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Answer: Our bodies lose heat more rapidly when the wind is blowing, which makes it "feel" colder than it really is, and wind chill is an estimate of the air temperature that would be required to produce the same rate of cooling in the absence of significant wind. A good explanation, an easy to use chart, and the formula used for calculations can be found at www.nws.noaa.gov/om/windchill/index.shtml.
Sep. 25, 2009 | Tags: apparent temperature, cold, cool sites, winds

Answer: The National Climatic Data Center makes a downloadable publication called "Climatic Wind Data for the United States" available on its web site. This includes monthly average wind direction and speed for several locations in each state. See www.ncdc.noaa.gov/oa/documentlibrary/wind/wind1996.pdf for that product. You can also access "wind roses" showing a more detailed monthly distribution of wind directions and speeds for several cities in our state at ftp://ftp.wcc.nrcs.usda.gov/downloads/climate/windrose/north_carolina/.
Sep. 7, 2009 | Tags: cool sites, past weather, winds

Answer: A tropical wave is characterized by an elongated trough of low pressure, with winds flowing through it in a curved manner (counterclockwise and usually toward the west in the Atlantic basin) but not in a closed circulation. When the system develops a low pressure center and a closed circular flow, it is then a cyclone that is called a tropical depression if sustained wind speeds are below 39 mph, and called a tropical storm when the winds reach that threshold.
Sep. 3, 2009 | Tags: hurricanes, winds

Answer: Sand and dust storms during the warmer half of the year in Iraq are largely driven by the Shamal wind pattern produced by a persistent low pressure trough that stretches from the northern Persian Gulf up into eastern Iraq and western Iran, and the pressure gradient between that trough and a semi-permanent high pressure area that reaches across the eastern Mediterranean into western Saudi Arabia. Northwest winds associated with this pattern can strengthen and weaken notably with subtle disturbances that cause the exact position and intensity of the trough to vary, and that affect the vertical alignment of wind speed and direction over the region. When the winds exceed critical thresholds, sand and talcum-like dust are scoured from the surface, especially from a number of source regions within the Tigris-Euphrates river valley comprised of dried lake beds and desiccated former wetlands, supplemented by a scattering of sources in central Syria and Jordan. The frequency of the enhanced wind periods varies naturally from year to year, but there has also been a significant drought across most of Iraq since late 2006 and early 2007. In addition to devastating effects on food production, this has resulted in loss of vegetative ground cover and even drier dust and sand source regions. This is likely playing a role in the more frequent dust storms, perhaps by increasing the area covered by easily disturbed source material, or by lowering the wind threshold (usually around 20-30 mph) required to initiate a significant event.
Jul. 24, 2009 | Tags: drought, winds

Answer: Derechos are widespread damaging wind events produced by convective storms, often in the form of a squall line or the bowing leading edge of a long-lived thunderstorm. They typically produce most damage by way of downburst winds that often occur along a preferred or dominant direction, but passage of several cells with somewhat differing gust directions, and the occasional tornado associated with some derechos, can complicate the damage pattern. In the event you asked about, there was also an unusual "wake low" mesoscale vortex that developed behind the initial squall line that led to sustained extreme winds over a large area, with the wind direction changing as the low moved along. You can read more about this system at en.wikipedia.org/wiki/May_2009_Southern_Midwest_derecho and www.crh.noaa.gov/lsx/?n=05_08_2009.
Jul. 15, 2009 | Tags: thunderstorms, winds

Answer: On the day in question (Tuesday June 16th, 2009) winds below about 6-8,000 feet became easterly as the day wore on, so that some fairly shallow rain showers were carried along toward the west. At the same time, deeper showers and rain generated at higher altitudes by a passing upper level disturbance were moved along toward the east-southeast by winds from the west-northwest above 6-8,000 feet. This provided a very good illustration of vertical wind shear.
Jun. 27, 2009 | Tags: weather radar, winds

Answer: It is possible for wind directions to be stated somewhat ambiguously. However, by convention meteorologists, along with aviation and maritime officials have settled on forecasts and observations that refer to the direction FROM WHICH the wind blows. Hence, a north wind is from the north, a southeasterly wind blows toward the northwest, an observation showing winds "W 15 mph" means a wind blowing from the west at 15 mph, and so on. Thus a balloon carried along by an east wind would move toward the west.
Jun. 12, 2009 | Tags: general meteorology, winds

Answer: A bow echo is the radar presentation of a thunderstorm that arcs or bows outward in the direction of storm movement, with the apex or most forward part of the bow often associated with strong and potentially damaging wind gusts. While most of the wind damage associated with bow echoes tends to arise from straight-line downbursts, tornadoes (usually weak and transient) can and do sometimes occur with these systems, often on the north side of the bow apex. There is a good overview of these systems available at www.crh.noaa.gov/lmk/soo/docu/bowecho.php.
Jun. 9, 2009 | Tags: thunderstorms, tornadoes, winds

Answer: Wind is just the movement of air, and the basic cause of that movement is the sun heating various portions of the earth at differing rates because of varying surface characteristics, elevations, and angles of solar radiation. The variations in temperature lead to horizontal gradients of density and pressure. This sets air in motion from higher pressure areas toward lower pressure, and the moving air can be further organized by effects of the earth's rotation and other factors.
May. 31, 2009 | Tags: coriolis, general meteorology, winds

Answer: That is correct. The person who coined the term derecho for a widespread convectively-induced damaging wind event based the name on the Spanish word for "direct" or "straight ahead" since most of the wind damage in a derecho is usually due to straight-line downburst winds. This is in contrast to a possible origin for the word tornado, which may be based on the Spanish word "tornar," which means "to turn." This background information on the term derecho is included as part of an extensive description of the phenomenon at www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm.
Jun. 1, 2009 | Tags: severe weather, winds