Topic: What's missing?

[Mike]

Perplexing question!  I've monitored the dew points, CAPE and lifted index values today and from 10:30am to 4pm dew points rose from 19 to 23, CAPE doubled to a maximum 1869 j/kg and the lifted index rose to -2.48C.  There's little or no cloud to speak of!!

Now the question is what is missing to initiate convection with these numbers?  What ingredient is missing that would spark cloud formation with this type of instability?  I know lifted index does not mean too much without something else but what is it?

GSF models indicate CAPE within this range for Thursday 27th with higher LI numbers, but if today is any indication there might not be too much of anything!  comments most welcome...

Mike

[Jimmy Deguara]

Mike,

Your questions and the topic in general fails to indicate location and a listing of the other variables. I'll change the name of the topic appropriately once I realise what you are suggesting in a little more detail.

Regards,

Jimmy Deguara

[Mike]

Strewth.

Okay, the numbers were for the Darwin region today 22nd September 07.  Forecast did not indicate any type of storm initiation but the numbers generally that i mentioned would be the norm for wet season sounding charts. With dew points high, CAPE levels at an moderate and quite healthy range what is missing for convection?  winds were at 500mb from the west and 850 winds were 25 from the east.  Suonding chart showed moist initially but dry in the mids to uppers so would that be the reason?  What other number do you want Jimmy?

[Jimmy Deguara]

Mike,

What is required to set things off is a trigger. This could be a surface trough, an upper trough, low level convergence or whatever. Sometimes one or more of these ingredients occur simultaneously. A buildup of moisture and so forth is only one of the requirements for storm initiation.

Regards,

Jimmy Deguara

[Mike]

Mm yes, there's still some things that I have to look for on the maps!  Just goes to show that you can have really nice numbers but without the spark to ignite the weather you can have nothing.  Looks like I'll be hitting the maps and books again to overcome the problem in the future!

Mike

[Michael Bath]

looking at 22nd Sep 2007 for Darwin
http://soundings.bsch.au.com/skew-t.html?source=wyoming&lat=-12.4239&lon=130.8925&gribdate=&month=09&day=22&year=2007&hour=00

Even if you get better surface obs and a trigger did occur, the rest of the low to mid levels are very dry and would be pretty hostile to any low level cloud development. The surface layer of good moisture is too shallow in this case.

regards, Michael

[Mike]

That's one thing I noticed looking back on it guys.  Air just too dry at the moment.  Plenty of cape but nothing to light the match.  All a long learning curve.

Mo

[David C]

also depends on how CAPE was calculated, since, as Michael said, there might have been a very shallow layer of moist air which would have rapidly mixed out with daytime heating, but which might have figured prominently in overstating CAPE.

Anyway, it wont be long before the first action happens up there!  Any bets on the start of the buildup; first storms or official start to the wet - I'll go with October 19 for the first top-end CB

[Mike]

Indeedy.  Not long to wait David.  I'll stick my guesses in the wet season thread I started weeks ago pending the storms .

Mike