Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
532
UXUS97 KBOU 041312
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0711 MDT Thursday, September 4, 2025
This forecast is for Thursday, September 4, 2025:
If the trigger temperature of 84.5 F/29.2 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1313 ft/min (6.7 m/s)
Maximum height of thermals.................. 18548 ft MSL (13255 ft AGL)
Forecast maximum temperature................... 89.0 F/32.1 C
Time of trigger temperature.................... 1200 MDT
Time of overdevelopment........................ 1800 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 7707 ft MSL (2414 ft AGL)
Thermal soaring outlook for Friday 09/05....... Poor
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT).........
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 16621 ft MSL (11328 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.................. 15307 ft MSL (10014 ft AGL)
Convective condensation level... 19477 ft MSL (14184 ft AGL)
Lifted condensation level....... 19071 ft MSL (13779 ft AGL)
Lifted index.................... +1.5
K index......................... +14.5
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 -64.2 -83.6 305 30 16 1.9 1.1 M M M M M
45000 -61.0 -77.8 300 30 16 2.3 1.3 M M M M M
40000 -57.1 -70.8 310 23 12 7.9 4.3 M M M M M
38000 -52.7 -62.9 305 23 12 7.3 4.0 M M M M M
36000 -48.3 -54.9 300 23 12 7.4 4.1 M M M M M
34000 -43.4 -46.1 300 21 11 8.4 4.6 M M M M M
32000 -37.7 -35.9 300 18 9 8.3 4.6 M M M M M
30000 -32.6 -26.7 295 17 9 8.7 4.7 42.6 108.7 8.3 M M
29000 -30.0 -22.0 290 17 9 8.7 4.7 42.2 108.0 8.1 M M
28000 -27.4 -17.3 285 17 9 8.6 4.7 41.9 107.5 8.0 M M
27000 -24.9 -12.8 285 17 9 8.5 4.7 41.3 106.4 7.6 M M
26000 -22.3 -8.1 290 18 9 8.5 4.7 40.8 105.5 7.3 M M
25000 -19.8 -3.6 290 18 9 8.7 4.8 40.5 104.8 7.1 M M
24000 -17.8 -0.0 300 18 9 5.9 3.2 39.2 102.6 6.1 M M
23000 -16.1 3.0 310 19 10 5.9 3.3 37.8 100.0 5.0 M M
22000 -14.3 6.3 325 20 10 6.0 3.3 36.5 97.7 4.0 M M
21000 -12.5 9.5 325 20 11 6.3 3.4 35.2 95.3 2.9 M M
20000 -10.6 12.9 320 20 10 6.3 3.5 33.9 93.1 1.8 M M
19500 -9.7 14.5 320 20 10 6.4 3.5 33.4 92.1 1.3 M M
19000 -8.8 16.2 320 20 10 5.6 3.1 32.8 91.0 0.8 M M
18500 -8.0 17.6 320 20 10 5.5 3.0 32.0 89.6 0.1 M M
18000 -7.3 18.9 320 20 10 6.0 3.3 31.3 88.3 -0.6 1278 6.5
17500 -6.2 20.8 325 20 11 8.2 4.5 30.9 87.6 -1.0 1231 6.3
17000 -5.0 23.0 325 21 11 8.1 4.4 30.6 87.1 -1.3 1182 6.0
16500 -3.8 25.2 325 22 11 9.4 5.1 30.4 86.8 -1.6 1129 5.7
16000 -1.7 28.9 320 22 12 9.5 5.2 30.4 86.6 -1.7 1044 5.3
15500 -0.2 31.6 320 22 12 9.9 5.4 30.3 86.6 -1.7 986 5.0
15000 1.2 34.2 320 22 11 9.9 5.4 30.4 86.6 -1.7 927 4.7
14500 2.7 36.9 325 22 11 9.7 5.3 30.4 86.7 -1.7 868 4.4
14000 4.2 39.6 325 21 11 9.7 5.3 30.4 86.7 -1.7 810 4.1
13500 5.6 42.1 325 21 11 9.5 5.2 30.4 86.7 -1.7 751 3.8
13000 7.0 44.6 325 21 11 9.3 5.1 30.3 86.5 -1.8 695 3.5
12500 8.4 47.1 325 20 11 9.5 5.2 30.2 86.4 -1.9 638 3.2
12000 9.9 49.8 325 20 10 9.8 5.4 30.2 86.4 -1.9 579 2.9
11500 11.3 52.3 325 20 10 9.7 5.3 30.2 86.4 -1.9 520 2.6
11000 12.7 54.9 325 19 10 9.0 4.9 30.2 86.3 -1.9 463 2.4
10500 14.1 57.4 325 19 10 5.1 2.8 30.1 86.2 -2.0 407 2.1
10250 14.4 57.9 325 19 10 6.1 3.3 29.6 85.3 -2.5 392 2.0
10000 15.2 59.4 320 19 10 11.9 6.5 29.7 85.4 -2.5 361 1.8
9750 16.0 60.8 320 18 9 10.6 5.8 29.7 85.5 -2.4 330 1.7
9500 16.7 62.1 320 18 9 9.9 5.5 29.8 85.7 -2.3 299 1.5
9250 17.4 63.3 320 18 9 7.7 4.2 29.7 85.5 -2.4 272 1.4
9000 18.0 64.4 320 17 9 8.8 4.8 29.6 85.3 -2.6 247 1.3
8750 18.7 65.7 320 17 9 10.2 5.6 29.6 85.3 -2.6 218 1.1
8500 19.4 66.9 315 17 9 9.4 5.1 29.6 85.3 -2.6 189 1.0
8250 20.1 68.2 315 16 8 8.6 4.7 29.5 85.2 -2.7 163 0.8
8000 20.7 69.3 310 16 8 8.2 4.5 29.4 85.0 -2.8 137 0.7
7750 21.3 70.3 310 15 8 8.1 4.4 29.3 84.8 -3.0 112 0.6
7500 21.9 71.4 305 15 8 7.9 4.3 29.2 84.5 -3.1 86 0.4
7250 22.4 72.3 300 15 8 7.8 4.3 29.0 84.3 -3.3 62 0.3
7000 23.0 73.4 295 15 8 7.6 4.2 28.9 84.0 -3.5 38 0.2
6750 23.5 74.3 295 15 8 7.2 3.9 28.7 83.7 -3.7 14 0.1
6500 23.8 74.8 290 14 7 -2.5 -1.4 28.3 82.9 -4.1 M M
6250 23.2 73.8 285 14 7 -10.7 -5.9 26.9 80.4 -5.5 10 0.1
6000 22.5 72.5 280 13 7 -5.5 -3.0 25.5 77.9 -6.9 23 0.1
5750 22.0 71.6 270 13 7 -12.5 -6.9 24.3 75.7 -8.2 31 0.2
5500 19.9 67.8 260 11 5 -41.0 -22.5 21.6 70.9 -11.0 85 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... +2.2 | CAPE... +4.1 LI... +0.6
CINH... 0.0 K Index... +18.6 | CINH... -10.7 K Index... +19.2
|
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 -64.7 -84.5 290 31 16 1.1 0.6 | -64.3 -83.7 290 36 19 0.8 0.4
45000 -62.2 -80.0 290 32 16 3.3 1.8 | -62.3 -80.1 280 39 20 2.7 1.5
40000 -56.7 -70.1 300 26 14 8.0 4.4 | -57.7 -71.9 275 28 14 8.8 4.8
38000 -52.1 -61.8 295 26 13 7.7 4.2 | -52.8 -63.0 275 29 15 8.2 4.5
36000 -47.4 -53.3 295 25 13 7.7 4.2 | -47.9 -54.2 275 30 15 8.2 4.5
34000 -42.7 -44.9 290 23 12 8.0 4.4 | -42.8 -45.0 275 30 16 8.5 4.7
32000 -37.9 -36.2 285 20 10 8.0 4.4 | -37.7 -35.9 280 31 16 8.5 4.7
30000 -32.3 -26.1 280 19 10 8.4 4.6 | -32.4 -26.3 280 29 15 7.8 4.3
29000 -29.8 -21.6 275 18 9 8.4 4.6 | -30.0 -22.0 275 28 14 7.8 4.3
28000 -27.3 -17.1 270 18 9 8.1 4.4 | -27.7 -17.9 275 27 14 7.3 4.0
27000 -24.9 -12.8 270 19 10 7.9 4.4 | -25.7 -14.3 280 26 13 6.8 3.7
26000 -22.5 -8.5 270 19 10 7.9 4.4 | -23.6 -10.5 280 24 12 6.8 3.7
25000 -20.2 -4.4 270 20 10 8.0 4.4 | -21.6 -6.9 280 23 12 6.7 3.7
24000 -18.1 -0.6 280 19 10 6.8 3.7 | -19.2 -2.6 285 22 11 8.2 4.5
23000 -16.0 3.2 290 19 10 6.8 3.7 | -16.8 1.8 290 21 11 8.2 4.5
22000 -14.0 6.8 300 20 10 6.8 3.8 | -14.3 6.3 295 21 11 8.2 4.5
21000 -12.0 10.4 305 20 11 6.9 3.8 | -12.3 9.9 300 21 11 6.4 3.5
20000 -9.9 14.2 305 21 11 7.0 3.8 | -10.4 13.3 300 21 11 6.4 3.5
19500 -8.9 16.0 305 21 11 7.2 3.9 | -9.5 14.9 300 22 11 6.5 3.6
19000 -8.0 17.6 305 22 11 4.1 2.2 | -8.6 16.5 300 22 11 5.2 2.9
18500 -7.5 18.5 310 22 11 3.8 2.1 | -7.9 17.8 300 23 12 5.0 2.8
18000 -7.0 19.4 315 23 12 4.4 2.4 | -7.3 18.9 305 25 13 5.5 3.0
17500 -6.2 20.8 315 22 12 6.9 3.8 | -6.3 20.7 305 25 13 8.2 4.5
17000 -5.3 22.5 315 22 11 6.7 3.7 | -5.1 22.8 305 25 13 8.1 4.4
16500 -4.2 24.4 320 21 11 9.4 5.1 | -3.2 26.2 305 24 12 9.8 5.4
16000 -2.8 27.0 320 20 10 9.6 5.2 | -1.7 28.9 305 23 12 9.8 5.4
15500 -1.3 29.7 320 19 10 9.6 5.2 | -0.3 31.5 305 22 12 9.4 5.2
15000 0.8 33.4 320 18 9 9.5 5.2 | 1.1 34.0 305 22 11 9.4 5.2
14500 2.2 36.0 320 18 9 9.6 5.3 | 2.5 36.5 305 21 11 8.8 4.9
14000 3.7 38.7 320 17 9 9.6 5.3 | 3.8 38.8 305 20 10 8.6 4.7
13500 5.1 41.2 320 16 8 9.4 5.2 | 5.1 41.2 305 18 9 8.3 4.6
13000 6.5 43.7 325 16 8 9.2 5.0 | 6.2 43.2 300 16 8 7.9 4.3
12500 7.8 46.0 325 15 8 9.2 5.0 | 7.4 45.3 300 14 7 8.0 4.4
12000 9.2 48.6 330 14 7 9.2 5.0 | 8.6 47.5 305 12 6 8.3 4.6
11500 10.6 51.1 330 14 7 9.2 5.0 | 9.8 49.6 305 10 5 8.3 4.5
11000 11.9 53.4 335 14 7 8.8 4.8 | 11.1 52.0 315 8 4 8.2 4.5
10500 13.3 55.9 340 14 7 4.7 2.6 | 12.3 54.1 325 7 4 4.8 2.6
10250 13.5 56.3 345 14 7 6.2 3.4 | 12.5 54.5 330 7 4 5.6 3.1
10000 14.3 57.7 345 15 8 12.7 6.9 | 13.2 55.8 340 7 3 10.8 5.9
9750 15.2 59.4 345 15 8 11.2 6.2 | 13.9 57.0 350 7 3 9.6 5.3
9500 16.0 60.8 345 15 8 10.6 5.8 | 14.6 58.3 355 7 3 9.4 5.1
9250 16.7 62.1 345 15 8 8.2 4.5 | 15.2 59.4 005 7 4 8.0 4.4
9000 17.3 63.1 345 16 8 8.8 4.8 | 15.8 60.4 010 7 4 9.0 4.9
8750 18.0 64.4 350 16 8 9.9 5.4 | 16.6 61.9 010 7 4 9.8 5.4
8500 18.7 65.7 350 16 8 9.2 5.1 | 17.3 63.1 015 7 4 9.9 5.4
8250 19.4 66.9 350 17 9 8.8 4.8 | 18.0 64.4 015 7 4 11.2 6.2
8000 20.1 68.2 350 17 9 8.2 4.5 | 18.9 66.0 015 7 4 10.3 5.6
7750 20.6 69.1 345 17 9 7.6 4.2 | 19.6 67.3 015 7 4 8.4 4.6
7500 21.2 70.2 345 18 9 7.6 4.2 | 20.2 68.4 015 7 4 9.9 5.4
7250 21.8 71.2 345 18 9 7.5 4.1 | 21.0 69.8 015 7 4 11.6 6.4
7000 22.3 72.1 340 18 9 7.5 4.1 | 21.9 71.4 015 7 4 11.0 6.0
6750 22.9 73.2 335 19 10 7.2 4.0 | 22.6 72.7 015 7 4 8.7 4.8
6500 23.2 73.8 330 19 10 0.5 0.3 | 23.3 73.9 015 7 4 9.8 5.4
6250 23.0 73.4 325 16 8 -3.7 -2.0 | 24.1 75.4 015 7 4 12.0 6.6
6000 22.7 72.9 320 14 7 -4.1 -2.3 | 25.0 77.0 015 7 4 10.3 5.6
5750 22.3 72.1 310 12 6 -4.8 -2.6 | 25.7 78.3 020 7 3 12.7 7.0
5500 22.2 72.0 300 7 4 5.3 2.9 | 27.1 80.8 020 7 3 23.3 12.8
09/04/2025 at 1500 MDT | 09/04/2025 at 1800 MDT
|
CAPE... +61.3 LI... -0.1 | CAPE... +78.2 LI... -0.7
CINH... -36.6 K Index... +21.6 | CINH... -52.5 K Index... +20.6
|
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 -63.9 -83.0 280 33 17 1.0 0.6 | -63.3 -81.9 280 32 16 1.1 0.6
45000 -61.6 -78.9 270 43 22 2.8 1.5 | -61.2 -78.2 275 44 23 2.0 1.1
40000 -57.1 -70.8 275 39 20 8.2 4.5 | -57.7 -71.9 270 47 24 8.5 4.7
38000 -52.5 -62.5 275 38 20 7.6 4.2 | -53.0 -63.4 275 47 24 7.9 4.3
36000 -48.0 -54.4 275 37 19 7.6 4.2 | -48.3 -54.9 275 48 25 7.9 4.3
34000 -43.1 -45.6 280 37 19 8.3 4.5 | -43.2 -45.8 280 46 23 8.7 4.8
32000 -38.2 -36.8 280 38 19 8.3 4.5 | -38.0 -36.4 280 42 22 8.7 4.8
30000 -32.9 -27.2 285 35 18 7.6 4.2 | -32.8 -27.0 285 37 19 7.2 4.0
29000 -30.6 -23.1 290 33 17 7.6 4.2 | -30.6 -23.1 285 34 18 7.2 4.0
28000 -28.3 -18.9 290 32 16 7.3 4.0 | -28.5 -19.3 290 32 16 7.1 3.9
27000 -26.3 -15.3 290 30 15 6.9 3.8 | -26.4 -15.5 290 30 15 6.9 3.8
26000 -24.2 -11.6 290 28 14 6.9 3.8 | -24.3 -11.7 285 29 15 6.9 3.8
25000 -22.1 -7.8 290 26 13 6.8 3.7 | -22.2 -8.0 285 27 14 6.9 3.8
24000 -19.8 -3.6 290 24 12 8.2 4.5 | -20.1 -4.2 285 26 13 7.3 4.0
23000 -17.3 0.9 290 22 11 8.2 4.5 | -17.9 -0.2 285 24 13 7.3 4.0
22000 -14.9 5.2 285 21 11 8.3 4.5 | -15.8 3.6 285 23 12 7.4 4.0
21000 -12.8 9.0 290 23 12 6.8 3.8 | -13.6 7.5 290 23 12 7.4 4.0
20000 -10.7 12.7 290 26 13 6.9 3.8 | -11.5 11.3 295 24 12 7.5 4.1
19500 -9.7 14.5 295 27 14 6.9 3.8 | -10.4 13.3 300 25 13 7.6 4.2
19000 -8.8 16.2 295 29 15 6.7 3.7 | -9.3 15.3 300 25 13 8.8 4.8
18500 -7.9 17.8 295 29 15 6.8 3.7 | -8.0 17.6 300 25 13 9.1 5.0
18000 -6.9 19.6 295 29 15 7.3 4.0 | -6.6 20.1 300 25 13 9.2 5.0
17500 -5.7 21.7 295 28 14 9.4 5.2 | -5.3 22.5 300 24 13 9.1 5.0
17000 -4.3 24.3 290 27 14 9.2 5.1 | -3.9 25.0 300 24 12 9.1 5.0
16500 -3.0 26.6 290 26 13 9.2 5.1 | -2.5 27.5 300 24 12 9.7 5.3
16000 -0.9 30.4 290 24 12 9.2 5.1 | -1.1 30.0 300 23 12 9.9 5.4
15500 0.5 32.9 290 23 12 9.1 5.0 | 1.0 33.8 300 22 11 9.2 5.1
15000 1.8 35.2 290 22 11 9.1 5.0 | 2.4 36.3 300 22 11 9.2 5.0
14500 3.2 37.8 290 20 11 9.2 5.1 | 3.8 38.8 300 21 11 9.3 5.1
14000 4.6 40.3 285 19 10 9.3 5.1 | 5.2 41.4 300 19 10 9.4 5.2
13500 5.9 42.6 285 18 9 9.1 5.0 | 6.6 43.9 300 18 9 9.4 5.2
13000 7.3 45.1 285 15 8 8.9 4.9 | 8.0 46.4 300 16 8 9.4 5.1
12500 8.6 47.5 285 12 6 8.7 4.8 | 9.4 48.9 300 14 7 9.3 5.1
12000 9.8 49.6 285 9 4 7.6 4.2 | 10.7 51.3 295 12 6 8.3 4.5
11500 10.9 51.6 275 5 3 7.7 4.2 | 11.9 53.4 295 10 5 8.4 4.6
11000 12.0 53.6 260 3 2 7.1 3.9 | 13.1 55.6 290 8 4 7.6 4.1
10500 13.0 55.4 240 2 1 10.2 5.6 | 14.2 57.6 285 6 3 9.4 5.2
10250 13.9 57.0 220 2 1 11.7 6.4 | 15.0 59.0 280 5 3 10.0 5.5
10000 14.5 58.1 220 2 1 8.5 4.7 | 15.6 60.1 275 5 2 7.9 4.4
9750 15.2 59.4 220 2 1 9.4 5.2 | 16.2 61.2 270 4 2 8.5 4.7
9500 15.9 60.6 215 2 1 9.1 5.0 | 16.9 62.4 265 4 2 8.3 4.6
9250 16.6 61.9 215 2 1 9.3 5.1 | 17.5 63.5 260 3 2 8.7 4.8
9000 17.3 63.1 215 2 1 9.7 5.3 | 18.1 64.6 260 3 2 9.0 4.9
8750 18.0 64.4 215 2 1 9.9 5.4 | 18.8 65.8 260 3 2 8.9 4.9
8500 18.7 65.7 215 2 1 9.9 5.4 | 19.4 66.9 260 3 2 8.9 4.9
8250 19.5 67.1 215 2 1 11.1 6.1 | 20.1 68.2 260 3 2 10.2 5.6
8000 20.3 68.5 215 2 1 10.4 5.7 | 20.9 69.6 260 3 2 10.1 5.5
7750 21.0 69.8 215 2 1 8.9 4.9 | 21.6 70.9 265 3 2 8.9 4.9
7500 21.7 71.1 215 2 1 9.6 5.3 | 22.3 72.1 265 3 2 9.5 5.2
7250 22.5 72.5 220 2 1 10.4 5.7 | 23.0 73.4 265 3 2 11.0 6.0
7000 23.3 73.9 220 2 1 10.4 5.7 | 23.8 74.8 265 3 2 10.9 6.0
6750 24.0 75.2 220 2 1 9.0 5.0 | 24.6 76.3 265 3 2 8.4 4.6
6500 24.7 76.5 220 2 1 10.0 5.5 | 25.2 77.4 270 3 2 8.9 4.9
6250 25.5 77.9 225 2 1 11.7 6.4 | 25.9 78.6 270 3 2 11.0 6.0
6000 26.4 79.5 225 2 1 11.0 6.0 | 26.8 80.2 270 3 2 11.1 6.1
5750 27.2 81.0 225 2 1 11.8 6.5 | 27.6 81.7 270 3 2 10.4 5.7
5500 28.3 82.9 225 2 1 19.6 10.7 | 28.3 82.9 270 3 2 11.3 6.2
________________________________________________________________________________
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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