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Question: What was the weather like for May 8th, 1997? What was the temperature high and low, and if it rained how much did we get? Need to know what was the weather like for my birth date. — Scott

Answer: You can always check that kind of data using the "Almanac" link on our main weather page and then selecting a date in the "Get Historical Data" section.

Taking a look there, we found that day to be partly to mostly cloudy, with a trace of rain late in the evening. The low temperature in the morning was 45 degrees, followed by a warm afternoon that reached 80. It was a bit breezy, with south to southwest winds that gusted as high as 24 mph at times in the afternoon.

If you're also interested in seeing daily weather maps that applied for the day you were born, or other dates of interest, they are available from NOAA at www.lib.noaa.gov/collections/imgdocmaps/daily_weather_maps.html.
Aug. 20, 2016 | Tags: cool sites, maps & codes, past weather, wral.com

Question: I have severe allergies year round. Where can I find what tree or bush has bloomed out on a certain date to track my allergies by them? — Diane Reed

Answer: We can't think of an online source with specific, wide-ranging reports of local species in bloom. You might be able to contact your nearest Agricultural Extension Office for good information, and more generally you can get some rundowns on the typical timing of tree, grass and weed pollens from sites like www.hickoryallergy.com/what-are-the-pollen-seasons-in-north-carolina/. The National Arboretum in DC has a site showing a fairly detailed rundown of what bloloms when there, and based on climate differences we might run a week or two ahead of them here. You can see their list at www.usna.usda.gov/Education/blooming.html.

In addition, we do make links to some potentially pertinent information available here on our web site. Just click on the "resources" link near the top of the main weather page, and scroll down to select the second page of the resources list. There you'll find links labeled "Daily Pollen Count Forecasts," which takes you to a map where you can click your way to a 5-day forecast of allergen levels and types for a number of cities across NC, and "NC Division of Air Quality Pollen Count," where you can see a graph of recent pollen counts taken in Raleigh. Near the top of that graph is also a link to see the latest available tabular report, which includes a listing of what the top observed pollen species are, and also includes a link to a calendar where you can retrieve previous written reports for any date during the season.
Aug. 19, 2016 | Tags: pollen, weather & health

Question: I am the S-E U.S. ride planner for Rotary Club motorcycle riders. After many requests to ride our Outer Banks I am planning a fall ride from Nags Head inland to Cedar Island. Ferry to Ocracoke Island and ride up to Nags Head. What can I expect, weather-wise, for the first weekend of October? Can you suggest a more favorable weekend? — Carlton Pernell

Answer: This far in advance, of course, we can't address any specific weather systems that might affect the area at that time, but we can give you a sense of the climatology for the region near the beginning of October (this changes fairly slowly, so a couple weeks either side isn't far off, making it hard to suggest a more favorable weekend, apart from potentially having a "rain date" in mind a week or two later in October, if a short-notice postponement is practical for your group). At the beginning of October, the normal low temperature is around 62 degrees and the normal high around 76, through temperatures have ranges as warm as around 90 and as cool as the upper 40s in that time frame. On a given date in early October, measurable rain (.01" or more) occurs about once out of every three years, while a tenth of an inch or more occurs about once in four years. The predominant wind direction that time of year is from the northeast, with a mean winds speed of around 4 mph for the inland part of your route and almost 10 mph along the Outer Banks (though winds in the 10-20 mph range are not uncommon there). Good luck with your planning, and with the ride!
Aug. 18, 2016 | Tags: normals

Question: I understand the basics of cloud formation, but still have questions after doing some research. Why are cumulus clouds discrete "puffs"? In other words, if conditions are favorable for cloud formation why isn't the sky completely covered? — Michael

Answer: There is actually a spectrum of cumulus cloud varieties that can range from the cotton-ball style "puffs" you're asking about, to piles of cloud that cover much of the sky and flattened "stratoccumulus" that can become an overcast covering the entire sky. Which type you see on a given day or at a given time depends on the particular horizontal and vertical distribution of temperature and moisture in place, along with the large and small scale movement of the air (both the horizontal wind and the upward or downward vertical velocity). The small to medimum-sized puffy fair weather cumulus clouds, called "cumulus humilis," are favored when there is a fairly limited amount of moisture in the air, and when overall vertical motion of the air is quite weak or when there is a general slight sinking of the air, which acts to warm the air and favors mostly clear skies. When this is the case, strong solar radiation during the day heats the ground, causing the lower levels of air to become warm enough to rise. This heating tends to be some what uneven, and results in pockets of heated air that become buoyant and rise more rapidly then the air around them. These pockets of rising air (called thermals) are analogous to the pockets of rising water you'll see develop on a flat saucepan bottom when you boil water, in that there are numerous cores of strong upward motion that are balanced by areas of compensating, weaker downward motion in between. Within the thermals, the rising air cools due to the reduction in air pressure with increasing altitude. If there is just enough moisture in the rising air, condensation will occur when the air cools to the dew point and below, forming the base of the cloud. The conversion of water vapor to liquid droplets also releases heat to the air around the droplets, which reinforces the buoyancy and encourages the cloud to grow further upward (however, to complicate things, there is also entrainment of drier, cooler surrounding air that happens along the side and at the top of the the thermal and therefore at the edges of the developing cloud. This has a balancing effect that can limit the size or life span of an individual cloud. So, the basis reason for the discrete nature of the cumulus clouds is that under the right conditions, the upward motions that cause them to form are concentrated into buoyant thermals, while the air in between either sinks at a slow rate or doesn't move up or don much at all, leaving it cloud-free. It doesn't take too much of a change from this balance to cause the character of the clouds to become very different. Less humid air moving in at low levels can cause the thermals to lack sufficient moisture to form any clouds, for example, or increased moisture at low levels combined with a strong temperature inversion a few thousand feet up can cause the cumulus clouds that develop to spread out underneath that inversion to the point where there is a lumpy overcast in which the cloud elements join together and are no longer discrete.
Aug. 17, 2016 | Tags: clouds, general meteorology

Question: I suffer from chronic migraines. Often when a storm system is approaching I will get a headache. While migraine experts recommend not going outside when barometric pressure is rising, I am wondering, is there a way to build a room that is not affected by barometric pressure? — Michele

Answer: It should be possible to build a room that maintains a near constant air pressure by sealing the room as tightly as possible so that air enters and leaves the room only through ventilation ports that are controlled in a way that offsets any measured changes in outside atmospheric pressure. Rooms in certain medical, research and manufacturing facilities are commonly designed with some ability to maintain a positive or negative pressure relative to the outside. In this case, the idea would be to maintain negative pressure when outside pressure is high and vice versa. While in theory this is fairly straightforward, we doubt it would be a very practical or economical way to avoid headaches associated with changing pressure when you consider the types of construction materials and methods, along with sensors, controllers and responsive ventilation systems that would be required to control it tightly. You'd also have to consider whether there needed to be an airlock-type entry and exit system for others to come in and out of the room without disrupting the constant pressure environment. As you would imagine, typical home and commercial construction involves enough "leakage" into and out of the structure that changes in outside air pressure, due to traveling weather systems and changes in temperature or humidity, are reflected indoors very quickly.
Aug. 16, 2016 | Tags: weather & health

Question: Where on the website can I find the barometric pressure? — Sheila Moore

Answer: Just look on our main weather page near the top for the "Current Conditions" link. When you click it, you'll see the latest observations from both the RDU aiport and here at the TV station. Both of those will include a pressure reading.
Aug. 15, 2016 | Tags: instruments, wral.com

Question: I have a La Cross weather station but the readings are always a good 5 degrees higher than what is being reported in Raleigh and I live on the state line north of Oxford (usually cooler). I have the outside unit covered to avoid direct sunlight but feel this may still be my problem. Can you recommend a proper size for a sun shield to get more accurate readings. — Lee Brantley

Answer: We aren't sure the specifications and constriction of your particular station model. Most stations have the temperature sensor inside a white or light-colored louvered enclosure that prevents direct sunlight on the thermometer while allowing a free flow of air through the housing. This usually precludes any further need for shade. In your case, a couple of thoughts come to mind. We wonder if the 5-degree difference you mentioned holds true around the clock, or if it is only the case during the daytime when the sun is shining on the unit or its surroundings. We'd also recommend you try to take note of how you temperature compares to RDU (and to the less distant reading from the Henderson-Oxford airport (HNZ)) on days and nights when it is cloudy and the wind is blowing, since these conditions tend to minimize local variations of temperature due to topography, elevation and exposure to sun or open sky. It's also worth making sure your temperature sensor isn't located close to a source of heat, like an HVAC exhaust ro above a paved area, etc, that would make it trend differently compared to the ideal of being located in an open area about 5-6 feet above a grassy surface.

If the sensor unit is not enclosed in a ventilated cover as mentioned above, and it reads higher in the daytime but not at night (or even lower than other nearby readings at night), then perhaps obtaining or constructing an instrument shelter would help (search the web for "Stevenson Screen," or see the article at www.weather.gov/rah/edu2). If you find that on days and nights with widespread cloudiness and significant wind, your temperature still runs consistently 5 degrees higher than nearby sites, you may simply have a calibration issue, and in that case you would check the documentation for your weather station to find out how to adjust your system so that the thermometer reads 5 degrees lower than it does now.
Aug. 14, 2016 | Tags: instruments

Question: I've always wondered why thunderstorms usually only occur in the afternoon or evening hours. I could probably count on one hand the number of times I have seen a morning thunderstorm. Why are they such a rare occurrence? — Anthony C.

Answer: While thunderstorms can occur any time of day and any time of year, they are certainly far more prevalent during the warmer months and during the afternoon and evening hours. The primary reason for this is that thunderstorms are most likely when the atmosphere is unstable, meaning that there is an especially strong decrease in temperature from the lowest levels to higher altitudes. When this is the case to a sufficient degree, air that is forced upward in the lower atmosphere will tend to accelerate upward due to buoyancy, rather than resist that motion or tend to sink back to its original level. While temperatures tens of thousands of feet above the surface do vary somewhat as disturbance track across the area, in many cases those variations are rather subtle, especially during the summer. On the other hand, solar heating of the surface brings strong temperature variations daily, and when the surface temperature heats up sufficiently, the likelihood of enough instability to initiate and maintain thunderstorms increases considerably. The opposite occurs as surface temperatures cool through the evening, with storms losing this energy source and typically dwindling in coverage and intensity. While this "diurnal" pattern of storm formation and dissipation is very common from late spring to early fall, with localized formation due to pockets of heated air rising, it is also possible for storms to form due to the passage of strong upper level disturbances or jet streaks, and to upward motion generated by cold or warm fronts, and these type features can lead to thunderstorms that can develop or persist at night or in the morning.
Aug. 13, 2016 | Tags: general meteorology, thunderstorms

Question: I love thunderstorms AND I was wondering are we going to see severe thunderstorms any time soon? — Amy

Answer: Since we often place these answers into the queue for posting several days in advance of when you see the response, these kinds of questions have to include a disclaimer that you should check our latest online forecasts, TV weathercasts and the "Weather Feed" here on the site to see if any changes have occurred. At the time we're writing this, we've had several days with little in the way of severe storms, when you keep in mind that "severe" is defined by winds gusting to 58 mph or higher, hail of 1-inch diameter or greater, and/or a tornado. Storms can produce lots of lightning and very heavy rain without being technically classed as severe. The potential for organized or numerous severe storms appears to remain low through mid-August. Generally, severe storms are favored when there is a combination of strong wind shear, disturbances to trigger storms, unstable air, relatively low freezing levels and large amounts of low level moisture. A few of these ingredients have been present of late, but generally not in favorable combinations. At this time, it's hard to see a notably more favorable combination in models projections before the middle of the month, but again, as with any forecast, you'll want to check for any updates as new observations come in.
Aug. 12, 2016 | Tags: severe weather, thunderstorms, wral.com

Question: Terrible lightning storm Sunday night July 31st in Chatham County. Lightning looked like a constant strobe light flashing rapidly for over an hour. Did not see streaks, just intensely bright flashes rapidly without stop. Can you tell me why it looked like this, and maybe how many lightning flashes per minute? It was nothing like I've seen before. Thanks! — Jan

Answer: Thunderstorms can occur within a variety of ambient environments, some of which are more conducive to the combination of strong vertical motions and mixtures of ice and liquid particles that favor charge separation. On the evening you mentioned, and in other scenarios that result in "excessive" amounts of lightning (typically defined as a thunderstorm cell that is producing 12 or more lightning strikes per minute), there is usually a very unstable layer of air that coincides with an altitude range where temperatures are between about -10 and -30 degrees C, there is sufficient moisture in this layer to form a notable concentration of small hail, graupel, ice crystals and supercooled liquid droplets, and often there is some larger feature in the atmosphere (jet streak, frontal boundary, upper level disturbance, etc) that enhances the likelihood of storms and the intensity of vertical motions in those that form. On the night you asked about most of this applied, in particular the very unstable mid-level air and the presence of a jet streak and upper level trough just to our northwest. While we are able to monitor flash rates in real time, unfortunately we don't have archived information available on that, and so the particular rate over Chatham County that night isn't available to pass along.

You can see a more detailed discussion of a different "excessive lightning" event that includes a nice rundown of factors that forecasters look for to gauge the likelihood of such storms, at www4.ncsu.edu/~nwsfo/storage/cases/20080708/. In particular, see the sections on "Anticipating Extreme Lightning" and "Lightning Checklist."
Aug. 11, 2016 | Tags: cool sites, lightning, thunderstorms

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