard of ‘78 Jan 26, 1978
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Ohio Surface MapOhio Surface Map
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Basic Surface Station ModelBasic 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
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Basic Surface Station ModelBasic Surface Station Model
Basic Weather Symbols
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Basic Surface Station ModelBasic 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 982.7 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 1002.7 mb
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Basic Surface Station ModelBasic Surface Station Model
Wind Speed (Knots) and Direction:
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Basic Surface Station ModelBasic Surface Station Model
Cloud Cover (Percent):
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Basic Surface Station ModelBasic Surface Station Model
Exercise 1
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Basic Surface Station ModelBasic Surface Station Model
Exercise 2
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Basic Surface Station ModelBasic Surface Station Model
Exercise 3
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Front Types and CharacteristicsElements of Weather
Cold Front Thunderstorms, severeweather
Stationary Front
Warm FrontSteady precipitation
Potential for long term precipitation ranging from benign to severe weather and flooding
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Surface FeaturesSurface Features
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How Low Pressure Systems Develop
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LOW PRESSURE DEVELOPMENT
In the area of the front, temperature, moisture, pressure and wind are out of balance.
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Low Pressure Development (Continued)
The front begins to move as winds change from along the front to across the front.
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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.
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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.
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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.
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Low Pressure Development (Continued)
The system has mixed the cold and warm air, into a cool mixture. Most of the energy is now gone.
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Low Pressure Development (Continued)
Finally, the low pressure system has nearly disappeared, and a new stationary front is ready to begin the process again.
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Low Pressure Development (Continued)
Now, lets put it all together and into motion.
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Severe Weather OutbreakSevere Weather Outbreak
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Jet Streams and Storm
Tracks
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Jet StreamJet Stream
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Prevailing Westerlies
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Jet Streams
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How do you think this airflow patterncould affect the weather in the U.S.?
Prevailing Westerlies Affected by the Jet Stream
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What kind of weather might youexpect from this airflow pattern?
Shift in the Jet Stream
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Jet Streams (Continued)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.
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Jet Streams (Continued)Jet Streams (Continued)
Low pressure forms off the South Carolina Coast the 15th of January.
A coastal (Nor’easter) snowstorm?
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Where would a low likely form? Where would a high likely form?
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Level Height
1000 mb 400 ft 850 mb 4,800 ft 700 mb 9,800 ft
500 mb 18,400 ft 300 mb 30,100 ft 200 mb 38,700 ft
Pressure Levels versus Height
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End of Weather Overview