Hindsight - Nov 5 OK/KS storms

[Phil Moyer]

I have a couple of newbie questions after yesterday evening's excitement.

First, people were calling the Oklahoma City-Ponca City-Arkansas City corridor on the evening of the 4th, well in advance of the SPC moderate risk update or MS discussions. What analysis factors caused you to pick that five or six county region so accurately? Was it data-driven or instinct driven? Were you looking at NAM Skew-T predictions, other model output, current observations? What differentiated those specific areas from adjacent areas that (correctly) didn't look as promising?

Second, at 1445 Central, the Oklahoma City WSR-88D was painting two nice targets: a large cell west of town, a little south of I-40, and a smaller cell just SW of Ponca City. The western cell, which became the Guthrie storm, was larger, had higher reflectivity, had earlier rotation, had a nice wall cloud - but the northern storm developed more rapidly and was tornado warned first. Why? What were the characteristics (or, "were there characteristics...) of the two storms that altered the development speed? Were there data sources that those of us 1,500 miles away should have been looking at to more accurately predict tornadogenesis?

I know these are pretty basic "understanding" level questions, so I apologize for not being up to speed....

Phil

 

[rdale]

I'd highly recommend in the future joining the chatroom - there were boatloads of chasers / mets / radar experts in there, as these types of questions are MUCH easier to answer in realtime vs trying to go back and figure out what we were saying and why.

 

[Skip Talbot]

Phil,

I think a lot of people were eyeballing areas from Wichita to Oklahoma City in the afternoon as this area had the best combination of instability and shear indicated on the forecast models. Given that the low level shear was forecasted to ramp up in the evening, I take it people were looking for a target a bit further east where storms/dryline/front would be after initiation. Ponca City is east and in between the two other cities, and has decent highways coming in and out of it.

As for the tornado warning. I believe the text said doppler radar indicated capable of producing a tornado. The NWS met must have seen more pronounced rotation in that cell at the time.

 

[Chad Cowan]

Phil- as far as forecasting goes, read and study as much as you can. There are TONS of free resources around the web, you just have to know where to look. Haby's Hints are a great place to start. Until you develop those skills, a good litmus test for where tornadoes are possible is the EHI forecast parameter available on some model websites. EHI= [Energy (CAPE) x Helicity] / 160,000. You need both CAPE and helicity for tornadoes and if either = 0, the output is 0.

 

[Shane Adams]

As far as my target, I was OKC/I-40 and south all the way, because my morning analysis/observations were confirming what the rapid model output was advertising. The SPC's "forecast tools" page is solid gold IMO, that's the one site I lock onto in the waning hours before I leave. It only updates once an hour, but the parameters measured are invaluable to assessing real-time situations and in turn, using those obs over the course of a few hours in the morning to try and identify trends. It was becoming quite obvious that there were two target regions in the meat of the SPC outlook, which was OKC and southwest, and NC to NE Oklahoma. I'm always about thermodynamics first, shear second, so I chose the area I felt would have the greatest instability prior to initiation. I had a feeling those who went to the OK/KS border would have good storms as well, but, along with the greater instability factor, I figured the storms south of I-40 would move a bit slower, as they would be further away from the influence of the main jet core.

As for why one storm was tornado warned and one wasn't, that's why we're doing all the research

 

[Benjamin Smith]

I'd highly recommend in the future joining the chatroom - there were boatloads of chasers / mets / radar experts in there, as these types of questions are MUCH easier to answer in realtime vs trying to go back and figure out what we were saying and why.

Sorry to have to ask this, but where is the chatroom located? Is this something that is only available during events?

 

[Dennis Sherrod]

Sorry to have to ask this, but where is the chatroom located? Is this something that is only available during events?

There are several around and the comment made to go to one was pretty vague and not very helpful.
Here is one of the newest:
http://www.SpotterChat.org

Also, here is a thread from not too long ago.
http://www.stormtrack.org/forum/showthread.php?t=18293&highlight=chat+rooms

 

[rdale]

Sorry to have to ask this, but where is the chatroom located?

Spotterchat.org - it's available 24/7.

 

[Angie Norris]

The parameters I mainly look at for my forecasting are surface temps, dewpoints, theta-e, and wind speeds from the surface up to 500mb. These parameters will let you find any boundaries, how much surface moisture is available, how much shear you have, and storm motion and speed. CAPE is also good to see how much instability is available (but you have to keep in mind that fall, winter, and early spring storms can get the job done with much less CAPE than late spring storms). I tend to not pay much attention to the models until about 48 hours out (since I hate working with the GFS...it seems to almost always be too aggressive).

The main thing that caught my eye with the models was that the WRF picked up on precip initiation in central OK south of the OKC metro between 18 and 0Z, and it persisted on several runs. It didn't break out precip further north until 0Z, which would have been after dark. This was one of the few times I based my forecast purely on the models, since I felt like the boundaries (and particularly the dryline) would hold back until well after dark...and I wanted daylight storms to go after.

 

[Chris Lott]

Even though I wasn't going to chase this event I still like to try my own at forecasting. The forecast skew-T's and model runs drew my attention to Ponca City due to the amount of shear and instability that was forecast to be in that area. The actual day of the event is when I rely heavily on surface obs and satellite images along with RUC guidance to try and help me better pinpoint an area. Although I still trusted this target, as the actual events of the day unfolded and seeing the sharp dryline approach from the West I started looking more to the SW for initiation, being that it would probably start before dark and with the daytime heating and instability this area would probably fire first but felt better about NE OK for possible tornadoes.