Today we ran a PROBWARN IOP for the area of W to C Texas, primarily using KMAF, KDFX and KSJT, as well as the SC_Multi gridded data. We ‘sectorized’ putting DanM. and Ron P. on the northern part and Dave H. and Dan P. on the southern. Storms had begun about an hour prior to our starting time of 2130z.

The southern group spent most of their time (if not entirely) on storms forming off of “Old Faithful” on the Mexican side of the US border west of Eagle Pass, TX and moving into US territory. These storms trained, and provided some difficulty to Dan P. and Dave primarily in how best to handle trending given that some storms would increase in severe potential and others would die out.

Dan M. and Ron worked on at least one storm that transitioned from an HP supercell with primarily a hail threat to a tornado threat.

Dan P. sneaks a peek at the other team’s warnings…

We ran until 7:30 pm and had some brief discussion before letting the forecasters take a look at some convection that moved into the CASA domain around 8 pm.

A few comments regarding the IOP follows:

• It had been considered a couple of times that sectorizng based on threat type would be an iteresting exercise. I.e., one forecaster analyzes/warns on hail, while the other focuses on tornado/wind threats.
• Workload issues were again brought up. Some had a hard time keeping multiple treats on the same storm (effectively tripling their warning issuance). And even those who were keeping up were losing situational awareness due to a “round robin” type of approach where the forecaster was going from storm to storm to nudge and move on. Main loss of S.A. in this case is in the vertical structure of the storm.
• Comment was maid regarding a forecaster worrying or not completely feeling comfortable with providing the trend info. Perhaps a better tool for providing this info would help. Dan M. suggests starting with something like the GFE temporal editor.
• Other software suggestions were having a transparency slider for the ProbGrid output. having the option to sync all the threat grids for the same storm to that storm’s motion

In the discussion that followed the exercise, some time was spent considering “exceeence thresholds” for different threats. For example, issuing a high probability for hail, but a low probability for hail larger than [golfball, baseball, etc.]. This adds another degree of freedom which A) allows the forecaster to provide greater detail, but B) adds another task for the warning forecaster and (potentially) increases workload.

Other concerns were the potential/likely inconsistency between forecasters and their probabilities. Should be an interesting discussion during the debrief.

Eve was impressed at the ability to “Virtual Storm Chase”

Kevin Manross (EWP Weekly Coordinator, 12-16 May)

Addendum:

Here is the first attempt at an “accumulated” ProgGrid for yesterday’s event. Later, I’ll divide these grids into storm type and compare to Rotation Tracks, Hail Tracks, LSRs, and NWS warnings.

Greg Stumpf (EWP Operations Coordinator)

Well, we tried really hard to get something in CASA, but, alas, the atmosphere didn’t want to cooperate with us.

We had Dan P. and Dave H. work with CASA and Dan M. and Ron P. worked again with PAR. This configuration was suggested so that we have an experienced user during realtime ops. (These same forecasters worked the same respective stations last night).

Regarding the weather scenario – we had a few attempts at initiation in the extreme Ern part of the CASA domain, but that was the best we saw. Storms initiated along the cold front to the NE of the OKC area and the PAR remained focused on those storms during the duration of the evening. These storms moved very slowly – remaining anchored to the front. There were a number of severe warnings and one storm near Prague that had some broad low-level rotation (which tightened up from time-to-time) but never drew a warning.

One of the interesting things we tried tonight was to issue PROBWARN on PAR. (Dan M. is an old pro with both) Should be an interesting case to review from that sense.

As I type (~0110z), we have legitimate echo on the edge of the CASA domain.

Speaking of CASA, Dan P. offers part of a discussion (while waiting for *anything* to happen in CASA) regarding Three-Body-Scatter-Spikes (TBSS). Given the low-level area of focus of CASA, TBSS will be rarely, if at all, seen on this network. This, of course is an often-used indicator for severe hail.

Here is a snapshot of our PAR/PROBWARN exercise

And this is the best we could get for CASA (after 3 hours of staring intently at the screen). Actually, this also shows the 3DVAR Wind analysis product (on the left).

Kevin Manross (EWP Weekly Coordinator, 12-16 May)

Given the dearth of severe weather today, we went ahead and had all the participants (Dan M. Dan P. Dave H., Eve G. and Ron P.) sit through the briefings for each project (CASA, PAR and PROBWARN) after the orientation.

This evening, Dan P. and Dave H. are running though a CASA case with Brenda and Ellen. Dan M. and Ron P. are working a PAR case with Greg S. and Arthur.

Greg has offered a few comments regarding the PAR playback case(s), in general. He notes that the incoming data may be arriving too quickly, effectively bogging down the display when viewing cross sections. [Note: this is something that I encountered trying to run/view the PAR in realtime over the past year or two.] We can certainly take care of this in the w2simulator, but Greg ponders whether this should be done for realtime viewing.

EDIT (by Greg): Since the PAR already updates so rapidly, we could consider updating a volume scan at a time. This would provide ~60s updates of all tilts at once, and only “lock up” the display one time per minutes, rather than every 5s which is the current wg polling interval.

Comments by Ron and Dan (as well as Greg and Arthur) suggest that getting 88D data (KTLX, KFDR, etc.) for the PAR playback cases would be very helpful.

Kevin Manross (EWP Weekly Coordinator, 12-16 May)

Cynthia and Craig’s warnings have two high probability hail swaths for the lead supercell and the trailing storm that continued to advect downstream and decrease slightly in probabilities until they updated the threat areas. At one point the NWS issued one SVR polygon to cover both the storms but then broke it up. Upon review, it’s apparent the advecting threat area allows for more continuous aging off of the swath on the back sides than the NWS severe wx statements. They kept updating everytime the storm moved out of the threat area. There is still some difficulty of comparing hail-only swaths with NWS polygons which cover hail and wind.

There some difficulties handling multi-vertex polygons, such as moving them. Cynthia struggled with moving the polygons. Sometimes she’d inadvertently create multiple vertices.

Brian and Bill were grappling with rapid cycling process of the lead supercell. Their probabilities were more marginal than that of the hail. There was no confirmation despite the number of chasers out there. But they kept the probabilities as high as they were given the mesocylone strengths and the potential for hidden tornadoes. Each meso quickly became wrapped in precip. Later on a line developed south of KDDC with intense horizontal shear across the gust front.

Several vortices wrapped up along the interface and as a response a long, low probability (20%) tornado threat area was added.

The NWS did not issue any tornado warning for the supercell.

There’s some discussion about what TOR probability constitutes a standard warning? Craig would go 40% and Bill would go 50%. Both Bill and Craig don’t relate their warning decision making to a number though Bill didn’t have a problem associating a warning threshold probability here.

Software ran well, even with the big TOR threat area that Brian put out on the squall line.

Jim LaDue (EWP Weekly Coordinator, 5-9 May)

There was little doubt today that convection would occur in the CASA and PAR domains. An upper low tracked across southern and central OK while the surface low tracked basically underneath. The strongest low-level jet and low-level vertical wind shear was to remain east of the dryline, or along I-35 south of OKC and points east. This is where most forecasters (e.g., SPC, EWP, WFO) thought the best tornado potential would be. However, we failed to appreciate the potential for large amounts of ambient vertical vorticity to produce tornadoes provided sufficient amounts of convection. The low-level low tightened amidst an abundance of cold core convection forming in western OK and eventually, central Oklahoma, where several nonmesocyclonic tornadoes formed including two in northern Oklahoma City, one just 2 miles south of the National Weather Center, and one near Paoli.

While in the CASA domain, the convection also helped intensify the cold front coming in from the west. The result was a damaging wind event. One area of convection surged across Lawton to Chickasha resulting in damaging winds in both places. In fact both the Lawton and Rush Springs radar sampled winds in excess of 60kts in the closest range gates. The Lawton radar stopped reporting for about an hour after it experienced severe winds.

The developing squall line came into central OK in two segments. A north-south segment approached OKC accompanied by a gust front with substantial vertical vorticity. One TVS formed near Lake Overholser producing a tornado there which tracked a couple miles to the northeast (see Travis Smith’s damage survey description). A second circulation developed near Edmond and tracked southeast. This segment of the squall line was centered within the larger scale low and the PAR could easily detect the rotation of individual cells around a common center. The PAR could also more easily detect the evolution of the circulation centers than with the KTLX radar. The other segment came in toward Norman from the southwest and represented the eastward continuation of the severe gust front within the CASA network. Substantial vertical vorticity along this gust front allowed one TVS to form just south of Norman which then produced an EF0 tornado along the Norman/Noble border. The PAR was focused on the OKC storms and thus was unable to cover the Norman TVS. However the TDWR did sample this feature at a one minute frequency and was able to detect a TVS with a 50kt Delta-V. Members of the EWP watched the ragged cone-shaped funnel to the south of the National Weather Center around 2225 UTC.

CASA summary:

Brian and Craig worked the CASA network. They found the following advantages:

• Gradients in velocity were much larger in the CASA than the 88D as noted in 2006 UTC
• Peak velocities were slightly larger in the CASA than the 88D. While both radar types showed severe values, the CASA radars showed those values at a much lower elevation. Both the Lawton and Rush Springs radar showed >60kts at their respective nearest range gates.
• The RHI were extremely useful and was used at least on 2032 UTC, 2121 UTC, and 2131 UTC. The RHI was generated automatically from each radar in each scan along the radial containing the highest reflectivity.
• The 3DVAR wind speed analysis proved especially useful to the forecasters as it depicted 2-D winds that appeared to have agreed with the radial velocity base data for several wind events, especially the Lawton area and then points northeast from there.
• The data appeared much cleaner than last year.

There were issues with the CASA too:

• The RHI, while useful, was too automated. The forecasters wished to have some control over this function in order to follow storm evolution. However the number of storms exhibiting a peak reflectivity in a particular radar’s domain from scan to scan kept changing the RHI azimuth.

PAR summary:

Kristen operated the PAR selecting 90 deg sectors while Bill evaluated its usefulness in warnings. There were certain advantages with the the PAR over the 88D

• At 2020 UTC, the PAR could detect low-level circulation 3-4 min prior to the 88D in the supercell approaching Pauls Valley.
• At 2131 UTC, the PAR showed an azimuthal velocity couplet (low-level circulation) at a merger of a small echo with a larger echo in northern Garvin county. The KTLX radar did not show it as well.
• At 2216 UTC, the PAR was able to track the evolution of small vortices along the gust front in western Oklahoma county. The KTLX radar could detect them but not track their evolution given the temporal frequency of its scans.
• At 2221 UTC, the PAR could easily track the 2-D motion of reflectivity echoes around a common center in northern Oklahoma county.

There were some issues with the PAR, and WDSS-II’s capability of displaying its data

• Storms moving across radials at close ranges required frequent sector updating
• Bill had issues attempting to view virtual volume scans with interlaced VCPs in WDSS-II
• The PAR data is very useful when looped at high speeds. WDSS-II needs the capability to display long loops at high speeds where users can scrub the loop back and forth with VCR and other types of controls (e.g., see Hunter/Gatherer software).

Jim LaDue (EWP Weekly Coordinator, 5-9 May)

Bill sais this is more intense than standard warning ops for the same event. It’s more mentally challenging. Though he thinks it’s a matter of learning the ropes and it’s not as bad as he thought it’d be.

Craig thinks it could be easier with more familiar software. He’d like it tailored to AWIPS. Good plugin for AWIPS2.

This was a messier day than expected due to mode of initiation and relatively dry boundary layer.

Today started in the middle of a supercell south of MAF. Bill and Kristen didn’t have a tor threat when they started though there was an official tornado warning. They weren’t really concentrating on the tor threat at the time.

There’s an interesting difference in shape of swath vs official warning at 2353 SW of MAF. The official warning polygon was county-centric.

Meanwhile in SE NM there was a supercell initiation with a classic split. The initial storm started with one swath and they followed the right mover with the same swath. The left split popped out of the threat until they recovered with a new swath.

At 0113 UTC, there’s a good example of a continuously updated threat that provided an advantage of leadtime in far eastern NM with the right-moving supercell.

Up with the north team, Craig and Brian, there was the triple point multicell with great promise but didn’t pan out. Meanwhile there was a NE-SW cluster of individual multicells south of LBB that was broadbrushed with a big hail threat area. Brian thought the storms were too pulse-like that precluded producing individual swaths given a one person team. Maybe experience would help. Brian thought the threat area IDs in the dialogue box should be color coded by threat type.

They had merging issues and new areas spawning in this loosely organized cluster of multicells. They issued a wind and tornado threat for some of the multicells exhibiting these signatures southeast of LBB. But I don’t think they would’ve issued a real tor warning.

At 0150 UTC, there’s a continuous swath while there’s a gap in official polygons west of Knox county.

Jim LaDue (EWP Weekly Coordinator, 5-9 May)

This evening featured a supercell with large hail near GCK that merged with a line to the east and became an outflow dominated multicell event. The hail threat decreased as largescale wind threat increased. This team consisting of Bill, Craig, Cynthia and Brian focused on hail threats given their unfamiliarity with the probwarn software.

The big difficulty today is going from single to large multicell mode. Craig wonders how much longer a probabilistic warning should continue after a legacy warning expires? Bill’s worried about how to transition from isolated to large multicell threat areas? This storm underwent such a transition and they kept the single cell mode for a long time after merger began.

The team consisted of one member operating the familiar D2D for radar base data analysis while another team member operated the probwarn software. Two other team members contributed to the discussion. This setup appeared to work very well with lot’s of interaction.

Given the probabilities, what do they mean? Bill sais he’s comfortable with them because he associates high probability to his thinking when he’s doing warning decision making in the current way.

Jim LaDue (EWP Weekly Coordinator, 5-9 May)

Note that the event occurred across 00 UTC, but we’ll label the summary on the starting date of operations…

We had several tornadic supercells in Central OK today. The first storm developed just west of Norman and noved over the eastern side of the OKC metro, producing a weak tornado. Two other storms developed north, and at least one of these produced a signficant tornado near Ralston.

Our visitors, Dave, Mike C., and Andy, worked a PAR IOP today with Pam and Les. Here is an image of the OKC supercell at the time it produced an F0 tornado:

Mike M. also worked a gridded warning IOP on the same storm, concentrating mostly on tornado threat areas. Our IOP lasted about 3 hours, after some gridded warning software issues delayed our start by 1 hour.

MM and I discussed the possibility of another type of warning team concept…use the NWS forecaster as the radar analyst, on the AWIPS machine, and making the decisions of warn, where, and the attributes, and let someone with better proficiency with WDSSII (perhaps an NSSL person) draw the contours. Something for us to think about in future weeks with the experiment, since the WDSSII knobology is a challenge for the visitors.

Greg Stumpf (EWP Weekly Coordinator, 28 April – 2 May)

We spent the day doing archive case playbacks again with all the participants. However, around 745pm, one severe storms developed in Western Nebraska, too late to begin an IOP (since they must end by 8:30pm). I did some more gridded warning testing and we found a few more minor bugs that need to be issued.

Previous blog entries capture some of the discussion about the gridded warning project. We hope to summarize more of this for the end of week summary. Also, we will be gathering feedback from the PAR and CASA folks.

Greg Stumpf (EWP Weekly Coordinator, 28 April – 2 May)

There was no IOP today.  The forecasters spent the day doing training and archive case playback on the various systems.  This summary will contain our notes from the Gridded Warning archive case playback.

Comments and thoughts from our forecasters:

Knobology of WDSSII getting in the way of science – not comfortable with tool. Perhaps in 3-4 more days, we could be more ready. Consider a 2 week tour with a one-week overlap between tours.

Would be nice to issue hail warnings on Ref and MESH in one pane, and tornado warnings on Ref and Vel on another pane, another monitor, or another workstation.

There was some discussion about the use of low-probabilities for “pre-warnings”. Actually, that is part of the NSSL concept of gridded threat areas – to provide some downstream users who need lower-probability longer lead time information between the watch and warnings time and space scales.

Paul started by issuing threat areas in “swath mode” as is done today in the WFOs, but quickly realized this and adjusted his threat areas accordingly (current threat only).

Paul would like to issue different probs for different parts of the threat area.

Paul and Dave had a hard time with motion vector because it is not shown on the screen. With warngen, there is an arrow and past and future positions.

Most of these technology issues go away if this is fully integrated into D2D.

Definitely helps to have someone who knows the system sitting next to the forecaster.

Dave comments that perhaps the 2nd-week forecasters in the above scenario are the ones issuing the warning, while the first weekers in in training mode – perhaps not working together, so that the “veterans” can really concentrate on the science.

Paul and Dave are concerned about the precision of the prob values – what about every 10%?

Andy – how do we calibrate our probabilities? Perhaps we can integratee the verification into the live system?

Andy – Verification system should be included in the NGWT from the get-go – lesson learned from WRH experience with GFE (see white paper).

Greg Stumpf (EWP Weekly Coordinator, 28 April – 2 May)