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Recent Questions

Question: Why is Elizabeth doing the evening weather? Where are you and Mike? — Judy

Answer: We got a number of questions about that, making reference to "musical meteorologists" and such! The schedule at the time had to accommodate myself and Nate attending an out of state workshop for the first three days of the week, while Mike Maze was away on vacation. So, we had a few days there with Mike Moss and Aimee covering mornings, while Elizabeth shifted to evenings.
Jan. 22, 2017 | Tags: wral.com

Question: In watching the coverage of the upcoming potential ice storm in middle of the country, I am reminded of maybe the worst case I have heard of: the massive ice storm that affected the Northeast U.S. and Quebec area a couple of decades ago. Do you know of a site that discusses this storm. As bad as an outage is around here, I can't imagine being without power for weeks with the much colder temps of the more Northern areas. — Dave Crotts

Answer: You're thinking of one of the worst cases of freezing rain and glaze icing on record, when freezing rain occurred for as many as six consecutive days over parts of the affected area and clear ice accumulations reached as high as one to nearly four inches. This brought down thousands of power line towers and poles and did tremendous damage otherwise, in addition to leading to at least 45 deaths in Canada and the northeastern U.S. The event has come to be known as the Great Ice Storm of 1998, and you can find quite a few articles and video reports about it with a web search. On site you may find interesting is a summary paper covering the event that is located on a server at McGill University, titled simply "Ice Storm '98." You can find it at www.meteo.mcgill.ca/extreme/Research_Paper_No_1.pdf. There was also a Discovery Channel episode of "Perfect Disaster" that addressed this storm, with a combination of dramatized re-enactments and news footage from the event.
Jan. 21, 2017 | Tags: past weather, winter weather

Question: 68 today, 47 tomorrow. Tonight I've heard thunder but the radar is totally clear. A dry thunder I suppose. Is that common? — Brian Lowery

Answer: While dry thunderstorms are a real phenomena, involving elevated storms that occur with a deep layer of low humidity below the cloud base, such that precipitation generated in the storm cloud evaporates before it reaches the surface, we suspect something not weather-related was behind the sound you heard. Your message was written on Friday night, Jan 13, 2017, and as you noted through the day and much of the evening there were no echoes nearby on radar (late in the evening a few spotty sprinkles and light showers developed west of the Triangle and drifted east, but these were around or after the time of your e-mail). We couldn't find any other evidence of storms in the region that day or night, so it seems likely you may have heard noise from a jet aircraft, a dump truck, transformer failing or some other source of noise that could sound like thunder under the right conditions. True "dry thunderstorms" are very rare in our part of the country, but somewhat more common in western parts of the United States. Of course, around here it isn't unusual to hear thunder and receive no rainfall at a given location, but that is generally associated with storm cells passing within ten miles or so (a typical distance beyond which thunder is usually not audible), with those storms producing rainfall that reaches the ground elsewhere. Incidentally, the high temperature on the day you wrote made it all the way to 76 degrees, while the afternoon high the following day ended up being 48.
Jan. 20, 2017 | Tags: general meteorology, thunderstorms

Question: Has this winter been more cloudy than usual? It seems like we've barely had any sunny/mostly sunny days since before Christmas. The current 7-day forecast seems to indicate it will continue. I want the sun! — Samantha

Answer: Records from RDU seem to bear that out. We took a look at sunrise to sunset cloud cover for December and the first 15 days of January, and found that there were 8 days through that period that were classed as clear to mostly sunny (0-3 tenths cloud cover), compared to a "normal" value of 14.5, so bright days have been a little limited compared to usual over that time frame. Longer range models are projecting more frequent sunshine over the last week or so of January, but that is far enough in the future that we can't place a lot of confidence in that just yet.
Jan. 19, 2017 | Tags: clouds, normals, past weather

Question: Where can I find today's actual recorded low temperature on the WRAL Weather site? Or do I need to go to another site? Best wishes. — Thomas Moorefield

Answer: The simplest way though our site to find the observed low for the day so far is to go to the "Almanac" page and click the "Send" button under "Get Historical Data." That will default to a summary of the current day's observations from the Raleigh-Durham airport, and will include a minimum temperature that would typically be the lowest observed around daybreak. You can also see the temperature trend in a graph by scrolling down a bit. If you're interested in a different location, there is a "search for another location" box along the right side of the summary window.
Jan. 18, 2017 | Tags: past weather, wral.com

Question: Why is sleet mistaken for snow on the Dual Doppler? What causes this? — Tommy

Answer: On both local and regional radar displays showing winter precipitation types, it is not the radar itself that determines precipitation type. Instead, the radar measures the intensity of the radar return. Software is then used to color code the returns according to whether the precipitation is snow (usually a blue shade), rain (shades of green, yellow and red) or a mix (usually shades of purple or pink, often indicating sleet and/or freezing rain). The software depends on a combination of inputs to assign the most likely precipitation type to each radar echo location, with surface observations of temperature and precipitation type playing a role, in addition to very short-range computer model analyses and forecasts that provide information on the vertical structure of temperature, pressure and humidity through the atmosphere. These algorithms do a generally good job at displaying the correct precipitation type, but are not perfect. In a recent winter storm, many models indicated that air a few hundred to a few thousand feet above the ground warm enough to change snow to sleet and freezing rain would remain a little farther southeast than it really was. This led to a band of radar echoes coded as snow, when sleet was actually the predominant precipitation type reaching the ground along that band. Note that these ways of color-coding the radar returns do not use the dual-polarization capabilities of our radar or that of the local NWS system. These "polarimetric" systems can do a good job of determining the most likely precipitation type based on direct measurements by the radar itself - however, they indicate the type of precipitation within the radar beam, which increases in height above the ground as you move out in distance from the radar location. Since the type of precipitation in the radar beam can change between falling below the beam height and reaching the ground in many wintry precipitation scenarios, using the model and surface observation-based software to color code the display often better reflects what is occurring at the surface.
Jan. 17, 2017 | Tags: snow, weather radar, winter weather

Question: What's the average temperature for NC in January? — Julie Davis

Answer: The overall "normal" January temperature for our state (defined as the 30-year average for the period 1981-2010) is 39.9 degrees F (with the normal high being 50.3 and the normal low of 29.4). Of course, a statewide average masks a lot of variation across different parts of the state - for example, the normal temperature for the northern mountains region is 34.9, while for the southern coastal plain it is 43.3 degrees. These numbers were calculated using tools available online at the National Centers for Environmental Information, using their "Climate at a Glance" feature.
Jan. 16, 2017 | Tags: cool sites, normals

Question: What is the difference between snow, sleet, and freezing rain, and which is the most dangerous? — Daniel

Answer: Snow falls as a lightweight crystal or a collection of crystals that are stuck together, while sleet reaches the ground in the form of pellets of ice (more or less like frozen rain droplets) and freezing rain reaches the ground as a cold liquid droplet that then spreads out and freezes on surfaces, covering them in a glaze of clear ice. The most basic factor controlling the kind of precipitation that reaches the ground is the way temperature varies as you move from high in the atmosphere down toward the ground. If there is enough moisture in a layer of the atmosphere with temperatures in the right range to form snow crystals, which is quite common through the colder half of the year, then those snow crystals (and when some clump together, snowflakes) can fall all the way to the surface if the air is near or below freezing all the way down, or if any layers that are above freezing are rather shallow so that the flakes do not have time to melt. If there is a layer along the way that is warm enough to melt the flakes (referred to as a melting layer, or sometimes "warm nose"), they become rain drops. If the air is mostly above freezing the rest of the way to the surface, they will reach the ground as rain. If they fall through another layer of air that is below freezing, however, and that layer is thick enough, they will freeze into clear ice pellets before reaching the ground. Finally, if they fall through only a shallow layer at ground level that is below or near freezing, they may arrive at the ground as liquid droplets that can spread out and then freeze when they encounter freezing or sub-freezing objects at the surface. This is the condition for freezing rain, which can lead to the formation of a clear glaze of ice. All of these wintry forms of precipitation can be dangerous in terms of creating hazardous driving conditions, or in the case of very heavy precipitation, overloading structures like rooftops and causing damage. However, in excessive amounts, freezing rain can be about the most destructive, since thick layers of clear ice are very heavy and can cause numerous branches to break and trees to fall, and often bring down power transmission lines and supporting structures as well, leading to extended power outages that are especially hard to deal with in cold weather.
Jan. 15, 2017 | Tags: general meteorology, preparedness, winter weather

Question: Why was there a winter storm watch on Thursday (1-5-17) even though you guys said it wouldn't snow until Friday night (1-6-17)? I thought watches meant there is a chance of it happening right now; please explain. — Panther

Answer: The lead time for different kinds of watches from the National weather Service varies somewhat with the type of event involved. A severe thunderstorm watch, for example, is usually issued shortly before or right at the beginning of the period in which conditions are favorable for severe storms to develop, in line with your perception of the timing of watches. However, for winter storms that are expected to affect an area, they strive to provide more advance notice that confidence in the occurrence of impactful wintry precipitation has reached a level that justifies highlighting the expected conditions in a watch. Depending on how confident the forecast has become, a winter storm watch may be issued as little as 18 hours before wintry precipitation sets in, or as much as 48 hours. As the storm gets closer and confidence in likely impacts becomes even higher, the watch may be upgraded to a warning.
Jan. 14, 2017 | Tags: maps & codes, preparedness, winter weather

Question: Is it true that each snow flake has a different pattern from any another one? If true, this is mind boggling as billions upon billions of snowflakes fall each year! Does each raindrop have the same basic shape and does each pellet of ice look similar? What is it about snow that reveals this miracle of creation? — Ed Thomas

Answer: On some level, it is impossible to absolutely guarantee that no two snow crystals have ever been at least very nearly the same, since trillions have formed and there is no way to observe more than a tiny fraction of them in detail. However, the manner in which snow crystals grow varies considerably depending on both temperature and relative humidity and since any growing group of snow crystals may move through a variety of surroundings during the time that the crystal grows, a huge variety of combinations become possible, with even slight variations over short distances leading to slightly different structures from one crystal to the next. In many cases, the appearance would be very similar at a glance, but in great detail small differences would become apparent. Small raindrops are almost spherical drops of water, so as long as they are about the same size, many would only be distinguishable on a molecular level. Larger raindrops can oscillate through a variety of shapes due to winds and to drag forces associated with falling through the air, but on average is something along the lines of a hamburger bun, rounded on top and flattened on the bottom. Sleet pellets would be somewhat similar, with small ones tending to be spherical and larger ones less so, but once frozen of course their shapes would not oscillate but remain more or less the same as when the water droplet froze (neglecting any change in shape due to sublimation). In order to keep this answer from getting much longer, we'll refer you to an interesting rumination on the question of uniqueness of snow crystals (incidentally, most snow "flakes" we see falling are collections of multiple snow crystals stuck together) that is available as part of a really nice web site on the subject of snow crystals. You can find the essay and links to all of the site's content at www.its.caltech.edu/~atomic/snowcrystals/alike/alike.htm.
Jan. 13, 2017 | Tags: cool sites, snow

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