Question Box:

[senorpepr]

OOOHHHHHHH!!!!! I have a question..... what are the "T-numbers" how high/low is the scale and what does it mean?? THANKS!!!!!

See if this can help you:

http://en.wikipedia.org/wiki/Dvorak_technique

Follow-up Question:

As I have understood it, T numbers are used when there is an absence of recon. TD 4 has a Dvorak indicating tropical storm strength yet I don't see Debby getting a name. Without recon to the contrary, what is the reasoning for this?

Dvorak isn't a sole tool used. Dvorak is used in association with other rules of thumb. The process is rather subjective. If the satellite presentation indicates a minimal tropical storm, but other facts (such as QuikSCAT) indicate otherwise, they will adjust the intensity as needed.

[LAwxrgal]

I have a question... I've often heard of shear and shear maps and shear tendencies but what exactly is it? Is it winds aloft? or water currents? I'm unsure as to what exactly it is... Thanks...

Shear is essentially a change in winds, whether it's a change in direction (directional shear) or a change in speed (speed shear). Shear can be figured as horizontal shear (a change in winds over the same altitude whether it's at the surface or aloft) and vertical shear (a change in winds over the same location, but at different altitudes).

The shear maps show how much of a change exists and the tendencies show what the trends are.

For overland thunderstorms, shear tends to help the system by adding a vent. However, tropical cyclones don't want this. The lower the shear (or the more uniform the atmosphere is), the better.

Okay, cool, thanks, that actually cleared a lot of stuff up for me. I kind of figured it was winds aloft but wasn't entirely sure. Thanks.

[senorpepr]

I have a question... I've often heard of shear and shear maps and shear tendencies but what exactly is it? Is it winds aloft? or water currents? I'm unsure as to what exactly it is... Thanks...

Shear is essentially a change in winds, whether it's a change in direction (directional shear) or a change in speed (speed shear). Shear can be figured as horizontal shear (a change in winds over the same altitude whether it's at the surface or aloft) and vertical shear (a change in winds over the same location, but at different altitudes).

The shear maps show how much of a change exists and the tendencies show what the trends are.

For overland thunderstorms, shear tends to help the system by adding a vent. However, tropical cyclones don't want this. The lower the shear (or the more uniform the atmosphere is), the better.

Okay, cool, thanks, that actually cleared a lot of stuff up for me. I kind of figured it was winds aloft but wasn't entirely sure. Thanks.

Here's an example... say the winds over Omaha at 5000ft is 30kt and at 6000ft is 50kt. There is 20kt/kft of shear over Omaha.

[mempho]

OOOHHHHHHH!!!!! I have a question..... what are the "T-numbers" how high/low is the scale and what does it mean?? THANKS!!!!!

See if this can help you:

http://en.wikipedia.org/wiki/Dvorak_technique

Follow-up Question:

As I have understood it, T numbers are used when there is an absence of recon. TD 4 has a Dvorak indicating tropical storm strength yet I don't see Debby getting a name. Without recon to the contrary, what is the reasoning for this?

Dvorak isn't a sole tool used. Dvorak is used in association with other rules of thumb. The process is rather subjective. If the satellite presentation indicates a minimal tropical storm, but other facts (such as QuikSCAT) indicate otherwise, they will adjust the intensity as needed.

OK, so they are splitting the difference between Dvorak and other tools.

[LAwxrgal]

I have a question... I've often heard of shear and shear maps and shear tendencies but what exactly is it? Is it winds aloft? or water currents? I'm unsure as to what exactly it is... Thanks...

Shear is essentially a change in winds, whether it's a change in direction (directional shear) or a change in speed (speed shear). Shear can be figured as horizontal shear (a change in winds over the same altitude whether it's at the surface or aloft) and vertical shear (a change in winds over the same location, but at different altitudes).

The shear maps show how much of a change exists and the tendencies show what the trends are.

For overland thunderstorms, shear tends to help the system by adding a vent. However, tropical cyclones don't want this. The lower the shear (or the more uniform the atmosphere is), the better.

Okay, cool, thanks, that actually cleared a lot of stuff up for me. I kind of figured it was winds aloft but wasn't entirely sure. Thanks.

Here's an example... say the winds over Omaha at 5000ft is 30kt and at 6000ft is 50kt. There is 20kt/kft of shear over Omaha.

Which, according to what you say above, would help in the development of severe thunderstorms in that area. Would this same logic apply to hurricanes? At 5000 ft the winds in an area of the ocean north of a storm are 10 kts and 6000 ft the winds are 40kts, would that mean the shear in that area is 30kts?

[brunota2003]

OOOHHHHHHH!!!!! I have a question..... what are the "T-numbers" how high/low is the scale and what does it mean?? THANKS!!!!!

See if this can help you:

http://en.wikipedia.org/wiki/Dvorak_technique

Follow-up Question:

As I have understood it, T numbers are used when there is an absence of recon. TD 4 has a Dvorak indicating tropical storm strength yet I don't see Debby getting a name. Without recon to the contrary, what is the reasoning for this?

Dvorak isn't a sole tool used. Dvorak is used in association with other rules of thumb. The process is rather subjective. If the satellite presentation indicates a minimal tropical storm, but other facts (such as QuikSCAT) indicate otherwise, they will adjust the intensity as needed.

OK, so they are splitting the difference between Dvorak and other tools.

from the 11 AM Discussion:

DVORAK INTENSITY ESTIMATES AT 12Z WERE 30 KT FROM TAFB AND AFWA...
AND 35 KT FROM SAB. SINCE THEN CONVECTION HAS DECAYED SOMEWHAT AND
SO THE ADVISORY INTENSITY WILL REMAIN 30 KT. HIGHER VALUES IN THE
8Z QUIKSCAT PASS ARE BELIEVED TO BE RAIN CONTAMINATED.

So as you can see, you have Dvorak, TAFB, AFWA, and SAB all running estimates, you have Quikscat, and you then have the forecasters looking at convective trends...all of those are taken into account when issueing the intensity for an advisory...then if you have Recon, they will mainly go by that and convective trends, but they still see how in agreement the recon data and Sat estimates are...

[mempho]

I have a question... I've often heard of shear and shear maps and shear tendencies but what exactly is it? Is it winds aloft? or water currents? I'm unsure as to what exactly it is... Thanks...

Shear is essentially a change in winds, whether it's a change in direction (directional shear) or a change in speed (speed shear). Shear can be figured as horizontal shear (a change in winds over the same altitude whether it's at the surface or aloft) and vertical shear (a change in winds over the same location, but at different altitudes).

The shear maps show how much of a change exists and the tendencies show what the trends are.

For overland thunderstorms, shear tends to help the system by adding a vent. However, tropical cyclones don't want this. The lower the shear (or the more uniform the atmosphere is), the better.

Okay, cool, thanks, that actually cleared a lot of stuff up for me. I kind of figured it was winds aloft but wasn't entirely sure. Thanks.

Here's an example... say the winds over Omaha at 5000ft is 30kt and at 6000ft is 50kt. There is 20kt/kft of shear over Omaha.

Which, according to what you say above, would help in the development of severe thunderstorms in that area. Would this same logic apply to hurricanes? At 5000 ft the winds in an area of the ocean north of a storm are 10 kts and 6000 ft the winds are 40kts, would that mean the shear in that area is 30kts?

On this question...doesn't shear hurt the vertical development of overland storms? I know some of our hail producing storms can get very, very high. It's hard to imagine that shear would help those storms.

[senorpepr]

OK, so they are splitting the difference between Dvorak and other tools.

Also, that tend to split the difference of Dvorak reporting agencies. For instance, if TAFB is reporting T1.5, SAB is reporting T2.0, and AFWA is reporting T2.5, NHC is likely to set the intensity at 30KT (T2.0).

[senorpepr]

Which, according to what you say above, would help in the development of severe thunderstorms in that area. Would this same logic apply to hurricanes? At 5000 ft the winds in an area of the ocean north of a storm are 10 kts and 6000 ft the winds are 40kts, would that mean the shear in that area is 30kts?

Shear helps overlands storms, but tropical cyclones (since they are a warm-core system) is hurt by shear. The less shear over the water, the less the tropical cyclone is disturbed.

[senorpepr]

On this question...doesn't shear hurt the vertical development of overland storms? I know some of our hail producing storms can get very, very high. It's hard to imagine that shear would help those storms.

No... shear helps to vent the storm and introduce more dry air, which helps an overland tstm. Actually, during a tstm that is producing hail, usually the shear is VERY high. It helps in the hail development process.

[LAwxrgal]

Which, according to what you say above, would help in the development of severe thunderstorms in that area. Would this same logic apply to hurricanes? At 5000 ft the winds in an area of the ocean north of a storm are 10 kts and 6000 ft the winds are 40kts, would that mean the shear in that area is 30kts?

Shear helps overlands storms, but tropical cyclones (since they are a warm-core system) is hurt by shear. The less shear over the water, the less the tropical cyclone is disturbed.

Ok, gotcha.

[mempho]

Thanks for your great answers, senorpepr!

[LAwxrgal]

Thanks for your great answers, senorpepr!

Ditto. What he said.

[senorpepr]

On this question...doesn't shear hurt the vertical development of overland storms? I know some of our hail producing storms can get very, very high. It's hard to imagine that shear would help those storms.

No... shear helps to vent the storm and introduce more dry air, which helps an overland tstm. Actually, during a tstm that is producing hail, usually the shear is VERY high. It helps in the hail development process.

Check this out: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/comp/wind/home.rxml

(You'll have to copy and paste the whole URL)

[wxmann_91]

On this question...doesn't shear hurt the vertical development of overland storms? I know some of our hail producing storms can get very, very high. It's hard to imagine that shear would help those storms.

No... shear helps to vent the storm and introduce more dry air, which helps an overland tstm. Actually, during a tstm that is producing hail, usually the shear is VERY high. It helps in the hail development process.

Shear helps tilt the updraft of the thunderstorm, thus separating the downdrafts and updrafts, and increasing the longetivity of the thunderstorm. Thus, with the updraft tilted and strong, separated from teh downdraft, large hail can result.

TC's are vertically stacked storms.

[Wthrman13]

On this question...doesn't shear hurt the vertical development of overland storms? I know some of our hail producing storms can get very, very high. It's hard to imagine that shear would help those storms.

No... shear helps to vent the storm and introduce more dry air, which helps an overland tstm. Actually, during a tstm that is producing hail, usually the shear is VERY high. It helps in the hail development process.

Shear helps tilt the updraft of the thunderstorm, thus separating the downdrafts and updrafts, and increasing the longetivity of the thunderstorm. Thus, with the updraft tilted and strong, separated from teh downdraft, large hail can result.

TC's are vertically stacked storms.

All this is definitely true, but there is an even more important effect that moderate vertical wind shear has on the organization of thunderstorm cells: dynamical pressure effects.

Basically, without getting too technical, a storm's updraft will interact with the changing speed and direction of the winds with altitude in the following two ways:

1) As the environmental wind speed increases with height, the updraft of the storm will be transporting lower-speed air from below into the higher wind speeds aloft. This has the effect of producing high pressure on the upstream side of the updraft, and low pressure on the downstream side of the updraft in the midlevels. This causes a preferential development of new updrafts on the downstream side of the old one and can help intensify and increase the longevity of the storm.

2) Rotation of the updraft. This is caused by the updraft tilting the horizontal vorticity present due to the environmental wind shear. The low pressure created in the rotating updraft at midlevels also leads to an enhancement of the updraft strength, due to an upward directed pressure gradient from the low-levels to the low pressure in the mid levels of the storm. Storms that have strong, deep, and persistent updraft rotation like this are called supercells.

These two effects combined can lead to a significant enhancement in the strength of the storm cell relative to another storm with the same buoyancy in a lower shear environment, simply due to these dynamic pressure effects.

I've glossed over a lot of stuff in this, but a full explanation can get rather technical and really requires diagrams to fully appreciate (at least for me). For a more thorough explanation, complete with nice diagrams and animations, check out:

http://meted.ucar.edu/topics_convective.php

and look for the topics entitled "Principles of Convection I, II, and III", particularly part III.

[GeneratorPower]

Senorpepr, are we talking about speed shear or directional shear?

[senorpepr]

Senorpepr, are we talking about speed shear or directional shear?

Well, both. Speed convergence or directional convergence can also help build a thunderstorm over land. However, with respect to the above comments on shear and hail, that's more of a directional situation.

[BreinLa]

this forum is awesome, thanks senor!!!!!!!!! A2K toooooo

[MississippiHurricane]

Thanks to EVERYONE!!!!!!!!