Category Archives: Climate

Can dust from Africa reach the United States?

Yes. Soil-derived aerosols, or dust, are abundant in our atmosphere. One source of dust is sandstorms over the Sahara. These storms whip small pieces of mineral dust from the desert into the atmosphere. Easterly winds then carry large plumes of Saharan dust away from the desert and over the Atlantic Ocean.

This weather system is referred to as a Saharan air layer, or SAL, and at times dust in the SAL has traveled to the Caribbean, Texas and Florida. Desert dust from the Sahara and Gobi deserts has been observed on the ice sheet of Greenland. Ice cores in Greenland provide a history of the dust deposition as it appears as layers in the ice. Continue reading

Category: Climate, Meteorology, Seasons

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What are the wettest and driest days of Madison’s warm season?

All things considered, we have really had a rather benign summer in southern Wisconsin thus far this year. Through Friday of last week, July was averaging just over 1 degree warmer than normal, with the majority of the contribution to this slightly warm month coming in the overnight lows, which have been 1.5 degrees above normal thus far. In addition, except for the 1.23 inches of rain we received when the heat broke July 23-24, we would be just about normal for July.

Somehow we got thinking about some characteristics of warm-season (May through October) precipitation in Madison in the midst of this spell of fine summer weather. Dr. Ed Hopkins at the State Climatologist’s Office was on the ready for our question, which was: What are the wettest and driest calendar days during the warm season in Madison? By “wettest” we mean the calendar day on which the most total accumulated precipitation has been recorded in Madison’s 153-year climatological record — and the least for the “driest” day. Continue reading

Category: Climate, Seasons

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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

Category: Climate, Meteorology, Severe Weather

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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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Has this been an unusually hot start to summer?

The recent stretch of warm, humid weather has got some people wondering if we have gotten off to an unusually hot start to summer this year in Madison.

There are a couple of ways one could approach that question. One way is to consider the departure from average for our daily high temperatures since May 1. From that perspective, we have been consistently warmer than normal with May daily highs averaging 3.2 degrees above normal and, June (through Friday) averaging 1.9 degrees above normal. Continue reading

Category: Climate, History, Seasons

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