Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
411
UXUS97 KBOU 111240
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0639 MDT Monday, August 11, 2025
This forecast is for Monday, August 11, 2025:
If the trigger temperature of 74.9 F/23.8 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 905 ft/min (4.6 m/s)
Maximum height of thermals.................. 15588 ft MSL (10332 ft AGL)
Forecast maximum temperature................... 83.0 F/28.8 C
Time of trigger temperature.................... 1145 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 10608 ft MSL (5353 ft AGL)
Thermal soaring outlook for Tuesday 08/12...... Excellent
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... No change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 16849 ft MSL (11593 ft AGL)
Wave soaring outlook for Tuesday 08/12......... Poor
Remarks... Light northwest flow aloft. More sunshine and only isolated showers/
storms mountains and palmer divide.
Sunrise/Sunset.................... 06:08:24 / 20:00:49 MDT
Total possible sunshine........... 13 hr 52 min 25 sec (832 min 25 sec)
Altitude of sun at 13:04:37 MDT... 65.23 degrees
Upper air data from numerical model forecast valid on 08/11/2025 at 0600 MDT
Freezing level.................. 14433 ft MSL (9177 ft AGL)
Convective condensation level... 12987 ft MSL (7731 ft AGL)
Lifted condensation level....... 13665 ft MSL (8410 ft AGL)
Lifted index.................... -2.5
K index......................... +23.0
Height Temperature Wind Wind Spd Lapse Rate ConvectionT Thermal Lift Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft deg C deg F Index fpm m/s
--------------------------------------------------------------------------------
50000 -60.9 -77.6 335 10 5 0.4 0.2 M M M M M
45000 -59.1 -74.4 340 14 7 3.4 1.9 M M M M M
40000 -53.7 -64.7 325 13 7 6.4 3.5 M M M M M
38000 -49.9 -57.8 325 17 8 6.2 3.4 M M M M M
36000 -46.2 -51.2 320 20 10 6.3 3.4 M M M M M
34000 -41.7 -43.1 320 22 11 7.8 4.3 M M M M M
32000 -36.4 -33.5 325 24 12 7.8 4.3 M M M M M
30000 -31.6 -24.9 325 23 12 8.1 4.4 44.6 112.2 12.3 M M
29000 -29.2 -20.6 325 22 11 8.1 4.5 44.0 111.1 12.0 M M
28000 -26.7 -16.1 325 21 11 7.9 4.3 43.5 110.3 11.8 M M
27000 -24.4 -11.9 325 19 10 7.7 4.2 42.5 108.6 11.2 M M
26000 -22.1 -7.8 320 17 9 7.7 4.2 41.8 107.2 10.7 M M
25000 -19.8 -3.6 320 15 8 7.8 4.3 41.1 105.9 10.2 M M
24000 -17.8 -0.0 320 13 7 6.4 3.5 39.9 103.8 9.4 M M
23000 -15.9 3.4 320 11 6 6.4 3.5 38.6 101.5 8.5 M M
22000 -13.9 7.0 315 9 5 6.4 3.5 37.5 99.5 7.6 M M
21000 -12.3 9.9 320 9 4 5.2 2.8 35.9 96.6 6.4 M M
20000 -10.8 12.6 330 9 5 5.2 2.9 34.3 93.7 5.0 M M
19500 -10.0 14.0 335 9 5 5.2 2.9 33.5 92.3 4.4 M M
19000 -9.2 15.4 335 10 5 5.7 3.1 32.8 91.0 3.8 M M
18500 -8.4 16.9 340 12 6 5.8 3.2 32.1 89.8 3.1 M M
18000 -7.6 18.3 340 13 7 5.9 3.3 31.4 88.6 2.5 M M
17500 -6.7 19.9 340 15 8 6.2 3.4 30.8 87.4 1.9 M M
17000 -5.8 21.6 340 16 8 6.2 3.4 30.2 86.3 1.3 M M
16500 -4.9 23.2 340 17 9 7.6 4.2 29.7 85.4 0.8 M M
16000 -3.8 25.2 335 17 8 7.8 4.3 29.3 84.8 0.4 M M
15500 -2.8 27.0 335 16 8 7.9 4.4 29.0 84.2 0.0 M M
15000 -1.6 29.1 330 16 8 8.0 4.4 28.7 83.7 -0.3 859 4.4
14500 0.1 32.2 330 14 7 8.5 4.6 28.3 82.9 -0.8 784 4.0
14000 1.4 34.5 335 13 7 8.5 4.7 28.1 82.6 -0.9 731 3.7
13500 2.7 36.9 340 12 6 8.1 4.4 27.9 82.2 -1.1 677 3.4
13000 3.9 39.0 340 11 6 7.8 4.3 27.6 81.6 -1.4 628 3.2
12500 5.0 41.0 340 10 5 7.9 4.3 27.3 81.1 -1.8 579 2.9
12000 6.2 43.2 345 8 4 8.1 4.4 27.0 80.5 -2.0 528 2.7
11500 7.4 45.3 345 7 4 7.9 4.3 26.7 80.1 -2.3 478 2.4
11000 8.5 47.3 340 6 3 7.2 4.0 26.4 79.4 -2.7 431 2.2
10500 9.5 49.1 330 5 3 4.7 2.6 26.0 78.8 -3.1 384 2.0
10250 9.7 49.5 330 5 3 3.6 2.0 25.4 77.8 -3.7 371 1.9
10000 10.2 50.4 315 5 2 9.1 5.0 25.2 77.4 -4.0 350 1.8
9750 10.9 51.6 295 4 2 11.4 6.2 25.2 77.4 -4.0 320 1.6
9500 11.6 52.9 270 5 2 7.7 4.2 25.3 77.5 -4.0 291 1.5
9250 12.0 53.6 255 5 3 2.8 1.5 24.9 76.8 -4.4 274 1.4
9000 12.2 54.0 240 6 3 5.8 3.2 24.4 76.0 -4.9 259 1.3
8750 12.7 54.9 230 7 4 8.8 4.8 24.3 75.7 -5.1 236 1.2
8500 13.3 55.9 220 8 4 6.2 3.4 24.1 75.4 -5.3 212 1.1
8250 13.6 56.5 215 9 5 4.5 2.5 23.8 74.8 -5.7 195 1.0
8000 13.9 57.0 215 9 5 5.3 2.9 23.4 74.1 -6.1 177 0.9
7750 14.3 57.7 215 10 5 5.8 3.2 23.1 73.5 -6.5 159 0.8
7500 14.7 58.5 210 10 5 5.4 3.0 22.8 73.0 -6.9 141 0.7
7250 15.0 59.0 210 9 5 4.6 2.5 22.4 72.3 -7.3 124 0.6
7000 15.3 59.5 205 9 5 6.1 3.4 22.0 71.6 -7.8 107 0.5
6750 15.7 60.3 205 9 5 3.8 2.1 21.7 71.1 -8.1 88 0.4
6500 15.7 60.3 200 8 4 -1.1 -0.6 21.0 69.9 -8.9 80 0.4
6250 15.6 60.1 185 6 3 -1.3 -0.7 20.2 68.4 -9.8 77 0.4
6000 15.4 59.7 165 5 3 -1.8 -1.0 19.4 66.9 -10.6 74 0.4
5750 15.2 59.4 155 5 3 -3.5 -1.9 18.4 65.2 -11.6 73 0.4
5500 14.9 58.8 140 4 2 -4.4 -2.4 17.4 63.3 -12.7 75 0.4
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/11/2025 at 0900 MDT | 08/11/2025 at 1200 MDT
|
CAPE... +88.1 LI... -0.7 | CAPE... +666.1 LI... -2.3
CINH... -150.7 K Index... +17.9 | CINH... -33.8 K Index... +17.4
|
Height Temperature Wnd WndSpd Lapse Rate | Temperature Wnd WndSpd Lapse Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft | deg C deg F Dir kt m/s C/km F/kft
--------------------------------------------------------------------------------
50000 -60.9 -77.6 350 13 7 -0.2 -0.1 | -60.9 -77.6 020 12 6 0.2 0.1
45000 -59.6 -75.3 335 14 7 3.7 2.0 | -59.2 -74.6 360 13 7 3.7 2.0
40000 -53.9 -65.0 300 11 6 6.4 3.5 | -53.0 -63.4 305 6 3 6.2 3.4
38000 -49.7 -57.5 310 15 8 6.2 3.4 | -49.3 -56.7 320 8 4 6.3 3.4
36000 -46.0 -50.8 315 19 10 6.0 3.3 | -45.5 -49.9 325 10 5 6.2 3.4
34000 -41.5 -42.7 320 21 11 7.8 4.3 | -41.3 -42.3 325 11 6 7.1 3.9
32000 -36.8 -34.2 320 24 12 7.8 4.3 | -37.0 -34.6 320 13 7 7.1 3.9
30000 -31.8 -25.2 325 23 12 8.5 4.7 | -32.2 -26.0 325 14 7 8.2 4.5
29000 -29.3 -20.7 325 22 11 8.5 4.7 | -29.8 -21.6 330 14 7 8.3 4.5
28000 -26.7 -16.1 325 21 11 8.4 4.6 | -27.3 -17.1 335 14 7 8.3 4.5
27000 -24.3 -11.7 330 20 10 8.2 4.5 | -24.2 -11.6 335 14 7 8.3 4.5
26000 -21.2 -6.2 330 20 10 8.2 4.5 | -21.8 -7.2 335 15 8 8.3 4.5
25000 -18.8 -1.8 335 19 10 7.8 4.3 | -19.3 -2.7 335 15 8 8.0 4.4
24000 -16.9 1.6 330 17 9 6.1 3.4 | -17.2 1.0 335 16 8 7.1 3.9
23000 -15.1 4.8 320 15 8 6.1 3.4 | -15.0 5.0 330 16 8 7.1 3.9
22000 -13.2 8.2 310 14 7 5.9 3.2 | -12.9 8.8 330 17 9 6.7 3.7
21000 -11.6 11.1 305 12 6 5.4 2.9 | -11.2 11.8 325 17 9 5.7 3.1
20000 -10.0 14.0 300 11 5 5.4 3.0 | -9.5 14.9 320 17 9 5.7 3.2
19500 -9.2 15.4 295 10 5 5.5 3.0 | -8.7 16.3 320 17 9 6.0 3.3
19000 -8.5 16.7 300 9 5 3.9 2.1 | -8.0 17.6 320 17 9 3.5 1.9
18500 -8.0 17.6 310 10 5 4.0 2.2 | -7.5 18.5 320 17 9 3.7 2.0
18000 -7.4 18.7 315 11 5 4.3 2.4 | -7.0 19.4 320 16 8 3.9 2.2
17500 -6.8 19.8 325 12 6 4.9 2.7 | -6.4 20.5 320 16 8 4.3 2.4
17000 -6.1 21.0 330 14 7 4.8 2.6 | -5.8 21.6 320 17 9 4.2 2.3
16500 -5.2 22.6 330 15 8 8.0 4.4 | -5.0 23.0 320 17 9 6.2 3.4
16000 -4.1 24.6 335 16 8 7.8 4.3 | -4.2 24.4 325 18 9 6.1 3.3
15500 -3.0 26.6 340 18 9 8.4 4.6 | -3.3 26.1 330 19 10 7.7 4.2
15000 -1.7 28.9 340 18 9 8.7 4.8 | -2.1 28.2 330 19 10 8.4 4.6
14500 -0.4 31.3 345 18 9 8.5 4.7 | -0.8 30.6 335 20 10 8.6 4.7
14000 0.8 33.4 345 18 9 8.2 4.5 | 0.5 32.9 340 20 10 9.0 4.9
13500 2.0 35.6 350 18 9 8.2 4.5 | 1.8 35.2 340 19 10 9.0 4.9
13000 3.2 37.8 350 17 9 8.3 4.6 | 3.9 39.0 345 18 9 9.1 5.0
12500 5.1 41.2 355 15 7 8.3 4.5 | 5.2 41.4 350 17 9 8.9 4.9
12000 6.3 43.3 350 13 7 8.2 4.5 | 6.5 43.7 345 16 8 8.8 4.8
11500 7.5 45.5 350 11 6 8.1 4.4 | 7.8 46.0 345 14 7 8.6 4.7
11000 8.7 47.7 345 10 5 7.7 4.2 | 9.1 48.4 345 12 6 8.3 4.5
10500 9.8 49.6 345 9 5 4.4 2.4 | 10.3 50.5 345 10 5 4.0 2.2
10250 10.0 50.0 340 9 5 3.6 2.0 | 10.4 50.7 345 10 5 3.6 2.0
10000 10.4 50.7 340 8 4 9.2 5.1 | 11.1 52.0 345 10 5 10.4 5.7
9750 11.1 52.0 340 8 4 10.7 5.8 | 11.8 53.2 345 9 5 10.6 5.8
9500 11.8 53.2 340 7 4 7.4 4.0 | 12.5 54.5 345 9 5 7.3 4.0
9250 12.1 53.8 335 6 3 3.5 1.9 | 12.9 55.2 345 8 4 3.8 2.1
9000 12.4 54.3 330 6 3 6.9 3.8 | 13.2 55.8 345 8 4 6.9 3.8
8750 13.0 55.4 320 5 2 9.1 5.0 | 13.8 56.8 340 7 4 8.4 4.6
8500 13.5 56.3 305 4 2 5.8 3.2 | 14.2 57.6 340 7 3 6.5 3.5
8250 13.8 56.8 300 3 1 3.8 2.1 | 14.6 58.3 340 6 3 5.6 3.0
8000 14.1 57.4 280 2 1 4.7 2.6 | 15.0 59.0 345 5 3 5.8 3.2
7750 14.3 57.7 245 1 1 3.8 2.1 | 15.3 59.5 350 5 2 6.0 3.3
7500 14.4 57.9 230 1 0 1.0 0.5 | 15.7 60.3 355 4 2 6.6 3.6
7250 14.4 57.9 000 0 0 0.3 0.2 | 16.1 61.0 360 5 2 6.8 3.7
7000 14.3 57.7 025 1 0 -0.6 -0.3 | 16.5 61.7 360 5 2 7.6 4.2
6750 14.2 57.6 020 1 1 1.9 1.1 | 16.9 62.4 005 5 3 10.0 5.5
6500 14.5 58.1 025 2 1 5.5 3.0 | 17.7 63.9 360 5 3 10.9 6.0
6250 14.9 58.8 030 3 1 5.3 2.9 | 18.5 65.3 360 5 3 10.6 5.8
6000 15.2 59.4 035 3 2 4.6 2.5 | 19.3 66.7 360 5 3 10.6 5.8
5750 15.7 60.3 030 3 2 11.5 6.3 | 20.2 68.4 360 5 3 17.8 9.7
5500 17.1 62.8 030 4 2 25.4 14.0 | 22.0 71.6 360 5 3 30.0 16.5
08/11/2025 at 1500 MDT | 08/11/2025 at 1800 MDT
|
CAPE... +101.3 LI... -1.1 | CAPE... +30.0 LI... -1.1
CINH... -22.3 K Index... +23.3 | CINH... -77.6 K Index... +27.3
|
Height Temperature Wnd WndSpd Lapse Rate | Temperature Wnd WndSpd Lapse Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft | deg C deg F Dir kt m/s C/km F/kft
--------------------------------------------------------------------------------
50000 -61.5 -78.7 015 8 4 -0.2 -0.1 | -60.7 -77.3 010 8 4 1.3 0.7
45000 -60.1 -76.2 005 14 7 3.9 2.1 | -58.3 -72.9 020 16 8 2.3 1.3
40000 -53.5 -64.3 010 7 4 6.8 3.7 | -53.9 -65.0 030 16 8 6.7 3.7
38000 -49.4 -56.9 005 8 4 6.9 3.8 | -49.8 -57.6 025 18 9 6.9 3.8
36000 -45.3 -49.5 005 9 5 6.8 3.8 | -45.7 -50.3 025 21 11 6.8 3.8
34000 -41.1 -42.0 005 10 5 7.0 3.8 | -41.5 -42.7 020 21 11 7.1 3.9
32000 -36.9 -34.4 010 11 6 7.0 3.8 | -37.2 -35.0 015 21 11 7.1 3.9
30000 -32.2 -26.0 010 12 6 8.1 4.4 | -32.2 -26.0 010 21 11 8.7 4.8
29000 -29.8 -21.6 010 12 6 8.1 4.4 | -28.9 -20.0 010 20 10 8.7 4.8
28000 -27.4 -17.3 010 13 6 8.2 4.5 | -26.4 -15.5 010 20 10 7.8 4.3
27000 -24.3 -11.7 005 13 7 8.3 4.6 | -24.1 -11.4 005 19 10 7.7 4.2
26000 -21.8 -7.2 360 14 7 8.3 4.6 | -21.8 -7.2 005 18 9 7.7 4.2
25000 -19.4 -2.9 355 15 8 7.8 4.3 | -19.5 -3.1 360 17 9 7.3 4.0
24000 -17.4 0.7 350 15 8 6.3 3.5 | -17.7 0.1 355 17 9 5.9 3.3
23000 -15.5 4.1 350 16 8 6.4 3.5 | -15.9 3.4 355 17 9 6.0 3.3
22000 -13.6 7.5 345 17 9 6.2 3.4 | -14.2 6.4 350 17 9 6.0 3.3
21000 -11.9 10.6 340 19 10 5.9 3.3 | -12.4 9.7 340 19 10 6.0 3.3
20000 -10.2 13.6 330 21 11 6.1 3.4 | -10.7 12.7 335 21 11 6.2 3.4
19500 -9.4 15.1 330 22 11 6.3 3.4 | -9.9 14.2 330 22 12 6.1 3.4
19000 -8.5 16.7 325 23 12 6.0 3.3 | -8.9 16.0 325 23 12 7.9 4.3
18500 -7.7 18.1 320 24 12 6.1 3.4 | -7.8 18.0 320 24 12 7.8 4.3
18000 -6.9 19.6 315 25 13 6.9 3.8 | -6.7 19.9 315 25 13 8.1 4.4
17500 -5.8 21.6 310 23 12 7.7 4.2 | -5.5 22.1 310 23 12 8.4 4.6
17000 -4.7 23.5 310 21 11 7.8 4.3 | -4.3 24.3 310 22 11 8.5 4.6
16500 -3.7 25.3 305 20 10 6.8 3.7 | -3.2 26.2 310 20 11 8.2 4.5
16000 -2.7 27.1 310 19 10 6.9 3.8 | -2.0 28.4 310 20 10 8.3 4.5
15500 -1.7 28.9 310 18 9 7.0 3.8 | -0.9 30.4 315 19 10 6.7 3.7
15000 -0.6 30.9 310 17 9 7.0 3.8 | 0.5 32.9 315 18 9 6.0 3.3
14500 0.5 32.9 315 16 8 7.1 3.9 | 1.5 34.7 320 17 9 7.8 4.3
14000 1.5 34.7 320 16 8 7.2 3.9 | 2.7 36.9 320 15 8 7.8 4.3
13500 2.6 36.7 325 15 8 7.3 4.0 | 3.8 38.8 325 13 7 7.4 4.0
13000 4.4 39.9 335 14 7 7.9 4.3 | 4.9 40.8 325 11 6 7.2 4.0
12500 5.6 42.1 340 13 7 8.1 4.5 | 6.0 42.8 330 9 5 7.4 4.1
12000 6.9 44.4 345 12 6 8.3 4.5 | 7.3 45.1 340 7 3 7.7 4.2
11500 8.1 46.6 355 10 5 8.4 4.6 | 8.5 47.3 355 5 2 7.9 4.3
11000 9.4 48.9 360 9 5 8.2 4.5 | 9.7 49.5 015 4 2 7.9 4.3
10500 10.7 51.3 010 8 4 2.8 1.5 | 10.8 51.4 035 4 2 2.9 1.6
10250 10.7 51.3 010 8 4 5.2 2.8 | 10.8 51.4 040 4 2 5.3 2.9
10000 11.6 52.9 010 7 4 14.2 7.8 | 11.7 53.1 040 4 2 13.6 7.5
9750 12.4 54.3 015 6 3 12.7 7.0 | 12.6 54.7 040 5 2 12.3 6.7
9500 13.2 55.8 015 6 3 9.0 4.9 | 13.4 56.1 040 5 2 9.5 5.2
9250 13.7 56.7 015 6 3 5.5 3.0 | 13.9 57.0 035 5 3 6.5 3.6
9000 14.2 57.6 015 6 3 10.2 5.6 | 14.6 58.3 035 5 3 10.5 5.8
8750 15.0 59.0 015 6 3 12.0 6.6 | 15.4 59.7 035 5 3 12.0 6.6
8500 15.8 60.4 015 6 3 9.9 5.4 | 16.2 61.2 030 5 3 10.1 5.5
8250 16.4 61.5 015 6 3 8.4 4.6 | 16.9 62.4 030 5 3 8.7 4.8
8000 17.1 62.8 015 5 3 10.1 5.5 | 17.6 63.7 025 5 3 9.8 5.4
7750 17.9 64.2 015 5 3 11.1 6.1 | 18.3 64.9 025 5 3 10.6 5.8
7500 18.7 65.7 015 5 3 9.9 5.4 | 19.1 66.4 025 5 3 10.1 5.5
7250 19.4 66.9 015 5 3 9.2 5.0 | 19.9 67.8 020 5 3 9.8 5.4
7000 20.1 68.2 015 5 3 10.5 5.8 | 20.6 69.1 020 5 3 9.9 5.4
6750 20.9 69.6 010 5 3 11.6 6.4 | 21.3 70.3 020 5 3 10.0 5.5
6500 21.8 71.2 010 5 3 10.7 5.9 | 22.1 71.8 020 5 3 10.2 5.6
6250 22.6 72.7 010 5 3 10.7 5.9 | 22.8 73.0 015 5 3 9.8 5.4
6000 23.3 73.9 010 5 3 10.0 5.5 | 23.6 74.5 015 5 3 11.2 6.1
5750 24.2 75.6 010 5 3 16.9 9.3 | 24.6 76.3 015 5 3 14.6 8.0
5500 26.0 78.8 010 5 3 30.3 16.6 | 25.7 78.3 015 5 3 16.2 8.9
________________________________________________________________________________
This product is issued twice per day, once by approximately 0630 MST/0730 MDT
(1330 UTC) and again by approximately 1830 MST/1930 MDT (0130 UTC). It is not
continuously monitored nor updated after its initial issuance.
The information contained herein is based on rawinsonde observation and/or
numerical weather prediction model data taken near the old Stapleton
Airport site in Denver, Colorado at
North Latitude: 39 deg 46 min 5.016 sec
West Longitude: 104 deg 52 min 9.984 sec
Elevation: 5285 feet (1611 meters)
and may not be representative of other areas along the Front Range of the
Colorado Rocky Mountains. Note that some elevations in numerical weather
prediction models differ from actual station elevations, which can lead to
data which appear to be below ground. Erroneous data such as these should
not be used.
The content and format of this report as well as the issuance times are subject
to change without prior notice. Comments and suggestions are welcome and should
be directed to one of the addresses or phone numbers shown at the bottom of this
page. To expedite a response to comments, be sure to mention your interest in
the soaring forecast.
DEFINITIONS:
CAPE (Convective Available Potential Energy) - An integrated measure of the
energy available for convective development, also known as the positive
area on a thermodynamic diagram. Units are Joules per kilogram. Larger
values are indicative of greater instability and the possibility of
stronger convective activity, including thunderstorms. Values around or
greater than 1000 suggest the possibility of severe weather should
convective activity develop.
CINH (Convective Inhibition) - An integrated measure of the amount of energy
needed to initiate convective activity, also known as the negative area on
a thermodynamic diagram. Units are Joules per kilogram. The more negative
this number, the more energy is required to initiate convection. This
inhibitive energy can be overcome through surface heating, cooling aloft,
lifting mechanisms (orographic, frontal, gravity waves, etc.)
Convective Condensation Level - The height to which an air parcel possessing the
average saturation mixing ratio in the lowest 4000 feet of the airmass,
if heated sufficiently from below, will rise dry adiabatically until it
just becomes saturated. It estimates the base of cumulus clouds that are
produced by surface heating only.
Convection Temperature (ConvectionT) - The surface temperature required to make
the airmass dry adiabatic up to the given level. It can be considered a
"trigger temperature" for that level.
Freezing Level - The height where the temperature is zero degrees Celsius.
Height of Stable Layer - The height (between 12,000 and 18,000 feet above
mean sea level) where the smallest lapse rate exists. The location and
existence of this feature is important in the generation of mountain
waves.
K Index - A measure of stability which combines the temperature difference
between approximately 5,000 and 18,000 feet above the surface, the amount
of moisture at approximately 5,000 feet above the surface, and a measure
of the dryness at approximately 10,000 feet above the surface. Larger
positive numbers indicate more instability and a greater likelihood of
thunderstorm development. One interpretation of K index values regarding
soaring in the western United States is given in WMO Technical Note 158
and is reproduced in the following table:
below -10 no or weak thermals
-10 to 5 dry thermals or 1/8 cumulus with moderate thermals
5 to 15 good soaring conditions
15 to 20 good soaring conditions with occasional showers
20 to 30 excellent soaring conditions, but increasing
probability of showers and thunderstorms
above 30 more than 60 percent probability of thunderstorms
Lapse Rate - The change with height of the temperature. Negative values indicate
inversions.
Lifted Condensation Level - The height to which an air parcel possessing the
average dew point in the lowest 4000 feet of the airmass and the forecast
maximum temperature must be lifted dry adiabatically to attain saturation.
Lifted Index (LI) - The difference between the environmental temperature at a
level approximately 18,000 feet above the surface and the temperature of
an air parcel lifted dry adiabatically from the surface to its lifted
condensation level and then pseudoadiabatically thereafter to this same
level. The parcel`s initial temperature is the forecast maximum
temperature and its dew point is the average dew point in the lowest 4000
feet of the airmass. Negative values are indicative of instability with
positive values showing stable conditions.
Lift Rate - An experimental estimate of the strength of thermals. It is
computed the same way as the maximum rate of lift but uses the actual
level rather than the maximum height of thermals in the calculation.
Also, none of the empirical adjustments based on cloudiness and K-index
are applied to these calculations.
Maximum Height of Thermals - The height where the dry adiabat through the
forecast maximum temperature intersects the environmental temperature.
Maximum Rate of Lift - An estimate of the maximum strength of thermals. It
is computed from an empirical formula which combines the expected maximum
height of thermals with the difference in the environmental temperatures
between the maximum height of thermals and the temperature 4,000 feet
above the ground. After this computation, further empirical adjustments
are made based on the value of the K-index and the amount and opacity of
middle and high level cloudiness expected between the time of trigger
temperature and the time of overdevelopment.
Middle/High Clouds - The amount and opacity of middle (altostratus, altocumulus)
or high (cirrus, cirrostratus, cirrocumulus) clouds. Broken means that
between 60% and 90% of the sky is covered by the cloud, with overcast
conditions occurring when more than 90% of the sky is covered by the cloud.
Thin implies that the clouds are predominantly transparent, meaning that
some sunlight is reaching the ground, in contrast to opaque which suggests
that little sunlight is reaching the ground.
Potential Height of Wave - The minimum of the following two heights:
1. Level above the height of stable layer (or 14,000 feet if none exists)
where the wind direction changes by 30 degrees or more
2. Level above the height of stable layer (or 14,000 feet if none exists)
where the wind speed no longer increases with height
PVA/NVA - Positive vorticity advection (PVA)/negative vorticity advection (NVA)
on the 500 millibar isobaric surface (approximately 18,000 feet above mean
sea level). Weak PVA has been shown to assist in mountain wave soaring.
Soaring Window - The time between the time the trigger temperature is reached
and the time of overdevelopment.
Thermal Index - The difference between the environmental temperature and the
temperature at a particular level determined by following the dry adiabat
through the forecast maximum temperature up to that level. Negative values
are indicative of thermal lift.
Thermal Soaring Index - An adjective rating (for sailplanes) based on the
computed maximum rate of lift, and the wind speed and middle and high
cloud cover expected during the soaring window (the time of the trigger
temperature and the time of overdevelopment) according to the following:
Maximum rate of lift Adjective Rating
>= 800 fpm Excellent
>= 400 and < 800 fpm Good
>= 200 and < 400 fpm Fair
< 200 fpm Poor
Time of Overdevelopment - The time one or more of the following phenomena,
which essentially shut off thermal lift, is expected to occur:
1. formation of broken to overcast convective cloud cover
2. formation of scattered to numerous downbursts
3. initiation of widespread precipitation
Time of Trigger Temperature - The time the surface temperature is expected to
reach the trigger temperature.
Trigger Temperature - The surface temperature required to make the first 4000
feet of the atmosphere dry adiabatic.
Wave Soaring Index - An empirical, adjective rating (for sailplanes) which
attempts to combine a variety of phenomena important in mountain wave
soaring into a single index number. Objective points are assigned to
these phenomena: wind speed and direction at 14,000 ft MSL, the static
stability in the 12,000-18,000 ft MSL layer, the wind speed gradient above
the stable layer, jet stream location and frontal and upper trough
movements.
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