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Posted by Ray
on 6/15/2012, 8:59 am, in reply to "Re: Thursday update"
74.67.144.48
...and thanks!
"...the thermals were there, but...some weren't getting to the convection layer": If there are thermals, then by definition they are in a convective layer. But not all convective layers are created equal. The lapse rate in such is never exactly dry adiabatic*. If it's almost but not quite exactly the theoretical value, thermals can still struggle up thru it. Then, if they reach a layer where the lapse rate is closer to perfect, they will get stronger. How could such a scenario happen? With an influx of slightly cooler, slightly more stable lake air, if the fetch is from that direction. So you could have that shallow (being more stable it resists upward mixing) layer underlying a previously-existing layer which is less stable, i.e. closer to perfectly dry adiabatic. Previously-existing: from the day before when things were cranking in the afternoon. So, for yesterday: right near the ground (i.e. the lowest meter or so), you had a slightly super-adiabatic layer, 'cause the sun is strong and made the ground warm. Positively-buoyant thermals coming off the ground then can push their way up thru the slightly-resistant, shallow layer of air oozing in from the Lake...but they move slowly (are weak). Once they make it to the top of the lake air, they get into the better layer above it, and rise faster. IF they rise high enough to form clouds, and IF the clouds have significant vertical development, then the thermals can get yet another boost, from the release of latent heat. You have experienced days when you pretty much have to stay at cloud base if you want to stay up.
It all makes sense when you think about it. Isn't science wonderful!
Five quarts of OJ, still no T-shirt.
*A discussion of the effect of "entrainment", ie mixing of the rising thermal with the air it is rising thru, will be deferred. Or you can read about it in a serious book on boundary layer meteorology.
--Previous Message--
: I was up as well for about 2.5 hours and
: Chuck's report is accurate. East looked
: very questionable, but the west looked good.
: I got to 5500 near Swain and headed south
: to attempt to connect with the lift what was
: in another large band south of Hornell.
: Just about that point I lost power to my
: Cambridge 302. That means no navigation,
: GPS, or PDA. I could not revive it, and it
: was after 3:00 pm, so I decided to just stay
: home.
:
: I think some real XC was not just possible,
: but even easier than it looked. Most of the
: thermals were reasonably easy to find, and
: 3-5 knots. I think the thermals were there,
: but is seemed that some of them were not
: getting to the convection layer, especially
: later in the day. Nearing pattern entry I
: found a very easy to work thermal down low
: that I collected 1000 easy feet on at almost
: 5:00Pm. I have a feeling there was a lot of
: that down low. I just would have taken some
: confidence to go off into the blue.
:
: Mark
:
: --Previous Message--
: Today is the day of the earliest sunrise for
: KDSV. Strong sun = strong thermals? Hell
: no, you need lots more. As in good lapse
: rate, best maintained by continuing cold
: advection. Last night's sounding reveals the
: great conditions Doug C reported
: on...textbook dry adiabatic up to about 4K
: (a bit lower than he got due to the Buffalo
: sounding being near Lake E). But we ain't
: gonna get that cold advection today. The
: latest winds aloft forecast for today (10 AM
: to 7 PM) shows two major problems:
: (1) The winds from the surface to ~ 3 K are
: ENE, and modest at < 12 mph. That means a
: fetch over Lake O, with a long residence
: time due to the slow flow. Which allows
: more time for thermal equilibrium with the
: lake water surface. How warm (read: cool) is
: the lake? Here's a great tool:
:
:
:
: http://www.crh.noaa.gov/greatlakes/?c=tmp&l=lo&p=a
:
: Note the wind direction, and the temperature
: which is ~ 68 max. Which means it will
: counteract the sun's attempt at warming it.
: Area forecast matrices have only 71 by 2 PM
: for Geneseo. If you follow that up a dry
: adiabat with this morning's sounding, you
: get to....< 4 K, before hitting a big
: inversion.
: (2) The forecast winds for 6K are 12 mph @
: 140 , compared with 12 mph @ 080 for 3K.
: That means the winds are veering to SE with
: height...which means warm, stabilizing
: advection.
: Hate to be negative, but there's a third
: problem. The latest Rapid Refresh output has
: cirrus most of the day.
:
: Hey the morning sounding just came in!
: Dictating no change whatsoever in the above
: discussion.
:
: Bottom line: you will work harder to stay up
: than yesterday afternoon. Much harder.
: Anyone who sustains longer than 2.5 hours
: gets a quart of not-from-concentrate OJ.
: Anyone who makes it to HH and back (without
: a relight!) get an FLSC T-shirt.
:
:
:
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