2015-04-22 EVENT: TX/OK

[Bob Schafer]

(@James) Not quite. The Hereford storm passed a bit N of Lockney. The Lockney storm was a discrete cell that formed to the SW of the Hereford storm and to my annoyance spit rain rain on us all day while we were trying to chase the Hereford storm. Everything pretty much congealed into one MCS at dusk.

 

[Michael Snyder]

Here are a couple of radar images from the supercell east of Hereford. Nice couplet, surprised there were no tornado reports from this. I hope someone that was on it will post. I did not have a chance to look at the HRRR earlier today but this looks like it was in the exact location that Jeff said was modeled by the HRRR and NAM 4km.


In the second two images, I marked the interface of the inbound/outbound winds in the velocity image, and then switched to the reflectivity image while leaving the marking - it seems oddly displaced from the hook, even though the radar updated by two minutes when I switched... Thoughts?

I was on it at this time and twice I saw dust on the ground, possible weak landspout rotation, twice. The MESO was rotating nicely for about 10 min at one point and there was a nice visible updraft rotation for about 1-2 min. I need to go through all my stuff to confirm anything, but I think it may be inconclusive.

 

[LocoAko]

Here are a couple of radar images from the supercell east of Hereford. Nice couplet, surprised there were no tornado reports from this. I hope someone that was on it will post. I did not have a chance to look at the HRRR earlier today but this looks like it was in the exact location that Jeff said was modeled by the HRRR and NAM 4km.

In the second two images, I marked the interface of the inbound/outbound winds in the velocity image, and then switched to the reflectivity image while leaving the marking - it seems oddly displaced from the hook, even though the radar updated by two minutes when I switched... Thoughts?

I noticed the same thing. I'm not 100% sure and could be wrong, but I believe this to be an example of vertical side-lobe effects contaminating the 0.5 degree velocity data. I recently got to hear Steve Piltz (MIC from Tulsa) talk about this very thing. In cases with an extremely strong vertical reflectivity gradient right above the surface in the overhang, the sidelobes can map the mid-level mesocyclone rotational signature down onto lower tilts. The reflectivity won't be too affected because of the significant decrease in power of the sidelobes compared to the main lobe, but the velocity data is included just the same in the processing of the data. Unfortunately I didn't think to take a look at the spectrum width yesterday while seeing the feature, but I think it may have been telling. If this is in fact the case, perhaps it isn't surprising there weren't tornado reports with it as I didn't notice too much of a velocity signature near the actual hook region (though I was admittedly only half paying attention, so someone correct me if I'm wrong).

Here's a link to a presentation on the subject by Steve Piltz and Don Burgess: http://www.slideserve.com/phuc/steve-piltz-wfo-tulsa-ok-don-burgess-cimss-norman-ok

Jake

 

[Jeff Duda]

Here are a couple of radar images from the supercell east of Hereford. Nice couplet, surprised there were no tornado reports from this. I hope someone that was on it will post. I did not have a chance to look at the HRRR earlier today but this looks like it was in the exact location that Jeff said was modeled by the HRRR and NAM 4km.


In the second two images, I marked the interface of the inbound/outbound winds in the velocity image, and then switched to the reflectivity image while leaving the marking - it seems oddly displaced from the hook, even though the radar updated by two minutes when I switched... Thoughts?

Pretty sure you're looking at either 1) de-aliasing failures in the velocity data, or 2) otherwise poor velocity estimates in a region of low SNR. If you look closely, those higher velocities are co-located with pixels of very low reflecitivity, indicative of a dearth of scatterers. Thus there is very little energy returning to the radar, and so much of the resulting signal consists of noise from the system + any random atmospheric noise. In other words, there isn't much legitimate meteorological signal in that area, and I believe the error of velocity measurements is somewhat a factor (albeit, indirectly) of SNR.