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Question: Is there a simple way to gather barometer readings over a period of time (week, month, etc.)? For the first time in my life I'm getting headaches and my doctor has run some tests but has told me to make a chart of air pressure to see whether changes influence to frequency of my headaches. — Einar Bohlin, Wake Forest

Answer: We're sorry to hear about the headaches, and wish you success in treating them. You can use the "Almanac" section of our web page to access data on barometric pressure, including hourly observations that can be graphed over a day, a week or a month's time. Just go to the Almanac page, then click the blue "send" button under "Get Historical Data." At the resulting page, you have the option to change to any date, and also can choose to display data in daily, weekly or monthly format. When you scroll down from the top of the page, you'll see a number of graphs, including one that shows pressure readings. On any daily page, you can also scroll down farther and see a listing of hourly observations that includes pressure. The pressure trace for the RDU airport should be reasonably representative for your purposes in Wake Forest, but if you'd like to check for consistency you can also use the "Search for another location" box along the right hand side of the page and choose to view data from the Louisburg airport. In either case, take care to pay attention to the vertical scale of the pressure graph, as it may vary some depending on how big a spread of pressures is covered during the span of time shown on the graph.
Jul. 25, 2016 | Tags: cool sites, past weather, weather & health, wral.com

Question: WRAL used to have temperature and heat index graphs for the entire day. Where can I find the max temp and heat index for a particular day? — Julia George

Answer: If you're referring to the graphs that project a forecast temperature and heat index for about two and a half days in to the future, those are now available by clicking the "hourly forecast" link on our main weather page, and then scrolling down a bit to see the graph. The graph defaults to show hourly temperature and precipitation probability, but you can click a blue selector box at the top of the graph to choose between a number of other variables to plot. One of those is called "feels like," and shows the heat index or wind chill value, whichever is appropriate to the season.
Jul. 24, 2016 | Tags: apparent temperature, wral.com

Question: Sometimes the hour by hour forecast says there is 50-50 shot at storms but nothing happens. Is there a reason? — Amy

Answer: Part of interpreting a probabilistic forecast like that is keeping in mind both potential outcomes that are implied. In this case, over the period that you see a 50% chance of thunderstorms, you would expect that given the weather pattern in place, about half the time storms would develop and impact your area, and half the time they would not (and so, nothing happens). Another way to look at it is that if you have ten days with a stretch of hours having a 50% chance of storms, storms should occur on about 5 of those days sometime during the period of the 50% chance, and should not occur on the others. Likewise, a 30% chance of rain implies that there is a 70% chance that it will not, and so on.
Jul. 23, 2016 | Tags: maps & codes, thunderstorms, wral.com

Question: Do you have a clip of the radar view of the purple martins showing up on radar leaving their perch early in the morning? I think it was somewhere around Beaufort and it was the most amazing site on the radar. Just wanted to share it with friends. I saw it during the Saturday morning broadcast with Mike Moss. — Ginger Mangum

Answer: We don't have that particular clip, but you can usually see the expanding purple martin "roost ring" on radar starting around sunrise on radar loops from about mid-June through early September or so. The sites can vary a bit over the years - right now, the most visible is just south of the Pamlico River in Beaufort County, and it shows up best in lapses of the Morehead City NWS radar. Mike did a blog post about these roosts and their appearance on radar a number of years back, and you can still access it by typing "radar birds" in the search box on our site, which should turn up a link labeled "Radar that's for the Birds!" That post includes a radar still image that includes radar rings from three roosts that were active around southeastern NC that summer.
Jul. 22, 2016 | Tags: weather radar, wral.com

Question: When is the thermal Equinox in Raleigh? — Don Wollum

Answer: We aren't aware that there is a physical or statistical property called thermal equinox, and the only thing that turned up in a web search was someone's informal, kind of joking, definition on a chat page. That being said, we wonder if you're looking for something along the lines of that person's take on the term, which was the halfway point during the year between warmest and coldest average temperatures. If that's what you had in mind, then for Raleigh those points come on April 16th and Oct 18th, when our average temperature is closest to 60.4 degrees. This number arises from splitting the difference between our warmest average temperature of the year (80.3, which occurs July 14-17) and our coldest (40.5, which occurs from January 5-12).
Jul. 21, 2016 | Tags: folklore, normals

Question: I have been looking for some specific 30 year (1981-2010) average climate data, hoping to find the data I need in the NOAA website but not having luck. Specifically I am looking for the (30 year) average monthly temperature and average monthly relative humidity (or dew point) for the 100 major cities in the US. — Phil

Answer: The kind of information you're looking for is contained in something called Comparative Climatic Data maintained by the National Centers for Environmental Information in Asheville. It provides monthly and annual normals or averages for a number of different variables (including temperatures in the Climate Normals section, and relative humidity in the Observed Data section) for about three hundred cities across the United States. You can find the tables at www.ncdc.noaa.gov/ghcn/comparative-climatic-data. Note that the tables may be best viewed with you browser maximized to full-screen size, and also that humidity averages are given for both morning (when temperatures are generally at a minimum and relative humidity at a maximum) and afternoon (vice versa) values. Also note that while the temperature normals are based on 30-year periods, the relative humidity averages may be based on other spans of time, which will be specified for each city.
Jul. 20, 2016 | Tags: cool sites, normals, past weather

Question: Do you know what these splotches are that appear when I click on Radar? — Nathalie

Answer: You sent along a link with your question, to www.ssd.noaa.gov/goes/east/ne/mflash-wv.html, which was a satellite loop instead of radar. In this particular case, we couldn't address the particular "splotches" you may have viewed since the link is to the most recent satellite time laps rather than the specific time frame that prompted you to ask about the imagery. However, in a more general sense, the type of satellite image involved senses the intensity of a certain range of wavelengths of infrared radiation that are especially sensitive to absorption and emission by water vapor and cloud particles in the middle and upper atmosphere. The resulting images generally are brightest or colored with "cold" shades where high-level clouds exist, and darkest or shaded in "warm" colors where the mid and upper levels of the atmosphere are quite dry. At in-between concentrations of water vapor, they are usually shown in varying shaded of gray, with lighter denoting more water vapor and vice versa. These areas where otherwise invisible water vapor concentrations are indicated can do a good job visualizing the wind flow in the middle and upper atmosphere, and the corresponding organization and movement of weather systems like upper-level troughs, ridges, lows, highs and jet streaks.
Jul. 19, 2016 | Tags: cool sites, instruments, maps & codes

Question: How do I get rid of the blue pointer on the iControl weather map that shows where I'm located? Every time that it's on the screen, the weather map immediately expands and has to be brought back in proper focus. — Bill Scott

Answer: Generally, if you're viewing the iCOntrol radar map on a home or business PC, there will not be a pointer icon indicated on the map. It will start in a default zoom level, and if you'd like to set a particular view to return to at will, you can do so by clicking the pointer icon in the lower left corner of the iControl window, and saving a view (or multiple views) with names of your choice. Then, clicking on any of those view selections will move the map to that location and zoom level. Note that if you are not "signed in" to the web site, these settings and names will be lost the next time you return to the site, or if you access the site on another PC. If you save the views you are interested in while signed in, they should be available the next time you visit iControl.

On a cell phone, the blue pointer appears if you have "locations services" turned on while using the feature. If you'd prefer not to see the pointer, then disabling location services (or clicking "do not allow" when iControl asks if it can use your current location) should result in a map view that does not include the pointer. You can then manipulate the map, save views, etc, the same as mentioned in the discussion about PCs.
Jul. 18, 2016 | Tags: maps & codes, weather radar, wral.com

Question: I love following the wet weather with Doppler 5000 online. If I want to see if the storm is about to hit, or watch when it will be over. Thank you for that service. My question: if there is nothing showing on radar as things move say west to east...appears clear...then all of a sudden a rain pocket shows up sometimes to the red. Why is that when the surrounding skies were clear? — Margie

Answer: There are a couple of ways this can happen. In rare instances, it is possible there was some kind of radar outage so that showers or storms are not visible, then the outage is resolved and all of a sudden any echoes in the vicinity become apparent.

The more likely and frequent explanation, though, especially in the late spring through early fall, is that a shower or thunderstorm simply developed very rapidly in an area that was previously rain-free. When the atmosphere is quite humid and unstable (meaning a strong decrease in temperature with increasing height, especially if there is also a drop-off of humidity with height as well), strong updrafts can develop that lead to precipitation that can go from non-existent to quite intense in a matter of just a few minutes. This can occur from buoyancy produced by uneven heating of the surface by strong sunshine, or in some cases the new showers or storm cells can be triggered by the passage of a fairly weak upper-level disturbance, or a low-level feature like a weak front or a leftover outflow boundary from a distant or even already-dissipated thunderstorm.
Jul. 17, 2016 | Tags: thunderstorms, weather radar, wral.com

Question: A number of times in the last few days I've noticed on iControl radar indications or lines moving quickly from northeast to southwest while all other indications are moving in their usual ways. Are these aircraft trails (similar to vapor trails)? — William Rothwell

Answer: We can't be quite certain from your description, but we strongly suspect you're noticing some echoes produced by thunderstorm outflow boundaries. These are effectively shallow cold fronts associated with rain-cooled air that descends rapidly in thunderstorm downdrafts, spreading rapidly outward from the storm when the cooler, dense air reaches the ground. Depending on the structure of overall ambient winds, these outflows may preferentially move in one direction, or they may spread out in a concentric ring or oval around a slow-moving storm. The boundaries usually appear as thin lines of rather light echoes, and they appear on radar because the winds flowing out from the storms cause a convergence when they run into the surrounding airmass, causing a concentration of dust and flying insects, and also leading to turbulent mixing along the boundary that creates pockets of varying temperature and humidity, all of which can act as weak radar reflectors. One thing that's a little tricky regarding these boundaries is that they tend to be shallow, extending just a few hundred to a few thousand feet above the ground. At these heights, the boundaries may only be visible when they are fairly close to a radar site, and can appear to dissipate when in fact they have simply moved out of range so that the radar beam is passing over top of them. Regarding your question as to whether these might be aircraft, that is unlikely to be the case. Most contrails left behind by aircraft are made of particles of ice that are too small to produce noticeable radar echoes.
Jul. 16, 2016 | Tags: general meteorology, thunderstorms, weather radar, wral.com

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