All Three Meso Detection Algorithms Struggle to ID Lone Supercell

Posted in News on by Tiffany.

CPTI upper left, New MDA upper right, legacy MDA lower right, digital MD lower left.

A discrete supercell tracked out of the Oklahoma Panhandle into southwest Kansas from 2120Z to 2220Z on 5/23/19.  During the first portion of this loop, the mesocyclone detection algorithms had a very difficult time latching on to one dominant meso, plotting up to four separate IDs for the same storm.  Eventually, both the legacy and new meso algorithms resolved one primary circulation, while the digital version continued to jump around a bit with the ID number and location.  For the last 15 min. of this animation, the MDA data completely dropped out.  The main point here is it was nearly impossible to utilize this product operationally because of the meso identification and data dropout issues.  It’s worth a mention that the legacy and new MDAs had about a 15-20 min. window of good meso tracking after the consolidation to one ID and before the data was lost. -Roy

AzShear Effectively Detects Anticyclonic Rotation

Posted in AzShear, HWT, NMDA on by Kristin Calhoun.

Two supercells southwest of Lubbock produced perplexing base radar signatures with a clear right-mover reflectivity signature but anticyclonic rotation evident in storm-relative velocity. To its credit, the MRMS AzShear product picked up on the anticyclonic circulation effectively and should be able to detect the rare anticyclonic tornado!

None of the mesocyclone detection algorithms picked up on the anticyclonic rotation. Perhaps this is part of their design. The New MDA tried to detect a mesocyclone southeast of the main anticyclonic circulation on the gradient of the strong outbound velocities, but it is incorrect.

-Atlanta Braves

Mid-Level Mesos

Posted in News on by Justin.

The merged AzShear product has done a solid job keeping up with low & mid level rotation tracks so far this afternoon in the Texas panhandle. Most of the storms over the last hour have exhibited weak low level rotation but much stronger mid level rotation. The merged AzShear product showcases it well with much hotter values on the mid-level product compared to low level. This also matches well with the threats observed so far with several reports of large hail, but any tornado threat has yet to materialize.

Dave Grohl

NUCAPS Procedures Usefulness

Posted in HWT, NUCAPS on by Kristin Calhoun.

The NUCAPS Quick  Guide from JPSS includes a few procedures. Here I show the utility of a few of those procedures for combining GOES Satellite data and NUCAPS data.

This procedure plots 400-200mb relative humidity and GOES-16 water vapor. You can see the representation of the dry air across the northern US and the systems in the Plains & southeast.

Another procedure compares GFS, HRRR, and NAM lapse rates with the NUCAPS lapse rate info. This is a good check to see if model lapse rates are performing well or where they need to be taken with a grain of salt.

Another procedure plots 850-300mb RH and low-level water vapor. The product shows the system in the Plains and the system in the Ohio Valley. Drying is also obvious in the southern Great Lake and North Dakota.

I like the procedures provided in the JPSS Quick Guide. I am starting to understand the applicability of the NUCAPS data little bit more. These procedures are helpful in contextualizing the provided data fields.

-Atlanta Braves

Decrease in GLM lightning activity coincident with 2 inch hail report

Posted in GLM, Live Blogs on by Justin.

A storm just northeast of Amarillo developed quickly along a frontal boundary, and quickly showed supercellular characteristics with mid level rotation and a 65+ dbz core reaching about 35 kft MSL. 2 inch hail was reported with this storm during this time. GLM data again shows a decrease in both Flash Extent Density (top right) and Event Density (top left) show a notable decrease in GLM lightning activity while ground based radar remains fairly unchanged, and both the IR satellite presentation (bottom right overlaid on visible imagery) and radar data (not shown) indicate the storm maintained intensity and if anything, had strengthened a bit.

-64BoggsLites

Comparing NUCAPS Modified Soundings and 18Z RAOBs

Posted in News on by Kristin Calhoun.

A satellite pass at around 19Z allowed us to compare NUCAPS modified soundings with 18Z RAOBs. A comparison of a NUCAPS sounding near Amarillo seemed to reasonably represent the mid and upper levels with the 18Z KAMA RAOB. The NUCAPS sounding had slightly lower freezing level and -20C and -30C heights compared with the RAOB (10.9, 19.0, and 23.2 kft vs 12.2, 20.8, and 25.4 kft, respectively). The midlevel lapse rates were comparable at around 8.0 C/km. However, the NUCAPS sounding appeared to struggle with the lower levels, not representing the subsidence inversion evident on the RAOB, and being too cool and dry at the surface (T/Td of 20/17C on the NUCAPS compared with 24/19C on the RAOB). This led to lower CAPE estimates from the NUCAPS than were observed by the RAOB.

Similar results were seen in a comparison of the 18z KLMN RAOB with a NUCAPS Modified sounding near Lamont, OK:

Ron Dayne

AllSky as a good proxy for dryline location and CI

Posted in AllSky, HWT on by Kristin Calhoun.

The AllSky Layer Precipitable  Water product showed utility in identifying and tracking the dryline as it moved into the Lubbock CWA. The dryline entered the CWA at about 1930 UTC.

Coincidentally, the KLBB radar shows convection initiation around 19:30 UTC as well.

And the convection continues to develop:

The AllSky product remains a very useful tool for situational awareness and 2-D environmental familiarization.

-Atlanta Braves

Significant Difference Between Operational and New MDA

Posted in News on by Justin.

Thursday afternoon convection continues to cook in the northern Texas panhandle. Several mesocyclones were detected by the different algorithms along a broad, down radial shear zone. The values from the operational MDA (bottom left) and digital (bottom right) were very high, topping out at 24+ LLRV for all three mesos detected at the lowest scan. That is much higher than values seen for some tornadic supercells earlier in the week, and does not match the velocity data with no strong, tight couplets evident. The new MDA is much more restrained and actually has the strongest RV values above the lowest scan, which matches up with the velocity data much better as the values should be lower with broad, weaker areas of rotation.

Dave Grohl

Comparing the modified and unmodified NUCAPS sounding from Western Oklahoma on May 23

Posted in News on by Michael Bowlan.

While waiting for any convection to develop in PA, I ventured into western Oklahoma to do a comparison of unmodified and modified NUCAPS soundings in an area under an enhacned risk of severe weather. The soundings examined were near the Texas border (point E below).

We’ll first look at the visible satellite and observations at 19Z.

Notice that point E is near a WSW/ENE oriented boundary. Obs near the point show temperatures in the mid 70s, with dew points in the mid 60s. So let’s take a look at the unmodified NUCAPS sounding first.

It uses a surface temperature of 63F, and a surface dew point of 50F, both more than 10 degrees below the nearby observations. These inaccurately low values give, as one would expect, no sign of instability (CAPE=0). Looking at the modified NUCAPS gives a different picture, however.

In the modified sounding, the surface temp is 69, and the dew point is 65, which is much closer to the observed surface obs. This changes your surface-based CAPE to 2055 J/kg, vs. 0 from the unmodified. It also has a sharper low level inversion, which one wood expect based on the stratus deck in place.

To “verify”, let’s look at the SPC mesoanalysis.

Sure enough, the mesoanalysis shows CAPE at around 2000 J/kg.   Clearly, this is another case where the modified NUCAPS sounding is a noticeable improvement over the unmodified sounding.

Thorcaster

Single-Radar AzShear Tornadogenesis Success

Posted in AzShear, HWT on by Brandon Smith.

Single-radar AzShear does a really good job of identifying preferred locations of circulation along a QLCS. The bullseye started as an elongated area of enhanced AzShear and then converges into a more concentrated area. This product provides a helpful heuristic for identifying tightening circulations in the midst of noisy velocity data with less-clear signatures.

One can easily see the congealing AzShear bullseye before the circulation tightens the tornado starts.

On the contrary, the Merged AzShear product demonstrated some latency issues that would lead to less confidence in circulation tightening.

This image, taken at the same time as the KEOX AzShear product, shows several unorganized areas of enhanced rotation right before the tornado started in the merged AzShear product. The tightening circulation is an important precursor to tornadogenesis and the merged product seems to struggle. -Atlanta Braves