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How does this summer dew point temperature compare with previous years?
The dew point temperature is the temperature to which the air must be cooled, at constant pressure, to get dew to form. As the grass and other objects near the ground cool and reach the dew point temperature, some of the water vapor in the atmosphere will condense into liquid water on the objects. While the dew point temperature is a temperature, it is also a measure of the humidity of the air. The higher the dew point temperature, the greater the amount of water vapor in the air.
To know how close the air is to saturation, we need to know the dew point and the air temperature. The closer the dew point is to the air temperature, the closer the air is to saturation. When the dew point equals the air temperature, the air is saturated, so the dew point temperature cannot be greater than the air temperature. Continue reading
Category: Climate, Meteorology, Seasons
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How far has summer beaten back the areal extent of cold air?
On more than one occasion in this column we have commented on the areal extent of air colder than 23 degrees Fahrenheit at 850 hPa (about 1 mile above the ground) as a measure of the extremity of winter.
In the middle of January, about 68 million square kilometers of the Northern Hemisphere are covered by air that cold at that level. Between about July 5 and July 20 that area shrinks to zero, and the complete absence of such air lasts only a very few days. At the beginning of August, we are just past the point in this summer that this area is beginning to increase again. Thus, despite the fact that we have been through a couple of really hot (and humid) weeks to end July, the return of winter has already begun in terms of this measure. Continue reading
Category: Meteorology, Seasons
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Comments Off on How far has summer beaten back the areal extent of cold air?
What is a heat dome?
“Heat dome” is a term used explain extreme heat conditions across large geographic regions.
The American Meteorological Society maintains a glossary of meteorological terms and defines a heat dome as, “An exceptionally warm air mass at middle latitudes during the warm season that that is associated with a synoptic-scale area of high pressure aloft. This area of high pressure aloft can have a doming effect on the warm air mass below by suppressing rising motion and the development of clouds and precipitation.” This is not the same as a heat wave, which is a spell of 3 or more abnormally hot days. Continue reading
How is rainfall intensity changing?
NOAA maintains observations of temperature and precipitation extremes in the U.S. The data indicate that cold extremes in the U.S. have become less frequent. Since the 1930s, there have been many more record-high temperatures compared to record-low temperatures. With warmer … Continue reading
What is a mesoscale convective complex?
Ordinary thunderstorms are a few miles in diameter and exist for less than an hour. The life cycle of an ordinary thunderstorm contains three stages: cumulus, mature and dissipating.
The cumulus stage is the initial stage of a thunderstorm as warm moist air near the ground rises. The mature stage of an ordinary thunderstorm begins when precipitation starts to fall from the cloud. During the mature stage, the thunderstorm produces the most lightning, rain, and can produce even small hail. The dissipating stage of a thunderstorm occurs when the updraft, which provides the required moisture for cloud development, begins to weaken and collapse. During this stage, the downdraft dominates the updraft and the storm begins to disappear. Continue reading
