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Category Archives: Seasons
Has it been unusually rainy so far this summer?
As we head into the last week of August, it is of interest to review aspects of this summer’s precipitation in Madison.
First of all, every one of the three traditional summer months has been wetter than normal with June, July, and August (through Aug 20) coming in at 0.26”, 1.55” and 2.02” above normal for a total surplus of nearly 4”. Continue reading
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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Does North America have a hurricane season?
Recently FEMA Director David Richardson claimed he was unaware that there is a hurricane season in the United States. There most certainly is such a season. The Atlantic hurricane season climatologically runs from June 1 through November 30, with the most active part of the season being mid-August through mid-October. Hurricanes are tropical storms over the Atlantic Basin (Atlantic Ocean, Caribbean Sea, and Gulf of Mexico). Based on a 30-year climate period from 1991 to 2020, the average Atlantic hurricane season has 14 named storms, 7 hurricanes, and 3 major hurricanes. A developing tropical cyclone is given a name when it reaches sustained winds of 39 mph and it becomes a hurricane at 74 mph.
Hurricanes can occur outside this season but these are the months with favorable conditions for formation of the storms. One such condition is the ocean temperature exceeding 79.7F, which is common in the Atlantic Basin between June and November. Hurricanes have difficulty forming off the U.S. west coast due to cold water, cold currents, and unfavorable winds. Continue reading
Is there a windiest time of year in Madison?
With the pollen season peaking in southern Wisconsin one may wonder if there actually is a windiest time of year in Madison. Of course, a windy day can come along just about any time of year (the record gust of 83 mph in Madison occurred in June 1975) but the climatology suggests that March and April are the windiest months of the year with average wind speeds of 11.3 and 11.4 mph, respectively. November through February are not far behind logging a four-month average of 10.5 mph.
The fact that it’s windier during the cold season is not surprising as that time of year is characterized by the highest frequency of mid-latitude cyclone activity. Mid-latitude cyclones are large in scale, covering several states simultaneously, and are often associated with very large differences in sea-level pressure over small distances. It is these pressure differences that drive the wind. Continue reading
Category: Climate, Seasons, Severe Weather
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