Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
611
UXUS97 KBOU 280117
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1915 MDT Wednesday, August 27, 2025
This forecast is for Thursday, August 28, 2025:
If the trigger temperature of 76.2 F/24.6 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 591 ft/min (3.0 m/s)
Maximum height of thermals.................. 12432 ft MSL (7131 ft AGL)
Forecast maximum temperature................... 80.0 F/27.1 C
Time of trigger temperature.................... 1145 MDT
Time of overdevelopment........................ 1500 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 8376 ft MSL (3074 ft AGL)
Thermal soaring outlook for Friday 08/29....... 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 NVA
Potential height of wave....................... 23746 ft MSL (18445 ft AGL)
Wave soaring outlook for Friday 08/29.......... Poor
Remarks...
Sunrise/Sunset.................... 06:24:24 / 19:36:44 MDT
Total possible sunshine........... 13 hr 12 min 19 sec (792 min 19 sec)
Altitude of sun at 13:00:34 MDT... 59.64 degrees
Upper air data from numerical model forecast valid on 08/28/2025 at 0600 MDT
Freezing level.................. 14925 ft MSL (9624 ft AGL)
Convective condensation level... 12675 ft MSL (7374 ft AGL)
Lifted condensation level....... 12654 ft MSL (7353 ft AGL)
Lifted index.................... -0.9
K index......................... +24.1
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 -64.5 -84.1 265 31 16 2.6 1.4 M M M M M
45000 -58.6 -73.5 270 54 28 6.1 3.3 M M M M M
40000 -49.5 -57.1 270 72 37 5.8 3.2 M M M M M
38000 -46.1 -51.0 275 72 37 5.8 3.2 M M M M M
36000 -42.6 -44.7 280 72 37 5.8 3.2 M M M M M
34000 -38.3 -36.9 275 65 33 7.3 4.0 M M M M M
32000 -33.9 -29.0 275 57 29 7.3 4.0 M M M M M
30000 -28.6 -19.5 270 48 24 7.8 4.3 47.6 117.7 16.0 M M
29000 -26.3 -15.3 265 43 22 7.9 4.3 46.9 116.5 15.7 M M
28000 -24.0 -11.2 265 39 20 7.0 3.8 46.2 115.2 15.3 M M
27000 -21.9 -7.4 265 36 19 6.9 3.8 45.1 113.1 14.5 M M
26000 -19.8 -3.6 265 33 17 6.9 3.8 44.0 111.2 13.9 M M
25000 -17.8 -0.0 265 30 16 6.7 3.7 43.1 109.5 13.3 M M
24000 -15.9 3.4 270 27 14 6.0 3.3 41.6 106.9 12.2 M M
23000 -14.1 6.6 270 24 12 6.0 3.3 40.3 104.5 11.2 M M
22000 -12.3 9.9 270 20 10 5.9 3.2 39.0 102.2 10.3 M M
21000 -10.7 12.7 275 18 9 5.7 3.1 37.5 99.5 9.1 M M
20000 -9.0 15.8 275 16 8 5.8 3.2 36.1 97.0 7.9 M M
19500 -8.2 17.2 280 15 8 5.9 3.3 35.5 95.8 7.4 M M
19000 -7.4 18.7 280 14 7 5.6 3.1 34.8 94.6 6.8 M M
18500 -6.6 20.1 280 14 7 5.7 3.2 34.1 93.3 6.1 M M
18000 -5.8 21.6 285 13 7 6.0 3.3 33.4 92.1 5.5 M M
17500 -4.9 23.2 280 12 6 6.3 3.4 32.8 91.0 4.9 M M
17000 -4.1 24.6 280 12 6 6.4 3.5 32.2 89.9 4.3 M M
16500 -3.2 26.2 280 12 6 6.3 3.5 31.6 88.9 3.8 M M
16000 -2.3 27.9 285 12 6 6.3 3.5 31.0 87.9 3.3 M M
15500 -0.9 30.4 285 12 6 6.5 3.6 30.2 86.4 2.5 M M
15000 0.1 32.2 290 12 6 6.4 3.5 29.7 85.4 2.0 M M
14500 1.0 33.8 295 12 6 7.1 3.9 29.1 84.5 1.5 M M
14000 2.1 35.8 300 12 6 7.1 3.9 28.7 83.7 1.1 M M
13500 3.1 37.6 305 13 7 7.6 4.2 28.3 82.9 0.7 M M
13000 4.2 39.6 310 13 7 7.8 4.3 28.0 82.4 0.3 M M
12500 5.3 41.5 315 13 7 8.0 4.4 27.7 81.8 0.0 M M
12000 6.5 43.7 315 14 7 8.2 4.5 27.4 81.4 -0.3 541 2.7
11500 7.7 45.9 320 14 7 8.1 4.5 27.2 80.9 -0.5 491 2.5
11000 8.9 48.0 315 15 8 7.9 4.3 26.9 80.4 -0.8 441 2.2
10500 10.1 50.2 315 15 8 5.0 2.7 26.7 80.0 -1.1 391 2.0
10250 10.3 50.5 315 15 8 4.7 2.6 26.1 79.1 -1.6 377 1.9
10000 10.9 51.6 315 15 8 9.9 5.4 26.0 78.8 -1.8 352 1.8
9750 11.6 52.9 315 15 8 10.9 6.0 26.1 78.9 -1.8 322 1.6
9500 12.3 54.1 315 15 8 7.9 4.3 26.1 79.0 -1.8 293 1.5
9250 12.7 54.9 315 15 8 4.5 2.5 25.8 78.4 -2.1 274 1.4
9000 13.1 55.6 310 15 7 7.1 3.9 25.4 77.8 -2.4 255 1.3
8750 13.7 56.7 310 13 7 8.9 4.9 25.3 77.6 -2.6 229 1.2
8500 14.3 57.7 310 12 6 5.9 3.2 25.2 77.3 -2.8 206 1.0
8250 14.6 58.3 310 11 6 3.5 1.9 24.7 76.5 -3.2 190 1.0
8000 14.8 58.6 305 10 5 5.2 2.8 24.3 75.8 -3.7 174 0.9
7750 15.2 59.4 305 9 5 6.2 3.4 24.0 75.3 -4.0 155 0.8
7500 15.6 60.1 300 7 4 4.3 2.4 23.7 74.7 -4.4 137 0.7
7250 15.8 60.4 295 7 3 3.0 1.6 23.2 73.8 -4.9 123 0.6
7000 16.0 60.8 290 6 3 3.9 2.2 22.7 72.9 -5.5 109 0.6
6750 16.2 61.2 280 5 2 3.5 1.9 22.3 72.1 -6.0 95 0.5
6500 16.4 61.5 275 4 2 2.2 1.2 21.8 71.2 -6.6 84 0.4
6250 16.5 61.7 270 4 2 2.0 1.1 21.2 70.1 -7.2 73 0.4
6000 16.6 61.9 265 3 2 2.3 1.2 20.6 69.1 -7.9 63 0.3
5750 16.6 61.9 255 3 1 -0.4 -0.2 20.0 68.0 -8.6 54 0.3
5500 16.3 61.3 240 2 1 -5.4 -2.9 19.0 66.2 -9.6 56 0.3
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/28/2025 at 0900 MDT | 08/28/2025 at 1200 MDT
|
CAPE... +394.6 LI... -2.1 | CAPE... +456.3 LI... -2.7
CINH... -53.2 K Index... +24.9 | CINH... -6.0 K Index... +23.4
|
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 -83.2 270 32 16 2.5 1.3 | -63.5 -82.3 270 31 16 2.7 1.5
45000 -58.5 -73.3 265 54 28 5.7 3.1 | -58.0 -72.4 270 53 27 4.9 2.7
40000 -50.0 -58.0 265 68 35 5.6 3.1 | -50.4 -58.7 265 67 34 5.7 3.1
38000 -46.6 -51.9 270 66 34 5.6 3.1 | -47.0 -52.6 275 69 36 5.7 3.1
36000 -43.3 -45.9 275 64 33 5.5 3.0 | -43.6 -46.5 285 73 38 5.7 3.1
34000 -38.7 -37.7 275 62 32 7.8 4.3 | -38.8 -37.8 280 69 35 8.3 4.6
32000 -34.0 -29.2 270 61 31 7.7 4.2 | -33.8 -28.8 275 64 33 8.2 4.5
30000 -28.9 -20.0 270 52 27 7.6 4.2 | -28.5 -19.3 270 56 29 7.7 4.2
29000 -26.6 -15.9 270 48 25 7.6 4.2 | -26.2 -15.2 265 52 27 7.7 4.2
28000 -24.3 -11.7 270 43 22 7.4 4.0 | -24.0 -11.2 265 49 25 6.6 3.6
27000 -22.1 -7.8 265 41 21 7.4 4.0 | -22.0 -7.6 260 45 23 6.6 3.6
26000 -19.9 -3.8 265 38 19 7.4 4.0 | -20.0 -4.0 260 42 22 6.6 3.6
25000 -17.7 0.1 260 35 18 7.0 3.8 | -18.0 -0.4 260 39 20 6.5 3.6
24000 -16.0 3.2 260 32 17 5.7 3.1 | -16.2 2.8 260 35 18 6.2 3.4
23000 -14.3 6.3 265 29 15 5.7 3.1 | -14.3 6.3 270 32 17 6.2 3.4
22000 -12.6 9.3 265 26 13 5.5 3.0 | -12.5 9.5 275 29 15 5.8 3.2
21000 -11.1 12.0 270 22 11 5.0 2.7 | -11.0 12.2 275 24 13 4.9 2.7
20000 -9.7 14.5 270 18 9 5.1 2.8 | -9.6 14.7 275 20 10 5.1 2.8
19500 -9.0 15.8 275 16 8 5.2 2.8 | -8.9 16.0 270 17 9 5.3 2.9
19000 -8.3 17.1 275 14 7 5.1 2.8 | -8.2 17.2 270 16 8 5.0 2.7
18500 -7.6 18.3 275 14 7 5.2 2.8 | -7.5 18.5 270 15 8 5.0 2.8
18000 -6.8 19.8 275 13 7 5.4 2.9 | -6.8 19.8 270 14 7 5.4 3.0
17500 -6.1 21.0 275 12 6 5.7 3.1 | -5.9 21.4 270 14 7 6.1 3.3
17000 -4.9 23.2 275 12 6 6.2 3.4 | -5.0 23.0 270 15 7 6.0 3.3
16500 -3.9 25.0 280 11 6 6.7 3.7 | -3.7 25.3 270 14 7 6.6 3.6
16000 -3.0 26.6 285 11 5 6.7 3.7 | -2.7 27.1 275 14 7 6.7 3.7
15500 -2.0 28.4 290 10 5 7.1 3.9 | -1.7 28.9 275 14 7 7.4 4.0
15000 -1.0 30.2 295 10 5 7.0 3.9 | -0.7 30.7 275 13 7 7.3 4.0
14500 0.1 32.2 300 10 5 7.4 4.0 | 0.4 32.7 280 12 6 7.7 4.2
14000 1.2 34.2 305 10 5 7.4 4.1 | 1.5 34.7 280 11 6 7.7 4.2
13500 2.2 36.0 310 10 5 7.7 4.2 | 2.6 36.7 280 11 5 7.8 4.3
13000 3.4 38.1 315 10 5 7.8 4.3 | 3.8 38.8 285 10 5 7.9 4.3
12500 4.5 40.1 320 10 5 7.9 4.3 | 4.9 40.8 290 9 5 8.1 4.4
12000 5.7 42.3 325 11 5 8.0 4.4 | 6.1 43.0 295 9 4 8.2 4.5
11500 6.9 44.4 325 11 6 8.1 4.4 | 7.3 45.1 300 8 4 8.0 4.4
11000 8.0 46.4 330 11 6 8.0 4.4 | 8.5 47.3 305 7 4 7.6 4.2
10500 9.2 48.6 330 11 6 5.2 2.9 | 9.6 49.3 315 7 4 4.3 2.4
10250 9.4 48.9 330 11 6 4.9 2.7 | 9.8 49.6 315 7 4 4.5 2.4
10000 10.0 50.0 330 11 5 9.8 5.4 | 10.4 50.7 320 6 3 10.0 5.5
9750 10.8 51.4 335 10 5 10.7 5.9 | 11.0 51.8 325 6 3 10.0 5.5
9500 11.5 52.7 335 10 5 7.8 4.3 | 11.7 53.1 335 5 3 7.4 4.1
9250 11.9 53.4 335 9 5 4.7 2.6 | 12.1 53.8 340 5 2 4.8 2.6
9000 12.3 54.1 335 9 5 7.8 4.3 | 12.5 54.5 345 4 2 8.2 4.5
8750 13.0 55.4 335 8 4 9.7 5.3 | 13.1 55.6 360 4 2 9.9 5.4
8500 13.6 56.5 330 8 4 7.0 3.8 | 13.7 56.7 015 3 2 8.0 4.4
8250 13.9 57.0 330 7 4 5.1 2.8 | 14.2 57.6 025 3 1 6.3 3.4
8000 14.3 57.7 325 7 4 6.7 3.7 | 14.7 58.5 040 3 1 9.5 5.2
7750 14.8 58.6 325 7 3 7.1 3.9 | 15.5 59.9 045 3 1 11.8 6.5
7500 15.2 59.4 325 6 3 4.4 2.4 | 16.3 61.3 045 3 2 8.9 4.9
7250 15.5 59.9 320 5 3 2.9 1.6 | 16.8 62.2 050 3 2 6.5 3.6
7000 15.7 60.3 320 4 2 4.3 2.3 | 17.4 63.3 050 3 2 11.5 6.3
6750 16.0 60.8 320 4 2 6.2 3.4 | 18.4 65.1 050 3 2 13.4 7.4
6500 16.4 61.5 315 3 1 6.2 3.4 | 19.2 66.6 050 3 2 9.5 5.2
6250 16.8 62.2 305 2 1 6.5 3.6 | 19.9 67.8 050 3 2 10.6 5.8
6000 17.2 63.0 285 1 1 4.4 2.4 | 20.7 69.3 050 3 2 8.3 4.6
5750 17.5 63.5 255 1 0 8.2 4.5 | 21.3 70.3 050 3 2 13.4 7.4
5500 18.5 65.3 250 1 0 20.9 11.5 | 22.8 73.0 050 3 2 27.8 15.2
08/28/2025 at 1500 MDT | 08/28/2025 at 1800 MDT
|
CAPE... +105.9 LI... -1.3 | CAPE... +151.0 LI... -1.7
CINH... -10.3 K Index... +29.1 | CINH... -29.2 K Index... +30.4
|
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 -63.6 -82.5 275 39 20 1.8 1.0 | -63.8 -82.8 275 40 21 2.1 1.1
45000 -59.1 -74.4 275 60 31 4.9 2.7 | -59.0 -74.2 275 60 31 4.9 2.7
40000 -51.3 -60.3 270 60 31 6.7 3.7 | -51.2 -60.2 275 58 30 6.7 3.7
38000 -47.3 -53.1 280 63 32 6.7 3.7 | -47.1 -52.8 280 58 30 6.7 3.7
36000 -43.3 -45.9 290 67 34 6.8 3.7 | -43.1 -45.6 290 59 30 6.9 3.8
34000 -38.5 -37.3 280 62 32 8.1 4.4 | -38.2 -36.8 280 55 28 8.4 4.6
32000 -33.6 -28.5 270 58 30 7.9 4.3 | -32.5 -26.5 270 51 26 8.7 4.8
30000 -28.2 -18.8 270 56 29 8.1 4.4 | -28.0 -18.4 265 50 26 7.5 4.1
29000 -25.8 -14.4 270 55 28 8.1 4.4 | -25.8 -14.4 265 50 26 7.6 4.2
28000 -23.5 -10.3 265 53 27 6.0 3.3 | -23.6 -10.5 265 49 25 6.5 3.6
27000 -21.6 -6.9 265 50 26 6.1 3.4 | -21.6 -6.9 265 48 25 6.6 3.6
26000 -19.7 -3.5 265 47 24 6.2 3.4 | -19.6 -3.3 265 47 24 6.6 3.6
25000 -17.9 -0.2 260 44 23 6.1 3.3 | -17.6 0.3 265 45 23 6.3 3.5
24000 -16.1 3.0 265 39 20 5.9 3.2 | -15.9 3.4 270 40 21 5.8 3.2
23000 -14.4 6.1 265 34 18 5.9 3.2 | -14.2 6.4 270 35 18 5.8 3.2
22000 -12.7 9.1 270 29 15 6.0 3.3 | -12.6 9.3 270 30 16 6.0 3.3
21000 -11.0 12.2 265 24 13 6.1 3.4 | -10.8 12.6 270 26 13 6.2 3.4
20000 -9.2 15.4 260 20 10 6.4 3.5 | -9.0 15.8 265 22 11 6.3 3.4
19500 -8.4 16.9 255 18 9 6.7 3.7 | -8.2 17.2 265 20 10 6.4 3.5
19000 -7.6 18.3 255 16 8 5.0 2.8 | -7.3 18.9 265 19 10 5.7 3.1
18500 -6.8 19.8 255 16 8 5.3 2.9 | -6.5 20.3 265 19 10 5.8 3.2
18000 -6.1 21.0 260 15 8 6.4 3.5 | -5.7 21.7 265 18 9 5.9 3.2
17500 -5.0 23.0 265 15 8 7.4 4.1 | -4.8 23.4 265 18 9 6.0 3.3
17000 -3.9 25.0 270 16 8 7.6 4.1 | -3.9 25.0 265 18 9 6.0 3.3
16500 -2.9 26.8 275 16 8 6.4 3.5 | -3.0 26.6 265 17 9 6.4 3.5
16000 -2.0 28.4 275 15 8 6.5 3.6 | -2.1 28.2 265 16 8 6.4 3.5
15500 -1.0 30.2 280 15 8 6.6 3.6 | -0.7 30.7 260 15 8 7.0 3.9
15000 -0.1 31.8 280 14 7 6.6 3.6 | 0.3 32.5 260 14 7 7.0 3.8
14500 0.9 33.6 285 12 6 6.8 3.7 | 1.3 34.3 260 12 6 7.5 4.1
14000 2.4 36.3 285 10 5 7.1 3.9 | 2.4 36.3 260 11 6 7.5 4.1
13500 3.4 38.1 290 9 5 7.5 4.1 | 3.5 38.3 260 9 5 8.0 4.4
13000 4.5 40.1 290 7 4 7.5 4.1 | 4.7 40.5 260 8 4 8.1 4.4
12500 5.7 42.3 285 6 3 7.9 4.3 | 5.9 42.6 260 6 3 8.1 4.5
12000 6.9 44.4 280 4 2 8.1 4.5 | 7.1 44.8 250 5 3 8.2 4.5
11500 8.1 46.6 270 3 2 8.5 4.7 | 8.4 47.1 240 4 2 8.3 4.6
11000 9.3 48.7 270 2 1 8.6 4.7 | 9.6 49.3 230 3 1 8.2 4.5
10500 10.6 51.1 000 0 0 3.4 1.8 | 10.8 51.4 205 2 1 3.8 2.1
10250 10.7 51.3 000 0 0 5.7 3.1 | 11.0 51.8 205 2 1 5.3 2.9
10000 11.5 52.7 000 0 0 13.7 7.5 | 11.8 53.2 195 2 1 12.7 7.0
9750 12.4 54.3 000 0 0 12.2 6.7 | 12.6 54.7 180 2 1 11.8 6.5
9500 13.3 55.9 000 0 0 8.5 4.7 | 13.4 56.1 170 2 1 8.7 4.8
9250 13.7 56.7 000 0 0 5.6 3.1 | 13.9 57.0 165 2 1 5.7 3.1
9000 14.3 57.7 000 0 0 11.4 6.2 | 14.5 58.1 165 2 1 10.1 5.5
8750 15.3 59.5 000 0 0 13.3 7.3 | 15.3 59.5 160 2 1 12.0 6.6
8500 16.2 61.2 000 0 0 9.3 5.1 | 16.1 61.0 160 2 1 9.1 5.0
8250 16.7 62.1 000 0 0 6.4 3.5 | 16.7 62.1 160 2 1 6.8 3.7
8000 17.3 63.1 000 0 0 11.0 6.0 | 17.2 63.0 160 3 1 9.5 5.2
7750 18.3 64.9 000 0 0 13.3 7.3 | 18.0 64.4 165 3 1 11.3 6.2
7500 19.1 66.4 000 0 0 9.2 5.1 | 18.8 65.8 170 3 2 8.8 4.8
7250 19.7 67.5 000 0 0 7.2 3.9 | 19.4 66.9 170 3 2 7.6 4.2
7000 20.4 68.7 000 0 0 11.5 6.3 | 19.9 67.8 170 3 2 8.6 4.7
6750 21.4 70.5 000 0 0 12.9 7.1 | 20.6 69.1 170 4 2 9.7 5.3
6500 22.1 71.8 000 0 0 9.4 5.2 | 21.3 70.3 170 4 2 9.4 5.1
6250 22.9 73.2 000 0 0 10.9 6.0 | 22.0 71.6 170 4 2 9.7 5.3
6000 23.6 74.5 000 0 0 7.5 4.1 | 22.7 72.9 170 4 2 7.8 4.3
5750 24.2 75.6 000 0 0 10.7 5.9 | 23.2 73.8 170 4 2 8.8 4.8
5500 25.5 77.9 030 1 0 25.2 13.8 | 24.1 75.4 170 4 2 16.1 8.8
________________________________________________________________________________
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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