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Question: We've had a few windy days lately. There have been days where the prediction call for gusts up to 35 mph. I would imagine it isn't too hard to predict that it will be windy. But how hard is it to be real close on the actual wind speed and gust predictions? — Joseph L Freeman

Answer: As with any other aspect of the forecast, wind speed and gusts pose a challenge at times and we can't get them absolutely right every time. That being said, we do have some tools that have allowed us to be increasingly accurate with assessing the most likely wind speeds and gust potential. That includes several medium to high resolution computer models that have outputs that include estimates of maximum gusts over, for example, a one-hour or three-hour period. Even better, there are model outputs of detailed vertical distributions of wind speed and direction, temperature and dew point that allow us to inspect how wind profiles will interact with heating and instability, and can examine these profiles to find expected depth of turbulent mixing of the lower atmosphere and the altitude to which downward transport of momentum will likely be effective. In those cases, it is frequently the case that surface gusts will reach around 80-90 percent of the highest ambient wind speed found within that mixing depth. Using a blend of these various tools and techniques, recent forecasts calling for gusts to 20-30 mph, 35-45 mph, and so on have frequently worked out quite well.
Mar. 8, 2017 | Tags: maps & codes, winds

Question: When was our last measurable rain in Henderson? — Pam

Answer: At the time you wrote your question, the most recent measurable rain appeared to have occurred on February 15th, while there may have been a trace (less than .01") on the 17th. Since that time, measurable rain has occurred on the 25th and again (heavy at times) on March 1st.
Mar. 7, 2017 | Tags: past weather, rain

Question: I was just wondering if NC has ever had such an early spring before? I always love to see the red bud trees blooming as one of the first signs of spring, but this year it seems like everything has bloomed but the red bud. Today I noticed some Bradford pear trees in bloom! — Darlene

Answer: The "meteorological winter" that just ended turned out to be the third warmest on record for the Raleigh area in 130 years of observations, while February was the warmest on record. While we don't have exact records on timing of blooms and other spring initiation phenomena at hand, we suspect that similarly early springs probably occurred in association with some of the warmest combinations of Jan-Feb temperatures, the warmest five of which were in 1890, 1932, 2017, 1990 and 1949.
Mar. 6, 2017 | Tags: past weather

Question: With this being such a warm winter, what are your predictions for summer? In the past with such warm weather in February was it followed by an extreme summer? — Kacy

Answer: February 2017 turned out to have highest mean temperature for the month of any February on record for Raleigh, going back to 1887, while "meteorological winter" (December through February) was the third warmest over the same period. It turns out, however, that neither winter seasonal temperatures or February monthly temperatures serve as useful predictors for the summer that follows. The overall 1888-2016 correlation between winter temperatures and the following summer is only about .14, while that for the current "normals" period of 1981-2010 is just .11, while a value of 1.0 would indicate a perfect linear relationship between the two. February mean temperature and the following summer for 1888-2016 is correlated at a level of .07, while for the normal period the value is -.23, which would actually suggest that during that period there is a very weak association of warm February temperatures with cooler summers and vice versa. All that said, based on current climate model projections, the Climate Prediction Center has our area outlooked with our chance of a warmer than normal summer a little higher than our chance of a near normal or cooler than normal summer.
Mar. 5, 2017 | Tags: heat, normals, past weather

Question: I love your Q & A. Now would you please explain the phenomenon I have read about called "the green flash"? My understanding is that one can see it around sunrise at the beach. What weather conditions favor its observance and when is one most likely to see it? If we lived on the west coast of the US, would we see it at sunset instead of at sunrise? How long does it last? I've always wanted to see it, but never have. — "Hopeful"

Answer: While it sounds like a comic book character, the "Green Flash" is an infrequently seen optical phenomenon that occurs when the upper limb of the setting sun is both dispersively refracted (meaning the blue, green and red portions of the light are separated vertically) and magnified at the same time by certain profiles of temperature and moisture in the air. The magnification makes a normally invisible upper green rim briefly more prominent and fleetingly visible (usually just for a few seconds if at all).

It tends to be seen more easily over large bodies of water due to the distant, smooth horizon and the ability to see the sun's upper limb just as it reaches it's lowest visible point in the sky (where the chance of magnifying the thin green rim is greatest). On the other hand, it is very rarely seen over land, where trees, terrain, buildings and such are more prone to block the view. This being the case, as you noted it would be generally easier to see at sunrise along the east coast and at sunset from the west coast.

The "Green Flash" phenomena can be difficult to convey and explain clearly in a small space like this. There are some very good resources online that include photos of green flashes and related phenomena, good explanations for why and how they occur, and even some slow motion animations that help to illustrate the concept further. See aty.sdsu.edu/pictures.html and www.atoptics.co.uk/atoptics/gf1.htm for excellent examples.
Mar. 4, 2017 | Tags: atmospheric optics, cool sites

Question: Is there a way to predict when the nasty pine pollen might visit us this year with the wacky (not) winter weather we're having? We're about to put our house on the market and I want to try and avoid having it listed and have that nasty pollen visit in the same week! Our outdoor spaces will look terrible all covered in yellow dust. — Cindy Berben

Answer: We don't know of a confident means of predicting exactly when the pine pollen (main producer of the really big yellow-green powder) releases will begin or cease. The pine pollen peak can vary some year to year, but it usually is most noticeable for about 2-4 weeks, typically beginning as early as mid-March and ending as late as early May. Given that many spring indicators have responded to the warm January and February temperatures this year around 2 weeks early or so, it seems reasonable to think there's at least a chance at pine pollen starting up within a few days of the start of the the month, and we could potentially be in the early stages already when you see this answer. Once it does get underway, you may want to make a note of when the first sizable coating occurs, and figure on around 3-4 weeks after that time for it to wrap up.

We do make links to some 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.
Mar. 3, 2017 | Tags: cool sites, pollen

Question: Is there anymore chance of frost in eastern NC this year? — Anonymous

Answer: We are still well within the time frame for additional freezing air temperatures or the occurrence of frost on surfaces, so even in the wake of a warm finish to "meteorological winter," we can't rule out some additional periods of colder weather that could include frosts and/or freezes. At RDU, the "normal" last freeze date is April 6th, but there have been years when the last freeze was as early as March 12th there, or as late as May 10th. As this was being written, we have some indications of possible freezing temperatures or frost over central and eastern parts of the state around the weekend of March 4th and potentially another stretch of a few days toward the following weekend. Of course, this is subject to change, so do plan to check for temperature forecast updates as we go along.
Mar. 2, 2017 | Tags: cold, normals

Question: How strong were the wind gusts in my neighborhood on Saturday, February 25th in Durham? — Judi Clifton

Answer: A cold front that marked the boundary between very warm air over the region on Saturday and much cooler and drier air to the west moved in late Saturday, and surrounding that we had gusty winds during the midday hours and on into the early evening. A reporting station in the Durham area recorded a maximum gust of 28 mph, but a number of stations in the general area picked up on some stronger peak winds, with gusts at RDU reaching up to 39 mph, Roxboro 38, Henderson 37 and Chapel Hill 33.
Mar. 1, 2017 | Tags: past weather, winds

Question: I am doing a science project on how climate affects the growth of a tree. I have a cross cut of a tree and have counted the rings to determine it is 90 years old. I wanted to know if you knew where I can find the records for the last 90 years for the recorded annual precipitation in Holly Springs? — Brooke

Answer: It's unlikely you can dig up precipitation totals specific to Holly Springs, but you can find data that far back for the "Raleigh area" using the climate data web page at xmacis.rcc-acis.org. Just mouse over "single station" and select the "Seasonal Time Series" option. Then click on Options and select the variable precipitation. Finally under "Station selection," choose "Raleigh area" and click "Go" to see the data.

Feb. 28, 2017 | Tags: cool sites, past weather, rain

Question: When was the last time we set a record low in the Raleigh area? It seems like recently we've set a lot of record highs but no record lows here. — Bill

Answer: The most recent record low we could find at RDU was set on October 19, 2015 when the temperature dipped to 32 degrees. Since that time, we've tied or set new record highs on ten dates, most recently February 12 of this year, when we reached 83 degrees.
Feb. 27, 2017 | Tags: records/extremes

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