Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
304
UXUS97 KBOU 040113
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1912 MDT Wednesday, September 3, 2025
This forecast is for Thursday, September 4, 2025:
If the trigger temperature of 83.2 F/28.4 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1285 ft/min (6.5 m/s)
Maximum height of thermals.................. 18498 ft MSL (13183 ft AGL)
Forecast maximum temperature................... 89.0 F/32.1 C
Time of trigger temperature.................... 1145 MDT
Time of overdevelopment........................ 1900 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 10280 ft MSL (4965 ft AGL)
Thermal soaring outlook for Friday 09/05....... 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....................... 22284 ft MSL (16969 ft AGL)
Wave soaring outlook for Friday 09/05.......... Poor
Remarks...
Sunrise/Sunset.................... 06:30:56 / 19:25:46 MDT
Total possible sunshine........... 12 hr 54 min 50 sec (774 min 50 sec)
Altitude of sun at 12:58:21 MDT... 57.10 degrees
Upper air data from numerical model forecast valid on 09/04/2025 at 0600 MDT
Freezing level.................. 15258 ft MSL (9943 ft AGL)
Convective condensation level... 19122 ft MSL (13807 ft AGL)
Lifted condensation level....... 18948 ft MSL (13633 ft AGL)
Lifted index.................... +0.9
K index......................... +16.8
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 -64.3 -83.7 305 33 17 1.7 1.0 M M M M M
45000 -61.3 -78.3 300 35 18 2.4 1.3 M M M M M
40000 -57.2 -71.0 305 27 14 7.9 4.3 M M M M M
38000 -52.7 -62.9 305 25 13 7.4 4.1 M M M M M
36000 -48.3 -54.9 310 22 11 7.4 4.1 M M M M M
34000 -43.3 -45.9 305 20 10 8.5 4.6 M M M M M
32000 -38.3 -36.9 305 18 9 8.5 4.7 M M M M M
30000 -32.4 -26.3 295 17 9 8.7 4.8 42.8 109.0 8.5 M M
29000 -29.8 -21.6 290 16 8 8.7 4.8 42.4 108.3 8.3 M M
28000 -27.2 -17.0 285 16 8 8.1 4.5 42.1 107.9 8.2 M M
27000 -24.9 -12.8 290 17 9 7.7 4.2 41.2 106.2 7.5 M M
26000 -22.6 -8.7 295 17 9 7.7 4.2 40.4 104.8 7.0 M M
25000 -20.3 -4.5 295 18 9 7.8 4.3 39.8 103.6 6.5 M M
24000 -18.4 -1.1 300 19 10 6.2 3.4 38.5 101.4 5.6 M M
23000 -16.5 2.3 305 21 11 6.3 3.4 37.3 99.1 4.6 M M
22000 -14.6 5.7 310 22 12 6.3 3.5 36.1 97.0 3.6 M M
21000 -12.7 9.1 310 22 12 6.5 3.6 34.9 94.8 2.6 M M
20000 -10.8 12.6 315 22 11 6.6 3.6 33.7 92.7 1.6 M M
19500 -9.9 14.2 315 22 11 6.6 3.6 33.2 91.8 1.2 M M
19000 -8.9 16.0 315 22 11 6.4 3.5 32.7 90.9 0.7 M M
18500 -8.0 17.6 320 22 11 6.4 3.5 32.1 89.8 0.1 M M
18000 -7.1 19.2 320 22 11 6.7 3.7 31.6 88.8 -0.4 1251 6.4
17500 -6.0 21.2 320 21 11 7.6 4.2 31.1 88.0 -0.9 1205 6.1
17000 -5.0 23.0 325 21 11 7.5 4.1 30.8 87.4 -1.2 1157 5.9
16500 -3.1 26.4 325 21 11 9.1 5.0 30.4 86.7 -1.6 1080 5.5
16000 -1.8 28.8 325 21 11 9.1 5.0 30.3 86.5 -1.7 1024 5.2
15500 -0.4 31.3 325 21 11 9.3 5.1 30.2 86.4 -1.8 969 4.9
15000 1.0 33.8 325 21 11 9.3 5.1 30.1 86.2 -1.9 913 4.6
14500 2.4 36.3 325 21 11 9.6 5.2 30.1 86.1 -2.0 857 4.4
14000 3.8 38.8 325 20 10 9.6 5.3 30.0 86.1 -2.0 799 4.1
13500 5.2 41.4 325 20 10 9.6 5.2 30.0 86.1 -2.1 742 3.8
13000 6.6 43.9 325 19 10 9.5 5.2 30.0 86.0 -2.1 684 3.5
12500 8.0 46.4 325 18 9 9.4 5.2 30.0 85.9 -2.2 627 3.2
12000 9.4 48.9 325 18 9 9.2 5.1 29.9 85.8 -2.3 571 2.9
11500 10.8 51.4 320 17 9 9.2 5.0 29.8 85.6 -2.4 515 2.6
11000 12.1 53.8 320 16 8 8.7 4.8 29.7 85.4 -2.5 460 2.3
10500 13.5 56.3 320 15 8 5.4 3.0 29.6 85.2 -2.6 405 2.1
10250 13.8 56.8 320 15 8 6.3 3.5 29.1 84.4 -3.1 389 2.0
10000 14.5 58.1 315 15 8 11.4 6.2 29.1 84.4 -3.1 359 1.8
9750 15.3 59.5 315 15 8 10.3 5.6 29.2 84.5 -3.0 329 1.7
9500 16.1 61.0 315 14 7 9.5 5.2 29.2 84.6 -3.0 298 1.5
9250 16.7 62.1 315 14 7 6.8 3.8 29.1 84.4 -3.1 273 1.4
9000 17.2 63.0 315 14 7 7.9 4.4 28.9 84.0 -3.4 250 1.3
8750 17.9 64.2 315 13 7 9.8 5.4 28.8 83.9 -3.4 222 1.1
8500 18.6 65.5 315 13 7 8.4 4.6 28.8 83.9 -3.4 194 1.0
8250 19.1 66.4 315 13 7 6.1 3.4 28.6 83.5 -3.6 170 0.9
8000 19.5 67.1 315 13 6 6.4 3.5 28.3 83.0 -3.9 150 0.8
7750 20.1 68.2 315 12 6 8.3 4.5 28.1 82.7 -4.1 125 0.6
7500 20.7 69.3 310 11 6 6.8 3.7 28.0 82.4 -4.3 100 0.5
7250 21.1 70.0 310 11 6 5.0 2.8 27.7 81.8 -4.6 81 0.4
7000 21.5 70.7 310 11 6 4.9 2.7 27.3 81.2 -5.0 62 0.3
6750 21.8 71.2 305 10 5 4.5 2.5 26.9 80.5 -5.4 44 0.2
6500 22.0 71.6 300 10 5 -1.0 -0.6 26.4 79.5 -5.9 32 0.2
6250 21.6 70.9 295 9 5 -5.8 -3.2 25.3 77.6 -7.0 35 0.2
6000 21.3 70.3 285 9 4 -2.5 -1.3 24.3 75.7 -8.2 39 0.2
5750 20.9 69.6 280 8 4 -9.3 -5.1 23.2 73.8 -9.2 41 0.2
5500 19.4 66.9 270 6 3 -30.9 -16.9 21.0 69.8 -11.5 81 0.4
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/04/2025 at 0900 MDT | 09/04/2025 at 1200 MDT
|
CAPE... 0.0 LI... +1.4 | CAPE... +14.0 LI... +0.7
CINH... 0.0 K Index... +16.6 | CINH... -4.7 K Index... +19.8
|
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 -64.3 -83.7 300 30 15 1.1 0.6 | -64.2 -83.6 290 31 16 1.1 0.6
45000 -61.9 -79.4 290 32 17 2.7 1.5 | -62.0 -79.6 280 36 19 2.3 1.3
40000 -57.4 -71.3 295 28 14 8.3 4.6 | -58.0 -72.4 280 31 16 9.1 5.0
38000 -52.7 -62.9 295 27 14 7.8 4.3 | -53.0 -63.4 280 31 16 8.4 4.6
36000 -48.0 -54.4 295 26 13 7.8 4.3 | -47.9 -54.2 285 30 16 8.4 4.6
34000 -43.1 -45.6 290 22 11 8.2 4.5 | -42.8 -45.0 285 30 15 8.6 4.7
32000 -38.2 -36.8 275 19 10 8.2 4.5 | -37.6 -35.7 285 30 15 8.6 4.7
30000 -32.7 -26.9 270 19 10 8.2 4.5 | -32.5 -26.5 285 30 15 7.3 4.0
29000 -30.2 -22.4 270 19 10 8.2 4.5 | -30.3 -22.5 285 30 15 7.3 4.0
28000 -27.7 -17.9 270 20 10 7.9 4.3 | -28.1 -18.6 285 29 15 7.1 3.9
27000 -25.5 -13.9 275 20 10 7.5 4.1 | -26.0 -14.8 285 28 14 6.9 3.8
26000 -23.3 -9.9 280 20 10 7.5 4.1 | -24.0 -11.2 285 27 14 6.9 3.8
25000 -21.0 -5.8 285 20 10 7.6 4.2 | -21.9 -7.4 280 25 13 6.8 3.7
24000 -18.8 -1.8 290 21 11 7.2 4.0 | -19.7 -3.5 285 24 12 7.8 4.3
23000 -16.7 1.9 295 22 11 7.2 4.0 | -17.4 0.7 285 23 12 7.8 4.3
22000 -14.6 5.7 300 23 12 7.2 4.0 | -15.1 4.8 290 22 11 7.9 4.3
21000 -12.8 9.0 300 23 12 5.9 3.2 | -13.1 8.4 290 22 11 6.5 3.6
20000 -11.1 12.0 305 22 12 6.0 3.3 | -11.2 11.8 295 23 12 6.6 3.6
19500 -10.2 13.6 305 22 11 6.1 3.3 | -10.2 13.6 295 23 12 6.6 3.6
19000 -9.4 15.1 305 22 11 6.5 3.6 | -9.3 15.3 295 23 12 7.1 3.9
18500 -8.4 16.9 310 22 12 6.7 3.7 | -8.2 17.2 295 23 12 7.3 4.0
18000 -7.5 18.5 310 22 12 6.8 3.7 | -7.2 19.0 300 24 12 7.4 4.1
17500 -5.8 21.6 315 23 12 7.8 4.3 | -5.5 22.1 300 24 12 7.9 4.3
17000 -4.6 23.7 315 23 12 8.1 4.5 | -4.3 24.3 300 24 12 8.1 4.4
16500 -3.3 26.1 315 22 11 9.4 5.1 | -3.1 26.4 305 24 12 8.7 4.8
16000 -1.9 28.6 315 22 11 9.3 5.1 | -1.8 28.8 305 24 12 8.6 4.7
15500 -0.5 31.1 315 22 11 9.3 5.1 | -0.5 31.1 305 23 12 9.3 5.1
15000 0.8 33.4 315 21 11 9.3 5.1 | 0.9 33.6 305 22 11 9.3 5.1
14500 2.2 36.0 320 21 11 9.3 5.1 | 2.2 36.0 305 21 11 9.1 5.0
14000 3.6 38.5 320 20 10 9.3 5.1 | 3.6 38.5 305 20 10 9.0 4.9
13500 5.0 41.0 320 20 10 9.2 5.0 | 4.9 40.8 305 19 10 8.9 4.9
13000 6.3 43.3 320 19 10 8.9 4.9 | 6.2 43.2 305 17 9 8.8 4.8
12500 7.7 45.9 320 19 10 8.9 4.9 | 7.5 45.5 305 15 8 8.9 4.9
12000 9.0 48.2 320 18 9 8.7 4.8 | 8.9 48.0 310 14 7 9.0 4.9
11500 10.3 50.5 325 17 9 8.7 4.8 | 10.2 50.4 310 12 6 9.0 4.9
11000 11.6 52.9 325 16 8 8.5 4.6 | 11.4 52.5 315 12 6 7.7 4.2
10500 12.9 55.2 325 15 8 5.2 2.9 | 12.5 54.5 315 11 6 11.2 6.1
10250 13.1 55.6 330 16 8 6.3 3.4 | 13.5 56.3 320 10 5 12.1 6.7
10000 13.9 57.0 330 15 8 11.4 6.3 | 14.2 57.6 320 9 5 8.2 4.5
9750 14.7 58.5 330 15 8 10.2 5.6 | 14.9 58.8 325 9 5 9.4 5.1
9500 15.4 59.7 330 15 8 9.9 5.4 | 15.6 60.1 325 8 4 8.8 4.8
9250 16.1 61.0 330 15 8 7.8 4.3 | 16.2 61.2 330 8 4 8.5 4.7
9000 16.7 62.1 330 15 8 8.4 4.6 | 16.9 62.4 330 8 4 9.5 5.2
8750 17.4 63.3 330 15 8 9.8 5.4 | 17.6 63.7 335 7 4 10.3 5.7
8500 18.1 64.6 330 14 7 8.9 4.9 | 18.4 65.1 340 7 4 10.0 5.5
8250 18.7 65.7 330 14 7 7.3 4.0 | 19.1 66.4 345 7 4 9.1 5.0
8000 19.2 66.6 330 15 8 7.4 4.1 | 19.7 67.5 345 7 4 9.5 5.2
7750 19.8 67.6 330 14 7 8.9 4.9 | 20.5 68.9 350 7 3 10.7 5.8
7500 20.5 68.9 330 13 7 7.4 4.1 | 21.3 70.3 350 7 3 9.9 5.4
7250 20.9 69.6 325 13 7 5.2 2.9 | 22.0 71.6 355 7 3 8.6 4.7
7000 21.3 70.3 325 13 7 5.4 2.9 | 22.6 72.7 355 7 3 9.1 5.0
6750 21.8 71.2 320 12 6 8.1 4.5 | 23.4 74.1 355 7 3 11.6 6.3
6500 22.3 72.1 315 10 5 4.2 2.3 | 24.3 75.7 360 6 3 11.4 6.3
6250 22.3 72.1 310 9 4 -0.1 -0.1 | 25.1 77.2 360 6 3 10.4 5.7
6000 22.4 72.3 305 7 4 0.6 0.3 | 25.8 78.4 005 6 3 10.0 5.5
5750 22.4 72.3 300 5 3 2.5 1.4 | 26.6 79.9 005 6 3 12.5 6.8
5500 22.8 73.0 280 4 2 9.3 5.1 | 27.9 82.2 005 6 3 22.8 12.5
09/04/2025 at 1500 MDT | 09/04/2025 at 1800 MDT
|
CAPE... +22.4 LI... -0.1 | CAPE... +45.4 LI... -0.5
CINH... -16.5 K Index... +23.1 | CINH... -24.8 K Index... +24.3
|
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 -64.2 -83.6 280 34 18 1.0 0.5 | -64.1 -83.4 280 39 20 1.2 0.6
45000 -62.0 -79.6 275 43 22 2.8 1.5 | -61.9 -79.4 275 47 24 2.5 1.3
40000 -57.4 -71.3 275 39 20 8.5 4.7 | -57.6 -71.7 275 50 26 8.6 4.7
38000 -52.7 -62.9 275 39 20 7.9 4.3 | -52.9 -63.2 280 48 25 7.9 4.3
36000 -48.0 -54.4 275 39 20 7.9 4.3 | -48.1 -54.6 285 46 24 7.9 4.4
34000 -42.9 -45.2 280 38 19 8.7 4.8 | -43.0 -45.4 285 45 23 8.9 4.9
32000 -37.7 -35.9 280 36 19 8.7 4.8 | -37.7 -35.9 280 43 22 8.9 4.9
30000 -32.3 -26.1 285 34 18 7.7 4.2 | -32.4 -26.3 280 39 20 7.3 4.0
29000 -30.0 -22.0 290 33 17 7.7 4.2 | -30.3 -22.5 280 36 19 7.3 4.0
28000 -27.7 -17.9 290 32 17 7.4 4.0 | -28.1 -18.6 285 34 17 7.3 4.0
27000 -25.6 -14.1 290 32 17 6.9 3.8 | -25.9 -14.6 285 33 17 7.4 4.0
26000 -23.5 -10.3 290 32 17 6.9 3.8 | -23.7 -10.7 285 32 16 7.4 4.0
25000 -21.5 -6.7 295 32 17 6.9 3.8 | -21.5 -6.7 285 31 16 7.4 4.1
24000 -19.4 -2.9 290 32 16 7.0 3.8 | -19.4 -2.9 285 30 16 7.0 3.9
23000 -17.3 0.9 290 31 16 7.1 3.9 | -17.3 0.9 285 29 15 7.1 3.9
22000 -15.3 4.5 290 30 15 7.2 3.9 | -15.2 4.6 290 29 15 7.1 3.9
21000 -13.2 8.2 290 30 15 7.0 3.8 | -13.2 8.2 290 26 14 6.9 3.8
20000 -11.2 11.8 290 30 15 7.0 3.9 | -11.2 11.8 290 24 12 7.1 3.9
19500 -10.2 13.6 290 30 15 7.1 3.9 | -10.3 13.5 290 22 11 7.1 3.9
19000 -9.2 15.4 295 30 15 7.7 4.2 | -9.2 15.4 290 21 11 8.0 4.4
18500 -8.0 17.6 295 29 15 8.0 4.4 | -8.0 17.6 290 19 10 8.4 4.6
18000 -6.9 19.6 295 27 14 8.0 4.4 | -6.8 19.8 285 17 9 8.4 4.6
17500 -5.7 21.7 295 26 13 8.5 4.7 | -5.6 21.9 285 16 8 8.1 4.5
17000 -4.4 24.1 295 24 12 8.5 4.7 | -4.3 24.3 280 15 8 8.1 4.5
16500 -3.2 26.2 290 22 11 8.7 4.8 | -3.1 26.4 280 14 7 9.0 4.9
16000 -1.2 29.8 295 20 10 8.8 4.8 | -1.7 28.9 285 13 7 9.3 5.1
15500 0.1 32.2 295 18 9 8.7 4.8 | 0.3 32.5 285 11 6 9.5 5.2
15000 1.4 34.5 295 16 8 8.8 4.8 | 1.7 35.1 290 10 5 9.5 5.2
14500 2.7 36.9 295 14 7 9.1 5.0 | 3.2 37.8 290 9 5 9.3 5.1
14000 4.1 39.4 295 13 7 9.4 5.1 | 4.5 40.1 295 8 4 9.1 5.0
13500 5.5 41.9 295 11 6 9.3 5.1 | 5.9 42.6 305 7 3 9.2 5.0
13000 6.9 44.4 295 9 5 9.1 5.0 | 7.2 45.0 310 6 3 9.2 5.1
12500 8.2 46.8 295 8 4 9.1 5.0 | 8.6 47.5 320 5 3 9.2 5.1
12000 9.6 49.3 290 6 3 9.1 5.0 | 10.0 50.0 335 4 2 9.1 5.0
11500 11.0 51.8 290 5 2 9.1 5.0 | 11.3 52.3 350 4 2 9.2 5.0
11000 12.2 54.0 285 4 2 7.7 4.2 | 12.6 54.7 010 4 2 7.7 4.3
10500 13.3 55.9 280 3 1 11.7 6.4 | 13.7 56.7 025 4 2 10.4 5.7
10250 14.4 57.9 280 2 1 13.0 7.1 | 14.6 58.3 035 4 2 11.5 6.3
10000 15.1 59.2 275 2 1 8.7 4.8 | 15.3 59.5 040 4 2 8.7 4.8
9750 15.8 60.4 275 2 1 10.2 5.5 | 16.0 60.8 040 4 2 9.5 5.2
9500 16.5 61.7 275 1 1 9.2 5.0 | 16.7 62.1 045 5 2 9.2 5.1
9250 17.2 63.0 270 1 1 8.0 4.4 | 17.3 63.1 045 5 3 7.6 4.2
9000 17.8 64.0 265 1 1 9.5 5.2 | 17.9 64.2 045 5 3 8.8 4.8
8750 18.6 65.5 265 1 0 11.0 6.0 | 18.7 65.7 045 6 3 10.8 5.9
8500 19.4 66.9 255 1 0 10.5 5.8 | 19.5 67.1 045 6 3 10.4 5.7
8250 20.1 68.2 000 0 0 8.3 4.6 | 20.2 68.4 045 6 3 8.6 4.7
8000 20.7 69.3 000 0 0 9.1 5.0 | 20.8 69.4 045 7 3 8.9 4.9
7750 21.5 70.7 000 0 0 11.4 6.3 | 21.6 70.9 045 7 4 10.8 5.9
7500 22.3 72.1 000 0 0 10.3 5.7 | 22.3 72.1 045 7 4 10.0 5.5
7250 23.1 73.6 120 1 0 9.1 5.0 | 23.0 73.4 040 8 4 8.6 4.7
7000 23.7 74.7 120 1 0 9.3 5.1 | 23.6 74.5 040 8 4 8.4 4.6
6750 24.5 76.1 115 1 1 11.5 6.3 | 24.3 75.7 040 8 4 10.2 5.6
6500 25.4 77.7 110 1 1 11.1 6.1 | 25.1 77.2 040 9 5 10.0 5.5
6250 26.1 79.0 105 1 1 9.8 5.4 | 25.8 78.4 040 9 5 9.0 4.9
6000 26.9 80.4 105 1 1 9.6 5.3 | 26.4 79.5 035 9 5 8.9 4.9
5750 27.6 81.7 105 2 1 11.8 6.5 | 27.1 80.8 035 9 4 10.0 5.5
5500 28.8 83.8 105 2 1 20.8 11.4 | 28.0 82.4 035 8 4 13.0 7.1
________________________________________________________________________________
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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