Updated List of NC State-NWS CSTAR Publications

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Figure depicting the change in surface based CAPE in the hours prior to severe convection in HSLC environments as described in King et al., 2017.

Shown below is a list of publications and abstracts developed as a part of the most recent NC State-NWS CSTAR project entitled “Understanding and Prediction of High Impact Weather Associated with Low-Topped Severe Convection in the Southeastern U.S.” Note that additional presentations are scheduled for upcoming conferences including the AMS 24th Conference on Probability and Statistics in July and the 17th Conference on Mesoscale Processes in July. In addition, manuscripts are being composed for multiple projects including the predictability study using ensembles and dynamical-statistical downscaling project.

Publications (most recent first):

1) King, J. R., M. D. Parker, K. D. Sherburn, and G. M. Lackmann, 2017: Rapid evolution of cool season, low CAPE severe thunderstorm environments. Wea. Forecasting, 32, 763-779. | PDF |

2) Sherburn, K. D., M. D. Parker, J. R. King, and G. M. Lackmann, 2016: Composite environments of severe and non-severe high-shear, low-CAPE convective events. Wea. Forecasting, 31, 1899-1927. | PDF |

Conference abstracts (most recent first):

1) Sherburn, K. D., and M. D. Parker, 2016: The origins of rotation within high-shear, low-CAPE mesovortices and mesocyclones. 28th Conference on Severe Local Storms, AMS, 7-11 November 2016, Portland, OR. | Recorded presentation | Manuscript |

2) Sherburn, K. D., and M. D. Parker, 2016: Insights from composite environments of high-shear low-CAPE severe convection. 28th Conf. on Severe Local Storms, AMS, 7-11 November 2016, Portland, OR. | Poster handout | Manuscript |

3) Blank, L., and G. Lackmann, 2016: Operational predictability of explicit high shear, low CAPE convection. 6th Conference on Transition of Research to Operations, AMS, 11-14 January 2016, New Orleans, LA. | Recorded presentation |

4) King, J. R., and M. D. Parker, 2015: Conditioning and evolution of high shear, low CAPE severe environments. 16th Conference on Mesoscale Processes, AMS, 2-6 August 2015, Boston, MA. | Recorded presentation | Manuscript |

5) Sherburn, K. D., and M. D. Parker, 2015: Examining the sensitivities of high-shear low-CAPE convection to low-level hodograph shape. 16th Conference on Mesoscale Processes, AMS, 2-6 August 2015, Boston, MA. | Recorded presentation | Manuscript |

6) King, J. R., and M. D. Parker, 2014: Synoptic influence on high shear, low CAPE convective events. 27th Conference on Severe Local Storms, AMS, 2-7 November 2014, Madison, WI. | Poster handout | Manuscript |

7) Sherburn, K. D., and M. D. Parker, 2014: High-shear, low-CAPE environments: What we know and where to go next. 27th Conference on Severe Local Storms, AMS, 2-7 November 2014, Madison, WI. | Recorded presentation | Manuscript |

8) Sherburn, K. D., and M. D. Parker, 2014: On the usage of composite parameters in high-shear, low-CAPE environments. 27th Conference on Severe Local Storms, AMS, 2-7 November 2014, Madison, WI. | Poster handout | Manuscript |

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The Utility of Non-NWS Upper Air Observations – NC State Soundings Support Severe Weather Operations at NWS Raleigh on May 4th and 5th, 2017

NC State sounding from 0103 UTC 05/05/2017 during a severe weather event.

There are several non-NWS organizations that take upper-air observations and share them with NWS forecasters. These organizations largely consist of universities, military installations or research laboratories. The motivation for taking these observations include research efforts as well as educational and training activities.

One example of such an organization is the “Sounding Club” at NC State University which is lead by students and overseen by professors within the Atmospheric Science department.  Some of the goals of the organization according to their website are to help students obtain hands-on experience in addition to collecting data for projects. In addition to professional development and project support, the soundings have been used by NWS forecasters to support operational needs.

A pair of soundings from the NC State Sounding Club were very helpful during the evening and overnight hours on May 4th and 5th when there was concern for severe convection (SPC reports).  NWS Forecaster Michael Strickler noted the utility of the soundings at approximately 01Z and 03Z on 05 May…

The soundings revealed that the low 70s/low 60s surface temperatures and dew points were already supportive of surface-based convection even prior to the arrival of the mT air mass from the southeast, but with only weak instability and low equilibrium levels. This information provided radar operators confidence of severe wind and tornado potential. The sounding also revealed the character and strength of the low level shear, with a greater degree of confidence relative to that of WSR-derived VWP winds/hodographs that tend to fluctuate/become noisy and are consequently often times less reliable. Pre-QLCS storm motion vectors, as indicated by the soundings, also proved beneficial from a pre-warning situational awareness standpoint.

NWS Chat message from 0525 UTC (0125 AM EDT) 05/05/2017 describing the near term environment.

UNC Asheville sounding from 0300 UTC 01/07/2017 during a winter storm that affected much of the Virginias and Carolinas.

NWS Raleigh forecasters obtain the soundings from the NC State Sounding Club in near real-time either through email, posts to the CSTAR mailing list, or via social media.  In addition to NC State, there are several other organizations that take upper air observations.  UNC Asheville has taken upper air observations during many winter storms in recent years as a part of their Sounding-based Experiment on Mixed Precipitation Events (SEMPE) project. These soundings have been used by the NWS offices in Greenville-Spartanburg, Blacksburg and Raleigh among others.

In the Southeast, we are aware of several organizations taking supplemental observations; some of them are shown in the list below:

  • NC State
  • UNC Asheville
  • UNC Charlotte
  • University of South Carolina
  • University of Alabama Huntsville
  • Mississippi State
  • University of Louisiana-Monroe
  • Simmons AAF Fort Bragg
  • Redstone Arsenal
  • NOAA Lab in Oak Ridge, TN

These observations have a great deal of potential to support NWS warning and forecast operations. Unfortunately, they are often underutilized for a variety of reasons including a lack of awareness and coordination of the sounding operations, limitations in the dissemination and display of the soundings, and an inability to ingest the data into AWIPS.

There is a desire to collect and organize these grass roots observations into a process to improve the awareness, communication, access and display of these observations among NWS forecasters. Collaborators with the NC State CSTAR group will be reaching out to those taking the observations to gauge interest in improve the flow of the data to the NWS and perhaps elsewhere.

Posted in CSTAR, Winter Weather | Leave a comment

2017 CSTAR Workshop and Mid-Atlantic and Southeast Sub-regional SOO Meeting Held in Raleigh

img_1718.jpg

Photo of the 2017 CSTAR workshop attendees.

On April 26th through 28th over 20 meteorologists from the National Weather Service (NWS) as well as faculty and students from N.C. State University (NCSU) gathered in Raleigh to get updates on various collaborative research activities, share operational and training successes and to look to the future toward planned and potential projects across our region.

Meteorologists from 9 NWS WFOs along with NWS Eastern Region Headquarters (ERH) met during a portion of Wednesday and Friday for a NWS Sub-regional SOO Meeting. This time was dedicated to meet some of the new SOOs/staff from around the area, discuss best practices and challenges unique to the region, and to look to the future of the science program. Thursday was largely dedicated to collaborative research with NC State including updates on a 3 year Collaborative Science, Technology, and Applied Research (CSTAR) project focused on high impact weather associated with low-topped severe convection in the Southeastern U.S.” In addition, other research activities at NC State including heavy banded snowfall, predictive modeling for storm surge and flooding, and quantifying radar uncertainty and ensemble QPE were presented.

Finally, a new CSTAR project entitled “Understanding fundamental processes and evaluating high-resolution model forecasts in high-shear low-CAPE severe storm environments” was introduced. This project will build off of previous collaborative research between NCSU and the NWS, which has had very successful research to operation results.

Presentations from the workshop are available via Google Drive at this URL: https://goo.gl/UJkSrP

Look for additional details on the workshop including follow up activities, highlights and updates in future blog posts. A virtual workshop is tentatively planned for October with a desire for another in person meeting next fall as the next CSTAR effort matures.

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Hurricane Matthew Gust Factors

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Tropical cyclone best track and wind radii data for Hurricane Matthew provided by the National Hurricane Center from 07 October to 09 October 2016.

To evaluate the performance of CSTAR related research to operations activities, the sustained winds, wind gusts, and gust factors for Hurricane Matthew (2016) were examined across coastal and eastern Georgia, South Carolina, North Carolina, and Virginia. The image above or to the right is the tropical cyclone best track and wind radii data for Hurricane Matthew which shows the track of the storm near and along much of the southeast U.S. coast. The track data is a subjectively smoothed representation of a tropical cyclone’s history over its lifetime, based on a post-storm analysis of all available data. The data also contains wind radii information which is the farthest distance from the cyclone’s center where sustained winds of 34-, 50-, and 64-kts are occurring in each of four quadrants about the storm (NE, SE, SW, and NW).

The map below is a subjective analysis of the maximum wind gusts observed across NC during Hurricane Matthew. Many locations across the immediate coast observed wind gusts in excess of 70 MPH with a few locations across the Outer Banks reporting wind gust greater than 80 MPH. Wind gusts of 50 MPH or more extended inland to the southern and central I-95 corridor.

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Subjective analysis of the maximum wind gusts (MPH) observed across North Carolina from 07 October to 09 October 2016 during Hurricane Matthew.

NWS Raleigh volunteer Victoria Oliva, examined the sustained winds, wind gusts, and gust factors for Matthew across coastal and eastern Georgia, South Carolina, North Carolina and Virginia. Hourly observations of winds and wind gusts from 60 regular ASOS or AWOS METAR locations impacted by the over land wind field associated with Tropical Storm Matthew were examined. The locations examined in this analysis extended from KSVN (Hunter Army Airfield near Savannah, Georgia) northeast along and just inland of the coast to KWAL (Wallops Island, Virginia).

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 kts 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 979 gust factors were computed for Matthew.

The maximum sustained wind contained in the Matthew data set was only 53 kts and the maximum wind gust was 70 kts with both observations from KHXD (Hilton Head, SC). The data set contained a large number of lower end sustained winds and wind gusts. Nearly 79% or 769 out of the 979 observations, contained in this data-set had sustained winds less than 25 kts. Only 85 observations, or around 9% of all observations, had sustained winds of 40 kts or more and only 8 observations had sustained winds of 40 kts or more.

mathew.regression

Scatter plot of sustained winds and gust factors for Hurricane Matthew for 60 METAR locations across coastal and eastern Georgia, South Carolina, North Carolina and Virginia.

The chart to the right is a scatter plot of the sustained winds in kts versus gust factors for the 979 observations included in the study along with a best fit regression curve (y = -0.231ln(x) + 2.2498). In general, the chart demonstrates an inverse relationship between the wind speed and gust factor. Not surprisingly, the gust factors with Matthew were rather variable at low sustained wind speeds and generally converged and decreased with increasing sustained wind speed. This chart is similar to the database of 15 storms used to develop the CSTAR TCM wind technique.

mathew.histogramA histogram of the frequency of gust factors for Matthew is shown to the right. The average gust factor for Matthew was 1.58 which is somewhat higher than the average of 1.53 for the database of 15 tropical cyclones used to develop the CSTAR TC wind technique. The histogram data noted that the gust factors were most frequently noted between 1.5 and 1.6.

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Comparison of gust factor regression equations associated with Hurricane Matthew and the 15 storm database used to develop the CSTAR TCM wind technique.

We generated a regression equation using the gust factor data set associated with Matthew and compared it to the regression equation used in the 15 storm database used to develop the CSTAR TCM wind technique. The figure to the right compares the Matthew regression equation (shown in red) to the 15 storm equation (shown in blue). They show a similar trend but the gust factors with Matthew are consistently a little higher than the 15-storm dataset.

Posted in CSTAR, TC Inland and Marine Winds, Uncategorized | Leave a comment

MOSHE now available in beta form on SPC Mesoanalysis

The effective version of the Modified Severe Hazards in Environments with Reduced Buoyancy parameter (i.e., modified SHERBE or MOSHE), detailed in Sherburn et al. (2016), is now available in beta form on the SPC Mesoanalysis page.


In observing the parameter’s trends over the past couple of days, I’ve noticed that there tend to be some “hot spots” associated with enhanced values of effective shear and low-level lapse rates. This is not entirely surprising, as our NARR values of effective shear did tend to show a low bias compared to the mesoanalysis values (hence, our term is weighted based on these lower values), and our dataset consisted entirely of low-CAPE cases (which inherently have less steep lapse rates). The omega field is also dependent on model setup and could have a different distribution in the RAP than what we saw in the NARR.

At any rate, I have been in touch with Rich Thompson at SPC about the potential of plotting the individual terms of the MOSHE on an internal page for us to monitor. This will allow for some troubleshooting to account for differences between the NARR and other analysis/forecast platforms. I could envision some changes to the relative weighting of terms or perhaps instituting some “caps” on the contributions of certain terms (similar to what is done in the STP/SCP) to limit false alarms while still maintaining the discriminatory skill of the parameter.

I’ll keep everyone up to date on the progress of the project to plot individual MOSHE terms. Until then, please monitor the real-time plots when you can and share any feedback with us. Thanks!

Posted in Convection, CSTAR, High Shear Low Cape Severe Wx | 3 Comments

HSLC materials from Severe Local Storms Conference available, HSLC composite maps manuscript published

In November, CSTAR student Keith Sherburn traveled to the AMS Severe Local Storms Conference in Portland, OR to present recent research involving HSLC idealized simulations (via a talk) and composite environments (via a poster). Materials for this conference are now available online and are linked below.

“The Origins of Rotation within High-Shear, Low-CAPE Mesovortices and Mesocyclones”, recorded talk

“The Origins of Rotation within High-Shear, Low-CAPE Mesovortices and Mesocyclones”, extended abstract

“Insights from Composite Environments of High-Shear, Low-CAPE Severe Convection”, poster handout

“Insights from Composite Environments of High-Shear, Low-CAPE Severe Convection”, extended abstract

The poster above largely acts as supplemental material to “Composite Environments of Severe and Nonsevere High-Shear, Low-CAPE Convective Events”, authored by Keith Sherburn, Matt Parker, Jessica King, and Gary Lackmann, which was published in the December 2016 edition of AMS’s Weather and Forecasting.

Please share your comments or questions about any of these materials here!

Posted in CIMMSE, Convection, CSTAR, High Shear Low Cape Severe Wx | Leave a comment

Precipitation Pattern across the North Carolina during Hurricane Matthew – Part 2 of 2: Classic Pattern for Enhanced Tropical Cyclone Rainfall across the Carolinas during Matthew

14591759_1088720037844214_3490765990052607790_nHurricane Matthew dumped a swath of 8 to 18 inches of rain across inland portions of eastern North Carolina during the period of 07 October through 09 October 2016. Several locations reported incredible rain amounts including 18.38 inches in Elizabethtown NC, 17.00 inches in Hope Mills NC, 16.71 in White Oak NC, 16.28 in Godwin NC, 15.62 in Fayetteville NC, and 15.56 in Goldsboro NC. Several all-time one day rainfall records were set as noted in the graphic below. The precipitation pattern was notable for several reasons including the fact that an ideal setup for enhanced rainfall associated with a tropical cyclone was in place and would contribute to the record breaking rainfall and subsequent flooding across eastern NC.

hurricanematthewrainfallhistorical

matthew-ani-lotThe animated regional radar reflectivity loop to the right is from 2358 UTC on 06 October through 0258 UTC on 09 October which shows the evolution of the precipitation across the Southeast during Matthew. Note that much of central and eastern North Carolina had more than 12 hours of moderate to heavy rainfall as noted by the 35 dBz reflectivity values (yellow to orange or red shading). In fact, Fayetteville NC reported a consecutive 14 hours and 5 minutes of moderate or heavy rain between 449 am and 653 pm on 08 October 2016.

The issue of enhanced precipitation associated with tropical cyclones (TCs) and the distribution of the heaviest rainfall associated with TCs has been examined in numerous studies including Croke (2006) which looked at 28 tropical cyclones that made landfall or tracked along coastal North Carolina from 1953 to 2004; Atallah, et. al. (2007) which investigated the precipitation distribution associated with landfalling tropical cyclones over the eastern United States; and DeLuca, Bosart, and Keyser (2004) which examined the distribution of precipitation over the Northeast during landfalling and transitioning tropical cyclones.

modelThe Croke (2006) study was conducted as a part of collaborative research between NC State and several Mid-Atlantic National Weather Service offices following the devastating impact of Hurricane Floyd (1999) which was responsible for killing 52 North Carolinians, including 36 from drowning. The goal of that research was to develop a conceptual model to determine the potential of enhanced precipitation due to the interaction of the TC with other meteorological features prior to landfall. This paradigm would give forecasters an indication of the potential for an enhanced precipitation event by identifying features that may exist at different temporal and spatial scales outside of the TC. From this work, a conceptual model for enhanced rain associated with tropical cyclones was developed. A cartoon of the primary features is shown in the image to the right, largely adapted from the Croke (2006) work.

The presence of the following features can create an environment favorable for enhanced precipitation across North Carolina:
1) An upper level trough over the Great Lakes and Ohio Valley
2) Strong upper-level divergence inland and poleward of the TC associated with a northern stream jet streak
3) Strong inland moisture flux prior to landfall
4) A cold air damming wedge of cooler/more stable air with a surface high pressure system centered over the northeast
5) Development of a coastal front
6) Slow to moderate TC translation speed and proximity to the Carolinas

Not surprisingly, the environment around Hurricane Matthew included all of these features to some extent which enhanced the precipitation across the region and lead to widespread record-breaking flooding. We’ll examine a few of these features relating to Matthew in the paragraphs below.

18_padv1) An upper level trough over the Great Lakes and Ohio Valley – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page showed a well-defined mid and upper-level trough and potential vorticity axis in the 400-250 mb layer across the Ohio and Tennessee Valleys at 18 UTC on 08 October. This larger scale feature is often identifiable 48 hours or more prior to landfall. The strength and southward extension of the PV can often be correlated to the heavier rain fall events.

18_300mb2) Strong upper-level divergence inland and poleward of the TC associated with the northern stream jet stream – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page at 18 UTC on 08 October showed a well-defined upper-level trough across the Great Lakes with a jet streak at 300 mb across the eastern Great Lakes. A well-defined region of enhanced upper-level divergence was analyzed over North Carolina, likely increasing vertical ascent and enhancing rainfall.

spc-sect17-06z-tran3) Strong inland moisture flux prior to landfall – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page showed a well-defined region of 850 mb moisture transport early in the morning on 08 October not only near the tropical cyclone center but also extending northward into the eastern and southern portion of North Carolina. This moisture transport analysis is from 06 UTC on 08 October as the heavy rain was poised to build and move into North Carolina.

spc_sect17_18z_bigsfc-small4) A cold air damming wedge with a surface high pressure system centered over the northeast – while not as pronounced as in other TC events, a cooler and more stable air mass became established across the Piedmont of North Carolina on 08 October. The METAR plot from 18 UTC on 08 October shows surface dew points in the mid and upper 60s across the Piedmont while dew points were in the lower to mid 70s across the Coastal Plain. The parent high pressure center was located off the New England coast which resulted in an in-situ cold air damming wedge across North Carolina. The wedge likely enhanced the rain in North Carolinas as warm moist air on the forward side of the storm was lifted up and over the surface based stable layer.

spc-sect17-18z-sfnt5) Development of a coastal front – The establishment of the in-situ cold air damming (CAD) wedge across the Piedmont can lead to the development of a low-level boundary along the eastern perimeter of the CAD region. The objective surface frontogenesis analysis from the Storm Prediction Center Mesoscale Analysis Page from 06 UTC on 08 October showed a region of surface frontogenesis shown in red contours extending northeast of the center of Matthew across eastern North Carolina. The coastal front marked the boundary of the strong easterly to southeasterly surface flow with a cooler north to northeast flow further inland. Several studies have shown that a surface boundary can focus heavy precipitation in a mesoscale band driven by low-level frontogenesis that often develops left and poleward of the storm track with enhanced precipitation falling along or in cold sector of the boundary.

track6) Slow to moderate TC translation speed and proximity to the Carolinas – while these features are rather intuitive, the Croke (2006) research suggests that at times they are not dominant. Other factors, such as synoptic or mesoscale features have proven to compensate for TC’s with less favorable tracks or translation speed. Still, absent of other features, a TC that is moving slower and closer to the North Carolina will have a greater potential for heavier rain across North Carolina than one that is moving faster and is removed from the coast.

The synoptic and mesoscale pattern across the eastern United States prior to and during the time in which Hurricane Matthew impacted North Carolina fit the paradigm for enhanced tropical cyclone precipitation. This event was a classic and efficient heavy rain producer with all of the features for enhanced heavy rain including: a strong upper level jet poleward of the tropical cyclone, an approaching upper trough, strong low-level moisture flux, a cold air damming region across the interior Piedmont, and a strong coastal front. Forecasters recognized the developing pattern during the days leading up to the storms arrival and it was highlighted in an Area Forecast Discussion from the National Weather Service Raleigh, NC which noted:

“.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/…
As of 345 PM Friday…

…Threat of life threatening flooding increasing across the Sandhills and Coastal Plain of NC as ideal setup for enhanced tropical rain becomes established…

The biggest threat and impact arises from the potential for extremely heavy rain with amounts forecast to exceed 10 inches across the southeastern and eastern portions of the CWA. The setup for tremendous rainfall associated with a non-land falling tropical cyclone are nearly ideal.

The combination of an approaching tropical cyclone with deep tropical moisture, a coastal front and a cold air damming air mass in the Piedmont providing an enhance region of ascent northward of the tropical cyclone and the approach of an upper trough and cold front that will lead to a left of track precipitation distribution should lead to storm total rain amounts that range near a foot…”

References

Atallah, E., L. F. Bosart, and A. Aiyyer, 2007: Precipitation distribution associated with landfalling tropical cyclones over the eastern United States. Mon. Wea. Rev.,135, 2185–2206.

Croke, M. S., M. L. Kaplan, L. Xie, and K. Keeter, 2005: Examining planetary, synoptic, and mesoscale features that enhance precipitation associated with Tropical Cyclones making landfall over North Carolina. Preprints, 21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction, Washington, DC, Amer. Meteor. Soc.

Croke, M.S. (2006) Examining Planetary, Synoptic and Mesoscale Features that Enhance
Precipitation Associated with Landfalling Tropical Cyclones in North Carolina, Thesis
(M.S.), North Carolina State University.

DeLuca, D. P., L. F. Bosart, and D. Keyser, 2004: The distribution of precipitation over the Northeast accompanying landfalling and transitioning tropical cyclones. 20th Conference on Weather Analysis and Forecasting, Seattle, WA., Amer. Meteor. Soc.

Posted in CIMMSE, Hydrology, TC and Boundary QPF | 1 Comment