WRAL.com: Raleigh, Durham, Fayetteville

The most direct way to find your question is to search for the name you used when you submitted it (first name, last name or both). If you did not include a name, then you can search using keywords from your question. Of course, since many weather-related terms are common to a lot of the questions we receive, this may turn up a number of others in addition to your own.

Thanks again for sending your questions to Ask Greg!

Answer: "Isolated" means that only about 5-20% of the forecast area is expected to be covered by storm cells, clusters or lines at any particular time, while the term "scattered" implies coverage of around 30-50%. "Widely Scattered" is occasionally used for situations that fall between those two. The probability of measurable precipitation at a given point in the forecast area corresponds roughly to the coverage figures above, when convective showers and storms are expected.
Jul. 18, 2009 | Tags: rain, thunderstorms

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: The charge separation required to generate lightning discharges in typical thunderstorms depends in part on precipitation-sized particles of water and/or ice, so that rain is almost always being produced. However, lightning can strike outside of the rainfall "footprint" in locations that are dry at the surface, or in some cases precipitation can evaporate before reaching the ground, leaving the surface dry where lightning occurs. This last process is one that initiates many wildfires in the western United States. In addition, "dry" lightning is sometimes generated in the ash clouds produced by erupting volcanoes.
Jul. 8, 2009 | Tags: lightning, rain, thunderstorms

Answer: Heat lightning is just an informal term that describes the appearance of regular lightning seen from a large distance, where thunder often can not be heard and the individual lightning channel can't be discerned, only a broad flickering light instead. It means that there is an active storm in the area where the lightning can be seen, but it doesn't necessarily signal a coming storm in your location. If the "heat lightning" gradually becomes brighter and you start to hear thunder and see individual strikes, then a cell may indeed be approaching.
Jun. 22, 2009 | Tags: lightning, thunderstorms

Answer: The reference was to a cloud type called altocumulus castellanus. Altocumulus is a mid-level cloud usually made up of puffy yet somewhat flattened individual elements with bases around 8-15,000 feet above the ground. The castellanus designation tells us that some of the elements have more of a turret-like appearance indicative of vertical development driven by a sharp decrease of temperature with height. This can be a clue that mid-levels of the atmosphere are unstable and may be favorable for strong updrafts and rapid thunderstorm development.
Jun. 14, 2009 | Tags: clouds, thunderstorms

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: Thunderstorms that form in an environment with very light ambient winds through most levels of the atmosphere may produce downdrafts that reach the ground moving almost straight toward the earth. In this case the winds at ground level may fan out in almost any direction from the base of the storm. When a storm exists in an environment with stronger surrounding winds, the downdrafts may carry a strong component of the direction of those winds, often more or less along the direction of storm movement.
Jun. 2, 2009 | Tags: thunderstorms, winds

Answer: Derechos, consisting of numerous damaging downburst winds over a large area that result from a fast-moving band of showers and thunderstorms, are most common along an arc from Minnesota to south of the Great Lakes and into Pennsylvania, and from northeast Texas into the middle Mississippi Valley. They do occur in our state as well, more often over the western half of the state than in the east.
May. 12, 2009 | Tags: thunderstorms, winds

Answer: That term (pronounced deh-RAY-cho) was coined to describe a widespread, long-lived series of severe straight line downburst winds, produced by a fast-moving band of convective showers and thunderstorms. Criteria for storms to be classified as derechos vary a bit, but generally the area of high wind impacts must cover at least 240 miles in length with numerous wind gusts exceeding 58 mph.
May. 21, 2009 | Tags: thunderstorms, winds

Answer: A supercell is a particular type of thunderstorm characterized by a long lifetime and an organized, rotating updraft area called a mesocyclone. A severe thunderstorm is defined as one that produces wind gusts to 58 mph or higher, hail three-quarters of an inch in diameter or greater, or a tornado. Many severe storms are supercells, but other kinds of thunderstorms can become severe as well.
Jun. 3, 2009 | Tags: hail, severe weather, thunderstorms, tornadoes, winds