Springfield Illinois Storms

Right now I’m analyzing the various new products to nowcast where and when storms will intensify. Currently I’m comparing ALLsky cape to the mesoanalysis from the spc. Right now the mesoanalysis is higher with cape compared to allsky. Over our area the it’s cloudy so the it’s taking data from the GFS.

A cell in our western counties ramped up very quickly while our computers were down. Prob severe immediately directed our eye to the cell. The probsevere lined  up with an uptick in vil values and velocity.

I’m comparing the actual sounding to what’s shown on nucaps, and allsky to see what’s initializing the best. The actual sounding shows 3025kj of surface lavyer cape and 1453 of mixed layer.

Around the same time allsky shows a similar value of cape.

The modified sounding was closest to the actual sounding with 1515kj of mixed layer cape

The nonmodified sounding is much lower when it comes to mixed layer and surface cape. In the case the modified sounding was more reliable and gave a more accurate picture of the current state of the atmosphere.

The all sky cape was much higher, around 2300kj.

That increase might be due to the fact that the sampled area of interest was filled in by the GFS. Whatever input the GFS was taking into might have lead to it overestimating the amount of CAPE.

I’m also looking at GLM products to see trends with convection. The combination of event density and GLM minimum flash area help me to see the rapidly growing updrafts as well as cell that are producing hail. That’s the case right now. My warned cell is producing penny size hail.

About an hour later the FED Is starting to pick up on longer flashes, but the event density is still showing higher values. The lines up with satellite which shows overshooting tops, but storms are overall keeping their intensity. The overall trend combined with looking at stability indices aids me in nowcasting that storms will at least maintain their strength over the next hour or so.

The Day Land Cloud convection RGB was helpful in analyzing different cloud tops. The color scale highlighted the thin cirrus compared to the lower thick clouds. It also dipicted the outflow boundary from our southern storms very well. It gives much more detail to the cloud types compared to the visible satellite.

Today I also got the chance to analyze and compare the merged TPW precipital water with the allsky.

During the afternoon the PW values stayed fairly steady across the northern half of the state while moisture increased in southern Illinois.

The TPW decreased PWATS to close to 1 inch as storms moved through. T

That data was sampled in a cloudy environment.

Meanwhile, the AllSky does show a decrease in PWATS but’s farther north compared to what actually happened. That data was pulled from the GFS since it was in a cloudy location. It was helpful to see how each product performed in this environment. It’s nice to have access to both in order to see which one has the best handle of the current atmosphere. That initialization helps me monitor trends and nowcast.

As storms moved south out of my DMA I used Day convection RGB just to monitor growing cells. It was clear to see the strongest storms because they had the bright yellow maxes.

Earlier in the day was able to compare NMDA with the low level azshear. Tornadoes were’t a major threat, but the NMDA did line up with peak areas of Azshear. That storm did produce wind damage, and strong wind gusts.

Taylor Johnson.

Situational Awareness Graphics

While monitoring convection across southern Missouri, the merged AzShear and ProbSevere have been great tools in diagnosing the primary severe threats: wind and hail.

AzShear has shown a few areas higher in shear, yet the ProbTor has been very low and V data has been unconvincing of the presence or threat of a tornado. ProbSevere has been useful in indicating the severe storm hazards that would be the most probable, and when compared with other data: GLM event density / avg group area, and V data, I’ve been able to issued warnings with higher confidence. GLM data will be increasingly useful with better understanding of what the different data sets mean in relation to convective development or decay.

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Perhaps tornadogenesis soon?

Lightning on FED starting to go up again, right as cell with rotation starts to meet up with east-west oriented boundary to the east of that cell (see bottom right spectrum width product).

AzShear product following that rotation over time well…watching for increase in intensity there.

March 3rd Eastern Alabama and Western GA AzShear Case (Mountain Bone)

Today’s case focuses on the March 3rd Eastern AL/Western GA AzShear Case, with the goal of evaluating the use of single radar AzShear and two merged AzShear products (i.e. 0-2km and 3 0 6km AGL).

The first tornadic event was a semi-discrete supercell located out ahead of a developing QLCS type storm. Pictured (Left) is the single-radar AzShear product at the 0.5 degree slice, (Top Right) base reflectivity and the 0.5 degree slice, (Bottom Right) in the base velocity at 0.5 degree slice.

The first, more discrete cell, in the event was very noticeable in the single-radar AzShear product, with pretty persistence high values (0.02 to 0.035 S^-1) evident throughout the eventual life-span of the tornado once overlaying the post-event analysis track. It did seem to become slightly more muted as the storm progressed further east (85km from the radar site), although, to its credit, the AzShear product looked more pronounced than the BV product at said magnitude from the radar site. From a warning forecasters point of view, if just using BV, this would become a benefit of the product, however, a quick conversion and/or use of SRM fixed this issue quickly on my end. More on distance…The product, similar to it’s ingested data, did seem to get displaced a bit once the feature progressed over 100km downstream of the radar beam, no longer matching up with the post-event analyzed damage survey track (example below).

AzShear (0-2km) merged product roughly 143km away from KMXX and 145km from KEOX.
The second Tornado event analyzed was a QLCS stlye embedded tornado that formed along the leading edge. Pictured (Left) is the 0.5 degree AzShear product, (Top Right) is the 0.5 degree base reflectivity product, (Bottom Right) is the Storm Relative Motion all from the KMXX radar.

There does seem to be some utility in utilizing the single-radar AzShear product when monitoring for embedded rotation in QLCS style events. In this case, a clear in-flow notch is not clearly evident via reflectivity, which can act as an identifier and/or precursor to a QLCS style tornadic event. Thus, using the AzShear product to monitor the entire bowing line segment became a valuable situational awareness tour, highlighting potential areas of interest ahead of time. It still, however, did not replace velocity’s utility, and I’d still prefer to use BV/SRM to draw any type of warning polygons in order to minimize unnecessary FAR within the eventual warned area.

Third area of weak rotation from a semi-discrete cell north of the line. Picture (Left) is the 0.5 degree AzShear product, (Top Right) is the 0.5 degree base reflectivity product, (Bottom Right) is the Storm Relative Motion all from the KMXX radar.

Interestingly, through the analysis process, the AzShear product picked picked up on some weaker rotation from a semi-discrete cell further North of the line, which caused me to investigate the feature further. If just monitoring BV/SRM, this feature likely would have gone unnoticed due to reflectivity/velocity cluttering around the feature. Thus reinforcing the suggestion of utilizing AzShear (All-Tilts) as a situational awareness tool to help trigger areas of interest for the weather radar operator on-shift.

Looking at features further from the radar, AzShear seemed to struggle at depicting some of the weaker features (likely due to the reliance on good velocity data input which also struggled about the same in these scenarios). It did, however, continue to pick up some of the stronger rotational couplets, doing a good job at highlighting those.

Taking a look at both the 0-2km and 0-6km merged products, I am still a bit frustrated by the SAILS induced “skipping” which is apparent. My suggestion here would be to somehow ignore the Sails slices, only producing a new product when all of the 0-2km and/or 0-6km scans are available to do so. This would make for a much cleaner picture… Yes, it would also induce latency issues, but I think the accuracy of what is being displayed would be more useful. The 0-2km and 0-6km merged products also seemed to run a little “hotter,” especially when analyzing the QLCS structure, likely picking up some significant mid-level shear associated with the linear storm-mode of convection/cold pool interaction.

Rapping up a few thoughts…

I think that single-radar AzShear is an excellent product and overall is fairly easy to read as a forecaster (although, not 100% sure of how to fully process the blue/negative colors within operations at this point) . I feel like its best utility lies with situational awareness in operations and in post-storm analysis (i.e. picking out potential damage swaths). Even with some resolution degradation in the 0-2km and 3-6km merged AzShear products, I feel they could also be useful, especially at a regional/national scale where the finer details may not be required/needed. The 0-2km may also be useful in HSLC or Tropical Tornado type environments, where the low to mid-level rotation may be a valuable pre-cursor to short-lived spinups.

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Expecting new tornadoes based on Rot-Track & AzShear

Now that convection has continued to move to the east, I’ve switched to the KEOX radar and, while reflectivity and velocity data show some interesting areas to look at, the AzShear product is guiding my attention to 3 areas, to the west, northwest and north-northwest of radar.

SRM shows a couple areas of possible rotation, but nothing substantial, at least yet. The more notable area is just east of the red/white marker. The 30-min 0-2km Rotation Track shows the recent AzShear history of the 3 cells. My most immediate concern for a developing tornado is the northern-most cell, about to pass north of the radar.

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AzShear & Merged AzShear Provides Great Situational Awareness

While tracking tornadoes in the beginning of this outbreak, a squall line of heavy convection has been present farther to the west. While notable in reflectivity, the AzShear & Merged AzShear products have been very useful for a quick-glance situational awareness of areas of higher concern for tornadoes. In areas that are equally far from multiple radars, forecasters would have to compare multiple velocity products to adequately interrogate areas along the squall line for rotation, including adjusting for SRM. The AzShear products readily and quickly highlight those areas that should be investigated further.

A secondary tornado near the KMXX radar has developed near the track of the larger tornado earlier. While this one doesn’t look as large, it was more apparent in the AzShear product, and after looking at the SRM of that area, my confidence in the presence of a secondary tornado was increased.

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Merged AzShear Useful for Large-Area Convective Development

The merged AzShear is quite useful in this case of a large convective system moving through the region. While single radar is useful, the merged product provides a much better overview of the region. Areas of highest shear are readily identifiable and can then be interrogated further with reflectivity and velocity data. My confidence in the existence of a tornado where the merged AzShear is showing white & yellow on the left image is solidified with the corroborating details in the reflectivity and velocity data.

South of the main tornadic signature in velocity, adjusting the velocity for SRM indicates 2 other weak couplets, neither of which I have high confidence are tornadoes on the ground based on the AzShear products.

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Single Radar AzShear

At first exposure the single radar AzShear product appears to highlight mesoscale regions of interest.  Looking at the 2/23/19 ern MS/wrn AL case beginning around 2308z there is a broad area of reflectivity with some evidence of an embedded supercell in east-central MS.  The AzShear product shows a linear region of positive values with enhanced values around the potential circulation.  Advancing to 2312z the linear AzShear feature has now taken on an S-shape, with enhanced values immediately northern portion of the S.  At this time there is a broad low-level circulation.

S-shape beginning to appear within the strong reflectivity region at 2312z.

By 2316z, there is now a break in the ‘S’ in the AzShear, and at this time the low-level circulation is  tightening as a supercell is apparent in the reflectivity.

2316z break in the ‘S’ in the AzShear

About two minutes later the low-level 0.5 degree circulation is now gate-to-gate.  AzShear values are high at the circulation, but also highlight shear along the interface of the FFD and the inflow, as well as along the RFD region.


This same general pattern would continue for the next several minutes.  However, by 2324z the trailing RFD or mesoscale cold front pushes ahead of the main circulation and merges with the FFD/inflow interface as the storm appears to mature and the main circulation becomes occluded.


After this time the main circulation fades and the convective organization appears to either transition or recycle.  In summary, the single radar AzShear product appears to highlight other regions of interest where shear is present outside the main circulation.  These features are important in tornado development and supercell life-cycle, but are not always apparent in reflectivity or in velocity.  Of note, the detail in the single radar product has a tendency to become lost or muted in the merged product.

One challenge would be color scales for different portions of the country.  Would a color scale for the southern plains be sufficient for the mid-Atlantic, or would smaller weaker features be less noticeable?

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AzShear Product a Good Tool to Use With Velocity Data

The single-radar AzShear product is quite useful in grabbing my attention to areas of high shear that could indicate the presence of tornado or higher level rotation. While not the best in indicating the location of the tornado (Velocity provides more precision), the AzShear helps identify those areas within the storm cell with strong shear, see Fig 1 below.

Figure 1: Single radar AzShear on left, Reflectivity top right, Velocity bottom right. The cursor indicates the center of the tornado based on Vel, but is more in the center of the highest shear on the AzShear product. Other ‘hotspots’–whites/light blues in the AzShear product may send forecasters on wild-goose chases, looking for tornadoes, but having velocity data on hand quickly helps toss out the non-tornadic areas.

The MergedAzShear (MAS) product is useful in a broader sense of scale, but probably not as useful as the single radar AzShear.  An MAS couplet often becomes distorted with the blending of multiple radar cuts from different radars. Sometimes a single couplet could show 1 or 2 echoes that will resolve into 1 couplet after another scan. For short-fused monitoring of a tornadic storm cell, its position could be misleading. Higher-level MAS, while useful in a broader storm environment seems less likely to depict a tornado, although it will indicate a broader area of high shear and changes in the wind fields. (See Fig. 2).

Figure 2: MergedAzShear (MAS) 3-6km AGL on left, Reflectivity on top right, Velocity on bottom right. The computer cursor is placed near the center of the Velocity-indicated tornado center.Ultimately, the AzShear is a good tool to use along with Velocity data to get an overview of what is going on within the atmospheric layer (0-2km or 3-6km), even when there is no tornado on the ground, but should be used in tandem with other radar data to help weed out false signals that may be due to ground clutter, etc.

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Feb 23rd, 2019 KGWX AZ Shear Evaluation (Mountain Bone)

For the first HWT exercise, I’ll be taking a look at the AzShear products, including a single radar AzShear product and two (MRMS) merged radar products at the ranges (0-2km) and (3-6km). This is my first time as a forecaster seeing/evaluating these products, and the case was mainly used as to build knobology on the local evaluation platform while also discussing potential conceptual uses for said products. Thus far, the single radar AzShear product seems to help illuminate areas of enhanced rotation nicely in an easily depict-able manner. It doesn’t, however, seem like it should be considered as a replacement for a velocity/SRM display in the near-term environment. This was proven true in several cases where it was hard to pinpoint exactly where the center of rotation was in the display (See image below).

(Left) AzShear product using a single radar site; (Top Right) Reflectivity; (Bottom Right) Storm Relative Motion; (Purple Line) Confirmed Tornado Track.

If I was a forecaster trying to draw a tornado warning polygon, I wouldn’t necessarily want to do so using the AzShear product alone, the use of SRM/BV would allow for a more finite tornado warning polygon to be drawn, which would result in a lower FAR with respect to those within said area who have the best chance of encountering a tornado on the ground. Also, I feel that this product will need a rather extensive color table to make it useful, and I’m just not convinced that there is enough precision to allow that to be possible knowing the resolution and reliability of the input.

With that being said, I do see some utility in this product, specifically as a supplement/tool for a radar operator in the near storm environment. Being able to pick out and follow areas of highest shear through the evolution of an event could be extremely useful, especially in linear or a cluttered storm type environment where picking out couplets using SRM/BV could be more difficult.

Briefly evaluated were the merged AzShear data-sets within the case. Generally, even more features which would be beneficial to a warning forecaster are being lost in the process of creating this product. On a CWA scale, the primary benefit for this would be for situational awareness purposes, or possibly through the use of the (0-2km) product in a tropical-type environment where low/mid-level rotation may indicate a pre-cursor to a short-lived weak tornado. A huge downside at this point is the incorporation of the “Sails” slices, which tends to make the product rather messy in-between. A suggestion would be to try to eliminate the sails slices, even if that ultimately limits the amount of time between new data production.

—————————————————————————————————– Mountain Bone

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