Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
625
UXUS97 KBOU 091317
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0614 MST Tuesday, December 9, 2025
This forecast is for Tuesday, December 9, 2025:
If the trigger temperature of 63.1 F/17.3 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 51 ft/min (0.3 m/s)
Maximum height of thermals.................. 8755 ft MSL (3499 ft AGL)
Forecast maximum temperature................... 61.0 F/16.6 C
Time of trigger temperature.................... None
Time of overdevelopment........................ 1100 MST
Middle/high clouds during soaring window....... Broken/overcast thin middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 7905 ft MSL (2649 ft AGL)
Thermal soaring outlook for Wednesday 12/10.... Poor
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1700 MST)......... No change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1700 MST)................ Weak NVA
Potential height of wave....................... 17066 ft MSL (11810 ft AGL)
Wave soaring outlook for Wednesday 12/10....... Fair
Remarks...
Sunrise/Sunset.................... 07:09:21 / 16:34:46 MST
Total possible sunshine........... 9 hr 25 min 25 sec (565 min 25 sec)
Altitude of sun at 11:52:04 MST... 27.31 degrees
Upper air data from numerical model forecast valid on 12/09/2025 at 0500 MST
Freezing level.................. 11824 ft MSL (6568 ft AGL)
Convective condensation level... 17949 ft MSL (12693 ft AGL)
Lifted condensation level....... 14127 ft MSL (8871 ft AGL)
Lifted index.................... +7.9
K index......................... +11.6
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 -65.8 -86.4 310 49 25 -1.9 -1.0 M M M M M
45000 -68.6 -91.5 300 52 27 -1.4 -0.8 M M M M M
40000 -64.6 -84.3 325 70 36 2.7 1.5 M M M M M
38000 -61.0 -77.8 325 74 38 7.7 4.2 M M M M M
36000 -56.4 -69.5 325 75 38 7.7 4.2 M M M M M
34000 -51.5 -60.7 325 73 38 9.4 5.1 M M M M M
32000 -45.9 -50.6 325 67 35 9.4 5.1 M M M M M
30000 -40.3 -40.5 325 60 31 9.1 5.0 36.1 97.1 15.1 M M
29000 -37.6 -35.7 325 55 28 9.0 5.0 35.8 96.4 15.0 M M
28000 -34.3 -29.7 320 49 25 9.0 5.0 35.5 96.0 15.0 M M
27000 -31.6 -24.9 320 45 23 8.0 4.4 35.2 95.3 14.9 M M
26000 -29.2 -20.6 320 44 23 8.1 4.4 34.5 94.0 14.5 M M
25000 -26.8 -16.2 320 43 22 8.1 4.4 33.9 93.0 14.2 M M
24000 -24.5 -12.1 320 42 22 6.3 3.5 33.2 91.8 13.8 M M
23000 -22.7 -8.9 315 41 21 6.2 3.4 31.8 89.3 12.8 M M
22000 -20.9 -5.6 315 39 20 6.2 3.4 30.5 87.0 11.8 M M
21000 -18.9 -2.0 315 38 19 7.8 4.3 29.4 85.0 11.0 M M
20000 -16.6 2.1 315 37 19 7.6 4.2 28.6 83.5 10.4 M M
19500 -15.5 4.1 315 37 19 7.6 4.2 28.3 82.9 10.2 M M
19000 -14.4 6.1 315 37 19 7.7 4.2 27.9 82.3 9.9 M M
18500 -13.3 8.1 320 37 19 6.7 3.7 27.5 81.6 9.7 M M
18000 -12.3 9.9 320 38 20 6.6 3.6 27.0 80.6 9.2 M M
17500 -11.3 11.7 320 39 20 6.5 3.6 26.5 79.6 8.8 M M
17000 -10.4 13.3 320 39 20 6.2 3.4 25.9 78.5 8.3 M M
16500 -9.5 14.9 320 40 21 6.2 3.4 25.3 77.5 7.8 M M
16000 -8.6 16.5 320 40 21 6.3 3.5 24.7 76.4 7.3 M M
15500 -7.6 18.3 320 40 21 6.4 3.5 24.1 75.4 6.8 M M
15000 -6.7 19.9 320 40 21 6.5 3.6 23.6 74.4 6.3 M M
14500 -5.7 21.7 320 39 20 6.6 3.6 23.0 73.4 5.9 M M
14000 -4.7 23.5 320 39 20 6.8 3.7 22.5 72.5 5.4 M M
13500 -3.7 25.3 320 37 19 7.1 3.9 22.1 71.7 5.0 M M
13000 -2.1 28.2 320 34 17 6.7 3.7 21.4 70.5 4.5 M M
12500 -1.1 30.0 320 31 16 6.6 3.6 20.9 69.6 4.0 M M
12000 -0.2 31.6 320 29 15 7.0 3.8 20.4 68.7 3.5 M M
11500 0.9 33.6 320 25 13 7.2 3.9 20.0 68.0 3.2 M M
11000 2.0 35.6 320 22 11 7.4 4.0 19.6 67.3 2.8 M M
10500 3.1 37.6 315 25 13 8.4 4.6 19.2 66.6 2.4 M M
10250 3.6 38.5 315 26 13 3.8 2.1 19.0 66.2 2.3 M M
10000 3.7 38.7 310 26 13 3.6 2.0 18.4 65.1 1.7 M M
9750 4.2 39.6 310 30 15 7.9 4.4 18.2 64.7 1.4 M M
9500 4.8 40.6 305 33 17 7.2 3.9 18.0 64.3 1.2 M M
9250 5.3 41.5 305 37 19 6.0 3.3 17.8 64.0 1.0 M M
9000 5.6 42.1 305 41 21 1.3 0.7 17.3 63.1 0.6 M M
8750 5.5 41.9 300 45 23 -0.9 -0.5 16.5 61.7 -0.2 249 1.3
8500 5.5 41.9 300 49 25 0.1 0.0 15.7 60.3 -0.9 243 1.2
8250 5.5 41.9 295 53 27 -2.4 -1.3 14.9 58.9 -1.7 237 1.2
8000 5.1 41.2 295 53 27 -5.4 -2.9 13.8 56.9 -2.8 239 1.2
7750 4.9 40.8 290 51 26 -1.2 -0.7 12.8 55.0 -3.8 240 1.2
7500 4.9 40.8 285 47 24 1.6 0.9 12.1 53.8 -4.4 231 1.2
7250 5.1 41.2 285 44 23 2.6 1.4 11.5 52.7 -5.1 220 1.1
7000 5.3 41.5 285 40 21 3.6 2.0 11.0 51.8 -5.5 204 1.0
6750 5.6 42.1 285 36 18 4.4 2.4 10.5 51.0 -6.0 189 1.0
6500 5.9 42.6 285 32 16 2.6 1.4 10.1 50.2 -6.4 172 0.9
6250 5.9 42.6 280 27 14 -1.2 -0.7 9.4 48.9 -7.2 164 0.8
6000 5.9 42.6 280 23 12 -0.2 -0.1 8.6 47.4 -8.0 159 0.8
5750 5.8 42.4 275 18 9 -4.0 -2.2 7.8 46.0 -8.8 154 0.8
5500 5.0 41.0 265 12 6 -18.8 -10.3 6.2 43.2 -10.4 171 0.9
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
12/09/2025 at 0800 MST | 12/09/2025 at 1100 MST
|
CAPE... 0.0 LI... +4.2 | CAPE... 0.0 LI... +4.0
CINH... 0.0 K Index... +12.5 | CINH... 0.0 K Index... +11.7
|
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 -65.1 -85.2 325 41 21 -1.9 -1.0 | -65.3 -85.5 320 48 24 -0.8 -0.4
45000 -67.9 -90.2 325 47 24 1.4 0.8 | -66.4 -87.5 330 60 31 0.5 0.3
40000 -64.3 -83.7 325 80 41 2.4 1.3 | -64.8 -84.6 295 72 37 1.1 0.6
38000 -60.9 -77.6 325 78 40 7.2 4.0 | -61.2 -78.2 295 70 36 8.5 4.7
36000 -56.6 -69.9 320 69 36 7.2 4.0 | -56.1 -69.0 305 63 32 8.5 4.7
34000 -51.8 -61.2 315 63 33 9.5 5.2 | -50.9 -59.6 310 59 30 9.2 5.0
32000 -46.1 -51.0 320 63 33 9.5 5.2 | -44.7 -48.5 315 62 32 9.2 5.0
30000 -39.9 -39.8 320 62 32 8.7 4.8 | -39.3 -38.7 315 63 32 8.8 4.8
29000 -37.3 -35.1 320 61 32 8.8 4.8 | -36.6 -33.9 320 62 32 8.8 4.8
28000 -34.7 -30.5 320 60 31 8.8 4.8 | -34.0 -29.2 320 62 32 8.8 4.8
27000 -32.2 -26.0 320 59 30 7.8 4.3 | -31.4 -24.5 320 60 31 8.1 4.5
26000 -29.8 -21.6 320 56 29 7.8 4.3 | -29.0 -20.2 320 59 30 8.2 4.5
25000 -27.5 -17.5 320 53 27 7.8 4.3 | -26.5 -15.7 315 57 29 8.2 4.5
24000 -25.2 -13.4 325 51 26 7.6 4.2 | -24.1 -11.4 315 55 28 8.1 4.4
23000 -23.0 -9.4 325 50 26 7.6 4.2 | -21.7 -7.1 315 53 27 8.1 4.4
22000 -20.7 -5.3 325 49 25 7.6 4.2 | -19.3 -2.7 315 51 27 8.1 4.4
21000 -18.4 -1.1 325 48 25 8.2 4.5 | -16.9 1.6 315 50 26 7.4 4.1
20000 -16.0 3.2 330 48 25 8.1 4.5 | -14.7 5.5 315 47 24 7.5 4.1
19500 -14.8 5.4 330 48 24 8.2 4.5 | -13.6 7.5 315 46 24 7.5 4.1
19000 -13.6 7.5 330 47 24 8.2 4.5 | -12.5 9.5 320 45 23 7.5 4.1
18500 -12.4 9.7 330 47 24 7.6 4.2 | -11.4 11.5 320 43 22 7.2 4.0
18000 -11.3 11.7 330 46 24 7.5 4.1 | -10.3 13.5 320 42 22 7.1 3.9
17500 -10.2 13.6 330 46 23 7.3 4.0 | -9.3 15.3 325 42 21 7.1 3.9
17000 -9.2 15.4 330 44 23 6.5 3.6 | -8.2 17.2 325 40 21 7.0 3.9
16500 -8.2 17.2 330 43 22 6.6 3.6 | -6.6 20.1 325 37 19 7.0 3.8
16000 -7.2 19.0 330 41 21 6.1 3.4 | -5.6 21.9 325 35 18 6.9 3.8
15500 -5.9 21.4 330 37 19 6.2 3.4 | -4.6 23.7 325 33 17 6.8 3.7
15000 -5.0 23.0 330 35 18 5.6 3.1 | -3.5 25.7 330 32 17 8.2 4.5
14500 -4.2 24.4 330 33 17 5.6 3.1 | -2.3 27.9 330 32 16 8.0 4.4
14000 -3.3 26.1 330 30 16 6.1 3.4 | -1.1 30.0 330 31 16 7.8 4.3
13500 -2.4 27.7 330 28 14 6.1 3.4 | 0.0 32.0 325 33 17 7.8 4.3
13000 -1.5 29.3 330 25 13 7.5 4.1 | 1.2 34.2 325 34 17 7.3 4.0
12500 -0.3 31.5 330 24 12 8.0 4.4 | 2.2 36.0 325 34 18 7.0 3.9
12000 0.9 33.6 325 22 11 8.6 4.7 | 3.3 37.9 320 34 18 6.6 3.6
11500 2.3 36.1 325 25 13 9.0 4.9 | 4.2 39.6 320 39 20 6.0 3.3
11000 3.6 38.5 325 27 14 8.1 4.5 | 5.1 41.2 315 43 22 4.4 2.4
10500 4.7 40.5 320 31 16 6.6 3.6 | 5.4 41.7 315 43 22 1.9 1.0
10250 5.3 41.5 320 32 17 10.7 5.9 | 5.6 42.1 310 43 22 3.4 1.8
10000 6.1 43.0 315 36 19 6.7 3.7 | 5.9 42.6 310 44 23 3.6 2.0
9750 6.2 43.2 315 37 19 -0.5 -0.2 | 6.0 42.8 305 45 23 1.8 1.0
9500 6.2 43.2 310 39 20 1.5 0.8 | 6.2 43.2 305 46 24 2.0 1.1
9250 6.3 43.3 310 40 21 0.9 0.5 | 6.3 43.3 300 47 24 1.8 1.0
9000 6.3 43.3 305 42 22 -1.8 -1.0 | 6.3 43.3 295 47 24 -2.7 -1.5
8750 6.0 42.8 305 44 23 -4.1 -2.3 | 6.0 42.8 295 47 24 -3.2 -1.7
8500 5.7 42.3 300 45 23 -3.6 -2.0 | 5.9 42.6 290 48 25 -0.2 -0.1
8250 5.4 41.7 295 46 24 -4.3 -2.4 | 5.8 42.4 290 50 26 -1.2 -0.7
8000 5.1 41.2 290 45 23 -5.7 -3.1 | 5.7 42.3 285 49 25 -1.7 -0.9
7750 4.7 40.5 290 43 22 -3.3 -1.8 | 5.6 42.1 285 44 23 -0.0 -0.0
7500 4.5 40.1 285 39 20 -3.1 -1.7 | 5.7 42.3 280 41 21 0.5 0.3
7250 4.3 39.7 285 36 19 2.0 1.1 | 5.7 42.3 280 37 19 3.1 1.7
7000 4.8 40.6 285 32 17 7.4 4.1 | 6.1 43.0 275 33 17 6.8 3.7
6750 5.3 41.5 280 29 15 6.4 3.5 | 6.6 43.9 275 30 15 6.8 3.7
6500 5.8 42.4 280 26 14 5.9 3.3 | 7.2 45.0 275 27 14 6.7 3.7
6250 6.1 43.0 275 23 12 2.8 1.5 | 7.6 45.7 270 23 12 4.2 2.3
6000 6.3 43.3 270 19 10 2.9 1.6 | 7.8 46.0 265 20 10 4.0 2.2
5750 6.5 43.7 265 16 8 -0.0 -0.0 | 8.1 46.6 260 16 8 1.1 0.6
5500 6.0 42.8 250 12 6 -12.8 -7.0 | 7.9 46.2 245 11 6 -5.3 -2.9
12/09/2025 at 1400 MST | 12/09/2025 at 1700 MST
|
CAPE... 0.0 LI... +4.5 | CAPE... 0.0 LI... +5.2
CINH... 0.0 K Index... +9.5 | CINH... 0.0 K Index... +7.0
|
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 -65.2 -85.4 305 48 25 -3.0 -1.7 | -65.1 -85.2 300 55 28 -3.3 -1.8
45000 -69.8 -93.6 320 69 35 2.0 1.1 | -69.9 -93.8 315 69 36 3.7 2.0
40000 -64.4 -83.9 300 76 39 3.7 2.0 | -63.2 -81.8 295 78 40 4.5 2.5
38000 -60.2 -76.4 300 74 38 8.6 4.7 | -59.1 -74.4 295 79 40 7.9 4.3
36000 -55.0 -67.0 300 69 35 8.6 4.7 | -54.4 -65.9 300 77 40 7.9 4.3
34000 -49.8 -57.6 300 66 34 8.9 4.9 | -49.6 -57.3 305 75 39 8.0 4.4
32000 -43.8 -46.8 300 67 34 8.9 4.9 | -44.2 -47.6 305 71 36 8.0 4.4
30000 -38.7 -37.7 305 67 34 8.0 4.4 | -39.2 -38.6 305 66 34 8.9 4.9
29000 -36.3 -33.3 305 66 34 8.0 4.4 | -36.5 -33.7 305 64 33 8.9 4.9
28000 -33.9 -29.0 310 66 34 8.0 4.4 | -33.8 -28.8 300 62 32 8.9 4.9
27000 -31.4 -24.5 310 65 33 8.5 4.7 | -31.2 -24.2 300 61 31 8.6 4.7
26000 -28.9 -20.0 310 63 33 8.5 4.6 | -28.6 -19.5 300 61 32 8.6 4.7
25000 -26.4 -15.5 310 61 32 8.5 4.6 | -26.0 -14.8 300 62 32 8.6 4.7
24000 -23.9 -11.0 310 59 31 8.1 4.4 | -23.5 -10.3 300 61 32 7.9 4.3
23000 -21.4 -6.5 310 56 29 8.1 4.4 | -21.2 -6.2 300 59 30 7.9 4.3
22000 -19.0 -2.2 310 53 27 8.1 4.4 | -18.8 -1.8 305 56 29 7.9 4.3
21000 -16.7 1.9 310 50 26 7.2 4.0 | -16.5 2.3 305 54 28 7.3 4.0
20000 -14.5 5.9 310 49 25 7.3 4.0 | -14.3 6.3 305 52 27 7.3 4.0
19500 -13.4 7.9 310 49 25 7.3 4.0 | -13.3 8.1 310 51 26 7.3 4.0
19000 -12.3 9.9 310 48 25 7.4 4.0 | -12.2 10.0 310 50 26 7.3 4.0
18500 -11.3 11.7 310 47 24 6.7 3.7 | -11.1 12.0 310 49 25 7.3 4.0
18000 -10.3 13.5 310 42 22 6.5 3.6 | -10.0 14.0 315 49 25 7.2 4.0
17500 -9.3 15.3 310 37 19 6.7 3.7 | -8.9 16.0 315 48 25 7.3 4.0
17000 -8.3 17.1 310 35 18 7.4 4.1 | -7.8 18.0 315 47 24 7.3 4.0
16500 -6.6 20.1 315 33 17 7.2 4.0 | -6.2 20.8 315 45 23 7.1 3.9
16000 -5.6 21.9 315 31 16 6.9 3.8 | -5.2 22.6 315 42 22 6.6 3.6
15500 -4.6 23.7 320 28 14 6.8 3.7 | -4.3 24.3 315 39 20 6.6 3.6
15000 -3.5 25.7 320 26 13 8.3 4.6 | -3.3 26.1 315 37 19 6.8 3.7
14500 -2.3 27.9 320 25 13 8.2 4.5 | -2.3 27.9 315 34 18 6.8 3.7
14000 -1.1 30.0 325 25 13 7.7 4.2 | -1.3 29.7 315 32 16 7.0 3.9
13500 0.1 32.2 325 23 12 7.6 4.2 | -0.2 31.6 320 30 15 7.1 3.9
13000 1.2 34.2 330 22 11 8.2 4.5 | 0.8 33.4 320 28 14 6.3 3.4
12500 2.5 36.5 325 26 13 8.5 4.7 | 1.7 35.1 320 24 12 5.8 3.2
12000 3.8 38.8 325 29 15 6.9 3.8 | 2.5 36.5 320 21 11 6.9 3.8
11500 4.5 40.1 325 27 14 4.9 2.7 | 3.7 38.7 325 22 12 8.2 4.5
11000 5.2 41.4 325 24 13 4.9 2.7 | 5.0 41.0 330 24 12 6.9 3.8
10500 5.9 42.6 320 28 15 5.3 2.9 | 5.7 42.3 325 28 15 5.0 2.7
10250 6.3 43.3 320 31 16 3.6 2.0 | 6.1 43.0 320 31 16 4.9 2.7
10000 6.4 43.5 320 31 16 1.6 0.9 | 6.4 43.5 320 32 16 3.7 2.0
9750 6.5 43.7 315 33 17 2.3 1.3 | 6.6 43.9 315 35 18 2.8 1.6
9500 6.7 44.1 310 35 18 2.3 1.3 | 6.8 44.2 315 38 19 2.8 1.6
9250 6.9 44.4 305 37 19 3.0 1.7 | 7.0 44.6 310 41 21 3.6 2.0
9000 7.0 44.6 305 40 21 0.7 0.4 | 7.2 45.0 305 44 23 -0.3 -0.2
8750 6.9 44.4 300 43 22 -3.4 -1.9 | 6.9 44.4 305 46 24 -4.2 -2.3
8500 6.6 43.9 295 44 23 -4.1 -2.2 | 6.6 43.9 300 48 25 -3.3 -1.8
8250 6.3 43.3 290 45 23 -3.4 -1.9 | 6.4 43.5 295 49 25 -3.8 -2.1
8000 6.1 43.0 290 45 23 0.2 0.1 | 6.0 42.8 295 48 25 -4.0 -2.2
7750 6.2 43.2 290 41 21 2.6 1.5 | 5.8 42.4 290 44 23 -1.1 -0.6
7500 6.4 43.5 285 38 19 1.7 0.9 | 5.8 42.4 290 41 21 0.1 0.1
7250 6.5 43.7 285 34 18 3.6 2.0 | 5.8 42.4 290 37 19 1.9 1.0
7000 6.9 44.4 285 31 16 6.2 3.4 | 6.1 43.0 290 33 17 5.0 2.7
6750 7.4 45.3 285 27 14 6.8 3.7 | 6.5 43.7 290 29 15 5.7 3.1
6500 7.9 46.2 285 24 13 7.3 4.0 | 6.9 44.4 290 26 13 6.3 3.4
6250 8.5 47.3 285 22 11 8.0 4.4 | 7.4 45.3 290 23 12 5.8 3.2
6000 9.1 48.4 285 19 10 8.7 4.8 | 7.8 46.0 290 19 10 5.3 2.9
5750 9.7 49.5 285 16 8 8.1 4.4 | 8.2 46.8 285 16 8 6.4 3.5
5500 10.3 50.5 280 13 7 6.5 3.6 | 8.6 47.5 285 12 6 3.9 2.1
________________________________________________________________________________
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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