General newbie questions (to be continued)

[ChristofferB]

I am doing some intense studying at the moment and new (newbie) questions popup all the time that I can't google easily. So, instead of polluting the entire forum I thought I'd start a thread where I, and other newbies, could post general questions about forecasting and storm chasing hoping that some of you more experienced will be kind enough to explain.

Most of these first questions are things I thought about after taking the SpotterNetwork training.

Wind directions
1. Which winds are determining the direction of the storm? Is that typically the midlevel (500 mb?) winds? Before I thought you could determine the direction of a storm by looking at the anvil but after watching radar images it seems like the best storms have an anvil going in another angle than the direction of the storm.

2. A continuation of the previous question. It IS preferable to have the anvil in another direction than the storm direction, right?

3. What do the surface inflow wind directions determine? As far as I understand they are just a part of creating the recipe for shear, right? Is it typically the surface winds that bring in the moisture?

Chasing from home

4. I was doing some "home chasing" during the last two nights of TX and FL storms in order to try to understand radar images better. I don't have any better program than the RadarPro iPad app at the moment but I was following this in Northern FL yesterday:



is this a:

a. Squall line? (my guess)
b. Multicluster thunderstorm?
c. Weather front with some thunderstorms and clouds in it?
d. Derecho? I know for a fact it isn't, but how could one tell, they have the same shape right?

I'm thinking a multicluster would be less "even" in its shape, right?

5. Is it possible to see what was observed from a storm afterwards. Like, if I want to check the "results" of a storm the day after. I'm thinking those kind of things that can be seen on GR LevelX (tornadoes reported, rotating wall clouds, hail size of x etc)?


Mesoscale

6. I'm trying to figure out what a mesocyclone really is. As far as I understand it is the upward, rotating column of air inside a supercell. You cannot see a mesocyclone but you can see the rotation of it on radar (?). A tornado is basically the bottom end of a huge rotating cyclone inside the supercell. Is that correct?

I was looking at a couple of the Moore May31-tornado videos and in one (I think in Skip Talbot's) he discuss that many didn't see that a much larger area was under a mesocyclone and that's a reason why the tornado could grow so rapidly. I could confuse that with Mike Hollingshead Storm Analysis 101-video as well, from a large SD-storm.

Well, basically...my question is. Is my understanding of a mesocyclone correct? Then, I assume that a tornado can spin out under a mesocyclone pretty much anywhere?

7. Regarding single cell and superell thunderstorms. Is it possible to see on one single cloud, during its maturing state if it will be a single cell or supercell? They all start as single cells but may continue to be a supercell. Is that correct?

I'm thinking about a note that most FL tornadoes are not created by supercells but merely single cell thunderstorms (and are weak). I assume it has to do with an abundande of moisture but weak shear?

8. I'm trying to figure out the horseshoe-shape of supercells and map that against the models, such as this one (from SpotterNetwork.org):



Are we looking into that horseshoe here (created by the purple and green inflow winds)?

9. I am trying to compare that horseshoe with this photo, that I took in KS on last year's chase (non-tornadic, high based supercell):



If there would have been a tornado in this storm, would it have been in the inner part of the U in that horseshoe?

10. Is it correct that the RFD notch is a band of colder, clear air (i.e. no clouds) that "cuts out" the mesocyclone? For example, do the red dots mark the RFD notch in the photo below?



11. Regarding downbursts. As far as I understand downbursts are not a conitnuous part of a storm but rather something that happens when a part of the storm collapse and bring a huge chunk of air to the ground? As opposed to a gust front, of a storm, which is always present?


Synoptic scale

12. Is it possible to see whether a weather system is HP or LP on a satellite photo? I image googled both:

https://www.google.com/search?q=low+pressure+satellite+photo
https://www.google.com/search?q=high+pressure+satellite+photo

...and they seem to look the same to me.

13. LP's have winds moving into the system, bringing them aloft (and HP) quite the opposite. This must mean that LP's have winds going out from the system aloft, right? I mean, the wind has to go somewhere? So, the winds moving into the system are surface or low level winds, is that correct?


....

I am very grateful for any answer to any of these questions!

 

[Rob H]

Wow, that's a lot, but I like these types of threads. I'll try not to hog the answers too much

Wind directions
1. Which winds are determining the direction of the storm? Is that typically the midlevel (500 mb?) winds? Before I thought you could determine the direction of a storm by looking at the anvil but after watching radar images it seems like the best storms have an anvil going in another angle than the direction of the storm.

Look into Bunkers motion (don't try to calculate it yourself). The 500mb winds are called the steering winds as they have the most influence on a storm's direction and speed. There are some shorthand approximations you can use like 70% of the 500+700 winds or 80% of the 500+850 winds - I forgot the exact numbers, but you'll want to pad any estimate anyways.

2. A continuation of the previous question. It IS preferable to have the anvil in another direction than the storm direction, right?

Anvil level winds are 9-11km and are higher in the atmosphere. If the anvil is aligned with the motion, you could end up dropping precip in the path of your storm, which isn't good.

3. What do the surface inflow wind directions determine? As far as I understand they are just a part of creating the recipe for shear, right? Is it typically the surface winds that bring in the moisture?

Primarily low level speed and directional shear. Surface conditions drive a lot though. Temperatures and dewpoints describe the moisture, instability, and cloud base level for example. 850mb is also a very important part of this that gets overlooked. I've seen otherwise primed areas fail because of a lack of 850mb moisture, and I've seen storms go nuts when the HRRR depicts an 850mb low level jet nosing into the area. Again, try to get out of the habit of thinking of these as discrete levels of the atmosphere. Moisture and winds *between* the surface and say 1km off the ground are what are fueling the storm's lower levels - not just 6m and 1km off the ground. The atmosphere also doesn't work on constant pressure surfaces, but isentropic analysis is a rather advanced concept and most chasers do well without ever digging into it.

Mesoscale

6. I'm trying to figure out what a mesocyclone really is. As far as I understand it is the upward, rotating column of air inside a supercell. You cannot see a mesocyclone but you can see the rotation of it on radar (?). A tornado is basically the bottom end of a huge rotating cyclone inside the supercell. Is that correct?

I was looking at a couple of the Moore May31-tornado videos and in one (I think in Skip Talbot's) he discuss that many didn't see that a much larger area was under a mesocyclone and that's a reason why the tornado could grow so rapidly. I could confuse that with Mike Hollingshead Storm Analysis 101-video as well, from a large SD-storm.

Well, basically...my question is. Is my understanding of a mesocyclone correct? Then, I assume that a tornado can spin out under a mesocyclone pretty much anywhere?

You can see a mesocyclone - those sculpted updrafts that are twisting are mesocyclones. If you're not in position or the storm is sloppy you'll need to infer from radar. Think of it as a series of cyclones all the way down: a low pressure system, a mesocyclone, a tornado cyclone, a tornado, individual vortices, etc. A tornado is *most likely* to form under a wall cloud which forms on the updraft/downdraft interchange under the meso. That's not the only place it can form though. You can also have occluding mesocyclones or tornado cyclones. I've seen supercells with two well defined couplets before and you just assume a tornado could be under either. With El Reno, I'm guessing the point was that the distinction between the various cyclones was extremely small on this huge storm as if the mesocyclone was touching the ground. Try not to think of the various levels as individual gears on a manual transmission for a car, think of it more like those continuously variable transmissions. Nature doesn't always fall nicely into discrete categories that humans come up with.

7. Regarding single cell and superell thunderstorms. Is it possible to see on one single cloud, during its maturing state if it will be a single cell or supercell? They all start as single cells but may continue to be a supercell. Is that correct?

I'm thinking about a note that most FL tornadoes are not created by supercells but merely single cell thunderstorms (and are weak). I assume it has to do with an abundande of moisture but weak shear?

SPC Mesoanalysis (and other places) have a supercell composite index. That will give you an idea of whether supercells are likely, but short of that there is nothing to indicate when or if a single cell will form a rotating, persistent updraft. Lack of shear is one of the biggest reasons for no supercells, but it could be too little (or even too much) of any of the four ingredients.

 

[kmreid]

I am a noob as well, so if I am wrong, someone please feel free to correct me.

As far as question #4, it very well could be a derecho (http://upload.wikimedia.org/wikipedia/commons/3/37/Derecho_development.png) as it has some of the visual characteristics of one. A bow echo is a sort of squall line that has areas of strong straight line winds, so at the very least, it is a bow echo that is depicted in the picture that you provided.

 

[Rob H]

A derecho is defined by longevity and reports, so you can't evaluate a static image on its own. From the SPC:

By definition, if the swath of wind damage extends for more than 240 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho.

 

[Mike Johnston]

With regard to storm motion, be aware you can get some idea on SPC's mesoanalysis map. If you look under the wind shear tab, there are several options for SR Helicity. Click on one of these and notice the map also has barbs that show direction and speed of expected storm motion. Always a good idea to at least glance at this before you leave for a chase, to give you some idea of what you're dealing with.

With ongoing storms, the GR Level 3 radar software has a algorithm that shows storm motion and speed for individual cells. While you can get an idea of storm motion in the immediate area, don't take it too literally though - and certainly don't try to track a tornado with it.

 

[Rick Schmidt]

I didn't see anyone address your synoptic scale questions, but when chasers use the terms LP and HP, we usually are describing a type of supercell. I would just refer to what you are talking about as high pressure and low pressure areas. Other terms that are used are 'trough' for low pressure, and 'dome' for high pressure areas. Well developed low pressure areas,(or systems), are easily identified as the pinwheel, or 'hurricane' looking areas on satellite views. Most high pressure areas, especially strong ones, don't have many visible clouds associated with them, since the air is sinking instead of rising. The best way to identify these types, is to notice the clouds travelling around the perimeter of the high pressure area. (clock-wise, instead of counter-clockwise with low pressure). Hope this helps, and someone correct me if I am wrong on something.

 

[Shane Adams]

If you go back to the very first (oldest) page on this section, there are a lot of old question/answer type posts that deal with a lot of basic visual things, as well as meteorology. It's a gold mine that's been there for six years, and I always refer new folks to that place. Just start at the oldest page and go from there, there are multiple pages of great stuff.

 

[ChristofferB]

THANK YOU so much everyone (special thanks to Rob)! That really straightened out some of the question marks I had. A few comments to your answers:

- 1. I think a general rule of thumb (like 500mb) is sufficient for my understanding at the moment, and I will go on with Bunkers motion later on. Basically, I am just trying to connect things together. Like if I see storms moving from E to W in a radar, I would like to know which wind map I should look at to see why.

- 3. Just as in the question above, there is just too much to take in at the moment so I will just consider rule of thumbs and go on to a more complex understanding as it goes.
- Re LP/HP. Oh, I didn't think about that. Noted! Clears out the word "trough" that have puzzled me as well.

- "be aware you can get some idea on SPC's mesoanalysis map. If you look under the wind shear tab, there are several options for SR Helicity" - Thanks, I'm starting to realize that this website is the only one that is really needed.

- Regarding the old threads. Good idea, I will check them out as well!

In general one of my major struggles is to find the correct map to each question I come up with. Like, why is there a Slight Risk in FL at the moment? I can see now it has wind shear (through the SPC mesoanalysis map as suggested: http://www.spc.noaa.gov/sfctest/new/viewsector.php?sector=18#). I can verify that to see the winds on different heights and see that they are in different directions. Why it's like this only in FL at the moment I have yet to understand, but I'll get there.

Lastly, I separated the un-answered questions in the quote below to make it a bit easier:

5. Is it possible to see what was observed from a storm afterwards. Like, if I want to check the "results" of a storm the day after. I'm thinking those kind of things that can be seen on GR LevelX (tornadoes reported, rotating wall clouds, hail size of x etc)?


Mesoscale



8. I'm trying to figure out the horseshoe-shape of supercells and map that against the models, such as this one (from SpotterNetwork.org):

View attachment 8228

Are we looking into that horseshoe here (created by the purple and green inflow winds)?

9. I am trying to compare that horseshoe with this photo, that I took in KS on last year's chase (non-tornadic, high based supercell):

View attachment 8229

If there would have been a tornado in this storm, would it have been in the inner part of the U in that horseshoe?

10. Is it correct that the RFD notch is a band of colder, clear air (i.e. no clouds) that "cuts out" the mesocyclone? For example, do the red dots mark the RFD notch in the photo below?

View attachment 8230

11. Regarding downbursts. As far as I understand downbursts are not a continuous part of a storm but rather something that happens when a part of the storm collapse and bring a huge chunk of air to the ground? As opposed to a gust front, of a storm, which is always present?


Synoptic scale

13. LP's have winds moving into the system, bringing them aloft (and HP) quite the opposite. This must mean that LP's have winds going out from the system aloft, right? I mean, the wind has to go somewhere? So, the winds moving into the system are surface or low level winds, is that correct?


....

I am very grateful for any answer to any of these questions!

Once again, thank you for all your help!

 

[ChristofferB]

As I mentioned I will fill out this thread with questions along the way:

If you see this cloud formation, you are looking at the flanking line and the storm is likely to move away from you, right?



...also, in the text related to this photo it says it has bad inflow. How can one see that?

 

[Rick Schmidt]

A flanking line is used to describe a feature of a supercell. Google 'flanking line' on their images page to see examples. Your photo shows a retreating thunderstorm, probably a single cell or multi-cell storm, and it shows the updraft tower. You are looking a the back side, although it could be moving to the right or left. 'Bad inflow' is kind of a strange term, but at that distance, it is hard to actually see 'inflow'. Supercells generally have distinct cloud bands that are indicative of inflow. The terms 'inflow band', and' beaver's tail' describe these features.

 

[kmreid]

This might help with #10, but it is hard to tell at that angle. http://www.erh.noaa.gov/rnk/SKYWARNonline_files/800x600/slide51.png

 

[Bob Schafer]

WRT storm motion, my advice is to just go by the motion suggested by the helicity graphic. That said, it is VERY IMPORTANT to understand that ANY calculation for storm motion is no more reliable than any other predicted parameter. Even more important: Storm motion is going to vary, perhaps to the extreme, depending on how the storm interacts with boundaries and inflow. Just look at 130531. That is so important for staying safe, at times.

 

[ChristofferB]

A flanking line is used to describe a feature of a supercell. Google 'flanking line' on their images page to see examples. Your photo shows a retreating thunderstorm, probably a single cell or multi-cell storm, and it shows the updraft tower. You are looking a the back side, although it could be moving to the right or left. 'Bad inflow' is kind of a strange term, but at that distance, it is hard to actually see 'inflow'. Supercells generally have distinct cloud bands that are indicative of inflow. The terms 'inflow band', and' beaver's tail' describe these features.

Thanks! I am trying to build a 3D-image in my head from all the models and compare those against radar images and photos from the web and from my own trips. Those darn storms just won't behave and conveniently look like the models though!

I have plenty of photos taken from this angle:



If the storm is moving to the right (and I remember wrong, that the anvil was above us) then what I am looking at is, I'm guessing either the Forward Flank Downdraft or the gust front (I'm guessing gust front) and the finger like, dark grey clouds at the bottom of the cloud are shelf clouds. Is that correct? If I google "shelf clouds" I find similar photos.

Can I draw the conclusion that if I find these "finger like" clouds at the bottom of a supercell, I am most likely looking at shelf clouds and that the storm is moving in (roughly) that direction?

What makes that confusing is that I would expect that area of the storm to be much more blurry with rain. Isn't it typically so? That is at least what I deduct from this diagram, taken from the Stormspotter course. I would also expect the anvil to be just above me, and I can't remember there being an anvil ahead of me.

 

[ChristofferB]

This might help with #10, but it is hard to tell at that angle. http://www.erh.noaa.gov/rnk/SKYWARNonline_files/800x600/slide51.png

Thanks. It's quite difficult to grasp, I have only seen RFD notches in these type of photos. Is it then the RFD that carves out the hole inside the horseshoe shape, as in my #9? It looks quite similar to my photo there, except that mine doesn't have a tornado and is more higher based.

 

[Rob H]

Your #9 is probably some sort of downdraft that punched a hole through the clouds. Sometimes you'll even see downdrafts bisecting wall clouds - so the "textbook" RFD might tend to only happen on a tornadic storm, which is why you only see it on those types of photos

Forward Flank Downdraft (FFD) will usually be associated with a gust front, which will usually have a single shelf cloud (you don't really have plural shelf clouds). A shelf cloud looks like a bookshelf - a long line separating thick cloud and clear air.

In your moderskeppet.jpg, it looks like you are SSW of the storm, viewing NNE. In that position, with a shelf cloud, the whole thing was probably expanded outwards towards you. I don't understand why you think it would be blurry with rain. I see a ton of heavy rain in your picture on the far left (that dark grey). If you're in the inflow region, a lot of the storm's internal structures are exposed to you. Which is also why that's where you want to be when spotting/chasing. Out of the path, in relative safety, and able to see everything important.