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Recent Questions

Question: What kind of tree pollen is out now? — Guy Cangelosi

Answer: You wrote in on Sep 16, 2014 and when we checked the pollen report for that day from the NC Division of Air Quality we found they had measured about 145 grains per cubic meter of tree pollens, which falls in tothe HIGH category. The main tree pollen species identified in that report was elm. You can check the pollen concentrations and predominant pollen types from the "Weather Resources" page on our site. Just look for the "NC Division of Air Quality Polen Count" link, and when you get to the graph of pollen concentrations, look for the "See latest..." link beneath the title.
Sep. 21, 2014 | Tags: pollen, wral.com

Question: I have seen online about snow coming early. Maybe as early as the end of September and beginning of October. I was just wondering if this is true. I am due to have my baby November 2nd so I would like to be prepared as much as possible. — Lauren

Answer: Congratulations on the impending arrival. We've received a number of questions along these lines, and as near as we can tell it all traces back to a satirical article posted on a website called the Empire News that is entirely fictional and quotes a couple of non-existent people with titles like "doctor of global weather" and "Senior Administrator of Meteorologists." There is also a map of the U.S. covered largely in shades of blue that indicate above normal snowfall, and frequent references to "bread and milk."

As it turns out, so far climatic signals for the upcoming winter for the U.S. are rather mixed, with current projections for the our state, along with our neighbors just north and south, given equal chances of above, near or below normal temperature and precipitation, following an October that is expected to have a better than average chance of being above normal for temperatures while having "equal chances" regarding temperature.

Historically, the earliest measurable snow for Raleigh occurred on November 6th, 1953 and we have had a trace of snow as early as October 24th, which happened in 1910.
Sep. 20, 2014 | Tags: folklore, snow, winter weather

Question: Do you know if a El Nino is going to develop this fall? If it does, what does that mean for NC this winter? — Karen

Answer: Both of those questions have answers that are not really clear cut as yet, but sea surface temperatures in the central and eastern Pacific are running a little above average and subsurface water even more so. At this point, a weak to moderate El Nino is given about a 60-65% chance of developing as we head through October and on through the winter, while neutral conditions have about a 35-40% chance of occurring and La Nina conditions (cooler than normal ocean temperatures) less than a 5% chance.

If the El Nino does develop, the overall general tendency is for our state to see lower temperatures and more precipitation than normal, but there are some complications to note. First, some recent research indicates that the specific configuration of the El Nino is important - of the warmest sea surface temperatures are focused on the central equatorial Pacific, we have quite a good chance of below normal overall temperatures for the season. However, if the main body of warm ocean temperatures is focused on the eastern Pacific, on average the temperatures here aren't much off normal, but there is a lot of variability from one event to another. So far, it isn't clear which type of El Nino will evolve this time, and given the uncertainty that remains, the Climate Prediction Center currently has our state, along with VA and SC, with "equal chances" for above, near or below normal winter temperatures and precipitation.
Sep. 19, 2014 | Tags: el nino/la nina, winter weather

Question: Has the continental United States ever been completely cloud free in a satellite photo? Is this even possible? — Tony Rice

Answer: We can't flatly state that it has not, but we are not aware of such an image and consider it very doubtful that one would be possible, given the size of the land mass relative to traveling weather disturbances that would almost always exist over some portion of the country. In addition, the existence of moisture sources from the Pacific, Atlantic and Gulf of Mexico and various rivers and lakes would almost certainly lead to the formation of small patches of low-level cloud cover even in the unusual event that other cloud-generating disturbances were absent. There are some "cloud-free" satellite images around of the U.S. and the globe, but these are composites formed by stitching together images taken at different times when those smaller areas happened to be clear (or nearly so - some of these images turn out to have a stray clump of clouds hidden away here and there that were missed in the process of compiling the product).
Sep. 18, 2014 | Tags: clouds, maps & codes

Question: I enjoy browsing through weather models, particularly from NOAA.gov but when I look for the Euro models all I can find is models for pressure and winds at different levels. I was wondering where I can find a good website where I can see precip and all the other parameters as well. When I hear you mention about the Euro stats when it comes to rainfall and storm tracks I can never find that. — Steven

Answer: Information from the European Model is generally more restricted than that from the U.S. government, so most web sites that provide extensive charts, numbers and graphics from that model charge fees to do so. A few examples of places you can check European graphics include at Weather Underground (wunderground.com/wundermap) where you can find a model layer which includes quite a few parameters that can be displayed from the Euro (ECMWF) and several other models. There is no cost associated with this site. Examples of paid sites with a broader range of products from the Euro model include www.weatherbell.com and www.stormvistawxmodels.com/home.
Sep. 17, 2014 | Tags: cool sites, maps & codes

Question: How come there is all this talk about global warming, and we never got to 100 degrees here, and we had one of the coldest winters we had in a while? — Geoffrey

Answer: It's mostly a matter of temporal and spatial scale differences. A frequent development of upper level troughs that dipped into and across the central and eastern United States helped bring a number of cold or relatively cool air intrusions to our area both last winter and this summer, but in both cases such areas of cooling were balanced by warmer than normal temperatures in, for example, central Europe and eastern Siberia. These kinds of season-to-season or year-to-year weather variations will always occur, even if a long-term trend toward warming on a global scale (with its own variability along the way) continues in the background. There are lots of resources on the web to track global distributions of temperature, along with the overall global average and how it is changing month-to-month or over the years. One example of both those kinds of data can be found at nsstc.uah.edu/climate/.

Sep. 16, 2014 | Tags: climate change

Question: How is likelihood of precipitation calculated? The written description might say 80% but the hourly for the same time period never shows more than a 50% chance. — Linda

Answer: There are several methods to estimate a probability of precipitation numerically, the most commonly utilized being "model output statistics" and "ensemble forecasting." The first utilizes regression equations that relate the values of a large number of variables projected by computer models to the occurrence or non-occurrence of precipitation in the past under similar conditions, while the ensemble technique makes either multiple runs of a single computer model starting from slightly "perturbed" initial conditions (simulating the kinds of errors and uncertainties in observed data that arise due to instrument errors and incomplete sampling of the atmosphere) or by using a group of different models with varying methods of treating the atmospheric physics involved. A form of precipitation probability is then assessed based on the number of model runs that indicate measurable precipitation for a certain time frame as a fraction of all the model runs for that period. In both cases, it is generally the case that a probability will tend to be higher for longer spans of time, i.e., the probability of rain for a 12-hour period is usually higher than for a 3-hour period somewhere within that 12 hours, simply because there is more time to account for faster or slower systems and other sources of uncertainty. So in a formal, technical sense, it would not be unusual to have an overall probability for a day be higher than individual probabilities for smaller portions of the day.

All of that said, the probabilities that you usually see on weathercasts or on our web site have an added subjective element based on the forecaster's judgement. The forecaster takes all of the calculated probabilities into account, along with an overall assessment of analyzed observations, satellite and radar data and computer model projections of the overall weather pattern, to arrive at a level of confidence that measurable rain will occur. This subjective probability is entered for the daily value, and we also then fill a database of hourly values so that we can indicate a better chance in the morning and lesser chances later, etc. None of the individual hourly probabilities should be higher than the daily value, but they can be lower. A common example would be a summer day when a few widely scattered afternoon showers and storms are expected. The probability may be 5-10% through the morning, before climbing to 20-30% for the mid and late afternoon hours, and a 30-40% chance for the day as a whole.
Sep. 15, 2014 | Tags: general meteorology, rain, wral.com

Question: Is it just my imagination or does a close lightning bolt really cause a brief increase in rainfall intensity? — Chuck Britton

Answer: It's probably not your imagination, as the "rain gush" phenomenon has been noted by many observers and has been documented in various studies going back to the 1960s. The exact mechanism or combination of mechanisms that can lead to the lightning flash followed by a burst of heavier rain remains somewhat uncertain, although both mechanical (coalescence of existing droplets or sudden conversion of supercooled droplets to ice crystals followed by rapid growth, both due to compression and rarefaction imposed by passing acoustic waves associated with thunder) and electrostatic (rapid reversals of electric field orientation acting on charged hydrometeors, either to cause them to increase their tendency to coalesce rapidly) explanations have been suggested. Most studies in more recent years seem to favor the electrostatic effects more so than the acoustic.
Sep. 14, 2014 | Tags: lightning, rain, thunderstorms

Question: What kind of a winter do you think we will have this upcoming season? — Gary W Gilliam

Answer: It's difficult to draw strong conclusions so far, as signals from large scale climate modulating features remain fairly weak. For example, most indicators regarding Pacific sea surface temperatures continue to lean toward development of an El Nino pattern, but compared to earlier projections the confidence is lower (about a 60-65% chance El Nino develops compared to a 30-40% chance of remaining neutral) and the strength of the El Nino appears weaker than before. While a few private forecasters have leaned toward colder than normal conditions for the eastern U.S. once we reach December into the winter, the Climate Prediction Center so far is going with "equal chance" projections for both temperature and precipitation in our part of the country due to the continued uncertainty about both the strength and type of El Nino pattern that may develop.
Sep. 13, 2014 | Tags: el nino/la nina, winter weather

Question: Does this summer's seemingly cooler weather mean we are more likely to have an early frost? — Anonymous

Answer: It doesn't really give us much to go in terms of when the first frost may occur, as there are competing indications. We did have several intrusions of cooler air through the course of the summer and if fairly strong fronts continue to arrive more frequently than usual, that might lead to an early frost. However, this pattern is certainly subject to change, and the Climate Prediction Center outlook for the September-December period is for a better chance of above normal temperatures than for normal or below normal temperatures. Of course, it is also quite possible that even if temperatures average above normal, that a brief round of colder temperatures could lead to some frost prior to the average date.

One additional point of interest here - although our summer featured considerable rain and cloudiness, with multiple intrusions of relatively cool air, on average we were actually a bit closer to the warm end of the range of past summer temperatures than to the cool end. The mean temperature for July-August for Raleigh was tied for the 26th coolest since 1887 and tied for 23rd warmest. The average high temperature for the summer tied for 32nd coolest and 30th warmest. We did have a string of notably warmer summers starting in 2005 that made these last two seem a good bit cooler by comparison.
Sep. 12, 2014 | Tags: dew/frost, normals, past weather

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