Dan Kokes
I live and chase storms in Northern Illinois. I seldom see the defined structure of an LP storm in Illinois. Many seem to be HP's, that travel rapidly, like the storms of 3-30-05. Can someone explain this to me?
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Andrew Pritchard
EF5
3-30 did have several LP's in central Illinois. I was on a couple near Lincoln...and there was one quite nice LP near Champaign, IL that had a nice round saucer base...like something from the plains. Several people got photos of it...but I will let them post them if they want. But, it does happen in Illinois.
Joel Wright
EF5
What causes an LP storm to form instead of an elevated supercell? Or are they essentially the same? Is it that everything needed to form a classic supercell comes together, with the exception of abundant moisture? My thought is the elevated supercell has a richer suply of moisture well above the surface, which is why it is based so high. I just don't understand how that can differentiate it from an LP.
I know all thunderstorms need the same basic ingredients to exist, but just take on different characteristics according to their environment.
I've seen plenty of powerfull elevated supercells in my area, but no LP's.
Kurt Hulst
EF5
Due north of Champaign IL this was taken off my short video on the 30th of March this year. It is a dying LP elevated supercell.
[Broken External Image]:http://midwestchasers.com/2005/March/30/hbLP.JPG
I think what was wrong was the LCLs were so high causing it to be elevated. The farther you went east of the Mississippi River the higher the LCLs were. The supercell over PIA became surfaced based but truthfully i never really saw any classic Sup characteristic’s. It looked HP dominant for the most part. Beautiful non the less.
Jeff Snyder
EF5
One theory is that the type of supercell is at least a function of mid-level storm-relative flow. Some research has shown that HPs tend to occur in environments characterized by weak mid-level SR-flow, LPs tend to occur in environments of high-SR flow, and classic supercells are in between. I tried to find the particular publication, but to no avail.
I think the discrimination of HP/CL/LP is dependant upon mid-level SR flow, mean parcel-depth relative-humidity, and (to a lesser extent) moisture depth. If you have a relatively dry boundary layer (i.e. large t-td deficit), then, to get surface-based convection (in most cases), you need a deeply-mixed boundary layer, which, given the large t-td deficit, means that the bases will be quite high (CAPE is also usually relatively small given that you only start to wet adiabatic at relatively high levels). The opposite situation for HP...Nic Wilson
EF2
Jeff is right as the most widely accepted method to determine supercell type is the anvil level storm relative winds. The theory is that anvil SR winds greater than 60 knots will detach the main precipitation core from updraft creating and LP supercell. 40 to 60 knots is ideal for classic supercells and less than 40 knots is typically HP in nature since the precipitation core is in close proximity and entraining moist air into the updraft.
Tomorrow will be a nice little case study to see how effective this technique is. I am happy that folks up from Colorado, Kansas and Nebraska are excited to chase the cold core landspout potential tomorrow, but much like this past Tuesday, they will be embedded within an HP mess of precipitation. This graphic won't be current after the next model run comes out in a few hours but if you can catch it in time, see that the anvil SR winds in north Kansas near the favored target of Salina, KS are only in the 35 kt range which favors HP cells. If supercells form along the dryline in OK they will be of classic nature with ideal SR anvil winds around 50 kts.
http://www.wxcaster2.com/CENTRAL_ETA212_AN...R-WIND_33HR.gifSimilar threads
