Familiar Weather Topics meteo 482: Weather Communications II

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Brad Guay April 1st, 2014
Familiar Weather Topics METEO 482: Weather Communications II

Wind Chill
Primary Points

Attempts to quantify how much energy is being lost from bare human skin

Originally Formulated by Antarctic researcher Paul Siple in the 1930s

Siple hung plastic bags of warm water in various temperature/wind combos

New wind chill values were implemented in 2001

New Formula used data from real human skin and modern heat transfer eqns.

New wind chill temps are notably “warmer” than the original values

Useful for general guidelines related to dangers of wind-related heat loss

Shortcomings: does not account for sunshine, humidity, individual health

Shortcomings: confusion with actual air temperatures

Shortcomings: only applies to humans, not animals or automobiles
Trivia and Stories

Siple grew up in Erie, PA, was an Eagle Scout and ‘frat boy’

Siple coined the term wind chill factor

Siple was opposed to wind chill temperature (wrong units) –“science geek”

Canada now uses the same scale…before 2001 it was different
Sound Bites

New Scale required some people to “freeze their face for science”

Wind chill “allows meteorologist to inflict further pain in bad weather”

Wind chill “further clutters the already cluttered world of weather info”

Additional Info


http://www.slate.com/id/2207326/ - Slate Magazine: Wind Chill Blows

Jet Stream

Primary Points

“Rivers” of strong winds aloft – typically found 30-45 thousand feet off the ground

Winds can flow at speeds in excess of 100 mph

Two main jets – strong “polar jet,” weaker “subtropical jet”

Formed by temperature gradients caused by irregular heating of the earth’s surface

Weaker in the summer when temperatures are more uniform from north to south

Generally a few miles thick and a few hundred miles wide

Continuous around the earth, though parts are weaker and parts are stronger

Flow from west to east, though they meander quite a bit

Jet streams generally divide air masses, cold to the north, warm to the south

They generally help to move along weather systems
Trivia and Stories

Pilots use the jet stream to expedite trips

Jet streams exist on other plants too

The strongest jet streams can reach speeds of 275+ mph

Jet streams were discovered in the 1920s by Japanese meteorologist Wasaburo Oishi
Sound Bites

“Soaring as high as a jet plane, jet streams are fast flowing, meandering rivers of air”

“Jet streams thrive when hot meets cold”

“Racing jets help push weather systems down the line”

Additional Sources
http://www.livescience.com/27825-jet-stream.html - LiveScience: What is a Jet Stream?

http://www.srh.noaa.gov/jetstream/global/jet.htm - National Weather Service: The Jet Stream


Primary Points

Violent, spinning columns of air that reach from clouds to the ground

Most form in supercells, powerful rotating thunderstorms

Ingredients: moist, unstable air at the surface, colder air aloft

Ingredients: change in wind direction with height (wind shear)

Ingredients: air mass boundary, front, or dry line

Range from just a few feet wide to over a mile wide

Most are weak (winds < 110 mph), though more powerful ones aren’t rare

Tornado alley brings all of the necessary ingredients

Tornado alley: hot and humid Gulf air meets cool, dry Canadian air mass

Hurricanes: generally predictable, large, form over warm tropical ocean
Tornadoes: small, isolated, difficult to forecast, form over land
Trivia and Stories
The first tornado prediction took place at Tinker Air Force Base in Oklahoma in 1948

Most powerful tornado: May 3, 1999 in Moore, OK – 317 mph winds

Tornadoes can happen in all 50 states, though Kansas sees the highest concentration
Sound Bites

“While violent and dangerous, tornadoes are simply rapidly spinning columns of air”

“Tornado alley brings together just the right mix of ingredients for a tornado recipe”

“While hurricanes can be predicted days in advance, individual tornadoes strike with just a few minutes’ notice”

Additional Sources

http://www.spc.noaa.gov/faq/tornado/ - Storm Prediction Center: Tornado FAQ

http://www.nssl.noaa.gov/education/svrwx101/tornadoes/ - NSSL: Tornadoes 101


Primary Points

Powerful low pressure systems that form over tropical oceans

Need warms water (>80 degrees), low amounts of wind shear, Coriolis force

Develop as clusters of thunderstorms become organized

Tropical Depression (<39 mph) to Tropical Storm (39-74 mph) to Hurricane (>75 mph)

Storm surge: water pushed on shore by strong winds

Most dangerous part is the eyewall – strong winds, driving rain

Eye is an area of calm winds and clear skies

Track forecast error: 50 miles (24 hours), 200 miles (5 days)

NHC forecasts go out 5 days – used to be 3 days before 2001

Forecasting difficulties: intensity is more of a challenge than track
Trivia and Stories

Hurricane Faith in 1966 traveled 6850 miles over the course of 3.5 weeks

Hurricane Wilma in 2005 went from Tropical Storm to Category 5 in 16 hours
Hurricane Ivan in 2004 spawned 117 tornadoes when it made landfall

2005 was the most active hurricane season with 28 storms, 15 hurricanes

Sound Bites

“Hurricanes, nature’s most powerful storms, originate from lowly tropical rain showers”

“Meteorologists like to talk about the wind, but a hurricane’s storm surge brings the greatest danger”

“Would you believe that you can find calm winds and clear skies at the center of the most powerful storm on Earth?”

Additional Sources

http://www.ready.gov/hurricanes – Ready.gov: Hurricanes

http://environment.nationalgeographic.com/environment/natural-disasters/hurricane-profile/ - National Geographic: Hurricanes

Radar/Doppler Radar

Primary Points

Traditional radar cannot detect rain or snow – based on surface observations

Dual polarization can detect precipitation type

Dual polarization radar sends out two radar waves, not just one

Dual polarization allows us to see the size and shape of particles in the air

Conventional radar only sees the location of precipitation

Doppler radar sees the motion of raindrops/snowflakes, towards or away from the radar
Most radars in the United States today are dual polarization Doppler radars

Drops moving rapidly away from the radar near drops moving towards = possible tornado

Rainfall estimates are made based on the reflectivity over time at a location

Radar beams shoot out at a slight upward angle

Low level precipitation may be missed far from the radar site where the beam is high up

Precipitation that is falling but not reaching the ground may also be shown

Ground clutter can be an issue
Trivia and Stories

World War II radar picked up echoes from rain/snow, this technology was commercialized later

First Doppler radars were installed nationwide in 1988 after NSSL research

Dual polarization was researched over the past 15 years – installation was completed in 2013

Sound Bites

“Doppler Radar allows meteorologists to see under the hood of storms”

“New Dual Polarization radar technology tells us where rain and snow are falling”

“Since the 1950s, radar has been scanning the skies for dangerous weather and even tornadoes”

Additional Sources

https://www.nssl.noaa.gov/tools/radar/ - NSSL: Radar

http://www.ig.utexas.edu/research/projects/mars/education/radar_works.htm - University of Texas: How Radar Works

El Nino/La Nina

Primary Points

El Nino: unusually warm water in the equatorial Pacific

El Nino: stronger subtropical jet stream pushes moisture into the US

El Nino: suppresses hurricanes in many cases

El Nino: cooler, wetter southern US, especially Gulf

El Nino: drier, warmer northern half of the US

La Nina: unusually cool water in the equatorial Pacific

La Nina: jet stream takes a more northern, variable track

La Nina: cooler, wetter northern US

La Nina: warmer, drier southern US

La Nina: more favorable conditions for US hurricanes

Not caused by global warming, though global warming could affect it

Trivia and Stories

El Nino may be to blame for historic famines and droughts – collapse of Columbian Incas

1998’s El Nino killed 16% of the world’s coral reefs

El Nino means “the boy” in Spanish; La Nina means “the girl”

Sound Bites

“One of the keys to our climate lies in the waters thousands of miles offshore”

“El Nino isn’t a storm – just a change in the ocean temperature”

“Want to find the subtropical jet stream? Just ask El Nino”

Additional Sources
http://www.pmel.noaa.gov/tao/elnino/el-nino-story.html - NOAA: El Nino

http://www.fi.edu/weather/nino/nino.html - The Franklin Institute: El Nino

Long Range Weather Prediction (Monthly/Seasonal)

Primary Points

Long range forecasts don’t try to be very specific – not a day-by-day prediction

Forecasts involve long-range models, analogs, El Nino

Predicting El Nino/La Nina holds great potential

Analogs: looking at past patterns to determine what might happen

Long range forecasts are most accurate late winter and late summer

Forecasts least accurate during the spring and fall when weather is changing rapidly

Precipitation forecasts are less accurate than temperature forecasts

All long range forecasts are only marginally accurate at this point

Lots of work needs to be done to improve long range prediction

Farmer’s Almanac = no science involved, simply a guess
Trivia and Stories

Almanac forecasts have been criticized for 100+ years by meteorologists

1956: Norman Phillips developed first climate model
Early 1980s: modern era of long range modeling begins at NCAR (CAM)
Sound Bites

“The idea of a 365-day forecast is alluring, but the reality is far less pleasant than the Old Farmer’s Almanac would have you think”

“El Nino could hold the key that unlocks the secrets of long range forecasting”

“Fall and spring bring changing weather which can elude the grasp of long range forecasts”

Additional Sources

http://www.wmo.int/pages/themes/climate/long_range_forecasting.php - WMO: Long Range Forecasting

http://www.washingtonpost.com/national/health-science/long-term-weather-forecasts-are-a-long-way-from-accurate/2013/04/15/1f9a2ac8-a05b-11e2-be47-b44febada3a8_story.html - Washington Post: Long-term weather forecasts are a long way from accurate


Primary Points

Caused by fast upward motion of unstable warm, humid air

When the air cools to saturation, rain/ice form and begin to fall, creating a downdraft

Best conditions: warm surface, cold aloft

Generally occur in the spring/summer because these seasons are warmer and wetter

Thunderstorms can occur in any season though

Types: single cell, multi cell, supercell
Supercell most dangerous, but least common

Strength is controlled by the instability of the air and the presence of vertical shear

Severe thunderstorms: 1 inch hail or 60 mph wind gusts

Nighttime storms: the atmosphere can still be unstable at night

Nighttime storms: warm air moving in at the surface, cold air moving in above

Lightning: rain drops and ice crystals collide, building charge difference with the surface

Trivia and Stories
Central Florida sees the most thunderstorms in the US – averaging 90 days each year!
Worldwide, approximately 1800 thunderstorms are happening at any given moment

Lightning heats the air around it to nearly 50000 F

Sound Bites

“A sticky summer day means the air is ripe for booming storms”

“Just like people, thunderstorms come in many shapes and sizes”

“In a thunderstorm, moist air hurtles upward until all of its water has been wrung out”

Additional Sources

http://www.erh.noaa.gov/lwx/swep/Spotting.html - NWS: Thunderstorms and Severe Weather Spotting

https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/ - NSSL: Thunderstorms

Climate Change

Primary Points
Greenhouse gases: carbon dioxide, methane, nitrous oxide, fluorinated gases

Emitted by industry and agriculture, though also naturally present in the air

Greenhouse effect: gases absorb radiation escaping from the earth, preventing cooling

Earth wouldn’t support life without the greenhouse effect

Too much of the greenhouse effect means it gets too hot on earth

The earth has been shown to be warming over the past few decades

Satellite observations of surface temperatures provide the best proof

Ozone hole: caused by emissions of aerosols into the atmosphere

Ozone hole: becoming less of a concern with harmful emissions on the decline

Climate predictions: generally made using models

Climate models: take into account emissions, snow melt, etc.
Trivia and Stories
Since 1971, 90% of warming has occurred in the ocean

If warming projections pan out, sea levels could rise by 1-2 feet by 2100

Warming has been observed to be the fastest near the poles
Sound Bites
“The greenhouse effect may sound evil, but it keeps us all alive”

“The best climate observations come from high above the earth”

“Greenhouse gases may be creating too much of a good thing”
Additional Sources
http://news.nationalgeographic.com/news/2004/12/1206_041206_global_warming.html - National Geographic: Global Warming

http://www.epa.gov/climatechange/ - EPA: Climate Change

Winter Precipitation
Primary Points
Precipitation type depends greatly on the temperatures across the column

Cold air near the surface, warm air aloft: freezing rain

Cold air near the surface, small layer of warm air above: sleet

Cold air throughout: snow

Sleet: snow that melted, re-froze on the way down

Hail: produced in thunderstorms by rain drops clumping together in updrafts

When the air is dry, snow can stay solid in above freezing temperatures

Powdery snow falls at lower temperatures

Fluffier snow generally falls when it is quite cold

Snow disappears by sublimation

Snow lifts into dry air, the sun plays a role
Trivia and Stories
A 15” snowflake was observed in Fort Keogh, MT in January of 1887

Snow has been observed as far south as Homestead, FL in the US in 1977

Silver Lake, CO recorded nearly 76 inches of snow in 24 hours in 1921
Sound Bites

“Don’t you dare call it hail – sleet is very different from its summer cousin”

“Believe it or not – it can rain when it’s below freezing – the secret lies just above the ground.”

“Depending on the temperature, snow can be as light as cotton or as heavy as fresh cement”

Additional Sources

https://nsidc.org/cryosphere/snow/index.html - National Snow and Ice Data Center: All About Snow

http://geonews.tamu.edu/weather-whys/718-sleet-vs-freezing-rain.html - Texas A&M: Sleet vs. Freezing Rain

Primary Points

Red sky caused by particles in the air diffracting the light – indicative of low pressure

Red sky in the east at sunrise: sun shining on approaching clouds to the west

Red sky in the west at sunset: sun shining on departing clouds to the east

Storms may fizzle before they reach you after a red sky in the morning

Ring around the sun/moon: caused by ice crystals in high altitude cirrus clouds

Cirrus clouds are usually the first layer of clouds seen from an approaching storm

Cirrus clouds aren’t always with a storm, so this isn’t always true

“March comes in like a lion, goes out like a lamb” – not scientifically supported

“No weather is ill, if the wind be still” – clear, calm conditions mean high pressure

Groundhog Day – no better than flipping a coin

Trivia and Stories

“Red sky by morning” dates back hundreds of years and is found in many languages

Some weather lore must be reversed in the southern hemisphere – rotation is opposite

Most weather lore is designed to apply to the mid-latitudes

Sound Bites

“Red sky by morning? Check your local meteorologist – a storm may be approaching.”

“When it comes to weather forecasting, Punxsutawney Phil is just a glorified rat.”

“Remember, weather lore is just that: lore. Storms may fizzle before you even see drizzle”

Additional Sources
http://www.cmos.ca/weatherlore.html - Environment Canada: Weather Lore and Proverbs

http://www.bbc.com/news/magazine-14087734 - BBC News - Weather lore: What’s the Science?

Lake (Sea)-Effect Snow/Rain
Primary Points

Lake effect snow is caused by the temperature difference between the wind and water

Water must be at least 20 F warmer than the air in the lowest mile of the atmosphere

When cold air moves over warm water, the air becomes unstable

Upward motion then ensues and clouds form and begin to drop snow

The size and shape of the lake determines the size and shape of bands

Larger lakes create more intense snow because more moisture is involved

When the lake freezes, the lake effect snow stops

Frozen lakes mean that the temperature difference between ground and air is gone

Lake effect rain happens in the fall when the lake is warm but the air is cooling

This also happens in the Great Salt Lake in Utah and Lake Tahoe

Ocean effect snow is common in Massachusetts Bay and Chesapeake Bay

International: Sea of Japan, Canadian Maritimes, Caspian Sea
Trivia and Stories
Buffalo, NY received 82 inches of snow in 5 days in December 2001

Lake effect snow was observed from the Atlantic off Cape Canaveral in 2003

Michigan’s Mt. Bohemia relies on lake effect snow, averaging 250-300” each year
Sound Bites
“What do you get when you combine wind, water, and winter? A whole lot of snow.”

“When the lake freezes, the snow pauses.”

“Just ask any resident of Buffalo: the Great Lakes can bring some great snows.”
Additional Sources

http://www.noaa.gov/features/02_monitoring/lakesnow.html – NOAA: Lake Effect Snow

http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/lake_effect_snow.html - University of Wyoming: Lake-effect snow

Optical Phenomena

Primary Points

Rainbows: caused by the reflection and refraction of light through water droplets

Rainbows: appear in the part of the sky opposite the sun

Rainbows: caused by the different wavelengths contained within light

Rainbows: can’t happen during snow – shape of flakes scatters light too much
Mirages: caused by the bending of light across a temperature gradient

Mirages: cold air is denser than warm air – light rays bend away from warm ground

Mirages: bending is most likely to happen with extreme heating at ground level

Mirages: instead of water, what you’re really seeing is the bluish sky

Sun Dogs: bright spots of light on either side of the sun

Sun Dogs: caused by the refraction of light through ice crystals in high clouds

Sun Dogs: much like rainbows, but constant

Halos: essentially like sun dogs, but a full circle

Stories and Trivia

The end of a rainbow is impossible to reach – it will always move away as you approach

Under the right circumstances, triple and quadruple rainbows can be seen

Besides sun dogs and halos, there are dozens of other arcs/halos that can be found

Sound Bites

“Sun dogs aren’t a type of hot dog– rather; they just mean there are cold clouds aloft”

“When you see water in the distance on a flat road on a hot day, you’re actually just looking at the sky”

“A ‘snowbow’ would be beautiful, but the irregular shape of the snowflakes makes them impossible”

Additional Sources

http://science.howstuffworks.com/nature/climate-weather/storms/rainbow.htm - How Stuff Works: Rainbows

https://nsidc.org/cryosphere/arctic-meteorology/phenomena.html - National Snow & Ice Data Center: Arctic Phenomena

Heat Index/Apparent Temperature

Primary Points

Heat index: based on temperature and dewpoint

Dewpoint: saturation temperature of the air

Measure of how hot it “feels” as opposed to the actual temperature

Relates temperature at high humidity to another one at low humidity

Base for the heat index: a dewpoint of 57 F

Humans cool by sweating – sweat evaporates less when it is humid

Limitations: the heat index makes many assumptions

Limitations: feeling may vary from person to person

Limitations: different people will suffer differently

Limitations: the heat index is useless outside of a certain range
Trivia and Stories

The Canadian heat index is called “humidex” and it uses a base of 45 F dewpoint

The highest heat index recorded was 176 F in Saudi Arabia in 2003 (108/95)

Appleton, WI recorded a heat index of 148 F on July 13, 1999 (101/90)

Sound Bites

“The saying goes: ‘it’s not the heat, it’s the humidity,’ and that’s exactly what the heat index is designed to measure”

“The heat index makes many assumptions – if you were to wear a wool suit out on a summer day, the heat index would fall short for you”

“When we sweat on a scorching summer day, we cool off. Humidity slows that process, and that’s where the heat index comes into play”

Additional Sources

http://nws.noaa.gov/os/heat/index.shtml – NWS: Heat: A Major Killer

http://www.weather.com/encyclopedia/charts/heat_index.html - The Weather Channel: Heat Index

Satellite Imagery

Primary Points

Three types of imagery: visible, infrared, water vapor

Visible: photographs taken from the sky

Visible: higher resolution, detects all clouds visible from above

Visible: only works during the day, not at night

Infrared: works based on radiation being sent up from the earth

Infrared: cold things made to appear bright (clouds), warm things appear dark (ground)

Infrared: lower resolution, may miss some low clouds and fog

Infrared: works at all times of the day and night

Water Vapor: used to identify areas of moisture in the mid-levels

Water Vapor: detects energy at wavelengths emitted by water vapor
Water Vapor: brighter colors mean more moisture in the mid-levels

Water Vapor: works both day and night

Satellites can also be used to determine temperature profiles and ozone concentration
Trivia and Stories

The first weather satellite was launched in 1959 (vanguard 2)

The first satellite image from space came from TIROS-1 in 1960

Temperature information from satellites has been available since Nimbus 3 in 1969

Sound Bites

“Miles above us, a fleet of satellites is charged with tracking storms around the world”

“Infrared sensors allow us to track clouds based on their temperature, even in the dead of night”

“A satellite’s sounder allows us to peel back the layers of the atmosphere and see the temperature at each place along the way”

Additional Sources

http://noaasis.noaa.gov/NOAASIS/ml/genlsatl.html - NOAA: NOAA’s Weather Satellites

http://www.accuweather.com/en/features/trend/evolution-of-weather-satellite/1184427 - AccuWeather: Evolution of Weather Satellites

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