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Question: What is the difference between humidity percent and dew point? It is extremely hot in NC right now. — Sarah Gonowon
Answer: We have certainly had some hot weather periods of late, including a couple of days reaching triple digits in some locations. Some of those days have been quite humid as well, and relative humidity (expressed in percent) and dew point (expressed in degrees) are two ways of quantifying the amount of moisture in the air around us and how that amount of moisture compares to an amount that would result in the air being saturated. The dew point changes in a way that directly reflects how much water vapor is in the air, and on hot days there's a pretty strong relationship of how humid and uncomfortable it feels to the dew point range, with 50s and below not really feeling humid, 60s feeling somewhat humid and 70s feeling very steamy and sticky. Relative humidity, in percent, is a ratio of the existing amount of water vapor to the amount that would result in saturation (beyond which any addition of moisture or a reduction in temperature would result in condensation that would form dew on surfaces, or fog or cloud droplets in the air. The relative humidity (RH) depends on both the air temperature and the amount of water vapor present. As an example, consider an afternoon with a temperature around 95 degrees. If the dew point was a fairly low and semi-comfortable 55 degrees, the RH would be 26%, a somewhat humid dew point of 65 degrees would equate to RH of 37% and a really steamy dew point of 75 would mean the RH would be 52%.
Jul. 31, 2017 | Tags: humidity/dew point, maps & codes
Question: I just saw your post about the 3.6 degree F drop. I have sometimes wondered if the Celsius scale is a bit too coarse. It might have been better to have the boiling point of water be 1000 degrees instead of 100. Then, almost any temperature precision of interest could be expressed with whole numbers. — Ronald W Garrison
Answer: Interesting outlook, and you have a point that has certainly been noticed by others, including many who prefer the Fahrenheit scale for the fact that whole degrees on that scale are smaller than whole degrees in Celsius, allowing for a bit more precision in describing temperatures and temperature changes without resorting to the use of decimals. A scale that goes from 0 at freezing to 1000 at boiling would certainly add a much greater level of whole number precision, but we're probably pretty much committed at this point to the three primary temperature scales of Celsius, Kelvin (which uses the same units as Celsius, but with a different zero point) and Fahrenheit. A fourth scale, Rankine, is still used in some engineering applications. Like Kelvin, it has a zero point of "absolute zero," but uses degrees that are the same size as Fahrenheit.
Jul. 30, 2017 | Tags: instruments, maps & codes
Question: What month are severe storms most common in? Or really does it depend if it occurs with the right amounts of ingredients in the atmosphere? — Justin
Answer: As you mentioned, it does depend on the combination of atmospheric ingredients and weather features that are in place on a given day, and in central NC we can have severe weather at any time of the year. However, the likelihood of severe weather (meaning storms that produce wind gusts of 58 mph or higher, hail of 1 inch in diameter or greater, or tornadoes) does tend to be greatest during the period from early spring to mid-summer. A severe weather climatology published by the Raleigh National Weather Service office shows that the peak month for tornadoes and large hail in our part of the state is May, while the top month for damaging wind gusts is June.
Jul. 29, 2017 | Tags: hail, normals, severe weather, tornadoes, winds
Question: Can you tell me the closest place to Raleigh where I can experience totality during the eclipse for at least 2 minutes? — Cleo
Answer: From Raleigh, the closest location that will meet your criteria is about 165 miles to the south-southwest, along a line from just south of Sumter, SC to Kingstree, SC. There is a great interactive Google map on a NASA site that shows you the location of the the path of totality, and when you click on any point on the map it will place a marker and show you the time of the eclipse at that location, along with the duration of totality. There is a "clear markers" button below the map in case you check a number of locations and want to reduce the clutter. The map is located at eclipse2017.nasa.gov/sites/default/files/interactive_map/index.html.
Jul. 28, 2017 | Tags: astronomy, cool sites
Question: Holly Springs seems to always miss out on the rain. When watching the radar it appears as if Fuquay-Varina, Apex, and Cary will get a substantial amount of rain while it just goes right around us. Is there something with our topography that causes this or is this just in my head? — Brian
Answer: We answered a very similar question just yesterday from someone in Apex, who feels all the storms miss that town and go around north or south (which would put some of them over Holly Springs!). As you may have seen in that answer, we suspect this is mostly an issue of perception, due to the combination of the hit or miss nature of warm-season convective rainfall on many days (a lot of people have dry weather on those days, but see or hear storms in the distance), and the tendency for radar to make it appear rain is covering a little more area than it really is. Also, with our local radars located over southeastern Wake County, it isn't unusual for cells that approach from the west to appear to shrink/split as they draw closer because they are moving closer to the radar location. Due to the increasing width of the beam with distance, the radar picks up increasing detail as the storms get closer and may show gaps in coverage that are "smeared over" when the cells are more distant. Also, the height of radar beams increases with distance, and there are times when you see considerable coverage at a distance from precipitation aloft, some of which doesn't make it to the surface. This effect decreases as the cells draw closer to the radar, since the beam is then sampling the rainfall closer and closer to the surface.
Jul. 27, 2017 | Tags: rain, thunderstorms, weather radar
Question: I live in Apex and would like to know why the majority of rain storms pass either to the north or to the south of Apex. In the last week alone I have had 0 drops of rain fall in my yard. But I can look out my windows and see lighting and dark grey storm clouds both to the north and south of me. This happens all the time. Unless there is a major storm the rain just seems to go around us. — Dave Nordaby
Answer: We suspect you're having a common perception that most of us do through the warmer half of the year, when convective showers and storms tend to occur in cells, clusters and small line segments that on a lot of days may only affect 10 or 20% of the area, so that by definition many more people see storms in the distance, hear thunder, or see them peppered about on radar displays (which tend to exaggerate a little how much surface area is actually receiving rain) than actually get rained on. This leads to the feeling that storms are almost always missing to the east, north, etc. However, we receive questions or comments to that effect from pretty much every corner of our viewing area, and when we check combined gauge and radar-based precipitation totals over the course of several weeks or months (along with long-term averages of those readings), we do not see notable small scale variations in the "normal" amounts, indicating that over time the coverage evens out. Through the course of late spring to early fall, almost all of us in the region can say that the majority of showers and storms pass us by, while a minority do cross over our locations and provide the sporadic rains (often including an occasional heavy downpour) that make up our overall precipitation during that span of time.
Jul. 26, 2017 | Tags: folklore, rain, thunderstorms, weather radar
Question: The new High Resolution Weather Sat image detail is great. Is it possible to place those images on your WRAL TV Weather web site too? If not, is there a web link that you can post to allow us to view them? — Rich Ben
Answer: We will probably have some of those GOES-16 images and loops on our web site eventually, however that may not be the case until the satellite is fully operational and moved to its final location as GOES-EAST, most likely sometime later in the fall. In the meantime, there are a couple of sites where you can check out the imagery on a provisional basis. You can see some multimedia examples of the range of capabilities of the new satellite at www.goes-r.gov/multimedia/goes-16DataAndImagery.html, and also note that near the top of the page there area some links to real-time products from a number of NOAA's academic partners. One that isn't listed there that you might also like to check out, is available at weather.cod.edu/satrad/exper/.
Jul. 25, 2017 | Tags: cool sites, instruments
Question: What happened over Bath, NC today that caused rain clouds to disperse in a growing ring around 6:45 am this morning (07/19/2017)? I saw it on weather radar. — Phil Parry
Answer: Those were not rain, or clouds, but instead a concentration of tens of thousands of purple martins that roost at a site on the far side of the Pamlico River and a little ways downstream from Bath, actually close to the PCS Phosphate plant near Aurora, NC. The expansion you are seeing begins just before sunrise most days, and shows the martins as they swarm outward and upward to go out in search of food to start the day. This kind of image on radar is known as a "roost ring." It's something we covered in a bit more detail in a blog post from a number of years back. See www.wral.com/weather/blogpost/1631522/ for more, and note that the post references an image "above." To see that image, you'll actually scroll down and click on a thumbnail a little below the text toward the right side.
Jul. 24, 2017 | Tags: cool sites, weather radar, wral.com
Question: We had a pretty severe thunderstorm in Archer Lodge yesterday afternoon and as I was watching the dual Doppler, I noticed out flow boundaries from two different cells that seemed to converge over our area. Would that lead to a more intense storm? — Doyle McGlone
Answer: There may be a small effect on intensity of storms that form when outflow boundaries converge because that process might deliver a more intense initial lifting of air to start the process, but we're not aware that there's a strong correlation there. Converging boundaries may increase the odds of new storm formation at that location a bit more than a single boundary passing through (which can also set off new development), but the intensity of the resulting storm is likely more related to the overall structure of the atmosphere in terms of the vertical profiles of temperature and humidity prior to the arrival of the boundary, along with how larger scale winds vary in speed and direction with height. When those variables all favor an intense storm, the manner in which it is triggered plays a fairly small role by comparison.
Jul. 23, 2017 | Tags: general meteorology, thunderstorms, weather radar
Question: I have a unusual question that I have searched the Internet and cannot find an answer. About a month ago in Rocky Mount we had tornado warnings it was very windy and the rain was hard and I thought my roof is going to fly off. Anyway I did have some damage to my roof and need to know the date in which that happened. — Tammy Weatherly
Answer: Based on the date you sent your question and the time frame you mentioned, we're pretty sure you're referring to a tornado warning that was issued at 5:39 PM on June 5, 2017. The warning was cancelled at 5:52 PM. While no tornado was observed or confirmed with the storm, there were strong gusts and heavy rain, as you mentioned, and there were storm reports in the warning area for flash flooding and also for a tree blown down onto a mobile home at Brook Valley Mobile Home park.
Jul. 22, 2017 | Tags: past weather, severe weather
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Published: 2007-10-09 14:40:00
Updated: 2014-06-24 16:06:51
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