Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
983
UXUS97 KBOU 220114
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1913 MDT Thursday, August 21, 2025
This forecast is for Friday, August 22, 2025:
If the trigger temperature of 86.4 F/30.2 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 76 ft/min (0.4 m/s)
Maximum height of thermals.................. 9235 ft MSL (3921 ft AGL)
Forecast maximum temperature................... 86.0 F/30.5 C
Time of trigger temperature.................... 1345 MDT
Time of overdevelopment........................ 1500 MDT
Middle/high clouds during soaring window....... Broken/overcast thin middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 8170 ft MSL (2856 ft AGL)
Thermal soaring outlook for Saturday 08/23..... Good
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....................... 16147 ft MSL (10833 ft AGL)
Wave soaring outlook for Saturday 08/23........ Poor
Remarks...
Sunrise/Sunset.................... 06:18:47 / 19:45:43 MDT
Total possible sunshine........... 13 hr 26 min 56 sec (806 min 56 sec)
Altitude of sun at 13:02:15 MDT... 61.72 degrees
Upper air data from numerical model forecast valid on 08/22/2025 at 0600 MDT
Freezing level.................. 17170 ft MSL (11856 ft AGL)
Convective condensation level... 16121 ft MSL (10807 ft AGL)
Lifted condensation level....... 14115 ft MSL (8801 ft AGL)
Lifted index.................... -2.3
K index......................... +22.9
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 -66.7 -88.1 285 26 13 0.5 0.3 M M M M M
45000 -62.4 -80.3 285 38 20 6.8 3.7 M M M M M
40000 -51.9 -61.4 290 39 20 8.0 4.4 M M M M M
38000 -47.1 -52.8 290 35 18 8.0 4.4 M M M M M
36000 -42.2 -44.0 290 32 16 8.0 4.4 M M M M M
34000 -37.5 -35.5 285 26 14 7.9 4.3 M M M M M
32000 -32.2 -26.0 280 20 10 8.4 4.6 50.1 122.1 14.9 M M
30000 -27.6 -17.7 285 18 9 7.7 4.3 48.3 118.9 13.9 M M
29000 -25.3 -13.5 285 18 9 7.7 4.2 47.6 117.6 13.5 M M
28000 -23.1 -9.6 290 17 9 6.6 3.6 46.7 116.0 12.9 M M
27000 -21.1 -6.0 295 16 8 6.6 3.6 45.4 113.7 12.0 M M
26000 -19.2 -2.6 300 15 8 6.7 3.7 44.3 111.7 11.2 M M
25000 -17.2 1.0 300 15 8 6.3 3.5 43.2 109.7 10.4 M M
24000 -15.4 4.3 305 16 8 6.2 3.4 41.8 107.2 9.4 M M
23000 -13.6 7.5 305 16 8 6.3 3.4 40.5 104.9 8.4 M M
22000 -11.7 10.9 305 17 9 7.2 4.0 39.4 102.9 7.5 M M
21000 -9.5 14.9 305 17 9 7.4 4.1 38.5 101.3 6.7 M M
20000 -7.4 18.7 310 17 9 7.5 4.1 37.7 99.9 6.1 M M
19500 -6.3 20.7 310 17 9 7.7 4.2 37.4 99.3 5.8 M M
19000 -5.1 22.8 310 16 8 8.5 4.6 37.1 98.8 5.6 M M
18500 -3.8 25.2 315 15 8 8.4 4.6 36.9 98.4 5.4 M M
18000 -2.5 27.5 315 14 7 8.9 4.9 36.7 98.0 5.2 M M
17500 -0.6 30.9 315 13 7 9.0 4.9 36.5 97.7 5.1 M M
17000 0.8 33.4 315 12 6 8.9 4.9 36.3 97.4 5.0 M M
16500 2.1 35.8 310 12 6 8.9 4.9 36.2 97.2 4.8 M M
16000 3.4 38.1 310 12 6 8.9 4.9 36.1 96.9 4.7 M M
15500 4.7 40.5 305 11 6 8.7 4.8 35.9 96.6 4.6 M M
15000 6.0 42.8 300 11 6 8.8 4.8 35.7 96.3 4.4 M M
14500 7.2 45.0 290 11 6 8.2 4.5 35.5 96.0 4.2 M M
14000 8.4 47.1 280 11 6 8.2 4.5 35.3 95.5 4.0 M M
13500 9.7 49.5 270 11 6 8.5 4.6 35.1 95.1 3.8 M M
13000 10.9 51.6 265 12 6 8.5 4.7 34.8 94.7 3.6 M M
12500 12.2 54.0 255 12 6 8.3 4.6 34.6 94.4 3.4 M M
12000 13.4 56.1 250 12 6 8.3 4.5 34.4 93.9 3.2 M M
11500 14.6 58.3 245 13 7 7.8 4.3 34.2 93.5 3.0 M M
11000 15.7 60.3 245 13 7 7.1 3.9 33.8 92.8 2.6 M M
10500 16.8 62.2 245 13 7 2.9 1.6 33.4 92.2 2.3 M M
10250 16.8 62.2 245 13 7 2.1 1.2 32.7 90.8 1.6 M M
10000 17.2 63.0 240 12 6 7.2 4.0 32.4 90.3 1.3 M M
9750 17.7 63.9 240 11 6 6.8 3.7 32.1 89.8 1.0 M M
9500 18.1 64.6 240 11 6 4.0 2.2 31.9 89.3 0.7 M M
9250 18.2 64.8 235 10 5 0.7 0.4 31.2 88.2 0.0 M M
9000 18.3 64.9 235 10 5 2.1 1.1 30.6 87.0 -0.6 267 1.4
8750 18.4 65.1 235 9 4 2.5 1.4 30.0 86.0 -1.2 257 1.3
8500 18.5 65.3 230 8 4 0.9 0.5 29.4 84.9 -1.9 246 1.3
8250 18.4 65.1 235 7 4 -0.5 -0.3 28.6 83.5 -2.7 241 1.2
8000 18.3 64.9 235 6 3 -0.0 -0.0 27.9 82.1 -3.5 236 1.2
7750 18.2 64.8 240 5 3 -0.2 -0.1 27.1 80.8 -4.3 231 1.2
7500 18.1 64.6 245 4 2 -1.1 -0.6 26.3 79.4 -5.2 227 1.2
7250 17.9 64.2 255 3 2 -1.2 -0.7 25.5 77.8 -6.1 225 1.1
7000 17.8 64.0 270 2 1 -2.2 -1.2 24.6 76.3 -7.0 223 1.1
6750 17.5 63.5 310 2 1 -0.3 -0.2 23.7 74.7 -8.0 224 1.1
6500 17.6 63.7 330 1 1 4.0 2.2 23.1 73.6 -8.6 212 1.1
6250 18.0 64.4 350 1 0 4.5 2.5 22.7 72.9 -9.1 195 1.0
6000 18.3 64.9 030 1 0 4.9 2.7 22.3 72.2 -9.5 178 0.9
5750 18.6 65.5 060 1 0 3.9 2.1 22.0 71.6 -9.9 161 0.8
5500 18.8 65.8 095 1 0 0.3 0.2 21.4 70.5 -10.5 149 0.8
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/22/2025 at 0900 MDT | 08/22/2025 at 1200 MDT
|
CAPE... +153.7 LI... -1.4 | CAPE... +612.5 LI... -3.0
CINH... -370.7 K Index... +24.4 | CINH... -111.6 K Index... +26.2
|
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 -66.2 -87.2 290 27 14 1.1 0.6 | -65.9 -86.6 285 26 13 1.1 0.6
45000 -61.7 -79.1 285 38 20 6.2 3.4 | -61.3 -78.3 285 36 19 6.3 3.4
40000 -52.0 -61.6 285 40 21 7.8 4.3 | -51.6 -60.9 280 41 21 7.6 4.2
38000 -47.3 -53.1 285 39 20 7.8 4.3 | -47.0 -52.6 280 39 20 7.6 4.2
36000 -42.6 -44.7 285 38 20 7.7 4.2 | -42.5 -44.5 285 38 20 7.5 4.1
34000 -37.5 -35.5 280 29 15 7.6 4.2 | -37.4 -35.3 280 32 16 7.5 4.1
32000 -32.9 -27.2 280 22 11 8.5 4.7 | -33.0 -27.4 280 27 14 8.3 4.6
30000 -28.1 -18.6 280 20 10 8.1 4.5 | -28.2 -18.8 275 24 12 8.0 4.4
29000 -25.6 -14.1 285 19 10 8.1 4.5 | -25.8 -14.4 275 22 11 8.0 4.4
28000 -23.4 -10.1 285 18 9 6.6 3.6 | -23.6 -10.5 275 21 11 7.2 4.0
27000 -21.4 -6.5 285 17 9 6.7 3.7 | -21.4 -6.5 275 20 11 7.3 4.0
26000 -19.4 -2.9 285 15 8 6.7 3.7 | -19.2 -2.6 275 20 10 7.3 4.0
25000 -17.5 0.5 285 14 7 6.1 3.4 | -17.1 1.2 280 20 10 6.3 3.4
24000 -15.7 3.7 290 15 8 5.9 3.2 | -15.4 4.3 280 20 10 5.8 3.2
23000 -14.0 6.8 295 16 8 5.9 3.3 | -13.7 7.3 280 19 10 5.9 3.2
22000 -12.2 10.0 300 17 9 6.9 3.8 | -12.0 10.4 285 19 10 6.5 3.6
21000 -10.2 13.6 300 17 9 7.1 3.9 | -10.1 13.8 285 17 9 6.7 3.7
20000 -8.1 17.4 305 16 8 7.2 4.0 | -8.1 17.4 285 15 8 6.8 3.7
19500 -7.1 19.2 305 16 8 7.5 4.1 | -6.6 20.1 285 14 7 7.6 4.2
19000 -5.2 22.6 305 15 8 8.6 4.7 | -5.5 22.1 285 14 7 7.7 4.2
18500 -4.0 24.8 305 14 7 8.6 4.7 | -4.4 24.1 285 13 7 7.9 4.3
18000 -2.7 27.1 305 13 7 8.7 4.8 | -3.1 26.4 290 13 7 8.7 4.8
17500 -1.4 29.5 305 12 6 8.7 4.8 | -1.8 28.8 290 13 7 8.7 4.8
17000 -0.1 31.8 305 12 6 8.9 4.9 | -0.6 30.9 295 13 7 8.8 4.8
16500 1.2 34.2 305 12 6 8.9 4.9 | 0.8 33.4 295 13 7 8.9 4.9
16000 2.5 36.5 305 12 6 9.0 4.9 | 2.1 35.8 295 13 7 8.9 4.9
15500 3.9 39.0 305 12 6 9.1 5.0 | 3.4 38.1 300 13 7 8.9 4.9
15000 5.2 41.4 305 12 6 9.1 5.0 | 4.7 40.5 300 13 7 9.0 4.9
14500 6.5 43.7 300 12 6 8.8 4.8 | 5.9 42.6 305 12 6 8.2 4.5
14000 7.8 46.0 300 12 6 8.8 4.9 | 7.2 45.0 305 11 6 8.3 4.6
13500 9.1 48.4 300 11 6 8.2 4.5 | 8.3 46.9 310 11 5 7.5 4.1
13000 10.3 50.5 295 11 5 8.2 4.5 | 9.4 48.9 315 10 5 7.4 4.1
12500 11.5 52.7 295 10 5 7.8 4.3 | 10.5 50.9 325 9 5 7.0 3.9
12000 12.6 54.7 295 9 4 7.6 4.2 | 11.4 52.5 330 8 4 6.9 3.8
11500 13.7 56.7 295 8 4 7.0 3.8 | 12.4 54.3 340 8 4 6.4 3.5
11000 14.7 58.5 295 7 3 6.4 3.5 | 13.3 55.9 350 8 4 5.8 3.2
10500 15.6 60.1 295 6 3 3.0 1.7 | 14.1 57.4 355 8 4 2.4 1.3
10250 15.7 60.3 290 6 3 3.0 1.6 | 14.1 57.4 355 9 4 2.4 1.3
10000 16.1 61.0 290 5 3 7.2 4.0 | 14.5 58.1 360 9 4 6.7 3.7
9750 16.6 61.9 295 5 3 6.8 3.7 | 14.8 58.6 360 9 5 5.9 3.2
9500 17.0 62.6 295 5 2 4.5 2.4 | 15.2 59.4 005 9 5 4.5 2.5
9250 17.2 63.0 295 4 2 1.9 1.1 | 15.4 59.7 005 9 5 3.5 1.9
9000 17.3 63.1 290 4 2 3.1 1.7 | 15.7 60.3 005 9 5 6.5 3.6
8750 17.5 63.5 300 4 2 3.3 1.8 | 16.3 61.3 005 10 5 7.7 4.2
8500 17.7 63.9 310 4 2 0.7 0.4 | 16.7 62.1 010 9 5 5.8 3.2
8250 17.5 63.5 320 4 2 -1.4 -0.8 | 17.0 62.6 010 9 5 3.8 2.1
8000 17.4 63.3 325 4 2 -0.3 -0.2 | 17.3 63.1 010 8 4 7.3 4.0
7750 17.3 63.1 335 4 2 0.7 0.4 | 18.0 64.4 015 8 4 10.5 5.8
7500 17.3 63.1 345 5 3 1.7 0.9 | 18.7 65.7 015 8 4 8.9 4.9
7250 17.4 63.3 355 6 3 1.5 0.8 | 19.3 66.7 015 8 4 7.6 4.2
7000 17.5 63.5 360 6 3 2.9 1.6 | 19.9 67.8 015 9 4 10.1 5.5
6750 17.8 64.0 010 7 3 7.2 3.9 | 20.8 69.4 015 8 4 12.4 6.8
6500 18.4 65.1 010 7 3 7.9 4.3 | 21.7 71.1 015 8 4 10.8 5.9
6250 18.9 66.0 010 6 3 7.6 4.2 | 22.4 72.3 015 8 4 10.6 5.8
6000 19.4 66.9 005 6 3 5.7 3.1 | 23.2 73.8 015 8 4 9.4 5.2
5750 19.9 67.8 005 6 3 10.5 5.7 | 24.0 75.2 015 9 4 15.8 8.7
5500 21.2 70.2 005 6 3 24.9 13.7 | 25.8 78.4 015 8 4 30.3 16.6
08/22/2025 at 1500 MDT | 08/22/2025 at 1800 MDT
|
CAPE... +922.7 LI... -3.4 | CAPE... +775.0 LI... -2.7
CINH... -9.4 K Index... +28.5 | CINH... -65.8 K Index... +32.2
|
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 -65.9 -86.6 290 26 13 0.6 0.4 | -66.8 -88.2 305 20 10 -0.6 -0.3
45000 -61.8 -79.2 285 36 19 6.2 3.4 | -63.3 -81.9 290 28 14 7.3 4.0
40000 -51.9 -61.4 285 40 21 8.1 4.5 | -51.8 -61.2 280 30 16 8.9 4.9
38000 -47.0 -52.6 285 39 20 8.1 4.5 | -46.4 -51.5 275 31 16 8.9 4.9
36000 -42.1 -43.8 285 37 19 8.0 4.4 | -41.1 -42.0 275 31 16 8.3 4.6
34000 -37.3 -35.1 285 36 18 8.0 4.4 | -36.3 -33.3 280 32 17 7.9 4.4
32000 -32.0 -25.6 285 35 18 8.3 4.6 | -31.0 -23.8 280 34 17 8.4 4.6
30000 -27.3 -17.1 280 32 16 7.8 4.3 | -26.6 -15.9 285 34 18 7.3 4.0
29000 -25.0 -13.0 275 30 16 7.8 4.3 | -24.5 -12.1 285 35 18 7.3 4.0
28000 -22.7 -8.9 275 29 15 7.7 4.2 | -22.4 -8.3 290 35 18 6.7 3.7
27000 -20.4 -4.7 275 28 14 7.7 4.2 | -20.4 -4.7 290 33 17 6.7 3.7
26000 -18.2 -0.8 275 27 14 7.7 4.2 | -18.4 -1.1 290 32 16 6.8 3.7
25000 -15.9 3.4 280 25 13 6.3 3.5 | -16.4 2.5 295 31 16 6.5 3.6
24000 -14.2 6.4 280 25 13 5.9 3.2 | -14.6 5.7 295 30 15 6.5 3.5
23000 -12.5 9.5 285 24 12 5.9 3.2 | -12.7 9.1 295 29 15 6.5 3.6
22000 -10.8 12.6 285 23 12 6.3 3.4 | -10.8 12.6 295 28 15 6.2 3.4
21000 -8.9 16.0 285 22 11 6.4 3.5 | -9.0 15.8 295 28 14 6.2 3.4
20000 -7.0 19.4 285 20 10 6.4 3.5 | -7.3 18.9 295 27 14 6.2 3.4
19500 -6.1 21.0 285 20 10 6.6 3.6 | -6.4 20.5 295 27 14 6.2 3.4
19000 -5.1 22.8 285 19 10 7.2 4.0 | -5.5 22.1 300 26 13 6.2 3.4
18500 -4.1 24.6 285 18 9 7.3 4.0 | -4.6 23.7 300 24 12 6.2 3.4
18000 -3.1 26.4 285 16 8 7.0 3.9 | -3.7 25.3 300 23 12 6.2 3.4
17500 -2.0 28.4 290 15 8 7.0 3.8 | -2.9 26.8 300 20 10 6.2 3.4
17000 -1.0 30.2 290 13 7 7.0 3.9 | -2.0 28.4 305 18 9 6.1 3.4
16500 0.5 32.9 300 10 5 7.2 3.9 | -1.1 30.0 300 16 8 5.7 3.1
16000 1.6 34.9 305 8 4 7.2 3.9 | -0.3 31.5 300 14 7 5.7 3.1
15500 2.6 36.7 315 7 3 7.1 3.9 | 1.1 34.0 300 11 6 6.7 3.7
15000 3.7 38.7 325 5 3 7.1 3.9 | 2.1 35.8 300 9 5 6.8 3.7
14500 4.7 40.5 335 5 2 6.9 3.8 | 3.2 37.8 300 8 4 8.0 4.4
14000 5.7 42.3 345 5 2 7.0 3.8 | 4.4 39.9 305 6 3 8.0 4.4
13500 6.6 43.9 355 5 3 6.9 3.8 | 5.6 42.1 305 5 3 7.3 4.0
13000 7.6 45.7 360 5 3 6.9 3.8 | 6.7 44.1 305 5 2 7.3 4.0
12500 8.6 47.5 010 5 3 7.4 4.1 | 7.7 45.9 305 4 2 6.9 3.8
12000 9.7 49.5 015 5 2 7.5 4.1 | 8.6 47.5 305 4 2 6.9 3.8
11500 10.8 51.4 025 5 2 7.5 4.1 | 9.5 49.1 300 3 2 6.7 3.7
11000 11.8 53.2 025 5 3 7.3 4.0 | 10.3 50.5 310 3 2 6.7 3.7
10500 12.8 55.0 030 5 3 3.7 2.0 | 11.1 52.0 320 3 2 3.5 1.9
10250 13.0 55.4 030 5 3 5.1 2.8 | 11.3 52.3 330 4 2 5.1 2.8
10000 13.6 56.5 035 5 3 9.5 5.2 | 11.9 53.4 335 4 2 9.8 5.4
9750 14.1 57.4 040 5 2 8.4 4.6 | 12.6 54.7 345 5 3 8.9 4.9
9500 14.7 58.5 040 5 2 7.1 3.9 | 13.1 55.6 350 6 3 5.8 3.2
9250 15.1 59.2 045 4 2 6.7 3.7 | 13.5 56.3 355 6 3 3.8 2.1
9000 15.7 60.3 045 4 2 10.8 5.9 | 13.9 57.0 355 6 3 7.8 4.3
8750 16.6 61.9 045 4 2 12.0 6.6 | 14.5 58.1 360 7 4 9.0 5.0
8500 17.3 63.1 045 4 2 9.4 5.1 | 15.0 59.0 005 8 4 5.9 3.2
8250 18.0 64.4 045 4 2 7.5 4.1 | 15.4 59.7 005 8 4 4.7 2.6
8000 18.6 65.5 045 4 2 10.7 5.9 | 15.8 60.4 010 9 5 7.5 4.1
7750 19.5 67.1 045 4 2 12.0 6.6 | 16.4 61.5 010 10 5 8.2 4.5
7500 20.3 68.5 045 4 2 9.1 5.0 | 16.9 62.4 015 10 5 5.9 3.2
7250 20.9 69.6 045 3 2 7.7 4.2 | 17.3 63.1 015 11 5 5.3 2.9
7000 21.5 70.7 045 3 2 11.3 6.2 | 17.7 63.9 015 11 6 8.0 4.4
6750 22.5 72.5 040 3 2 12.7 7.0 | 18.4 65.1 020 12 6 8.7 4.8
6500 23.3 73.9 040 3 2 9.9 5.4 | 18.9 66.0 020 12 6 6.3 3.5
6250 24.1 75.4 040 3 2 10.9 6.0 | 19.4 66.9 020 12 6 7.3 4.0
6000 24.9 76.8 040 3 1 8.9 4.9 | 19.8 67.6 020 13 7 5.9 3.2
5750 25.6 78.1 040 3 1 14.7 8.1 | 20.3 68.5 020 12 6 9.1 5.0
5500 27.3 81.1 040 3 1 29.8 16.3 | 21.3 70.3 020 10 5 17.7 9.7
________________________________________________________________________________
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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