Devastation in the Mid-South

Tornadoes wreaked havoc across the U.S. Mid-South on Friday night into Saturday, as an energetic shortwave trough tapped into the abundant moisture and atmospheric instability in the southern U.S. One supercell, persisting for at least 11 hours, spawned a very long tornado (probable path length > 200 miles), generating some of the night's worst damage in Mayfield, Kentucky. Meteorologist Jack Sillin documented the forecast of the supercell's evolution and some preliminary facts (Figure 1). With over 100 tornado deaths, the day was the deadliest since 2011. 

Figure 1: Depiction of NWS forecast evolution of the Quad-State Supercell, by Jack Sillin.

ProbSevere guidance is used by NWS forecasters to aid in warning decision making. A new version of ProbSevere (version 3) is being developed and tested at the University of Wisconsin, honing and improving the probabilistic guidance. For the quad-state supercell, ProbSevere v3 (PSv3) was generally 10-20% higher than PSv2 in the hours before it became severe (Figure 2). For instance, PSv3 was 68% at 22:28 UTC, compared to 46% for PSv2. The top predictors contributing to the higher probability were:

1. 1-3 km mean wind (48 kts)
2. 3-6 km MRMS AzShear (0.011 /s)
   
3. 0-2 km MRMS AzShear (0.012 /s)
4. Effective bulk shear (65 kts)
   
5. Effective SigTor Parameter (1.73)
   
6. Normalized satellite growth rate (2.8%/min; "moderate")

Tornado probabilities were higher for v2 than v3, which we've found to often be the case (i.e., ProbTor v3 is more conservative). However, the trends in both PTv3 and PTv2 matched the trending threat of the supercell well. Users can inspect the storm's trends in probabilities and predictors here. 

Figure 2: Time series of ProbSevere v2 and ProbSevere v3 for the quad-state supercell. Note that severe reports are preliminary. 

Figure 3: ProbSevere v3 contours with MRMS MergedReflectivity at 03:30 UTC and NWS severe active weather warnings, when the tornadic quad-state supercell was in Mayfield, KY. 

Mesoanalysis Summary for E. CO

Looking at a surface map there looks to be a boundary, possibly a weak warm front, over E CO that storms are firing off of.  A similar feature can also be seen in the satellite data taken at the same time.

 

Lightning:

The FED did not give as much information about the growth stage of the updrafts as the flash minimum area did.  Also noticed the VII trend resembled a similar trend as the flash minimum area did.

The flash minimum area is also a good way to help catch the eye of what updrafts are strengthening, especially if the trend of low flash minimums persists.  Great tool to use at first glance of which storms need to be watched and which don’t.

-Dwight Schrute and Accas

Saw several examples of the flash density for lightning either muting out or not showing the trend the flash minimum area was showing.  In the past I have been using the flash minimum area to help me see trends in the lightning, but am now seeing that I should be using the flash minimum area instead if I want to see trends in lightning activity.  I use the lightning trends to help me know if the storm is rapidly intensifying or suddenly weakening and possibly about to generate a severe downdraft.  Being able to see these sorts of trends better can also help communicate a potential threat for storm intensification or severe wind development to those in the path of the storm.

-Accas

Area of coverage greater for the  minimum flash vs extent density.

Next time stamp, we can see increased minimum flash area lightning over the new updraft and a pixel from the flash extent density. So the minimum flash area would likely be the best bet for using the tool with decision support services in mind due to its higher sensitivity.

-Dwight Schrute

This was a scenario where we were baffled by how little lightning was being shown from both the minimum flash area and flash extent density products. We asked why so little lightning compared to how much ice is in the storm, combined with MESH indicating a 2” hail stone.  The lightning with this maturing storm was not being sampled well.

-Dwight Schrute

Gridded NUCAPS Issue WI/MN

 

Sampling Total PW gridded NUCAPS with contours overlaid on top, we see that the values are unrealistically high (over 3 inches). The 18 UTC soundings from the Twin Cities offices shows PWATs only around 1.30” which confirms this is incorrect. Also, the contours are in centimeters, not inches which is what the images. I plotted the NUCAPS sounding points to see if the points were “yellow” but it looks like the points were unavailable at this time step.

From this time step, the gridded NUCAPS matched up very well with the special 18 UTC soundings and the total PW values are realistic and make sense given the environment. Also the NUCAP points are all green which solidifies that the satellite was able to obtain a good sample.

– Fear the Shear

NUCAPS in the ARX Area

 

Comparison of a modified 18z NUCAPS sounding in far southern MN suggested a fairly accurate temperature profile (surface temperatures in southern MN were warmer than up at MSP.). NUCAPS did miss a pronounced dry layer around 700 mb, while it was too dry higher up especially around 500mb.

We also noticed some erroneous gridded NUCAPS precipitable water data round 16z across the Midwest (values of 3 to 4 inches). These looked more reasonable with the pass at 18z.

There was also 120 to 150% 850mb and 925mb RH.

The only satellite pass around that time was Metop-A. While the soundings were yellow, they generally were ok and didn’t match the gridded data.

– Barry Allen

ProbSevere On Some Early Storms Near ARX

 We noticed a relatively high ProbSeverev3 (53%) on a rather innocuous looking storm (MESH around 0.5”) around 2030z. This was higher than the v2 value of 36%. The individual probs were relatively evenly weighted at lower values near 30%.

(clockwise from top left) MRMS 18dbz echo top, MESH, reflectivity and ProbSevere (storm in center), and low-level MRMS azimuthal shear.

(clockwise from top left) GLM FED, GLM MFA, reflectivity and ProbSevere (storm in center-right), and GLM TOE.

GLM FED was unimpressive, though it’s unclear how much of this is related to lower detection efficiencies in this area. ENI total lightning was halfway decent. High DCAPE values and other environmental parameters may have been sending the ProbSevere v3 higher.

Timeseries for the storm of interest.

Another storm further to the west over SE MN had slightly lower MESH (.39”) but in this case PSv2 was higher at 48% vs Psv3 at 23%.

– Barry Allen

ProbSevere Time Series

 I found the ProbSevere time series helpful today as we “triaged” storms and tried to identify storms that may become severe. While the capping inversion stayed strong and therefore prevented storms from becoming severe, it was great to see storms follow a similar intensification process identified by the Prob time series time graph. Most storms intensified in a similar fashion but capped out when ProbSevere reached ~40%. After 40% storms would remained steady state and then gradually weaken. Noticing these trends and seeing them plotted visually helped us pick up on the trends. Any storm that deviated from this and grew upscale faster would be easy to identify on the ProbSevere time series graphs. We knew what the “norm” was for storms in this capped environment because of the time series graphs. We surmised that once the cap broke (which would be after the experiment ended), we could quickly ascertain when storm would finally be able to grow upscale by looking at their respective time series.

– Fear the Shear

Progressive Disclosure and GLM Flash Points

 When loading GLM Flash Points, there is no preset density of the data.

This does affect how much flash point data is displayed depending on the zoom level of the map. In the 2 maps below, within the red square of the larger map, 13 flash points are indicated as opposed to 15 once you have zoomed in further:

Unless the forecaster knew to increase density to max, this could obscure some important clusters of lightning coincident with storm evolution.

– Guillermo

GLM Flash Points

 Noted GLM flash points really help speed up the process of identifying where the cell of interest was located.  In the past, I would have to make a manual, on the fly “calculation” in my head where the actual cell was located.  If there was only one cell, that was easy by looking at radar.  When you get into the complex thunderstorm situations, that can be difficult and in the worse cases, it is too involved.  Seeing how the flash points seems to fix and/or surround the updraft, really helps speed this process up and give confidence to the forecaster which cell is the cell to be worried about.  This could also help with warning confidence.  The  image below shows an prominent example of this.

It is hard to see the flash points but there are 6 points surrounding the core of this small storm.  I chose this one to verify the positioning as it was on its own so it was easy to figure out which one it came from.  As such, seeing how close this is to the core, it makes it much easier to identify which FED “spike” is from which core.  

When looking at satellites with flash points, it also help confirm the location of the core as the ABI imagery is parallax corrected.

– Strato-Dragon

GLM Lightning Preset 4-Panels

 GLM lightning data provides very useful information to the operational forecaster, especially when properly combined with radar/satellite imagery. Would it be possible to take best practices suggestions from frequent users to lead to the creation of some pre-set 4-panel procedures that could be found in the AWIPS GLM data section (similar to what is available with radar base date, etc.)?

Sample 4-panel image pulled from the GLM Quicklook Guide

– Guillermo

Derived Motion Winds in AWIPS vs Rabin Optical Winds

 Had attempted to compare the AWIPS Derived Motion Winds to Bob’s Optical Winds: https://www.ssec.wisc.edu/~rabin/winds/goes16/b13/1/m1/iris/layers_loop.html but encountered eventual CAVE crashes each time. While, on occasion, being able to display and toggle different layers of DMW in AWIPS before crashing, I did find that the Optical winds had much higher resolution wind data than what was available in AWIPS (with max density) and wind directions, by layer, seemed to well agree.

It is my opinion, though, that, while the DMW winds in AWIPS could be useful, they seem resource-intensive and come with a significant likelihood of freezing or crashing the CAVE instance. I find it much quicker and more reliable to view the similar data via Bob’s webpage.

– Guillermo

Modified NUCAPS Soundings-FSD

 Noticed some issues with the modified NUCAPS soundings in the FSD area.  In some of the cases where the odd errors in the soundings.  Not sure what caused them or why they showed up but here are some examples.

First pass of NOAA-20.

Note the odd look of the temperature trace in the mid levels (note the sharp increase in temp just above 700mb).  This was noticed in a number of the neighboring dots.  This error seemed to get better the further away you got from this location.  We were hoping this would improve when the second pass came overhead later at 20Z.  Below is an example of this error from the second pass.

Second pass NOAA-20.

As can be seen from the image above, the second pass still had this error (note the sudden change in the temperature trace at about 600mb).  After looking at the conditions in the area, several questions as to why this was occurring came up.  It appeared the surface temperatures were rather reasonable and the atmospheric conditions were also close to what the sounding may be trying to depict.  There was some thought the modified NUCAPS may be having difficulty with the moisture trace rather than the temperature trace.

It was also noted that when using the “pop up skew-T” function it would not see this error.  It was discovered the reason for this is the “pop up skew-T” function would not see the modified soundings that Nsharp would display.  

Why this was occurring I really could not tell.  One of the PIs indicated the algorithm may not be handling the moisture trace well.  It was also noticed the surface wind fetch was coming from the southwest and that is coming off the sandhills of Nebraska.  This is a very wet area and is perpetually wet.  Is it possible that some localized moisture advection was not accounted for?  Can’t say for sure but mention it here to indicate what could be going one.  

-Strato-Dragon

NUCAPS Multi-Sat Sampling

 I was pleasantly surprised to see that when multiple sources of NUCAPS data were displayed at the same time that I could sample, via the pop up Skew-T and moving the mouse across the sounding swath, all sets of NUCAPS data and that it wasn’t dependent on which source of NUCAPS was ‘editable’.

However, depending on WHICH source of NUCAPS soundings was indicated as ‘Editable’ (in this case, the METOP-A – in blue), only those soundings could be opened in the NsharpEditor. Not necessarily a big deal but it is something that some folks may need to have explained to them.

Additionally, I have found the pop up Skew-T doesn’t always work. Often, it seems that when the NUCAPS data is more than an hour old or so, moving the mouse across the soundings results in no changes in the pop up readout. Is this related to the ‘age’ of the NUCAPS data or a bug with the pop up Skew-T?

Similarly, a new pass of data came in and I was unable to get updated readouts from the pop up Skew-T, therefore I ‘unloaded the “Radar Popup SkewT” (green legend, above), turned off sampling, then went back through the process of Volume > Popup Skew-T, turning on Sampling (right click), and sample cloud heights from NUCAPS (top of right click menu) and was able to then sample the NUCAPS.

– Guillermo

NUCAPS Sounding Near Charleston

 I made some comparisons between a NUCAPS sounding at 1824z near Charleston, SC and the 12z observed sounding at Charleston, SC. Both soundings were manually modified to a surface temp/dew point of 87/72 (modified NUCAPS soundings were unavailable at this location). Overall the NUCAPS sounding matches the overall profile fairly well with mid-level drying and a fat CAPE profile aloft, with similar SBCAPE, PWATs, and DCAPE values.  I did notice a warm layer centered near 700mb (the base of what appears to be an elevated mixed layer), which resulted in higher MLCIN values and higher 700-500mb lapse rates. This could indicate more capping than is actually present, though perhaps stronger convection where the cap does break. This warm layer also appears warmer than in an 18z HRRR initialized sounding at the same location.

'

I also looked at Gridded NUCAPS 700mb temperature data compared to 18z 700mb temperatures from the RAP and GFS. While there was some missing data in the area of interest from Gridded NUCAPS, the values just south of that area are higher than what the models were showing.

Late day update: the modified NUCAPS soundings eventually filled in.

It was a few degrees cooler at the surface, but that may be because it went off the 17z RTMA rather than the 18z METARs at that time.

– Barry Allen

ProbSevere and GLM with Supercell Moving Offshore the South Carolina Coast

 

A thunderstorm located east of Charleston appeared to have some supercell characteristics as it moved south-southeastward towards the coast, with a kidney bean shape in reflectivity and a weak mid-level mesocyclone, as well as some deviant motion from the northwesterly flow. As it was over land it appeared to be strong but sub-severe, and maintained generally consistent 20 to 35 percent ProbSevere in v3. ProbSevere v3 seemed more consistent overall, with v2 jumping up and down more often, dropping down into the single digits at times. ProbSevere v3 did jump down below 20 percent briefly when GLM FED really dropped down. But the consistent lower-end probabilities at least indicated that this was a storm to be watched relative to the lower v2, and this may have at least allowed lead time on a low-end special marine warning before it moved offshore and strengthened.

The timeseries is somewhat useful if you just have one storm to look at, but with multiple storms I would probably just look at the loop in the ProbSevere plan view instead.

After it moved offshore, GLM FED increased, slightly in advance of a jump in MESH and associated jump in ProbSevere v3. ProbSevere v2 jumped ahead of v3 in probabilities as often occurs, though at that time MESH around 0.9 inches may have warranted the more conservative ~50-60% v3 approach. Later MESH jumped up to around 1.3 inches, and ProbSevere v3 jumped above 70 percent at this time as well.

Clockwise from top left: MRMS 18dbz echo top, MESH, reflectivity/ProbSevere/low-level azimuthal shear at 2130z.

Clockwise from top left: GLM FED, minimum flash area, reflectivity/ProbSevere, total optical energy at 2130z.

– Barry Allen

ProbSevere v3 for Low End Storms

 In the training we reviewed for ProbSevere v3, it was frequently mentioned that overall the values we would see in v3 would tend to be a bit lower than in v2, which is what you’d expect in a better calibrated model. (Given what we know about storms and their potential severity, v2 often seemed a little too sure of itself, right?)

However, in looking at the relatively puny convection over Charleston’s CWA today, I’m seeing a lot of the opposite. That is, instances where v3 is noticeably higher than v2. As I think about it, I believe we’re seeing more evidence here of a better calibrated model, as it’s ultimately showing less certainty than v2 about storms not being severe which seems to make sense intuitively. We’ve all had our share of days where a storm one thinks is relatively benign ends up overperforming and though I don’t have any actual evidence to prove this, it appears that ProbSevere is, in its way, taking that into account. Ultimately, this is giving me a bit more confidence in its output.

An example of a somewhat low end thunderstorm where v3’s percentage (29%) is noticeably higher than v2’s (2%). V2 seems a bit too certain that this storm is not severe. As forecasters, we know better.

– Earl Grey Tea

Random NUCAPS Observations

Thunderstorms in the Charleston CWA are marginally interesting at best today so I have been spending some time browsing some parameters that aren’t necessarily severe weather related. NUCAPS availability across the eastern United States looks pretty good today!

I haven’t had the opportunity to use the pop-up skew-t functionality in AWIPS until now (didn’t even know it existed, in fact). It is a bit buried and it took me a few tries to get it to work, but this makes it a lot easier to go through all of these different points and try to find an area of interest without having to go into the occasional information overload that is NSHARP unnecessarily.

After looking at some soundings I went to explore the gridded NUCAPS data, which looks very promising. There was a slight learning curve as I had to get used to the polar orbiting satellite paradigm once again, but being able to see the data from all of the points in a plan view format can help with the information overload mentioned above. I noticed the gridded NUCAPS has some ozone and Haines Index fields. Air quality and fire weather are kind of a big deal where I forecast out west, so these fields will be fun to explore once they’re available in my home AWIPS. Seems like the Ozone Anomaly fields might be a bit easier to understand than the Total Ozone, as apparently Dobson units measure the ozone differently than something like PPM. I tried to investigate this data for the west after that NUCAPS pass came in today but a lot of the gridded data was incomplete. I suspect it was due to the lack of available soundings (saw a fair amount of yellow and red for whatever reason). I’ll take another look tomorrow.

ProbSevere in Jacksonville

 

The 0.5 degree SRM from JAX shows a concentrated area of wind within the cluster of storms in St. John County, FL with radar estimates of the wind near 50kts. Given the lightning jump illustrated by FED values quickly rising to ~170 flashes per 5 min, the storm is intensifying.

However, ProbSevere values are rather low with version 3 showing only 22% and version 2 showing 33%. ProbWind surprisingly was even lower with only 19%. This is a reflection of the lack of base radar data involved in the ProbSevere and ProbWind algorithms. Especially for ProbWind, base radar velocity data needs to be included in ProbWind for this product to be useful in identifying wind producing severe thunderstorms.

It would be useful to integrate base radar data from multiple single radars and combine these values into one algorithm. It may be useful to identify notable/sharp changes within velocity data between pixels which could help in picking out downdrafts.

– Fear the Shear

Modified NUCAPS Sampling: Pop-Up vs. NSHARP

 When trying to sample NUCAPS and modified NUCAPS soundings (via Volume > Popup SkewT) I realized that the popup SkewT only showed the actual NUCAPS profile (there was a notable peculiarity in the modified profile boundary layer that I was looking for in the popup).

I don’t think this was an error in AWIPS, because when right-clicking and selecting ‘sample cloud heights/radar skewT’, the options presented only include NUCAPS, not also modified NUCAPS. So, by my understanding, when displaying modified NUCAPS, the popup SkewT will reference the original.

This second image, perhaps, further illustrates the issue. When displaying only the modified NUCAPS on the map and selecting the profile of interest (in the FSD CWA), the sounding with the interestingly-generated inversion (I believe the subject of another blog post) displays in NsharpEditor. However, the popup SkewT profile does not, because it seems to be showing the original NUCAPS profile.

– Guillermo

Storms in Northern and Central Florida

 GLM

On the afternoon of June 15, 2 different convective regimes were noted across Florida, with different GLM lightning characteristics. A cold front was sinking southward towards the Florida panhandle, with convection developing along the Gulf sea breeze along the FL panhandle. Convection of more uncertain forcing developed in Central Florida.

Convection along the FL panhandle had higher MLCAPE and DCAPE due to mid-level drier air and steeper lapse rates, with somewhat lower PWATs. SBCAPE in excess of 5000 J/kg and MLCAPE in excess of 3000 J/kg was unusually high for this region. Convection in central FL was in a more tropical air mass, with PWATs at or above 2 inches and more saturated profiles. Convection in the FL panhandle developed in an area with very high microburst composite parameter values, indicating conditions very favorable for microbursts and localized damaging wind gusts.

12z TAE sounding:

15z XMR sounding:

MLCAPE 19z:

19z DCAPE:

19z PWATs:

Microburst composite parameter 19z:

The FL panhandle convection was more intense on radar and also had higher flash extent densities. It also tended to have lower minimum flash areas, centered on locally strong updrafts. Notable hail cores were observed aloft, and melting of these hailstones caused strong downdrafts and damaging wind reports, and in a few instances quarter size hail made it to the ground, with one instance of golf ball size hail..

1920z:

The central FL convection was weaker and had also been going on for longer, so there was some convective debris stratiform precipitation with larger minimum flash areas. Flash extent densities were lower than in the FL panhandle. There were still areas of lower minimum flash area centered on the updrafts.

The GLM flash points were very useful and lined up with the NLDN and ENTLN strikes and flashes. The parallax correction was especially useful for DSS purposes as partners often request notification on lightning strikes within a particular radius on the order of 8 to 20 miles, so an accurate location is important. At first glance there were much less flash points but this appeared to be due to the data only being 1 minute data without having the 5 minute accumulation that the NLDN and ENTLN offers. Having this similar 5 minute accumulation would be imperative for using the GLM flash points in operations. The sampled metadata for the flash points appeared less useful operationally. The flash area would be more of interest than the duration, but with a large number of flash points some sort of graphical depiction would be needed, and flash extent density seems to serve this purpose.

ProbSevere:

One interesting thing that was noted was v3 had much lower ProbHail than v2, while still having decent ProbSevere (mainly wind-driven values). We speculated that this was due to some of the machine learning based on environment and climatology, since severe hail would be less likely this time of the year with higher freezing levels/hot surface temperatures causing melting. However, in this case a golf ball size hail LSR was issued at 19:59z (report time appeared to be incorrect) for 2 ENE Saunders in Bay County, FL. This was comparable to MRMS MESH which maxed out at 1.89”.

On the technical side, I did want to note that typically I have sampling turned off in AWIPS, but then double-click on something that I want to sample. Since the ProbSevere timeseries plugin is also opened by double-clicking on the object, sometimes when I meant to double-click to sample the ProbSevere values I accidentally ended up opening a time series. And then I would double-click outside the ProbSevere area to sample something else or turn off sampling and I would get a black banner. Perhaps the timeseries doubleclick function could be turned on and off by making the ProbSevere product editable or not editable in the legend.

NUCAPS:

Gridded NUCAPS and individual NUCAPS soundings at 1840z showed steeper 700-500mb lapse rates than what was shown on the SPC mesoanalysis and some of the morning soundings, in areas away from convection. It’s hard to say which one was right, but the hail cores observed do seem more consistent with 700-500 mb lapse rates of near 7 C/km or greater. (Note that it would be useful to have contours to go with the images on the gridded NUCAPS plots.)

NOAA-20 sounding availability and example sounding (1823z)

1840z gridded NUCAPS 700-500mb lapse rate:

18z SPC mesoanalysis 700-500mb lapse rate:

NUCAPS also indicated the more saturated profiles/weaker lapse rates in the central FL convective regime.

NUCAPS did indicate some of the higher CAPE values, but with missing data in much of the area of interest as convection had already initiated when the pass occurred.

– Barry Allen