Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
800
UXUS97 KBOU 171325
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0724 MDT Tuesday, June 17, 2025
This forecast is for Tuesday, June 17, 2025:
If the trigger temperature of 74.0 F/23.3 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 102 ft/min (0.5 m/s)
Maximum height of thermals.................. 9672 ft MSL (4310 ft AGL)
Forecast maximum temperature................... 75.0 F/24.3 C
Time of trigger temperature.................... 1130 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................. 8408 ft MSL (3046 ft AGL)
Thermal soaring outlook for Wednesday 06/18.... Good
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... Trending the same
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 22090 ft MSL (16728 ft AGL)
Wave soaring outlook for Wednesday 06/18....... Fair
Remarks...
Sunrise/Sunset.................... 05:31:01 / 20:30:04 MDT
Total possible sunshine........... 14 hr 59 min 3 sec (899 min 3 sec)
Altitude of sun at 13:00:33 MDT... 73.63 degrees
Upper air data from numerical model forecast valid on 06/17/2025 at 0600 MDT
Freezing level.................. 15383 ft MSL (10021 ft AGL)
Convective condensation level... 10815 ft MSL (5453 ft AGL)
Lifted condensation level....... 10111 ft MSL (4749 ft AGL)
Lifted index.................... -8.7
K index......................... +27.1
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 -61.3 -78.3 255 35 18 1.6 0.9 M M M M M
45000 -58.0 -72.4 250 39 20 4.2 2.3 M M M M M
40000 -51.7 -61.1 260 47 24 4.4 2.4 M M M M M
38000 -49.0 -56.2 255 44 23 4.5 2.5 M M M M M
36000 -46.3 -51.3 255 42 22 4.5 2.5 M M M M M
34000 -43.1 -45.6 250 36 19 4.9 2.7 M M M M M
32000 -40.1 -40.2 250 29 15 4.9 2.7 M M M M M
30000 -36.2 -33.2 245 27 14 7.5 4.1 38.9 101.9 11.4 M M
29000 -33.9 -29.0 245 26 14 7.5 4.1 38.0 100.3 10.8 M M
28000 -31.7 -25.1 245 26 13 7.4 4.1 37.2 99.0 10.3 M M
27000 -29.3 -20.7 245 27 14 8.1 4.5 36.5 97.6 9.9 M M
26000 -26.9 -16.4 245 28 14 8.1 4.5 35.8 96.5 9.4 M M
25000 -24.5 -12.1 245 29 15 8.1 4.5 35.3 95.5 9.1 M M
24000 -22.2 -8.0 245 30 15 7.5 4.1 34.6 94.2 8.6 M M
23000 -20.0 -4.0 245 32 16 7.5 4.1 33.7 92.6 7.9 M M
22000 -17.8 -0.0 245 33 17 7.4 4.1 32.9 91.2 7.3 M M
21000 -15.4 4.3 245 33 17 8.6 4.7 32.3 90.2 6.9 M M
20000 -12.8 9.0 250 33 17 8.6 4.7 31.9 89.4 6.6 M M
19500 -10.9 12.4 250 32 17 8.6 4.7 31.6 88.9 6.4 M M
19000 -9.6 14.7 250 32 16 9.1 5.0 31.5 88.7 6.3 M M
18500 -8.3 17.1 255 31 16 9.1 5.0 31.4 88.4 6.2 M M
18000 -6.9 19.6 255 30 16 9.1 5.0 31.3 88.3 6.1 M M
17500 -5.6 21.9 255 29 15 9.1 5.0 31.1 88.1 6.1 M M
17000 -4.2 24.4 260 28 15 9.1 5.0 31.0 87.9 6.0 M M
16500 -2.9 26.8 260 27 14 9.2 5.1 30.9 87.7 5.9 M M
16000 -1.5 29.3 260 26 13 9.2 5.1 30.9 87.5 5.8 M M
15500 -0.2 31.6 260 24 13 8.9 4.9 30.8 87.4 5.8 M M
15000 1.1 34.0 260 22 12 8.7 4.8 30.6 87.1 5.6 M M
14500 2.3 36.1 260 20 10 8.6 4.7 30.4 86.8 5.4 M M
14000 3.5 38.3 265 18 9 7.8 4.3 30.1 86.3 5.1 M M
13500 4.6 40.3 265 16 8 8.0 4.4 29.8 85.7 4.8 M M
13000 5.6 42.1 265 13 7 7.0 3.8 29.5 85.0 4.4 M M
12500 6.6 43.9 270 11 6 7.3 4.0 29.0 84.3 3.9 M M
12000 7.5 45.5 275 9 4 6.2 3.4 28.6 83.4 3.4 M M
11500 8.3 46.9 285 6 3 6.3 3.5 28.0 82.4 2.8 M M
11000 9.1 48.4 300 5 2 5.2 2.9 27.4 81.3 2.1 M M
10500 9.8 49.6 325 4 2 4.9 2.7 26.7 80.0 1.3 M M
10250 10.1 50.2 340 4 2 6.3 3.4 26.3 79.3 0.9 M M
10000 10.6 51.1 345 4 2 6.1 3.4 26.1 78.9 0.6 M M
9750 10.9 51.6 350 5 2 4.5 2.5 25.7 78.2 0.2 M M
9500 11.2 52.2 350 5 3 5.6 3.1 25.3 77.6 -0.2 293 1.5
9250 11.5 52.7 355 5 3 3.2 1.7 25.0 76.9 -0.6 277 1.4
9000 11.5 52.7 355 6 3 1.3 0.7 24.3 75.8 -1.3 268 1.4
8750 11.6 52.9 355 6 3 2.3 1.3 23.7 74.7 -2.0 258 1.3
8500 11.7 53.1 355 6 3 1.7 1.0 23.1 73.6 -2.6 248 1.3
8250 11.8 53.2 355 7 3 3.3 1.8 22.5 72.5 -3.2 238 1.2
8000 12.1 53.8 360 7 4 4.7 2.6 22.1 71.8 -3.7 222 1.1
7750 12.4 54.3 010 8 4 4.3 2.4 21.7 71.1 -4.1 206 1.0
7500 12.6 54.7 010 8 4 4.3 2.4 21.3 70.3 -4.6 190 1.0
7250 13.0 55.4 015 9 4 4.6 2.5 20.9 69.6 -5.0 173 0.9
7000 13.3 55.9 020 10 5 4.8 2.6 20.5 68.9 -5.4 156 0.8
6750 13.6 56.5 020 10 5 5.5 3.0 20.1 68.3 -5.8 138 0.7
6500 14.0 57.2 020 10 5 5.4 3.0 19.8 67.7 -6.2 119 0.6
6250 14.4 57.9 015 10 5 4.5 2.5 19.5 67.0 -6.6 101 0.5
6000 14.7 58.5 010 9 5 4.2 2.3 19.1 66.3 -7.0 84 0.4
5750 15.0 59.0 005 9 5 5.2 2.9 18.7 65.6 -7.4 67 0.3
5500 15.5 59.9 005 7 4 9.0 4.9 18.5 65.2 -7.7 45 0.2
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
06/17/2025 at 0900 MDT | 06/17/2025 at 1200 MDT
|
CAPE... +1430.4 LI... -4.9 | CAPE... +1745.4 LI... -6.3
CINH... -75.8 K Index... +23.3 | CINH... -46.3 K Index... +26.1
|
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 -59.9 -75.8 275 31 16 1.5 0.8 | -58.6 -73.5 285 30 15 1.7 0.9
45000 -57.0 -70.6 265 36 18 3.4 1.9 | -55.6 -68.1 280 33 17 3.1 1.7
40000 -51.9 -61.4 260 40 20 3.9 2.2 | -50.9 -59.6 260 32 17 3.2 1.8
38000 -49.1 -56.4 250 36 19 4.6 2.5 | -48.8 -55.8 260 30 16 3.5 1.9
36000 -46.3 -51.3 245 34 17 4.6 2.5 | -46.7 -52.1 260 29 15 3.5 1.9
34000 -43.1 -45.6 240 30 16 5.0 2.7 | -44.2 -47.6 260 26 13 4.7 2.6
32000 -40.1 -40.2 240 27 14 5.0 2.7 | -41.0 -41.8 255 22 12 4.7 2.6
30000 -36.8 -34.2 235 24 12 5.9 3.2 | -37.4 -35.3 255 20 10 6.9 3.8
29000 -35.0 -31.0 235 22 11 5.9 3.2 | -35.3 -31.5 255 19 10 6.9 3.8
28000 -33.3 -27.9 235 20 10 5.8 3.2 | -33.3 -27.9 260 19 10 6.9 3.8
27000 -31.1 -24.0 240 22 11 8.0 4.4 | -31.0 -23.8 260 20 10 7.7 4.2
26000 -28.7 -19.7 245 25 13 8.0 4.4 | -28.7 -19.7 260 22 11 7.8 4.3
25000 -26.4 -15.5 245 28 14 8.0 4.4 | -26.4 -15.5 265 24 12 7.8 4.3
24000 -23.8 -10.8 250 30 15 8.8 4.8 | -24.0 -11.2 265 26 13 8.3 4.6
23000 -21.2 -6.2 250 31 16 8.8 4.9 | -21.6 -6.9 270 27 14 8.3 4.6
22000 -18.6 -1.5 250 32 17 8.9 4.9 | -19.1 -2.4 270 28 14 8.3 4.6
21000 -16.0 3.2 250 33 17 8.9 4.9 | -16.6 2.1 270 28 14 8.2 4.5
20000 -13.3 8.1 250 32 16 8.9 4.9 | -14.2 6.4 270 27 14 8.2 4.5
19500 -12.0 10.4 250 32 16 8.9 4.9 | -13.0 8.6 270 27 14 8.2 4.5
19000 -10.0 14.0 255 31 16 9.1 5.0 | -11.8 10.8 275 26 13 8.5 4.6
18500 -8.7 16.3 255 30 15 9.1 5.0 | -10.5 13.1 275 25 13 8.9 4.9
18000 -7.3 18.9 255 29 15 9.1 5.0 | -9.2 15.4 275 24 13 8.9 4.9
17500 -5.9 21.4 255 28 14 9.2 5.0 | -7.8 18.0 275 24 12 9.1 5.0
17000 -4.6 23.7 255 27 14 9.2 5.0 | -6.5 20.3 275 23 12 9.2 5.0
16500 -3.2 26.2 260 27 14 9.2 5.1 | -5.1 22.8 275 22 11 9.3 5.1
16000 -1.8 28.8 260 26 13 9.2 5.1 | -3.7 25.3 275 22 11 9.6 5.2
15500 -0.5 31.1 260 25 13 9.2 5.0 | -1.6 29.1 275 21 11 9.5 5.2
15000 0.9 33.6 260 25 13 9.1 5.0 | -0.2 31.6 280 20 10 9.4 5.2
14500 2.3 36.1 260 24 12 9.0 4.9 | 1.2 34.2 280 19 10 9.3 5.1
14000 3.5 38.3 260 22 11 8.1 4.5 | 2.6 36.7 280 18 9 9.2 5.0
13500 4.6 40.3 260 21 11 8.3 4.5 | 3.9 39.0 280 17 9 9.1 5.0
13000 5.7 42.3 260 19 10 6.6 3.6 | 5.2 41.4 280 16 8 8.5 4.6
12500 6.6 43.9 260 16 8 7.0 3.8 | 6.5 43.7 280 15 7 8.7 4.8
12000 7.4 45.3 260 13 7 5.6 3.1 | 7.5 45.5 280 13 7 6.3 3.5
11500 8.1 46.6 255 10 5 5.9 3.2 | 8.4 47.1 285 11 6 6.8 3.8
11000 8.8 47.8 255 7 4 4.4 2.4 | 9.2 48.6 290 10 5 4.3 2.3
10500 9.3 48.7 255 6 3 4.0 2.2 | 9.7 49.5 295 8 4 4.8 2.6
10250 9.5 49.1 255 5 2 5.9 3.2 | 10.0 50.0 300 7 4 3.6 2.0
10000 9.9 49.8 265 4 2 5.1 2.8 | 10.2 50.4 300 7 4 3.9 2.2
9750 10.1 50.2 275 4 2 2.4 1.3 | 10.5 50.9 305 7 3 5.2 2.9
9500 10.3 50.5 280 4 2 3.5 1.9 | 10.8 51.4 315 6 3 5.8 3.2
9250 10.5 50.9 285 3 2 1.9 1.0 | 11.1 52.0 330 6 3 2.3 1.3
9000 10.5 50.9 285 3 2 0.6 0.3 | 11.2 52.2 330 5 3 2.4 1.3
8750 10.5 50.9 300 4 2 1.2 0.7 | 11.5 52.7 335 6 3 6.0 3.3
8500 10.5 50.9 315 4 2 0.6 0.3 | 11.8 53.2 340 6 3 5.1 2.8
8250 10.5 50.9 320 5 3 2.6 1.4 | 12.1 53.8 345 6 3 3.8 2.1
8000 10.8 51.4 330 5 3 4.7 2.6 | 12.3 54.1 350 6 3 4.2 2.3
7750 11.1 52.0 335 6 3 4.4 2.4 | 12.7 54.9 355 6 3 7.2 4.0
7500 11.4 52.5 345 7 4 4.6 2.5 | 13.2 55.8 360 6 3 6.9 3.8
7250 11.7 53.1 350 8 4 4.3 2.3 | 13.6 56.5 005 6 3 4.9 2.7
7000 12.0 53.6 355 9 4 4.3 2.3 | 13.9 57.0 010 6 3 4.7 2.6
6750 12.4 54.3 355 9 5 7.1 3.9 | 14.3 57.7 015 6 3 9.4 5.1
6500 13.0 55.4 360 10 5 8.7 4.7 | 15.0 59.0 020 6 3 10.1 5.6
6250 13.6 56.5 360 9 5 7.9 4.3 | 15.7 60.3 025 6 3 7.8 4.3
6000 14.1 57.4 355 9 5 7.6 4.2 | 16.3 61.3 025 6 3 7.8 4.3
5750 14.7 58.5 355 9 5 9.5 5.2 | 16.9 62.4 025 6 3 12.1 6.6
5500 15.6 60.1 355 8 4 15.0 8.2 | 18.1 64.6 025 5 3 21.4 11.7
06/17/2025 at 1500 MDT | 06/17/2025 at 1800 MDT
|
CAPE... +1617.3 LI... -5.4 | CAPE... +1021.0 LI... -4.2
CINH... -59.4 K Index... +27.9 | CINH... -62.4 K Index... +26.7
|
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 -58.1 -72.6 290 31 16 1.6 0.9 | -58.6 -73.5 305 34 18 2.3 1.3
45000 -55.5 -67.9 290 38 19 2.4 1.3 | -55.4 -67.7 305 45 23 1.7 0.9
40000 -51.6 -60.9 280 32 17 3.4 1.9 | -52.6 -62.7 305 46 24 4.3 2.3
38000 -49.4 -56.9 280 27 14 3.7 2.0 | -49.6 -57.3 300 36 19 4.9 2.7
36000 -47.2 -53.0 280 21 11 3.7 2.0 | -46.6 -51.9 290 27 14 4.9 2.7
34000 -44.1 -47.4 275 20 10 6.0 3.3 | -43.2 -45.8 285 23 12 6.2 3.4
32000 -40.6 -41.1 270 21 11 6.0 3.3 | -39.5 -39.1 280 20 10 6.2 3.4
30000 -36.3 -33.3 260 24 12 7.9 4.4 | -35.4 -31.7 275 22 11 7.3 4.0
29000 -34.0 -29.2 260 25 13 8.0 4.4 | -32.7 -26.9 275 24 13 7.3 4.0
28000 -31.6 -24.9 260 27 14 8.0 4.4 | -30.5 -22.9 275 26 14 7.3 4.0
27000 -28.7 -19.7 260 29 15 7.7 4.2 | -28.4 -19.1 275 28 14 7.2 3.9
26000 -26.4 -15.5 260 30 15 7.8 4.3 | -26.2 -15.2 280 30 15 7.2 3.9
25000 -24.1 -11.4 265 31 16 7.8 4.3 | -24.1 -11.4 285 31 16 7.2 3.9
24000 -21.9 -7.4 265 31 16 7.2 3.9 | -22.0 -7.6 285 33 17 7.1 3.9
23000 -19.8 -3.6 265 32 17 7.2 3.9 | -19.9 -3.8 285 34 17 7.1 3.9
22000 -17.7 0.1 270 33 17 7.2 3.9 | -17.8 -0.0 290 35 18 7.1 3.9
21000 -15.6 3.9 270 33 17 7.1 3.9 | -15.8 3.6 290 36 18 6.8 3.7
20000 -13.5 7.7 275 33 17 7.2 3.9 | -13.8 7.2 290 36 19 6.8 3.7
19500 -12.5 9.5 280 33 17 7.2 3.9 | -12.8 9.0 290 37 19 6.9 3.8
19000 -11.4 11.5 280 33 17 7.4 4.0 | -11.8 10.8 295 37 19 7.3 4.0
18500 -10.3 13.5 280 33 17 7.6 4.2 | -10.6 12.9 295 37 19 8.2 4.5
18000 -9.2 15.4 285 33 17 7.5 4.1 | -9.4 15.1 295 37 19 8.2 4.5
17500 -8.1 17.4 285 32 17 8.2 4.5 | -8.3 17.1 295 36 18 8.2 4.5
17000 -6.9 19.6 285 32 16 8.2 4.5 | -7.1 19.2 300 35 18 8.2 4.5
16500 -5.7 21.7 290 31 16 8.4 4.6 | -5.9 21.4 300 34 17 8.2 4.5
16000 -4.4 24.1 290 30 16 8.6 4.7 | -4.7 23.5 300 33 17 8.1 4.5
15500 -3.1 26.4 290 29 15 8.6 4.7 | -3.0 26.6 305 30 16 7.9 4.3
15000 -1.9 28.6 295 28 14 7.9 4.3 | -1.8 28.8 305 28 15 7.7 4.2
14500 -0.8 30.6 295 27 14 8.0 4.4 | -0.7 30.7 305 27 14 7.6 4.2
14000 0.3 32.5 295 25 13 7.1 3.9 | 0.3 32.5 305 24 13 7.3 4.0
13500 1.8 35.2 300 22 11 7.1 3.9 | 1.4 34.5 310 22 11 7.3 4.0
13000 2.8 37.0 300 20 10 7.0 3.8 | 2.3 36.1 310 20 10 6.6 3.6
12500 3.8 38.8 305 18 9 7.0 3.9 | 3.3 37.9 315 17 9 6.7 3.7
12000 4.8 40.6 310 16 8 7.2 3.9 | 4.2 39.6 315 15 8 6.2 3.4
11500 5.9 42.6 315 15 8 7.2 3.9 | 5.1 41.2 320 13 7 6.2 3.4
11000 6.9 44.4 320 14 7 7.1 3.9 | 6.0 42.8 325 12 6 6.5 3.6
10500 7.9 46.2 325 13 7 7.6 4.2 | 6.9 44.4 335 11 6 7.4 4.1
10250 8.3 46.9 330 13 7 4.0 2.2 | 7.4 45.3 340 11 5 2.7 1.5
10000 8.5 47.3 330 12 6 4.9 2.7 | 7.4 45.3 340 10 5 3.5 1.9
9750 9.1 48.4 335 12 6 8.8 4.8 | 8.0 46.4 350 11 5 8.5 4.7
9500 9.7 49.5 340 11 6 8.2 4.5 | 8.5 47.3 355 11 6 7.8 4.3
9250 10.2 50.4 345 11 6 5.0 2.8 | 9.0 48.2 360 11 6 4.2 2.3
9000 10.4 50.7 345 10 5 4.5 2.5 | 9.2 48.6 005 11 6 3.9 2.1
8750 10.8 51.4 350 10 5 7.3 4.0 | 9.6 49.3 010 12 6 7.4 4.1
8500 11.3 52.3 355 10 5 6.4 3.5 | 10.1 50.2 015 12 6 6.4 3.5
8250 11.7 53.1 355 9 5 4.9 2.7 | 10.4 50.7 020 12 6 4.8 2.6
8000 11.9 53.4 360 8 4 5.0 2.7 | 10.7 51.3 020 12 6 5.0 2.7
7750 12.4 54.3 010 8 4 7.3 4.0 | 11.1 52.0 025 11 6 7.9 4.3
7500 12.8 55.0 015 9 5 6.8 3.8 | 11.7 53.1 030 11 6 7.6 4.1
7250 13.2 55.8 015 9 5 5.4 2.9 | 12.1 53.8 030 10 5 5.9 3.2
7000 13.6 56.5 020 9 5 5.5 3.0 | 12.5 54.5 035 10 5 5.9 3.2
6750 14.1 57.4 025 9 5 9.8 5.4 | 13.0 55.4 035 10 5 9.9 5.4
6500 14.9 58.8 025 10 5 10.2 5.6 | 13.8 56.8 040 9 5 10.7 5.9
6250 15.5 59.9 030 10 5 8.0 4.4 | 14.5 58.1 040 9 5 8.9 4.9
6000 16.1 61.0 030 9 5 7.9 4.3 | 15.2 59.4 040 9 5 8.9 4.9
5750 16.8 62.2 030 9 5 12.0 6.6 | 15.8 60.4 035 9 4 11.6 6.4
5500 18.0 64.4 035 9 5 22.2 12.2 | 16.9 62.4 040 8 4 18.8 10.3
________________________________________________________________________________
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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