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Don't give up at the end of the day... I certainly got a surprise...
Between 4:45 pm and 5:15 pm
(Sunset about 7:00 pm) I was able to take the L-13 (alone) to just
over 6,500 agl ( 7,100 msl ).
The day started strong with reports of several flights to 6,000
agl by about 2:00 pm. By 5:15 pm
the clouds were dissipating and the lift was beginning to subside,
however I certainly could have
stayed up longer...
Also note that we generally assume that N.E. winds mean lousy conditions
-- this is generally true,
but not this time...
The ground is drying out -- no significant rain lately. The
"Heat Flux" is still
strong, forecast to be from -230 to +25... cool dry air aloft provided
the instability
to produce 3-5 kn thermals to just over 7,000 msl. Cloud base
was observed to be
at about 7,300 msl from 3:00 to 5:00 pm. I was seeing 3-4
kt thermals at about
5:00 pm, others reported 5-9 kt thermals earlier. I was able
to achieve altitudes
slightly above cloud base on the south west side of a large CU in
clear air...
interestingly this was on the downwind side of the cloud, where
the sun was shining...
Upper Winds at Silvercreek -- September 12
Below are the soundings for 1 and 4 pm based on the NOAA Eta model
data.
Note that the computed Lift Data is based on a "guess" of the surface
temperature
at the given time... What is important is to watch the Temperature
profile between
3,000 and 6,000 msl as this is the key to (thermal) buoyancy.
Silvercreek @ 1:00 pm ( Data collected: 09/12
@ 9:00 pm )
Silvercreek @ 4:00 pm ( Data collected:
09/12 @ 9:00 pm )
July 23, 2000 -- Near Joliet, IL (about 40 miles S.W. of Chicago)
This flight started at about 1:00 pm -- in a Pegasus 101P (15 m Standard
Class). The duration
was about 2 hrs and 25 min, with a voluntary return -- very good
conditions, very light N.E.
winds and scattered CU's. I spent most of my time above 5,000
msl with a low point of about
4,500 and a high point of about 5,700 msl. The cloud bases
increased in height slightly through
the afternoon... the high of 5,700 was just under the base level
at about 3:00 pm.
Based on an expected High Temperature of 76 F the Eta model sounding
for 4:00 pm shows an
expected cloud base of about 6,500 msl. The height for a Thermal
Index of [ - 2 C ] is computed
to be about 5,500 msl... should be the theoretical limit of usable
lift.
Chicago Glider Club (41d 26m, 88d 15m) @ 4:00 pm (21z)
-- NOAA Archived Data
The photo below is of an interesting thermal that broke through and
formed the interesting vertical column.
I went over to investigate and it dissipated within about ten minutes...
about 5 miles S.E. of Morris and about
12 miles S.W. of Joliet... nothing on the surface to explain this
interesting development.
May 30, 1999 -- Front Royal, VA (about 55 miles W.S.W. of Washington, D.C.)
This was an "endurance" flight of five hours and six minutes -- "Sprite"
(SGS 1-36). This was somewhat of a "duel"
with Dave Bruner in his SGS 1-26. Dave was doing his five
hour flight for the "Silver / Gold Badge" requirements. These
two aircraft are reasonably matched except that the 1-26 has a slightly
lighter wing loading and the Sprite penetrates
better into the wind (slightly higher cruse speeds). I was
working hard to get a picture looking down on Dave in the
1-26... a very difficult task as he is very good at finding good
thermals... My maximum altitude for the flight was 8,500 msl,
and yes, I did get that photo looking down at him... I landed
at about 6:30 pm, and Dave landed at about 6:45 (Sunset was
at about 8:32 pm) -- we both came down voluntarily as the lift was
diminishing, but still a bit active.
The sky was clear all afternoon, but a bit hazy as evening approached...
the [ - 2 C ] Thermal Index level was very hard to
judge given these conditions. This is because the temperature
profile is derived for a time very near the expected high
for the day. Note that the Temperature Profile closely parallels
the Dry Adiabatic Rate up to 8,000 msl.
Front Royal, VA (FRR -- 38d, 55 m, 78d, 15m) @ 5:00
pm (21z) -- NOAA Archived Data
Here we are at about 8,000 msl (3 miles S.W. of FRR)
-- looking "down" on Dave in his SGS 1-26...
Two months earlier (March 12, 1999) he took this ship
to 18,200 msl for a seven hour Diamond Altitude
flight at Petersburg, W.V. By the way, he started
flying (no previous experience) ten months earlier;
received his Private Pilot Certification on December
6, 1998... you don't need to be an "old-timer"
to be an achiever...
May 18, 2003 -- Reasons for "Sled Ride" Days...
After a couple of weeks of rain -- record setting Severe
Weather for the Plains -- the ground in the St. Louis
area is quite wet.
Silvercreek Glider Club -- May 18,2003
Cold dry air aloft is most desirable in Thermal development... along
with good ground heating...
The overnight Low Temperature (at the surface) is generally the (Surface)
Dew Point temperature of the Air Mass
(about 64 F on Saturday and 68 F on Sunday). The low point
to high point changes (2M Temperature and Heat Flux)
are favoring Sunday as the better of the two days -- in terms of
potential thermal development. The Ground Moisture
Content is decreasing to about 754 KG/M2 -- by sunset. This
equates to 1,662 lb. (200 gallons) per square meter,
or 809,000 gallons per acre... Ground moisture is an important factor
in absorbing heat that would otherwise heat the
air in contact with the surface.
On the morning of May 18, we had fog and low ceilings, mist, and
light rain. The projected sounding below indicates the
conditions expected at 1:00 pm.
Silvercreek (38.93, 89.66) @ 1:00 pm (18z) -- May 18, 2003
The high (surface) Dew Point temperature (68 F) indicates a lot
of moisture in the atmosphere... the convergence of the Dew
Point Depression and Environmental Temperature plots (2,000 - 3000
msl) indicates saturation at this level... note that the
Environmental Temperature plot shows cooling at nearly the Saturated
Adiabatic rate to about 9,000 msl, then at a rate slightly
less that the Saturated Adiabatic rate up through 16,000 msl.
This is a very stable condition... above 3,500 msl. Rain did
occur, however no T-Storm development occurred... it was more like
Fall Weather...
Below is another example of a "Sled Ride" day.
New Market, Virginia (8W2 -- 38.6, 78.7) @ 1:00 pm
-- NOAA Archived Data
Based on an afternoon temperature of 70 F we should have had
good thermal action up through 5,000 msl. Relatively low
(Surface) Dew Point Temperature (48 F) indicates low amounts of
atmospheric moisture.
Showers in the area left the ground wet (standing water in places)...
The sun was shining, winds were light, the RAOB Plot
looked good -- but No Thermal Action occurred.
In Summary -- Look for Dry Air aloft, And Dry
Ground, with plenty of Sun Light to provide warming. Rocks on the
side of
Mountain slopes, Gravel Pits, Asphalt Parking Lots, etc. are good
places to look for Thermals. Watch for low overnight
temperatures (overnight low, at the surface, will rarely be lower
than the Dew Point of the of the Air-Mass). A grater change
form the overnight low to the afternoon high will indicate greater
potential for good thermal action.
Certainly standing water on the surface, or large amounts of soil
moisture will act as a Heat Sink absorbing energy that
would otherwise heat the air in contact with the surface.
Remember also that Over-development, or high Cirrus, can also
prevent surface heating and spoil an otherwise good soaring situation.