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Weather Questions tagged “rain”

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Question: Can you tell me the daily rainfall amounts in Roxboro from 10/5 to 10/10/16? — Linda Ward

Answer: We looked that up using the "Daily Data Listing" feature of the Applied Climate Information System web site at - you can check such information for Roxboro and many other sites around the region and nationally. In your case, the rainfall reported for Roxboro on those days was, in order from 5-10 Oct, 0, 0, .21, 1.07, 3.53 and 0 inches. Of course, precipitation can vary notably over short distances. You might want to also check daily archived contours of precipitation amount based on gauge-adjusted radar estimates, at
Oct. 28, 2016 | Tags: cool sites, past weather, rain

Question: Could you please tell me how much rainfall there was in Spring Lake from the hurricane? — Diane

Answer: We couldn't find a specific gauge report from Spring Lake, but did turn up several sites nearby that showed a range of rainfall totals from the hurricane, together with the frontal boundary that brought some light rain the day before it arrived, that ranged from around 9 inches to as much as almost 15. Some examples include 8.6 inches at Pope Field, 9.8 inches at Simmons AAF, 10.7 and 14.7 inches at volunteer observer sites just southwest and just north of Fayetteville, and 14.9 inches at the Fayetteville airport. Anyone who'd like to check totals at other locations can find reports from official airport sensors through the "Almanac" page on our web site by using the "get historical data" function and then changing from the default RDU location to other sites, and you can also find numerous reports from the volunteer network called the Community Collaborative Rain, Hail and Snow network (CoCoRaHS) at
Oct. 21, 2016 | Tags: hurricanes, past weather, rain

Question: I placed a five gallon sheetrock bucket in the back yard in a open place Friday evening as Matthew approached and accumulated 10.25 inches of rain. Would that be an accurate measurement? — Bruce

Answer: That seems like a reasonably good measurement, assuming the bucket has a flat bottom and the sides are vertical (perpendicular to the bottom). It's also important that the bucket was sitting level and was not in an area where it would be affected by nearby trees or buildings that can affect the reading, by either blocking some of the rain, or by concentrating rain that runs off the side of a roof or some branches of a tree, etc). You did note an "open area," and your number does run pretty close to other radar and gauge estimates from nearby locations.
Oct. 20, 2016 | Tags: hurricanes, instruments, rain

Question: Often, there is a significant delay between the intense part of a heavy storm like Matthew and the onset of the worst flooding. I believe this was true of Katrina. What accounts for the fact that flooding can be at its most severe long after the rain has stopped? — Jay Exum

Answer: Two types of flooding that can somewhat overlap but can also be rather distinct can occur with situations like we saw with Matthew's passage, and as you mentioned, in Katrina back in 2005. In that storm, a number of levees and large pumps in the New Orleans area initially held up to the heavy rains and high winds associated with the storm, but eventually failed and allowed very substantial flooding to develop rapidly on a delayed basis.

In our area with Matthew, the very heavy and sustained downpours that occurred later Friday night into Saturday evening resulted in many initial reports of flash flooding as small creeks and streams quickly filled up and overflowed, and many drainage systems in urban or semi-urban areas simply could not keep up with the rapid runoff, especially where debris from gusty winds clogged entry points. In the longer term, the water that fell onto larger watersheds gradually collects from all of those small streams to larger tributaries, some running off across the surface, some soaking into the ground but still flowing slowly toward those streams, and eventually emptying into main stem rivers like the Tar, Neuse, Cape Fear and Roanoke, along with some smaller rivers within those watershed basins. This process gradually concentrates water from a very large area into much smaller ones in a slow surge that travels down those drainage basins toward the coast, and can result in days of elevated water levels at locations successively downstream. Hence, we've seen increasing flood problems on a delay of a couple of days in places like Rocky Mount, Tarboro and Greenville along the Tar River; Smithfield, Goldsboro and Kinston along the Neuse; and Lumberton along the Lumber, among a number of other locations and waterways, some of these requiring evacuations and rescues by means of high-clearance vehicles, boats or helicopters.
Oct. 16, 2016 | Tags: flooding, rain

Question: What is an areal flood? — Arr Schaller

Answer: It's probably easiest to describe by comparing it to the other common flood warnings that the National Weather Service may issue, since they differ largely in the sense of how quickly the onset of flooding may occur, and how localized flooding is expected to be. They define flash flood warnings and areal flood warnings in the following ways:

A Flash Flood Warning is issued for flooding that normally occurs within six hours of heavy or intense rainfall. This results in small creeks and streams quickly rising out of their banks. Dangerous flooding in areas near these creeks and streams, as well as low-lying flood prone areas, develops very quickly and is a significant threat to life and/or property.

An Areal Flood Warning is normally issued for flooding that develops more gradually, usually from prolonged and persistent moderate to heavy rainfall. This results in a gradual ponding or buildup of water in low-lying, flood prone areas, as well as small creeks and streams. The flooding normally occurs more than six hours after the rainfall begins, and may cover a large area. However, even though this type of flooding develops more slowly than flash flooding, it can still be a threat to life and property.

A third type to be aware of is the River Flood Warning, which is issued when runoff from extended periods or large areas of heavy precipitation cause rivers to reach or exceed established elevation levels that correspond to minor, moderate or major flooding levels at designated gauge locations along the river. While the other warnings typically remain in place for a few to several hours, river warnings can sometimes stay in effect for days.
Sep. 25, 2016 | Tags: flooding, preparedness, rain

Question: Take a look at the WRAL 24-hr rainfall map. What is up with the rainfall in Greenville? It looks like they are reporting rain from Hermine in centimeters rather than in inches. — Dave Salman

Answer: We noticed that, too, and in fact there were a couple of different locations that we were not directly plotting the values on our maps where we saw that color contours in the background had areas that were obviously contaminated with readings that were too high, so that we turned off that background layer for on-air purposes. We aren't absolutely sure what the problem was yet, but have seen instances in the past with reports from the type of automated sensor used at the Greenville airport in which display software adds up rainfall cumulative rainfall totals as if they were sequential un-related values instead, leading to a significant over-calculation of the reported amount. Other nearby stations, along with radar-based estimates, make it appear most areas in the vicinity of Greenville received around 6-8 inches of rain Thursday through Saturday from the combination of a frontal boundary and Hermine.
Sep. 7, 2016 | Tags: instruments, maps & codes, rain

Question: Will it ever, ever rain in Raleigh again?? Will the air in Raleigh ever be cool again? — Candy

Answer: Rain has certainly been less widespread and frequent for the past few weeks, and that general pattern may not change all that much soon. However, by the time you read this response, it is quite possible there will have been some showers and storms associated with a passing cold front, and some rain generated by an interaction of that front and a tropical storm moving by to our southeast. Those systems didn't absolutely guarantee substantial rain everywhere in the vicinity of Raleigh, but they did involve a high probability of having some, and also a good chance of temperatures running notably cooler, with less humidity, for a few days. This may be followed by another round of fairly hot weather, but we'll be heading into the fall over the next few weeks and you can be assured that, with a few ups and downs along the way, we'll trend toward cooler weather.
Sep. 3, 2016 | Tags: general meteorology, heat, rain

Question: What does a double rainbow mean? Thank you. — Pat

Answer: The principal indication given by a double bow is that the raindrops that are refracting and reflecting sunlight are of medium to large size, rather than being very small or tiny droplets. The larger droplets produce narrower and brighter bows, making the secondary bow more visible than it would be with smaller drops. The primary bow, produced by light rays reflected once within the drops, occurs along a circle that is about a 42-degree angle from the center of that circle, while the secondary bow, produced by light rays that reflect twice within the drops, occurs at about a 51-degrees angle. One thing to notice when you see a double bow is that due to the second reflection the colors are reversed - the primary bow is red on the outside edge, while the secondary is red on the inside.The secondary bow is a good deal fainter than the primary, so that when the drops are small and the bow is faint, it may not be noticed at all. There's a lot of great information about rainbows, along with diagrams explaining how they form and photographic examples of the many different forms, at
Jul. 14, 2016 | Tags: atmospheric optics, rain

Question: Storm just rolled through and at 9:10PM the temp has dropped to around 74 degrees. On your hour by hour forecast, it is predicted to be around 80 degrees about now. When temperatures drop this time of night due to rain, will the temperatures rise even though there is no sun to heat the air back up? Also, can we expect the overnight temperature to be lower since we are now cooler than expected for this time of night. — Joseph

Answer: The situation you describe has enough variables involved that there isn't a single yes or no answer. As with many situations in weather, "it depends" on a number of factors, and there will be times when the rain-cooled air will regain some of the lost temperature (if, for example, the cooled air is rather shallow and mixing brings warmer air down from above, or the rain-cooled air covers a small horizontal area and advection causes warmer air from another location to flow back over the area that had cooled some, or if the ground had become very warm during the day and some stored heat is released that is able to overcome other cooling effects during the night). On the other hand, absent some of those effects, it is also possible for the temperature to remain near, or to simply fall from, the newly reduced level. The most rapid fall would typically occur if skies clear out after the rain and winds remain light. A similar set of considerations affects whether the rain-cooled air will eventually fall to a lower temperature than it would have in the absence of the rain - in some cases, yes, in some no. On the night you asked about, the temperature at RDU fell from 82 just before the rain to 75 just after (at about 9 PM), then ticked up to 76 by 1 AM before dropping to 74 at 2 AM, only to edge back up to 75 at 3 AM. After that it drifted as low as 72 right around sunrise.
Jul. 13, 2016 | Tags: general meteorology, rain

Question: One of the questions references an almanac and rainfall amounts. Is that Online? — Lyn Triplett

Answer: It is indeed. The particular product showing how rain at RDU compares to "normal" over the past five years is located in the "Almanac" section of our web site. Just look for the link in the upper part of the web page. Then, on the Almanac page, you'll see a link for "RDU rainfall Charts," where you'll find graphs of cumulative rain totals versus cumulative normals for several periods ranging from 30 days to 5 years.
Jul. 12, 2016 | Tags: past weather, rain,

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