Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
514
UXUS97 KBOU 231220
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0620 MDT Sunday, August 23, 2026
This forecast is for Sunday, August 23, 2026:
If the trigger temperature of 85.2 F/29.5 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1245 ft/min (6.3 m/s)
Maximum height of thermals.................. 16776 ft MSL (11446 ft AGL)
Forecast maximum temperature................... 93.0 F/34.3 C
Time of trigger temperature.................... 1115 MDT
Time of overdevelopment........................ 1700 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 11302 ft MSL (5972 ft AGL)
Thermal soaring outlook for Monday 08/24....... 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)................ Weak PVA
Potential height of wave....................... 24061 ft MSL (18731 ft AGL)
Wave soaring outlook for Monday 08/24.......... Poor
Remarks...
Sunrise/Sunset.................... 06:19:30 / 19:44:36 MDT
Total possible sunshine........... 13 hr 25 min 7 sec (805 min 7 sec)
Altitude of sun at 13:02:03 MDT... 61.46 degrees
Upper air data from numerical model forecast valid on 08/23/2026 at 0600 MDT
Freezing level.................. 16590 ft MSL (11260 ft AGL)
Convective condensation level... 15263 ft MSL (9933 ft AGL)
Lifted condensation level....... 15830 ft MSL (10500 ft AGL)
Lifted index.................... -3.0
K index......................... +27.9
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 -65.0 -85.0 275 21 11 1.5 0.8 M M M M M
45000 -60.8 -77.4 265 29 15 5.1 2.8 M M M M M
40000 -52.4 -62.3 245 27 14 8.0 4.4 M M M M M
38000 -47.6 -53.7 245 24 13 8.0 4.4 M M M M M
36000 -42.2 -44.0 250 22 11 8.4 4.6 M M M M M
34000 -37.1 -34.8 250 19 10 8.4 4.6 M M M M M
32000 -32.1 -25.8 255 17 9 8.6 4.7 50.3 122.5 12.2 M M
30000 -27.4 -17.3 260 16 8 7.9 4.3 48.6 119.4 11.1 M M
29000 -25.0 -13.0 265 15 8 7.9 4.3 47.9 118.2 10.8 M M
28000 -22.8 -9.0 265 15 8 7.1 3.9 47.2 116.9 10.3 M M
27000 -20.6 -5.1 270 15 8 7.2 4.0 46.1 115.0 9.5 M M
26000 -18.5 -1.3 270 15 8 7.2 4.0 45.2 113.3 8.8 M M
25000 -16.4 2.5 275 15 8 6.8 3.7 44.3 111.8 8.2 M M
24000 -14.5 5.9 280 14 7 6.5 3.6 43.0 109.4 7.2 M M
23000 -12.6 9.3 280 13 7 6.5 3.6 41.8 107.3 6.2 M M
22000 -10.7 12.7 280 12 6 6.2 3.4 40.8 105.4 5.4 M M
21000 -8.9 16.0 285 13 7 6.0 3.3 39.3 102.8 4.2 M M
20000 -7.2 19.0 290 13 7 6.1 3.3 38.1 100.5 3.1 M M
19500 -5.8 21.6 295 13 7 6.5 3.6 37.2 98.9 2.3 M M
19000 -4.8 23.4 300 14 7 6.7 3.7 36.6 97.9 1.8 M M
18500 -3.9 25.0 300 14 7 6.7 3.7 36.1 97.0 1.3 M M
18000 -2.8 27.0 300 14 7 7.4 4.0 35.6 96.2 0.9 M M
17500 -1.8 28.8 305 15 8 7.3 4.0 35.2 95.4 0.5 M M
17000 -0.7 30.7 305 15 8 7.5 4.1 34.8 94.7 0.1 M M
16500 0.4 32.7 305 15 8 7.5 4.1 34.4 94.0 -0.3 1011 5.1
16000 1.5 34.7 305 15 8 7.6 4.2 34.1 93.3 -0.7 963 4.9
15500 2.6 36.7 305 15 8 7.7 4.2 33.7 92.7 -1.0 915 4.6
15000 3.7 38.7 305 16 8 7.7 4.2 33.4 92.1 -1.4 867 4.4
14500 4.8 40.6 305 16 8 8.4 4.6 33.1 91.6 -1.7 818 4.2
14000 6.0 42.8 310 16 8 8.4 4.6 32.9 91.2 -1.9 766 3.9
13500 7.3 45.1 310 16 8 8.7 4.8 32.7 90.8 -2.2 715 3.6
13000 8.6 47.5 310 16 8 8.7 4.8 32.5 90.5 -2.4 662 3.4
12500 9.8 49.6 310 16 8 8.8 4.8 32.4 90.2 -2.6 609 3.1
12000 11.1 52.0 305 17 9 8.8 4.8 32.2 90.0 -2.7 555 2.8
11500 12.4 54.3 305 17 9 8.6 4.7 32.1 89.7 -2.9 501 2.5
11000 13.7 56.7 305 17 9 8.1 4.4 31.9 89.4 -3.1 449 2.3
10500 14.9 58.8 300 17 9 2.4 1.3 31.7 89.0 -3.4 396 2.0
10250 14.9 58.8 305 17 9 4.1 2.3 30.9 87.6 -4.1 390 2.0
10000 15.7 60.3 300 17 9 12.8 7.0 31.0 87.8 -4.1 358 1.8
9750 16.5 61.7 300 17 9 11.5 6.3 31.1 88.0 -4.0 326 1.7
9500 17.3 63.1 295 17 9 8.1 4.5 31.2 88.2 -3.9 294 1.5
9250 17.7 63.9 295 16 8 4.4 2.4 30.8 87.5 -4.3 276 1.4
9000 18.2 64.8 295 15 8 8.1 4.5 30.6 87.0 -4.5 254 1.3
8750 18.9 66.0 290 15 8 10.0 5.5 30.5 87.0 -4.6 226 1.2
8500 19.5 67.1 285 15 8 7.2 3.9 30.5 86.9 -4.7 199 1.0
8250 19.9 67.8 285 14 7 4.9 2.7 30.2 86.3 -5.0 180 0.9
8000 20.3 68.5 285 14 7 5.6 3.1 29.8 85.7 -5.3 160 0.8
7750 20.7 69.3 275 13 7 5.4 3.0 29.5 85.1 -5.7 141 0.7
7500 21.1 70.0 270 13 7 5.1 2.8 29.2 84.5 -6.0 122 0.6
7250 21.4 70.5 265 13 7 4.9 2.7 28.8 83.8 -6.5 105 0.5
7000 21.8 71.2 260 12 6 5.2 2.8 28.4 83.2 -6.9 87 0.4
6750 22.1 71.8 250 13 6 3.7 2.0 28.0 82.5 -7.3 71 0.4
6500 22.2 72.0 235 13 7 1.6 0.9 27.5 81.5 -8.0 60 0.3
6250 22.2 72.0 230 13 7 0.6 0.3 26.8 80.3 -8.7 53 0.3
6000 22.2 72.0 225 12 6 3.2 1.8 26.2 79.1 -9.4 45 0.2
5750 22.3 72.1 215 14 7 -4.4 -2.4 25.6 78.1 -10.1 36 0.2
5500 21.0 69.8 210 10 5 -24.0 -13.2 23.8 74.8 -12.1 65 0.3
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/23/2026 at 0900 MDT | 08/23/2026 at 1200 MDT
|
CAPE... +967.7 LI... -1.5 | CAPE... +673.9 LI... -3.1
CINH... -110.7 K Index... +26.2 | CINH... -16.1 K Index... +26.0
|
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 -83.9 280 19 10 2.3 1.3 | -64.2 -83.6 275 18 9 2.2 1.2
45000 -59.9 -75.8 270 26 13 4.2 2.3 | -59.6 -75.3 260 25 13 4.6 2.5
40000 -52.7 -62.9 245 30 16 8.0 4.4 | -52.0 -61.6 240 34 18 7.4 4.0
38000 -47.9 -54.2 240 28 15 8.0 4.4 | -47.6 -53.7 240 34 17 7.4 4.0
36000 -42.5 -44.5 235 26 14 8.4 4.6 | -42.6 -44.7 235 32 17 8.2 4.5
34000 -37.4 -35.3 245 22 12 8.4 4.6 | -37.6 -35.7 240 28 14 8.2 4.5
32000 -32.4 -26.3 255 19 10 8.5 4.6 | -32.7 -26.9 245 24 12 8.7 4.8
30000 -27.7 -17.9 260 16 8 7.8 4.3 | -27.9 -18.2 245 21 11 8.1 4.4
29000 -25.4 -13.7 265 15 8 7.8 4.3 | -25.5 -13.9 250 19 10 8.1 4.4
28000 -23.1 -9.6 270 14 7 7.3 4.0 | -23.1 -9.6 255 18 9 7.1 3.9
27000 -21.0 -5.8 270 14 7 7.4 4.0 | -21.0 -5.8 255 18 9 7.2 4.0
26000 -18.8 -1.8 275 14 7 7.4 4.0 | -18.8 -1.8 260 17 9 7.2 4.0
25000 -16.6 2.1 275 14 7 6.8 3.7 | -16.7 1.9 260 17 9 6.4 3.5
24000 -14.7 5.5 275 13 7 6.5 3.5 | -14.9 5.2 265 17 9 6.0 3.3
23000 -12.8 9.0 275 13 7 6.5 3.6 | -13.2 8.2 270 18 9 6.0 3.3
22000 -10.9 12.4 275 13 7 6.2 3.4 | -11.4 11.5 275 19 10 6.0 3.3
21000 -9.1 15.6 280 12 6 6.0 3.3 | -9.7 14.5 275 18 9 6.0 3.3
20000 -7.4 18.7 285 11 6 6.1 3.3 | -8.0 17.6 275 18 9 6.0 3.3
19500 -6.1 21.0 285 11 6 6.6 3.6 | -7.1 19.2 280 17 9 6.2 3.4
19000 -5.1 22.8 290 11 6 6.7 3.7 | -5.7 21.7 280 16 8 6.8 3.7
18500 -4.1 24.6 290 11 5 6.8 3.7 | -4.7 23.5 280 15 8 6.9 3.8
18000 -3.1 26.4 295 11 5 7.0 3.8 | -3.7 25.3 285 14 7 7.3 4.0
17500 -2.1 28.2 295 11 6 7.0 3.8 | -2.6 27.3 285 13 7 7.3 4.0
17000 -1.1 30.0 300 11 6 7.3 4.0 | -1.5 29.3 285 12 6 8.0 4.4
16500 -0.0 32.0 305 11 6 7.4 4.1 | -0.3 31.5 290 12 6 8.2 4.5
16000 1.0 33.8 310 11 6 7.6 4.2 | 0.9 33.6 295 11 6 8.4 4.6
15500 2.2 36.0 315 11 6 8.1 4.4 | 2.2 36.0 300 11 6 8.9 4.9
15000 3.4 38.1 315 12 6 8.0 4.4 | 3.5 38.3 300 11 6 8.8 4.9
14500 4.6 40.3 320 13 6 8.6 4.7 | 4.8 40.6 305 12 6 9.1 5.0
14000 5.9 42.6 325 13 7 8.5 4.7 | 6.2 43.2 305 12 6 9.1 5.0
13500 7.2 45.0 325 14 7 8.8 4.8 | 7.5 45.5 310 13 7 9.2 5.0
13000 8.5 47.3 325 15 8 8.8 4.8 | 8.9 48.0 310 14 7 9.2 5.0
12500 9.8 49.6 325 16 8 8.9 4.9 | 10.2 50.4 310 15 8 9.3 5.1
12000 11.1 52.0 320 17 9 8.9 4.9 | 11.6 52.9 305 16 8 9.4 5.1
11500 12.4 54.3 320 18 9 8.8 4.8 | 13.0 55.4 305 17 9 8.9 4.9
11000 13.7 56.7 320 19 10 8.5 4.7 | 14.2 57.6 305 17 9 8.6 4.7
10500 15.0 59.0 315 20 10 3.6 2.0 | 15.4 59.7 305 18 9 3.2 1.8
10250 15.1 59.2 315 20 10 5.3 2.9 | 15.5 59.9 305 18 9 5.7 3.1
10000 15.9 60.6 315 21 11 12.3 6.7 | 16.3 61.3 305 16 8 12.6 6.9
9750 16.7 62.1 310 21 11 11.0 6.0 | 17.0 62.6 305 15 8 11.2 6.2
9500 17.4 63.3 310 22 11 8.1 4.4 | 17.7 63.9 305 14 7 8.1 4.5
9250 17.9 64.2 310 22 11 5.6 3.1 | 18.2 64.8 305 13 7 6.7 3.7
9000 18.4 65.1 310 22 11 8.7 4.8 | 18.9 66.0 305 12 6 11.1 6.1
8750 19.0 66.2 310 21 11 9.5 5.2 | 19.7 67.5 310 12 6 11.7 6.4
8500 19.7 67.5 310 21 11 8.1 4.4 | 20.5 68.9 310 12 6 8.9 4.9
8250 20.2 68.4 310 20 11 7.0 3.8 | 21.0 69.8 310 11 5 6.1 3.3
8000 20.7 69.3 310 20 10 8.0 4.4 | 21.6 70.9 310 9 5 10.1 5.5
7750 21.4 70.5 305 19 10 8.2 4.5 | 22.5 72.5 315 10 5 12.2 6.7
7500 21.9 71.4 305 19 10 6.7 3.7 | 23.2 73.8 315 10 5 8.6 4.7
7250 22.4 72.3 305 18 9 5.5 3.0 | 23.8 74.8 315 9 5 6.5 3.6
7000 22.8 73.0 305 17 9 7.7 4.2 | 24.4 75.9 315 8 4 10.6 5.8
6750 23.4 74.1 305 16 8 7.7 4.2 | 25.3 77.5 315 9 5 13.9 7.6
6500 23.8 74.8 300 14 7 4.1 2.2 | 26.2 79.2 315 9 5 10.9 6.0
6250 24.0 75.2 295 12 6 3.1 1.7 | 27.0 80.6 320 9 4 10.4 5.7
6000 24.2 75.6 290 9 5 4.4 2.4 | 27.8 82.0 320 8 4 9.3 5.1
5750 24.5 76.1 285 6 3 7.3 4.0 | 28.6 83.5 320 7 3 15.4 8.5
5500 24.9 76.8 270 5 3 9.3 5.1 | 30.2 86.4 325 6 3 29.5 16.2
08/23/2026 at 1500 MDT | 08/23/2026 at 1800 MDT
|
CAPE... +640.5 LI... -3.4 | CAPE... +877.3 LI... -3.0
CINH... -13.1 K Index... +30.3 | CINH... -21.7 K Index... +32.0
|
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 -63.7 -82.7 275 16 8 1.6 0.9 | -64.0 -83.2 275 19 10 1.7 1.0
45000 -59.7 -75.5 255 25 13 4.6 2.5 | -59.7 -75.5 260 28 14 4.7 2.6
40000 -52.1 -61.8 240 41 21 7.4 4.1 | -52.0 -61.6 250 39 20 7.3 4.0
38000 -47.7 -53.9 240 37 19 7.4 4.0 | -47.6 -53.7 250 39 20 7.3 4.0
36000 -42.7 -44.9 240 33 17 8.0 4.4 | -42.7 -44.9 250 39 20 7.8 4.3
34000 -37.9 -36.2 240 30 16 8.0 4.4 | -37.9 -36.2 250 34 17 7.9 4.3
32000 -33.1 -27.6 240 27 14 8.6 4.7 | -33.2 -27.8 245 29 15 8.3 4.6
30000 -28.2 -18.8 245 24 13 8.1 4.4 | -28.5 -19.3 250 26 14 7.9 4.3
29000 -25.8 -14.4 245 23 12 8.1 4.4 | -26.2 -15.2 250 25 13 7.9 4.3
28000 -23.4 -10.1 250 22 11 7.0 3.8 | -23.9 -11.0 255 24 12 7.2 3.9
27000 -21.3 -6.3 255 23 12 7.1 3.9 | -21.8 -7.2 260 23 12 7.2 4.0
26000 -19.2 -2.6 260 23 12 7.1 3.9 | -19.6 -3.3 265 22 11 7.3 4.0
25000 -17.1 1.2 265 24 12 6.3 3.4 | -17.5 0.5 270 21 11 6.7 3.7
24000 -15.5 4.1 270 24 12 5.7 3.1 | -15.6 3.9 275 20 10 6.3 3.5
23000 -13.8 7.2 275 24 12 5.8 3.2 | -13.8 7.2 285 20 10 6.3 3.5
22000 -12.1 10.2 275 24 12 6.3 3.4 | -11.9 10.6 290 19 10 6.7 3.7
21000 -10.2 13.6 280 23 12 6.5 3.6 | -9.9 14.2 295 19 10 6.9 3.8
20000 -8.4 16.9 285 22 12 6.6 3.6 | -7.9 17.8 300 20 10 7.0 3.8
19500 -6.9 19.6 285 22 11 7.6 4.2 | -6.9 19.6 305 20 10 7.0 3.9
19000 -5.7 21.7 290 22 11 7.8 4.3 | -5.3 22.5 305 20 10 7.5 4.1
18500 -4.6 23.7 290 21 11 7.9 4.4 | -4.2 24.4 305 20 11 7.5 4.1
18000 -3.4 25.9 290 21 11 8.7 4.8 | -3.1 26.4 310 20 11 7.7 4.2
17500 -2.1 28.2 295 21 11 8.6 4.7 | -2.0 28.4 310 20 10 7.7 4.2
17000 -0.8 30.6 295 20 10 8.9 4.9 | -0.9 30.4 310 20 10 8.1 4.4
16500 0.5 32.9 295 20 10 9.0 4.9 | 0.3 32.5 310 19 10 8.2 4.5
16000 1.8 35.2 300 20 10 8.9 4.9 | 1.5 34.7 310 18 9 8.4 4.6
15500 3.0 37.4 300 19 10 8.8 4.8 | 2.7 36.9 310 16 8 8.9 4.9
15000 4.3 39.7 300 18 10 8.9 4.9 | 4.0 39.2 310 15 8 8.9 4.9
14500 5.6 42.1 300 17 9 8.8 4.8 | 5.4 41.7 310 13 7 9.3 5.1
14000 6.8 44.2 300 15 8 8.8 4.8 | 6.7 44.1 310 12 6 9.3 5.1
13500 8.1 46.6 300 14 7 9.0 4.9 | 8.1 46.6 310 11 6 9.1 5.0
13000 9.4 48.9 305 12 6 9.0 4.9 | 9.4 48.9 310 9 5 9.1 5.0
12500 10.7 51.3 305 10 5 9.4 5.2 | 10.8 51.4 305 8 4 9.3 5.1
12000 12.1 53.8 305 10 5 9.5 5.2 | 12.2 54.0 305 7 4 9.4 5.1
11500 13.6 56.5 305 9 5 9.7 5.3 | 13.6 56.5 300 6 3 9.3 5.1
11000 15.0 59.0 305 8 4 9.6 5.2 | 15.0 59.0 295 6 3 9.0 5.0
10500 16.5 61.7 305 8 4 4.3 2.3 | 16.3 61.3 290 5 3 4.5 2.4
10250 16.6 61.9 305 7 4 6.0 3.3 | 16.5 61.7 275 3 2 6.5 3.6
10000 17.6 63.7 305 7 4 13.7 7.5 | 17.4 63.3 275 4 2 13.5 7.4
9750 18.5 65.3 310 7 3 12.5 6.8 | 18.3 64.9 275 4 2 12.6 6.9
9500 19.4 66.9 310 7 3 9.4 5.2 | 19.2 66.6 275 5 2 8.8 4.8
9250 19.9 67.8 310 6 3 7.7 4.2 | 19.7 67.5 245 3 1 6.8 3.7
9000 20.6 69.1 310 6 3 11.2 6.2 | 20.4 68.7 235 3 2 11.1 6.1
8750 21.5 70.7 310 6 3 11.6 6.3 | 21.3 70.3 250 4 2 11.7 6.4
8500 22.3 72.1 315 6 3 10.1 5.5 | 22.1 71.8 255 4 2 9.6 5.3
8250 23.0 73.4 315 5 3 8.5 4.7 | 22.7 72.9 230 4 2 7.3 4.0
8000 23.7 74.7 315 5 2 10.0 5.5 | 23.3 73.9 200 4 2 10.0 5.5
7750 24.5 76.1 315 5 2 10.8 5.9 | 24.1 75.4 225 4 2 11.4 6.3
7500 25.2 77.4 315 5 2 9.2 5.1 | 24.9 76.8 235 5 2 8.5 4.6
7250 25.9 78.6 315 4 2 8.0 4.4 | 25.4 77.7 215 5 3 6.2 3.4
7000 26.5 79.7 320 4 2 9.9 5.5 | 25.9 78.6 200 6 3 9.6 5.3
6750 27.4 81.3 320 4 2 12.2 6.7 | 26.8 80.2 210 6 3 12.9 7.1
6500 28.2 82.8 320 4 2 10.9 6.0 | 27.7 81.9 220 6 3 9.9 5.4
6250 29.0 84.2 320 4 2 10.5 5.8 | 28.3 82.9 205 6 3 7.5 4.1
6000 29.8 85.6 320 4 2 9.1 5.0 | 28.9 84.0 195 7 4 10.3 5.7
5750 30.5 86.9 320 4 2 13.8 7.6 | 29.7 85.5 215 5 3 11.1 6.1
5500 32.0 89.6 320 4 2 26.4 14.5 | 30.3 86.5 205 5 2 5.7 3.2
________________________________________________________________________________
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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