Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
732
UXUS97 KBOU 250039
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1838 MDT Sunday, August 24, 2025
This forecast is for Monday, August 25, 2025:
If the trigger temperature of 73.2 F/22.9 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 92 ft/min (0.5 m/s)
Maximum height of thermals.................. 9515 ft MSL (4212 ft AGL)
Forecast maximum temperature................... 74.0 F/23.8 C
Time of trigger temperature.................... 1600 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Broken/overcast opaque middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 8017 ft MSL (2714 ft AGL)
Thermal soaring outlook for Tuesday 08/26...... Poor
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....................... 40801 ft MSL (35498 ft AGL)
Wave soaring outlook for Tuesday 08/26......... Poor
Remarks... Afternoon thunderstorms
Sunrise/Sunset.................... 06:21:36 / 19:41:16 MDT
Total possible sunshine........... 13 hr 19 min 41 sec (799 min 41 sec)
Altitude of sun at 13:01:26 MDT... 60.70 degrees
Upper air data from numerical model forecast valid on 08/25/2025 at 0600 MDT
Freezing level.................. 15006 ft MSL (9703 ft AGL)
Convective condensation level... 11743 ft MSL (6440 ft AGL)
Lifted condensation level....... 10391 ft MSL (5088 ft AGL)
Lifted index.................... -1.2
K index......................... +27.4
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 -84.1 305 39 20 1.8 1.0 M M M M M
45000 -60.5 -76.9 295 52 27 4.5 2.5 M M M M M
40000 -53.3 -63.9 285 61 31 7.2 3.9 M M M M M
38000 -48.9 -56.0 285 60 31 7.2 4.0 M M M M M
36000 -44.6 -48.3 285 59 31 7.1 3.9 M M M M M
34000 -39.0 -38.2 290 55 28 8.4 4.6 M M M M M
32000 -34.0 -29.2 295 51 27 8.9 4.9 M M M M M
30000 -29.3 -20.7 295 49 25 7.8 4.3 47.2 116.9 18.1 M M
29000 -26.9 -16.4 300 48 25 7.8 4.3 46.5 115.7 17.8 M M
28000 -24.6 -12.3 300 46 24 7.3 4.0 45.8 114.5 17.5 M M
27000 -22.5 -8.5 305 44 22 7.1 3.9 44.7 112.5 16.8 M M
26000 -20.3 -4.5 305 41 21 7.1 3.9 43.7 110.7 16.2 M M
25000 -18.2 -0.8 310 38 20 7.1 3.9 42.9 109.1 15.7 M M
24000 -16.3 2.7 310 35 18 6.5 3.6 41.6 106.9 14.8 M M
23000 -14.4 6.1 310 30 16 6.6 3.6 40.4 104.8 13.9 M M
22000 -12.5 9.5 310 26 13 6.5 3.6 39.4 102.9 13.1 M M
21000 -10.8 12.6 310 23 12 5.6 3.1 37.9 100.2 11.9 M M
20000 -9.2 15.4 310 21 11 5.7 3.1 36.4 97.6 10.7 M M
19500 -8.4 16.9 310 20 10 5.7 3.1 35.8 96.4 10.1 M M
19000 -7.6 18.3 310 18 9 6.0 3.3 35.1 95.2 9.6 M M
18500 -6.7 19.9 310 17 9 6.1 3.3 34.5 94.0 9.0 M M
18000 -5.8 21.6 305 16 8 6.0 3.3 33.8 92.9 8.5 M M
17500 -4.6 23.7 305 13 7 5.6 3.1 32.8 91.0 7.6 M M
17000 -3.8 25.2 310 11 6 5.8 3.2 32.1 89.8 7.0 M M
16500 -2.9 26.8 310 9 5 6.3 3.4 31.5 88.7 6.5 M M
16000 -2.0 28.4 310 8 4 6.1 3.4 30.9 87.6 6.0 M M
15500 -0.9 30.4 305 8 4 7.9 4.3 30.5 86.8 5.6 M M
15000 0.2 32.4 305 7 4 7.7 4.2 30.1 86.2 5.3 M M
14500 1.4 34.5 305 7 4 8.0 4.4 29.8 85.6 5.0 M M
14000 2.6 36.7 305 7 4 8.1 4.4 29.5 85.2 4.7 M M
13500 3.8 38.8 300 7 4 7.9 4.3 29.3 84.7 4.5 M M
13000 4.9 40.8 305 7 4 7.7 4.2 28.9 84.1 4.2 M M
12500 6.0 42.8 305 7 3 7.3 4.0 28.6 83.5 3.9 M M
12000 7.0 44.6 310 6 3 6.8 3.7 28.1 82.6 3.5 M M
11500 8.0 46.4 310 6 3 6.4 3.5 27.7 81.8 3.0 M M
11000 8.8 47.8 305 5 2 5.2 2.9 27.0 80.6 2.3 M M
10500 9.5 49.1 295 3 2 4.1 2.2 26.3 79.4 1.6 M M
10250 9.7 49.5 290 3 2 3.0 1.7 25.8 78.4 1.1 M M
10000 10.0 50.0 290 3 1 5.4 3.0 25.3 77.6 0.6 M M
9750 10.4 50.7 280 2 1 6.7 3.7 25.1 77.1 0.3 M M
9500 10.8 51.4 265 2 1 5.1 2.8 24.8 76.6 -0.0 291 1.5
9250 11.0 51.8 275 1 1 2.9 1.6 24.3 75.8 -0.5 276 1.4
9000 11.2 52.2 295 1 1 3.9 2.1 23.8 74.8 -1.0 262 1.3
8750 11.6 52.9 335 2 1 5.4 3.0 23.4 74.2 -1.4 245 1.2
8500 11.9 53.4 350 2 1 3.8 2.1 23.0 73.5 -1.9 228 1.2
8250 12.0 53.6 355 3 2 2.4 1.3 22.5 72.5 -2.4 216 1.1
8000 12.2 54.0 360 4 2 3.1 1.7 22.0 71.5 -3.0 204 1.0
7750 12.4 54.3 005 5 3 3.7 2.0 21.5 70.7 -3.6 191 1.0
7500 12.6 54.7 010 6 3 3.5 1.9 21.0 69.8 -4.1 178 0.9
7250 12.8 55.0 010 7 3 3.1 1.7 20.5 68.9 -4.7 165 0.8
7000 13.0 55.4 010 7 4 3.2 1.8 20.0 68.0 -5.2 151 0.8
6750 13.2 55.8 010 8 4 4.9 2.7 19.6 67.2 -5.7 137 0.7
6500 13.6 56.5 010 8 4 6.0 3.3 19.3 66.7 -6.0 117 0.6
6250 14.0 57.2 010 8 4 5.9 3.3 19.0 66.1 -6.4 98 0.5
6000 14.4 57.9 010 8 4 5.0 2.7 18.7 65.6 -6.7 78 0.4
5750 14.7 58.5 010 8 4 5.5 3.0 18.3 64.9 -7.1 61 0.3
5500 15.3 59.5 010 7 3 9.7 5.3 18.1 64.6 -7.3 37 0.2
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/25/2025 at 0900 MDT | 08/25/2025 at 1200 MDT
|
CAPE... +598.5 LI... -2.6 | CAPE... +755.4 LI... -2.7
CINH... -29.3 K Index... +27.5 | CINH... -14.1 K Index... +27.9
|
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 37 19 1.8 1.0 | -64.1 -83.4 305 36 19 1.7 1.0
45000 -60.3 -76.5 300 51 26 4.8 2.7 | -60.1 -76.2 295 52 27 4.7 2.6
40000 -52.7 -62.9 290 61 32 6.6 3.6 | -52.8 -63.0 290 61 32 6.5 3.6
38000 -48.7 -55.7 285 60 31 6.7 3.7 | -48.8 -55.8 285 59 30 6.6 3.6
36000 -44.1 -47.4 280 59 30 7.1 3.9 | -44.4 -47.9 285 57 29 7.1 3.9
34000 -39.3 -38.7 285 55 28 8.1 4.4 | -39.4 -38.9 285 53 27 8.2 4.5
32000 -34.4 -29.9 295 52 27 8.6 4.7 | -34.5 -30.1 290 48 25 8.7 4.8
30000 -29.7 -21.5 295 47 24 7.9 4.3 | -29.7 -21.5 290 44 22 7.9 4.3
29000 -27.3 -17.1 300 45 23 7.9 4.3 | -27.4 -17.3 290 41 21 7.9 4.4
28000 -25.0 -13.0 300 42 22 7.3 4.0 | -25.1 -13.2 295 39 20 7.2 3.9
27000 -22.9 -9.2 300 40 20 7.1 3.9 | -23.0 -9.4 295 37 19 7.0 3.8
26000 -20.8 -5.4 300 37 19 7.1 3.9 | -20.9 -5.6 295 35 18 7.0 3.9
25000 -18.7 -1.7 300 34 18 7.1 3.9 | -18.8 -1.8 300 33 17 7.0 3.8
24000 -16.6 2.1 305 32 16 6.8 3.7 | -16.9 1.6 300 31 16 6.6 3.6
23000 -14.7 5.5 305 29 15 6.8 3.7 | -15.0 5.0 300 29 15 6.6 3.6
22000 -12.7 9.1 310 26 13 6.7 3.7 | -13.0 8.6 300 27 14 6.6 3.6
21000 -11.0 12.2 310 24 12 5.8 3.2 | -11.1 12.0 300 24 12 6.5 3.6
20000 -9.3 15.3 310 21 11 5.9 3.2 | -9.2 15.4 300 22 11 6.5 3.6
19500 -8.5 16.7 305 20 10 5.9 3.2 | -8.3 17.1 300 20 10 6.6 3.6
19000 -7.2 19.0 305 18 9 5.6 3.1 | -6.9 19.6 305 19 10 5.7 3.2
18500 -6.4 20.5 305 17 9 5.6 3.1 | -6.1 21.0 305 18 9 5.8 3.2
18000 -5.6 21.9 305 16 8 6.4 3.5 | -5.3 22.5 305 17 9 5.6 3.1
17500 -4.7 23.5 305 16 8 6.5 3.6 | -4.5 23.9 305 16 8 5.6 3.1
17000 -3.7 25.3 305 15 8 6.4 3.5 | -3.7 25.3 310 15 8 5.9 3.2
16500 -2.8 27.0 300 14 7 6.0 3.3 | -2.8 27.0 310 14 7 6.4 3.5
16000 -2.0 28.4 300 13 7 6.0 3.3 | -1.9 28.6 310 14 7 6.4 3.5
15500 -1.0 30.2 300 12 6 6.4 3.5 | -1.0 30.2 310 13 7 6.4 3.5
15000 -0.1 31.8 305 11 6 6.4 3.5 | -0.0 32.0 310 12 6 6.4 3.5
14500 0.9 33.6 305 10 5 7.0 3.8 | 0.9 33.6 310 11 6 6.6 3.6
14000 1.9 35.4 310 9 5 7.1 3.9 | 1.9 35.4 310 10 5 6.6 3.6
13500 3.0 37.4 315 9 4 7.5 4.1 | 2.9 37.2 315 9 5 7.0 3.8
13000 4.1 39.4 325 8 4 7.7 4.2 | 3.9 39.0 320 8 4 7.2 3.9
12500 5.2 41.4 330 7 4 7.5 4.1 | 5.0 41.0 325 7 4 7.0 3.9
12000 6.3 43.3 340 7 3 7.2 4.0 | 6.0 42.8 335 6 3 6.8 3.7
11500 7.3 45.1 350 6 3 7.0 3.8 | 6.9 44.4 345 5 3 6.6 3.6
11000 8.2 46.8 350 6 3 6.3 3.5 | 7.8 46.0 350 4 2 6.1 3.3
10500 9.1 48.4 350 6 3 4.5 2.5 | 8.7 47.7 360 3 1 4.0 2.2
10250 9.3 48.7 355 6 3 2.7 1.5 | 8.8 47.8 360 2 1 2.8 1.6
10000 9.6 49.3 350 5 3 5.6 3.1 | 9.2 48.6 005 2 1 6.5 3.6
9750 10.0 50.0 350 5 2 7.3 4.0 | 9.7 49.5 010 1 1 8.1 4.4
9500 10.4 50.7 345 4 2 5.0 2.7 | 10.1 50.2 000 0 0 5.4 2.9
9250 10.6 51.1 340 4 2 2.2 1.2 | 10.4 50.7 000 0 0 2.3 1.3
9000 10.8 51.4 340 4 2 2.8 1.6 | 10.6 51.1 070 1 0 4.3 2.3
8750 10.9 51.6 340 3 2 3.4 1.9 | 10.9 51.6 125 1 0 5.5 3.0
8500 11.1 52.0 340 3 1 3.1 1.7 | 11.2 52.2 145 1 0 5.0 2.8
8250 11.3 52.3 345 3 1 2.6 1.4 | 11.5 52.7 140 1 0 4.5 2.5
8000 11.5 52.7 345 3 1 3.8 2.1 | 11.8 53.2 120 1 0 6.1 3.3
7750 11.8 53.2 350 3 1 5.8 3.2 | 12.4 54.3 120 1 0 8.4 4.6
7500 12.1 53.8 360 2 1 4.1 2.2 | 12.9 55.2 000 0 0 7.9 4.3
7250 12.3 54.1 355 3 1 2.1 1.2 | 13.4 56.1 000 0 0 6.4 3.5
7000 12.5 54.5 355 3 2 3.7 2.0 | 13.9 57.0 355 1 0 9.4 5.2
6750 12.9 55.2 355 3 2 8.0 4.4 | 14.7 58.5 010 1 0 11.5 6.3
6500 13.5 56.3 355 3 2 8.8 4.8 | 15.5 59.9 015 1 0 9.8 5.4
6250 14.0 57.2 360 3 2 8.0 4.4 | 16.2 61.2 010 1 0 10.2 5.6
6000 14.6 58.3 360 3 2 6.2 3.4 | 16.9 62.4 010 1 0 8.9 4.9
5750 15.0 59.0 360 3 2 7.9 4.3 | 17.7 63.9 345 1 1 14.0 7.7
5500 15.9 60.6 355 3 2 17.8 9.7 | 19.2 66.6 345 1 1 26.2 14.4
08/25/2025 at 1500 MDT | 08/25/2025 at 1800 MDT
|
CAPE... +565.7 LI... -2.6 | CAPE... +521.7 LI... -2.6
CINH... -1.0 K Index... +28.7 | CINH... -8.1 K Index... +29.9
|
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 -64.0 -83.2 300 38 19 1.7 0.9 | -64.1 -83.4 305 38 20 2.1 1.2
45000 -60.2 -76.4 295 52 27 4.4 2.4 | -59.7 -75.5 290 52 27 4.1 2.3
40000 -52.7 -62.9 285 61 32 7.2 3.9 | -52.8 -63.0 280 61 32 7.4 4.1
38000 -48.4 -55.1 285 58 30 7.2 3.9 | -48.4 -55.1 280 56 29 7.4 4.0
36000 -44.1 -47.4 285 55 28 7.3 4.0 | -44.0 -47.2 280 51 26 7.5 4.1
34000 -39.3 -38.7 285 52 27 8.1 4.4 | -38.9 -38.0 280 48 24 8.5 4.6
32000 -34.5 -30.1 290 49 25 7.9 4.4 | -33.8 -28.8 280 45 23 8.3 4.6
30000 -29.6 -21.3 295 46 24 8.1 4.4 | -29.0 -20.2 285 43 22 8.0 4.4
29000 -27.2 -17.0 295 45 23 8.1 4.4 | -26.0 -14.8 285 42 22 8.0 4.4
28000 -24.8 -12.6 300 43 22 7.6 4.1 | -23.7 -10.7 290 42 21 6.9 3.8
27000 -22.2 -8.0 295 40 21 7.2 3.9 | -21.6 -6.9 290 40 21 7.0 3.9
26000 -20.1 -4.2 295 37 19 7.2 4.0 | -19.6 -3.3 290 38 20 7.1 3.9
25000 -18.0 -0.4 295 35 18 6.8 3.8 | -17.5 0.5 290 37 19 6.9 3.8
24000 -16.1 3.0 295 33 17 6.4 3.5 | -15.6 3.9 295 33 17 6.6 3.6
23000 -14.3 6.3 295 31 16 6.4 3.5 | -13.6 7.5 295 30 15 6.7 3.7
22000 -12.4 9.7 295 29 15 6.3 3.5 | -11.7 10.9 300 26 13 6.1 3.4
21000 -10.6 12.9 300 26 14 6.3 3.4 | -10.1 13.8 300 24 12 5.5 3.0
20000 -8.7 16.3 300 24 12 6.3 3.4 | -8.6 16.5 305 22 11 5.5 3.0
19500 -7.8 18.0 300 23 12 6.3 3.5 | -7.8 18.0 305 20 11 5.5 3.0
19000 -6.9 19.6 300 22 11 6.5 3.6 | -7.0 19.4 305 19 10 5.7 3.1
18500 -5.9 21.4 300 21 11 6.5 3.6 | -6.2 20.8 305 18 9 5.7 3.1
18000 -5.0 23.0 300 20 10 6.3 3.5 | -5.3 22.5 305 17 9 5.8 3.2
17500 -4.1 24.6 295 19 10 6.2 3.4 | -4.5 23.9 305 16 8 5.9 3.2
17000 -3.2 26.2 295 18 9 6.2 3.4 | -3.6 25.5 310 15 8 5.9 3.2
16500 -2.3 27.9 295 17 9 6.3 3.5 | -2.8 27.0 310 13 7 5.9 3.2
16000 -1.4 29.5 295 16 8 6.3 3.5 | -1.9 28.6 315 12 6 5.9 3.2
15500 -0.5 31.1 300 14 7 6.2 3.4 | -1.1 30.0 320 10 5 6.1 3.3
15000 0.4 32.7 300 13 7 6.2 3.4 | -0.2 31.6 325 9 5 6.2 3.4
14500 1.2 34.2 305 11 6 5.9 3.2 | 0.7 33.3 330 8 4 6.5 3.5
14000 2.0 35.6 310 9 5 5.5 3.0 | 2.1 35.8 345 7 4 6.9 3.8
13500 2.8 37.0 315 7 4 5.6 3.1 | 3.1 37.6 355 7 4 6.5 3.6
13000 3.6 38.5 330 5 3 5.8 3.2 | 4.0 39.2 360 7 3 6.4 3.5
12500 4.4 39.9 355 4 2 5.9 3.2 | 4.9 40.8 010 7 3 6.5 3.6
12000 5.8 42.4 040 3 2 6.7 3.7 | 5.8 42.4 010 5 3 6.5 3.6
11500 6.8 44.2 065 3 2 6.6 3.6 | 6.8 44.2 020 4 2 6.4 3.5
11000 7.7 45.9 080 4 2 6.6 3.6 | 7.6 45.7 035 3 2 6.2 3.4
10500 8.5 47.3 090 4 2 2.6 1.4 | 8.5 47.3 070 2 1 3.4 1.9
10250 8.7 47.7 090 4 2 4.8 2.6 | 8.7 47.7 075 3 1 4.3 2.4
10000 9.3 48.7 090 5 2 12.1 6.7 | 9.2 48.6 090 3 2 10.0 5.5
9750 10.2 50.4 090 5 3 11.6 6.4 | 9.9 49.8 100 4 2 10.4 5.7
9500 10.8 51.4 090 5 3 7.6 4.2 | 10.6 51.1 105 5 3 7.3 4.0
9250 11.2 52.2 090 5 3 4.5 2.4 | 11.0 51.8 105 6 3 4.2 2.3
9000 11.7 53.1 090 5 3 11.4 6.3 | 11.4 52.5 105 6 3 9.5 5.2
8750 12.8 55.0 090 5 3 13.9 7.6 | 12.3 54.1 110 7 3 12.2 6.7
8500 13.6 56.5 090 5 3 8.3 4.6 | 13.0 55.4 110 7 4 8.0 4.4
8250 14.1 57.4 090 5 3 5.5 3.0 | 13.5 56.3 110 8 4 5.8 3.2
8000 14.6 58.3 085 5 3 10.8 5.9 | 14.0 57.2 110 8 4 8.6 4.7
7750 15.6 60.1 085 5 2 13.0 7.1 | 14.7 58.5 110 8 4 10.3 5.7
7500 16.3 61.3 085 5 2 8.7 4.7 | 15.4 59.7 110 8 4 8.4 4.6
7250 16.9 62.4 085 5 2 7.0 3.9 | 16.0 60.8 110 8 4 7.0 3.8
7000 17.5 63.5 080 5 2 12.2 6.7 | 16.5 61.7 105 8 4 10.3 5.6
6750 18.6 65.5 080 5 2 13.6 7.5 | 17.4 63.3 105 8 4 11.0 6.0
6500 19.4 66.9 075 5 2 9.3 5.1 | 18.0 64.4 105 8 4 8.1 4.5
6250 20.2 68.4 075 5 2 11.6 6.3 | 18.7 65.7 105 8 4 9.4 5.2
6000 20.9 69.6 075 5 2 7.0 3.8 | 19.3 66.7 100 8 4 7.2 3.9
5750 21.4 70.5 070 5 2 11.3 6.2 | 19.8 67.6 100 7 4 8.8 4.8
5500 23.0 73.4 070 4 2 30.8 16.9 | 20.7 69.3 100 7 3 17.4 9.6
________________________________________________________________________________
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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