Questions?

[Danny Neal]

I have written three educational blogs and have been really busy with the blizzard and the clean up so I haven't been able to write any more. I know a lot of you have enjoyed them and may have learned something! I want to do a little something different this time. Since this is a beginner forum I thought I would open up the floor to basic questions from people who are not quite sure about some basic weather terms or features. If you pose a question and I can gather information and use my own media/pics, I will gladly write a blog on it. I can write about tornadoes and supercells all day, but I know some of you are still trying to figure out how to read a basic surface chart. I have free time coming up before I start a new job next week, so if you ask some basic questions that you may not be sure about then I can answer in a day or two. Storm chasing is a number one hit nowadays and probably as popular as it has ever been. Instead of shunning the newbs, I am going to try to educate. Like it or not people are going to be out there that are less experienced than us so if others take the initiative to educate then we may see a lot less Camaro dudes out there!

Remember since this is the basic forum it must be something that every body can understand. You can PM me for anything a little more in depth or advanced (nothing TO advanced I am not THAT good... yet lol) Post away StormTrackers.

 

[DRMabe]

First question, what's a "Camaro Dude"? Lol.

I'm new to chasing for the most part. Live in NC, so nowhere near as many tornadoes here as out on the plains. I have chased some around here, but plan to get serious this season and Chase in NC, VA, SC, and northern GA. Planning my first plains trip for the 2012 season (last 2 weeks on May). I'll be driving out there alone and hopefully I can meet up with a few members here that have some experience. I've enjoyed reading your post and have learned a lot from them.

 

[Danny Neal]

First question, what's a "Camaro Dude"? Lol.

I'm new to chasing for the most part. Live in NC, so nowhere near as many tornadoes here as out on the plains. I have chased some around here, but plan to get serious this season and Chase in NC, VA, SC, and northern GA. Planning my first plains trip for the 2012 season (last 2 weeks on May). I'll be driving out there alone and hopefully I can meet up with a few members here that have some experience. I've enjoyed reading your post and have learned a lot from them.

Lol, the Camaro dude was some kid that filmed himself going 120 through traffic in his Camaro to catch up to the Kirksville, MO tornado on May 13th, 2009. He got right in the circulation and ended up getting pretty cool footage but was clearly inexperienced and probably was lucky he didn't end up a missile. More wreckless and irresponsible than anything else.... although I don't think all the training in the world would have changed any mindset there!

 

[DRMabe]

Common sense isn't something everybody possesses....

 

[Jim Parsons]

What do you look for to determine your chase target area or the storm initiation point?

 

[J Tyler]

Danny-

Congrats on the new job! Tough to get these days. Also, thanks for the two previous write ups, as I really enjoyed both. I've got some things I've been reading a lot on lately trying to get a clearer understanding, maybe you'd like to tackle....

RFD.
Every dark cloud is incorrectly called in as a "wall cloud", and every wind gust is incorrectly called "RFD". These two seem to be the big "buzzwords" of storm chasing these days. I've read everything from scientific papers to wikipedia on Rear Flank Downdraft, and I get the basic idea, but I'm still fuzzy on exactly what causes it. I like your writing style because you use plain english! Can you explain what CAUSES the RFD?

Day of forcasting:
Knowing WHEN and WHERE on the DAY OF. Once the storms first fire, its all easy. But how do you know storms are going to fire at 4pm near Ardmore OK, and know that at 8am? Are you just using models, or are you working this out on your own? Are you using models to get a basic idea, and then refining on your own? Specifically, which models do you use? The cap breaking when and where is a tough one for me.

 

[Jeremy Perez]

Danny, your articles are excellent and very much appreciated. A topic I would find helpful is Nighttime Escape Strategy.

As sunlight tapers away and afternoon/evening convection merges into an advancing MCS with possibly embedded supercells, what strategies are helpful to avoid being overrun by the worst of it? Certainly having up-to-date and reliable radar is a key to staying out of harm's way--but that can be unreliable at times. Thanks for all your helpful input!

 

[Jordan Hartley]

I agree with Jeremy Perez a Nighttime Escape Strategy would be helpful. 9/15/10 I ended up chasing longer than I should have. With no radar I ended up out in front of the main core at dark. My dumb*** decided bailing south as fast as I could on back country roads was a great idea instead of driving 20 miles out of my way just to get home. The core ended up taking me over and for a good 5 miles I drove through a wall of rain and golf balls. Some how I found a E/W paved road and bailed east which took me into Dexter, Ks where I parked my car underneath a gravel building made out of concrete. Got off really lucky... again. Actually getting tired of that cause one day its going to cost me. This single event has changed my view of storm chasing blind(no radar) and after sunset. Would be nice to hear some of the seasoned vets opinions on their nighttime escape strategies.

 

[Danny Neal]

Excellent topics fellas. Let's see what I can whip up. I have a good night chase experience to tell and how it could have gotten ugly fast in bad terrain. I sort of hinted on wall clouds and rfd's but I can definitely go deeper into RFD's. Day of forecasting and target selection and what to look for is BIG. I will definitely enjoy that one. Maybe I can bang one out tonight and post it. It wouldn't be til later on though. Thanks! I can write about things forever but I tend to get repetitive, it is nice to have specifics to write about and so I can stay on track.

 

[Danny Neal]

Danny-

Congrats on the new job! Tough to get these days. Also, thanks for the two previous write ups, as I really enjoyed both. I've got some things I've been reading a lot on lately trying to get a clearer understanding, maybe you'd like to tackle....

RFD.
Every dark cloud is incorrectly called in as a "wall cloud", and every wind gust is incorrectly called "RFD". These two seem to be the big "buzzwords" of storm chasing these days. I've read everything from scientific papers to wikipedia on Rear Flank Downdraft, and I get the basic idea, but I'm still fuzzy on exactly what causes it. I like your writing style because you use plain english! Can you explain what CAUSES the RFD?

Day of forcasting:
Knowing WHEN and WHERE on the DAY OF. Once the storms first fire, its all easy. But how do you know storms are going to fire at 4pm near Ardmore OK, and know that at 8am? Are you just using models, or are you working this out on your own? Are you using models to get a basic idea, and then refining on your own? Specifically, which models do you use? The cap breaking when and where is a tough one for me.

http://www.stormtrack.org/forum/showthread.php?26600-RFD-Additional-Energy-source

Hey Jeff,

Before I specifically delve into your RFD question, I thought I would direct you into a little more in depth discussion about the meat and potatoes of RFD's. It is a great thread and I am definitely learning things there too! If after reading that you still have something to be desired, I will certainly go into it a little more dumbed down (reading the technicalities sometimes makes my head want to explode).

 

[J Tyler]

How funny! That thread is what got me to digging into more detail on RFD. Several of the posts in that thread -seemed- to contradict one another, and kind of confused me as to warm vs cold, when does the RFD choke off the inflow to the updraft vs the RFD helping form a tornado. And, I'm still not completely sure what CAUSES the RFD to happen. I read the two papers from Markowski, and they were REALLY interesting, but I would like to hear the PBS Kids "Mr. Wizard" version so I don't have to think so dang hard!

SO, there you go Danny! I hereby name you "Mr. Wizard"! Get that sock puppet out of the closet and explain RFD to me! LOL!

Oh, and I'm REALLY glad you're willing to take on the "Day Of Forcasting and Target Selection" topic!!! I look forward to seeing not only YOUR thoughts, but also the discussion that will follow.

Thanks Danny. Errrr, I mean THANKS Mr Wizard.

 

[Nicholas_Scherber]

Since you seam to be able to right things in terms that i understand, i need help with forcasting. I am slowly picking it up on things but you could probably save me a lot of time. I know that your intercept thread taught me about the same amount in 10 minutes as doing my own research took me hours.

 

[Danny Neal]

I actually opened up the floor to the rest of the Convective Addiction members to chime in their thoughts on the topics too. So if you see another member chime in a blog about it, don't discount that. I plan on tackling the forecasting and night chase scenarios later tonight or for sure tomorrow. Adam Lucio offered to take on the RFD one so look for his post. I know Skip Talbot has some good knowledge about RFD's too so maybe the three of us will collaborate into putting together something. Thanks for the ideas! Forecasting is very important anyone can look on SPC or their local news, but to truly succeed on less than obvious days there are things that you should look out for and I will definitely outline things (at least from own personal experience.)

 

[Andrew Pritchard]

RFD.
Every dark cloud is incorrectly called in as a "wall cloud", and every wind gust is incorrectly called "RFD". These two seem to be the big "buzzwords" of storm chasing these days. I've read everything from scientific papers to wikipedia on Rear Flank Downdraft, and I get the basic idea, but I'm still fuzzy on exactly what causes it. I like your writing style because you use plain english! Can you explain what CAUSES the RFD?

There still is not a 100% consensus on *what* specifically causes an RFD. Unfortunately the literature is fairly hard to understand because it's simply getting into the more complicated dynamic processes that occur in a supercell thunderstorm. It's not something that can easily be put into plain English. Some could argue that there isn't even any distinction to be made between the RFD, FFD, and occlusion downdraft. The best theory I can explain for the processes behind the RFD that separate it from the FFD is that unlike the saturated column in the FFD, you've got the presence of relatively drier air which fuels evaporational cooling which can accelerate the air downward. There is still debate among where this actually occurs. As has been touched on in the other RFD thread *relatively* warm and moist RFD tends to be more commonly associated with significant tornado producing supercells, so it's theorized that this is originating from a lower level in the atmosphere than the *relatively* cooler and drier RFD that can be associated with non-tornadic supercells which would originate from a higher level.

I'm trying to find some of Erik Rasmussen's stuff on the "blob theory" but am coming up with a bunch of broken links right now. If you can dig up something on that, it'd be worth a read.

 

[Skip Talbot]

What do you look for to determine your chase target area or the storm initiation point?

Day of forcasting:
Knowing WHEN and WHERE on the DAY OF. Once the storms first fire, its all easy. But how do you know storms are going to fire at 4pm near Ardmore OK, and know that at 8am? Are you just using models, or are you working this out on your own? Are you using models to get a basic idea, and then refining on your own? Specifically, which models do you use? The cap breaking when and where is a tough one for me.

There's a lot that goes into picking a target and forecasting initiation. I'll try and hit the basics here and go into a little more detail on when and where to expect initiation with regards to capping, and perhaps explain the other facets in more detail later. I take an ingredients based approach when forecasting for chases. I'll throw out some good starter values here with an example for TwisterData so you can follow along, and we'll assume its the morning of the event. Keep in mind these are rough estimates and broad rules of thumb. There are always exceptions to the rules and special circumstances. Hopefully, you're in the ballpark for a classic spring time setup though.

Supercells require four things:

• Moisture - Check the surface dewpoint plots
  http://www.twisterdata.com/index.ph...12&parameter=DPTF&level=2&unit=M_ABOVE_GROUND
  We're looking for values greater than 55-60 F. You'll want a little more later on in the season (at least 65 come June). For high plains setups (Texas panhandle, Colorado) or cold core/air setups (meaning cold air aloft, not just cold at the surface) greater than 45 F can work. Moisture is the limiting factor in late winter early spring. If I don't see some yellows edging into the plains, I don't look further.
• Instability - Check the CAPE plots
  http://www.twisterdata.com/index.ph...our=12&parameter=CAPE&level=SURFACE&unit=none
  We want at least 1500 J/Kg for a shot at decent supercells and tornadoes. You can squeek by with 750 J/Kg in early season setups and even less in setups with an extreme amount of shear. The more instability we have, the larger and more robust your supercells will be. Instability is in part determined by moisture, so you'll notice that if we don't have sufficient moisture, we probably don't have any instability.
• Shear - Check the 0-6km Bulk Shear plots
  http://www.twisterdata.com/index.ph...=12&fhour=12&parameter=SHRM&level=500&unit=MB
  We need at least 30 knots to sustain supercells, and we're looking great at 50-60 knots. Too little and your storms may remain linear, or quickly transition to HP and gust out. Other shear plots to check out are the 0-3km storm relative helicity, for supercell potential and 0-1km storm relative helicity for tornadoes. Values over 150 are good for each corresponding level/threat. If you have a site that plots Effective Shear, or Effective Storm Relative Helicity such as Earl Barker's site or SPC Mesoanalysis, use these plots instead as they are superior.
• Lift - Check out the temperature and dewpoint plots
  http://www.twisterdata.com/index.ph...12&parameter=TMPF&level=2&unit=M_ABOVE_GROUND
  We're not looking for specific values here, we're looking for where there are sharp gradients (ie fronts and boundaries). Where is the warm front, the cold front, the dryline? These are your sources of lift.
  Check out the 500 mb wind plots
  http://www.twisterdata.com/index.ph...=12&fhour=12&parameter=WSPD&level=500&unit=MB
  These winds will indicate where the longwave or shortwave trough and the upper level energy. Where the jet hits your frontal boundaries, are areas that will have enhanced lift. So line up where the streaks of higher values on this plot, bisect the temperature/dewpoint gradients on the other plot. If you don't see a well defined front or trough, you probably don't have enough lift for storm initiation. Texas panhandle and Colorado chasers, note that the rise in terrain is often your source of lift, so just look for an east wind at the surface.

Alright, so we've found a spot where all the best ingredients overlap, but when and where do the storms actually go up. Forecasting initiation can be tricky and there is a lot involved. Of the above ingredients, we want to focus most on lift. When and where the lift is, determines when the storms go up. Go through the forecast hours and watch where the fronts and troughs are going. Remember, if its the morning of the event, our 12z model run and 0 forecast hour corresponds to 6 or 7am. Go through the hours to 15 or so (which would be 9 or 10pm). Your ingredients will probably peak somewhere in the 9 to 12 hour time frame which is afternoon/evening. Where are the fronts and troughs then? That's where we want to look for storm initiation. If you have a trough over a front, you've got your lift. There is a crucial player here that will make or break your chase forecast, however, and that is the cap:

• Cap - Check the CINH plots
  http://www.twisterdata.com/index.ph...hour=12&parameter=CIN&level=SURFACE&unit=none
  This plot measures the strength of the capping inversion or lid on the atmosphere. Values above 50 will suppress thunderstorm initiation unless you've got a well defined trough bisecting your front. Values above 150 are probably always going to suppress thunderstorm initiation. The cap is double edged sword and should not always be loathed. If there is no CINH being plotted in the morning hours, and you've already got a trough overhead, your storms may very well initiate before the rest of your ingredients are at their peak. The cap plays a huge role on how your chase day pans out. If it erodes too soon, you'll wind up with a large number of junky storms in the morning. Too late and you'll be chasing well after dark, or not at all.
  
  Some prefer the 700 mb temperatures to determine the cap's strength:
  http://www.twisterdata.com/index.ph...=12&fhour=12&parameter=TMPC&level=700&unit=MB
  This can be a good estimate of cap strength, but varies depending on the time of year and location.
  
  The 700 mb level may not be the actual location of the capping inversion though, so I prefer lid strength index or cap index from Earl Barker's site:
  http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_12HR.gif
  This shows the width of the cap as plotted on a sounding, as opposed to the area of the cap which the CINH plots. I believe this to be a better indicator fo the cap's strength and friendlier plot to look at. You'll notice it plots values where the CINH plots do not. 0 indicates no cap, and 1-2 a modest cap that can be overcome with some lift. 3 requires a strong trough bisecting a sharp front. Surface based thunderstorms will probably not initiate with values higher than that. What you want to see here is the cap eroding down below by early to mid afternoon with a hole that is larger than a county, and you want that hole to stay open for several hours.

"But Skip," you say, "its 9am and there are already storms over my target, and the CINH and Cap Index plots say there is too much of a cap. How can that be?" With a strong cap, thunderstorms still can go up. However, they fire above the capping inversion, meaning they pull their inflow not off the surface, but much higher up in the atmosphere. These are called elevated storms, and can still pose a risk for severe weather, but you need surface based supercells if you want a shot at a tornado. Elevated storms often have rather junky looking structure as well. If your cap erodes, and storms fire, but then the cap quickly fills back in, your storms may also become elevated unless there is a good chunk of low level instability left.

So in conclusion, once you've got an overlapping area of all the necessary ingredients, look for the best sources of left, and when and where there is going to be a hole in the cap. That's your best bet for storm initiation. If you've got your other ingredients, but no source of lift, you've got no storms. So don't pick a target with 6000 CAPE that's 200 miles away from the nearest boundary or trough, as there's no lift there. Then its a matter of waiting for the cap to erode. If your Cap Index plot never drops below 3 for an extended period of time, you'll probably find yourself on a sun tanning trip despite having all the best ingredients you could ask for. All the CAPE in the world will not help to break a cap. You need strong lift and a weakening cap.