*Note that because of squall line last night (Friday June 13), the power appears to be out at the profiler site and data is not available, it was fixed, I promise!

The data is now displayed on the following websites:
http://www.esrl.noaa.gov/psd/data/obs/ (Click on one of the dots next Clayton)
https://madis-data.noaa.gov/cap/profiler.jsp (Click on the dot over central NC)

Image of Clayton wind profiler wind analysis
http://www.esrl.noaa.gov/psd/data/obs/realtime/Radar915/Images/ctn/2013/163/ctn1316318a_cbarb.gif

This is a multi-agency success story that couldn’t have been accomplished without several key partners, and in particular to Nick Witcraft (NC DENR), Elliot Tardif (NC DENR), Bradley Mclamb (NC DENR), George Bridgers (US EPA) and the cadre of HMT field deployment expert team of meteorologists and engineers.

The data can be accessed at the URL below. The loop is courtesy of the Cooperative Institute for Research in the Atmosphere (CIRA). Crank up the animation speed and enjoy.

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=dev/lindsey/loops/goes14_vis2&image_width=1020&image_height=720&number_of_images_to_display=50

Figures 1 and 2 below show the familiar TSS vs. threshold plots for NWS Southern Region and Eastern Region, respectively. In these figures, the TSS is measured as the parameters’ ability to discriminate between all significant severe reports and nulls, regardless of environment. Figures 3 and 4 are similar, except that the TSS is calculated discriminating between all significant tornadoes and nulls, with no environmental constraints.

Figure 1. TSS at discriminating between significant severe reports and nulls with no environmental constraints for NWS Southern Region.

Figure 2. As in Fig. 1 but for NWS Eastern Region.

Figure 3. As in Fig. 1 but for significant tornadoes against nulls.

Figure 4. As in Fig. 2 but for significant tornadoes against nulls.

There are several noteworthy features of these plots. First, regardless of environment, the SHERBE is the most skillful composite parameter at discriminating between significant severe reports and nulls in both Southern and Eastern Region. Not only is it the most skillful parameter, it also shows a consistent optimal threshold relative to other existing composite parameters, including the SHERBS3. The SHERBS3 and Significant Tornado Parameter (STP) have comparable or slightly higher skill when discriminating between significant tornadoes and nulls; however, their thresholds must be adjusted downward for this to be true. At their conventional thresholds, the SHERBE outperforms the SHERBS3 and STP (along with all other tested parameters) at discriminating between significant tornadoes and nulls. Finally, even when using no environmental constraints, the STP’s optimal threshold is below 1, suggesting that the threshold of 1 from Thompson et al. (2004) may not be ideal for our CSTAR domain.

These findings are robust, as they provide evidence that the SHERBS3 and particularly SHERBE can be used with confidence across all environments within our CSTAR domain. In the future, we will cite these findings in an attempt to get the SHERBS3 and SHERBE plotted real-time on platforms such as the SPC Mesoanalysis.

An upper level ridge strengthening over the plains (and extending north into Canada) on Tue/Wed will result in strengthening NW flow aloft downstream over the TN/OH valley and Mid-Atlantic on Wed, and the advection of a modified elevated mixed layer into the region, with H7-H5 lapse rates on the order of 7-8 c/km across NC.  A robust shortwave in NW flow aloft is expected to approach the mountains 12-15Z Thursday, crossing NC/VA Thursday afternoon/evening, with an attendant sfc low deepening to 997-999 mb as it tracks east through VA and the DELMARVA. In advance of the shortwave, strengthening southerly low-level flow will advect rich boundary layer moisture northward under the modified EML, resulting in strong instability by peak heating Thu, with MLCAPE values of 2000-3000 J/kg across central NC.  Additionally, 0-6 km shear is progged to be on the order of 35-45 knots, which would be sufficient for supercellular organization, especially given steep mid-level lapse rates and strong instability.  It appears that the stage is set for an enhanced severe weather event Thu aft/eve, though specifics remain difficult to ascertain given that this is still 72+ hrs out and that there may be ongoing convection that ‘outruns’ the forcing over the TN/OH valley late wed/wed night, potentially crossing the Appalachians Thu morning. Whether or not convection would survive across the mountains is difficult to say, steep mid-level lapse rates will contribute to 1000-2000 J/kg of MUCAPE wed night over central NC, though CIN will rapidly increase within several hours after sunset.  At any rate, it seems like the primary severe weather threat in central NC on Thu would be very large hail and damaging winds, perhaps significant wind given DCAPE values progged as high as 1500 J/kg.  The tornado threat is a bit more difficult to pin down, though it would appear that the best tornado threat would be in VA and the DELMARVA in closer vicinity to the surface low and warm front where the best low-level shear would be present, with increasingly straight hodographs further south in NC.  Additionally, any discrete mode in NC would likely be short lived given strong instability, little or no CIN during peak heating, and high DCAPE that would foster strong cold pools and relatively quick upscale growth into an MCS, though that could result in a significant damaging wind threat, especially in eastern portions of NC/VA.

I see SPC mentioned us in the Day 4-8 outlook, though they didn’t add a 30% prob.  Anyone else have thoughts on the upcoming severe potential on Thu?

-Brandon V.

H7-H5 Lapse Rates Mon-Thu via 00Z (or 06Z) 06/10/2013 GFS

00Z (or 06Z) 06/10/2013 GFS/NAM Mon-Thu

00Z GFS sounding 06/10/2013 valid 18Z Thu 06/13/2013

1) Did a PRE occur over South Carolina on June 5, 2013?

In order to objectively determine whether or not the persistent region of convection over South Carolina on June 5, 2013 was a PRE, the four criteria proposed by Galarneau et al. (2010) for PRE identification need to be examined for this case.

1) Radar reflectivity values ≥35 dBZ within a coherent area of rainfall persisting for at least 6 h.

Base Reflectivity at Charleston, SC radar site from 1800 5 June – 0600 6 June 2013

Radar reflectivities ≥35 dBZ did occur over a 12 h period from 1800 UTC June 5 – 0600 UTC June 6 2013. Therefore, it appears Criteria 1 was met.

2) The average rainfall must be ≥100 mm (24 h)^-1 over the entire life of the PRE.

24 h QPE Accumulation ending at 1200 UTC 6 June 2013. PRE region circled in white over South Carolina.

After examining the 24 h QPE Accumulation (Radar only – not Stage IV), it appears that the average rainfall was not ≥100 mm (24 h)^-1 over the entire life of the PRE. However, the 24 h rain gauge measurements obtained from CoCoRaHS indicate that rainfall amounts ≥100 mm (24 h)-1 or ≥~4 in (24 h)-1 did occur in isolated spots over a broad region in the South Carolina Lowcountry.

24 h CoCoRaHS rain gauge measurements ending at 1200 UTC 6 June. Rainfall amounts ≥~4 in (24 h)-1 are indicated by orange and red dots.

3) There must be a clear separation on the radar imagery between the coherent area of rainfall and the TC rain shield.

WPC 0000 UTC 6 June 2013 Surface Analysis.

It certainly appears that there was a clear separation between the convection along the stationary boundary in South Carolina and the main TC rainfall shield located over central and southern Florida.

4) Deep tropical moisture directly associated with the TC must be advected away from the TC into the region of the coherent area of rainfall. (Click on image below to see loop.)

RUC precipitable water values from 1800 UTC 5 June – 0600 UTC 6 June 2013. Plots courtesy of InstantWeatherMaps.com

It does appear that deep tropical moisture was in place over South Carolina throughout the duration of the rainfall event. The slow, northward movement of the high precipitable water values from central South Carolina into central North Carolina at 0600 UTC 6 June does indicate that Tropical Storm Andrea might have played a role in advecting deep tropical moisture into the region of coherent rainfall.

In summary, most of the criteria appear to have been met for the heavy rainfall event over South Carolina on 5 June 2013 to be classified as a PRE. However, the second criteria (average rainfall must be ≥100 mm (24 h)-1) is only marginally met.

2) Did CAD occur over the Carolinas and Virginia on June 5-6, 2013?

Another topic of discussion yesterday (5 June 2013) was the development of a surface pressure ridge indicative of weak CAD and its possible implications on the track and precipitation distribution of Tropical Storm Andrea as it moves northward over the Carolinas. While the pressure ridge did appear in surface analyses, was CAD identified using the objective CAD detection criteria developed by Bailey et al. (2003)?

These criteria include:

• The mountain-normal Laplacian of sea level pressure must be negative and exceed in magnitude one standard deviation of the average of all the negative mountain-normal Laplacian values in the dataset.
• The mountain-normal Laplacian for potential temperature must be greater than zero.
• Sea level pressure must be greater at the center station relative to the end stations.
• The difference in the pressure along line D must be greater than 1.5 mb between either GSP and GSO or GSO and RIC, with higher values to the northeast.
• All requirements must be met for at least six consecutive hours on at least one of the mountain-normal lines (A-C).

These criteria are examined along four lines outlined below.

Surface stations and lines used in the objective CAD-detection algorithm developed by Bailey et al. (2003).

Looking at surface temperature and sea-level pressure observations from 2100 UTC 4 June – 2000 UTC 6 June 2013 (below), reveals that none of the criteria were met along the northernmost Line A and southernmost Line C. However, the criteria for CAD were met along Line B (North Carolina) from 1300 UTC – 2000 UTC 5 June 2013. This suggests that weak CAD occurred over North Carolina during the daytime hours of 5 June. Additionally, the difference in the pressure along line D was greater than 1.5 mb between either GSP and GSO or GSO and RIC, with higher values to the northeast for the entire 48 h period. The higher pressure to the northeast indicates the presence of a high pressure ridge extending southward as surface analyses indicated.

Analysis of CAD criteria from 2100 UTC 4 June – 2000 UTC 5 June 2013. Hours with CAD criteria met for 6 or more hours are highlighted in yellow.

In summary, when considering pressure observations alone, CAD occurred from 2100 4 June – 2000 6 June 2013 (Line D). However, when incorporating temperature observations, only weak CAD developed over North Carolina (Line  B) from 1300 UTC – 2000 UTC 5 June 2013.

It will certainly be interesting to see what enhancements the PRE over South Carolina might make to total rainfall accumulations in that region after Tropical Storm Andrea passes. However, since CAD does not appear to be currently present (June 6), it appears unlikely that CAD will be a major player in modulating the precipitation distribution and track of Tropical Storm Andrea as it moves northward over the Carolinas.

Regional reflectivity imagery from ~03Z 2013/06/06 highlighting the convection associated with Andrea across central and southern Florida and more scattered convection across the Southeast associated with a stalled frontal zone.

The CSTAR Tropical Cyclone QPF/Boundary Interaction project has been examining Tropical Strom Ernesto from August/September 2006. Tropical Storm Ernesto was a modest tropical cyclone that interacted with a fairly strong boundary across the Southeast. Jordan Dale from NC State has been investigating the role of a Predecessor Rain Event (PRE) on the development of cold air damming, frontal position, and eventual track/rainfall associated with Hurricane Ernesto.

The development of Tropical Storm Andrea late this afternoon and its anticipated track across the Southeast appears to provide another case where a tropical cyclone interacts with a larger scale frontal zone, where there is potential for fairly significant precipitation possibly meeting the definition of a PRE, and the potential for cold air damming across portions of the Carolinas and Virginia.

Earlier on Wednesday before Andrea was officially named, Weather Prediction Center (WPC) noted the development of weak cold air damming and how it may influence the track of the low…

SHEARED CONVECTIVE LOW MOVING UP THE EAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z UKMET/00Z ECMWF BY DEFAULT
CONFIDENCE:  AVERAGE

THERE IS QUITE A BIT OF SPREAD WITH THIS SYSTEM.  THE 12Z NAM/09Z SREF MEAN ARE THE FARTHEST TO THE LEFT, ALLOWING THE SYSTEM TO CROSS MID-LEVEL HEIGHT AND 1000-500 HPA THICKNESS LINES MOVING IT CLOSE TO THE APPALACHIANS.  THE OTHER GUIDANCE IS QUITE DIFFERENT, ALLOWING THE SYSTEM TO ESCAPE ALONG A COASTAL ROUTE, WITH THE 12Z GFS THE QUICKEST, THOUGH IT HAS SLOWED DOWN SOME OVER ITS PAST DAY OF RUNS.  THE 12Z UKMET IS THE SLOWEST.  SINCE THE SYSTEM IS EXPECTED TO MAINTAIN AN AREA OF THUNDERSTORMS FAIRLY CLOSE TO ITS
CIRCULATION CENTER, IT SHOULD NOT BE OCCLUDING/CROSSING MID-LEVEL HEIGHT AND THICKNESS LINES, WHICH RULES OUT THE NAM/SREF MEAN SOLUTIONS.  A COASTAL ROUTE LOOKS BEST AS A WEAK RIDGE OF HIGH PRESSURE SHOULD BECOME REINFORCED BY THE SYSTEM’S INCREASINGLY COMMA HEAD RAIN PATTERN, ESTABLISHING THE WEAKER FORM OF COLD AIR DAMMING EAST OF THE APPALACHIANS AND DIVERTING ITS TRACK TOWARDS THE COAST.  THE 00Z GLOBAL ENSEMBLE GUIDANCE SHOWS SPREAD AS WELL, WITH THE GEFS MEMBERS OUTPACING THE ECMWF/CANADIAN ENSEMBLE MEMBERS.  THE GFS/GEFS MEMBERS CAN TRACK SYSTEMS WHICH HAVE YET TO ORGANIZE INTO TROPICAL/SUBTROPICAL CYCLONES TOO QUICKLY, AND THE ECMWF GUIDANCE TENDS TO ACCELERATE SYSTEMS INTO THE WESTERLIES TOO SLOWLY.  THE PIECES OF GUIDANCE ON THE QUICK SIDE OF THE ECMWF MEMBERS AND SLOW SIDE OF THE GEFS MEMBERS ARE THE 00Z ECMWF/12Z UKMET.  THE 17Z MEDIUM RANGE COORDINATION CALL WITH THE NATIONAL HURRICANE CENTER — NHC — CONFIRMED THIS IDEA.  THE 00Z ECMWF/12Z UKMET ARE PREFERRED HERE WITH AVERAGE CONFIDENCE CONSIDERING ITS PROGRESSIVE NATURE.  CONSULT NATIONAL HURRICANE CENTER (NHC) TROPICAL WEATHER OUTLOOKS FOR THE LATEST ON ITS CURRENT DEVELOPMENTAL STATUS/CYCLONE PHASE.

Also, NESDIS put out a precipitation discussion this afternoon referencing a possible PRE associated with disorganized convection over SC during the afternoon…

EVENT…WEAK PRE SIGNAL…LOTS OF BOUNDARIES…INCREASING MOISTURE…WEAK DISTURBANCE FOR LOCALLY HVY RAINS ALONG BOUNDARIES…MORE RAINFALL FOR
THURSDAY INTO FRIDAY…
.
SATELLITE ANALYSIS AND TRENDS…VERY HIGH MOISTURE IN THE EASTERN GULF OF MEXICO AT CLOSE TO 2.6″ PWAT OR 160 PERCENT OF NORMAL WAS SHOWING SOME WEAK ADVECTION INTO GEORGIA AND SOUTH CAROLINA AT 700MB FLOW. VARIOUS BOUNDARIES WERE ACROSS THE AREA TO ALLOW FOR A LITTLE BETTER FOCUS TO HEAVY RAINFALL.  MID/UPPER LEVEL WINDS WERE GENERALLY 10- 20KTS SO THAT MOVEMENT OF CELLS WERE MOVING BUT COULD STILL PUT DOWN A QUICK 0.5″-1.5″ IN A AN HR TIME PERIOD.  ALL THESE FACTORS NOT QUITE ADDING UP TO IDEAL PREDECESSOR RAINFALL EVENT (PRE) CONDITIONS…BUT COULD IN SOME ISOLATED PLACES ALLOW FOR THE MAIN CRITERIA TO BE MET OF 4″ PER 24HRS. AT THE MOMENT…N-S CONVECTIVE OUTFLOW WAS PUSHING WEST ACROSS E CENTRAL AND SE GEORGIA FOR SOME LOCALLY HVY RAIN THERE.  MORE OF A FRONTAL BOUNDARY WAS HELPING IGNITING CONVECTION ACROSS FAR SOUTHERN GEORGIA WEST INTO EXT SE ALABAMA INTO THE FL PANHANDLE.   AND AN ELEVATED BOUNDARY WAS AFFECTING CENTRAL SOUTH CAROLINA AND INTERACTING WITH THE NORTHERN PORTION OF THE SEA BREEZE BOUNDARY IN CENTRAL SOUTH CAROLINA MENTIONED ABOVE.    COLDEST CLOUD TOP AT -60C ASSOCIATED WITH OVERSHOOTING CLOUD TOP NEAR AIKEN COUNTY WAS ALSO HELPED ALONG BY MERGER AND JUST NORTH OF THE NOSE OF THE GOES WATER VAPOR JET LET CROSSING SOUTHERN GEORGIA WEAK SHORT WAVE THAT HAS RECENTLY PASSED FROM EASTERN GEORGIA INTO SOUTH CAROLINA

Participants in the CSTAR Tropical Cyclone QPF/Boundary Interaction project will be watching this event during the next few days as it provides an excellent real time case to examine.

Bryce began the call by updating collaborators on the potential improved interpolated wind fields to be used in the TCMWindTool. The new method subtracts off an empirically-based error function from the modified Rankine vortex interpolated wind fields. Images showing the proposed new wind field for recent tropical cyclones has been posted online. Collaborators were encouraged to examine the images and provide comments/observations to Bryce by July 1, 2013. The comments will be used to develop a summary report that will be submitted to the TCMWindTool developers, encouraging them to test out the new interpolation method for future Atlantic tropical cyclone seasons.

Bryce also discussed the status of the modeling aspect of the study. A recent survey of literature suggests very few studies have been conducted using WRF-LES for examining the boundary layer structure of tropical cyclones. Bryce has set up his first simulation, which will be run on the NCAR supercomputing environment. The simulation is for Irene (2011). The inner most domain has a grid spacing of 100 m and is centered near the location of landfall. Bryce hopes to conduct a TKE budget at various locations within the inner domain and examine gust factors within the region. Results will be compared to the recent gust factor work conducted in the CSTAR project as well as to a recent paper by Zhu (2008), where a WRF-LES budget was conducted for Ivan (2004).

Jonathan and Reid concluded the call by providing an update to the TCMWindGustFactor and TCMWindReductionFactor tools that will be tested at participating offices this tropical cyclone season. Jonathan is in the process of writing up instructions for installing the tools at the participating WFOs. Reid and Jonathan will lead a webinar soon where they will instruct the participants how to use the tool.

The next conference call is scheduled to take place Wednesday, July 10, 2013 at 11 AM.

Conference Call Slides

4 participants

• Barrett Smith (RAH)
• Gary Lackmann (NCSU)
• Jordan Dale (NCSU)
• Jonathan Blaes (RAH)

Notes:

• Jordan Dale continues to investigate the role of a Predecessor Rain Event (PRE) on the development of cold air damming, frontal positioning, and eventual track/rainfall associated with Hurricane Ernesto.

• Jordan is using potential vorticity to assess the strength of the PRE in the RUC analysis and WRF control run.  The initial findings indicate that the WRF simulation of the PRE was too weak, compared to RUC analysis (which also showed PV slightly further to the south).  This may explain why the WRF simulations have done a poor job in simulating the strength of the CAD.

• The PV analysis shows the two main PV features with Ernesto and a synoptic scale trough over the Ohio Valley merging as the Ernesto moves inland and undergoes extra-tropical transition.  This likely explains the northwestward turn in the track of Ernesto as it moved north across Virginia.

•  It was hypothesized that the PV generated from latent heating in the PRE may have had an impact on the track of Ernesto by altering the larger scale flow.  This can be studied by inverting the PV with the PRE to see how to large scale flow changes.  At the moment Jordan is not sure if there will be time to tackle this before his thesis defense.

• Analysis of relative humidity fields suggests the WRF simulation were too moist at low levels, which would also have limited the amount of stabilization and CAD development.

• To build upon on the findings that the WRF under-represented the CAD, Jordan plans to rerun the WRF model and reduce the relative humidity in hopes of strengthening the CAD.  This is in progress at the moment.

•  Jordan plans to defend his thesis in late June or early July.

Figure 1: Normalized sustained wind speed error as a function of quadrant and distance from storm center for the 271 tropical cyclone analyses examined.

In order to quantify the error as a function of distance from storm center and quadrant, a four degree polynomial fit was applied to the data. Due to the sensitivity in the interpolation to the radius of maximum winds and the likely errors in the HWind analyses near the storm center, data points outside the radius of maximum winds were excluded when developing the error function. The resulting R^2 values were well above .90, indicative of a good fit to the data. Figure 2 shows the averaged wind speed data along with the developed polynomial fits.

Figure 2: Average error as a function of quadrant and distance from storm center (black dots) and four degree polynomial fit to the data (red solid curve).

Outside of the radius of maximum winds, the error functions were subtracted from the modified Rankine vortex interpolated wind field. Figure 3 shows a sample comparison for Danielle (2008) of the HWind analysis, modified Rankine Vortex wind field, and the new interpolated wind field after the error function was applied to the data. The new wind field displays much more similarity to the HWind analysis. This is particurly true within a distance of 200 km from the storm center, where the wind field is reduced to values much more in line with the HWind analysis. Furthermore, the four quadrant asymmetries are more defined in the new interpolated wind fields. After examining all 271 new wind fields, the error function consistently reveals these features.

As a next step, the research team is currently collaborating with the TCMWindTool developers for potential additions to future versions of the tool. Since the new wind field is simply an additive to the existing interpolated wind field, the incorporation of the improved wind field into the TCMWindTool is not expected to be labor intensive. The goal is in future years to have the various Weather Forecasting Offices with the option to apply the error function to the interpolated wind fields prior to outputting the raw sustained wind speed grids prior to forecaster modification.

Figure 3: HWind analyzed (left), modified Rankine vortex interpolated (center), and wind speeds after the error function is applied (right) valid at 12z 28 August 2008.

Keith’s presentation summarized much of his research into the climatology of High Shear, Low CAPE (HSLC) convection and improving the forecasting of HSLC significant severe convection including:
•    background on why High Shear, Low CAPE (HSLC) severe convection is such a critical forecasting problem
•    summary of his research data and methods
•    environmental climatology
•    development of new forecasting techniques and parameters including the Severe Hazards in Environments with Reduced Buoyancy (SHERB) parameter
•    verification of several formulations of the SHERB parameter
•    summary and future work

This research is highly relevant to NWS operations and was a collaborative project between NC State University, nearly a dozen WFOs, and the Storm Prediction Center. The presentation is available to NOAA Google drive account holders at this link.

Congratulations Keith!