An Example of How GOES-14 Super Rapid Scan Operations for GOES-R Helped During Warning Operations at NWS WFO Raleigh, NC on 18 August 2014

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) was operating over North Carolina on Monday August 19th during severe weather operations at WFO Raleigh. During the event, there were several instances where having the increased temporal resolution was very advantageous during radar interrogation and warning operations. At around 2000 UTC a multi-cellular broken line of showers and thunderstorms approached the Greensboro and Winston-Salem area from the northwest (Fig. 1).

KRAX 1951 UTC 18 AUG 2014

Figure 1. KRAX reflectivity data from 1951 UTC 18 Aug 2014 showing a multi-cellular line of convection moving into the Triad. A perceived boundary is indicated on the image.

 

 

 

 

 

 

 

 

 

 

 

 

 

Based on differential heating patterns, surface observations, and the linear structure to the convective pattern, it was clear that there was some kind of boundary in the area, but it was not clearly defined by surface observations (too far apart) or by radar observations (large gaps between cells). By looking at the one-minute Super Rapid Scan data, the boundary was clear and continuous in the cloud pattern, stretching from Iredell County northeastward to Orange County (Highlighted on Fig. 2).

GOES-14 Visible Imagery 1953 UTC 18 August 2014

Figure 2. GOES-14 visible image from 1953 UTC 18 AUG 2014 showing a boundary across the northwest Piedmont region of NC. An overshooting top of a storm producing a waterspout can also be seen over the Pamlico Sound.

 

An overshooting top can clearly be seen over Alamance County indicating a developing storm prior to it showing any severe characteristics on radar. This overshooting top seen at 1953 UTC would identified 45 minutes before a severe thunderstorm warning was issued on the same cell. In addition, the location of a meso-low was also clear as lower altitude clouds were seen traveling northward to the east of the storm, and southward to the west of the storm, indicating the counterclockwise motion seen with a low pressure system. Also of note in figure 2 is the special marine warning over the Pamlico Sound. Here an overshooting top can also be seen from a storm producing a waterspout at the time in the Newport/Morehead City, NC county warning area.

The motion of the boundary was easily traceable with subsequent one-minute visible images and were used to anticipate where future convection might occur. A bit later in the event, it was clear that the western side of this boundary began to accelerate to the southeast. Meanwhile, the eastern side remained fairly slow moving and toward the south. A small meso-low could be seen moving through the boundary with an area of strong low-level convergence over northern Alamance County (Fig. 3).

GOES-14 Visible image from 2038 UTC 18 AUG 2014

Figure 3. GOES-14 Visible image from 2038 UTC 18 AUG 2014 showing progression of a boundary along with a surface meso-low near Greensboro, NC.

The result was a strong thunderstorm that was deemed worthy of a severe thunderstorm warning with radar reflectivity presentation of a large 65 dBz reflectivity core up to 20 kft, indicative of potential severe hail (Fig. 4).

4.0 degree KRAX Reflectivity from 2039 UTC 18 AUG 2014

Figure 4. KRAX 4.0 degree reflectivity image from 2039 UTC 18 AUG 2014, showing a 65 dBz hail core near 20 kft over Northern Alamance County, NC.

So how did having the Super Rapid Scan Operations for GOES-R impact our warning operations here at WFO RAH? First, knowing where the boundary was at all times, how fast it was moving, and in what direction allowed us to narrow down our area of focus for potential severe convection. This boundary was also a catalyst for some weak low level rotation within several small cells along the NC/VA border. Knowing how the boundary was evolving led us to begin to see small features in the flow, such as the meso-low pressure and associated area of low-level convergence on the east side of the low which led to the growth of the storm over Northern Alamance County.

Did having the Super Rapid Scan push us over the edge to warn on a storm before radar indications of its severity? No, but warning operations involve so much more than that one warn/no warn decision point. So much of warning operations hinges on forecaster confidence in their decision and evidence leading up to the issuance of a warning. While the greater temporal resolution of the satellite imagery did not ultimately make us warn based on that data alone, it certainly increased our confidence in our warning decisions and ultimately made the process more efficient because that evidence was coming in quicker than ever before. That alone made having the Super Rapid Scan data very valuable and very worthwhile, and something that should be able to be built into everyday operations at NWS weather forecast offices around the country.

To see SRSOR data from other cases please visit http://cimss.ssec.wisc.edu/goes/srsor2014/GOES-14_SRSOR.html.

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GOES-14 will be in Super Rapid Scan Operations with imagery over the Carolina’s and Virginia’s available today and Monday

View of

GOES-14 Super Rapid Scan visible satellite imagery from 1441 UTC on 17 August viewed via the CIRA web site.

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) began on 14 August and will continue for through 28 August. Super Rapid Scan Operations (SRSO) will provide 1-minute imagery to support multiple research and GOES-R/S user readiness activities. The SRSO domain is usually selected a day or two in advance. The domain schedule along with selected imagery from prior days is available at:  http://cimss.ssec.wisc.edu/goes/srsor2014/GOES-14_SRSOR.html#sched_and_movies

Regional partners were able to have the SRSO domain centered such that it will include portions of the Carolina’s and Virginia’s today and with an even more favorable location on Monday. This will be a great opportunity to view the data over our region. For the first time, forecasters at WFO Charleston, SC and Raleigh, NC will have access to some of this data in real-time in AWIPS.

Imagery including visible, infrared, and water vapor is available on the web at the links below…

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NASA SPoRT LIS Soil Moisture Assessment – Application for the U.S. Drought Monitor

NASA SPoRT has developed a real-time configuration of the NASA Land Information System (LIS) that runs over much of the central and eastern United States at 3-km grid spacing.  The LIS produces several products including a suite of soil moisture products that can be used as a tool for assessing drought and flooding potential.  WFO Raleigh along with WFOs Houston and Huntsville are participating in an assessment of these products during August and September. SPoRT created a couple of training modules (LIS Primer module and LIS Applications Module) to prepare NWS forecasters for this new dataset.

There are four LIS soil moisture products that are made available to WFO Raleigh forecasters in AWIPS-2 and which are available online at http://weather.msfc.nasa.gov/sport/case_studies/lis_SEUS.html for the Southeast and http://weather.msfc.nasa.gov/sport/case_studies/lis_NC.html for North Carolina.  The products include:

  1. Volumetric Soil Moisture (0 to 10cm) [SOIM0-10]
  2. Below Ground Relative Soil Moisture (0 to 10cm) [RSOIM]
  3. Below Ground Relative Soil Moisture (0 to 200cm) [INT-RSOIM]
  4. Below Ground One Week Change in Column Relative Soil Moisture (0 to 200cm) [RSOIMDIFF]

Each week, WFO Raleigh Hydrologist Michael Moneypenny serves as a member of the North Carolina Drought Management Advisory Council (NCDMAC) which provides recommendations to the U.S. Drought Monitor (USDM).  The USDM consists of a consortium of academic and government partners, including the University of Nebraska-Lincoln National Drought Mitigation Center (NDMC) and various other federal and state agencies.

WFO Raleigh started receiving the LIS soil moisture products in July and evaluating the products in August. The products were first used during the weekly NCDMAC collaboration call on Tuesday August 5th.  The LIS data was used to expand the D0 (abnormally dry) category at a sub-county level into portions of Robeson and Scotland Counties. In particular, the 0-200 cm Relative Soil Moisture Weekly Change product was used to show changes in the deep layer soil moisture. In figure 1 below, the upper image was referenced by the NCDMAC during the August 5th collaboration call to recommend expansion of D0 at the sub-county scale in the area circled.

In addition, a more formal demonstration of the full suite of LIS soil moisture products was conducted during the weekly NCDMAC collaboration call on Tuesday August 12th. In figure 1 below, the lower image was used to inspect the short time scale improvement of soil moisture conditions in the areas under D0 drought designation. While the graphic shows marked improvement from significant rainfall, the D0 areas were not modified as lingering 30 and 60 day rainfall deficits in these areas (in addition to crop reports), overshadowed the short term improvement.

The NCDMAC will be examining how best to utilize these products for drought assessment. Preliminary ideas include: 1) how the products can be correlated to the observed well level observations available via the USGS and state networks, and 2) how the SPoRT products can be used to enhance or complement the Standardized Precipitation Index product produced by the NC State Climate office.

Figure 1. The 0-200 cm Relative Soil Moisture Weekly Change products ending at 08/05/2014(top) and 08/12/2014(bottom) are shown above. The U.S. Drought Monitor status is shown in the insert in the lower left with the area of abnormally dry conditions (D0) shown in the yellow shading.

Figure 1. The 0-200 cm Relative Soil Moisture Weekly Change products ending at 08/05/2014 (top) and 08/12/2014 (bottom) are shown above. The U.S. Drought Monitor status is shown in the insert in the lower left with the area of abnormally dry conditions (D0) shown in the yellow shading.

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Hurricane Arthur’s Wind Gust Factors and a CSTAR Research to Operations Success

Note this is a multi-part review of Arthur, with the focus in this post on the creation the wind gust forecasts.

To evaluate the performance of CSTAR related research to operations activities, we examined the sustained winds, wind gusts, and gust factors for Hurricane Arthur (2014) across coastal North Carolina. The map below is a subjective analysis of the maximum wind gusts observed during Hurricane Arthur. Many locations across and near the Outer Banks reported wind gusts in excess of 70 MPH with a few locations in the southern and central Outer Banks reporting wind gust greater than 90 MPH. The western edge of the enhanced wind gusts directly associated with Arthur extended to near Interstate 95 with values of around 25 MPH.

Subjective analysis of the maximum wind gusts (MPH) observed from 03 July to 04 July 2014 during Hurricane Arthur.

Subjective analysis of the maximum wind gusts (MPH) observed from 03 July to 04 July 2014 during Hurricane Arthur.

Hourly observations of winds and wind gusts from 16 regular ASOS or AWOS METAR locations impacted by the over land wind field associated with Hurricane Arthur were examined. The locations examined in this analysis include KECG, KEDE, KEWN, KFFA, KHSE, KMQI, KMRH, KNBT, KNCA, KNJM, KNKT, KOAJ, KOCW, KONX, KPGV, and KSUT. Only observations from routine hourly METARs were used (special observations and observations not at the top of the hour were excluded). In addition, gust factors were only calculated for sustained winds of 10 MPH or greater. For each observation, the hourly wind gust factor was computed. The gust factor is defined as the ratio between the wind gust of a specific duration to the mean (sustained) wind speed for a period of time.  A total of 344 gust factors were computed for Arthur.

Note that a previous blog post highlighted the examination of gust factors for ten tropical cyclones across the Carolinas and Virginia – A Wind Gust Factor Database from 10 Tropical Cyclones for Use with GFE Tool Development.  This previous post discusses the creation of the database used to develop a regression equation included within a GFE smart tool that is used to create a wind gust factor grid. The discussion below examines the winds, wind gusts, and gust factors associated with Arthur and compares them to the database of 10 tropical cyclones.

Scatter plot of sustained winds and gust factors for Hurricane Arthur for 16 METAR locations in eastern North Carolina.

Scatter plot of sustained winds and gust factors for Hurricane Arthur for 16 METAR locations in eastern North Carolina.

The chart to the right is a scatter plot of the sustained winds in MPH versus gust factors for the 344 observations included in the study along with a best fit regression curve (y = -0.274ln(x) + 2.3599). In general, the chart demonstrates an inverse relationship between the wind speed and gust factor as well as a decrease in the number and variability of observations as wind speeds increase. This chart is very similar to the scatter plot created from the database of the 10 tropical cyclones.

The gust factors with Arthur were rather variable at low sustained wind speeds but generally converged and decreased with increasing sustained wind speed. The maximum sustained wind contained in the Arthur data set was only 48 MPH and the maximum wind gust was 71 MPH. The data set contained a large number of lower end sustained winds and wind gusts. More than 69% or 239 out of the 344 observations contained in this data-set had sustained winds less than 20 MPH.  Only 30 observations or less than 9% of all observations had sustained winds of 30 MPH or more.

Histogram of 344 gust factors for Hurricane Arthur across 16 observing locations in eastern North Carolina.

Histogram of 344 gust factors for Hurricane Arthur across 16 observing locations in eastern North Carolina.

A histogram of the frequency of gust factors for Arthur across the North Carolina is shown to the right.  The average gust factor for Arthur was 1.58 which is somewhat higher than the average of 1.47 for the database of 10 tropical cyclones. The average gust factor for Arthur was identical to the average gust factor for Hurricane Sandy. Both Arthur and the 10 tropical cyclone database had gust factors that were very similar to several previous studies (see comparison chart from a previous blog post). Schroder (2002) found an average gust factor of 1.49 during tropical cyclones at several airport locations while Krayer and Marshall (1992) found an average gust factor of 1.55 in a data set standardized to open terrain.  The histogram data noted that the gust factors were most frequently in the bin between 1.5 and 1.6. While the distribution of gust factors for Arthur is shifted to the right with higher gust factors when compared to the 10 storm database, the pattern and character of the distribution for Arthur is very similar to the 10 storm study.

Forecasters at NWS offices in Charleston, Newport, Raleigh, and Wilmington tested an experimental GFE methodology during Hurricane Arthur based on research activities associated with the CSTAR project. In this methodology, the forecaster initially populates a WindGustFactor grid based on the regression equation derived from the dataset of 10 tropical cyclones that uses the sustained wind speed as an input. The forecaster can then adjust the WindGustFactor grid to account for local effects such as boundary layer stability, prior to calculating the wind gust. The product of the wind forecast and the WindGustFactor is then computed as the wind gust forecast.

The 23-hour NDFD Wind gust forecast from midnight EDT on 3 July valid at 11pm EDT on 3 July, 2014. WFOs Charleston, Newport, Raleigh, and Wilmington which are located to the east or right of the thin yellow line used the new methodology.

The 23-hour NDFD Wind gust forecast from midnight EDT on 3 July valid at 11pm EDT on 3 July, 2014. WFOs Charleston, Newport, Raleigh, and Wilmington which are located to the east or right of the thin yellow line used the new methodology.

The example to the right is the 23-hour NDFD wind gust forecast from midnight EDT on 3 July valid at 11pm EDT on 3 July, 2014 which demonstrates a consistent and well collaborated wind gust forecast from the 4 WFOs using the new methodology. The area to the right or east of the thin yellow line encompasses the WFOs that used this experimental methodology. It is difficult to identify the CWA borders among the 4 offices within the yellow semi circle but the CWA borders among other WFOs or between participating and non-participating WFOs straddling the yellow line can be more easily identified. During Arthur, forecasters provided positive feedback on this methodology and noted the much improved consistency and an improved quality of the forecast wind gusts using this approach when compared to past experiences.  This event demonstrated a notable CSTAR research to operation success of the new CSTAR motivated methodology.

References

A Wind Gust Factor Database from 10 Tropical Cyclones for Use with GFE Tool Development

Krayer, William R., Richard D. Marshall, 1992: Gust factors applied to hurricane winds. Bull. Amer. Meteor. Soc., 73, 613–618.  [Available online at http://dx.doi.org/10.1175/1520-0477(1992)073<0613:GFATHW>2.0.CO;2]

Schroeder, J. L., M. R. Conder, and J. R. Howard, 2002: “Additional Insights into Hurricane Gust Factors,” Preprints, Twenty-Fifth Conference on Hurricanes and Tropical Meteorology, San Diego, California, 39-40.

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Hurricane Arthur Provided an Opportunity to Demonstrate a CSTAR Research to Operations Success in Creating Tropical Cyclone Sustained Wind Forecasts

Note this is a multi-part review of Arthur, with the focus in this post on the creation the sustained wind forecasts.

On 3 July through 4 July, 2014 Hurricane Arthur impacted portions of eastern North Carolina with strong winds and very heavy rain as it moved northeast along the Carolina coast.  Arthur’s track took the storm northeast, largely parallel to the South Carolina coast and then across the far eastern portion of North Carolina including much of the Outer Banks. This was a climatologically favored track and one that forecasters are very familiar with.  Given this path, the strongest winds from Arthur were confined to the eastern Coastal Plain and especially the coastal region of North Carolina.  To evaluate the performance of CSTAR related research to operations activities, we wanted to briefly share an analysis of the maximum sustained winds and the maximum wind gusts from Arthur along with a sampling of the NDFD wind and wind gust forecasts.

The map below is a subjective analysis of the maximum sustained winds observed from 03 July to 04 July 2014 during the time in which Arthur impacted North Carolina. Sustained winds of 35 MPH or more were generally confined to the counties along the immediate coast or adjacent to the sounds. Observations of sustained winds of 50 MPH or more were restricted to locations close to the storm track across the Outer Banks and near Pamlico Sound. Only a few locations reported hurricane force sustained winds, they included Cape Lookout (CLKN7), a WeatherFlow observation from Pamlico Sound, and a WeatherFlow observation in Salvo.

Subjective analysis of the maximum sustained winds (MPH) observed from 03 July to 04 July 2014 from Hurricane Arthur.

Subjective analysis of the maximum sustained winds (MPH) observed from 03 July to 04 July 2014 from Hurricane Arthur.

The map below is a subjective analysis of the maximum wind gusts observed during Hurricane Arthur. Not surprisingly, the strong wind gusts covered a larger portion of eastern North Carolina compared to the sustained winds.  Wind gusts of at least 35 MPH or more impacted all of the coastal region and much of the eastern Coastal Plain. Wind gusts of at least 50 mph reported across nearly all of the North Carolina coastal counties. Many locations across and near the Outer Banks reported wind gusts in excess of 70 MPH with a few locations in the southern and central Outer Banks reporting wind gust in excess of 90 MPH.  The Cape Lookout station reported the strongest gust of 101 MPH just after 11 PM EDT on 3 July just as the hurricane was about to make landfall. Two WeatherFlow reporting stations observed wind gusts of 99 MPH, one at Ocracoke and the other in Pamlico Sound.

Subjective analysis of the maximum wind gusts (MPH) observed from 03 July to 04 July 2014 during Hurricane Arthur.

Subjective analysis of the maximum wind gusts (MPH) observed from 03 July to 04 July 2014 during Hurricane Arthur.

A snapshot of the new TCMWindTool made available for the 2014 hurricane season. Two new options are available based on results from the NC State-NWS CSTAR CSTAR project including a wind field bias correction and incorporating the WindReductionFactor grids.

A snapshot of the new TCMWindTool made available for the 2014 hurricane season. Two new options are available based on results from the NC State-NWS CSTAR CSTAR project including a wind field bias correction and incorporating the WindReductionFactor grids.

A snapshot of the new TCMWindTool made available for the 2014 hurricane season. Two new options are available based on results from the NC State-NWS CSTAR CSTAR project including a wind field bias correction and incorporating the WindReductionFactor grids.

At the 2013 NOAA Hurricane Conference following the 2013 hurricane season, the NC State-NWS CSTAR tropical cyclone winds research group requested additional support for their project and the ability to test some experimental methodologies and tools. Following the conference, collaborators from NWS Weather Forecast Offices (WFOs), the National Hurricane Center (NHC), the Hurricane Research Division, and the Earth Systems Research Laboratory worked together to make improvements to the TCMWindTool including implementing some of the CSTAR research results. Developers at ESRL modified the TCMWindTool and added the ability to use a Modified Rankine Error Function (MREF) wind model which was developed as a part of the NC State-NWS CSTAR project and acts as a bias correction to the TCM wind guidance. In addition, the TCMWindTool now fully integrates the NC State-NWS CSTAR project methodology of creating grids of wind reductions.  With this methodology, forecasters edit WindReductionFactor grids of reductions of the TCM guidance that can vary both temporally and spatially instead of a single over land reduction that was used previously. In addition, the WindReductionFactor grid can be viewed by adjacent WFOs improving collaboration and assisting in realizing better consistency in the NDFD.

Forecasters at NWS offices in Charleston, Newport, Raleigh, and Wilmington tested these new GFE methodologies during Hurricane Arthur. During Arthur, forecasters provided mainly positive feedback on this methodology and noted the much improved consistency and an improved quality of the wind forecast s using this approach when compared to past experiences.  We continue to evaluate the performance of the updated tool and methodology. While some issues were identified, the result was largely an improvement or previous methods and has made editing much easier than in the past.  Some of the feedback provided by forecasters included:
•    “It certainly led to better coordinated wind grids”
•    “Produced realistic output”
•    “The integrated tool was “even more efficient than in past years, likely due to the tweaks to the TCMWindTool.”
•    “The process seemed to go well and I think the output was reasonable”
•    “The tool allows for more science”

While a detailed verification of the NDFD wind forecasts is not available, most forecasters believed the process did an effective job of downscaling the TCM guidance from the NHC to produce a realistic and accurate wind filed across North Carolina. An example of some of the NDFD wind forecasts are shown in the figure below. This event demonstrated a notable CSTAR research to operation success of the new CSTAR motivated methodology.

NDFD wind (top row) and wind gust (bottom row) forecasts valid at 11 PM EDT on 07/03 and issued at 07/01 9 PM EDT, 07/02 9 PM EDT, and 07/03 9 PM EDT,

NDFD wind (top row) and wind gust (bottom row) forecasts valid at 11 PM EDT on 07/03 and issued at 07/01 9 PM EDT, 07/02 9 PM EDT, and 07/03 9 PM EDT,

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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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