Clues that a storm is dying

[Andrew Clope]

What clues do you guys use to determine the health of a storm?

I usually look at vis satellite, infrared, and height, but I've noticed that this doesn't seem to really always answer that question well.

What should I be looking for to determine how healthy a storm/updraft is? Or if it does not have potential?

 

[Marcus Diaz]

Watch the base. If it's shrinking and there's not a strong LLJ, that storm is toast. If the base becomes elevated, usually means SBCIN has filled in. This is typical with crashing cold front setups. Also, if you're in the inflow region (i.e. usually anywhere east of it) and you have cold outflow, it's done. Sometimes when the lightning becomes very infrequent, or stops all together, its usually a sign of pulsing or death. That's what I use visually to know whether or not to continue chasing a storm.

 

[Andrew Clope]

^^^ Thanks Marcus!

 

[Jeff Duda]

If the storm isn't so big that you can't see the entirety of the anvil, look at the edge of the anvil. If the edge of the anvil becomes very wispy, that's a good sign the updraft has weakened and the storm may be dying. If the edge of the anvil is crisp, that means you're looking at a healthy updraft and storm.

 

[Andrew Clope]

Jeff, what about if a storm doesn't produce an anvil, due to it not reaching the TP? Does this mean that the overall background environment, or that particular storm is weak?

 

[Jeff Duda]

That's a little more complicated. In the middle of the warm season, ALL thunderstorm tops should be reaching the tropopause. The tropopause contains very stable lapse rates and is the sink for all the kinetic energy in an updraft. If an air parcel/updraft can't even reach the tropopause, that's usually a sign that there is so little CAPE that the EL is below the tropopause, so the air parcel is only minimally warmer than the environment over a great depth of the tropopause.

However, with very dynamic synoptic disturbances that have big dips in the tropopause level (or tropospheric folds), the tropopause can come down to pressures of 400 or 500 mb, maybe even lower. You can have convective instability in such cases where the EL is all the way down at 500 mb or so, which is also where the tropopause happens to be in those cases. Those storms will look puny and short, but they are usually associated with very strong deep shear and can produce severe weather of all sorts, including tornadoes. These types of disturbances usually occur during the fringe months of the warm season (e.g., Feb-Apr or maybe Oct-Dec). The thing is, however, these storms will probably still have an anvil since the tropopause will still have stable lapse rates and will force air to spread out as it leaves the updraft.

So your general idea is correct: if a storm is so weak that it is not producing an anvil, then it's hardly even a true thunderstorm. If you don't see an anvil, a storm is not worth paying attention to. It may be growing into a robust thunderstorm, though. Again, look for crisp cauliflower-like tops to the cumulus clouds. Also look for wide towers. Skinny towers are less likely to survive due to entrainment weakening the core of the updraft.

If you're chasing and you're in a situation where you have a lot of agitated/towering cumulus around you, start looking for the fattest ones or the ones that start producing anvils. Those will be the ones you'll want to focus your efforts on initially. Usually, though, since those clouds get so large, once one of them spawns into a robust storm it will obstruct your view of others that are in the same line of sight, so you'll have to start going off of radar reflectivity at that point.

Hopefully I didn't just confuse you with that :/

 

[Andrew Clope]

^^ Not at all Jeff! Thank you for taking the time to write that explanation.

 

[Ben Holcomb]

Honestly the VIL product on Level3 data is probably the best judge for updraft strength/health for easy glance. If the VIL's are intense in multiple spots, you have a multi cell cluster or back building, if you go from 1 intense spot to 2 intense spots, you probably have splitting storms. If the VIL struggles after being intense, the storm is likely dying.

 

[Royce Sheibal]

Visible kisses of death of storms in Nebraska:
RFD OVERLOAD: Toward the end of the tornadic cycle, the RFD will often go bonkers and 'gust out'. This will often be visible even before the circulation is gone. It's a giant white wall of wind and hail pulling around from the downdraft, and instead of staying put, it starts to push into the warm sector at 70mph. Not a good time, my 1st chase this happened. You can see this on the velocity radar pretty well, also noticeable by a fast drop in VIL in the main updraft. Why does this all happen? Cape gone, CIN, inflow, whatever. Keep an eye out for the white wall.
Choked from inflow: Normally you're watching the wonderful inflow into the storm from the SE. Suddenly you see one or two towers start to pop in your inflow sector, or on the tail. Unless the storm is on a SW to NE boundary and can retrograde the circulation, you're probably toast, as the new cells will ruin storm relative inflow.
Having your wife chase with you: It's a simple fact, if my wife is chasing with me, the second we get close to the cell, it will either die, go HP, or drop a secondary funnel on top of my head. All of which will quickly kill your storm and your day.

 

[Dan Robinson]

Lightning and VILs have been my most reliable indicators of storm strength. VILs a little less so, as it is relatively common for a storm to cycle up and down. However, a long, gradual decrease in VIL values is a good sign the storm is having real trouble. Shrinking base/VIL reflectivity, decreasing lightning and mushy tops all happening together are a pretty safe bet to write the storm off.

You still need to pay attention to the downstream/later-in-time environment regardless of what a storm is doing. A struggling storm can suddenly go nuts when it encounters a better environment - deeper moisture, an outflow boundary, a ramping LLJ at dusk or an upper impulse arriving. Protection, KS on April 23, 2007 was a great example of this. It looked terrible for a long time, then suddenly went crazy right at dusk as it tapped better CAPE as the LLJ kicked in.

 

[Matt Sellers]

When it shrivels like that or it goes ice-machine mode like the May 9 storm in CO as it passed US-40 that quickly took on a OFD appearance... those are two indicators.

 

[David Williams]

Also, I believe in Skip's video about identifying storm features, he mentions that the whale's mouth is a big signal the storm is dying and becoming outflow dominant. The whales mouth is a cavernous arching cloud on the inside of the gust front. Correct me if I'm wrong, but as the downdraft expels rain cooled air it blocks the warm, moist inflow from reaching the updraft and choking off the storm's fuel.

 

[Marshall Stoner]

When you look at a strong storm usually the darkest part of the sky is directly against the precipitation curtain. The updraft/downdraft interface is sharp. If a brighter area appears up against the precipitation curtain or you see a lumpy cloud base that raises in the direction of the precipitation, that's usually an indicator of dry outflow. If you see evidence of dry outflow the storm is finished in terms of tornado potential.

High based LP storms can be deceptive though. Sometimes large hail will out of a storm that doesn't seem impressive up close (not very dark, small ragged base, very little CG lightning). Only from a distance can you see the evidence of an intense updraft. A tornado isn't likely, but you still have to watch out for the hail!

 

[Chad Alcares]

One way using NEXRAD radar is to look at different base reflectivity levels. The 0.5 scan, 1.5, and 2.5. If you see reflectivity at the 2.5 and 1.5 but not very much at 0.5 then you can assume this is a rapidly forming thunderstorm holding most precip aloft. Now if you see the opposite, reflectivity at 0.5... but reduction in reflectivity at 1.5 and 2.5 it's telling you that the storm has become mostly precip and no longer has enough updraft to sustain precip higher up thus dying.

 

[Todd Rector]

I am sure the second I post my opinion on this, a meteorologist will refute it, but... When I see a strong hail core on radar that starts to diminish, I question the overall strength of the updraft.