FAQ: Temperature, temperature records
Q: What's the highest elevation in the USA ever to record a reliable 100-degree reading?
A: The record may well be Jackson, Wyo., (elevation 6,200 feet), which recorded a high of 101° on July 17, 1934. In general, it would appear that an elevation of 6,000 to 6,500 feet is the upper limit throughout the West for 100° to be recorded. However, Santa Fe (elevation 7,000 feet) reached 99.5° on June 26, 1994, during the worst heat wave on record in the Southwest USA.
For more, this USA TODAY page lists each state's high temperature record.
(Answered by Christopher Burt, author of Extreme Weather, Sept. 24, 2007)
Q: What's the highest temperature ever recorded in Hawaii?
A: The Aloha States record high temperature of 100°F was set at Pahala, on the south side of the Big Island, on April 27, 1931. Thanks to the moderating influence of the surrounding Pacific Ocean, temperatures above the low 90s in Hawaii are unusual. Hawaiis all-time high is unusually cool -- every other states record high is above 100°F, with the exception of Alaska, which also has an all-time high of just 100°F.
(Answered by Doyle Rice, USA TODAY's weather editor, September 16, 2007)
Q: Why do bank thermometers tend to run warm? And how accurate are car thermometers?
A: Quite often, the temperature sensors for bank thermometers arent placed in the shade away from pavement and other objects. This leads to temperature readings that exceed the "official" temperature, typically taken at the nearest airport. Car thermometers, often located behind the front bumper or near the grill, are typically well-shaded. Locating the sensor near fresh air intakes helps to prevent an influence from the engine compartment. However, car thermometers can run slightly warm, mainly due to the warming influence of pavement.
There's plenty more about temperature on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, September 12, 2007)
Q: What's the record for the highest nighttime temperature ever recorded?
A: Death Valley, Calif., recorded a low of 104° on the night of July 23-24, 2003, which is the highest overnight low anywhere in the world that I could find. Outside of the U.S. Desert Southwest, the only 100° minimum Ive seen was 100° on July 30, 1989, at Muscat, Oman. During this summer's heat wave in southern Italy, the town of Cefalu, Sicily, dropped to only 98.1° on the night of June 24-25. This was the highest minimum on record for Europe.
This page from Death Valley National Park has more about the weather and climate of the hottest, driest place in the USA.
(Answered by writer Christopher Burt, author of Extreme Weather, Sept. 10, 2007)
Q: Along which type of front is the 'worst' weather
found in winter? Is this the same in summer?
Q: Which places have the same weather most of the year?
A: Because of the Earth's tilt, every place on Earth receives an amount of solar radiation that varies during the course of the year. This input of energy tends to be the most constant at the equator. Therefore, tropical locations near the equator tend to have constant heat and humidity nearly year-round. Tropical islands receive the additional benefit of the moderating influence of water, keeping their weather even more constant.
Learn more about how Earth's tilt impacts the seasons on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, April 9, 2007)
Q: What major U.S. cities have the highest yearly average temperatures?
A: Christopher Burt's book Extreme Weather reports that Key West, Fla., with an annual average temperature of 78.0°F, is the warmest city in the USA by this definition. Other warm cities include Honolulu (77.5°F), Miami (76.6°F) and Fort Lauderdale (75.7°F). But despite its year-round warmth, Key West has only reached 100°F once, in August 1886. On the other end of the spectrum, the coldest major U.S. city is Fairbanks, Alaska, with an annual average of 26.7°F.
You can check monthly average temperartures for most major U.S. cities on USATODAY.com's city guide pages.
(Answered by Doyle Rice, USA TODAYs weather editor, April 2, 2007)
Q: Is there a city or town in the USA that maintains a 70°F temperature year round?
A: The one location I found that comes closest is Hilo, Hawaii, a town on the east side of the Big Island. Hilo has an annual average temperature of 74°F, with July being the warmest month at 76°F and January the coolest at 71°F. The all-time records arent too extreme in Hilo, either, with a record high of 94°F and a record low of 53°F. But bring your raincoat Hilo is also very wet, with an annual average of nearly 130 inches of rain.
(Answered by Doyle Rice, USA TODAYs weather editor, March 26, 2007)
Q: Does wind affect the temperature on a thermometer?
A: No, wind has no effect on the actual temperature on a thermometer. However, wind can affect the way the temperature feels on your skin. As the wind blows, it cools your body. This is why forecasters report the wind-chill temperature, which is how cold the air feels to the average person at a specific wind speed.
Learn more about wind chill on this USA TODAY resource page.
(Answered by meteorologist Julya Johnson from WBIR-TV in Knoxville, Tenn., March 7, 2007)
Q: Why does the frost line go deeper when the temperature starts getting warmer?
A: The frost line, also known as the freezing depth, is the depth to which the ground freezes during the winter. More specifically, it is the water within the soil that freezes. The frost line starts near the surface and gets deeper during the course of the winter. Just as it takes a prolonged period of cold air temperatures to begin the freezing process in the ground, there is also a lag time before warmer temperatures at the surface make an impact on the frost line well below ground level. The frost line may penetrate even deeper during this lag time.
Due to differences in wintertime temperatures from region to region, the frost line will be deeper in colder climes, while the ground may not freeze at all in warmer locations. The frost line is important, particularly to builders. Building codes require that foundations be dug at least to the depth of the frost line. Failure to do so would compromise the structural integrity of the building as the ground shifts, or heaves, during the freezing process.
For more about how ground freezes, check out this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor)
Q: What's the difference in the temperature in the shade versus in the sun? Is there a rule of thumb - such as it's usually 10°F cooler in the shade?
A: Temperatures in the sun, naturally, are warmer than
those in the shade. But the best way to determine the difference is to actually
measure the temperature in the shade vs. the temperature in the sun.
(Answered by meteorologist Howard Bernstein of WUSA-TV
in Washington, D.C., February 19, 2007)
Q: Why does the coldest part of the winter come one month after the shortest day of the year?
A: Its mainly because it takes time for the atmosphere to adjust to the decreased amount of solar energy that occurs in the winter. This atmospheric lag is due to the huge volume of water in the oceans, which cover 71% of the Earths surface and are a major contributor of energy to the atmosphere. Less solar energy in winter slowly lowers the temperature of water in the oceans, which in turn slowly cools the atmosphere. This is the reason for the temperature lag in winter, as well as during the summer, when the warmest weather occurs several weeks after the longest day.
For a real-life example that explains the summertime lag, turn on a stove and feel over the burner the air is heated almost immediately (analogous to land on long, sunny days near the summer solstice). Put a pot of water over the heat, however, and the air above the water is not nearly as warm as it was before. It takes more energy to increase the temperature of water, which in turn warms the air above the water.
To learn more about the Earth's seasons, check out this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, February 5, 2007)
Q: Is the urban heat island effect as evident in winter as in summer?
A: The urban heat island effect results when solar radiation heats up pavement and building surfaces in urban areas while this same energy is used for evaporation and transpiration in rural areas. At night, energy from Earth radiates more rapidly to space in rural locations, while building inhibits the same amount of heat loss in cities. Thus, the urban heat island tends to keep cities warmer, sometimes up to 10 to 15° F, both day and night than the surrounding countryside.
We don't think about life-threatening heat waves during
the winter, but the urban heat island effect can still keep cities significantly
warmer than surrounding areas. While the lower angle of the sun and shorter
days reduce solar radiation everywhere in the winter, the concentration of heating
sources in cities can still keep urban areas much warmer than rural locations.
There's plenty more about urban heat islands on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, February 4, 2007)
Q: Why is it warmer at lower elevations and cooler at higher elevations, since you're closer to the sun at higher elevations?
A: It is true that the sun's energy, particularly its ultraviolet radiation, can be more intense high in the mountains and can lead to some nasty sunburns if you're not careful.
However, the main source of energy for the troposphere the lowest layer of the atmosphere where we live and most weather happens is not the sun directly, but rather the sun-warmed surface of the Earth. Due to the effect of gravity, air is densest near the surface of the Earth. Air, heated at the surface, becomes less dense than its surroundings and rises. Since pressure also decreases with elevation, this rising air expands and cools as it rises. The temperature of the troposphere thus decreases as you climb to higher elevations.
Beyond the troposphere, the temperature of the stratosphere
actually increases with altitude, due to the concentration of ozone which increases
with altitude in the stratosphere. Since ozone absorbs ultraviolet energy from
the sun, the stratosphere is warmest where the ozone concentration is greatest.
Learn more about temperature on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's
assistant weather editor, January 25, 2007)
Q: Can hot water freeze in cold air before hitting the ground?
A: Given the right conditions, it can. One necessary condition
is that the air be very cold, on the order of -35°F or colder. If the water
temperature is close to the boiling point, it is close to evaporating anyway.
Now toss the water out of its cup and into the air, and it will have more surface
area, increasing the amount of evaporation. A cloud of frozen ice crystals will
Learn more about the phases of water on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, January 23, 2007)
Q: How many states have never recorded a temperature below 0°?
A: Just one Hawaii. The lowest temperature ever recorded in Hawaii was 12°, measured on May 17, 1979, at the Mauna Kea Observatory on the Big Island. Most states have record lows well below 0°, except for Florida, which has an all-time low of -2°. That record was set in Tallahassee on Feb. 13, 1899.
(Answered by Doyle Rice, USA TODAYs weather editor, January 22, 2007)
Q: What's the difference between "arctic" and "polar" air?
A: An air mass is simply a large volume of air that has
similar temperature and water vapor content throughout. Air masses tend to take
on characteristics of the areas where they form. In the case of arctic air,
the source region for the air mass is above the Arctic Circle. This cold and
dry air tends to only form during the winter. Polar air masses form at high
latitudes, but not typically above the Arctic Circle. While not as cold or dry
as arctic air, polar air can result in winter storms in the USA as well as welcome
relief during hot summer months.
Learn more about air masses on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, January 15, 2007)
Q: Where are the USA's coolest temperatures found during the summer?
A: If you are looking to stay cool in the summertime, head for Alaska. Barrow, located north of the Arctic Circle on the Arctic Ocean, has a chilly average summertime high temperature of 47°F. Nome sees average highs near 58°F in the summertime. Othern Alaskan average highs include 62°F in Anchorage, 59°F in Valdez, and 57°F in Dutch Harbor and Kodiak.
Remember that summer temperatures in Alaska can get much warmer. Temperatures in Anchorage, Fairbanks and Valdez regularly hit the 70s to low 80s at least a few times in summer.
In the lower 48, the coasts of northern California, Oregon and Washington are the coolest spots, with daytime high temperatures in the 50s and low 60s, thanks to cold ocean waters flowing south from higher latitudes
Places like Astoria, Ore., and Cape Disappointment, Wash., are cool because of the cold "California Current," which flows south and causes upwelling of even cooler ocean waters right along the coast. When warm air from inland locations moves over the cold ocean, fog frequently forms near the ocean, holding daytime temperatures to the 50s and low 60s.
Cape Disappointment is the foggiest place in the USA, with
106 days of fog per year. Astoria, Ore., has average highs near 62°F in
the middle of summer with frequent fog as well.
A quote commonly misattributed to Mark Twain once said, "the coldest winter I ever spent was a summer in San Francisco." While it is true that clouds and low fog frequently hug the California coast holding temperatures to the 50s and low 60s in the summertime, these conditions are frequently interrupted by much warmer, "offshore," wind events, where temperatures climb into the 90s...far from cool.
(Answered by meteorologist Nick OKelly of KUSA-TV in Denver, December 19, 2006)
Q: Is there a difference between the centigrade and Celsius temperature scales?
A: No, they are two names for the same metric temperature scale, where 0° is the freezing point and 100° is the temperature at which water boils. The USA is one of the only nations in the world that still uses the Fahrenheit temperature scale for measuring temperatures. However, the entire scientific world (including the USA) uses the Celsius scale. After a brief surge of interest in the 1970s, the USAs attempt to switch to the metric system soon fizzled out.
This USA TODAY resource page shows how to convert between the Fahrenheit and Celsius temperature scales.
(Answered by Doyle Rice, USA TODAY's weather editor, November 27, 2006)
Q: At what temperature can wind chill injure or kill you?
A: Wind chill is not the actual air temperature, but rather the temperature it feels like to humans and animals based on the rate of heat loss due to the wind. Meteorologists use the wind chill index to determine how cold it feels to the average person. However, the way it feels to people will vary depending upon age, health and how much clothing is worn. While different for each person, wind chill temperatures below zero can become dangerous.
For more, check out this National Weather Service wind chill FAQ.
(Answered by meteorologist Julya Johnson of WBIR-TV in Knoxville, Tenn., November 15, 2006)
Q: Why is the coldest weather associated with light or no wind?
A: The coldest temperatures usually occur when the wind is light or calm because the air isnt mixing. During light or calm winds, the coldest air settles toward the Earths surface, where we live. However, when its windy, air feels colder to the exposed skin because of the wind chill.
This USA TODAY resource page has more about wind chill.
(Answered by Cindy Preszler, John Fuller, Scott Connell and Mike Roberts of the KSDK-TV weather team in St. Louis, November 14, 2006)
Q: At what time of day do the daily high and low temperatures usually occur? Are there exceptions to this?
A: High temperatures usually occur between 3:00 and 4:00 p.m., usually at about 3:00 p.m. in the winter and 4:00 p.m. in the summer. The sun is at its highest point in the sky at noon, but theres always a "lag" in temperature response. (This "lag" also takes place as the seasons change; for example, although the sun's angle is most direct on the summer solstice in June, the warmest months are in July and August.)
The daily low temperatures usually occur just before sunrise, after the heat from the day escapes back into space overnight.
(Answered by meteorologist Tony Pann of WUSA-TV in Washington, November 6, 2006)
Q: Two fields are exposed to the same amount of sunlight. The one field is covered with water and the other field is dry. Over which field will the air temperature be higher?
A: When sunshine hits the ground, its energy goes into
increasing the temperature of the soil which, in turn, heats the surrounding
air. When the soil is wet, however, some of the sun's energy goes into changing
liquid water in the soil into water vapor. This takes away from the energy available
to heat the ground. Therefore, the air temperature over dry soil would be warmer
than the air temperature over wet soil.
Learn more about phase changes of water on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, October 15, 2006)
Q: Why is it that since our body temperature is 98.6°, when we are outside in 85° weather, we feel hot? Shouldn't we feel cold?
A: Your body is always creating heat through internal processes
and exercise, as well as losing heat to your surroundings. The body, particularly
a part of the brain called the hypothalamus, tries to maintain a balance between
this heat creation and heat loss, maintaining a core temperature around 98.6°.
When at rest, this balance is most easily attained when surrounding temperatures
are near 70°. When the air temperature is higher, the body must take
steps to increase heat loss, including sweating and increasing blood flow to
There's plenty more about how the body regulates temperature on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's
assistant weather editor, September 28, 2006)
Q: When a daily record high or low temperature is recorded for a location, is it averaged into the statistics for the following year?
A: No. Climate scientists generally use a 30-year average to which current temperatures can be compared as "departures from normal." This 30-year period is often referred to as the "climate normal, and is updated every 10 years for the most recent 30-year period (the data set widely used now is from 1971-2000; previous data sets were from 1951-80 and 1961-90). We are now starting to use a 100-year (1901-2000) normal for national statistics.
But once a daily record temperature is verified, its included in a historical data set, which includes all data for the location's period of record, which is different from the climate normal data set.
(Answered byJay Lawrimore, chief of the Climate Monitoring Branch at the National Oceanic and Atmospheric Administration, Sept.25, 2006)
Q: What's the difference between a frost and a freeze?
A: Frost is defined as a fuzzy covering of ice crystals that forms on surfaces at or below freezing. A frost also has come to mean a brief dip in temperatures to freezing or just below, with or without ice crystals. With ice crystals, the technical name is hoarfrost. Black frost refers to a dry freeze without ice crystals, which kills vegetation, turning it black.
A freeze, on the other hand, occurs when the temperature
drops well below freezing and may or may not include ice crystals. The amount
of time below freezing to warrant a freeze warning varies depending on geography.
Freeze warnings are issued when temperatures will be below freezing for a sufficient
amount of time to do damage to vegetation.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, September 12, 2006)
Q: If the Arctic and northern Canada have more daylight than the USA in the summer, why isn't it warmer up there?
A: It's not so much the length of daylight but the sun's angle that determines how warm a location might become. Locations at high latitudes, despite longer daylight hours in the summer, receive only a glancing blow from the sun's rays, while latitudes closer to the equator receive much more intense radiation and therefore more solar energy that contributes to daytime heating.
That said, while parts of Alaska and Canada can be bitterly
cold during the winter, they can be quite comfortable places to visit during
There's plenty more about Alaskan summer weather
on this USA
TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, September 6, 2006)
Q: Is International Falls, Minnesota, the official "Icebox of the Nation"? One source claimed that Tower had the record with a temperature -60°F and Embarrass only -57°F, another source said Embarrass had hit -64°F, which location is the nation's true cold spot?
A: From a meteorological or climatological standpoint, determining what location deserves to call itself the "Icebox of the Nation" depends on the criteria used.
Of the three cities listed, Tower has the lowest annual mean temperature, at 34.6°F. Embarrass isn't far behind, however, at 34.9°F. The annual mean temperature at International Falls is 37.4°F, the lowest of any National Weather Service first-order station located at a city in the contiguous USA.
Focusing just on daily minimum temperatures, the normal (1971-2000 average) value is 26.1°F at International Falls and 20.3°F at Tower. Although no official normals data are available for Embarrass, the average daily minimum temperature there, based on data from 1994-2001, is 22.9°F. The normal daily low during January typically the coldest month is -8.4°F at International Falls and -13.6°F at Tower, while the average daily low for January at Embarrass (again, based on data from 1994-2001) is -9.6°F.
In terms of number of days per year at or below 0°F, Tower averages about 71 days per year, while Embarrass and International Falls each average about 64 days per year.
Tower has also been colder, officially, than any city in Minnesota, a designation it achieved when the NWS Cooperative observer there recorded a low temperature of -60°F on February 2, 1996, setting a new official, all-time state record low. Less than two weeks prior, on January 21, 1996, Embarrass recorded its official all-time record low of -57°F. Unofficially, the mercury at Embarrass dipped as low as -64°F on February 2 of that year, while the same morning a thermometer placed in a swamp near the Tower observing site reportedly registered -74°F. The official low in International Falls that day was -45°F. The record low for International Falls is -55°F, recorded on January 6, 1909.
Whether this earns Tower the right to officially call itself the "Icebox of the Nation" may be a contentious legal issue. In 1987, both International Falls and Fraser, Colo., submitted applications to secure a trademark to the title, "Icebox of the Nation." Fraser ultimately was granted the trademark, and a two-year legal battle between the cities ensued.
In 1989, just as the case was to be heard by the U.S. Trademark Trial and Appeal Board, Fraser agreed to give up the rights to use the title nationally or with manufacturers who wish to conduct cold-weather product testing, in exchange for $2,000 to cover legal fees. Although Fraser retained the right to use the title within the state of Colorado, a recent article in the Denver Post describes how some residents are now mounting an effort to scrap the label altogether.
Meanwhile, the rivalry between the three northern Minnesota
towns continues, as discussed in a
2004 article in The New York Times.
Other cities that have called themselves "The Icebox of the Nation" (or "The Nation's Icebox") include Pellston, Mich., Truckee, Calif., Stanley, Idaho, and West Yellowstone, Mont.
Based on USA TODAY's archive of U.S. daily national temperature extremes since April 1995, which are provided by the National Weather Service, Stanley, Idaho, has been the nation's cold spot (outside of Alaska) more often than any other location, having recorded or tied for the lowest temperature in the contiguous USA a total of 478 days. This is followed by West Yellowstone, Mont. (385 days), Gunnison, Colo. (208 days), Truckee, Calif. (184 days), and Saranac Lake, N.Y. (143 days). During the same period, Fraser has recorded the lowest temperature in the nation 103 times, while International Falls has done so a total of 75 times.
Incidentally, the lowest temperature ever recorded in the lower 48 states was -69.7°F which was rounded off to -70°F at Rogers Pass, Mont., on Jan. 20, 1954. For more, see our article on state record low temperatures.
(Answered by Sean Potter, a certified consulting meteorologist
and science writer in New York City, August 9, 2006)
Q: I live in Boston and the heat has me wondering. What makes one day 97 and the next day 79 if both days are sunny and clear?
A: While energy from the sun does serve to warm the air, other factors affect air temperature, especially the direction of the wind. A process called advection, in which the wind transports a colder or warmer air mass into an area, can sometimes overwhelm the heating of the sun. That is to say, a cold wind from the north can lower the temperatures during a day that is sunny. Likewise, a warm southerly breeze can make the mercury climb, even on an overcast day.
Existing soil conditions also contribute to how quickly
the mercury rises on a sunny day. Much of the solar energy that moves through
the atmosphere does not directly heat the air. Rather, the sunshine reaches
the ground and warms it, which in turn heats the air near the surface. If the
soil is dry without much green vegetation, the sun quickly warms it and air
temperatures climb quickly. If there has been a recent rain and soils are wet,
much of the solar energy goes into evaporating water in the soil, rather than
heating the soil.
Learn more about air temperature on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's
assistant weather editor, August 2, 2006)
Q: Why does northern Japan tend to be so much colder than Ireland, even though it's closer to the equator?
A: It is true that northern Japan is closer to the equator than Ireland. By way of example, Sapporo is at 43°N latitude, while Dublin is around 53°N latitude. It is also true that northern Japan is colder than Ireland, but only in the winter. The average high in Sapporo in January is 31°F, while Dublin averages 46°F. However, the average August high in Sapporo is 73°F, but only 66°F in Dublin.
It should be remembered that temperature is not determined
solely by average sun angle during the year. Especially in the case of these
two island nations, the surrounding ocean temperatures can have a significant
influence on air temperature. Ireland is far warmer than locations at similar
latitudes in Canada or Russia due to the warming influence of the warm North
Atlantic Current. Northern Japan, on the other hand, is influenced by the cold
Oyashio Current. Northern Japan can also get reinforcing blasts of continental
polar air blowing in from Siberia, located to the northwest.
Learn more about the ocean's impact on temperature on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's
assistant weather editor, July 31, 2006)
Q: In the summer, why are coastal locations usually cooler than those inland?
A: Sea breezes help keep coastal locations cooler during the summer than those inland. They form during the day, when land heats up more quickly than nearby ocean water. As the land heats up, warm, light air above the ground begins to rise. Cooler air over the ocean, which is heavier and denser, pushes inland to replace the rising warm air, creating a cooling sea breeze.
The opposite occurs during the night, when the ocean water stays warm and the land cools off quickly. The cooler air over the land moves offshore to replace the warm, rising air over the ocean. This cycle creates a mild land breeze during the night at the beach.
Coastal locations not only stay cooler than inland areas during the summer, but they are usually milder during the winter as well. The nearby ocean water acts as a temperature moderator, since water takes longer to both heat and cool than land. As a result, areas near the ocean often stay warmer than inland locations during the winter.
Learn more about sea breezes on this USA TODAY resource page.
(Answered by Greg Seroka of USA TODAYs weather staff, July 25, 2006)
Q: What is a cooling degree day?
A: A cooling degree day is used during warm weather to estimate the required energy for cooling indoor air to a comfortable temperature. One cooling degree day occurs for each degree a days average air temperature is above 65°F. Large cooling degree day values imply warm weather and, thus, a large energy demand for cooling.
(Answered by meteorologist Tracy McCormick of the National Weather Service in Taunton, Mass., June 14, 2006)
Q: What is the average temperature of the Earth?
A: According to the World
Meteorological Organization and the National
Climatic Data Center, the average temperature of the Earths surface
in 2005 was 58.1°F. This was the second-warmest year since record-keeping
began in 1861. The warmest year on record was 1998. The global average is based
on readings from more than 7,200 ground weather stations around the world and
from ships and buoys at sea.
Learn more about the Earth's average temperature in 2005 on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, January 17, 2006)
Q: Has the average temperature
of the Earth risen over the last hundred years or so?
A: According to the National
Climatic Data Center, global surface temperatures rose about 1°F between
1880 to 2001. This increase, however, was not uniform across the globe and has
been greatest over North America and Eurasia. The United Nations' Intergovernmental
Panel on Climate Change suggests said that by the end of this century, average
global temperatures should increase from 2.5°F to 10°F.
Learn more global warming and climate change on this USA
TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, January 12, 2006)
Q: How do changes in the Gulf
Stream's temperature and speed affect the weather?
A: Near the Gulf Stream, the
ocean temperature modifies the lower layers of the atmosphere, which results
in stronger winds and thunderstorm development. The speed of the Gulf Stream
can also affect local conditions by interacting with the wind to change the
characteristics of wind-driven waves. When the wind blows in an opposite direction
to a strong ocean current, the waves tend to be steeper and break more frequently.
(Answered by Joe Sienkiewicz, science and operations officer with NOAAs Ocean Prediction Center in Camp Springs, Md., January 5, 2006.)
Q: How are Fahrenheit temperatures converted to Celsius?
A: Celsius is the unit of temperature measurement in the metric system. The easiest way to convert Fahrenheit to Celsius is to subtract 32 from the Fahrenheit reading, divide that number by 9, then multiply the result by 5. To reverse the process, multiply a Celsius reading by 9, divide the answer by 5, then add 32 to the result.
According to the U.S.
Metric Association, the only other countries other than the USA that have
not officially adopted the metric system are Liberia (in western Africa) and
Myanmar, in Southeast Asia.
Learn more about temperature conversions on this USA TODAY resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, January 3, 2006)
Q: Has a temperature of 100°F ever been recorded in January in the USA?
A: According to the records of the National Climatic Data Center, it's never happened. The highest temperature ever recorded in the USA in January was a reading of 95°F in Los Angeles on January 18, 1971. December is the only other month without a 100°F reading in the USA.
Check out our record of daily national high and low temperatures back to 1995.
(Answered by Doyle Rice, USA TODAY's weather editor, January 2, 2006)
Q: Why are temperatures typically
lowest around sunrise?
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, December 6, 2005)
Q: What are the highest and lowest temperatures ever recorded on the nine planets of the solar system?
A: With the sun being the main source of energy for all
planets in the solar system, it would seem obvious that Mercury, being the closest
to the sun, would be the hottest planet. However, since Mercury does not have
an atmosphere, Venus holds the record of hottest in the solar system, with an
average temperature around 867°F. Pluto, the most distant from the sun,
is the coldest planet with an average temperature of -369°F.
NASA's Goddard Space Flight Center maintains a page of planet facts on this resource page.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather editor, December 4, 2005)
Q: I know the highest air temperature in U.S. history is 134°F in Death Valley, but what is the record for highest ground temperature?
A: Long-term records are kept only for air temperature. These readings are typically taken over open, grassy surfaces about two meters above ground level. Unfortunately, there are no records kept for ground temperatures. However, the EPA reports that pavement can range from 120°F to 140° F, while some roofs can reach 150°F to 190°F. Pavement and buildings contribute to the urban heat island effect.
Learn more about urban heat islands on this USA TODAY resource page.
(Answered by Bob Swanson, USA TODAY's assistant weather editor, November 15, 2005)
Q: Why is the day's warmest temperature usually a couple of hours after noon, when the sun is highest in the sky, and the coldest temperture usually just after the sun comes up in the morning?
A: The easiest way to understand whate happens is to first just think of the air that's staying in place; we won't consider what happens when cold or warm air move in. This can change the general picture.
Then, let's think of the air in any place as being like a bank account. If you add money to a bank account, it grows. If you add heat to air it warms up. The Earth is always losing heat, like a bank account that you're always taking some money from. If the amount of heat arriving from the sun is exactly equal to the amount leaving, the temperature stays the same.
As the sun climbs higher into the sky on a sunny day, the balance tips to more heat arriving than leaving. This is like adding money to the account faster than you are withdrawing it. The air grows warmer and warmer. At non the day, the amount of heat arriving is greatest. But, even after the sun begins to dip lower in the sky, the amount of heat arriving is more than the amount leaving. It's like continuing to add more money to the bank account than you're taking out, even though you are adding less than you were before. Finally, after around 3 p.m., the heat "account" is in balance. From then on, more heat is leaving than arriving and the day grows cooler.
When the sun sets, the Earth begins cooling off even faster because no solar energy is arriving. The earth continuescooling all night and even after the sun begins to rise because more heat is leaving the "account" than arriving. But the sun doesn't have to be very high in the sky before more solar energy is arriving and leaving and the day begines to warm up.
The summer's warmest days come in July about a after the solstice when days are longest and the winter's coldest days occur in January or early February, a month or more after the winter solstice when days are shortest for the same reasons. The USATODAY.com FAQ on the seasons has more on this.
Q: Where was the highest and lowest temperature ever recorded on Earth?
A: : The highest worldwide temperature was 136 degrees and was recorded Sept. 13, 1922 in El Azizia, Libya. Vostok, Antarctica recorded the lowest temperature ever of -129 on July 21, 1983.
Q: If it's zero degrees outside and tomorrow it's going to be twice as cold. What will the temperature be?
A: The first thought might be to change the zero into the other common scale, which rids you of the troublesome "zero." Assuming the teacher means zero Fahrenheit, the same temperature is minus 17.7 degrees Celsius. If the zero is Celsius, changing it to Fahrenheit gives you 32 degrees.
If the question was, it will be zero and tomorrow the temperature will be twice as low, what will it be. we could say minus 35.4 degrees C, which is the same as -31.7 F.
But, it says, "it's going to be twice as cold," and that is something completely different and more complicated. Stop and ask, "What are we talking about here?"
The way this question is posed means you "should focus on the issue of heat (energy)," Bob Weinbeck of the American Meteorological Society's Education Office said when we sent the question to the AMS. "Cold is really the presence of minimal heat. Temperature only reflects the amount of heat - and on an arbitrary scale. One could use the absolute temperature scale."
By "absolute temperature scale" Weinbeck means a scale that begins at absolute zero; that is at the temperature at which there is no molecular motion. For more on this, see the USATODAY.com graphic that explains how temperature is really a measurement of molecular motion. The most common absolute scale is the Kelvin (K) scale, which is based on the Celsius scale with minus 273.16 degrees C being 0 degrees K. To change C to K, just add 273.16 degrees to the C reading. If you have learned algebra, you know that -17.7C will be 255.46 degrees K. (Since -17.7 is a negative number you subtract it from 273.16 when you add the two.)
Our converting between temperature scales page has more on the different scales.
Once you have converted to the Kelvin scale you're ready to figure out what twice as cold means. "Twice as cold would mean only half the heat energy," Weinbeck says. "So that the absolute temperature would be half of 255.46 K or 127.73 K. Such temperatures would certainly shiver your timbers!"
To see how much it would shiver your timbers, convert back to Celsius. Since you added 273.16 to the Celsius temperature to get the Kelvin temperature, you'd do the opposite to go the other way. That is, subtract 273.16 from 127.73 K to get the Celsius temperature of minus 145.43 degrees. This is a lot colder than the world record cold of minus 89.6 degrees C. set July 21, 1983 at the Russian Vostok Station in Antarctica. If tomorrow is really going to be that cold, the sun must be dying.
Q: What are the coldest and the hottest temperatures in each of the states in the USA, in history.
A: If you go to the USATODAY.com Weather extremes page you'll find links at the top of the page the lists of the highest and lowest temperatures for each of the 50 U.S. states. When you go to those pages you'll see a graphic at the top of each on the warmest and coldest records. Scroll down for the complete list of state records. Our extremes page has the nation's highest and lowest readings for the past week plus links to a lot more U.S. and global information on weather extremes.
Q: Does the "wind chill" actually lower the temperature of the air?
A: No. A USATODAY.com file on Wind chill applies only to people and animals explains why.
Q: What is the global temperature index? How is it calculated and how does one interpret the numbers?
A: Don't feel bad about being clueless on the ABC Morning News "temperature index." No one on the USATODAY.com Weather Team could figure it out. In 1998 Chris Vaccaro called ABC and find out what's going on. Here's his report:
"I finally spoke with Ronnie Riece who is the only person there during the daytime. She is the daytime producer for ABC World News Now. She asked me if I was familiar with the show, I said no. She then went on to explain that the shows is on early in the morning and isn't exactly the most serious news show. The temperature index has been on the program for a few years now. Its purpose is to poke fun at the other indexes that people don't understand. She said there is an actual mathematical formula that only one person knows and computes using data from several cities. She also said that its just for viewers to see that if the index goes up its going to be hotter and if it goes down its going to be cooler."
What can we say? At USATODAY.com we try to help our readers make sense of the world, not make fun of them.
Q: Should you measure temperature in the sun or shade?
A: Thermometers - which measure temperature - should always be in the shade to give a more accurate reading. Direct sunshine warms the instrument, making readings warmer than the air. Thermometers should also be at least three feet above the ground and away from buildings which give off heat.
Q: What do forecasts of normal, above normal or below temperatures mean?
A: In weather and climate, "normal" is the same thing as "average." To be more precise, normals generally refer to averages of a 30-year period. Right now, in the USA and many other countries, they are 1961 through 1990 averages. By the 2002 , they will become the 1971-2000 averages. The USATODAY.com Online weather almanac has links to guides to the month-to-month weather of cities around the world. Among other things, these include the normal temperatures for each month.