Topic: Extreme CAPE!

[Mike]

Check this RUC image out!  CAPE values were an unbelievable 10,000j/kg!  I've never heard of values so high.  The RUC was for Winnipeg which got slammed by big supercells Wednesday night.  Thanks to Reed Timmer for the loan of the graphic for us to see.

Mike

[Reed Timmer]

Thanks for starting this thread Mike!  I've never seen CAPE values analyzed this high by the RUC, or by any model for that matter.  To put this in perspective, the CAPE values in central TX on May 27, 1997 (date of the F-5 tornado that hit Jarrell, TX) were in the 7000-9000 J/kg range, and this event is known as a high CAPE/low shear tornado day.  As can be seen in the map above, CAPE values exceeded 10000 J/kg in southern Manitoba today!

However, I'm quite certain that these RUC analyzed CAPE values are not the best measure of the true instability in the atmosphere.  Surface dewpoints in this region exceeded 80oF over a large area, but these extreme dewpoint values can be attributed largely to evapotranspiration from the extensive canola and corn fields in southern MB, and thus were extremely shallow -- confined to a small layer at the surface.  Consequently, due to vertical/horizontal mixing in the vicinity of the thunderstorm updrafts, the true accessible moisture of these storms was much lower.  This is a perfect case were mixed-layer CAPE is a better proxy for the "actual instability" than surface-based CAPE.   

[Mike]

Welcome Reed to the forum!  I have never heard of such large CAPE values, not even in any literature I've read - perhaps the wrong ones!  Interesting numbers and if you could upload a photo or two of the storms that initiated in the areas you mentioned that would be great.

Mike

[Jimmy Deguara]

Reed,

Can you perhaps provide some estimate of the modified sounding's CAPE value you think was more representative of the atmosphere on this day of at all possible - or perhaps some range.

What sort of thunderstorms affected the region in question given it is related to this specific high CAPE event.

Regards,

Jimmy Deguara

[Reed Timmer]

Hey Jimmy,

I didn't save any images, but from what I recall, the mixed-layer CAPE values were in the 3000-5000 J/kg range...not quite 10000, but still extreme!

The wind shear was rather weak yesterday in MB, with upper-level flow nearly parallel to the rapidly advancing cold front; so storms that initiated on the front were not able to move off the boundary and were quickly undercut or involved in cell mergers.  Some of the cells on the south end of the line briefly exhibited supercellular structure.  I'd bet if the front were moving slower there could have been at least a few supercells in that environment, but the tornado threat would still have been negligible with the 10 knots at 850. 

I posted some pictures of the Manitoba storms from yesterday on our blog at tornadovideos.net if anyone is interested in checking them out. 

Things could get interesting in the upper MS River Valley today!

[David C]

subcontinent' refers to the Indian subcontinent which includes Bangladesh.  www.bangladeshtornadoes.org has some soundings, as well as surface and upper air data during the brief tornado season there.

[Jimmy Deguara]

Hi,

Yes David suggested he has observed extreme CAPEs in this region and the sounding looked like the leaning Tower of Pisa:) The surface based lifted Index values were also of the order of -17 - incredible! The shear also combined with it if I recal to produce a potent situation and a nasty tornado outbreak!

I have even heard of predicted parameters in tornado watches issued for the regions of hail to 5 inches and hail to 6 inches.

Reed, why do you think the summarised value would be so relatively low in your opinion ie 3000 to 5000? Was the moisture that shallow - you mentioned evapotranspiration? I have heard that evapotranspiration can provided relatively significant moisture to the northern plains but that is another point of discussion in a separate new topic.

Regards,

Jimmy Deguara

[Mike in Canada]

I'm wondering how high the CAPE values would be for Alberta and Saskatchewan today. There are already severe thunderstorms erupting west of Edmonton, and a few of them appear to be supercells, from what I can see on the radar and satellite pics. It's hot and humid today - it's currently 31°C with the dewpoint at 17°C.

There was a spectacular thunderstorm with nearly continuous lightning late ast night after midnight in Edmonton, though I didn't see any hail.

[Mike]

Hi Mike, you've had big storms to the west as I saw on the radar in Whitecourt and Drayton Valley.  Trying to pinpoint a site where I can get CAPE models to show, but got this one for now with Alberta up in the corner i think.  Values are high as you can see 5000+ and even 8000+ to the west!   Also got you a Lifted Index chart - some huge numbers up in your area -12 even - we'd sell our grandmothers for that kind of Lifted Index numbers.  Will keep digging....hope this helps for now.



Mike

[Mike in Canada]

I wish I had my camera with me, but unfortunately, I left it in Vancouver and won't see it again until about a week from now!

[Mike in Canada]

I just managed to see a supercell pass by to the south of Edmonton this evening. At 7:00 pm, I decided to check out one of the storms closest to the city, so I had to walk to the edge of the river valley, as I live in an area of highrises (obviously NOT good for stormspotting!) but the view from the river valley's edge to the SW, S and SE is great for observing approaching storms. At first, the mesocyclone was some 50 km distant and I could just barely make out the meso due to water vapour/smog haze. But the structure gradually became more visible as it got closer. It looked like the storm was falling apart at first, but managed to reorganize as it approached. The RFB in the meso didn't appear to have precipitation underneath, hence it was a classic supercell.

The meso had a very well defined "bell" or "cow-catcher" shape to it with some striations resembling somewhat what you'd find on a soft-serve ice cream and from time to time short, stubby inflow bands could be seen to the right. A high-based midlevel cloud platform sat just above the meso, and most of the upper half of the updraft was obscured by intervening clouds. A fairly long inflow band formed within about 2-3 minutes at one point. The supercell didn't seem to be very electrified compared to the dazzling lightshow of last night's thunderstorm, but it was putting out large CGs every several minutes immediately to the right of the meso.

Under the meso, I could sometimes see what looked like a wall cloud, but the thing was too distant for me to tell clearly. I was able to watch the storm for about a little over an hour, and it was apparently beginning to die out in the end, the meso becoming half-hidden by the rain curtain. The meso was about 20-30 km away at its closest to where I was, and it never rained more than a drop or two on me the whole tiime. Large, fat mammatus clouds were appearing on the anvil base.

[Mike]

 Are there storms forecast later on? ( I gather it's getting late there???)  Was any hail reported from that supercell?  Could you dig up some info on the cell if possible from anyone in that area you know?

Mike

[Mike in Canada]

That supercell I saw last night, I never heard any reports or from the media regarding hail or high winds, etc. But I wouldn't have been surprised if that storm was dropping hail at least the size of quarters or even loonies (Canadian $1 coin - slightly larger than a quarter).

Apparently additional storms were forecast, because Edmonton was still under a severe thunderstorm watch until after midnight. But after that supercell passed, there was what appeared to be another storm, but it wasn't. The skies just cleared up to the point that there were almost no clouds around by the time the sun had set at around 9:30-10 pm. Remember that because of Edmonton's latitude at about 53.5° N, summer days tend to be quite long with long periods of twilight - one of my favourite parts of summer.

[Mike]

There's some beaut photos of supercells in Canada that we have mentioned - even a funnel or two.  Nice photos at http://tornadovideos.decadehost.com/index.cfm/do/blog.home/startdate/07-01-07/enddate/07-31-07 if you want a view....

Mike

[Mike in Canada]

Checked out the tornadovideos.net site. About the Drayton Valley supercell - that was the one I saw in the distance to the SW. Looks like it did sprout a tornado after all! I never heard about it in the media, but then again, some of the area around Drayton Valley (pop. ~7,000) is pretty sparsely populated farmland interspersed with aspen parkland/boreal forest.