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Category Archives: Severe Weather
What is a “wake low”?
Wake lows are short-lived mesoscale phenomena. Mesoscale weather ranges from about 5 kilometers to 1,000 kilometers in size.
Wake lows are relatively uncommon. They produce strong winds after a storm moves out. The term “wake low” was defined by Ted Fujita, the same meteorologist who came up with the F-scale ranking of tornadoes. These areas of low-pressure form on the backside of heavy rain, causing winds to surge in at fast speeds. Continue reading
What causes a thunderstorm?
Thunderstorm development requires three basic ingredients: moisture, unstable air and upward motion.
Moisture comes from regions like oceans, lakes and vegetation that provide the water vapor necessary for cloud formation and precipitation. Continue reading
How important was the weather forecast on D-Day?
D-Day was the name given to the June 6, 1944, invasion of the beaches at Normandy in northern France by troops of the Allied Forces during World War II. The goal was to cross the narrow, often stormy, English Channel into Nazi-occupied France.
The successful D-Day invasion required a combination of environmental factors: initial invasion around sunrise and at at low tide; nearly clear skies; at least 3 miles of visibility; close to a full moon; relatively light winds; non-stormy seas; and good conditions persisting for at least 36 hours and preferably for four days. To make the task of forecasting even more difficult, the Allies needed at least two days advance notice of these conditions —and because the science of meteorology was only just beginning to modernize, at the time this was a nearly hopeless task. Continue reading
Category: History, Severe Weather, Weather Dangers
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What is fire weather?
Wildfires need three essential elements: heat, oxygen and dry fuel. Fire weather refers to a mix of meteorological conditions that make it easy for wildfires to ignite and spread quickly. The main weather factors are low humidity, strong winds, warm temperatures and atmospheric instability.
When humidity is low, moisture is drawn out of plants, turning them into highly combustible fuel for fires. Extended dry spells or droughts remove the moisture that helps prevent ignition, making the physical environment more vulnerable. Strong winds provide fires with oxygen and carry hot embers ahead of the fire line, starting new fires. Warm temperatures heat dry vegetation, making it more likely to ignite. Unstable atmospheric conditions allow smoke plumes to rise rapidly, intensify fires, and create unpredictable shifting winds. Continue reading
Who or what triggers the decision to sound a tornado siren?
The National Weather Service is responsible for issuing forecasts, watches and warnings for a variety of weather and water hazards. A “warning” is issued when hazardous weather poses an immediate threat to life or property.
A warning can be issued for a variety of hazardous weather, including tornadoes, thunderstorms and flash floods. These threats can form quickly, last a few minutes and impact a small area. Forecasters must rely heavily on observational data from Doppler radar, satellite, and other ground-based equipment and sensors to inform them during the warning process. Continue reading
Category: Meteorology, Severe Weather, Weather Dangers
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