Ask Greg

Recent Questions

Question: It hailed bad at my residence in Franklinton between 820 and 920 pm on April 8th. I cannot find any reports of hail here at those times. Can you support these times with reports? — Brooks Finch

Answer: We checked local storm reports and archives of warnings issued by the Raleigh National Weather Service office that evening. Your part of Franklin County was included in two severe thunderstorm warnings leading up to that time frame, and there were several reports from the Franklinton and Bunn areas that verified large hail was observed. The time of these reports ranged between 8:10 PM and 8:24 PM for the Franklinton area to as late as 8:50 PM around Bunn, with hails sizes ranging as large as Golf Ball size (1.75" diameter) near Franklinton to around 2.25" near Bunn. The times on these reports indicate when the NWS received word about the hail sizes from spotters and do not necessarily mean the hail had ended by then. In addition, a report from Franklinton of Ping Pong ball size hail (1.5") was received at 8:24 PM EDT (0024 UTC), within the window of time that you mention in your question.

You can find all of these reports listed among others using the Storm Prediction Center's Storm Reports Database at www.spc.noaa.gov/climo/reports/150408_rpts.html. Note that the times are given in Universal Time and in 24-hour format. Also, it can help to use your browser "find" function to locate reports from Franklinton amongst the many other hail reports from that day.
May. 28, 2015 | Tags: cool sites, hail, past weather

Question: I wanted to watch your Weather Documentary that aired recently but missed it. Will it be aired again or can I watch it on WRAL's website? — Tracy

Answer: That documentary, called "Exploring Climate Change," is available any time for viewing on demand at our web site. Just go to wral.com/14536286/ and click the blue "play" button on the title image near the center of the page.
May. 27, 2015 | Tags: climate change, wral.com

Question: I have a research project that I would like your help with if you can. I need to get the daily rainfall totals for the last 20 years. I know this is a tremendous amount of data but I really could use your help if this data is readily available. — Dale Homan

Answer: That is a lot of information, but there are some readily available sources for it, some more work than others, and some that would involve a fee. You can find archived observations that include daily rainfall totals through the "Almanac" section of our weather page, by using the "get historical data" function. This takes you to a Weather Underground site that allows you to, for example, check month by month data going back - on each monthly page, there is a table at the bottom that includes daily precipitation.

A potentially faster and more efficient place to look is on a site of the Automated Climate Information System, at xmacis.rcc-acis.org, where you would select the "Single-Station -> Daily data Listing" functions, choose the start and end dates under "options," where you can also choose whether to include any other variables besides the date and precipitation value, and then select the station ("Raleigh Area" or "Raleigh-Durham" will return data from RDU for the time frame you're interested in), and click GO. You can select whether to have the information returned as an HTML table or a comma delimited file.

Finally, if you'd prefer to request the data be collected and prepared by someone else, the State Climate Office of NC has a an automated data request form at nc-climate.ncsu.edu/services/request.php. Note that this method may require a fee.
May. 26, 2015 | Tags: cool sites, past weather, rain

Question: Can a tropical system that has moved inland continue to be supported by feeder bands that are still in the ocean? — Wilson Cheeley

Answer: Feeder bands that remain over warm water often remain rather active after the center of a tropical cyclone has moved over land, and may continue to bring heavy rains and strong winds, especially near the immediate shore. However, even when there are a couple of feeder bands flowing in from offshore, a tropical system that is substantially inland tends to decay rather rapidly, due to the loss of warmth and moisture provided by the sea surface, as well as to friction associated with terrain, buildings, trees and the like. So, it's reasonable to say that feeders do offer some support to the core of the system, but also that this support rarely if ever is enough to offset the changes acting to weaken the system.
May. 25, 2015 | Tags: general meteorology, hurricanes

Question: I like watching the weather on WRAL and you do a great job. One quibble: Could you kindly list the relative humidity along with the dew point? I get that the dew point is a measure of up thousands of feet and that it is more complete, but I live in the first 5'10" of said column and at 60 have a much better take on humidity. — Gordon Clay

Answer: We do include the relative humidity (RH) on our display of current conditions, along with the dew point, but generally show maps with dew point instead of relative humidity, since dew point is more directly tied to how much water is in the air. One point we'd make, though, regarding your question. When we show dew point observed at the airport, or a map of dew points around the area, these are not averaged or integrated over thousands of feet, but represent the dew point value measured at the very same location as the RH. One reason we like following dew point is that if it changes, we know the amount of moisture in the air has changed. If RH changes, it could be that the amount of moisture increased, decreased or stayed the same, depending on what the temperature did during the same time. Looking at a recent Sunday, for example, at 6AM the temperature was 63, the dew point 59 and the the RH was 87%. By 4PM, the temperature was 87, dew point was 64 and the RH was 46%. Moisture in the air actually increased in that first 5' 10" of the atmosphere, but because of the increase in temperature the RH fell considerably.

In general, in very warm or hot weather, humidity is quite low for dew points in the 40s or lower, very tolerable to comfortable for dew points in the 50s, increasingly humid feeling for dew points through the 60s, and steamy to oppressive as dew points climb through the 70s.
May. 24, 2015 | Tags: humidity/dew point, maps & codes

Question: I understand that large cities often record higher temperatures than the surrounding residential areas particularly in the summer; thus heating the surrounding air mass which affects the weather. Does the physicality of the I-95 corridor have any such significant effect on the weather along that corridor? — Roderick Thompson

Answer: While it is the case that sizable cities have a "heat island" effect as you noted, there is no evidence that the impact of a generally 4-6 lane roadway such as I-95 has a detectable effect on weather in its vicinity, at least beyond a very small scale. Any sizable road surface will tend to capture and release heat somewhat differently from surrounding grasslands or forests, but these effects are small in relation to the forces that drive large, synoptic weather systems, and even smaller cells and bands of convection like thunderstorms and squall lines. It's true you'll hear us mention I-95 from time to time in relation to the location of certain weather features, but that is just a matter of it being a conveniently located and widely known geographical marker. It does happen to neatly coincide on some occasions with the influence of some genuinely significant large-scale topographic and geological features, though, due to the fact it more or less parallels the Atlantic coast to the east and the Appalachian mountains to the west.
May. 23, 2015 | Tags: general meteorology

Question: Last year on 5/15/14, an EF1 tornado passed one block away from my home. There was considerable property damage with many trees down. The only notice was Greg Fishel telling me to head for the basement on my phone. Back when I lived in the Midwest, there were sirens in every neighborhood to warn of severe weather. My question is; why don't we have sirens in the Triangle? — Mike Bethelzs

Answer: Compared to many populated areas in the midwest and parts of the plains, central North Carolina has historically had considerably fewer tornadoes, in particular of the more violent variety (there has never been a documented F5 or EF5 tornado in our state, for example) and this probably led to resources being directed to other things besides procuring and maintaining siren systems that would be rather rarely used in many communities. A few other considerations include the difficulty of hearing them inside homes, vehicles and businesses that, through the years, became increasingly buttoned up and resistant to sound from outdoors, the potential for confusion between weather sirens, volunteer fire department sirens and nuclear power plant/civil defense sirens, and the density of the siren network that would be required to overcome rolling terrain and thick tree cover that limits the distance a given siren could cover. In more recent times, the ubiquity of weather information available by way of radio, television, internet, home phone and cell phone has further reduced the call for sirens related to weather. Despite this, debate on the issue continues and a few locations in our state have added sirens in recent years, for use in flash flooding or severe weather events, and several college campuses have done the same.
May. 22, 2015 | Tags: spotters/skywarn, tornadoes

Question: I've seen predictions that this hurricane season will be quieter than normal. Is there any correlation between the frequency of named Atlantic tropical systems in a given year when the 1st named system forms prior to the start of the Atlantic hurricane season (i.e. Ana)? — William, Roanoke Rapids

Answer: It turns out the answer depends on where the early season or pre-season systems initially form into tropical or subtropical cyclones. In general, there is little correlation between early season and overall season activity, so that a quiet start to the season isn't a good predictor of an active season or vice versa. However, it has been observed that if early activity involves storms that develop south of 22 N latitude and east of 77 W longitude, then in that case overall seasonal activity tends to be average or high. This is probably related to years in which that area has especially early warming of sea surface temperatures and relaxation of vertical wind shear.

As for the development of Ana this season, it first developed as a non-tropical low (as a wave on an old decaying cold frontal boundary) and then gradually took on tropical characteristics, being classified subtropical at a latitude of 31.5 north, well outside of the area indicating a higher correlation of early season to later season activity. So, while there's no way to be certain how the overall season will play out, Ana's formation in early May doesn't in itself indicate that the predictions of relatively low Atlantic activity this year are off target.
May. 21, 2015 | Tags: hurricanes, normals

Question: Hello, I am tasked to find annual/monthly global wind averages at ground speed and/or at different altitudes no greater than 15,000 feet AGL. Could you point me in the right direction to obtain this data? — Scott Carter

Answer: This isn not an especially simple or easy task. A couple of resources we thought might get you going include surface wind roses that can be generated for many locations worldwide using a tool created by the Iowa Environmental Mesonet site. You can start at a map of NC with clickable stations that will produce seasonal and monthly wind roses for the selected location, and also note that a drop-down box near the top of the page provides access to maps of other regions. The address for this tool is mesonet.agron.iastate.edu/sites/locate.php?network=NC_ASOS.

In addition, the International Research Institute for Climate & Society, though Columbia University, has a site with access to multiple climatological tools available at iridl.ldeo.columbia.edu/maproom/Global/Climatologies/index.html. There is a zoomable monthly wind climatology tool included in this page, which allows inspection of wind information at multiple levels, ranging from near the surface (1000 mb) to 10 mb. Based on your requirements, you'd be most interested in data from 925 mb (approximately 2500 ft AGL on average), 850 mb (about 5,000 ft), 700 mb (about 10,000 ft) and 500 mb (about 18,000 ft).
May. 20, 2015 | Tags: cool sites, normals, winds

Question: I thought an outflow from some thunderstorms just passed by the house. I looked on iControl, but did not see anything, but it clearly showed up on DualDoppler. Why didn't it show up on the iControl view? — Sandy McNeill

Answer: Outflow boundaries can be visible on radar due to convergence of air along the boundary concentrating dust, insects, birds and other reflectors, in addition to creating a turbulent mixture of contrasting airmasses with differing temperature, humidity and density properties. This is a low-altitude phenomenon that is usually also a rather weak echo. From our own DualDoppler 5000 (both the images/lapses and the live stream), we display a more or less raw reflectivity image with relatively little additional processing or manipulation. On the other hand, iControl is a viewer that consolidates information from the entire network of National Weather Service Doppler radars into a national mosaic. In the process of putting together, it is likely that some processing is being applied that is meant to remove, to the extent possible, spurious echoes, ground returns, and non-precipitation echoes. It is quite possible the automated algorithms that carry out this processing filter out small, weak features having little vertical consistency, and in so doing remove most if not all very shallow, narrow outflow boundary echoes.
May. 19, 2015 | Tags: instruments, weather radar, wral.com

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