Long-Time Collaborator Larry Lee Retires from the NWS Greenville-Spartanburg

larry.leeLaurence G. Lee, Science and Operations Officer at WFO Greenville-Spartanburg in Greer, SC, will retire on 2 August 2014 with 41 years of Federal service. Larry, a native of Hendersonville, NC, received his B.S. in meteorology from the University of Wisconsin-Madison in 1969 and a M.S. in meteorology from the University of Oklahoma in 1972. Larry’s career included stops at the National Center for Atmospheric Research (NCAR) in Boulder, National Climate Data Center (NCDC) in Asheville, WSFO Anchorage, WSFO Atlanta, WSFO Raleigh-Durham, WSFO Louisville and WFO Greenville-Spartanburg.

Larry made tremendous contributions to the science of meteorology, especially across the Southeast. He authored and co-authored reports, summaries, and articles in Monthly Weather Review, Weather and Forecasting, Journal of Atmospheric and Oceanic Technology, Bulletin of the American Meteorological Society, National Weather Digest, Physical Geography, and Landslides. He has collaborated in projects with UNC-Asheville, UNC-Charlotte, Clemson University, Appalachian State University, NC State University, the NC Geological Survey, and neighboring WFOs. He has greatly contributed to the infusion of science into forecast operations and the professional development and mentoring of many NWS meteorologists. His science smarts and down to earth personality have made him a key contributor to the collaboration for improved meteorology in the mid-Atlantic and southeast and he will be missed.

Thanks to Larry Gabric for contributing to this biography.

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Change in NWS Doppler Radar Scanning Strategy Will Provide Much Needed Data and Should Lead to Improved Warnings

A new software upgrade installed at the National Weather Service (NWS) Raleigh Doppler radar (KRAX) today, July 8th, is expected to have a significant impact in severe weather operations. Around two-thirds of all NWS Doppler radars have been upgraded as of today, with the rest likely occurring during the next few months. You can view the current build of each NWS radar here (radar’s with the upgrade have the RPG build listed as “14.1″). The software change will allow the WSR-88D radar to obtain the lowest level radar scan more frequently during severe weather events.

With this upgrade, a new feature called SAILS (Supplemental Adaptive Intra-Volume Low-Level Scan) will enable the radar to insert an additional 0.5 degree scan in the middle of a volume scan (see the illustration below for more details). Currently, the WSR-88D radar completes its lowest scan in 3 to 4.3 minutes (during severe weather), depending on the range of the storms from the radar. With SAILS, the radar can now perform this low-level scan every 1.9 to 2.5 minutes, obtaining a 0.5 degree scan almost twice as frequently as before and providing NWS meteorologists with the ability to observe rapidly changing weather phenomenon more frequently and issue more timely severe weather warnings.

A training presentation was provided to NWS Raleigh partners detailing some of the changes with the build, it can be accessed here.  The Warning Decision Training Branch (WDTB) has other training resources that are available online as well – RDA/RPG Build 14.0/RPG Build 14.1 training.

RAH.SAILS.infographic

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Data Sets Provided by Collaborative Research Partners to Provide a Unique Look at Arthur

The 449MHz-Wind Barb Plot for New Bern , NC (click to open real-time data).

The 449MHz-Wind Barb Plot for New Bern , NC (click to open real-time data).

The HMT-Southeast Pilot Study (HMT-SEPS) is a field project intended to be the first step in examining various scientific questions across the Southeast. The HMT-SEPS project will largely focus on quantitative precipitation estimation (QPE) in western portions of North Carolina with some observational resources placed or supported in central and eastern North Carolina and other portions of the Southeast.  The HMT-SEPS project has an instrumentation package in New Bern , NC that includes a 449 MHz Digital Wind Profiler, a surface meteorological observation package, and other equipment. New Bern is located rather close to the forecast track of Arthur and these data sets will be interesting to watch during the event.

 Coastal Emergency Risks Assessment-CERA Real-Time Storm Surge and Wave Visualization Tool (click to open real-time data).

Coastal Emergency Risks Assessment-CERA Real-Time Storm Surge and Wave Visualization Tool (click to open real-time data).

Another interesting data set to watch will be the Coastal Emergency Risks Assessment- CERA Real-Time Storm Surge and Wave Visualization Tool. The CERA tool was created at Louisiana State University in collaboration with the Department of Homeland Security Coastal Hazards Center of Excellence housed at the University of North Carolina at Chapel Hill. The information shown on the  CERA websites is produced by a system that generates real-time surge and wave guidance based on two models: ADCIRC for surge and Simulating Waves Nearshore (SWAN) for waves. ADCIRC and SWAN produce different output than what you get with SLOSH and wave models that you currently view because they use different inputs, are coupled, or dependent, on each other’s data, have different science within the model, and are run at different resolutions.

Coastal Emergency Risks Assessment-CERA Real-Time Storm Surge and Wave Visualization web site.

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TS Arthur and Frontal Interaction – Surface Analysis Best Practices

The combination of Tropical Storm Arthur passing close to the Carolina coast and a cold front approaching from the west this week may lead to some additional mesoscale forecast concerns, namely TC-frontal interaction and qpf.  It is well-known that the presence of a frontal boundary prior to and during the landfall of a tropical cyclone can alter, sometimes dramatically, the resulting rainfall distribution. In the upcoming event, some models are already indicating a potential PRE (Predecessor Rain Event) over the Mid-Atlantic States and New England.

During the recent CSTAR Tropical Cyclone/QPF project, there were numerous discussions on how to  anticipate and identify surface front features that may play an important role in modifying the precipitation distribution with a land-falling storm.  The research group, along with invaluable help from RAH forecasters, created a list of surface analysis tips and techniques, many of which can be directly applied to a tropical event.  In light the impending potential interaction with TS Arthur, this is a prime opportunity to share the guidance.  Please note that this is by no means a complete list of techniques, as there are countless ways to recognize/identify boundaries in observations and data.  If you have other methods that are not listed, please feel free to share!!

Surface Analysis Best Practices (click to view pdf)

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Tropical Depression One Brings an Opportunity to Test CSTAR Research to Operations Initiatives

The 2014 version of the TCMWindTool includes two CSTAR supported components, the GFE wind reduction methodology and the NC State bias correction.

The 2014 version of the TCMWindTool includes two CSTAR supported components, the GFE wind reduction methodology and the NC State bias correction.

A recently completed Collaborative Science, Technology, and Applied Research (CSTAR) project with North Carolina State University and over a half dozen WFOs in the Southeast examined ways to add science and improve inland wind and wind gust forecasts associated with tropical cyclones.  One outcome of this project is the development of a GFE methodology in which forecasters create grids of wind reductions (from the NHC TCM guidance) and wind gust factors (applied to the wind to determine the wind gust).  This methodology was initially tested last year with limited but favorable results. This approach should result in improved forecasts with better inclusion of science as forecasters now have the opportunity to vary these grids both spatially and temporally, they can now more efficiently collaborate across WFO boundaries resulting in improved consistency, and the grids are persistent from shift to shift.  This year, forecasters now have an opportunity to evaluate an experimental bias correction scheme for the NHC TCM product that was developed at NC State. This bias correction attempts to account for systematic biases in the TCM product that become problematic when forecasters downscale the NHC TCM product into 2.5 km2 gridded wind forecasts.

These two CSTAR outcomes (the wind reduction methodology and the NC State bias correction) have been incorporated into the TCMWindTool for operational evaluation this year by six NWS Weather Forecast Offices (WFOs) in the Southeast. The development of Tropical Depression One in the Atlantic on Monday evening provided these WFOs with the first opportunity to begin using these CSTAR research to operations deliverables.

The first image below is the wind forecast using these new CSTAR supported techniques to produce a meteorologically sound, consistent forecast by WFOs AKQ, MHX, ILM, and RAH.  The second image shows the Wind Reduction Factor grid used by the WFOs to account for the decrease of wind speeds because of friction over land, fetch, air mass stability, and other influences. The ability to edit this reduction factor over time and space and to see the values used by other WFOs is a great asset to the forecaster.

Wind forecast for portions of the Carolinas and Virginias valid at 06 UTC on 04 July.

Wind forecast for portions of the Carolinas and Virginias valid at 06 UTC on 04 July.

Wind Reduction Factor grid valid at 06 UTC on 04 July.

Wind Reduction Factor grid valid at 06 UTC on 04 July.

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TC Wind Cluster Office Update Conference Call 6/25/14

Call Attendees: Reid Hawkins (WFO Wilmington), Jonathan Blaes (WFO Raleigh), John Billet (WFO Wakefield), Carin Goodell (WFO Morehead), Scott Kennedy (WFO Morehead), David Glenn (WFO Morehead), Frank Alsheimer (WFO Charleston), Bob Bright (WFO Charleston), Bryce Tyner (North Carolina State University)

Members of the Wilmington, Raleigh, Morehead City, Charleston, and Wakefield National Weather Service offices will be testing a set of new TCMWind procedures for the 2014 tropical cyclone season. The tested procedures are based on results of the CSTAR inland winds project and are featured changes in the TCMWindTool. In particular, the TCMWindTool has the additional options of applying a climatologically-based error correction of the National Hurricane Center TCM product as well as the added use of WindReductionGrids. The attached slides describe the new process of developing the sustained wind speed and gust grids based on these new options.

cc_062514

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An 8 Year Lightning Climatology of North Carolina

This week is Lightning Safety Awareness Week across the United States.  North Carolina is no stranger to the dangers of lightning; “Storm Data” ranks North Carolina sixth in the U.S. for the number of lightning fatalities between 1995 and 2010. This week the Insurance Information Institute reported that North Carolina ranked third in the nation in the number of lightning-related insurance claims filed by property owners.  To further investigate this problem, NWS Raleigh constructed an eight year (2003-2010) cloud-to-ground (CG) lightning climatology using lightning data from the National Lightning Detection Network (NLDN) to explore the influences of the season, time of day, various geophysical features, and mesoscale processes on the spatial and temporal distribution of CG lightning across the state.

2003-2010 average annual flash density in flashes/km2.

2003-2010 average annual flash density in flashes/km2.

An 8-year average annual flash density analysis for North Carolina was created and it shows some interesting features.  The largest flash densities are located in the southern Coastal Plain, the coastal region, and the Sandhills where sea breeze boundaries, the Sandhills convergence zone, and the Piedmont trough provide a focus for convection. The greatest flash density across the state is located in the southern Coastal Plain with the lightning capital of NC located near Tabor City, located south of Lumberton, near the SC border. The elevated amounts of lightning across the southern coastal region likely results from a coastline orientation that promotes inland penetration and collisions of sea breeze boundaries. The maximum in the Sandhills region likely results from enhanced surface convergence along the clay-sand soil transition zone on the western perimeter of the region referred to as the Sandhills convergence zone (Wootten et. al 2010). In addition, the Piedmont trough (Koch and Ray, 1997) can be identified with the localized maximum that stretches from northeast to southeast from Raleigh to Charlotte with a local minimum just to the west.

Percent of annual flashes that occur in a month.

Percent of annual flashes that occur in a month.

An examination of monthly CG lightning statistics reveals that the greatest amount of lightning occurs in July, comprising 33% of the yearly amount, followed by 23% in August and 22% in June.  June, July, and August account for 78% of the annual statewide lightning while November, December, January, and February combine for only 1% of the annual total. The monthly percentage of all flashes loosely resembles a bell shaped distribution with a more gradual increase in flashes during the spring and a dramatic decline in flashes from August to September likely resulting from the climatologically drier fall.

Statistical point data was computed for eight selected cities using a 25 km2 grid box centered over the associated airport location (AVL, CLT, ECG, EWN, FAY, GSO, ILM and RDU). Examining the location specific daily data reveals that Wilmington has the greatest number of total strikes per year while Greensboro has the fewest.  The top three locations in number of strikes per year; Wilmington, Fayetteville, and New Bern are located in southeastern NC where climatologically there is the greatest instability and sea breeze boundaries, the Sandhills convergence zone, and the Piedmont trough provide local foci for convection. Asheville has the greatest number of days with lightning strikes (nearly 57 which is 5 more days than the next city, Wilmington). Interestingly, Asheville had the second fewest number of strikes per year with Wilmington having the most. All 8 locations experience days with excessive lightning with 50% of the total annual lightning occurring on just 4 to 6 days.

Chart of daily lightning statistics from 2003-2010 for 8 cities across NC that includes the total number of CG lightning strikes, average number of strikes per year, average number of days per year with strikes, as well as exceedance and daily threshold counts.

Chart of daily lightning statistics from 2003-2010 for 8 cities across NC that includes the total number of CG lightning strikes, average number of strikes per year, average number of days per year with strikes, as well as exceedance and daily threshold counts.

Percent of annual flashes that occur during a particular hour.

Percent of annual flashes that occur during a particular hour.

The statewide percent of all CG strikes per hour indicates that the average peak hour is 21 UTC or 5pm EDT when 12% of all CG strikes occur.  More than 59% of all strikes occur between 18-23 UTC while the fewest number of strikes occur during the 13 UTC hour.

Average flash density in flashes/km2 for a specific hour.

Average flash density in flashes/km2 for a specific hour.

Hourly flash density plots show an interesting evolution in the diurnal cycle of thunderstorms in NC. The hourly charts show that lightning typically develops across the mountains and the favored sea-breeze locations along the southern coast during the 17 and 18 UTC hours when local forcing for ascent from differential heating in the mountains and sea-breeze convergence along the coast helps initiate convection. During the next few hours, lightning likely connected to the sea-breeze moves inland slowly while lightning across the southern mountains near Asheville moves east toward Charlotte and Hickory. Eventually the signal becomes less clear as the lightning converges toward the central part of the state toward evening.

The diurnal evolution described above can also be seen in hourly lightning counts at Asheville, Raleigh and Wilmington. Not the very focused distribution of hourly lightning at Asheville and a somewhat similar but not as focused distribution at Wilmington with both locations showing a dramatic ramping up of lightning in the early afternoon.  In contrast, Raleigh shows a much flatter distribution and more general increase and decrease owing to the varied mechanisms for initiating and maintaining convection.

Average hourly lightning counts at Asheville, Raleigh and Wilmington.

Average hourly lightning counts at Asheville, Raleigh and Wilmington.

Examining the location specific hourly data reveals that the peak hour at Asheville and Wilmington occurs the earliest, at 19 UTC or 3pm EDT.  The three locations in central NC, Charlotte, Greensboro, and Raleigh had the latest peak time, averaging around 22 UTC or 6pm EDT.

Chart of hourly lightning statistics from 2003-2010 for 8 cities across NC that includes the hour with the most CG lightning strikes, the hour with the fewest strikes, the percent of strikes in the peak hour, and the percent of strikes during various 4 hour windows.

Chart of hourly lightning statistics from 2003-2010 for 8 cities across NC that includes the hour with the most CG lightning strikes, the hour with the fewest strikes, the percent of strikes in the peak hour, and the percent of strikes during various 4 hour windows.

Additional Information

A summary of the lightning climatology is available in this presentation:
http://www.erh.noaa.gov/rah/science/presentation.20120315.central.nc.ams.lightning.climo.ppt

Additional analysis images including statewide seasonal, monthly and hourly charts along with other imagery from the project are available at the following URL:
http://www.erh.noaa.gov/rah/lightning/

References

Koch, S. E., and C. A. Ray, 1997: Mesoanalysis of summertime convergence zones in central and eastern North Carolina. Wea. Forecasting, 12, 56–77.

Wootten, A., S. Raman, and A. Sims, 2010: Diurnal variation of precipitation over the Carolina Sandhills region.  J. Earth Syst. Sci. 119, No. 5, October 2010, pp. 579–596.

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