Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
779
UXUS97 KBOU 100156
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1856 MST Tuesday, December 9, 2025
This forecast is for Wednesday, December 10, 2025:
If the trigger temperature of 53.4 F/11.9 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 355 ft/min (1.8 m/s)
Maximum height of thermals.................. 11387 ft MSL (6089 ft AGL)
Forecast maximum temperature................... 58.0 F/14.9 C
Time of trigger temperature.................... 1145 MST
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Overcast thin high
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 8972 ft MSL (3675 ft AGL)
Thermal soaring outlook for Thursday 12/11..... Fair
Wave Soaring Index............................. Good
Wave Soaring Index trend (to 1700 MST)......... Decreasing
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1700 MST)................ Neither
Potential height of wave....................... 31077 ft MSL (25779 ft AGL)
Wave soaring outlook for Thursday 12/11........ Poor
Remarks...
Sunrise/Sunset.................... 07:10:10 / 16:34:52 MST
Total possible sunshine........... 9 hr 24 min 41 sec (564 min 41 sec)
Altitude of sun at 11:52:31 MST... 27.23 degrees
Upper air data from numerical model forecast valid on 12/10/2025 at 0500 MST
Freezing level.................. 9212 ft MSL (3914 ft AGL)
Convective condensation level... 12672 ft MSL (7374 ft AGL)
Lifted condensation level....... 12121 ft MSL (6823 ft AGL)
Lifted index.................... +7.5
K index......................... +10.7
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 -84.1 305 62 32 -0.8 -0.5 M M M M M
45000 -65.7 -86.3 300 82 42 0.3 0.1 M M M M M
40000 -63.1 -81.6 305 107 55 1.8 1.0 M M M M M
38000 -59.5 -75.1 310 107 55 8.0 4.4 M M M M M
36000 -54.7 -66.5 315 103 53 8.0 4.4 M M M M M
34000 -50.0 -58.0 320 103 53 7.3 4.0 M M M M M
32000 -45.7 -50.3 325 109 56 7.3 4.0 M M M M M
30000 -41.1 -42.0 330 110 57 8.5 4.7 35.6 96.2 15.9 M M
29000 -38.5 -37.3 325 105 54 8.5 4.7 35.1 95.1 15.7 M M
28000 -35.4 -31.7 320 100 51 8.5 4.7 34.5 94.2 15.5 M M
27000 -32.8 -27.0 315 96 49 8.9 4.9 34.2 93.5 15.4 M M
26000 -30.1 -22.2 315 93 48 8.9 4.9 33.7 92.7 15.3 M M
25000 -27.5 -17.5 315 90 47 8.9 4.9 33.4 92.2 15.2 M M
24000 -24.9 -12.8 310 88 45 7.9 4.3 33.1 91.6 15.1 M M
23000 -22.6 -8.7 310 86 44 7.8 4.3 32.3 90.1 14.6 M M
22000 -20.3 -4.5 310 85 44 7.8 4.3 31.6 88.9 14.2 M M
21000 -18.1 -0.6 315 83 42 6.1 3.4 30.8 87.5 13.7 M M
20000 -16.2 2.8 315 79 41 6.3 3.5 29.6 85.2 12.7 M M
19500 -15.3 4.5 315 77 40 6.4 3.5 29.0 84.2 12.3 M M
19000 -14.4 6.1 315 76 39 6.5 3.5 28.4 83.2 11.8 M M
18500 -13.5 7.7 315 74 38 4.6 2.5 27.8 82.0 11.3 M M
18000 -12.9 8.8 315 71 36 4.2 2.3 26.8 80.2 10.5 M M
17500 -12.3 9.9 315 68 35 4.1 2.3 25.9 78.6 9.7 M M
17000 -11.7 10.9 315 65 33 3.6 2.0 24.8 76.7 8.9 M M
16500 -11.2 11.8 315 61 32 3.7 2.0 23.8 74.8 8.0 M M
16000 -10.7 12.7 315 58 30 3.4 1.8 22.8 73.0 7.1 M M
15500 -10.2 13.6 315 54 28 3.4 1.9 21.7 71.0 6.1 M M
15000 -9.7 14.5 315 51 26 4.1 2.2 20.6 69.2 5.2 M M
14500 -8.7 16.3 310 46 24 4.5 2.5 19.3 66.8 4.1 M M
14000 -8.0 17.6 310 44 23 5.0 2.7 18.5 65.3 3.3 M M
13500 -7.3 18.9 310 42 21 5.0 2.7 17.7 63.9 2.6 M M
13000 -6.5 20.3 310 40 20 5.4 3.0 17.0 62.6 1.9 M M
12500 -5.7 21.7 305 38 19 5.5 3.0 16.3 61.3 1.3 M M
12000 -4.9 23.2 305 36 19 5.9 3.3 15.6 60.1 0.6 M M
11500 -4.0 24.8 300 35 18 6.0 3.3 15.0 59.1 0.1 M M
11000 -3.1 26.4 300 33 17 6.4 3.5 14.5 58.0 -0.5 418 2.1
10500 -2.2 28.0 300 32 16 7.0 3.9 13.9 57.1 -1.0 374 1.9
10250 -1.7 28.9 295 31 16 4.4 2.4 13.7 56.6 -1.3 353 1.8
10000 -1.5 29.3 295 31 16 3.8 2.1 13.2 55.7 -1.8 339 1.7
9750 -1.1 30.0 295 29 15 6.9 3.8 12.9 55.1 -2.1 319 1.6
9500 -0.5 31.1 295 28 14 7.9 4.3 12.7 54.8 -2.3 295 1.5
9250 -0.0 32.0 295 27 14 5.4 3.0 12.5 54.5 -2.5 272 1.4
9000 0.2 32.4 295 25 13 2.4 1.3 12.0 53.6 -3.0 258 1.3
8750 0.4 32.7 290 22 12 2.1 1.2 11.4 52.5 -3.6 245 1.2
8500 0.5 32.9 290 18 9 1.8 1.0 10.8 51.4 -4.2 234 1.2
8250 0.6 33.1 285 15 8 0.4 0.2 10.1 50.3 -4.8 224 1.1
8000 0.6 33.1 285 11 6 -0.6 -0.3 9.4 48.8 -5.6 218 1.1
7750 0.5 32.9 280 8 4 -0.8 -0.4 8.6 47.4 -6.4 212 1.1
7500 0.4 32.7 275 3 2 -1.2 -0.7 7.7 45.9 -7.3 208 1.1
7250 0.3 32.5 220 1 0 -0.9 -0.5 6.9 44.4 -8.1 203 1.0
7000 0.2 32.4 115 2 1 -1.1 -0.6 6.1 43.0 -8.9 198 1.0
6750 0.2 32.4 105 5 3 -0.7 -0.4 5.3 41.5 -9.7 193 1.0
6500 0.2 32.4 115 8 4 3.2 1.8 4.6 40.3 -10.4 184 0.9
6250 0.6 33.1 125 9 4 5.3 2.9 4.2 39.6 -10.8 165 0.8
6000 1.0 33.8 130 10 5 5.7 3.1 3.9 39.0 -11.2 147 0.7
5750 1.3 34.3 135 11 6 2.1 1.1 3.5 38.4 -11.6 128 0.7
5500 1.1 34.0 140 9 4 -6.9 -3.8 2.6 36.7 -12.5 127 0.6
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
12/10/2025 at 0800 MST | 12/10/2025 at 1100 MST
|
CAPE... 0.0 LI... +7.5 | CAPE... 0.0 LI... +6.8
CINH... -0.3 K Index... +10.6 | CINH... 0.0 K Index... +10.6
|
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 -64.7 -84.5 305 62 32 -1.0 -0.6 | -65.0 -85.0 310 59 31 -1.6 -0.9
45000 -66.2 -87.2 300 78 40 0.7 0.4 | -67.3 -89.1 310 75 39 0.8 0.4
40000 -63.9 -83.0 310 92 47 1.5 0.8 | -63.4 -82.1 315 79 41 2.6 1.4
38000 -60.0 -76.0 315 92 48 7.7 4.2 | -59.9 -75.8 315 80 41 7.2 3.9
36000 -55.4 -67.7 325 92 47 7.7 4.2 | -55.6 -68.1 320 81 41 7.2 3.9
34000 -50.6 -59.1 330 92 47 8.5 4.7 | -50.8 -59.4 320 81 42 9.2 5.1
32000 -45.5 -49.9 325 92 47 8.5 4.7 | -45.3 -49.5 320 81 42 9.2 5.1
30000 -40.1 -40.2 325 91 47 9.3 5.1 | -39.8 -39.6 320 81 42 9.1 5.0
29000 -37.4 -35.3 320 89 46 9.3 5.1 | -36.4 -33.5 315 80 41 9.1 5.0
28000 -34.6 -30.3 320 88 45 9.3 5.1 | -33.7 -28.7 315 79 41 9.1 5.0
27000 -31.9 -25.4 320 87 45 8.1 4.4 | -31.1 -24.0 315 78 40 8.3 4.5
26000 -29.4 -20.9 320 86 44 8.2 4.5 | -28.6 -19.5 315 77 40 8.3 4.5
25000 -27.0 -16.6 325 86 44 8.2 4.5 | -26.1 -15.0 315 77 39 8.3 4.6
24000 -24.5 -12.1 325 85 44 7.5 4.1 | -23.7 -10.7 315 75 39 7.5 4.1
23000 -22.3 -8.1 325 81 42 7.4 4.0 | -21.4 -6.5 315 74 38 7.6 4.2
22000 -20.2 -4.4 325 78 40 7.4 4.0 | -19.2 -2.6 315 72 37 7.6 4.2
21000 -18.0 -0.4 325 75 39 6.7 3.7 | -17.0 1.4 320 70 36 6.9 3.8
20000 -15.5 4.1 320 73 37 6.8 3.7 | -14.9 5.2 320 66 34 6.9 3.8
19500 -14.5 5.9 320 71 37 6.8 3.7 | -13.9 7.0 320 64 33 7.0 3.8
19000 -13.5 7.7 320 70 36 6.7 3.7 | -12.9 8.8 320 62 32 7.1 3.9
18500 -12.6 9.3 320 69 36 4.9 2.7 | -11.9 10.6 320 60 31 5.7 3.1
18000 -11.9 10.6 320 68 35 5.1 2.8 | -11.1 12.0 320 58 30 5.7 3.1
17500 -11.2 11.8 320 67 34 4.7 2.6 | -10.3 13.5 320 57 29 5.4 3.0
17000 -10.5 13.1 320 65 33 4.5 2.5 | -9.5 14.9 320 56 29 4.9 2.7
16500 -9.9 14.2 320 63 33 4.4 2.4 | -8.8 16.2 320 55 28 5.0 2.8
16000 -9.3 15.3 320 61 31 3.9 2.2 | -8.2 17.2 325 54 28 4.1 2.2
15500 -8.7 16.3 320 59 30 4.0 2.2 | -7.3 18.9 325 51 26 4.2 2.3
15000 -8.2 17.2 320 56 29 3.3 1.8 | -6.6 20.1 320 50 26 4.7 2.6
14500 -7.7 18.1 320 54 28 3.4 1.8 | -6.0 21.2 320 48 25 4.7 2.6
14000 -7.2 19.0 315 51 26 4.1 2.2 | -5.3 22.5 320 46 24 4.8 2.6
13500 -6.6 20.1 315 48 25 4.1 2.3 | -4.6 23.7 315 44 23 4.8 2.6
13000 -5.9 21.4 310 45 23 4.8 2.6 | -3.9 25.0 315 42 22 4.7 2.6
12500 -5.2 22.6 310 42 22 5.0 2.7 | -3.2 26.2 310 40 21 4.7 2.6
12000 -4.5 23.9 305 40 20 5.4 2.9 | -2.5 27.5 310 38 20 4.9 2.7
11500 -3.7 25.3 305 37 19 5.5 3.0 | -1.8 28.8 305 35 18 4.8 2.7
11000 -2.8 27.0 305 35 18 6.2 3.4 | -1.0 30.2 300 33 17 6.7 3.7
10500 -1.9 28.6 300 34 17 6.9 3.8 | -0.0 32.0 300 32 17 8.1 4.5
10250 -1.4 29.5 300 33 17 4.2 2.3 | 0.5 32.9 300 32 16 2.3 1.3
10000 -1.2 29.8 300 33 17 2.8 1.5 | 0.5 32.9 295 32 17 3.0 1.7
9750 -0.9 30.4 300 32 16 6.1 3.3 | 1.1 34.0 295 31 16 9.1 5.0
9500 -0.4 31.3 300 30 15 7.4 4.1 | 1.7 35.1 295 30 15 8.3 4.5
9250 0.1 32.2 295 27 14 5.4 3.0 | 2.3 36.1 290 29 15 5.4 2.9
9000 0.4 32.7 295 26 13 3.1 1.7 | 2.5 36.5 290 28 14 2.7 1.5
8750 0.6 33.1 295 24 12 4.0 2.2 | 2.8 37.0 290 26 13 5.7 3.1
8500 1.0 33.8 295 19 10 4.9 2.7 | 3.3 37.9 285 23 12 6.5 3.6
8250 1.3 34.3 290 15 8 2.5 1.4 | 3.7 38.7 285 21 11 3.8 2.1
8000 1.4 34.5 285 12 6 1.3 0.7 | 3.8 38.8 280 18 9 1.8 1.0
7750 1.4 34.5 280 9 4 -0.0 -0.0 | 4.1 39.4 275 16 8 4.2 2.3
7500 1.3 34.3 245 5 2 -1.3 -0.7 | 4.4 39.9 265 13 7 4.3 2.4
7250 1.3 34.3 200 4 2 -0.2 -0.1 | 4.6 40.3 260 11 6 2.2 1.2
7000 1.3 34.3 175 5 3 0.4 0.2 | 4.8 40.6 245 10 5 1.7 1.0
6750 1.3 34.3 160 7 4 -1.5 -0.8 | 4.9 40.8 235 9 4 2.6 1.4
6500 1.1 34.0 150 9 5 -0.5 -0.3 | 5.2 41.4 215 8 4 3.5 1.9
6250 1.2 34.2 150 10 5 1.8 1.0 | 5.4 41.7 205 7 3 3.8 2.1
6000 1.3 34.3 150 11 5 2.1 1.1 | 5.7 42.3 190 6 3 2.8 1.5
5750 1.5 34.7 145 11 6 -1.1 -0.6 | 5.9 42.6 175 6 3 6.7 3.7
5500 1.0 33.8 145 8 4 -9.6 -5.3 | 6.8 44.2 170 6 3 16.8 9.2
12/10/2025 at 1400 MST | 12/10/2025 at 1700 MST
|
CAPE... 0.0 LI... +5.0 | CAPE... 0.0 LI... +4.0
CINH... 0.0 K Index... +11.9 | CINH... -0.0 K Index... +10.4
|
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 -65.4 -85.7 310 56 29 -1.9 -1.1 | -65.3 -85.5 310 54 28 -1.1 -0.6
45000 -68.2 -90.8 310 67 35 0.6 0.3 | -66.8 -88.2 305 66 34 1.8 1.0
40000 -64.3 -83.7 315 75 39 2.7 1.5 | -64.4 -83.9 320 75 39 1.8 1.0
38000 -60.4 -76.7 320 77 40 7.8 4.3 | -60.5 -76.9 320 75 39 8.2 4.5
36000 -55.7 -68.3 325 78 40 7.8 4.3 | -55.6 -68.1 320 74 38 8.2 4.5
34000 -50.7 -59.3 325 78 40 9.1 5.0 | -50.4 -58.7 320 72 37 9.1 5.0
32000 -45.3 -49.5 325 77 40 9.1 5.0 | -44.9 -48.8 320 70 36 9.1 5.0
30000 -39.8 -39.6 325 75 38 9.3 5.1 | -39.4 -38.9 320 67 34 9.3 5.1
29000 -36.3 -33.3 325 73 38 9.3 5.1 | -36.0 -32.8 315 65 34 9.3 5.1
28000 -33.5 -28.3 320 71 37 9.3 5.1 | -33.2 -27.8 315 64 33 9.3 5.1
27000 -30.8 -23.4 320 71 36 8.7 4.8 | -30.6 -23.1 310 64 33 8.5 4.7
26000 -28.2 -18.8 315 70 36 8.7 4.8 | -28.0 -18.4 310 64 33 8.5 4.6
25000 -25.6 -14.1 315 70 36 8.7 4.8 | -25.5 -13.9 310 64 33 8.5 4.6
24000 -23.1 -9.6 315 69 36 7.6 4.2 | -23.1 -9.6 310 63 33 7.3 4.0
23000 -20.8 -5.4 315 66 34 7.7 4.3 | -20.9 -5.6 315 61 32 7.4 4.1
22000 -18.5 -1.3 315 64 33 7.8 4.3 | -18.7 -1.7 315 60 31 7.4 4.1
21000 -16.3 2.7 315 61 32 6.8 3.7 | -16.6 2.1 315 57 29 6.4 3.5
20000 -14.3 6.3 320 58 30 6.8 3.8 | -14.7 5.5 315 53 27 6.4 3.5
19500 -13.2 8.2 320 57 29 6.9 3.8 | -13.7 7.3 320 52 27 6.5 3.5
19000 -12.2 10.0 320 55 29 7.0 3.9 | -12.8 9.0 320 50 26 6.4 3.5
18500 -11.3 11.7 320 55 28 5.3 2.9 | -11.8 10.8 320 48 25 6.8 3.7
18000 -10.5 13.1 320 55 28 5.5 3.0 | -10.8 12.6 320 46 24 6.8 3.7
17500 -9.7 14.5 325 54 28 5.8 3.2 | -9.8 14.4 320 44 23 7.2 4.0
17000 -8.8 16.2 325 54 28 6.3 3.5 | -8.7 16.3 320 43 22 7.5 4.1
16500 -7.9 17.8 325 53 27 6.3 3.5 | -7.5 18.5 320 42 22 7.5 4.1
16000 -7.0 19.4 325 52 27 5.9 3.2 | -6.5 20.3 325 41 21 7.0 3.8
15500 -6.1 21.0 325 50 26 6.0 3.3 | -5.4 22.3 325 40 20 7.0 3.8
15000 -5.3 22.5 325 48 25 5.7 3.1 | -4.4 24.1 325 39 20 7.5 4.1
14500 -4.4 24.1 325 45 23 5.7 3.1 | -3.2 26.2 325 38 20 7.6 4.2
14000 -3.6 25.5 325 42 22 5.8 3.2 | -2.1 28.2 325 38 19 7.3 4.0
13500 -2.3 27.9 320 39 20 6.0 3.3 | -1.1 30.0 325 36 19 7.1 3.9
13000 -1.4 29.5 320 37 19 5.8 3.2 | 0.5 32.9 320 36 18 6.3 3.4
12500 -0.6 30.9 320 37 19 5.8 3.2 | 1.4 34.5 320 37 19 6.4 3.5
12000 0.3 32.5 315 37 19 6.3 3.4 | 2.2 36.0 315 38 19 4.9 2.7
11500 1.2 34.2 315 37 19 6.4 3.5 | 2.9 37.2 315 37 19 4.8 2.7
11000 2.1 35.8 310 38 19 5.3 2.9 | 3.6 38.5 310 37 19 4.6 2.5
10500 2.8 37.0 305 39 20 5.8 3.2 | 4.2 39.6 305 40 20 5.1 2.8
10250 3.2 37.8 300 40 20 1.7 0.9 | 4.6 40.3 305 41 21 2.3 1.3
10000 3.2 37.8 300 40 21 2.7 1.5 | 4.6 40.3 305 42 22 2.6 1.4
9750 3.6 38.5 300 40 21 7.1 3.9 | 5.0 41.0 300 42 22 5.3 2.9
9500 4.1 39.4 295 40 21 6.7 3.7 | 5.3 41.5 300 43 22 5.3 2.9
9250 4.5 40.1 295 40 21 4.0 2.2 | 5.7 42.3 295 43 22 2.7 1.5
9000 4.7 40.5 290 40 21 3.2 1.8 | 5.7 42.3 295 44 23 2.0 1.1
8750 5.1 41.2 290 38 20 7.0 3.8 | 6.0 42.8 295 43 22 5.1 2.8
8500 5.7 42.3 290 36 19 7.6 4.2 | 6.4 43.5 290 41 21 5.3 2.9
8250 6.2 43.2 290 34 17 5.7 3.1 | 6.7 44.1 290 40 21 3.7 2.1
8000 6.5 43.7 290 32 16 4.5 2.4 | 7.0 44.6 290 38 20 3.5 1.9
7750 6.9 44.4 290 29 15 7.4 4.1 | 7.4 45.3 290 36 18 8.2 4.5
7500 7.5 45.5 290 27 14 7.8 4.3 | 8.1 46.6 290 33 17 9.4 5.2
7250 8.0 46.4 290 24 12 4.9 2.7 | 8.7 47.7 285 30 16 7.1 3.9
7000 8.3 46.9 285 22 11 3.6 2.0 | 9.2 48.6 285 28 15 6.1 3.4
6750 8.6 47.5 285 19 10 4.7 2.6 | 9.7 49.5 285 26 13 9.3 5.1
6500 9.0 48.2 285 15 8 3.9 2.2 | 10.4 50.7 285 23 12 7.0 3.9
6250 9.2 48.6 285 12 6 3.0 1.6 | 10.7 51.3 285 20 10 2.2 1.2
6000 9.4 48.9 285 10 5 2.5 1.4 | 10.9 51.6 280 17 9 4.6 2.5
5750 9.6 49.3 280 8 4 5.1 2.8 | 11.2 52.2 280 14 7 -0.2 -0.1
5500 10.2 50.4 275 6 3 11.6 6.4 | 10.7 51.3 275 9 5 -12.4 -6.8
________________________________________________________________________________
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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