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Changing Skies Over Central North Carolina VOLUME 10, ISSUE 1 SPRING 2013 NOAA’S NATIONAL WEAT HER SERVICE RALEIGH, NC Understanding a Derecho: What Is It?

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Changing Skies Over Central North Carolina VOLUME 10, ISSUE 1 SPRING 2013 NOAA’S NATIONAL WEAT HER SERVICE RALEIGH, NC Understanding a Derecho: What Is It? Changing Skies Over Central North Carolina VOLUME 10, ISSUE 1 SPRING 2013 NOAA’S NATIONAL WEAT HER SERVICE RALEIGH, NC Understanding a Derecho: What is it? INSIDE THIS One of the biggest severe and record gusts were rec- duce destruction similar to ISSUE: weather events of last year orded at Fort Wayne, IN, that of tornadoes, the damage was the derecho that crossed Zanesville, OH and Hunting- typically is directed in one Forecast 2 the Midwest into the Mid ton, WV. While the derecho direction along a relatively Formats Atlantic states in late June. only clipped North Carolina, straight swath. As a result, The storm affected 11 states there was plenty of buzz for the term "straight-line wind Wireless Emer- 3 including IL, IN, OH, PA, KY, the next several weeks and damage" sometimes is used gency Alerts WV, MD, VA, NC, DE and the buzzword was “derecho.” to describe derecho damage. NJ. Unfortunately, 22 people Soon every thunderstorm By definition, if the wind dam- New NWS 3 were killed, mostly from was being called a derecho. age swath extends more than Director trees falling on homes and So as we approach severe 240 miles (about 400 kilome- vehicles. Over 5 million peo- season we thought this would ters) and includes wind gusts Precipitation 4 ple were without power. This be a good time to talk about of 58 mph (93 km/h) or Modeling was the first derecho to real- derechos and their various greater along most of its length, then the event Drought Update 8 may be classified as a derecho. StormFest 9 Wind Strength By definition, winds in NWS Welcomes 10 Blake Ellis a derecho must meet the National Weath- er Service criterion for severe wind gusts (greater than 57 mph) at most points along the derecho path. But in stronger derechos, winds may exceed 100 mph. For exam- ple, as a derecho roared through northern Wisconsin on July 4, 1977, winds ly capture widespread major characteristics. media attention as it rolled of 115 mph were measured. through big markets like Chi- Definition More recently, the derecho cago, Indianapolis, Baltimore, that swept across Wisconsin Washington D.C. and Tide- A derecho (pronounced simi- and Lower Michigan during water, VA. This was a pro- lar to "deh-REY-cho") is a the early morning of May 31, gressive derecho that cov- widespread, long-lived wind 1998 produced a measured ered 600 miles in 10 hours storm that is associated with wind gust of 128 mph in east- averaging 60 mph. Wind a band of rapidly moving ern Wisconsin, and estimated speeds within the derecho showers or thunderstorms. gusts up to 130 mph in gusted from 80 to 100 mph Although a derecho can pro- (continued on page 6) P A G E 2 Print and Mobile Options for Your Forecast The NWS office in Raleigh is vance. That is a lot of infor- print and display their neigh- always searching for new mation! This forecast infor- borhood forecast for their and better ways to serve the mation can be presented in customers, employees, and people of central NC. In a variety of ways, tailored students on a daily basis. addition to our dense obser- for specific users (such as Here is how to get to this vation network, detailed fire weather partners) or page: aviation forecasts, and full for general use. One such suite of watch/warning/ way is the Printable Fore- 1.) Go to www.weather.gov/ advisory products, we pro- cast Page – a simple, unclut- raleigh (our local web page). duce hourly forecasts of tered, single-page display of 2.) Click on your location on temperatures, humidity, rain the 7-day forecast. This is a the map to see your local chances, wind, and numer- great way for businesses, forecast. ous other weather parame- hotels, schools, government (continued on page 5) ters, all out to 7 days in ad- agencies, and others to “The NWS office in Raleigh is always searching for new and better ways to serve the people of Central NC.” An Example Printable Forecast Page From NWS Raleigh CHANGING SKIES VOLUME 10, ISSUE 1 P A G E 3 Wireless Emergency Alerts on Your Mobile Device Imagine this: You’re driving vice no matter where you are. won’t have to open it up to down the highway, humming read it. NOAA’s NWS will broadcast along to your favorite tunes, warnings via WEA for weather The Wireless Emergency when the cell phone stowed in emergencies that are most dan- Alert system relies on “best- your bag suddenly makes a gerous to life and property: tor- effort” networks, so delivery strange noise. To investigate, nadoes, flash floods, hurricanes, of alerts at a given place and you take the next exit and safely extreme wind, blizzards and ice time is not guaranteed. The pull over to check the screen. storms, tsunamis, and dust new alert system is not a re- Good thing you did: Your phone storms. Severe thunderstorm placement for other alert sys- just alerted you to a tornado a warnings will not be part of the tems, and you should not rely on it as a sole source of emer- gency information. A weather alert sent through WEA is intended to notify the public that a warning has been issued and that you should seek addi- tional information. Remember: Not all phones are capable of An Example of a Wireless Emergency Alert receiving Wireless Emergency Alerts. few miles away in the same initial rollout of broadcast mes- Cell service customers can county you’re driving through. sages because they are so fre- opt out of weather alerts, but Sound plausible? It is. Last June, quent; however, these will con- we strongly discourage you America’s wireless industry tinue to be broadcast by NOAA from doing so. These weather rolled out a new nationwide text Weather Radio, media outlets alerts are a vital public service emergency alert system, called and Internet-based services. that ultimately helps America Wireless Emergency Alerts When your phone receives a become a more weather- (WEA), which will warn you WEA message, it will alert you ready nation. Armed with late when weather threatens. with a unique ring tone and vi- -breaking weather warnings, The text alert service is free and bration. These 90-character people will have the timely automatic – there’s no need to messages are a “heads up” to information they need to sign up or download an app, and prompt you to seek further in- make smart decisions about this service will not use any of formation about the threat. how to protect themselves, your paid text messages or The message will look like a their families, their friends and minutes. As long as your cell text, but it’s not a traditional neighbors, and their personal phone is WEA-capable, you’ll get text message most people are property. wireless alerts for the most dan- used to. This text message will -Nick Petro gerous types of weather from automatically pop up on your NOAA’s National Weather Ser- cell phone’s screen and you P A G E 4 Do More Models Make it Merrier? A winter storm from the past Feb- ruary provides a good example of the utility of en- sembles. Predicted liquid equivalent precipitation from the SREF members and the SREF mean for the February 16-17 winter storm is shown at left. The plot is viewed from right to left with amount of precipitation in tenths of an inch shown in the verti- Short Range Ensemble Forecast (SREF) members showing various cal axis and the “A winter storm forecasts for liquid equivalent precipitation amounts. color of the lines indicating likely from the past A weather forecast is an esti- al forecasting that allows for precipitation type. At about mate of the future state of a rapid and scientifically- the same time as the SREF February provides a the atmosphere. It is created based comparison of multiple output shown at left, one of good example of the by estimating the current model forecasts. The ensem- our primary models, the state of the atmosphere using ble forecasts give the fore- NAM, indicated 0.03” of liq- utility of observations and then calcu- caster a much better idea of uid equivalent precipitation lating how this state will what weather events may during the event, while the ensembles..” evolve in time using a Nu- occur at a particular time. By other primary model, the merical Weather Prediction comparing these different GFS, indicated 0.34”, a big (NWP) computer model. forecasts the forecaster can spread between the two. The Forecasters have always un- decide how likely a particular SREF output suggests that derstood the value of exam- weather event will be. If the confidence in precipitation ining multiple NWP forecasts forecasts vary a lot then the amount is low as its members to help produce a more relia- forecaster knows that there have values ranging from ble forecast. Instead of run- is a lot of uncertainty about 0.05” to 0.78”. A majority of ning just a single forecast, an what the weather will actual- the SREF members are clus- ensemble approach runs the ly do, but if the forecasts are tered in the 0.10” to 0.30” computer model a number of all very similar forecasters range with a few outliers times from slightly different will have more confidence in indicating much greater starting conditions, model predicting a particular event. amounts. In the end, SREF frameworks, or model config- Forecasters at the NWS Ra- mean value indicated 0.28” urations.
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