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Category Archives: Meteorology
Are heat waves increasing?
A heat wave is a period of abnormally and uncomfortably hot and usually humid weather.
The World Meteorological Organization is specific in its definition by stating that a heat wave is when the daily maximum temperature for more than five consecutive days exceeds the average maximum temperature by 9 degrees. Continue reading
What causes lightning?
Charges form in a storm composed of ice crystals and liquid water drops. Winds inside the storm cause particles to rub against one another, causing electrons to be stripped off, making the particles either negatively or positively charged.
The charges get grouped in the cloud, often negatively charged near the bottom of the cloud and positively charged up high. This is an electric field, and because air is a good insulator, the electric fields become incredibly strong. Continue reading
What happens to the wintertime cold pool in summer?
We have commented a number of times in the past few years about the areal extent of the hemispheric cold pool of air at 850 mb — about 1 mile above the surface — during the winter. As one might expect, that pool expands dramatically from October through February and then begins to contract as we move toward spring and summer.
Our analysis uses the minus 5 degrees Celsius (23 degrees Fahrenheit) isotherm (line of constant temperature) and has shown that the average winter cold pool area has systematically shrunk in the past 75 years. Continue reading
Category: Climate, Meteorology, Seasons
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What is an atmospheric river?
Atmospheric rivers are relatively narrow regions in the atmosphere — typically 250 to 375 miles wide and well over 1,000 miles long.
These sky rivers transport water vapor outside of the tropics to mid-latitude and polar regions. We estimate that 90% of Earth’s north to south water vapor transport is done through atmospheric rivers. Continue reading
Did weather forecasting play a role in D-Day?
Last week was the 78th anniversary of the Allied invasion of Europe that began with the landings on the beaches at Normandy. The combined land, air and sea assault of June 6, 1944, remains the largest such event in history.
The success of the invasion was extraordinarily dependent on weather conditions. More than three months before the invasion, a combined British and American forecasting team began rigorous forecast exercises designed to iron out the physical and logistical kinks of such a coordinated effort. Continue reading
