Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
817
UXUS97 KBOU 011400
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0759 MDT Monday, September 1, 2025
This forecast is for Monday, September 1, 2025:
If the trigger temperature of 74.7 F/23.7 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 958 ft/min (4.9 m/s)
Maximum height of thermals.................. 16475 ft MSL (11152 ft AGL)
Forecast maximum temperature................... 86.0 F/30.5 C
Time of trigger temperature.................... 1100 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 13162 ft MSL (7839 ft AGL)
Thermal soaring outlook for Tuesday 09/02...... 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)................ Neither
Potential height of wave....................... 22570 ft MSL (17247 ft AGL)
Wave soaring outlook for Tuesday 09/02......... Poor
Remarks...
Sunrise/Sunset.................... 06:28:08 / 19:30:31 MDT
Total possible sunshine........... 13 hr 2 min 22 sec (782 min 22 sec)
Altitude of sun at 12:59:20 MDT... 58.20 degrees
Upper air data from numerical model forecast valid on 09/01/2025 at 0600 MDT
Freezing level.................. 14644 ft MSL (9321 ft AGL)
Convective condensation level... 15061 ft MSL (9738 ft AGL)
Lifted condensation level....... 15805 ft MSL (10483 ft AGL)
Lifted index.................... -2.7
K index......................... +12.4
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 -62.3 -80.1 290 37 19 2.8 1.6 M M M M M
45000 -57.5 -71.5 290 52 27 4.1 2.3 M M M M M
40000 -51.3 -60.3 295 50 26 3.4 1.9 M M M M M
38000 -49.3 -56.7 300 43 22 3.5 1.9 M M M M M
36000 -47.2 -53.0 305 37 19 3.6 2.0 M M M M M
34000 -42.6 -44.7 315 34 17 7.6 4.2 M M M M M
32000 -38.0 -36.4 320 33 17 7.6 4.2 M M M M M
30000 -33.4 -28.1 325 29 15 7.6 4.2 42.3 108.1 9.3 M M
29000 -31.2 -24.2 330 27 14 7.6 4.2 41.5 106.7 8.8 M M
28000 -28.9 -20.0 330 24 13 7.7 4.2 40.8 105.5 8.4 M M
27000 -26.5 -15.7 335 24 12 7.8 4.3 39.9 103.9 7.8 M M
26000 -24.2 -11.6 335 24 12 7.8 4.3 39.2 102.5 7.3 M M
25000 -21.9 -7.4 340 24 12 7.7 4.2 38.5 101.4 6.9 M M
24000 -19.8 -3.6 340 24 13 6.9 3.8 37.5 99.4 6.1 M M
23000 -17.7 0.1 340 26 13 6.9 3.8 36.4 97.5 5.3 M M
22000 -15.6 3.9 340 27 14 6.9 3.8 35.5 95.9 4.5 M M
21000 -13.6 7.5 340 26 13 6.7 3.7 34.3 93.8 3.6 M M
20000 -11.6 11.1 340 25 13 6.7 3.7 33.3 91.9 2.7 M M
19500 -10.6 12.9 340 24 13 6.6 3.6 32.8 91.0 2.3 M M
19000 -9.6 14.7 340 24 12 7.7 4.2 32.3 90.2 1.9 M M
18500 -7.9 17.8 345 22 11 7.7 4.2 31.8 89.2 1.4 M M
18000 -6.7 19.9 345 21 11 7.6 4.1 31.4 88.6 1.1 M M
17500 -5.6 21.9 345 20 10 7.5 4.1 31.1 87.9 0.8 M M
17000 -4.5 23.9 345 19 10 7.1 3.9 30.7 87.3 0.4 M M
16500 -3.5 25.7 345 18 9 6.6 3.6 30.1 86.3 -0.1 952 4.8
16000 -2.5 27.5 345 17 9 6.6 3.6 29.6 85.3 -0.5 908 4.6
15500 -1.6 29.1 345 17 9 6.7 3.6 29.1 84.4 -1.0 864 4.4
15000 -0.6 30.9 345 17 9 6.6 3.6 28.6 83.4 -1.5 819 4.2
14500 0.4 32.7 345 16 8 7.3 4.0 28.1 82.6 -2.0 774 3.9
14000 1.5 34.7 345 16 8 7.3 4.0 27.7 81.9 -2.4 728 3.7
13500 2.6 36.7 340 16 8 8.0 4.4 27.3 81.2 -2.8 681 3.5
13000 3.7 38.7 340 16 8 8.3 4.5 27.1 80.8 -3.1 631 3.2
12500 4.9 40.8 335 15 8 8.6 4.7 26.9 80.4 -3.4 581 3.0
12000 6.1 43.0 330 13 7 8.9 4.9 26.7 80.1 -3.7 529 2.7
11500 7.4 45.3 320 11 6 8.2 4.5 26.6 79.8 -4.0 478 2.4
11000 8.4 47.1 310 10 5 7.6 4.2 26.2 79.2 -4.4 432 2.2
10500 9.4 48.9 305 8 4 5.2 2.9 25.9 78.6 -4.9 386 2.0
10250 9.7 49.5 305 7 4 4.6 2.5 25.4 77.7 -5.3 371 1.9
10000 10.2 50.4 305 7 3 8.5 4.7 25.2 77.3 -5.6 349 1.8
9750 10.8 51.4 305 6 3 9.1 5.0 25.1 77.2 -5.7 322 1.6
9500 11.4 52.5 305 5 2 7.6 4.2 25.0 77.1 -5.8 296 1.5
9250 11.9 53.4 315 4 2 5.8 3.2 24.8 76.6 -6.1 275 1.4
9000 12.4 54.3 325 3 2 8.5 4.7 24.5 76.2 -6.3 253 1.3
8750 13.1 55.6 330 3 2 10.0 5.5 24.6 76.2 -6.4 223 1.1
8500 13.8 56.8 335 3 2 7.2 3.9 24.5 76.0 -6.5 197 1.0
8250 14.3 57.7 340 3 1 5.8 3.2 24.2 75.6 -6.7 175 0.9
8000 14.7 58.5 350 3 1 7.4 4.1 23.9 75.1 -7.0 153 0.8
7750 15.3 59.5 345 3 1 6.9 3.8 23.8 74.8 -7.1 128 0.6
7500 15.7 60.3 340 3 2 4.4 2.4 23.4 74.2 -7.5 108 0.6
7250 16.0 60.8 340 3 2 3.2 1.8 23.0 73.4 -8.0 93 0.5
7000 16.3 61.3 340 4 2 6.3 3.4 22.6 72.6 -8.4 77 0.4
6750 16.7 62.1 325 4 2 2.8 1.5 22.3 72.2 -8.8 57 0.3
6500 16.6 61.9 320 4 2 -2.6 -1.4 21.5 70.6 -9.6 53 0.3
6250 16.5 61.7 310 4 2 -1.1 -0.6 20.6 69.1 -10.5 50 0.3
6000 16.3 61.3 305 4 2 -1.6 -0.9 19.8 67.6 -11.4 46 0.2
5750 16.0 60.8 300 4 2 -7.1 -3.9 18.8 65.8 -12.4 47 0.2
5500 15.2 59.4 290 3 1 -15.9 -8.7 17.1 62.9 -14.1 67 0.3
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/01/2025 at 0900 MDT | 09/01/2025 at 1200 MDT
|
CAPE... 0.0 LI... +0.4 | CAPE... +56.5 LI... +0.6
CINH... -0.3 K Index... +12.3 | CINH... -8.7 K Index... +12.1
|
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 -62.4 -80.3 295 37 19 2.7 1.5 | -62.4 -80.3 295 37 19 2.4 1.3
45000 -57.7 -71.9 295 52 27 4.1 2.3 | -58.1 -72.6 300 50 26 3.9 2.2
40000 -51.6 -60.9 295 48 25 3.5 1.9 | -52.2 -62.0 295 44 23 3.9 2.1
38000 -49.4 -56.9 300 41 21 3.6 2.0 | -49.9 -57.8 300 38 20 3.9 2.1
36000 -47.3 -53.1 310 36 19 3.7 2.0 | -47.2 -53.0 310 32 16 3.7 2.1
34000 -42.7 -44.9 320 34 17 7.7 4.2 | -42.8 -45.0 315 30 15 7.8 4.3
32000 -38.1 -36.6 330 33 17 7.6 4.2 | -38.1 -36.6 325 29 15 7.8 4.3
30000 -33.4 -28.1 330 28 15 7.9 4.4 | -33.2 -27.8 330 26 13 8.1 4.4
29000 -31.0 -23.8 335 26 13 7.9 4.4 | -30.8 -23.4 330 24 12 8.1 4.4
28000 -28.6 -19.5 335 23 12 7.7 4.2 | -28.4 -19.1 330 22 11 7.5 4.1
27000 -26.3 -15.3 340 24 12 7.6 4.2 | -26.2 -15.2 335 22 11 7.3 4.0
26000 -24.0 -11.2 340 24 13 7.6 4.2 | -24.1 -11.4 340 22 11 7.3 4.0
25000 -21.8 -7.2 345 25 13 7.6 4.2 | -21.9 -7.4 340 22 12 7.3 4.0
24000 -19.7 -3.5 345 26 14 6.9 3.8 | -19.6 -3.3 345 24 12 7.6 4.2
23000 -17.6 0.3 350 28 14 6.9 3.8 | -17.3 0.9 350 26 13 7.6 4.2
22000 -15.5 4.1 350 30 15 6.8 3.7 | -15.1 4.8 355 28 14 7.3 4.0
21000 -13.6 7.5 350 28 14 6.5 3.6 | -13.1 8.4 350 27 14 6.6 3.6
20000 -11.7 10.9 350 26 13 6.5 3.6 | -11.1 12.0 350 25 13 6.6 3.6
19500 -10.7 12.7 350 24 13 6.4 3.5 | -10.1 13.8 350 25 13 6.6 3.6
19000 -9.7 14.5 345 23 12 7.4 4.1 | -9.1 15.6 350 24 12 7.1 3.9
18500 -8.1 17.4 345 22 11 7.3 4.0 | -7.6 18.3 345 23 12 7.1 3.9
18000 -7.0 19.4 345 21 11 7.5 4.1 | -6.5 20.3 345 22 11 7.1 3.9
17500 -5.9 21.4 345 20 10 7.5 4.1 | -5.5 22.1 340 22 11 7.1 3.9
17000 -4.8 23.4 345 19 10 7.4 4.1 | -4.4 24.1 340 21 11 6.9 3.8
16500 -3.7 25.3 345 19 10 7.3 4.0 | -3.4 25.9 340 21 11 6.8 3.8
16000 -2.6 27.3 345 18 9 7.3 4.0 | -2.4 27.7 340 20 11 6.8 3.8
15500 -1.6 29.1 345 18 9 6.8 3.8 | -1.4 29.5 340 20 10 6.8 3.8
15000 -0.6 30.9 345 17 9 6.9 3.8 | -0.4 31.3 335 19 10 6.8 3.7
14500 0.4 32.7 345 17 9 6.7 3.6 | 0.6 33.1 335 19 10 7.1 3.9
14000 1.4 34.5 345 16 8 6.7 3.6 | 1.6 34.9 335 18 9 7.1 3.9
13500 2.4 36.3 345 15 8 7.1 3.9 | 2.7 36.9 335 18 9 7.4 4.0
13000 3.4 38.1 345 15 8 7.2 3.9 | 3.8 38.8 335 17 9 7.4 4.1
12500 4.5 40.1 345 15 8 8.1 4.4 | 4.8 40.6 335 17 9 7.5 4.1
12000 5.7 42.3 350 15 8 8.5 4.7 | 5.9 42.6 335 16 8 7.5 4.1
11500 7.0 44.6 350 15 8 8.7 4.8 | 7.0 44.6 340 15 8 7.6 4.2
11000 8.3 46.9 350 15 8 8.7 4.8 | 8.0 46.4 345 14 7 7.7 4.2
10500 9.5 49.1 350 14 7 6.3 3.5 | 9.1 48.4 350 13 7 5.5 3.0
10250 9.9 49.8 350 14 7 6.1 3.3 | 9.4 48.9 355 12 6 6.6 3.6
10000 10.4 50.7 350 13 7 9.6 5.3 | 10.1 50.2 355 12 6 10.8 5.9
9750 11.1 52.0 345 12 6 10.0 5.5 | 10.9 51.6 360 12 6 10.6 5.8
9500 11.7 53.1 345 10 5 7.3 4.0 | 11.6 52.9 360 11 6 8.2 4.5
9250 12.1 53.8 340 9 5 5.1 2.8 | 12.1 53.8 005 11 6 6.5 3.5
9000 12.5 54.5 340 8 4 7.6 4.2 | 12.7 54.9 005 11 6 9.6 5.3
8750 13.1 55.6 340 7 4 8.7 4.8 | 13.5 56.3 005 10 5 10.6 5.8
8500 13.6 56.5 340 7 3 6.8 3.7 | 14.1 57.4 005 10 5 8.1 4.4
8250 14.1 57.4 340 6 3 5.9 3.3 | 14.6 58.3 005 9 5 6.5 3.6
8000 14.6 58.3 345 6 3 7.7 4.2 | 15.2 59.4 005 9 5 10.5 5.8
7750 15.2 59.4 340 6 3 6.8 3.7 | 16.1 61.0 005 8 4 11.7 6.4
7500 15.5 59.9 340 6 3 4.0 2.2 | 16.8 62.2 005 8 4 8.3 4.6
7250 15.8 60.4 335 6 3 3.2 1.8 | 17.4 63.3 005 8 4 7.2 4.0
7000 16.1 61.0 335 6 3 5.7 3.1 | 18.0 64.4 005 8 4 11.9 6.5
6750 16.6 61.9 330 6 3 4.4 2.4 | 19.0 66.2 010 8 4 13.2 7.3
6500 16.7 62.1 325 5 3 1.1 0.6 | 19.8 67.6 010 8 4 9.3 5.1
6250 16.8 62.2 325 5 3 2.0 1.1 | 20.6 69.1 010 7 4 10.9 6.0
6000 16.9 62.4 320 5 2 1.7 0.9 | 21.3 70.3 010 7 4 8.6 4.7
5750 17.2 63.0 315 4 2 7.7 4.2 | 22.0 71.6 010 7 4 14.7 8.1
5500 18.1 64.6 315 3 2 17.6 9.7 | 23.7 74.7 010 7 3 30.5 16.7
09/01/2025 at 1500 MDT | 09/01/2025 at 1800 MDT
|
CAPE... +7.9 LI... +1.3 | CAPE... +7.9 LI... +1.6
CINH... -20.8 K Index... +17.2 | CINH... -54.8 K Index... +21.1
|
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 -62.3 -80.1 295 37 19 2.8 1.5 | -62.1 -79.8 295 38 20 3.0 1.7
45000 -57.9 -72.2 295 47 24 3.3 1.8 | -57.6 -71.7 290 49 25 3.0 1.7
40000 -52.8 -63.0 295 43 22 4.6 2.5 | -52.8 -63.0 295 46 24 4.7 2.6
38000 -50.1 -58.2 295 38 20 4.5 2.5 | -50.0 -58.0 300 39 20 4.7 2.6
36000 -47.4 -53.3 300 33 17 4.6 2.5 | -47.2 -53.0 305 32 17 4.6 2.5
34000 -42.6 -44.7 310 29 15 7.6 4.2 | -42.5 -44.5 305 27 14 7.4 4.1
32000 -38.1 -36.6 315 26 13 7.5 4.1 | -38.0 -36.4 310 22 12 7.4 4.0
30000 -33.3 -27.9 320 24 12 8.0 4.4 | -33.4 -28.1 315 22 11 7.8 4.3
29000 -30.9 -23.6 325 23 12 8.0 4.4 | -31.0 -23.8 320 21 11 7.8 4.3
28000 -28.5 -19.3 325 22 11 7.3 4.0 | -28.7 -19.7 325 21 11 7.3 4.0
27000 -26.4 -15.5 330 22 11 7.0 3.9 | -26.6 -15.9 330 21 11 7.2 3.9
26000 -24.3 -11.7 335 22 11 7.0 3.9 | -24.4 -11.9 335 21 11 7.2 3.9
25000 -22.2 -8.0 340 22 11 7.2 3.9 | -22.3 -8.1 340 22 11 7.4 4.0
24000 -19.9 -3.8 345 23 12 7.8 4.3 | -19.9 -3.8 340 22 11 8.0 4.4
23000 -17.6 0.3 350 24 12 7.9 4.3 | -17.5 0.5 340 21 11 8.0 4.4
22000 -15.2 4.6 350 25 13 7.6 4.2 | -15.1 4.8 345 21 11 7.9 4.3
21000 -13.1 8.4 350 24 12 7.2 4.0 | -12.8 9.0 340 21 11 7.8 4.3
20000 -10.9 12.4 345 23 12 7.2 4.0 | -10.5 13.1 335 21 11 7.8 4.3
19500 -9.8 14.4 345 23 12 7.2 4.0 | -9.4 15.1 335 21 11 7.8 4.3
19000 -8.8 16.2 345 23 12 7.1 3.9 | -8.3 17.1 330 22 11 7.3 4.0
18500 -7.2 19.0 340 23 12 7.1 3.9 | -7.2 19.0 325 22 11 7.4 4.0
18000 -6.2 20.8 335 23 12 7.2 4.0 | -5.6 21.9 320 23 12 7.1 3.9
17500 -5.1 22.8 335 23 12 7.3 4.0 | -4.6 23.7 320 23 12 7.2 3.9
17000 -4.1 24.6 330 24 12 7.4 4.0 | -3.6 25.5 315 24 12 7.1 3.9
16500 -3.0 26.6 330 24 12 7.4 4.1 | -2.6 27.3 320 23 12 7.0 3.8
16000 -1.9 28.6 325 24 12 7.4 4.0 | -1.6 29.1 320 23 12 7.0 3.8
15500 -0.9 30.4 325 23 12 6.8 3.7 | -0.6 30.9 325 21 11 6.7 3.7
15000 0.1 32.2 325 23 12 6.8 3.7 | 0.3 32.5 325 20 10 6.6 3.6
14500 1.1 34.0 330 21 11 7.0 3.8 | 1.4 34.5 330 18 10 7.7 4.2
14000 2.1 35.8 335 20 10 7.0 3.8 | 2.5 36.5 335 17 9 7.6 4.2
13500 3.1 37.6 340 18 9 7.7 4.2 | 3.6 38.5 340 15 8 7.5 4.1
13000 4.3 39.7 340 16 8 7.8 4.3 | 4.7 40.5 345 14 7 7.5 4.1
12500 5.4 41.7 345 15 8 8.1 4.4 | 5.9 42.6 355 12 6 8.2 4.5
12000 6.6 43.9 350 13 7 8.2 4.5 | 7.1 44.8 360 11 6 8.4 4.6
11500 7.8 46.0 355 12 6 8.6 4.7 | 8.3 46.9 010 10 5 9.0 4.9
11000 9.1 48.4 360 12 6 8.8 4.8 | 9.7 49.5 015 10 5 9.2 5.0
10500 10.3 50.5 005 11 6 4.1 2.2 | 11.0 51.8 020 10 5 3.8 2.1
10250 10.6 51.1 005 11 6 6.4 3.5 | 11.2 52.2 015 10 5 6.6 3.6
10000 11.4 52.5 005 11 6 13.4 7.4 | 12.1 53.8 020 10 5 14.1 7.7
9750 12.3 54.1 005 11 6 12.2 6.7 | 13.0 55.4 025 10 5 12.3 6.7
9500 13.1 55.6 005 11 6 8.7 4.8 | 13.8 56.8 025 10 5 8.6 4.7
9250 13.7 56.7 005 11 6 6.5 3.6 | 14.3 57.7 030 10 5 6.4 3.5
9000 14.3 57.7 010 11 6 11.2 6.1 | 15.0 59.0 030 10 5 11.4 6.2
8750 15.2 59.4 010 11 6 12.6 6.9 | 15.9 60.6 030 10 5 12.6 6.9
8500 16.0 60.8 010 11 5 9.3 5.1 | 16.7 62.1 035 10 5 9.0 4.9
8250 16.7 62.1 010 11 5 7.4 4.1 | 17.3 63.1 035 10 5 7.1 3.9
8000 17.3 63.1 010 11 5 11.2 6.2 | 17.9 64.2 035 10 5 10.7 5.9
7750 18.3 64.9 015 11 5 12.2 6.7 | 18.9 66.0 035 10 5 11.8 6.5
7500 19.0 66.2 015 10 5 8.7 4.8 | 19.6 67.3 035 11 5 8.7 4.8
7250 19.6 67.3 015 10 5 7.3 4.0 | 20.2 68.4 040 11 5 7.5 4.1
7000 20.2 68.4 015 10 5 11.8 6.5 | 20.8 69.4 040 11 6 11.7 6.4
6750 21.3 70.3 015 10 5 13.2 7.2 | 21.9 71.4 040 11 5 12.5 6.9
6500 22.1 71.8 015 10 5 9.5 5.2 | 22.6 72.7 040 11 5 8.9 4.9
6250 22.8 73.0 015 10 5 11.0 6.0 | 23.3 73.9 040 10 5 10.2 5.6
6000 23.6 74.5 015 10 5 8.6 4.7 | 24.1 75.4 040 10 5 8.7 4.8
5750 24.3 75.7 020 10 5 14.6 8.0 | 24.7 76.5 040 10 5 10.7 5.9
5500 26.0 78.8 020 9 5 30.3 16.6 | 25.8 78.4 040 9 5 17.5 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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