Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
047
UXUS97 KBOU 041223
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0522 MST Thursday, December 4, 2025
This forecast is for Thursday, December 4, 2025:
If the trigger temperature of 40.3 F/4.6 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 194 ft/min (1.0 m/s)
Maximum height of thermals.................. 8274 ft MSL (2970 ft AGL)
Forecast maximum temperature................... 38.0 F/3.8 C
Time of trigger temperature.................... 1500 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................. 6776 ft MSL (1472 ft AGL)
Thermal soaring outlook for Friday 12/05....... Fair
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1700 MST)......... Becoming good by 1300 MDT
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1700 MST)................ Neither
Potential height of wave....................... 18100 ft MSL (12796 ft AGL)
Wave soaring outlook for Friday 12/05.......... Good
Remarks... Stable layer develops today, with increasing flow aloft.
Sunrise/Sunset.................... 07:04:56 / 16:34:52 MST
Total possible sunshine........... 9 hr 29 min 55 sec (569 min 55 sec)
Altitude of sun at 11:49:54 MST... 27.84 degrees
Upper air data from numerical model forecast valid on 12/04/2025 at 0500 MST
Freezing level.................. Entire airmass below 32 F / 0 C
Convective condensation level... 14539 ft MSL (9235 ft AGL)
Lifted condensation level....... 11941 ft MSL (6637 ft AGL)
Lifted index.................... +11.4
K index......................... -6.3
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 -56.5 -69.7 335 32 16 1.2 0.6 M M M M M
45000 -54.7 -66.5 340 36 18 1.1 0.6 M M M M M
40000 -52.0 -61.6 340 32 17 1.9 1.0 M M M M M
38000 -51.0 -59.8 340 31 16 0.6 0.4 M M M M M
36000 -50.7 -59.3 335 30 16 0.6 0.3 M M M M M
34000 -50.3 -58.5 335 30 15 0.4 0.2 M M M M M
32000 -48.6 -55.5 335 28 14 2.9 1.6 M M M M M
30000 -46.8 -52.2 340 26 13 3.8 2.1 M M M M M
29000 -45.2 -49.4 340 23 12 5.7 3.1 28.8 83.8 19.2 M M
28000 -43.5 -46.3 340 21 11 5.7 3.1 27.2 80.9 18.2 M M
27000 -41.8 -43.2 345 18 9 5.8 3.2 25.7 78.2 17.3 M M
26000 -39.9 -39.8 345 18 9 6.8 3.8 24.4 75.8 16.5 M M
25000 -37.8 -36.0 350 19 10 6.9 3.8 23.2 73.7 15.8 M M
24000 -35.8 -32.4 350 21 11 6.8 3.7 22.2 71.9 15.1 M M
23000 -34.0 -29.2 350 21 11 4.7 2.6 20.8 69.4 14.2 M M
22000 -32.5 -26.5 345 18 9 4.8 2.6 18.9 66.0 12.8 M M
21000 -31.1 -24.0 335 16 8 4.7 2.6 17.2 62.9 11.5 M M
20000 -29.5 -21.1 320 15 8 5.9 3.3 15.6 60.1 10.4 M M
19500 -28.6 -19.5 310 15 8 5.9 3.3 14.9 58.9 9.8 M M
19000 -27.7 -17.9 300 15 8 5.9 3.3 14.3 57.7 9.3 M M
18500 -26.8 -16.2 295 16 8 5.9 3.2 13.6 56.6 8.8 M M
18000 -25.8 -14.4 290 17 9 7.4 4.1 13.1 55.6 8.4 M M
17500 -24.7 -12.5 285 17 9 7.7 4.2 12.7 54.9 8.2 M M
17000 -23.5 -10.3 285 18 9 7.7 4.2 12.4 54.3 7.9 M M
16500 -21.8 -7.2 285 18 9 7.7 4.2 11.9 53.3 7.5 M M
16000 -20.7 -5.3 285 19 10 7.6 4.2 11.5 52.7 7.2 M M
15500 -19.5 -3.1 290 19 10 7.6 4.2 11.1 52.1 6.9 M M
15000 -18.4 -1.1 290 19 10 7.3 4.0 10.8 51.4 6.6 M M
14500 -17.4 0.7 295 18 10 6.8 3.7 10.3 50.5 6.2 M M
14000 -16.4 2.5 300 18 9 6.7 3.7 9.8 49.7 5.8 M M
13500 -15.4 4.3 300 18 9 6.6 3.6 9.3 48.7 5.3 M M
13000 -14.4 6.1 305 17 9 6.5 3.6 8.8 47.8 4.9 M M
12500 -13.5 7.7 305 17 9 6.4 3.5 8.2 46.8 4.4 M M
12000 -12.5 9.5 310 16 8 6.5 3.6 7.7 45.8 3.9 M M
11500 -11.5 11.3 315 16 8 7.0 3.9 7.2 45.0 3.5 M M
11000 -10.5 13.1 315 15 8 6.9 3.8 6.8 44.2 3.1 M M
10500 -9.5 14.9 315 15 8 6.3 3.5 6.3 43.3 2.6 M M
10250 -9.0 15.8 315 15 8 7.2 4.0 6.0 42.8 2.3 M M
10000 -8.5 16.7 315 15 7 4.0 2.2 5.8 42.4 2.1 M M
9750 -8.3 17.1 315 14 7 4.4 2.4 5.2 41.4 1.6 M M
9500 -7.8 18.0 315 14 7 7.9 4.4 5.0 41.0 1.4 M M
9250 -7.3 18.9 315 14 7 7.0 3.8 4.8 40.7 1.2 M M
9000 -6.8 19.8 310 14 7 6.0 3.3 4.6 40.2 1.0 M M
8750 -6.4 20.5 310 14 7 5.2 2.9 4.2 39.6 0.6 M M
8500 -6.0 21.2 310 14 7 5.8 3.2 3.9 39.0 0.3 M M
8250 -5.6 21.9 305 13 7 4.9 2.7 3.6 38.4 -0.0 192 1.0
8000 -5.3 22.5 305 13 7 3.4 1.8 3.1 37.6 -0.5 176 0.9
7750 -5.0 23.0 305 13 6 3.5 1.9 2.6 36.7 -1.0 162 0.8
7500 -4.8 23.4 300 12 6 3.9 2.1 2.2 35.9 -1.4 146 0.7
7250 -4.5 23.9 300 12 6 3.1 1.7 1.7 35.1 -1.9 131 0.7
7000 -4.3 24.3 295 11 6 2.2 1.2 1.2 34.1 -2.4 118 0.6
6750 -4.1 24.6 290 10 5 3.5 1.9 0.6 33.1 -3.0 105 0.5
6500 -3.9 25.0 285 10 5 -0.4 -0.2 0.1 32.1 -3.5 92 0.5
6250 -4.2 24.4 280 9 5 -4.9 -2.7 -1.0 30.3 -4.6 93 0.5
6000 -4.5 23.9 275 8 4 -3.6 -2.0 -2.0 28.4 -5.6 95 0.5
5750 -4.8 23.4 265 7 4 -5.3 -2.9 -3.0 26.5 -6.7 97 0.5
5500 -5.4 22.3 250 6 3 -10.7 -5.9 -4.4 24.1 -8.0 107 0.5
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
12/04/2025 at 0800 MST | 12/04/2025 at 1100 MST
|
CAPE... 0.0 LI... +7.9 | CAPE... 0.0 LI... +8.3
CINH... 0.0 K Index... -14.8 | CINH... 0.0 K Index... -16.7
|
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 -56.9 -70.4 335 32 17 1.1 0.6 | -57.7 -71.9 340 36 19 2.3 1.3
45000 -55.2 -67.4 335 33 17 1.0 0.5 | -54.1 -65.4 325 39 20 2.6 1.4
40000 -50.5 -58.9 320 34 17 3.1 1.7 | -49.7 -57.5 295 35 18 3.0 1.6
38000 -49.2 -56.6 315 33 17 0.5 0.3 | -48.3 -54.9 290 35 18 1.3 0.7
36000 -48.9 -56.0 315 31 16 0.5 0.3 | -47.5 -53.5 285 33 17 1.3 0.7
34000 -48.6 -55.5 310 29 15 0.5 0.3 | -46.7 -52.1 285 32 17 1.3 0.7
32000 -47.5 -53.5 310 27 14 1.9 1.0 | -46.4 -51.5 285 31 16 0.5 0.3
30000 -46.4 -51.5 310 26 13 1.8 1.0 | -46.0 -50.8 280 30 15 3.3 1.8
29000 -45.1 -49.2 315 26 13 5.1 2.8 | -44.4 -47.9 285 29 15 5.3 2.9
28000 -43.2 -45.8 315 25 13 5.0 2.8 | -42.8 -45.0 285 27 14 5.3 2.9
27000 -41.7 -43.1 320 25 13 5.0 2.7 | -41.3 -42.3 290 26 13 5.3 2.9
26000 -39.8 -39.6 320 24 13 7.4 4.0 | -39.6 -39.3 290 26 13 5.9 3.2
25000 -37.6 -35.7 320 24 12 7.4 4.1 | -37.8 -36.0 295 26 13 5.9 3.2
24000 -35.3 -31.5 325 24 12 7.4 4.1 | -36.0 -32.8 300 26 14 6.0 3.3
23000 -33.1 -27.6 325 24 12 7.5 4.1 | -34.0 -29.2 305 27 14 7.9 4.4
22000 -30.9 -23.6 330 23 12 7.5 4.1 | -31.6 -24.9 305 27 14 8.0 4.4
21000 -28.7 -19.7 330 22 12 7.6 4.2 | -29.2 -20.6 310 27 14 8.0 4.4
20000 -26.7 -16.1 330 21 11 6.3 3.5 | -26.8 -16.2 310 26 14 7.8 4.3
19500 -25.7 -14.3 330 21 11 6.3 3.5 | -25.6 -14.1 310 26 13 7.8 4.3
19000 -24.8 -12.6 325 20 10 6.4 3.5 | -24.5 -12.1 310 26 13 7.8 4.3
18500 -23.8 -10.8 320 20 10 6.5 3.5 | -23.3 -9.9 310 25 13 7.9 4.3
18000 -22.9 -9.2 320 19 10 5.1 2.8 | -22.2 -8.0 310 25 13 7.1 3.9
17500 -22.2 -8.0 310 19 10 5.0 2.7 | -21.1 -6.0 310 25 13 7.1 3.9
17000 -21.4 -6.5 300 19 10 4.8 2.6 | -20.0 -4.0 310 25 13 6.8 3.7
16500 -20.8 -5.4 295 18 9 4.5 2.5 | -19.1 -2.4 305 24 13 6.4 3.5
16000 -20.1 -4.2 290 18 9 4.6 2.5 | -17.7 0.1 305 23 12 5.4 3.0
15500 -19.3 -2.7 285 18 9 6.1 3.3 | -16.9 1.6 300 22 12 5.0 2.7
15000 -18.4 -1.1 285 18 9 6.0 3.3 | -16.2 2.8 295 22 11 4.6 2.5
14500 -17.5 0.5 280 17 9 5.9 3.3 | -15.5 4.1 290 20 10 4.2 2.3
14000 -16.2 2.8 285 17 9 6.1 3.3 | -14.9 5.2 285 18 10 4.2 2.3
13500 -15.3 4.5 285 16 8 5.9 3.3 | -14.3 6.3 285 17 9 4.3 2.4
13000 -14.4 6.1 285 15 8 5.9 3.2 | -13.7 7.3 285 15 8 4.4 2.4
12500 -13.6 7.5 290 14 7 5.8 3.2 | -12.9 8.8 285 13 7 5.1 2.8
12000 -12.7 9.1 290 13 7 5.9 3.3 | -12.2 10.0 280 12 6 5.2 2.9
11500 -11.8 10.8 290 12 6 6.3 3.5 | -11.4 11.5 280 10 5 6.0 3.3
11000 -10.9 12.4 295 12 6 6.1 3.4 | -10.5 13.1 280 9 5 6.2 3.4
10500 -10.0 14.0 295 12 6 5.6 3.0 | -9.5 14.9 285 8 4 7.0 3.8
10250 -9.6 14.7 300 11 6 6.4 3.5 | -8.9 16.0 290 7 4 7.7 4.2
10000 -9.2 15.4 300 11 6 3.3 1.8 | -8.4 16.9 290 7 4 4.7 2.6
9750 -9.0 15.8 300 11 6 5.2 2.9 | -8.1 17.4 295 7 4 6.1 3.3
9500 -8.3 17.1 300 11 5 9.7 5.3 | -7.4 18.7 305 8 4 10.1 5.5
9250 -7.7 18.1 305 10 5 8.4 4.6 | -6.8 19.8 310 10 5 8.9 4.9
9000 -7.1 19.2 305 11 5 7.6 4.2 | -6.1 21.0 315 11 6 7.7 4.2
8750 -6.5 20.3 305 13 7 8.0 4.4 | -5.7 21.7 310 15 8 5.3 2.9
8500 -5.9 21.4 305 15 8 9.7 5.3 | -5.3 22.5 305 18 9 4.8 2.6
8250 -5.2 22.6 305 18 9 7.5 4.1 | -5.0 23.0 300 22 11 4.4 2.4
8000 -4.7 23.5 300 20 10 5.8 3.2 | -4.7 23.5 295 23 12 2.7 1.5
7750 -4.3 24.3 300 23 12 4.0 2.2 | -4.5 23.9 290 24 12 4.5 2.4
7500 -4.2 24.4 295 24 12 2.4 1.3 | -4.1 24.6 285 22 12 6.6 3.6
7250 -3.9 25.0 295 24 13 5.0 2.8 | -3.6 25.5 285 21 11 7.4 4.1
7000 -3.5 25.7 295 22 12 5.1 2.8 | -3.0 26.6 285 19 10 8.3 4.5
6750 -3.1 26.4 295 21 11 8.7 4.8 | -2.4 27.7 280 17 9 8.4 4.6
6500 -2.4 27.7 295 19 10 2.4 1.3 | -1.8 28.8 280 16 8 7.0 3.8
6250 -2.8 27.0 290 16 8 -6.4 -3.5 | -1.4 29.5 275 13 7 5.5 3.0
6000 -3.1 26.4 280 12 6 -3.4 -1.9 | -1.0 30.2 270 10 5 5.2 2.9
5750 -3.5 25.7 270 10 5 -6.5 -3.6 | -0.6 30.9 255 8 4 7.2 4.0
5500 -4.3 24.3 245 6 3 -16.0 -8.8 | 0.2 32.4 245 6 3 13.9 7.6
12/04/2025 at 1400 MST | 12/04/2025 at 1700 MST
|
CAPE... 0.0 LI... +7.4 | CAPE... 0.0 LI... +6.0
CINH... 0.0 K Index... +0.7 | CINH... 0.0 K Index... -0.9
|
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 -57.1 -70.8 340 35 18 3.2 1.8 | -57.2 -71.0 335 34 17 4.3 2.4
45000 -52.3 -62.1 330 41 21 3.0 1.6 | -50.7 -59.3 320 36 18 3.7 2.1
40000 -48.3 -54.9 305 42 22 2.7 1.5 | -47.1 -52.8 315 43 22 2.3 1.3
38000 -47.0 -52.6 295 43 22 0.9 0.5 | -46.3 -51.3 315 43 22 0.1 0.1
36000 -46.5 -51.7 295 40 21 0.9 0.5 | -46.2 -51.2 315 41 21 0.1 0.1
34000 -46.0 -50.8 290 38 20 0.9 0.5 | -46.1 -51.0 310 39 20 0.3 0.2
32000 -45.5 -49.9 290 38 20 0.8 0.5 | -45.5 -49.9 325 39 20 1.1 0.6
30000 -45.0 -49.0 295 38 20 2.3 1.3 | -44.8 -48.6 345 42 22 1.4 0.8
29000 -43.7 -46.7 295 38 20 4.2 2.3 | -43.6 -46.5 340 44 23 4.5 2.5
28000 -42.5 -44.5 295 39 20 4.2 2.3 | -41.9 -43.4 340 46 24 4.5 2.5
27000 -41.2 -42.2 295 39 20 4.3 2.3 | -40.6 -41.1 340 47 24 4.4 2.4
26000 -39.5 -39.1 295 38 20 6.7 3.7 | -39.1 -38.4 335 48 25 5.6 3.1
25000 -37.5 -35.5 295 38 20 6.8 3.7 | -37.4 -35.3 335 49 25 5.6 3.1
24000 -35.5 -31.9 295 38 19 6.8 3.7 | -35.7 -32.3 330 49 25 5.6 3.1
23000 -33.4 -28.1 300 36 19 7.2 4.0 | -33.7 -28.7 330 49 25 7.7 4.2
22000 -31.2 -24.2 300 35 18 7.2 4.0 | -31.4 -24.5 330 47 24 7.8 4.3
21000 -29.0 -20.2 300 33 17 7.2 3.9 | -29.1 -20.4 330 46 24 7.7 4.2
20000 -26.8 -16.2 300 32 16 7.9 4.3 | -26.6 -15.9 330 42 22 8.2 4.5
19500 -25.6 -14.1 300 31 16 7.9 4.3 | -25.4 -13.7 325 40 21 8.2 4.5
19000 -24.4 -11.9 300 31 16 7.9 4.4 | -24.2 -11.6 325 38 20 8.2 4.5
18500 -23.2 -9.8 295 31 16 8.0 4.4 | -22.9 -9.2 325 36 19 8.3 4.5
18000 -22.1 -7.8 295 30 16 7.3 4.0 | -21.8 -7.2 320 34 18 7.4 4.1
17500 -21.0 -5.8 295 29 15 7.2 3.9 | -20.7 -5.3 315 32 16 7.4 4.1
17000 -19.9 -3.8 290 27 14 6.7 3.7 | -19.5 -3.1 315 29 15 6.5 3.6
16500 -18.6 -1.5 295 25 13 5.8 3.2 | -18.7 -1.7 315 28 14 5.6 3.1
16000 -17.7 0.1 295 23 12 4.5 2.5 | -17.9 -0.2 315 26 14 5.6 3.1
15500 -17.2 1.0 295 21 11 3.6 2.0 | -17.1 1.2 315 25 13 5.3 2.9
15000 -16.7 1.9 300 19 10 3.4 1.9 | -16.3 2.7 320 24 12 5.4 3.0
14500 -16.2 2.8 300 18 9 3.2 1.8 | -15.2 4.6 320 21 11 4.8 2.6
14000 -15.7 3.7 305 17 9 3.4 1.9 | -14.6 5.7 320 19 10 4.9 2.7
13500 -15.1 4.8 310 15 8 4.4 2.4 | -13.8 7.2 325 17 9 5.5 3.0
13000 -14.5 5.9 310 13 7 4.5 2.4 | -13.0 8.6 325 15 8 5.7 3.1
12500 -13.7 7.3 315 11 6 6.3 3.4 | -12.0 10.4 325 13 7 6.9 3.8
12000 -12.7 9.1 315 10 5 6.4 3.5 | -11.0 12.2 320 11 6 7.1 3.9
11500 -11.5 11.3 315 9 5 9.3 5.1 | -9.8 14.4 320 10 5 8.9 4.9
11000 -10.2 13.6 315 9 4 9.3 5.1 | -8.5 16.7 320 9 5 8.8 4.8
10500 -8.7 16.3 315 10 5 10.0 5.5 | -7.1 19.2 315 12 6 8.9 4.9
10250 -7.9 17.8 310 11 6 11.4 6.2 | -6.4 20.5 310 14 7 10.3 5.7
10000 -7.2 19.0 310 12 6 6.1 3.3 | -5.7 21.7 310 16 8 5.1 2.8
9750 -6.9 19.6 305 14 7 5.4 2.9 | -5.6 21.9 305 18 9 3.0 1.7
9500 -6.3 20.7 305 18 9 9.9 5.5 | -5.2 22.6 300 22 11 6.6 3.6
9250 -5.6 21.9 300 22 11 9.4 5.2 | -4.7 23.5 295 26 14 5.9 3.2
9000 -5.0 23.0 300 26 13 5.4 2.9 | -4.3 24.3 295 30 16 4.5 2.5
8750 -4.8 23.4 295 27 14 3.0 1.7 | -4.1 24.6 290 31 16 3.9 2.1
8500 -4.4 24.1 290 27 14 5.0 2.7 | -3.7 25.3 290 30 15 4.9 2.7
8250 -4.1 24.6 290 26 14 5.4 3.0 | -3.4 25.9 285 29 15 5.2 2.8
8000 -3.6 25.5 285 25 13 8.2 4.5 | -2.9 26.8 285 28 14 6.9 3.8
7750 -2.9 26.8 285 23 12 8.6 4.7 | -2.4 27.7 280 26 13 7.5 4.1
7500 -2.3 27.9 285 21 11 8.2 4.5 | -1.8 28.8 280 23 12 7.5 4.1
7250 -1.7 28.9 285 19 10 7.4 4.0 | -1.3 29.7 280 21 11 7.1 3.9
7000 -1.2 29.8 285 16 8 6.8 3.8 | -0.8 30.6 275 19 10 6.6 3.6
6750 -0.7 30.7 285 13 7 5.9 3.2 | -0.3 31.5 275 17 9 6.8 3.7
6500 -0.3 31.5 285 10 5 6.8 3.7 | 0.2 32.4 270 15 7 6.8 3.7
6250 0.3 32.5 280 8 4 9.8 5.4 | 0.7 33.3 265 12 6 6.6 3.6
6000 1.1 34.0 280 7 4 10.2 5.6 | 1.2 34.2 260 10 5 7.0 3.8
5750 1.8 35.2 275 6 3 9.7 5.3 | 1.7 35.1 245 8 4 5.8 3.2
5500 2.5 36.5 275 6 3 10.0 5.5 | 1.9 35.4 230 7 3 0.3 0.1
________________________________________________________________________________
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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