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Question: I have a question about humidity. We live on a neighborhood pond here in Cary. Recently our board introduced a fountain which throws water about 25ft in the air. Since the installation of the fountain it seems the humidity is much higher about 20-30% according to my temperature sensor. This morning it's reading 86% at 930am. My question is, is this possible or is it just coincidental with the changing weather conditions? — Phil Moore
Answer: It's certainly possible for a fountain of that sort to increase humidity on a localized basis due to evaporation of some of the water that is lofted into the air and broken into droplets (this raises the available surface area compared to the same pond prior to the fountain being added). However, we'd imagine the effect is fairly small and should be dependent on whether or not the wind is blowing from the fountain toward your home. On the other hand, we have had a lengthy period with humidity levels higher than average this summer, and it may turn out that you're simply noticing the unusually humid conditions at the same time as the fountain happened to be put into place. As context, we checked observations from some nearby airport weather stations in that time frame. At 9 AM that morning, the RDU airport relative humidity was 85% and Chapel Hill reported 82%, and at 9:20am the airport at Sanford still had a relative humidity of 93%! Note that it isn't unusual through much of the year for humidity in the morning hours (especially around sunrise) to be well above 90%. Relative humidity in general peaks around the time of the daily minimum temperature and reaches a low point around mid-afternoon near the time of the warmest temps.
Aug. 27, 2016 | Tags: humidity/dew point
Question: How many days have had 90 degree temps in Raleigh in 2016 so far? Were they all consecutive days in a row? — Paula
Answer: As we write this response, we're about to have a break from 90s for a few days, but through the third weekend of August (ending the 21st) there had been 51 days reaching that level or higher. That puts us at the tenth most days with 90 degrees by that point in the year in records going back to 1887, with 11 years having had more than that and the highest total (68 days) recorded in 2010. They have not all been in a row, but there have been two streaks of 13 consecutive days along the way, and two other runs of 5 straight days. In addition, our humidity levels have been higher than average through much of the summer, adding to the overall level of discomfort.
Aug. 26, 2016 | Tags: heat, past weather, records/extremes
Question: What happened to Roxboro on the NWS weather radio at 162.55 MHz? Roxboro is also missing from your reporting at WRAL. — Jeff Scharver
Answer: The Automated Weather Observation System at the airport there went out of service on August 1st, and then was brought back online on August 15th and seems to be operating and communicating normally since that time. These systems, generally located at smaller airports around the state, are maintained by the NC DOT Aviation Division, while similar stations at a smaller number of larger airports (RDU, CLT, FAY, etc) are maintained by the National Weather Service.
Aug. 25, 2016 | Tags: instruments, weather radio
Question: I enjoyed Mike Moss' chart showing change in temperature by month. But his comments, I think, indicate that when daylight periods begin getting shorter in the summer, that trend escalates in the fall. I thought the change was stable from one day to the next from peak to trough, etc. — Robert
Answer: Due to the combination of the earth's rotational axis tilt and its orbit about the sun, the change in daylight length (sunrise to sunset) is not constant through the year, but follows a sinusoidal pattern where the peak length (summer solstice) and minimum length (winter solstice) occur within periods where the tilt toward or away from the sun slows down before reversing, leaving us with a good number of days in a row where the change in day length from one day to the next is only a few seconds. On the other had, as the tilt of the poles relative to the sun swings back toward the other solstice, the rate of change of day length peaks at the time of the equinoxes. For our latitude (around 35 deg N), the day length changes at that time of year by well over two minutes per day. The change is more extreme at higher latitudes, and of course day length is constant and does not change from day to day at the equator. There is a graph that visualizes this nicely at www.physicalgeography.net/fundamentals/6i.html, where you can see how the change slows near the solstices and is greatest around the equinoxes.
Aug. 24, 2016 | Tags: astronomy, cool sites
Question: What does La Nina mean for this winter in terms of temperature and precipitation? — Snow Miser
Answer: The patterns that are favored on average by the presence of a moderate to strong La Nina (meaning sea surface temperatures in the central and eastern equatorial Pacific that are well below normal for a sustained period) tend to favor winters in the southeastern U.S., including central ad eastern NC, that are warmer and drier than normal. However, it's worth noting that this is an average result over a number of La Nina winters, and that individual events do vary a good bit. In addition, earlier projections for La Nina developing this fall and winter have become somewhat less confident as we've moved through the summer. At this time, most projections favor a weak La Nina, with about a 55-60% chance on develops by mid to late fall, and about a 40-45% chance that the Pacific pattern remains neutral instead of falling into the La Nina or El Nino categories.
Aug. 23, 2016 | Tags: el nino/la nina, winter weather
Question: We've had a stretch of really warm and muggy weather. It has been hot during the day, but the lack of cooling overnight seems a bit abnormal. I think we've had a couple of nights where it only dropped to 77 at the coolest point near daybreak. Are we close to a record for the highest overnight low temperature during this stretch? — Joseph
Answer: It has been sultry at night as you noted, but while we've frequently been near the upper end of the historical range on low temperature readings over the past several weeks, when we look back at June, July and August (so far), the only day that managed a record for warmest low was August 13th, with a low of 77 that tied the previous record on that date from 1999. However, it has been pretty consistently warm in the mornings - as an example, we looked at the period from July 15 through August 15, and found that only one year (2010) has averaged a higher value (and only by .1 degree) for low temperatures during that time.
Aug. 22, 2016 | Tags: past weather, records/extremes
Question: Why do cumulus clouds sometimes look like they're sitting on a flat surface? Is it a temperature boundary? — Michael
Answer: What you've noticed is the result of something called the convective condensation level, or CCL. Fair weather cumulus clouds form due to rising air that is heated by contact with the ground. As the parcels of heated air rise they encounter lower pressure, expand and cool down until they reach saturation and cloud droplets form. The height where this occurs depends on the temperature and dew point near the surface, and these are typically rather uniform across a local area, so that the bases of the clouds, which form at the height of the convective condensation level mentioned above, are often rather flat and uniform from cloud to cloud within your field of vision. You can make a rough estimate of what the height of the cloud base should be by taking the difference between the temperature and dew point (in degrees F) and multiplying by 200.
Essentially, the rising bubbles of heated air become cool enough to form clouds just as the air passes upward through that "flat surface" you imagined. Above that level, non-uniform mixing and entrainment of drier air from above and to the sides of the cloud lead to evaporation that yields the puffy, lumpy appearance of the upper portion of the clouds.
Aug. 21, 2016 | Tags: clouds
Question: What was the weather like for May 8th, 1997? What was the temperature high and low, and if it rained how much did we get? Need to know what was the weather like for my birth date. — Scott
Answer: You can always check that kind of data using the "Almanac" link on our main weather page and then selecting a date in the "Get Historical Data" section.
Taking a look there, we found that day to be partly to mostly cloudy, with a trace of rain late in the evening. The low temperature in the morning was 45 degrees, followed by a warm afternoon that reached 80. It was a bit breezy, with south to southwest winds that gusted as high as 24 mph at times in the afternoon.
If you're also interested in seeing daily weather maps that applied for the day you were born, or other dates of interest, they are available from NOAA at www.lib.noaa.gov/collections/imgdocmaps/daily_weather_maps.html.
Aug. 20, 2016 | Tags: cool sites, maps & codes, past weather, wral.com
Question: I have severe allergies year round. Where can I find what tree or bush has bloomed out on a certain date to track my allergies by them? — Diane Reed
Answer: We can't think of an online source with specific, wide-ranging reports of local species in bloom. You might be able to contact your nearest Agricultural Extension Office for good information, and more generally you can get some rundowns on the typical timing of tree, grass and weed pollens from sites like www.hickoryallergy.com/what-are-the-pollen-seasons-in-north-carolina/. The National Arboretum in DC has a site showing a fairly detailed rundown of what bloloms when there, and based on climate differences we might run a week or two ahead of them here. You can see their list at www.usna.usda.gov/Education/blooming.html.
In addition, we do make links to some potentially pertinent information available here on our web site. Just click on the "resources" link near the top of the main weather page, and scroll down to select the second page of the resources list. There you'll find links labeled "Daily Pollen Count Forecasts," which takes you to a map where you can click your way to a 5-day forecast of allergen levels and types for a number of cities across NC, and "NC Division of Air Quality Pollen Count," where you can see a graph of recent pollen counts taken in Raleigh. Near the top of that graph is also a link to see the latest available tabular report, which includes a listing of what the top observed pollen species are, and also includes a link to a calendar where you can retrieve previous written reports for any date during the season.
Aug. 19, 2016 | Tags: pollen, weather & health
Question: I am the S-E U.S. ride planner for Rotary Club motorcycle riders. After many requests to ride our Outer Banks I am planning a fall ride from Nags Head inland to Cedar Island. Ferry to Ocracoke Island and ride up to Nags Head. What can I expect, weather-wise, for the first weekend of October? Can you suggest a more favorable weekend? — Carlton Pernell
Answer: This far in advance, of course, we can't address any specific weather systems that might affect the area at that time, but we can give you a sense of the climatology for the region near the beginning of October (this changes fairly slowly, so a couple weeks either side isn't far off, making it hard to suggest a more favorable weekend, apart from potentially having a "rain date" in mind a week or two later in October, if a short-notice postponement is practical for your group). At the beginning of October, the normal low temperature is around 62 degrees and the normal high around 76, through temperatures have ranges as warm as around 90 and as cool as the upper 40s in that time frame. On a given date in early October, measurable rain (.01" or more) occurs about once out of every three years, while a tenth of an inch or more occurs about once in four years. The predominant wind direction that time of year is from the northeast, with a mean winds speed of around 4 mph for the inland part of your route and almost 10 mph along the Outer Banks (though winds in the 10-20 mph range are not uncommon there). Good luck with your planning, and with the ride!
Aug. 18, 2016 | Tags: normals
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Published: 2007-10-09 14:40:00
Updated: 2014-06-24 16:06:51