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Question: I get that the dew point is a measure of the moisture in the air up to (what?) 25,000 ft or so. Couldn't it be argued though that the relative humidity is more relevant to the first seven feet or so of altitude in which we live? — Gordon Clay
Answer: Dew point is directly proportional to the amount of water vapor in any parcel of air, whether at the surface, 25,000 feet or 40,000 feet. Relative humidity is a different way to describe moisture content, but is not a straightforward measurement since it depends on both the amount of water vapor present and also the temperature. Which quantity is more relevant depends on what it is being used for, so you could indeed make an argument about which is more useful at any given altitude. Near the surface, relative humidity would be more relevant if you're trying to assess the potential for fog to form, for example, but if you're interested in a quick assessment of how muggy the air might feel or if you're tracking the movement of moist and dry air, dew point is typically the more relevant variable. Likewise, at higher altitudes, profiles of dew point are great for monitoring the movement of moist and dry airmasses and very helpful in assessing stability and the related potential for convection and possible severe weather. On the other hand, relative humidity can play a larger role in assessing whether clouds will form in a given layer of air, or how likely precipitation development might be in that layer. We make extensive use of both variables, depending on the problem at hand.
Aug. 17, 2014 | Tags: general meteorology, humidity/dew point
Question: How does humidity affect how we feel cold temperatures? My brother clams that it exacerbates all temperatures (i.e., makes hot temperatures feel hotter - as in heat index -but also makes cold temperatures feel colder). I disagree with him but don't know for sure. — Kathy Thomas
Answer: Humidity levels have a well-documented impact on perceived temperature during hot weather because increased humidity inhibits the cooling effect of evaporating sweat. At cold temperatures, there isn't much direct physical reason that variations in humidity alone would make a big difference in perceived temperature, but for a variety of indirect reasons, many people do seem to feel colder when humidity is greater. The most likely reason for this is that in very humid cold conditions clothing may absorb water vapor and become damp, thus reducing the insulating properties of the clothes and allowing a more rapid escape of heat than would be the case if the clothes remained dry. In addition, cold humid days are more likely to feature extensive cloud cover than cold days with low humidity, which would remove some of the radiant warming provided by the sun.
Aug. 16, 2014 | Tags: apparent temperature, cold
Question: Will a lightning strike on the surface effect a scuba diver at a given depth? — Jeremy
Answer: Concrete numbers are hard to come by on this, but the general idea is that lightning strikes on water tend to direct most of their energy across the surface, while current down into the water is rapidly dissipated. NOAA's lightning safety web site doesn't provide numbers, but does note that scuba divers well below the surface are generally safe from strikes. Of course, the bigger issue then becomes the time when the diver is forced to surface and is in a much more dangerous location while swimming back to a boat or awaiting pick-up, or is in the process of climbing back aboard. Another consideration is whether the dive boat is a rather large one with a protected interior cabin for shelter, or is a small completely open vessel, in which case the diver might be more at risk while in the boat than during a dive.
Aug. 15, 2014 | Tags: lightning, weather & health
Question: I remember 20 years ago or so, there was a waterspout in the Neuse river near Minnesott point. People reported the river draining out hundreds of feet when it happened. If I'm not mistaken, the river is 3 miles wide at that point. Is it really possible for a waterspout to pull that much water out of the river? — Dan
Answer: We couldn't find any written references on that event to get a specific date that would allow checking some related weather observations, but the general idea is that for a river like the Neuse at that location, a waterspout on its own would not be likely to cause such an effect on water levels over a widespread area. Waterspouts mainly have winds that blow across the surface of the water rather than lifting significant amounts of moisture up from the surface. It does seem possible that if the waterspout was stationary or very slow moving, and was aligned properly with the shore, that winds blowing offshore could push water away sufficiently that over a localized area it could uncover a sizable width of normally covered gently sloping river bottom, to produce the effect that was described. Much larger intense circulations such as tropical cyclones or nor'easters are occasionally known to have their strong winds align along river basins, sweeping large amounts of water seaward and exposing wide swaths of the river bottom that are normally covered (the reverse is also true, which can lead to serious flooding as water is pushed into and up the river). Even less intense low pressure areas and high pressure circulations, when their more gentle winds are persistent from a direction that largely blows into or out of a river basin, can cause water levels to run above or below the normal elevations by way of this "sweeping" action.
Aug. 14, 2014 | Tags: flooding, hurricanes, past weather, winds
Question: Around 3:45 PM on July 30th we had an intense storm where rain was horizontal and wind blowing from all directions at once. Trees twisted and down, our cypress uprooted & on neighbor's garage, Howard & North Creek Run in Raleigh. What happened here? No warnings. — Barbara Barkley
Answer: Based on radar archives for the date, one cell out of an isolated cluster that formed just west of your location very rapidly intensified and then weakened as it moved east out of Durham County and then east-southeast across your area. It appears to have produced a sudden downdraft/microburst at that time, without showing strong radar indications of severe weather beforehand. Surprisingly, based on your description, there were no reports of severe weather (called "local storm reports," or LSRs) logged by the NWS that day, but it sounds likely that over a short time and a small area, it may have indeed produced severe winds (gusts that reach or exceed 58 mph). These type systems, often referred to as "pulse" storms, are very difficult to warn for because in many cases they are small and isolated and may occur in environments that aren't favorable overall for severe storms. By the time it is apparent that a storm of this sort is pulsing to a severe level, any warning the NWS would issue for it would be too late for any preparations and the storm would not remain severe long enough for the warning to have any impact farther along its path. We suspect that it why no warning was issued for this storm.
Aug. 13, 2014 | Tags: past weather, severe weather, thunderstorms
Question: What is the likelihood of a Sharknado ever coming to Raleigh? How would I prepare my family to survive such a meteorological disaster? — Alex DiLalla
Answer: You may have thought we'd just ignore this question, but... we'll bite! We expect that likelihood is low enough that the only place a Sharknado will occur in Raleigh is in pictures on various sorts of screens. If you really want to protect your family just the same, you might consider investing in some of that chain-mail armored clothing, as seen, for example, at neptunic.com/products/sharksuits.
Aug. 12, 2014 | Tags: folklore
Question: I have noticed that it is unseasonably cold this weekend. What is the cause of it? — Austin
Answer: You were writing about the weekend of August 2nd and 3rd, and probably thinking of Friday the 1st as well. That entire period featured an upper level trough over the eastern United States that brought the jet stream a good deal farther south than it usually resides this time of year. This had the dual effect of allowing relatively cool air of Canadian origin to funnel south into the area, and also kept a frontal boundary to our southeast active in producing periods of thick cloud cover and rainfall, both of which helped hold temperatures well below the seasonal normal at that time of highs around 90. On Friday and Saturday, highs held in the 70s, including a high of 70 degrees at RDU on Saturday August 2nd that was a new record for the date, breaking the old "coolest high" record of 71 set back in 1916. Our coolest high ever in August, though, was in the upper 50s!
Aug. 11, 2014 | Tags: fronts & airmasses, general meteorology, past weather, records/extremes
Question: How or where can you go to get local rain fall totals? Last night on WRAL at the beginning of the forecast it showed 2.43 inches of rain for us in Wayne Co and then when the weather segment started it was under 1 inch. I have been all over the internet and cannot find a good site that shows daily rainfall totals, please advise. — Debbie
Answer: On place to look is in the archive section of Weather Underground, which we link to in the "archive" section of our web site. A quick way to check there is to use the "monthly" view of past weather data, which includes a table near the bottom of the page that shows daily highs, lows and precipitation totals, among other things. In your case, you would want to check the readings from KGSB (Seymour Johnson AFB and KGWW (Goldsboro-Wayne County airport). The direct link to get to those observations is www.wunderground.com/history/airport/KGSB/2014/8/3/MonthlyHistory.html?req_city=NA&req_state=NA&req_statename=NA. When you want to chenge to another location, use the "airport" box along the right hand sidfe of the page, where you could enter KGWW, KRDU, etc to switch locations. You can also go forward and backward by month, week or day.
Since observations at airports may or may not well represent conditions across an entire county or region, you may also like to estimate rainfall amounts using contour maps from the NWS Precipitation Analysis Page at water.weather.gov/precip/. Here, select the "NWS WFOs" radio button under "Locations", and scroll to Raleigh, NC, which should zoom the map in to central NC. You can then add county lines and highways/city labels using the boxes just below the map to help orient you. You can then make any number of selections regarding the amount of time to cover and whether to show observed rain, percent of normal, etc.
Aug. 10, 2014 | Tags: past weather, rain
Question: How did the sand desk not melt with all the rain that we have had during its tenure??? Or was it covered when not in use?? — Mary Holt
Answer: You answered your own question quite correctly! WHile there were some intense storms and heavy rainfall events since the SandDesk was built (and as you know by now it's still in use), there is a tent that we keep nearby that can be quickly moved over the desk to shelter it during rainy and windy periods.
Aug. 9, 2014 | Tags: preparedness, wral.com
Question: We hear and see many weather patterns impacted by the I-95 corridor. Why does the rain, snow, split/dump directly over the I-95 Corridor? It seems the Highway has an impact/effect on the weather. Is it pollution from the traffic, heat from the asphalt? Why? — Kathy Lamm
Answer: The I-95 corridor happens to lie along a zone in which typical meteorological patterns related to the geography of our region (mountains to our west and the Atlantic to our east, along with a transition from the higher, hillier Piedmont to the lower and flatter coastal plain, all of which run more or less parallel with that highway) and that of the Unites States in general, frequently leads to airmass boundaries, frontal zones and precipitation type, coverage or intensity transitions in that general area. The highway itself has little if anything to do with this, but does serve as a convenient, widely-known marker for quickly describing the location of these focused events or transition zones.
Aug. 8, 2014 | Tags: folklore, general meteorology, maps & codes
Questions 31 - 40 of 4340.
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Published: 2007-10-09 14:40:00
Updated: 2014-06-24 16:06:51
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