Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
933
UXUS97 KBOU 090120
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1919 MDT Friday, August 8, 2025
This forecast is for Saturday, August 9, 2025:
If the trigger temperature of 76.2 F/24.6 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1072 ft/min (5.4 m/s)
Maximum height of thermals.................. 17625 ft MSL (12342 ft AGL)
Forecast maximum temperature................... 89.0 F/32.1 C
Time of trigger temperature.................... 1100 MDT
Time of overdevelopment........................ 1600 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 11398 ft MSL (6115 ft AGL)
Thermal soaring outlook for Sunday 08/10....... Good
Wave Soaring Index............................. Good
Wave Soaring Index trend (to 1800 MDT)......... Becoming poor
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 46346 ft MSL (41063 ft AGL)
Wave soaring outlook for Sunday 08/10.......... Fair
Remarks... Scattered afternoon thunderstorms
Sunrise/Sunset.................... 06:06:31 / 20:03:20 MDT
Total possible sunshine........... 13 hr 56 min 49 sec (836 min 49 sec)
Altitude of sun at 13:04:56 MDT... 65.81 degrees
Upper air data from numerical model forecast valid on 08/09/2025 at 0600 MDT
Freezing level.................. 15454 ft MSL (10171 ft AGL)
Convective condensation level... 13950 ft MSL (8667 ft AGL)
Lifted condensation level....... 14650 ft MSL (9367 ft AGL)
Lifted index.................... -5.1
K index......................... +22.8
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 -62.7 -80.9 280 32 16 -0.4 -0.2 M M M M M
45000 -61.8 -79.2 275 44 23 3.8 2.1 M M M M M
40000 -55.3 -67.5 270 43 22 6.7 3.7 M M M M M
38000 -51.3 -60.3 265 42 22 6.8 3.7 M M M M M
36000 -47.2 -53.0 265 41 21 6.6 3.6 M M M M M
34000 -42.2 -44.0 270 41 21 8.8 4.9 M M M M M
32000 -36.9 -34.4 270 41 21 8.8 4.8 M M M M M
30000 -31.6 -24.9 270 40 21 8.7 4.8 44.7 112.5 9.9 M M
29000 -28.4 -19.1 270 40 20 8.7 4.8 44.2 111.6 9.7 M M
28000 -25.9 -14.6 270 39 20 7.6 4.2 43.9 111.0 9.5 M M
27000 -23.7 -10.7 275 39 20 7.3 4.0 42.8 109.1 8.8 M M
26000 -21.5 -6.7 275 40 20 7.3 4.0 41.9 107.5 8.1 M M
25000 -19.3 -2.7 275 40 20 7.2 4.0 41.1 106.0 7.6 M M
24000 -17.4 0.7 275 40 21 6.2 3.4 39.8 103.6 6.5 M M
23000 -15.6 3.9 275 41 21 6.2 3.4 38.5 101.2 5.5 M M
22000 -13.8 7.2 275 42 22 6.2 3.4 37.3 99.1 4.5 M M
21000 -12.1 10.2 275 42 22 6.0 3.3 35.9 96.5 3.3 M M
20000 -10.3 13.5 275 43 22 6.0 3.3 34.5 94.2 2.2 M M
19500 -9.5 14.9 275 43 22 5.9 3.2 33.9 93.0 1.6 M M
19000 -8.5 16.7 275 43 22 7.2 3.9 33.4 92.1 1.1 M M
18500 -7.5 18.5 275 43 22 7.2 4.0 32.9 91.3 0.7 M M
18000 -6.4 20.5 275 43 22 7.4 4.1 32.5 90.5 0.3 M M
17500 -5.3 22.5 275 41 21 7.8 4.3 32.1 89.8 -0.0 1067 5.4
17000 -4.2 24.4 275 39 20 7.8 4.3 31.8 89.3 -0.3 1018 5.2
16500 -3.0 26.6 275 37 19 8.6 4.7 31.5 88.8 -0.6 968 4.9
16000 -1.7 28.9 275 35 18 8.6 4.7 31.4 88.4 -0.8 915 4.6
15500 -0.4 31.3 275 32 17 8.9 4.9 31.2 88.1 -1.0 862 4.4
15000 0.9 33.6 275 30 15 9.1 5.0 31.1 87.9 -1.1 807 4.1
14500 2.9 37.2 275 27 14 9.2 5.0 30.9 87.6 -1.3 724 3.7
14000 4.3 39.7 270 25 13 9.2 5.1 30.8 87.5 -1.4 668 3.4
13500 5.7 42.3 270 24 12 9.0 4.9 30.7 87.3 -1.5 612 3.1
13000 6.9 44.4 265 22 11 8.7 4.8 30.6 87.0 -1.7 559 2.8
12500 8.2 46.8 265 20 11 8.0 4.4 30.4 86.7 -1.9 507 2.6
12000 9.2 48.6 260 18 9 6.6 3.6 29.9 85.9 -2.4 463 2.4
11500 10.1 50.2 250 16 8 6.2 3.4 29.5 85.0 -2.9 421 2.1
11000 10.7 51.3 240 14 7 4.5 2.5 28.7 83.7 -3.8 387 2.0
10500 11.3 52.3 225 12 6 2.5 1.4 27.9 82.3 -4.7 355 1.8
10250 11.4 52.5 225 11 6 2.6 1.5 27.3 81.1 -5.3 345 1.8
10000 11.7 53.1 220 11 5 6.4 3.5 26.9 80.4 -5.8 328 1.7
9750 12.1 53.8 210 10 5 6.3 3.5 26.6 79.9 -6.1 310 1.6
9500 12.4 54.3 200 9 5 5.9 3.2 26.3 79.4 -6.5 291 1.5
9250 12.8 55.0 190 9 5 4.9 2.7 26.0 78.8 -6.9 274 1.4
9000 13.2 55.8 185 9 5 6.7 3.7 25.7 78.2 -7.3 255 1.3
8750 13.7 56.7 175 10 5 8.5 4.7 25.5 78.0 -7.5 232 1.2
8500 14.2 57.6 170 10 5 7.1 3.9 25.4 77.7 -7.7 208 1.1
8250 14.7 58.5 165 11 6 5.4 3.0 25.1 77.2 -8.0 188 1.0
8000 15.1 59.2 160 12 6 6.9 3.8 24.8 76.7 -8.4 169 0.9
7750 15.6 60.1 160 13 7 9.5 5.2 24.7 76.5 -8.5 144 0.7
7500 16.3 61.3 155 14 7 7.5 4.1 24.7 76.4 -8.6 117 0.6
7250 16.8 62.2 160 14 7 5.2 2.9 24.4 75.8 -8.9 96 0.5
7000 17.2 63.0 160 13 7 6.3 3.5 24.1 75.3 -9.2 74 0.4
6750 17.8 64.0 165 13 7 7.5 4.1 23.8 74.9 -9.4 50 0.3
6500 18.4 65.1 170 12 6 6.6 3.6 23.7 74.6 -9.5 24 0.1
6250 18.9 66.0 175 11 6 5.0 2.8 23.3 74.0 -9.8 2 0.0
6000 19.4 66.9 175 10 5 6.6 3.6 23.0 73.5 -10.1 M M
5750 19.9 67.8 180 10 5 3.4 1.9 22.8 73.0 -10.3 M M
5500 19.8 67.6 180 7 4 -5.2 -2.8 21.9 71.5 -11.1 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/09/2025 at 0900 MDT | 08/09/2025 at 1200 MDT
|
CAPE... +999.7 LI... -4.2 | CAPE... +1025.4 LI... -3.8
CINH... -90.4 K Index... +19.5 | CINH... -20.6 K Index... +21.9
|
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 -61.9 -79.4 275 24 13 -0.6 -0.3 | -61.7 -79.1 260 25 13 0.3 0.2
45000 -61.2 -78.2 265 40 21 3.3 1.8 | -60.4 -76.7 265 43 22 2.1 1.2
40000 -55.8 -68.4 265 42 21 6.9 3.8 | -56.6 -69.9 260 44 23 7.5 4.1
38000 -51.7 -61.1 265 41 21 6.9 3.8 | -52.2 -62.0 260 43 22 7.4 4.1
36000 -47.6 -53.7 270 41 21 6.8 3.7 | -47.7 -53.9 260 42 21 7.3 4.0
34000 -42.5 -44.5 270 41 21 8.9 4.9 | -42.6 -44.7 260 40 21 8.8 4.8
32000 -37.2 -35.0 270 40 20 8.9 4.9 | -37.4 -35.3 260 39 20 8.8 4.8
30000 -31.5 -24.7 270 39 20 8.3 4.6 | -31.8 -25.2 260 38 20 8.2 4.5
29000 -29.0 -20.2 270 38 20 8.3 4.6 | -29.4 -20.9 260 38 20 8.2 4.5
28000 -26.5 -15.7 270 38 19 7.6 4.2 | -26.9 -16.4 260 38 19 7.7 4.3
27000 -24.3 -11.7 270 37 19 7.4 4.0 | -24.7 -12.5 265 38 19 7.6 4.2
26000 -22.1 -7.8 270 37 19 7.4 4.0 | -22.4 -8.3 265 37 19 7.6 4.2
25000 -19.9 -3.8 270 37 19 7.3 4.0 | -20.1 -4.2 265 37 19 7.5 4.1
24000 -18.0 -0.4 270 37 19 6.2 3.4 | -18.3 -0.9 265 38 19 6.2 3.4
23000 -16.2 2.8 270 38 19 6.3 3.4 | -16.4 2.5 265 38 20 6.2 3.4
22000 -14.3 6.3 275 38 20 6.3 3.4 | -14.6 5.7 270 39 20 6.3 3.4
21000 -12.5 9.5 275 39 20 6.2 3.4 | -12.7 9.1 265 39 20 6.6 3.6
20000 -10.7 12.7 275 39 20 6.2 3.4 | -10.8 12.6 265 38 20 6.6 3.6
19500 -9.8 14.4 275 39 20 6.2 3.4 | -9.8 14.4 265 38 19 6.6 3.6
19000 -8.9 16.0 275 39 20 7.0 3.8 | -8.8 16.2 265 37 19 7.1 3.9
18500 -7.9 17.8 275 39 20 7.1 3.9 | -7.8 18.0 265 37 19 7.2 3.9
18000 -6.8 19.8 275 40 20 7.4 4.1 | -6.8 19.8 265 36 19 7.6 4.2
17500 -5.7 21.7 280 39 20 8.2 4.5 | -5.5 22.1 265 35 18 8.4 4.6
17000 -4.5 23.9 280 39 20 8.1 4.4 | -4.3 24.3 265 34 17 8.4 4.6
16500 -3.2 26.2 280 38 19 8.8 4.9 | -3.0 26.6 265 32 17 9.0 4.9
16000 -1.2 29.8 280 35 18 8.9 4.9 | -1.0 30.2 265 30 15 9.0 4.9
15500 0.0 32.0 280 33 17 8.2 4.5 | 0.3 32.5 265 29 15 8.5 4.7
15000 1.3 34.3 275 31 16 8.3 4.5 | 1.6 34.9 265 28 14 8.6 4.7
14500 2.5 36.5 275 29 15 8.5 4.6 | 2.8 37.0 265 27 14 8.6 4.7
14000 3.8 38.8 275 27 14 8.5 4.7 | 4.1 39.4 270 25 13 8.6 4.7
13500 5.1 41.2 275 24 13 8.7 4.8 | 5.4 41.7 270 24 12 8.3 4.6
13000 6.4 43.5 270 22 11 8.8 4.8 | 6.6 43.9 270 21 11 8.2 4.5
12500 7.7 45.9 270 20 10 8.6 4.7 | 7.8 46.0 270 18 9 8.3 4.6
12000 8.9 48.0 265 18 9 8.4 4.6 | 9.1 48.4 270 15 8 8.6 4.7
11500 10.1 50.2 265 16 8 8.0 4.4 | 10.3 50.5 270 13 7 8.6 4.7
11000 11.1 52.0 260 14 7 6.8 3.7 | 11.5 52.7 270 10 5 8.1 4.4
10500 12.1 53.8 255 12 6 3.9 2.1 | 12.7 54.9 270 7 4 3.6 2.0
10250 12.2 54.0 250 11 6 3.4 1.9 | 12.8 55.0 270 6 3 4.7 2.6
10000 12.6 54.7 245 10 5 7.5 4.1 | 13.5 56.3 265 5 3 11.6 6.4
9750 13.0 55.4 240 9 5 7.2 3.9 | 14.2 57.6 265 4 2 10.5 5.7
9500 13.4 56.1 230 9 4 6.4 3.5 | 14.9 58.8 260 2 1 8.6 4.7
9250 13.8 56.8 220 8 4 4.6 2.5 | 15.4 59.7 265 2 1 6.2 3.4
9000 14.1 57.4 215 8 4 5.5 3.0 | 15.9 60.6 270 1 1 9.4 5.2
8750 14.4 57.9 205 8 4 6.9 3.8 | 16.7 62.1 285 1 0 11.6 6.4
8500 14.8 58.6 195 9 4 5.5 3.0 | 17.4 63.3 000 0 0 9.5 5.2
8250 15.1 59.2 190 8 4 3.4 1.9 | 18.0 64.4 045 1 0 6.7 3.7
8000 15.3 59.5 180 8 4 5.4 3.0 | 18.5 65.3 050 2 1 9.2 5.1
7750 15.8 60.4 175 8 4 8.4 4.6 | 19.3 66.7 055 2 1 12.6 6.9
7500 16.4 61.5 175 8 4 7.1 3.9 | 20.2 68.4 060 2 1 9.5 5.2
7250 16.8 62.2 170 8 4 5.4 3.0 | 20.7 69.3 055 2 1 6.5 3.5
7000 17.2 63.0 165 7 4 7.1 3.9 | 21.2 70.2 055 2 1 9.1 5.0
6750 17.9 64.2 165 7 4 10.8 5.9 | 22.1 71.8 055 2 1 13.4 7.4
6500 18.7 65.7 165 7 4 10.3 5.6 | 23.1 73.6 060 2 1 11.7 6.4
6250 19.4 66.9 160 6 3 8.3 4.5 | 23.8 74.8 055 3 1 9.5 5.2
6000 20.0 68.0 160 6 3 9.1 5.0 | 24.5 76.1 050 3 1 9.2 5.0
5750 20.8 69.4 160 6 3 14.0 7.7 | 25.3 77.5 055 3 1 16.1 8.8
5500 22.1 71.8 160 5 3 21.3 11.7 | 27.1 80.8 055 3 1 31.1 17.1
08/09/2025 at 1500 MDT | 08/09/2025 at 1800 MDT
|
CAPE... +557.8 LI... -2.3 | CAPE... +500.3 LI... -2.2
CINH... -11.6 K Index... +28.0 | CINH... -17.9 K Index... +28.7
|
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 -61.9 -79.4 260 25 13 -0.1 -0.0 | -61.4 -78.5 260 17 9 -0.3 -0.2
45000 -61.0 -77.8 270 40 20 2.4 1.3 | -60.8 -77.4 265 26 13 2.1 1.1
40000 -56.6 -69.9 275 44 23 8.1 4.5 | -56.8 -70.2 270 38 20 8.5 4.7
38000 -51.7 -61.1 270 41 21 8.1 4.5 | -51.6 -60.9 260 35 18 8.6 4.7
36000 -46.9 -52.4 265 38 20 8.1 4.4 | -46.4 -51.5 255 33 17 8.6 4.7
34000 -41.7 -43.1 260 39 20 8.6 4.7 | -41.1 -42.0 255 33 17 8.9 4.9
32000 -36.6 -33.9 265 40 20 8.5 4.6 | -35.8 -32.4 250 32 17 8.8 4.8
30000 -31.9 -25.4 260 41 21 7.6 4.2 | -30.7 -23.3 250 36 19 7.1 3.9
29000 -29.0 -20.2 260 42 22 7.6 4.2 | -28.6 -19.5 250 38 20 7.2 3.9
28000 -26.8 -16.2 260 43 22 6.7 3.7 | -26.4 -15.5 245 40 21 7.2 3.9
27000 -24.9 -12.8 260 43 22 6.5 3.6 | -24.3 -11.7 245 40 21 7.2 4.0
26000 -22.9 -9.2 260 42 22 6.6 3.6 | -22.2 -8.0 245 40 21 7.2 4.0
25000 -21.0 -5.8 260 42 22 6.8 3.7 | -20.0 -4.0 245 40 21 7.2 3.9
24000 -18.9 -2.0 260 42 22 7.3 4.0 | -18.1 -0.6 245 39 20 6.7 3.7
23000 -16.7 1.9 260 42 22 7.4 4.0 | -16.1 3.0 250 38 20 6.8 3.7
22000 -14.6 5.7 260 43 22 7.4 4.1 | -14.1 6.6 250 37 19 7.0 3.8
21000 -12.4 9.7 260 40 21 7.4 4.1 | -12.0 10.4 255 34 17 7.4 4.0
20000 -10.3 13.5 260 38 19 7.5 4.1 | -9.8 14.4 255 30 16 7.4 4.1
19500 -9.2 15.4 260 36 19 7.5 4.1 | -8.8 16.2 260 28 15 7.5 4.1
19000 -8.1 17.4 260 35 18 7.6 4.2 | -7.7 18.1 260 27 14 6.9 3.8
18500 -7.0 19.4 260 32 17 7.6 4.2 | -6.7 19.9 260 25 13 7.0 3.8
18000 -5.9 21.4 260 30 15 7.9 4.4 | -5.7 21.7 260 23 12 7.4 4.0
17500 -4.6 23.7 260 28 14 8.3 4.6 | -4.6 23.7 265 22 11 7.9 4.3
17000 -3.4 25.9 260 26 13 8.3 4.5 | -3.4 25.9 265 20 10 7.8 4.3
16500 -2.1 28.2 260 24 12 9.3 5.1 | -2.2 28.0 260 18 9 8.8 4.8
16000 -0.7 30.7 260 22 11 9.2 5.0 | -0.9 30.4 260 16 8 8.8 4.8
15500 0.6 33.1 260 19 10 8.9 4.9 | 0.4 32.7 260 13 7 8.9 4.9
15000 1.9 35.4 255 17 9 8.8 4.8 | 1.8 35.2 255 11 6 9.0 4.9
14500 3.2 37.8 255 14 7 8.9 4.9 | 3.1 37.6 250 9 5 9.0 4.9
14000 4.5 40.1 250 12 6 8.9 4.9 | 4.4 39.9 250 8 4 9.1 5.0
13500 5.8 42.4 245 10 5 8.9 4.9 | 6.4 43.5 250 6 3 8.9 4.9
13000 7.8 46.0 235 7 4 8.7 4.8 | 7.7 45.9 255 5 2 8.9 4.9
12500 9.1 48.4 225 5 3 8.9 4.9 | 9.0 48.2 265 3 2 9.0 4.9
12000 10.4 50.7 220 4 2 9.1 5.0 | 10.4 50.7 280 3 1 9.2 5.1
11500 11.8 53.2 205 3 1 9.2 5.0 | 11.7 53.1 305 2 1 9.2 5.1
11000 13.1 55.6 195 2 1 8.9 4.9 | 13.1 55.6 330 2 1 8.9 4.9
10500 14.5 58.1 175 2 1 3.9 2.2 | 14.4 57.9 350 3 1 3.8 2.1
10250 14.6 58.3 175 2 1 5.7 3.1 | 14.6 58.3 350 3 1 5.5 3.0
10000 15.4 59.7 160 2 1 13.4 7.4 | 15.4 59.7 360 3 2 13.3 7.3
9750 16.3 61.3 150 2 1 12.4 6.8 | 16.3 61.3 005 3 2 12.1 6.6
9500 17.2 63.0 135 2 1 8.9 4.9 | 17.2 63.0 010 4 2 9.2 5.1
9250 17.7 63.9 135 2 1 6.3 3.4 | 17.7 63.9 010 4 2 6.5 3.6
9000 18.3 64.9 130 2 1 10.9 6.0 | 18.3 64.9 015 4 2 10.3 5.7
8750 19.2 66.6 120 2 1 12.9 7.1 | 19.2 66.6 020 5 3 12.3 6.8
8500 20.1 68.2 115 3 1 10.1 5.5 | 20.0 68.0 020 5 3 9.9 5.5
8250 20.7 69.3 110 3 1 6.0 3.3 | 20.6 69.1 020 6 3 6.2 3.4
8000 21.2 70.2 110 3 2 9.9 5.4 | 21.1 70.0 020 6 3 9.3 5.1
7750 22.2 72.0 105 3 2 14.0 7.7 | 22.0 71.6 025 6 3 13.4 7.4
7500 23.1 73.6 100 4 2 10.1 5.5 | 22.9 73.2 025 7 4 9.7 5.3
7250 23.7 74.7 095 4 2 7.1 3.9 | 23.4 74.1 025 7 4 6.6 3.6
7000 24.3 75.7 095 4 2 9.7 5.3 | 24.0 75.2 025 7 4 8.8 4.8
6750 25.2 77.4 090 4 2 13.1 7.2 | 24.8 76.6 030 8 4 12.0 6.6
6500 26.1 79.0 090 4 2 11.0 6.0 | 25.7 78.3 030 8 4 10.4 5.7
6250 26.8 80.2 085 4 2 8.8 4.8 | 26.3 79.3 030 8 4 8.2 4.5
6000 27.5 81.5 085 4 2 9.1 5.0 | 27.0 80.6 030 8 4 9.0 4.9
5750 28.3 82.9 085 4 2 15.4 8.5 | 27.7 81.9 030 8 4 13.1 7.2
5500 29.9 85.8 080 4 2 26.9 14.7 | 28.9 84.0 030 8 4 19.1 10.5
________________________________________________________________________________
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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