Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
080
UXUS97 KBOU 211233
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0633 MDT Friday, August 21, 2026
This forecast is for Friday, August 21, 2026:
If the trigger temperature of 89.5 F/31.9 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1560 ft/min (7.9 m/s)
Maximum height of thermals.................. 21283 ft MSL (15986 ft AGL)
Forecast maximum temperature................... 99.0 F/37.7 C
Time of trigger temperature.................... 1045 MDT
Time of overdevelopment........................ 1600 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 13146 ft MSL (7849 ft AGL)
Thermal soaring outlook for Saturday 08/22..... 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....................... 14380 ft MSL (9083 ft AGL)
Wave soaring outlook for Saturday 08/22........ Poor
Remarks... Hot today. Scattered microbursts after 3 pm.
Sunrise/Sunset.................... 06:17:37 / 19:47:31 MDT
Total possible sunshine........... 13 hr 29 min 54 sec (809 min 54 sec)
Altitude of sun at 13:02:34 MDT... 62.14 degrees
Upper air data from numerical model forecast valid on 08/21/2026 at 0600 MDT
Freezing level.................. 17051 ft MSL (11754 ft AGL)
Convective condensation level... 16916 ft MSL (11619 ft AGL)
Lifted condensation level....... 17846 ft MSL (12549 ft AGL)
Lifted index.................... -5.3
K index......................... +23.4
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 -64.5 -84.1 315 32 16 0.6 0.3 M M M M M
45000 -61.3 -78.3 320 40 21 5.0 2.7 M M M M M
40000 -52.7 -62.9 320 39 20 7.9 4.3 M M M M M
38000 -47.9 -54.2 310 35 18 7.9 4.3 M M M M M
36000 -43.2 -45.8 305 33 17 7.5 4.1 M M M M M
34000 -38.8 -37.8 300 30 15 7.4 4.1 M M M M M
32000 -34.3 -29.7 300 27 14 7.7 4.2 M M M M M
30000 -29.9 -21.8 305 25 13 7.5 4.1 45.9 114.6 6.6 M M
29000 -27.6 -17.7 305 24 13 7.5 4.1 45.1 113.2 6.0 M M
28000 -24.9 -12.8 310 24 12 7.4 4.1 44.0 111.3 5.3 M M
27000 -22.7 -8.9 310 24 12 7.4 4.1 43.1 109.5 4.6 M M
26000 -20.5 -4.9 315 24 12 7.4 4.1 42.2 108.0 3.9 M M
25000 -18.3 -0.9 315 23 12 6.7 3.7 41.4 106.5 3.3 M M
24000 -16.3 2.7 315 21 11 6.9 3.8 40.2 104.4 2.3 M M
23000 -14.3 6.3 315 19 10 7.0 3.8 39.2 102.6 1.4 M M
22000 -12.3 9.9 315 17 9 7.4 4.1 38.3 100.9 0.6 M M
21000 -10.1 13.8 305 16 8 7.4 4.1 37.4 99.3 -0.2 1533 7.8
20000 -7.9 17.8 290 15 8 7.4 4.1 36.6 97.9 -0.9 1438 7.3
19500 -6.8 19.8 285 15 8 8.6 4.7 36.3 97.3 -1.2 1390 7.1
19000 -5.4 22.3 290 15 8 9.3 5.1 36.2 97.1 -1.3 1334 6.8
18500 -4.1 24.6 290 14 7 9.3 5.1 36.1 97.0 -1.4 1278 6.5
18000 -2.7 27.1 290 13 7 9.1 5.0 36.0 96.8 -1.5 1223 6.2
17500 -1.4 29.5 290 13 7 9.1 5.0 35.9 96.6 -1.7 1168 5.9
17000 -0.1 31.8 290 12 6 8.9 4.9 35.8 96.5 -1.8 1114 5.7
16500 1.2 34.2 285 11 6 8.7 4.8 35.6 96.1 -2.0 1061 5.4
16000 2.5 36.5 280 10 5 8.8 4.8 35.5 95.8 -2.2 1009 5.1
15500 3.8 38.8 275 8 4 9.1 5.0 35.3 95.6 -2.4 954 4.8
15000 5.1 41.2 270 7 4 9.0 5.0 35.2 95.4 -2.5 899 4.6
14500 7.2 45.0 270 7 4 9.3 5.1 35.1 95.1 -2.7 816 4.1
14000 8.5 47.3 270 8 4 9.3 5.1 35.0 95.0 -2.7 760 3.9
13500 9.9 49.8 270 8 4 8.7 4.8 34.9 94.8 -2.9 705 3.6
13000 11.1 52.0 265 8 4 8.8 4.8 34.7 94.5 -3.1 652 3.3
12500 12.4 54.3 260 9 4 8.7 4.8 34.6 94.2 -3.3 599 3.0
12000 13.7 56.7 260 9 4 8.8 4.8 34.4 93.9 -3.5 546 2.8
11500 15.0 59.0 255 9 4 8.7 4.7 34.2 93.6 -3.7 493 2.5
11000 16.2 61.2 255 8 4 9.0 4.9 34.1 93.3 -3.9 441 2.2
10500 17.2 63.0 250 8 4 3.6 2.0 33.6 92.5 -4.4 396 2.0
10250 17.5 63.5 250 8 4 7.6 4.2 33.2 91.8 -4.8 379 1.9
10000 18.3 64.9 250 8 4 12.0 6.6 33.3 91.9 -4.8 349 1.8
9750 19.1 66.4 250 8 4 9.8 5.4 33.4 92.1 -4.7 318 1.6
9500 19.7 67.5 250 7 4 7.0 3.8 33.3 91.9 -4.9 293 1.5
9250 20.1 68.2 250 7 4 6.4 3.5 33.0 91.4 -5.2 273 1.4
9000 20.6 69.1 250 7 4 8.9 4.9 32.9 91.1 -5.4 250 1.3
8750 21.3 70.3 245 7 4 8.4 4.6 32.8 91.1 -5.5 222 1.1
8500 21.8 71.2 245 7 3 6.1 3.3 32.6 90.7 -5.7 200 1.0
8250 22.2 72.0 245 6 3 5.2 2.9 32.3 90.1 -6.0 181 0.9
8000 22.6 72.7 245 6 3 7.1 3.9 32.0 89.6 -6.4 161 0.8
7750 23.2 73.8 245 6 3 6.3 3.4 31.8 89.3 -6.6 137 0.7
7500 23.5 74.3 245 5 3 3.4 1.9 31.4 88.5 -7.0 121 0.6
7250 23.7 74.7 245 5 3 3.2 1.7 30.9 87.6 -7.5 107 0.5
7000 23.9 75.0 245 5 3 4.5 2.4 30.4 86.8 -8.0 92 0.5
6750 24.2 75.6 240 5 2 0.4 0.2 30.0 86.0 -8.5 77 0.4
6500 23.9 75.0 250 5 2 -4.3 -2.3 29.0 84.2 -9.5 77 0.4
6250 23.7 74.7 255 5 2 -1.9 -1.0 28.0 82.4 -10.5 77 0.4
6000 23.4 74.1 260 5 3 -6.7 -3.7 27.1 80.7 -11.5 78 0.4
5750 22.4 72.3 245 5 3 -16.8 -9.2 25.4 77.8 -13.3 101 0.5
5500 20.8 69.4 225 5 2 -20.4 -11.2 23.2 73.8 -15.7 142 0.7
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/21/2026 at 0900 MDT | 08/21/2026 at 1200 MDT
|
CAPE... +282.5 LI... -0.3 | CAPE... +401.2 LI... -1.1
CINH... -261.7 K Index... +22.1 | CINH... -32.6 K Index... +20.7
|
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 -65.2 -85.4 315 29 15 0.3 0.1 | -65.6 -86.1 310 28 14 1.0 0.5
45000 -61.9 -79.4 320 36 19 5.9 3.2 | -61.7 -79.1 320 32 16 5.6 3.1
40000 -52.1 -61.8 315 37 19 7.9 4.4 | -52.2 -62.0 320 35 18 7.7 4.2
38000 -47.3 -53.1 310 35 18 7.9 4.4 | -47.5 -53.5 320 33 17 7.7 4.2
36000 -42.6 -44.7 310 33 17 7.2 4.0 | -42.9 -45.2 315 31 16 7.4 4.1
34000 -38.4 -37.1 310 31 16 7.0 3.8 | -38.5 -37.3 315 30 16 7.4 4.1
32000 -34.2 -29.6 310 30 15 7.4 4.0 | -34.1 -29.4 320 29 15 7.4 4.1
30000 -30.0 -22.0 310 25 13 7.1 3.9 | -30.0 -22.0 315 24 12 6.9 3.8
29000 -27.8 -18.0 310 23 12 7.1 3.9 | -28.0 -18.4 315 22 11 6.9 3.8
28000 -25.2 -13.4 315 22 11 7.1 3.9 | -25.2 -13.4 315 20 10 8.1 4.4
27000 -23.1 -9.6 320 22 11 7.1 3.9 | -22.8 -9.0 320 21 11 8.1 4.4
26000 -21.0 -5.8 325 22 11 7.2 3.9 | -20.4 -4.7 325 22 11 8.1 4.4
25000 -18.8 -1.8 325 22 11 7.8 4.3 | -18.1 -0.6 325 22 11 7.5 4.1
24000 -16.5 2.3 325 20 10 7.7 4.2 | -15.8 3.6 325 21 11 7.5 4.1
23000 -14.2 6.4 325 19 10 7.7 4.2 | -13.6 7.5 325 19 10 7.6 4.1
22000 -12.0 10.4 320 17 9 7.2 4.0 | -11.4 11.5 325 18 9 7.2 3.9
21000 -9.9 14.2 315 15 8 7.3 4.0 | -9.3 15.3 320 17 9 7.2 4.0
20000 -7.7 18.1 310 13 7 7.4 4.1 | -7.1 19.2 315 15 8 7.2 3.9
19500 -6.7 19.9 305 12 6 7.9 4.3 | -6.1 21.0 310 15 8 8.0 4.4
19000 -5.5 22.1 300 11 6 8.1 4.4 | -4.8 23.4 310 14 7 8.3 4.5
18500 -4.3 24.3 290 11 5 8.1 4.4 | -3.6 25.5 310 14 7 8.3 4.5
18000 -3.1 26.4 285 10 5 8.7 4.8 | -2.5 27.5 310 13 7 8.1 4.4
17500 -1.9 28.6 290 10 5 8.6 4.7 | -1.3 29.7 310 13 7 8.1 4.4
17000 -0.6 30.9 290 9 5 9.1 5.0 | -0.1 31.8 310 12 6 8.4 4.6
16500 0.8 33.4 295 9 5 9.3 5.1 | 1.1 34.0 310 11 6 8.5 4.7
16000 2.2 36.0 295 9 5 9.3 5.1 | 2.4 36.3 310 10 5 8.6 4.7
15500 3.5 38.3 300 9 5 9.1 5.0 | 3.7 38.7 315 10 5 9.0 4.9
15000 4.9 40.8 300 9 5 9.1 5.0 | 5.0 41.0 315 11 5 9.0 4.9
14500 6.9 44.4 305 10 5 9.1 5.0 | 6.9 44.4 320 11 6 8.8 4.9
14000 8.2 46.8 305 11 5 9.0 5.0 | 8.2 46.8 325 11 6 8.9 4.9
13500 9.5 49.1 305 11 6 9.0 4.9 | 9.5 49.1 325 12 6 8.8 4.8
13000 10.9 51.6 310 12 6 8.9 4.9 | 10.8 51.4 330 12 6 8.8 4.8
12500 12.2 54.0 310 12 6 9.3 5.1 | 12.2 54.0 330 12 6 9.3 5.1
12000 13.6 56.5 310 12 6 9.3 5.1 | 13.5 56.3 335 13 6 9.3 5.1
11500 14.9 58.8 310 13 7 8.8 4.8 | 14.9 58.8 335 13 7 8.9 4.9
11000 16.2 61.2 310 13 7 9.3 5.1 | 16.2 61.2 335 13 7 9.5 5.2
10500 17.2 63.0 310 13 7 3.3 1.8 | 17.2 63.0 335 13 7 4.0 2.2
10250 17.6 63.7 310 13 7 8.0 4.4 | 17.6 63.7 335 13 7 9.2 5.1
10000 18.4 65.1 305 12 6 12.4 6.8 | 18.4 65.1 335 13 7 12.6 6.9
9750 19.2 66.6 305 12 6 9.8 5.4 | 19.3 66.7 340 13 7 10.2 5.6
9500 19.8 67.6 305 12 6 7.0 3.8 | 19.9 67.8 340 13 7 7.4 4.1
9250 20.3 68.5 305 12 6 6.8 3.7 | 20.5 68.9 340 13 6 8.2 4.5
9000 20.9 69.6 305 12 6 8.8 4.8 | 21.2 70.2 340 12 6 10.8 5.9
8750 21.6 70.9 300 12 6 8.6 4.7 | 21.9 71.4 335 11 6 10.1 5.5
8500 22.1 71.8 300 11 6 7.4 4.0 | 22.6 72.7 335 10 5 8.6 4.7
8250 22.7 72.9 300 11 6 7.2 3.9 | 23.2 73.8 335 9 5 8.2 4.5
8000 23.2 73.8 300 11 5 7.7 4.2 | 23.8 74.8 330 8 4 10.0 5.5
7750 23.7 74.7 295 10 5 6.1 3.3 | 24.6 76.3 325 7 4 10.7 5.9
7500 24.0 75.2 295 10 5 4.4 2.4 | 25.3 77.5 325 7 4 9.6 5.3
7250 24.3 75.7 295 10 5 4.5 2.5 | 26.0 78.8 325 7 4 9.6 5.3
7000 24.7 76.5 290 9 5 4.9 2.7 | 26.7 80.1 325 7 4 10.6 5.8
6750 24.9 76.8 290 9 5 1.7 1.0 | 27.6 81.7 325 7 4 10.9 6.0
6500 24.8 76.6 290 8 4 -0.8 -0.4 | 28.3 82.9 325 7 3 10.1 5.5
6250 24.8 76.6 290 8 4 -0.5 -0.3 | 29.1 84.4 325 7 3 10.3 5.7
6000 24.7 76.5 285 7 4 0.8 0.5 | 29.9 85.8 320 6 3 10.1 5.6
5750 24.8 76.6 280 6 3 7.1 3.9 | 30.8 87.4 320 6 3 16.3 9.0
5500 25.5 77.9 270 4 2 12.7 7.0 | 32.4 90.3 320 6 3 26.8 14.7
08/21/2026 at 1500 MDT | 08/21/2026 at 1800 MDT
|
CAPE... +293.4 LI... -0.8 | CAPE... +157.8 LI... +0.2
CINH... -16.1 K Index... +24.1 | CINH... -115.2 K Index... +23.4
|
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 -64.4 -83.9 310 30 15 1.0 0.5 | -66.2 -87.2 320 34 17 -0.3 -0.2
45000 -60.8 -77.4 315 36 19 5.1 2.8 | -63.1 -81.6 320 41 21 6.4 3.5
40000 -52.0 -61.6 320 39 20 7.6 4.2 | -52.3 -62.1 320 41 21 8.5 4.7
38000 -47.5 -53.5 320 36 19 7.6 4.2 | -47.2 -53.0 320 36 18 8.5 4.7
36000 -42.9 -45.2 320 34 18 7.7 4.2 | -42.2 -44.0 320 31 16 7.7 4.2
34000 -38.2 -36.8 325 34 18 7.7 4.2 | -37.5 -35.5 315 30 16 7.7 4.2
32000 -33.6 -28.5 325 34 17 8.1 4.5 | -32.9 -27.2 310 29 15 7.8 4.3
30000 -29.2 -20.6 320 29 15 7.4 4.0 | -28.6 -19.5 320 26 14 7.4 4.0
29000 -26.5 -15.7 315 26 13 7.4 4.1 | -26.4 -15.5 330 26 13 7.4 4.0
28000 -24.4 -11.9 310 23 12 7.0 3.8 | -23.7 -10.7 330 25 13 7.2 3.9
27000 -22.3 -8.1 305 21 11 7.0 3.8 | -21.6 -6.9 325 26 13 7.2 3.9
26000 -20.2 -4.4 300 19 10 7.0 3.8 | -19.5 -3.1 320 26 13 7.2 4.0
25000 -18.2 -0.8 295 18 9 7.5 4.1 | -17.3 0.9 320 26 13 7.6 4.2
24000 -16.0 3.2 295 16 8 7.5 4.1 | -15.1 4.8 315 24 12 7.6 4.2
23000 -13.8 7.2 300 15 8 7.5 4.1 | -12.9 8.8 310 23 12 7.7 4.2
22000 -11.5 11.3 305 14 7 7.8 4.3 | -10.7 12.7 305 21 11 7.8 4.3
21000 -9.2 15.4 305 14 7 7.8 4.3 | -8.4 16.9 310 19 10 7.9 4.3
20000 -7.0 19.4 305 13 7 7.8 4.3 | -6.1 21.0 315 18 9 7.9 4.3
19500 -5.8 21.6 305 13 7 7.7 4.2 | -5.0 23.0 320 17 9 8.2 4.5
19000 -4.7 23.5 310 13 7 7.7 4.2 | -3.7 25.3 320 16 8 8.3 4.6
18500 -3.6 25.5 310 12 6 7.7 4.2 | -2.5 27.5 325 16 8 8.3 4.6
18000 -2.4 27.7 315 12 6 8.4 4.6 | -1.3 29.7 330 15 8 7.8 4.3
17500 -1.2 29.8 320 12 6 8.4 4.6 | -0.2 31.6 330 15 7 7.8 4.3
17000 0.0 32.0 325 12 6 8.6 4.7 | 1.0 33.8 330 14 7 8.0 4.4
16500 1.3 34.3 330 12 6 8.7 4.8 | 2.2 36.0 330 13 7 8.0 4.4
16000 2.6 36.7 335 13 6 8.7 4.8 | 3.3 37.9 330 12 6 8.0 4.4
15500 3.9 39.0 335 12 6 8.8 4.8 | 4.5 40.1 330 12 6 8.1 4.5
15000 5.9 42.6 345 12 6 8.7 4.8 | 5.7 42.3 330 11 6 8.1 4.4
14500 7.1 44.8 345 11 6 8.6 4.7 | 7.7 45.9 325 10 5 9.0 4.9
14000 8.4 47.1 350 10 5 8.6 4.7 | 9.0 48.2 325 9 5 9.0 4.9
13500 9.7 49.5 350 9 5 9.6 5.3 | 10.3 50.5 325 9 5 8.9 4.9
13000 11.1 52.0 355 9 4 9.6 5.3 | 11.6 52.9 325 8 4 9.0 4.9
12500 12.5 54.5 355 8 4 9.3 5.1 | 13.0 55.4 320 8 4 8.8 4.8
12000 13.9 57.0 355 8 4 9.3 5.1 | 14.3 57.7 320 7 4 8.8 4.8
11500 15.3 59.5 350 8 4 9.7 5.3 | 15.6 60.1 315 7 4 8.9 4.9
11000 16.7 62.1 350 8 4 10.4 5.7 | 16.9 62.4 315 7 4 9.4 5.2
10500 17.7 63.9 350 8 4 4.5 2.5 | 18.0 64.4 310 7 4 4.1 2.2
10250 18.3 64.9 350 8 4 10.4 5.7 | 18.4 65.1 310 7 4 8.6 4.7
10000 19.2 66.6 350 8 4 13.8 7.6 | 19.2 66.6 305 8 4 12.1 6.7
9750 20.2 68.4 345 8 4 11.5 6.3 | 20.0 68.0 305 8 4 10.2 5.6
9500 20.9 69.6 345 8 4 7.8 4.3 | 20.7 69.3 300 8 4 6.9 3.8
9250 21.4 70.5 345 8 4 8.7 4.8 | 21.2 70.2 300 8 4 7.1 3.9
9000 22.2 72.0 345 8 4 12.1 6.7 | 21.8 71.2 300 9 5 10.4 5.7
8750 23.1 73.6 345 8 4 11.4 6.2 | 22.6 72.7 295 9 5 9.8 5.4
8500 23.9 75.0 345 8 4 9.7 5.3 | 23.2 73.8 295 10 5 7.8 4.3
8250 24.6 76.3 345 8 4 9.4 5.1 | 23.8 74.8 295 10 5 7.1 3.9
8000 25.3 77.5 340 8 4 10.0 5.5 | 24.3 75.7 295 11 6 8.1 4.4
7750 26.1 79.0 340 8 4 10.3 5.6 | 24.9 76.8 290 11 6 8.3 4.6
7500 26.9 80.4 340 8 4 10.0 5.5 | 25.5 77.9 290 12 6 7.5 4.1
7250 27.6 81.7 340 8 4 10.0 5.5 | 26.0 78.8 290 13 6 7.7 4.2
7000 28.4 83.1 340 8 4 10.2 5.6 | 26.6 79.9 285 13 7 6.9 3.8
6750 29.1 84.4 340 8 4 10.2 5.6 | 27.1 80.8 285 14 7 8.0 4.4
6500 29.9 85.8 340 8 4 10.2 5.6 | 27.7 81.9 285 14 7 9.7 5.3
6250 30.6 87.1 335 8 4 9.8 5.4 | 28.4 83.1 285 13 7 9.0 4.9
6000 31.4 88.5 335 8 4 11.3 6.2 | 29.0 84.2 280 13 7 10.1 5.5
5750 32.4 90.3 335 7 4 18.0 9.9 | 29.9 85.8 280 12 6 13.3 7.3
5500 34.0 93.2 335 7 4 24.4 13.4 | 30.9 87.6 280 11 6 15.7 8.6
________________________________________________________________________________
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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