1/31/2013 HSLC Conference Call Notes

Attendees: Matt Parker, Jason Davis, and Keith Sherburn (NCSU), Andrew Zimmerman (AKQ), Mike Cammarata and Tony Petrolito (CAE), Frank Alsheimer (CHS), Justin Lane, Pat Moore, and Larry Lee (GSP), Jonathan Blaes (RAH).

1. Jason gave an update on his work. His power point can be found here. (Note: the power points will not be viewable unless you have a NOAA gmail account). The azimuthal shear component (available in WDS-II) of his work brought up the issue of how this quantity is derived, and how it compares with GR2’s NROT. The methodologies are very similar, as both employ the concept of a linear least squares derivative scheme to estimate the rotational component of the wind field. My dumbed down understanding of how NROT is computed is that the rate of azimuthal change in the radial velocity (i.e., the azimuthal gradient) is calculated. The calculation is made at each pixel, with the gradient calculated across the surrounding  9 x 9 pixel area.  The result of this calculation can be called the “ROT.” This value is then normalized (divided by a default or user-defined number) based upon range from the radar. If you want a better understanding of the methodology (someone else can probably understand and explain it better than I!), here is a paper describing it: Smith and Elmore (2004).

There was further discussion of azimuthal shear and NROT. There was a general feeling that there should be something similar to these fields made available in AWIPS. That is one of the possible outcomes of this study.

2. Keith gave an update on his work. His power point can be found here. The gist of what he is working on now is that he is trying to make the SHERB universal (i.e., applicable to the entire country and not just our region). So far, he hasn’t had a lot of luck with this. Part of the reason is that there may be 2 (or more) HSLC regimes (i.e., the typical “Eastern” HSLC environment, but also largely nocturnal “classical” Midwest severe environments in which SBCAPE is small, but MUCAPE large). SHERB is unlikely to apply to the latter case.

Keith is also beginning to work on numerical simulations. Attendees agreed that it would be beneficial for him to show some of the results of these simulations in future calls.

There was a discussion about the 30-31 Jan HSLC event. There were significant tornadoes in FFC’s area, and some significant wind events toward the end of the episode in AKQ’s area, but severe weather was marginal in most areas in between. SHERB was generally high (~1.25) across the entire area at some point during the event, so there was some speculation as to why this appeared to be a marginal event for the majority of the WFOs in the study area. Andy at AKQ did show some interesting slides of an axis of elevated SHERB over southeast Virginia toward the end of the event, with a subsequent   intensification of radar echoes and uptick in severe weather reports noted as the QLCS interacted with this air mass. JB followed up on this with a brief presentation that should be in your e-mail.

3. Critical Action Item:  It has been discovered that the method for calculating NROT in GR2 changed in September 2011 (Version 1.8) to accommodate the 88Ds “superres” functionality.  The result is that values of NROT for any given radar volume scan may be different depending upon what version of GR2 you’re using. Please make sure that you have been using version 1.8 or later.  If you haven’t, you will need to update any work you’ve done with the later version. Sorry!  The latest version can be found here.  

4. All WFOs are hopefully continuing to work on their case study(s). I’ll take this opportunity to remind you of the case study methodology, found here. I have yet to receive any requests for modified RUC proximity soundings, so just a reminder that a) this is a component of our case studies and b) I can get you this data in a RAOB format (via Dave Radell at ERH). If some of you are using NSHARP or other software packages that allow you to display data from GEMPAK files, even better.

5. JB led a brief discussion on R2O activities. A small team needs to be assembled to act as liaison with WDTB. This needs to happen sooner rather than later. If you are interested in leading such a team, please contact JB.

This entry was posted in CIMMSE, Convection, CSTAR, High Shear Low Cape Severe Wx. Bookmark the permalink.

1 Response to 1/31/2013 HSLC Conference Call Notes

  1. justingsp says:

    This post has been updated. After rereading it, my explanation of how NROT is calculated was a bit…odd. Also, the critical action item has been updated with new instructions.

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