ProbTor during Tornado Warning

Posted in AzShear, HWT, ProbSevere on by Michael Bowlan.

The NWS office in Little Rock started issuing tornado warnings on storms along the line so I pulled up the ProbTor product to see how it performed. For the storm near Knoxville, I can’t figure out what’s going on but I’ll attempt to document it here. For each time, I plot CPTI top left, LZK SRM top right, low-level AzShear bottom left, and spectrum width bottom right.

At 1902, the algorithm has a 60% ProbTor based on high LLAzShear (0.021 /s). I don’t see any high values on the low-level AzShear product, but perhaps I’m missing something.

At 1904, a bullseye of high LLAzShear pops up just east of Knoxville. ProbTor is still 60%, which now makes sense to me. This identified shear region is not in the right place for a tornado and is just convergence along the line, but the ProbTor uses what it has and seems to generate an understandable ProbTor.

At 1906 the LLAzShear bullseye east of Knoxville persists,  but now the ProbTor drops to 19% with a LLAzShear max value of (0.009 /s). I still sample 0.020 /s in the bullseye. Spectrum width is not horrible (~7 kts) in the area of the AzShear bullseye. The AzShear detection is obviously misleading for a tornado, but the ProbTor product does not seem to be performing as we’d expect it.

At 1908 the bullseye in AzShear goes away and the ProbTor drops even further to 6% (as expected). The persistence of the bullseye in AzShear with an associated significant drop in ProbTor is perplexing for this case! -Atlanta Braves.

 

Single-Radar AzShear vs MRMS Merged Shear: Lag Time

Posted in News on by Thea.

An advantage of single-radar vs. merged az shear jumped out right at the start of today’s simulation: lag time. The single radar product looks to have a 2-3 minute jump on the merged data with respect to low-level rotation, as shown in the time sequence below. The tightening/strengthening rotation couplet begins to jump off the screen in the single-radar data at the 2000 scan further intensifies through 2004. The area of strengthening low level rotation is much more muted in the merged data at 2000. It is more noticeable in the 2002 scan before becoming quite obvious by 2004. This small lag may not be significant, but it could be the difference of a  few minutes worth of lead time in warning decisions.

Dave Grohl

Single Radar AzShear Helpful in picking out strongest rotations

Posted in News on by Thea.

In going through the case of March 3, 2019, One if the useful items that stood out was the single radar AzShear Product. See the screenshot below.

Looking at the base velocity product in the upper right window, there are several circulations that can be seen. Similarly, the reflectivity image (lower right) shows several cells of potential interest. Fortunately, the AzShear product (left) highlights the cells you should investigate first by looking at the cells with the highest AzShear Values. This will be very helpful in decision making on the warning desk in a forecast office.

Thorcaster

 

 

ProbSevere Running Hot in SGF CWA

Posted in News on by Michael Bowlan.

Looking at convection developing upstream across southern MO, I noticed prob severe had an object advertising 71% for TOR in the northern portion of the SGF  CWA (about a county and a half south of the CWA bondary. This particular cell does not show any rotation in the SGX base data, the Azimuthal shear doesn’t show much, and GLM lightning shows no electrical activity with this cell. I’m assuming the algorithm is keying more on environmental factors than anything else in coming up with this probability?

-64BoggsLites

EWP Operations Tuesday, May 21

Posted in News on by Michael Bowlan.

Today we are continuing on with the strong upper level trough moving into the Midwest. Today will be focused on mainly linear convection focusing on a QLCS moving through Arkansas and Missouri this afternoon. We will be operating in the St. Louis and Little Rock CWAs with an opportunity to also monitor for developing convection back near the center of the upper low in central Kansas later this afternoon.

-Michael

 

An artifact in AllSky Products…

Posted in AllSky, HWT on by Michael Bowlan.

I was taking a first look at AllSky products this afternoon and put together a four-panel procedure. I expected to see some noise/sharp gradients in the data because differing pixel population methodology, but viewing a loop revealed an interesting artifact:

There appears to be an artifact in northern Arkansas that looks a little bit like a dinosaur head. This artifact is visible in parcel Lifted Index (to 500 mb), all PWAT products, and CAPE, but not in Total Totals, K Index, or Showalter Index fields. The artifact does not appear to be dependent on the Cloud Type field. Perhaps this artifact is associated with terrain in Arkansas but warrants further investigation. -Atlanta Braves

Comparing All Sky LAP CAPE with RAOBs

Posted in News on by Michael Bowlan.

One of the forecast problems of the day for the LSX forecast area is determining how far north the reservoir of instability will extend. It may be useful to monitor the all-sky LAP CAPE product in concert with surface obs to assess the destabilization throughout the day. Looking at a comparison of the product with selected 12Z RAOBs, the product appears to have a reasonable representation of CAPE values so far.

The ILX RAOB is in the stable air well north of the warm front:

Although the MLCAPE at SGF is zero, the LAP CAPE produce is indicating around 400 J/kg of CAPE, which appears to reflect the MUCAPE in the sounding:

The LAP CAPE product underestimated the CAPE at LZK, but still gets the general idea:

While some of the details may not be correct, and it is blocky in places, the LAP CAPE product appears to be doing a reasonable job at depicting the reservoir of instability over the southern Plains. By 18Z, it showed the northward spread of instability in concert with the northward advancing warm front:

Ron Dayne

All Sky LAP CAPE

Posted in News on by Michael Bowlan.

Looping the AllSky LAP CAPE product, moisture and instability is noted spreading northward toward the LSX CWA, which remains to the north of a warm front. One thing I noted is the western edge of the instability plume across eastern Texas jumps back and forth when looped. Not sure if this associated with the product itself or some other issue, but it was noteworthy. Otherwise the product seems to do a nice job depicting the instability plume spreading northward.

 

-64BoggsLites

 

GLM RGB first view…

Posted in GLM on by Tiffany.

So, here’s an interesting concept…GLM data merged with GOES-16 IR (10.3 um) to create an RGB.  I think I like it!  Data fusion concepts like this are increasingly important in data-heavy AWIPS, especially during severe weather events and for situational awareness activities.  So, this RGB uses Flash Extent Density as the Red component, Minimum Flash Area as the Green component, and 10.3 um imagery from GOES as the Blue component.  The RGB has been tailored such that high FED results in increased red values, while Minimum Flash Area is reversed with respect to green colors (lower values equal increased green) and the IR temperatures from the 10.3 um band are also reversed so that lower temperatures result in higher blue colors.  So, for example, the end result is that high FED, low minimum flash area and cold IR temperatures result in brighter colors (near white) that physically indicate intense lightning, collocated with intense updrafts and cold cloud tops.  Meanwhile, anvil-type lightning (cold cloud tops, generally low FED and high minimum flash area result in colors more towards purple.  Colors leaning towards reds, yellows are relatively young, but intense convection in new, warmer convective cloud tops.  This shows up well, watching young convection feeding into an area of ongoing convection at the tail end of the convective complex today.  Ok…I’m writing this at the tail end of activities today, so I had to rush through this.  =)

Kris

Poor Correlation: GLM vs. Ground-Based Lightning Networks

Posted in GLM, Live Blogs on by Kristin Calhoun.

Lightning data in the Texas panhandle late this afternoon showed low correlation between GLM output and data from ground based lightning networks. The output from the GLM flash extent density product appears underdone when compared to data from ENTLN, which has numerous areas of clustering in the vicinity of stronger thunderstorm updrafts. Meanwhile, the GLM flash extent density data shows low values and not much variance within the same general vicinity.  The problem does not appear as significant in western Oklahoma where the GLM flash extent density product shows much higher values in concert with clustering in the ENTLN data. It is difficult to pinpoint what might be causing this issue just by looking at the data alone.  Dave Grohl