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Posted by Ray
on 4/20/2009, 10:39 am
69.205.81.50
Since anyone watching the weather knew this past weekend would be good, I didn't bother stating the obvious. Sometimes however I'll post a post-weekend review when something unusual occures, the case here.
The lack of rain hereabouts in April so far has led to excellent (except for farmers) semi-arid conditions conducive to soaring. Although we didn't fly, Friday was surely a diamond-task day, what with a good lapse rate, high sun angle, and a very transparent ("cobalt blue"
sky clearly seen on the water-vapor satellite imagery. On Saturday, the high cirrus had come into the upper troposphere and it was hazy with diminished visibility. But the PBL (meteorolist's term for the layer we thermal in, the "planetary boundary layer", was already well-mixed (or equivalently, a deep dry-adiabatic layer had become well established), so once the sun heated the surface sufficently to produce a shallow super-adiabatic layer there (one of only two ways to get soarable thermals going), things were cranking. I got to the airport too late to fly (most ships were airborne and visible, according to Rick Roman, only as "tiny little dots", but not too late to help retrieve the Bergfalke, which had landed at Hanna Acres in an introductory cross-country lesson for Junior Member Alex. The fact that that ship (which doesn't penetrate anything like the 21) scooted up there against a significant headwind component so readily (and surely could have gone further) is indicative of the superb thermalling conditions. Not to mention there was obvious wave evidence all over the sky, although no one was lucky enough to contact.
Sunday was even more interesting. The upper level flow had changed (I'll skip the synoptic analysis), sweeping out the upper-level cirrus haze and bringing in clear air aloft, but not sweeping out the PBL, which as stated was already well-primed for convection. The winds at 6000' were forecast (http://www.usairnet.com/cgi-bin/Winds/Aloft.cgi?location=BUF&Submit=Get+Forecast&hour=06&course=azimuth to be 340 @ 20 mph till 10AM, switching to 090 @ 9 mph the rest of the day. Surface winds generally NE all day. This information immediately excited me...why? Normally, either a NW or NE wind coming across relatively cold Lake Ontario this time of year spells death for strong thermals. But, with the PBL afternoon winds more or less easterly, there is no longer a lake-water fetch for Dansville. Rather, the fetch is across the almost lake-free center (lattitudinaly) of NY State, which has been dry and previously well-mixed. Which suggests good soaring from Dansville to someplace far to the west. I really think one could have flown to Columbus Ohio yesterday. At 3:30 I saw the poor, neglected Bergefalke sitting forlornly on the ground, unwanted, and wistfully waiting for someone to take her up. After verifying that no one else wanted the ship, I took off and found good lift (in spite of no yaw string), especially of course on the East side of the valley. Now normally, as I discovered from my Master's thesis, when the surface temperature drops by only a few degees, the roots of the thermals are cut off and the convective field collapses. But as stated above, there's one other way to get an adiabatic layer going, since thermodynamically it is actually neutrally stable, not intrinsicaly unstable. The latter occurs when you heat the surface and form a superadiabatic layer (which IS intrinsically unstable), OR, of course, when you mechanically lift a parcel. Having forgotten this, by around 5 PM I expected things to fall apart and have to land. But the west side of the valley provided some upward push, augmented no doubt by the vehicle traffic on 390. At about this time I saw Doug Cline bravely exploring the east side, where I was loath to go with the Bergfalke. Later he told me he saw the Pegasus vario firmly pegged on down while there. AT ~ 5:45 I called the field to see if people were still partying, as is the general mode in our social club, only to find them anxious to put the ugly duckling away and go home, so I landed (I owe all of them lunch or dinner, they can collect whenever). When I had to land, I was near Sonyea, and flew an exploratory all down the west ridge till well south of Dansville, to find nearly continuous lift or zero. So I suspect the valley effect was getting organized, the conditions were surely conducive. We need to get position lights on at least one ship, you could probably have stayed up untill midnight.
P.S. Will someone please correct my phone number on the membership list? I've been trying to get this changed for two years. My cell is 716-560-2059, NOT what's now listed!
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