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Weather Questions tagged “rain”

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Question: Is this the wettest year (most total annual precipitation) on record for RDU area? Thank you for responding. — Kurt Hube

Answer: If you restrict the search to reported totals at the RDU airport since 1944, 2014 was "close, but no cigar." It was a very wet year, with 55.25 inches there, but this comes in second place to 1996, which brought 59.14 inches.

If we stretch the record back in time to 1887 by using previous official reporting sites of record for Raleigh, we find that 2014 comes in 11th out of 128 full years of data. The wettest year in that list was 1936, with 64.22 inches of precipitation. The year just ahead of 2014 was 1889, when 55.39 inches were reported.
Jan. 14, 2015 | Tags: past weather, rain, records/extremes

Question: What is the rain total for the last few days? Over the last 24hrs ending late Christmas Eve in particular. — Maudeileen M Huxhold

Answer: Rainfall can vary a good bit from location to location, but most of our area received anywhere from 1.5 to as much as 4 inches or so of rain during the several days leading up to Christmas. For a more specific example, the Raleigh-Durham airport recorded 3.08 inches of rain when you combined Sunday through Wednesday of that week. On Christmas Eve itself (Dec 24th, from midnight to midnight) 1.71 inches fell there, setting a new record for the date and surpassing the old record of 1.21 inches from 1986.
Dec. 28, 2014 | Tags: past weather, rain, records/extremes

Question: What happened to the heavy rain indications on radar Saturday morning Dec 6th, and what made them fizzle out as they approached Wake County and then seem to regroup east of us? — Scott deBrauwere

Answer: We took a look at archived radar, along with surface and upper air maps and soundings of temperature, humidity and winds over NC for that day, and it appears that early in the day there was a weak mid-level disturbance moving northeast across the state in the morning as a band of rain and rain showers preceding a cold front and larger upper level trough to our west approached our area. The smaller disturbance aloft likely enhanced upward motion in parts of the band, and may have briefly increased instability as well, leading to a period of stronger radar echoes as pockets of precipitation intensified. That disturbance appeared to have moved on as the band progressed eastward, allowing the rain band to shrink some in size and intensity as it crossed central NC. As the day progressed and the larger trough to the west drew closer, it generated some addition rain and helped keep showers going as they moved into eastern parts of the state. Soundings showed that the eastern coastal plain was a good deal more unstable than central and western parts of the state, and this probably also helped enhance the intensity of showers in that area.
Dec. 14, 2014 | Tags: past weather, rain, weather radio

Question: In reference to the week of 2-6 Nov, when did we have a rainy/windy event? I had some storm damage to my RV that I just found, and am trying to file an insurance claim. Thanks in advance for your help. — Bill Davies

Answer: We don't know what your exact location was, but our best estimate is that you're referring to a frontal passage that occurred late in the day on Thursday, November 6th. That cold front brought about 2 tenths of an inch of rain at the RDU airport, along with a wind gust there as high as 36 mph. Rain was heavier in a band not far north and west of Raleigh, and winds around the region in general gusted up to 30 to 40 mph, with some 40 to 50 mph gusts in areas near the coast.
Nov. 22, 2014 | Tags: past weather, rain, winds

Question: Did it rain in Goldsboro during the week of October 18th-25th? — Angela W. McCoy

Answer: That week fell within a generally dry period for much of our region, and rainfall records from stations in the area, along with archived radar rainfall estimates available at water.weather.gov/precip/, appear to indicate no rain fall in the Goldsboro area during that period, with the most recent prior rainfall there reported on October 15th.
Oct. 30, 2014 | Tags: cool sites, past weather, rain

Question: I live just West of Jordan Lake (Chatham County) and have noticed on many occasions that rain moving towards the east will diminish as it approaches the Jordan Lake area. Is the lake itself a factor that causes this? — Tom Coleman

Answer: Moving areas of rain, including convective showers and thunderstorms, are subject to a large number of influences, some local and some larger scale, that can cause them to vary substantially in size, shape and intensity over short periods of time. While it is possible for lakes (like Jordan), rivers and topography in general to affect low level temperature and humidity fields in a way that can feed into the behavior of some nearby showers and storms, it can be very difficult to generalize about what those effects are, or to separate those influences from any number of others for a particular episode or series of episodes such as you've noticed in Chatham County from time to time. One aspect of this whole issue that you may find interesting, though, is one of perception. Radar imagery of most showers and thunderstorms, especially at some distance from the radar site, tends to make them appear larger than they really are, and causes some individual cells to appears merged into one larger area. One result of this is that less area may be affected by rain, or by heavy rain and storminess, than one might expect when scanning radar loops. In addition, people focus very closely on how these cells behave near their location, but not so closely on how other cells are evolving in locations they are less interested in. This is evident to us because of the fact that we frequently receive questions like yours (what makes storms split up or dissipate when they approach my town?) from pretty much every part of our viewing area!
Oct. 16, 2014 | Tags: general meteorology, rain, weather radar

Question: How do you find out how much rain you received on a previous day and date, specifically, how much rain did i get zip 27603 9/23,24,25, 2014. It rained all night the 23rd and all day the 24th. I know it takes a lot of rain to receive 2 inches. I think we received 1 1/2 inches. Is that about right? I have tried 3 or 4 web sites with no luck. — Vicky

Answer: We checked a site run by the State Climate Office and found rainfall at a station not far from you (Lake Wheeler) that rainfall during that period totaled 1.25". We also checked readings from numerous sites that are part of a volunteer observation network, a number of which are peppered around you general part of Wake County, and found a range fro that time frame from about .5" on the low end to around 2 inches. This general range was in agreement with radar-based estimates for that time span from the NWS Precipitation Analysis page that indicated roughly 1.5" around your part of the county. The sites we used take a bit of effort to learn your way around, but if you'd like to have a look they are www.nc-climate.ncsu.edu/cronos, www.cocorahs.org/ViewData/ListDailyPrecipReports.aspx and water.weather.gov/precip/.
Oct. 14, 2014 | Tags: cool sites, past weather, rain

Question: I noticed that rain on Wednesday Sep 24th came from SE to NW and seemed to be in a counterclockwise rotation. Is this a tropical system that just developed late or is it a different type of system that moves in this manner? — Robert

Answer: There was not a tropical cyclone in the area that day, but some significant moisture from the western Atlantic area was pulled into the system that brought moderate to heavy rain our way. That system was made up of a nearly stationary surface front along the coast, with a trough of low pressure at successively higher levels in the atmosphere that tilted westward so that the trough axis at, say, 10,000 feet up was stretched more or less along the I-95 corridor well inland. Winds through that trough didn't make a complete circle, but did curve in a counterclockwise manner that gave the appearance of rotation that you noted.
Oct. 3, 2014 | Tags: past weather, rain

Question: How is likelihood of precipitation calculated? The written description might say 80% but the hourly for the same time period never shows more than a 50% chance. — Linda

Answer: There are several methods to estimate a probability of precipitation numerically, the most commonly utilized being "model output statistics" and "ensemble forecasting." The first utilizes regression equations that relate the values of a large number of variables projected by computer models to the occurrence or non-occurrence of precipitation in the past under similar conditions, while the ensemble technique makes either multiple runs of a single computer model starting from slightly "perturbed" initial conditions (simulating the kinds of errors and uncertainties in observed data that arise due to instrument errors and incomplete sampling of the atmosphere) or by using a group of different models with varying methods of treating the atmospheric physics involved. A form of precipitation probability is then assessed based on the number of model runs that indicate measurable precipitation for a certain time frame as a fraction of all the model runs for that period. In both cases, it is generally the case that a probability will tend to be higher for longer spans of time, i.e., the probability of rain for a 12-hour period is usually higher than for a 3-hour period somewhere within that 12 hours, simply because there is more time to account for faster or slower systems and other sources of uncertainty. So in a formal, technical sense, it would not be unusual to have an overall probability for a day be higher than individual probabilities for smaller portions of the day.

All of that said, the probabilities that you usually see on weathercasts or on our web site have an added subjective element based on the forecaster's judgement. The forecaster takes all of the calculated probabilities into account, along with an overall assessment of analyzed observations, satellite and radar data and computer model projections of the overall weather pattern, to arrive at a level of confidence that measurable rain will occur. This subjective probability is entered for the daily value, and we also then fill a database of hourly values so that we can indicate a better chance in the morning and lesser chances later, etc. None of the individual hourly probabilities should be higher than the daily value, but they can be lower. A common example would be a summer day when a few widely scattered afternoon showers and storms are expected. The probability may be 5-10% through the morning, before climbing to 20-30% for the mid and late afternoon hours, and a 30-40% chance for the day as a whole.
Sep. 15, 2014 | Tags: general meteorology, rain, wral.com

Question: Is it just my imagination or does a close lightning bolt really cause a brief increase in rainfall intensity? — Chuck Britton

Answer: It's probably not your imagination, as the "rain gush" phenomenon has been noted by many observers and has been documented in various studies going back to the 1960s. The exact mechanism or combination of mechanisms that can lead to the lightning flash followed by a burst of heavier rain remains somewhat uncertain, although both mechanical (coalescence of existing droplets or sudden conversion of supercooled droplets to ice crystals followed by rapid growth, both due to compression and rarefaction imposed by passing acoustic waves associated with thunder) and electrostatic (rapid reversals of electric field orientation acting on charged hydrometeors, either to cause them to increase their tendency to coalesce rapidly) explanations have been suggested. Most studies in more recent years seem to favor the electrostatic effects more so than the acoustic.
Sep. 14, 2014 | Tags: lightning, rain, thunderstorms

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