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Recent Questions

Question: Is there a place I can look up whether we were under the influence of High or Low systems by the day for each month? — Done

Answer: The most straightforward way we can think of to do that is to examine weather maps that show the pressure patterns across the United States on a daily basis, to examine them an see if a center or ridge of high pressure, or a center or trough of low pressure, were in place over NC or nearby on the days in question (sometimes you might find that we fall somewhere in between, during a transition day of sorts). If you are interested in seeing daily weather maps for your dates of interest, they are available from NOAA at www.lib.noaa.gov/collections/imgdocmaps/daily_weather_maps.html. Note that this link includes access to weather maps going back to 1871. If you are interested in maps for dates since September 1, 2002, a more direct address is www.wpc.ncep.noaa.gov/dailywxmap/index.html.
Jul. 3, 2017 | Tags: cool sites, maps & codes, past weather

Question: What is the Radar near Hwy 50 & 98? — Michael

Answer: You are no doubt referring to the radar tower and radome visible just off Old Creedmoor Rd northwest of the 50/98 intersection you mentioned. That is the Terminal Doppler Weather Radar (TDWR) that serves the Raleigh-Durham airport. It is a more localized radar than the National Weather Service NEXRAD radar located near Clayton. The TDWR system is part of an FAA-operated network of radars that are designed to provide short-range, high-resolution detection of wind shear, gust fronts, microbursts, heavy precipitation and other weather phenomena that are potentially dangerous to aircraft in the immediate vicinity of airports.
Jul. 2, 2017 | Tags: weather radar

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: Durham is missing on your weather map. Can you explain why? — Suzanne

Answer: Upon checking back with you, we found you were asking about the radar display, where we can move around and zoom in or out to highlight areas of precipitation or thunderstorms that are crossing the area. When we do that, the display software automatically picks town and city labels depending on the zoom level and what part of the area is shown, and it works to avoid having labels from nearby towns overlap with one another. It may have been that by chance at the time you were watching we set a couple of views where the software left Durham off. When moving around the range of available views, there are times when almost every town (including larger ones like Durham, Raleigh and Fayetteville), are labeled and others where those labels disappear in favor of some other nearby places. We use a number of other maps that have standard views (like our current temperature maps, some of our model-projected temperature, wind or dew point maps, our viewing area forecast map, and some others) and the great majority of those include Durham specifically.

On the radar view, it might be possible to force certain cities to always be labeled. However, we try to avoid that since if we set a couple of key places to always be there, it would preclude some other nearby locations from ever showing up, and we like to allow some of the smaller communities to appear as well. We could also set it so a lot more town names are visible at the same time, but then we’d end up covering a lot of the radar data we’re trying to show with labels, so we try our best to find a happy medium somewhere in between.
Jun. 30, 2017 | Tags: maps & codes, weather radar

Question: This time of year, through August, overnight low temperatures do not seem to vary much. Forecasts can go for days with lows being close to 70 degrees. We have some cool nights in the long range with lows about 10 degrees below what we normally see. How unusual is that? I would guess the odds of an overnight low being close to 60 for mid June through mid to late August to be about 1%. — Joe Freeman

Answer: At the time you wrote, we were forecasting a low around 57 degrees on June 28th, which is indeed fairly unusual. The normal low for that date is 69 degrees, with a standard deviation of about +/5 degrees (as you noted, temperatures are less variable in the summer - in January, the standard deviation for the low is about +/- 11 degrees). The record low for June 28th is 53, from back in 1988, so it can get notably cooler than 60 degrees. As for the odds, it turns out that temperatures have dipped to 60 or below in Raleigh on June 28th about 15% of the time in observations going back to 1887. More generally, for "meteorological summer" overall, the average chance of falling to 60 or below on any given day is about 11 percent.
Jun. 29, 2017 | Tags: normals, records/extremes

Question: How good will the viewing of the total eclipse be in Raleigh? Should we consider going elsewhere to see it? — Susana Merritt

Answer: The Raleigh area is outside the path of totality, and so a partial solar eclipse will be seen from here. At maximum coverage, the moon will stretch about 94% of the way across the sun's diameter, leaving a crescent of the sun visible. While this can make for an impressive image, even a relatively small crescent is very bright, and there is a big difference in experiencing a total eclipse and even a substantial partial eclipse. Several phenomena associated with totality, such as shadow bands, Baily's beads, the "diamond ring" effect at the onset and end of totality, and visibility of the sun's corona and chromosphere, do not occur in areas seeing a partial eclipse. To experience those effect would require traveling to a location within the path of totality.
Jun. 28, 2017 | Tags: astronomy

Question: With temps in Phoenix AZ. 120. What is the feel like temp? With the humidity low, is the feel like temp lower than 120? — Russ

Answer: Heat index charts and equations weren't really developed for cases where humidity is very low, but can be extended to give some approximation of the idea that low humidity can make it feel a little less hot than it would if humidity were at even moderate levels. In the case of Phoenix last week, we found that on the hottest day (Tue, June 20th) the airport reached 119 degrees, with a corresponding dew point of 37 and relative humidity of 6 percent. If you check tables or calculators that allow figuring of heat index outside the typically specified valid ranges for the tables and equations (available at, for example, www.iweathernet.com/educational/heat-index-calculator-and-conversion-table), you find the heat index for that combination is estimated to be about 110 degrees.
Jun. 27, 2017 | Tags: apparent temperature, cool sites, heat, humidity/dew point, past weather

Question: I am heading to Junaluska in the Carolina mountains next week. Will CINDY have any effect on the weather there? — John McCanless

Answer: The system that had been Cindy did contribute a little to some shower and thunderstorm activity in the mountains, but it moved rather rapidly and along a somewhat northerly track, and given those circumstances it appears the mountains will end up with some very pleasant weather through a good part of your time there, with a fair amount of sunshine, very low rain chances, high temperatures in the 70s and humidity that is lower than average for this time of year.
Jun. 26, 2017 | Tags: humidity/dew point, lakes and rivers

Question: Could you please explain to me why it is always much cooler on March 21st than Sept 21st when the sun is in exactly the same position relative to the equator? — John Coleman

Answer: That's a good question, and the principal answer is that you are seeing the effects of where the sun has been for the months leading up to those dates more so than the exact positioning on the two equinoxes themselves (note that equinox dates vary a bit from year to year, and in 2017 the vernal equinox fell on March 20, while the autumnal will occur on September 22). At the RDU airport, the normal high temperature on March 21 is 65 degrees, while the mean dew point for the date is 40 degrees. On September 21, the normal high is 81 degrees and he mean dew point is 63. On both dates, the sun's position, together with refraction by the atmosphere and our definition of sunrise and sunset, results in about 12 hours and 8-9 minutes of sunlight. However, in the months leading up to March, the days are much shorter for a while, allowing for outgoing radiation at night to exceed incoming radiation for the day, and a gradual net cooling into midwinter, in addition to prompting changes in the upper level flow and average jet stream position that results in (typically) frequent intrusions of cold air from the north. This results in cold ground temperatures and cooling of oceans and other large bodies of water, which in turn results in lower amounts of water vapor in the air (hence the lower average dew point in March). Lower water vapor amounts allow for somewhat more efficient cooling by longwave radiation overnight. As we move through the summer, of course, the opposite happens, as longer days and short nights allow more heating of soils and water, which evaporates more moisture in to the air (in addition, considerable moisture is transpired into the air by much more abundant leaf, grass and plant cover through the summer and early fall). The combined effects of stored heat, and water vapor that somewhat limits loss of heat by radiative cooling at night, leads to the continued warmth of late September, and the overall lag of both heating and cooling leads to a much cooler equinox in March than in September. Some of the same factors also play a role in our warmest and coldest average temperatures being displaced a couple of weeks after the summer and winter solstices that mark the longest and shortest daylight periods of the year.
Jun. 25, 2017 | Tags: general meteorology, normals

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

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