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Weather Questions tagged “rain”

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Question: What is it about Harvey that this hurricane dropped so much rain? — Linda Gulya

Answer: The primary factor that led to such tremendous rainfall totals with Harvey was the storm's motion, which essentially ground to a halt once it moved a fairly short distance inland over Texas. That left a sizable portion of the storm's circulation over the Gulf of Mexico, which happened to have especially warm water temperatures over a significant depth at the time. The combination of strong evaporation of moisture from the warm Gulf and the continued onshore flow of the resulting moist, unstable air into eastern Texas over a long period of time (due to the storm's slow movement) produced rainfall that reached the range of 30-50 inches in some places.
Sep. 8, 2017 | Tags: flooding, hurricanes, rain

Question: I was reading about a cloud burst - how rare is this to happen in North Carolina? — April

Answer: A "cloudburst" is informally defined as a sudden, very heavy rainfall, usually showery in nature (meaning the intensity can change rapidly over short periods of time or over short horizontal distances), sometimes resulting in localized flooding. There is no official criteria for the rate or amount of rainfall required to consider a rain event a cloudburst, but we wouldn’t consider them especially rare in our state. Under warm, humid conditions it isn’t unusual for a few showers or thunderstorms to occasionally produce brief, heavy, and often localized downpours that could fit the popular conception of the term.
Aug. 16, 2017 | Tags: careers & education, flooding, rain

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: Hi! Is there a calendar online that shows when we last had rain; specific daily rainfall amounts for the area (instead of aggregate monthly or yearly data for the area (or less helpfully - the State))? Getting the right amount of water to my summer garden is tricky and being able to look back and determine how much water it needs would be helpful - relying on my memory alone is a faulty system. — Anonymous

Answer: There are a number of resources we can suggest, keeping in mind that rainfall can vary a good bit over a short distance. In terms of looking at specific dates and how much was received in rain gauges at individual stations, you can use the "Almanac" function of our web site to check a selected date - when you do that, the default is to show a single day's info for RDU. However, you can then change the view to "monthly," which will allow you to quickly scan a table of observations near the bottom of the page that includes daily precipitation observations for the entire month - you can also use the "Search for Another Location" box to change the observation site to another town. Another place to look for a fairly dense network of daily precipitation observations is the Community Collaborative Rain, Hail & Snow network, at www.cocorahs.org. Once you learn your way around the site a bit, you can get good localized history of recent precipitation for the region there. Another option is a National Weather Service Precipitation Analysis page that uses radar estimates of precipitation, adjusted to fit with rain gauge reports, to plot daily contours of precipitation that you can step through. The advantage here is that radar fills in some of the gaps between fixed observation sites. The page also allows you to view precipitation amounts summed over the past week, past month, past 90 days, etc, and to view how those amounts compare to normal. The address is water.weather.gov/precip/, and you might like to go to the "location" button, select "WFO," choose "Raleigh" and click on the county borders for a good view of our area.
Jul. 17, 2017 | Tags: cool sites, past weather, rain

Question: Elizabeth displayed a green chart this morning showing rain days and how much each day of June. Will this be posted on line? I would like to see this calendar page posted each month. It would help when planning when to plant and water. — Reginald tharrington

Answer: We're glad you liked that graphic, which shows the current month and how much precipitation was recorded at RDU on each day. Right now, we show that on a sporadic basis on the air, and post it on occasion in the "Weather Feed" space on our web site and app. We can look into posting it on a more regularly scheduled basis. We would also note that there are a couple of resources you can find on our site already that convey the same information in different forms. One is the set of cumulative rainfall graphs for RDU that cover the past 30 days, 90 days, year to date and past year. These graphs also include a line showing what would be the "normal" rainfall over those periods. In addition, you can go to our "Almanac" page, and click the "send" button under the "Enter Date" box - if you leave the date blank, it will default to the current day - this will take you to a history page for RDU. If you click the "Monthly" tab at that page and scroll to the bottom, you'll find a table that includes a column with daily precipitation values for each day of the selected month.
Jul. 8, 2017 | Tags: cool sites, past weather, rain, wral.com

Question: Is there a place where I can find running 24 hour rainfall totals? — Glenn

Answer: There are a couple of locations where you can get running 24-hour precipitation estimates based mainly on radar returns. One map of that sort is hosted at the Southeast River Forecast Center, at www.weather.gov/images/serfc/24_hour_precip.png, and a similar, but zoom-able, and more interactive, map at www.iweathernet.com/total-rainfall-map-24-hours-to-72-hours (you can click on any point there, and after a short delay, a box will appear that shows the estimated precipitation amount for that location).
Jul. 1, 2017 | Tags: cool sites, rain, weather radar

Question: My husband and I take our morning walks along the "Mountain to the Sea" trail along the Neuse River. The last few days the river appears to be very low. Any idea as to why? — Janie McAdams

Answer: The Corps of Engineers regulates flow from the Falls Lake dam into the Neuse River downstream based on the amount of inflow to the lake from upstream, the elevation of the lake surface and the need for flow downstream from the lake. Starting around a week into June, flows into the lake became rather low and by around the 10th or 11th of the month, the lake level had fallen and outflow from the lake downstream was minimized, which likely led to the low river level you noticed not far downstream from the lake before sending in your question on June 16th. Conversely, very heavy rain upstream of the lake on the 19th into the 20th has sent inflows and the lake level sharply upward, and we suspect you may have seen, or will shortly, noticeably higher river levels due to increased releases from the lake. You can check on a variety of level, inflow, outflow and water temperature data for Falls Lake at epec.saw.usace.army.mil/fall.htm, and more generally for lakes in our region at epec.saw.usace.army.mil/index.asp.
Jun. 24, 2017 | Tags: cool sites, lakes and rivers, rain

Question: Recently something is not working for me with the Doppler that was working before and I wondered if there was an explanation. For example, this morning at 10 am the Doppler showed Raleigh and most of NC clear with just a few scattered rain area SW from SC. I use 30 mph for approximate movement, which should have put any rain here pretty late in the day or night. Now it is 1 pm and heavy rain is falling with a large area of storming over central NC. I have used the Doppler successfully for a long time to plan my day (painting, clothes drying, hiking, etc) but now it does not seem to be working. It is causing problems. Do you have any explanation? — Margaret Parrish

Answer: We're actually a little surprised that planning based on a view of Doppler radar returns at any given time has worked all that well for planning out long periods of the day, since the radar can only show precipitation that currently exists, or, in time lapses, how it has evolved over a period of time. While one can reasonably extrapolate for a short time into the future based on the recent movement of rain areas or storm cells/bands, etc, it is quite common for rain areas and convective cells (showers and thunderstorms) to rather rapidly increase or decrease in size and intensity, to speed up or slow down in terms of forward motion, for existing rain areas to dissipate, or for new showers or storms to develop where none previously existed. We attempt to account for this as best we can in forecasts based on projecting current patterns, accounting for the typical behavior of the atmosphere when certain features (fronts, lows, upper troughs, etc) are in the vicinity, and using computer models that produce projected estimates of the future location and intensity of precipitation areas. We'd suggest combining your use of the Doppler display with checking the probability of precipitation in hourly forecasts, reading the text discussion of the forecast in our 7-day forecast, using extra tools such as the "FutureCast Radar" layer in our iControl display, and checking in on TV in the morning, when we often show forecast models that give a rough sense of the timing and location of any precipitation areas throughout the day ahead.
Jun. 9, 2017 | Tags: general meteorology, rain, weather radar, wral.com

Question: Why don't you show the monthy and ytd rainfall totals vs historical avg. At least put it on your website and update it. — James Spoo

Answer: We actually do that already, and then some. Just look in the "Weather Resources" section of our site, go to the second page and you'll see a link for "RDU Rainfall Totals -- Normal vs. Actual." It shows graphs and boxes with observed versus normal rainfall at RDU over periods that include, 30 days, 90 days, year-to-date, one year and five years. The direct address is www.wral.com/weather/page/1934052/.
Jun. 7, 2017 | Tags: normals, rain, wral.com

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