Recent Articles
  • Warmer than normal temps on tap here the next 2 weeks; the northbound moisture with Tropical Storm“Imelda’s” remnants, responsible for up to 21” of rain & twisters in the Houston, TX area Wed, may fuel Sunday downpours here

    CLICK TO ENLARGE

  • What are heating and cooling degree days?

    Dear Tom, What are heating and cooling degree days? Colin McIntyre,  Chicago Dear Colin, Heating and cooling degree days are measures that indicate the departure of a day’s average temperature from a base of 65 degrees. When the day’s average temp (the sum of the midnight-to-midnight, CST, high and low temperatures, divided by two) is below 65 degrees, the number of degrees of departure is called heating degree days; when above, cooling degree days. Degree day units are a useful […]

  • Dry conditions following cool, wet first half of summer

    Click to Enlarge

  • Saturday heat/humidity gave way to cooler less humid air

    Click to Enlarge

  • Air temperature in the sun and in the shade

    Dear Tom, Parade Magazine’s Marilyn Savant says air temperature is the same in the sun as in the shade, but placing a thermometer in the sun heats up the thermometer. Does that make sense? If true, what do they use to measure air temperature? Mike Beirl, Bolingbrook Dear Mike, Air temperature is always measured in a shady location because in the shade the thermometer is measuring the actual air temperature, and only the air temperature. A thermometer placed in the […]

  • Why you will never hear of a wind speed of 11 mph in a weather report

    Dear Tom, I have never heard a wind speed of 11 mph in a weather report, and I have listened for years. Bill Walkor, Chicago Dear Bill, You are correct to observe that a wind speed of 11 mph has never been announced. This may seem strange, but here’s the explanation. The National Weather Service measures wind speeds in knots (nautical miles per hour) in accordance with international practice. However, in the United States we use statute miles for measures […]

  • On the solstices at Chicago, how many degrees north or south of due east and due west are the sunrises and sunsets?

    Dear Tom, On the solstices at Chicago, how many degrees north or south of due east and due west are the sunrises and sunsets? Frank Stachyra, Oak Park Dear Frank, Chicago experiences a sunrise directly in the east twice a year on the spring and fall equinoxes. On those days, the sun also sets directly in the west and if the weather is clear, east-west travel is difficult as the sun’s rays shining directly down the streets make it difficult […]

  • Where and how often do derechos occur?

    Dear Tom, I’m wondering where and how often derechos occur. Margaret Robertson Chicago Dear Margaret, Severe thunderstorms can occur anywhere, given the ingredientsof warmth, moisture, instability, converging low-level winds and diverging winds aloft. The Midwestis prone to derechos, a high wind event in which winds,often in excess of 100 mph, plow out of a line of fast-moving thunderstorms, producing swaths of damage that extend for hundreds or even thousands of miles.The highest incidence is from midsummer through early fall. Chicago […]

  • Brief warming/Storms possible Thursday – workweek ends on windy note

    With deep low pressure passing to our west and north Thursday, first the associated warm front will move through the Chicago area from the south late in the day, followed soon aft     er by the storm’s cold front. This puts a least a portion of our area in the position of briefly experiencing the “warm sector” of this storm system- strong late afternoon-early evening warming well into the 60s and t-storms (a few severe storms possible). Strong westerly winds gusting […]

  • What are the world high and low temperature records, and Chicago’s?

    Dear Tom, What are the world high and low temperature records, and Chicago’s? Alvira Franko, Chicago Dear Alvira, Of all the world’s locations that are candidates for extreme temperature occurrences, two places rank above all others: Deserts for heat and polar regions for cold. Among the world’s deserts, Death Valley, California, claims the world’s heat record: 134 degrees recorded there on July 10, 1913. Death Valley is located in the east-central part of the Mojave Desert. The Earth’s south polar […]

Notice: you are using an outdated browser. Microsoft does not recommend using IE as your default browser. Some features on this website, like video and images, might not work properly. For the best experience, please upgrade your browser.