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Answers: Rising and Sinking Air

By Jack Williams ©2015

Q: In your AOPA Flight Training Magazine, January 2010 article you say that the curving path of upper air winds cause air to sink in some areas, creating high pressure at the surface, and to rise in other areas creating or strengthening areas of low pressure at the surface.  My question: How does adding rising air to an area, which... »

Answers: Inside Weather Fronts

By Jack Williams ©2015
Cold air is advancing from left to right--the blue arrow. The green arrow indicates warm air that's being pushed up. NWS image.

Q: In the November issue of AOPA Flight Training, you discuss extratropical cyclones, including the movement of cold air under warm air and vice versa. If I understand this correctly, the fronts themselves do not discriminate between the cold or warm air ahead of them.  How  do you explain movement under (cold into warm) or movement over (warm into cold)? Kevin,... »

Answers: Storm Winds

By Jack Williams ©2015
A satellite image of Hurricane Katrina on August 29, 2005, the day it hit Louisiana and Mississippi, clearly shows the storm's structure. NOAA image.

Q: Why doesn't an extratropical cyclone continue to rotate around a 360-degree axis, like a hurricane?  I've always wondered why a cold front begins to the northwest of the low center and then dies out on the northeast side. Why doesn't it continue to just rotate?  How does the Coriolis effect play into all of this? Jeff, Pensacola, Florida A:  The answer... »

Answers: Extratropical Cyclone Winds

By Jack Williams ©2015
Forecast for Oct. 15, 7 a.m. ET. Storm center forms. NWS image.

Q: My question is about your article in the November  AOPA Flight Training magazine on tropical cyclones.  I'm trying to reconcile two potentially different ideas: first, that a cyclone has swirling air (which I assume to mean the the air masses are rotating around the Low), and second, that the warm front and cold front are generally in the same... »

Ask Jack: Upper Air Temperatures

By Jack Williams ©2015
Pilots, such as those of this Airbus A 380 taking off from Oshkosh, Wis., on July 31, 2009, use upper air temperature data to calculate aircraft performance. Photo by Darlene Shields

Q: I am trying to find out how many degrees Fahrenheit the temperature decreases with each 1,000 feet of elevation. Thanks for your response. -Harry, Phoenix, Ariz. A: The exact rate at which the temperature changes with elevation differs from day to day and place to place, but I suspect that you are looking for something like an average rate.... »

Ask Jack: Rising Air

By Jack Williams ©2015
   Latent heat supplies much of the energy for supercell thunderstorms like this one that pelted Chaparral, N.M., with two-inch hail stones in April 2004. NOAA photo by Greg Lundeen.

Q: Why does moist air cool less rapidly than drier air when rising? What would be a good analogy for this? A: The... »

Ask Jack: Weather Textbook

By Jack Williams ©2015

Q: Would the AMS Weather Book be a good text book to use for a high school meteorology class? How similar is it to the USA TODAY Weather Book? A: The new book would be a much better text than the old one. To begin with, since I last revised the  the USA TODAY Weather Book in 1997 much has happened that... »

Ask Jack: College Advice

By Jack Williams ©2015

Q: As a young, soon-to-be meteorologist, I am wondering what would be a good college for me to go to? A: I  hate to try to recommend any particular college because the one that's best for you might be one that I don't know about. If you know what kind of meteorologist you want to be, that will help. For example, if... »

Ask Jack: Humid Air

By Jack Williams ©2015
Rising, warm, humid air formed this cumulus congestus cloud inland from Neptune Beach, Florida. Photo by Darlene Shields

Q: Why is humid air less dense than dry air? Matt, LaGrange, Ga. A: At first it might seem strange that humid air is actually less dense than dry air at the same temperature.  Most of the time we say things... »

Ask Jack: Wind Chill

By Jack Williams ©2015
Kansas ice storm

Q:  If the temperature is above 32 degrees and the wind chill is below 32 degrees, will water freeze? —Kirsten H., Somerville, MA A:  No. Most people are aware that they feel colder when the wind is blowing, but this is because the wind carries away the layer of air around you that your body’s heat has warmed. The big danger of air... »