Mega hail in India and Bangladesh

I'd like to point out that the (CAPE)^1/2 estimate for maximum wind speed is based on parcel theory, which represents the maximum possible wind speed given only thermodynamic forcing (i.e., the thermodynamic speed limit). Generally, though, updrafts will not achieve this maximum in efficiency due to dry air entrainment (which limits the CAPE by reducing the dewpoint), downward directed perturbation pressure gradient forces (which literally oppose the vertical growth of the updraft), and liquid water loading. Thus, though large CAPE is a necessary ingredient for mega hail, it is insufficient.

For instance, on May 9, 2006, a large area of extreme instability (>5000 j/kg) developed over southern and eastern Oklahoma. Yet, the hail observed on that day was only marginally severe (~1 inch in diameter). I suspect that dry entrainment was partially responsible for the meager hail size. On the other hand, large hails has been observed on days with relatively low CAPE. These latter cases were associated with strong updraft rotation, which promotes much stronger updrafts than the thermodynamic forcing alone supports (by means of large perturbation pressure gradient forces).

As far as large/violent tornadoes in Bangladesh are concerned, I suspect that the development of such is relatively rare. I think this is primarily due to the *ridiculously* strong elevated mixed layers (i.e., capping inversions) that develop off the Himalayas. That is, though steep lapse rates and CAPE might be impressive, the cap keeps the atmosphere from realizing its potential (most of the time). However, when the cap does break in Bangladesh, all bets are off.

Gabe
 
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Gene Moore makes a good point.. it's tough in the Plains states to hold your dewpoint above 70 once surface temps have mixed past 100F. Moreover, initiation is rather unlikely in these hot environments until you get near/west of longitude 100W, where really deep mixing and increasingly elevated terrain plays a role. I've seen 100/77 at Huron, SD and 101/70 at Sioux City, IA... and each case was a late July "cap bust" near a triple point low & at the nose of the hot prod.

The 06/12/42 event near OKC (posted by Bobby Prentice a while back) may be the closest thing we've ever seen to a Bangladesh-type severe storm environment, in terms of extreme low-level theta-e and actually achieving initiation. http://bangladeshtornadoes.org/UScases/061242/0613420030zsf.gif
 
Correct me if I am wrong, but reading some of the answers here suggests extreme CAPE in Bangladesh leads to big tornadoes, I thought shear was the main ingredient for big tornados. You can get an F4/5 on 1500 CAPE in certain situations, right? I know there was a an F4 on 2000 CAPE in S Africa a couple of years back for example.

I can understand big CAPE (5000+) combined with very strong updrafts being a factor with grapefruit or cannonball sized mega hail though.
 
MJ Poore said:
Correct me if I am wrong, but reading some of the answers here suggests extreme CAPE in Bangladesh leads to big tornadoes, I thought shear was the main ingredient for big tornadoes. You can get an F4/5 on 1500 CAPE in certain situations, right? I know there was a an F4 on 2000 CAPE in S Africa a couple of years back for example. I can understand big CAPE (5000+) combined with very strong updrafts being a factor with grapefruit or cannonball sized mega hail though.
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You're correct, early in the thread we got off on the CAPE part of the equation and that's been more of a focus in this thread. I believe this happened because the shear is a given and not drastically different than the US. The CAPE contribution is different since the Indian Ocean produces such high T-Td (temp-dew point) readings in the prestorm environment. This is directly related to CAPE or positive area in the sounding.

The question you ask is loaded (if you will) because it's still not clear just how much CAPE vs shear is needed for a large/ violent tornado. There are many studies on this topic, but we do know that too much CAPE can on occasion spoil the mixture (with heavy rain and intense down drafts) and too much wind can shear out the updraft. In keeping with the original intent of the thread allow me to answer the shear question like this.... Very large hail, that is hail at or over 4 inches requires a mesocyclone "and" a mesocyclone requires shear. Of course once we include mesocyclone we have a supercell. When I originally heard this concept I believe it was 3 inch hail, so I've modified it somewhat based on my own experience. I have seen some squall lines produce hail 3 inches in diameter, but it could be argued that both shear and or a mesocyclone was present in some form, imbedded or aloft. Elevated mesocyclones sorta get dismissed by the chaser community, but they can have a huge influence on severe weather production and longevity of the storm. Thus for a 3 inch hail event you might have to look for evidence of a clear cut mesocyclone, but very likely in a 4 inch hail event it will be obvious. If someone wants to dig deep enough they may find exceptions to this concept, but I'm betting they will be few.

From what I've seen the ingredients required for giant hail are very close to those for significant tornadoes....instability, shear etc all the way down to WBZ (wet bulb zero) levels. With that in mind it's easier to make the argument for large or violent tornadoes. Since the actual production of a tornado from any mesocyclone is iffy at best I can imagine the very large hail incidents are more likely to happen in a supercell than a big tornado. That said, there is documented evidence of both very large hail and violent tornadoes in India and Bangladesh. And it's likely some are not being reported because of visibility constraints (dense tree or foliage growth).

Backtracking a bit, the incident we were discussing earlier of the high death event having 125 MPH winds. Even through this was published I do have some reservations about the claim. I have stood (it's very difficult) in measured 100 MPH winds (as have other chasers here). I find it difficult to make the leap that adding +25 MPH will cause great loss of life (outside of building collapse etc). What I think is happening here is the structures cannot be rated any higher than that range. Remembering that the Greensburg KS tornado out on an open desolate plain is EF-0.....until it hits something that can be measured by our EF-ruler. Regardless, there are no short easy answers to your question....so I hope other continue with their opinions.

*If someone wants a cite on the 3 inch hail vs mesocyclone I'll ask Les Lemon.
 
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Gene Moore said:
From what I've seen the ingredients required for giant hail are very close to those for significant tornadoes....instability, shear etc all the way down to WBZ (wet bulb zero) levels. With that in mind it's easier to make the argument for large or violent tornadoes. Since the actual production of a tornado from any mesocyclone is iffy at best I can imagine the very large hail incidents are more likely to happen in a supercell than a big tornado. That said, there is documented evidence of both very large hail and violent tornadoes in India and Bangladesh. And it's likely some are not being reported because of visibility constraints (dense tree or foliage growth).
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It seems to me that giant (>4 inch) hail occurs most often with extreme instability and mid level shear. Violent tornadoes seem to be more reliant on high RH at the surface, low-level instability, and low-level shear. I remember a day I was chasing in SW OK and an elevated supercell produced 4.5 inch hail north of the warmfront near OKC. It was in mid 40’s at the surface but the supercell managed to thrive on the strong 850 jet that was overriding surface warmfront.
 
Gene Moore said:
Very large hail, that is hail at or over 4 inches requires a mesocyclone "and" a mesocyclone requires shear. Of course once we include mesocyclone we have a supercell. When I originally heard this concept I believe it was 3 inch hail, so I've modified it somewhat based on my own experience. I have seen some squall lines produce hail 3 inches in diameter, but it could be argued that both shear and or a mesocyclone was present in some form, imbedded or aloft. Elevated mesocyclones sorta get dismissed by the chaser community, but they can have a huge influence on severe weather production and longevity of the storm. Thus for a 3 inch hail event you might have to look for evidence of a clear cut mesocyclone, but very likely in a 4 inch hail event it will be obvious. If someone wants to dig deep enough they may find exceptions to this concept, but I'm betting they will be few.

*If someone wants a cite on the 3 inch hail vs mesocyclone I'll ask Les Lemon.
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Your argument makes a lot of sense Gene, thanks. It's also worth noting here that many of the reports of mega hail storms on the Indian sub-continent appear to locate the convective event upslope on the Himalayas, suggesting they are upslope storms, which don't normally rotate, but have very strong updrafts. In the case of the Himalayan slopes you could conceivably have massive temp/dew combinations and very cold air mixing instantly. Add some kind of lifting mechanism (like a strong upslope wind from the plains going northwards) and you would be going thermonuclear very quickly, no rotation needed. That's as I understand it.
 
scott r currens said:
It seems to me that giant (>4 inch) hail occurs most often with extreme instability and mid level shear. Violent tornadoes seem to be more reliant on high RH at the surface, low-level instability, and low-level shear. I remember a day I was chasing in SW OK and an elevated supercell produced 4.5 inch hail north of the warmfront near OKC. It was in mid 40’s at the surface but the supercell managed to thrive on the strong 850 jet that was overriding surface warmfront.
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No doubt there are exceptions and I expected you to come up with some. As for your example, I had to laugh when I read it....don't ya just hate it when you chase somewhere else and the big show is where you came from.:D

I agree with your statement, but I think such cases are in the minority. Specifically there are big tornado day and big hail day differences, strong low level shear is certainly one of them. Still, many of the parameters are in agreement. It seemed the gorilla hail (if you will) generally came from more complete mesocyclones, that is, one's that were quite capable of producing a tornado, but something kept them from it. More often than not that something was a high base, or higher than usual LCL. I remember a storm near Laverne OK that dropped windshield smashing hail on chasers from the anvil way in advance of the storm. It never produced a tornado but the whole storm was rotating from cloud base to the bottom of the anvil. How about the Aurora NE supecell that produced the worlds largest hail, did it produce a tornado? Seems chasers were in disagreement on that one. I never saw a good tornado image from that storm. We were about a mile on the other side of the Interstate taking part in a data collection program for the Army Research Lab and missed any tornadoes.
 
Gene Moore said:
No doubt there are exceptions and I expected you to come up with some. As for your example, I had to laugh when I read it....don't ya just hate it when you chase somewhere else and the big show is where you came from.:D

I agree with your statement, but I think such cases are in the minority. Specifically there are big tornado day and big hail day differences, strong low level shear is certainly one of them. Still, many of the parameters are in agreement. It seemed the gorilla hail (if you will) generally came from more complete mesocyclones, that is, one's that were quite capable of producing a tornado, but something kept them from it. More often than not that something was a high base, or higher than usual LCL. I remember a storm near Laverne OK that dropped windshield smashing hail on chasers from the anvil way in advance of the storm. It never produced a tornado but the whole storm was rotating from cloud base to the bottom of the anvil. How about the Aurora NE supecell that produced the worlds largest hail, did it produce a tornado? Seems chasers were in disagreement on that one. I never saw a good tornado image from that storm. We were about a mile on the other side of the Interstate taking part in a data collection program for the Army Research Lab and missed any tornadoes.
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This is often the case in the UK. Storms that produce large or even giant hail here in the UK rarely, if ever produce tornadoes. These 'Spanish Plume' events are charactorised by an elevated layer of hot air capping warm, moist air below. The warm, moist air is usually released either by insolation or by 'isentropic upgliding' tantamount evidence being Ac cast drifting northwards a day or so ahead of a thundery break-down. The storms that produce these large hail often have a high base, and therefore have little or no frictional inter-reaction with the surface of the earth.

Tornado producing storms here in the UK... yes they do occur, and very rarely up to an EF2, are generally low level storms and normally in cooler air-masses. Tornadic storms only rarely produce hail of large size. This would suggest to me that part of the function of tornadogenesis would partly be due to frictional effects of the ground on a low based storm in a moist, almost SALR atmosphere. Indeed recent research here in the UK suggests that the 'topographical tornado' is in fact relatively common, a storm cell caused to spin by way of movement around a range of hills or an island.

N.
 
It is probably worth adding that typically only a portion of the CAPE profile (layer between the -10C to -30C) is considered in hail forecasting, so total CAPE may not be as meaningful a value. It would seem important as well that the environment lapse rate in that layer closer to dry adiabatic might aid in accelerating the updraft through this layer where wet hail growth is maximized. Undoubtedly, there needs to be relatively few ice nuclei as well to allow for maximal growth on just a few particles. The role of the mesocyclone seems important, presumably because it is aiding in the updraft strength, though you would want it to have the strongest rotation near the top of the hail growth layer (so that the PVPGF is pointed upward) to maximize this effect. Or, perhaps the mesocyclone role for hail production is more related to limiting mixing allowing undiluted surface parcels to reach the hail growth layer. Getting back closer to the original intent, perhaps there are climatological differences in the mid-troposphere lapse rates between the Great Plains and Bangladesh area (owing perhaps to differences in the geography of the two regions).
 
Interesting discussion.

Just to add to some of the important points with respect to the high death toll and population density, I think once must also consider the quality of infrastructure and the effectiveness of warnings if any.

I would also like to pose one point: when I studied the typical tracks associated with tornadoes in Bangladesh, I see a significant proportion of southwesterly tracks (if my memory serves me). What it led to in my mind given the extreme CAPE envrionments was the possibility of perhaps similar tornado behaviour to Jarrell. What are the thoughts of others on this forum? I know this is speculation, but it might be a possibility.

Regards,

Jimmy Deguara
 
As far as I know, environment that produced storm in Jarrel was characterized by extreme CAPE but relatively low level wind shear. Track of the storm was unusual, opposite to the low level flow and this induced quite high low level storm relative winds and some helicity which aided the mesocyclone formation.
However, in Bangladesh, there are environments with both extreme CAPE and significant wind shear ( strong subtropical jet, etc...). Besides, we are discussing Bangladesh only, but 1kg hailstones were reported also from China and Kazahstan ( sorry for incorrect spelling of the country, but I do not recall what exactly is its name in English). In 1986 or 87 hailstorm killed around 100 people there. Has anyone seen sounding from China hailstorms environment?
 
Jimmy Deguara said:
Interesting discussion. I would also like to pose one point: when I studied the typical tracks associated with tornadoes in Bangladesh, I see a significant proportion of southwesterly tracks (if my memory serves me). What it led to in my mind given the extreme CAPE environments was the possibility of perhaps similar tornado behavior to Jarrell. What are the thoughts of others on this forum? I know this is speculation, but it might be a possibility. Regards, Jimmy Deguara
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There are the days with instability is so intense that strong rotating storms will persist further south out of the main jet. Jerrell is an example, but so was the F4 killer tornado at Castell TX a few years later. This back building supercell was in the Jarrell class, but struck in a more rural area. Another example was the stationary supercell south of the Aurora NE (record) hailstorm that produced hours of tornadoes. Most storm seasons that persist well into June are likely to produce an event similar to Jarrell (high CAPE backbuilding) somewhere on the southern edge of the jet stream flow, be it Texas to the Dakotas. Last season the Dimmitt TX supercell in early June may have fit this mold as it drifted slowly south producing a SW moving tornado. Granted it was not an EF-5, but it met many of the same characteristics to include that is was not particularly anticipated early that day.

Given the frequency of this occurrence here in the US I have little doubt we will have similar setups in other tornado prone regions of the world. It's often better to look at known similarities for answers instead of trying to ferret out particulars of the region in question. What matters most for India and Bangladesh is the presence of both high shear and high CAPE. Thus many of the particulars we see here in the US may also be found in that region of the world. As discussed already it's the Indian Ocean borne CAPE that gets so outrageous in their setups. So it's not a stretch to imagine on the southern edge of shearing winds where high CAPE is prevalent we may see southwesterly moving tornadoes. Without digging deeply into particular situations I'm betting these are high CAPE back building setups.

There is a second way of getting southwest moving tornadoes in a westerly jet stream. This can occur when the anchor surface low on a triple point experiences greater pressure falls to the southwest. This situation will back winds east of the low and pull the area of greatest convergence further south and west. Also, it will likely drag the warm front south with it. We think of supercells as being created from instability and shear, but all storms are first creatures of convergence. They will follow that convergence where ever it leads, or the storm will not last. So the question must be answered about why the surface low retreated and was that, not extreme CAPE the reason for southwest moving tornadoes. A few quick reasons for a low retreating here in the US include: (deeper pressure falls west in the lee of the rockies, a new short wave/ divergence aloft further south and or west, late day extreme heat to the southwest especially behind the dryline (common near DDC and LTS during the late spring early summer).

The exception to these reasons for southwest moving supercells is that larger supercells reach a point where they can generate their own storm to synoptic scale convergence. Thus sustaining themselves using convergence from their own outflow boundary. If the air within the outflow is cold it may push south taking the storm scale convergence with it. If this is happening in the region in question the first place to look would be radar data....if it's available. Another feature that adds to this phenomena is the strengthening LLJ (low level jet) at night, a common late day event in the plains. I have not studied the generation of the LLJ in the India/ Bangladesh region, but it may yield interesting results.

I think if one applies the known parameters of SW moving tornadic supercells here in the US they will find many similarities in India and Bangladesh as Jimmy is doing. Only I would suggest taking it further for all situations including the huge hail reports.
 
Gene,

Thanks for that clarification. Yes some of the paths in Bangladesh are southwest but some are also south. I would guess high wind shear envrionments have easterly tracks.

Another point in question is the existence of outflow boundaries moving southwest from the Cherrapunji Hills due to previous overnight convection perhaps MCS activity mentioned on the website. If such outflow boundaries align themselves and track slowly southwest, then I am wandering if extreme CAPE environment can enhance the focus for new updraft development or perhaps separate tornadic supercells. Of course we are talking losely here as each setup have to be considered separately.

One person in this thread referred to people dying after being hit by giant hailstones in relation to LP supercells. I suspected a few years ago that LP supercells developing along the dryline may be the culprit given they don't look terribly intense. It may not even begin raining and giant chunks of ice begin falling. Anyone caught in the open fields may have little warning.

Just a thought anyway.

Regards,

Jimmy Deguara
 
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Jimmy Deguara said:
Gene, One person in this thread referred to people dying after being hit by giant hailstones in relation to LP supercells. I suspected a few years ago that LP supercells developing along the dryline may be the culprit given they don't look terribly intense. It may not even begin raining and giant chunks of ice begin falling. Anyone caught in the open fields may have little warning.Jimmy Deguara
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Agree, with just a few exceptions over the years the largest hail I've witnessed (4-7 inches and both record holding storms) were from LP's, or very close to it. Of course lightning is also a big hazard during LP supercells. The public associates a bad storm with "blackness" and it's just not there much of the time.

Merry Christmas everyone!!
 
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