What a microburst signature looks like on NEXRAD

[Scott Dennstaedt, PhD]

Check out this microburst caught on camera in the Raleigh, NC area.  The important thing to notice is just how benign this looks underneath the cloud deck...lots of locations with blue skies in the distance.  

 https://twitter.com/i/status/1151556735406096385

Here's the dual-node signature you'll see on the NEXRAD radial velocity (Doppler) when it is occurring. Green represents hydrometeors moving toward the radar and red are hydrometeors moving away from the radar.  The image below is time stamped at 1850Z, when in fact, the microburst began around 1845Z based on the camera's time stamp.

Here's the NEXRAD loop you can see how quickly the microburst occurs (each frame is about five minutes apart).  

[ArtVandelay]

Great visuals, that could ruin your day if in the wrong place at the wrong time.


Tom

[Scott Dennstaedt, PhD]

13 minutes ago, ArtVandelay said:

Great visuals, that could ruin your day if in the wrong place at the wrong time.

Tom

You are correct Tom!  These are not generally caused by ominous-looking supercell thunderstorms.  In fact, they tend to occur with deep, moist convection that may not have any lightning strikes.  The area of weather can look rather benign so it's rather tempting to believe it's safe to fly underneath.  Simple rule: Never fly under deep, moist convection.    

[mooneyflyfast]

This is what hit Bulverde Airpark (north San Antonio) a couple of weeks ago. It caused substantial damage to hangars and several airplanes. Blew down and broke dozens of trees.  Note the blue sky at the top.  I wouldnt have wanted to be flying anywhere close.

[Scott Dennstaedt, PhD]

Definitely a supercell thunderstorm.

[kmyfm20s]

 

This one kept me from landing about 4 years ago. It literally grew in front of my eyes and I circled for 15-20 minutes then was able to land.  Centered on top of KMYF in San Diego. Below are just a few of the casualties. About 20 planes severely damaged.

 

 

[kortopates]

 
This one kept me from landing about 4 years ago. It literally grew in front of my eyes and I circled for 15-20 minutes then was able to land.  Centered on top of KMYF in San Diego. Below are just a few of the casualties. About 20 planes severely damaged.
 

I remember that one. Closest we come to seeing a tornado drop in!
In fairness to those that see real tornadoes, this was a long ways from a tornado, but we just don't see much crazy convection, just some earth moving


Sent from my iPhone using Tapatalk

[RobertE]

On 7/19/2019 at 7:13 AM, scottd said:

You are correct Tom!  These are not generally caused by ominous-looking supercell thunderstorms.  In fact, they tend to occur with deep, moist convection that may not have any lightning strikes.  The area of weather can look rather benign so it's rather tempting to believe it's safe to fly underneath.  Simple rule: Never fly under deep, moist convection.    

Scott:  I took your skew t course so I know how deeply you understand these things.  Let me pose a question to you that I posed to Mooneyspace with only a couple of answers that directly addressed the question.

While In Bozeman, MT recently I noticed that many afternoons the towering cumulus clouds form most afternoons around noon on the ridges surrounding the city that, by 3 pm are thunderstorms.  My question concerned how one decides whether or not to fly beneath those TCs at noon.  If there are, say, 3K feet between the mountain  peaks and the bases of those TCs at noon how much vertical development is too much to fly beneath?  No rain shafts, no lightning strikes, just very tall clouds.  How big is too big?  Any other ways to make the judgement call?

[Scott Dennstaedt, PhD]

14 hours ago, RobertE said:

Scott:  I took your skew t course so I know how deeply you understand these things.  Let me pose a question to you that I posed to Mooneyspace with only a couple of answers that directly addressed the question.

While In Bozeman, MT recently I noticed that many afternoons the towering cumulus clouds form most afternoons around noon on the ridges surrounding the city that, by 3 pm are thunderstorms.  My question concerned how one decides whether or not to fly beneath those TCs at noon.  If there are, say, 3K feet between the mountain  peaks and the bases of those TCs at noon how much vertical development is too much to fly beneath?  No rain shafts, no lightning strikes, just very tall clouds.  How big is too big?  Any other ways to make the judgement call?

Robert,

Thanks for taking that Skew-T course!  Lots of good information there.  

There's no precise measuring stick when it comes to knowing what's safe to fly under (or over).  I covered this in my Inflight Hazard Avoidance Strategies live webinar I did several months ago (it was recorded and can be purchased here).  Of course, I could have spent the entire 4 hours talking about this one specific issue, so it only provides some basic guidance.  So without writing a book, here are a few important things to consider.   

Rule #1: Pay considerable attention to deep, moist convection with a very high base (again, there's no precise measuring stick, but I generally start to get concerned with bases of 8,000 or more). 

Rule #2:  Any towering cumulus (deep, moist convection) that has reached the tropopause (they start to flatten at the top and lose that cauliflower-like appearance), then avoid flying under those. 

Rule #3:  When the cloud is taller than you can fly your airplane and is about 4-5 times tall as it is wide at the base, then it time to start thinking about flying around it, not under it.    

Rule #4:  Be careful of deep non-precipitating clouds when there are nearby clouds producing showery precip or thunderstorms.  Are there lots of cells in the area with some producing precipitation?  Generally speaking, if these are single billowing clouds sprinkled down a ridgeline and none of them are generating precipitation, then they are likely harmless to fly under.  But if you see some of them producing precipitation and they have high bases, see rule #1.   Or if you begin to see them hit the tropopause (they start to flatten out at the top), then I would remain clear - see rule #2).

Rule #5:  If you cannot easily decipher what's on the other side of the cloud because it's just too big and obscuring the area, then it's not a good idea to fly under it.    See below.

These clouds below are fine to fly under.  Not enough depth and the height to width ratio is below 4 or 5:1.

  Hope this helps.

[hoot777]

I’m about to retire from “sludge air” and have been around the block 25 k plus hours. - I’m senior- and I read a Business and Commercial Aviation article years ago about thunderstorms and all part 121 hull losses had occurred when the lifted index was minus six or worse. I study this chart before every flight and the worse the lifted index the more cautious I become. While I’m writing please remember nexrad is a great planning tool. It is not weather radar . I can go on about two fatal GA accidents caused by pilots trying to penetrate wx on nexrad . Do not rely on it for tactical wx  penetration. Fly safely and have a great day.

[apenney]

What source do you use to obtain your lifted index chart values?

[Scott Dennstaedt, PhD]

3 hours ago, hoot777 said:

I’m senior- and I read a Business and Commercial Aviation article years ago about thunderstorms and all part 121 hull losses had occurred when the lifted index was minus six or worse. I study this chart before every flight and the worse the lifted index the more cautious I become. 

The problem with the lifted index is that it is highly dependent on what is happening at 500 mb. With low topped convection or a meager lapse rate at 500 mb it can be very misleading as to the threat.  In fact, the SPC rarely mentions it.  A better index is Convective Available Potential Energy or CAPE which provides a more comprehensive view of how the atmosphere is poised. Therefore, from an instability perspective it is the preferred index by most forecasters.  It is true, however, that when CAPE is large, the lifted index will be negative. I like to use the lifted index when it is highly positive (greater than 15). You know it’s likely to be great flying weather.   

Also, these convective indices only show there is convective instability not that convection will form.  You can have a lifted index of -12 and CAPE over 5000 and have zero chance of thunder. I know there are some apps like Aerovie that put out that your route will encounter high CAPE regardless of whether or not there’s any chance of convection. Personally I think that’s not a good approach.    

Here's an example for tomorrow morning.  The lifted index forecast in southern Texas below shows LIs in the -6 to -10 range (fairly significant). 

However, the SPC is not forecasting any convection for tomorrow morning in this same area.

 

Even though there's a negative LI (-4) and high CAPE (3420), there's also a huge hill to climb called convective inhibition (-185) as you can see from this forecast sounding for tomorrow morning.

The other aspect of lifted index or CAPE is that there are multiple flavors. Most pilots use surface-based indices which don’t always catch the potential for elevated convection which is often embedded.  So it’s important to know what index you are using and it’s limitations. 

[hoot777]

There is no exact tool or index . The lifted index is another tool that had served me well over many years of flying.