Anticipating and dealing with rain wrapped tornadoes

JeremyS

EF2
Mar 12, 2014
170
214
11
Omaha, NE
I wanted to start this thread to ask a couple of questions on rain wrapped tornadoes. I was out chasing yesterday in Kansas and finally made it around to the front of the monster cell that was producing the rain wrapped wedge. I came east down I70 to Lawrence, dropping south on Hwy 59 with anxious excitement of finally getting a view of what I hoped would be a big tornado and instead all I could see was....rain. I ended up stopping at Hwy 460 just south of Pleasant Grove and then continued to follow it to the east/northeast all the way to Bonner Springs, but never got a view of the tornado. Looking at the radar/velocity couplet, I was worried it would be rain wrapped, but sometimes you get surprised. There's nothing more disappointing on a chase than not being able to see the tornado that is actually there but obscured by precip!
That being said, I was a bit surprised it was rain wrapped, especially seeing some of the other visible tornadoes from other parts of Kansas. What set of factors will usually make a tornado rain wrapped? Is there a definite reason on why yesterday's tornado was rain wrapped? Do you guys ever look at forecast soundings and think for sure the tornadoes are going to be rain wrapped? I always think of upper level venting of the storm and will usually look at those wind speeds to get an idea. I remember reading yesterday at 500mb the winds were supposed to be 60-70 knots which is great, but didn't see what they were up higher. If there are strong winds at the mid and upper levels, but the winds are at the same speed or maybe even decrease a tiny bit as you go up in the atmosphere(i.e. 60 knots to 50 knots) will that cause potential issues with HP/rain wrapped tornadoes? I know the air was juicy with low 70's dews and the spread between T/Td was pretty low, so low LCL's as well. Could that be a part of the cause?
Sorry for all the random thoughts and questions. Just wanting to get an idea of people's thoughts on this subject. Thanks in advance!
 
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Jeff Duda

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Oct 7, 2008
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What set of factors will usually make a tornado rain wrapped? Is there a definite reason on why yesterday's tornado was rain wrapped? Do you guys ever look at forecast soundings and think for sure the tornadoes are going to be rain wrapped? I always think of upper level venting of the storm and will usually look at those wind speeds to get an idea. I remember reading yesterday at 500mb the winds were supposed to be 60-70 knots which is great, but didn't see what they were up higher. If there are strong winds at the mid and upper levels, but the winds are at the same speed or maybe even decrease a tiny bit as you go up in the atmosphere(i.e. 60 knots to 50 knots) will that cause potential issues with HP/rain wrapped tornadoes? I know the air was juicy with low 70's dews and the spread between T/Td was pretty low, so low LCL's as well. Could that be a part of the cause?
I think you're well on your way to understanding and anticipating rain-wrapped tornadoes and HP supercells in general, Jeremy, as you already pointed out several of the factors that are very useful in determining this issue. I bolded specific statements you made that are most prudent. I would say you want to pay attention to near-storm-top storm-relative winds at least as much as mid-level storm-relative winds. I usually look at storm relative flow near the equilibrium level. The higher the storm relative wind speed, the less likely you are to deal with excessive precip in and around the updraft. However, I don't think that fully tells the story.

I think flat-out moisture content is a major factor, too. Even if it dries out above the PBL, a given volume of atmosphere can only contain so much liquid water. If you have very high PBL moisture (dewpoints well into the 70s and/or 1 km mean mixing ratios getting into the 15 g/kg-and-above range), that's just a lot of water that will be coming out of the storm, and I believe it would take even stronger than normal storm-relative flow to blow all that water away from its source (the updraft).

However, there is one element you didn't mention that I think may be particularly crucial in the case of the Lawrence storm yesterday: discreteness. That storm appeared to have other updrafts immediately behind it, each creating hydrometeors that were subsequently dumped into the updraft region of the Lawrence storm (consider the storm relative wind vector around that storm...mid- and upper-level storm-relative flow was to the northeast, which would blow rain/hail northeastward). This behavior occurs rather frequently, as one storm tends to promote other storms nearby given the broad lift generated by the updraft and associated low-level convergence. Only in cases where there is widespread moderate CIN to resist new storms and the first storm formed in an area of concentrated stronger lifting (like the dryline or a triple point or other boundary intersection, for examples) are you likely to see a sustained isolated cell persist.

I think a combination of all of these factors led to the rain-wrapped nature of the Lawrence tornado.
 

JeremyS

EF2
Mar 12, 2014
170
214
11
Omaha, NE
Awesome Jeff! Thanks for the reply, I always appreciate your knowledge and insight on this forum and how much you are willing to share that information!:)


I think you're well on your way to understanding and anticipating rain-wrapped tornadoes and HP supercells in general, Jeremy, as you already pointed out several of the factors that are very useful in determining this issue. I bolded specific statements you made that are most prudent. I would say you want to pay attention to near-storm-top storm-relative winds at least as much as mid-level storm-relative winds. I usually look at storm relative flow near the equilibrium level. The higher the storm relative wind speed, the less likely you are to deal with excessive precip in and around the updraft. However, I don't think that fully tells the story.

I think flat-out moisture content is a major factor, too. Even if it dries out above the PBL, a given volume of atmosphere can only contain so much liquid water. If you have very high PBL moisture (dewpoints well into the 70s and/or 1 km mean mixing ratios getting into the 15 g/kg-and-above range), that's just a lot of water that will be coming out of the storm, and I believe it would take even stronger than normal storm-relative flow to blow all that water away from its source (the updraft).

However, there is one element you didn't mention that I think may be particularly crucial in the case of the Lawrence storm yesterday: discreteness. That storm appeared to have other updrafts immediately behind it, each creating hydrometeors that were subsequently dumped into the updraft region of the Lawrence storm (consider the storm relative wind vector around that storm...mid- and upper-level storm-relative flow was to the northeast, which would blow rain/hail northeastward). This behavior occurs rather frequently, as one storm tends to promote other storms nearby given the broad lift generated by the updraft and associated low-level convergence. Only in cases where there is widespread moderate CIN to resist new storms and the first storm formed in an area of concentrated stronger lifting (like the dryline or a triple point or other boundary intersection, for examples) are you likely to see a sustained isolated cell persist.

I think a combination of all of these factors led to the rain-wrapped nature of the Lawrence tornado.