Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
253
UXUS97 KBOU 120056
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1853 MDT Saturday, October 11, 2025
This forecast is for Sunday, October 12, 2025:
If the trigger temperature of 73.7 F/23.2 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 260 ft/min (1.3 m/s)
Maximum height of thermals.................. 9033 ft MSL (3746 ft AGL)
Forecast maximum temperature................... 73.0 F/23.2 C
Time of trigger temperature.................... 1415 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................. 7871 ft MSL (2584 ft AGL)
Thermal soaring outlook for Monday 10/13....... Fair
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... Diminishing
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 40260 ft MSL (34973 ft AGL)
Wave soaring outlook for Monday 10/13.......... Fair
Remarks...
Sunrise/Sunset.................... 07:07:17 / 18:24:21 MDT
Total possible sunshine........... 11 hr 17 min 3 sec (677 min 3 sec)
Altitude of sun at 12:45:49 MDT... 42.41 degrees
Upper air data from numerical model forecast valid on 10/12/2025 at 0600 MDT
Freezing level.................. 14642 ft MSL (9355 ft AGL)
Convective condensation level... 16401 ft MSL (11114 ft AGL)
Lifted condensation level....... 13713 ft MSL (8427 ft AGL)
Lifted index.................... +4.1
K index......................... -0.7
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 -66.5 -87.7 240 69 35 3.1 1.7 M M M M M
45000 -60.6 -77.1 240 93 48 6.3 3.4 M M M M M
40000 -51.1 -60.0 240 109 56 6.7 3.7 M M M M M
38000 -47.0 -52.6 235 106 55 6.9 3.8 M M M M M
36000 -42.8 -45.0 235 104 54 6.9 3.8 M M M M M
34000 -39.2 -38.6 235 96 50 5.4 3.0 M M M M M
32000 -35.5 -31.9 235 83 43 5.4 3.0 M M M M M
30000 -31.8 -25.2 230 74 38 6.7 3.7 44.3 111.8 16.4 M M
29000 -29.8 -21.6 230 70 36 6.7 3.7 43.1 109.7 15.7 M M
28000 -27.8 -18.0 230 66 34 6.7 3.7 42.1 107.8 15.0 M M
27000 -25.5 -13.9 230 63 33 8.0 4.4 41.2 106.2 14.5 M M
26000 -23.1 -9.6 225 62 32 8.1 4.4 40.5 104.9 14.1 M M
25000 -20.7 -5.3 225 60 31 8.1 4.4 39.9 103.9 13.8 M M
24000 -18.4 -1.1 225 58 30 6.0 3.3 39.1 102.5 13.3 M M
23000 -16.6 2.1 225 56 29 6.2 3.4 37.8 100.0 12.4 M M
22000 -14.7 5.5 225 53 27 6.3 3.4 36.5 97.8 11.5 M M
21000 -12.7 9.1 230 50 26 7.5 4.1 35.5 95.8 10.7 M M
20000 -10.5 13.1 230 45 23 7.4 4.1 34.6 94.2 10.0 M M
19500 -9.4 15.1 230 43 22 7.4 4.1 34.2 93.5 9.8 M M
19000 -8.3 17.1 230 41 21 7.5 4.1 33.8 92.8 9.5 M M
18500 -7.2 19.0 230 39 20 6.3 3.5 33.4 92.1 9.1 M M
18000 -6.3 20.7 230 36 19 6.1 3.4 32.7 90.9 8.6 M M
17500 -5.4 22.3 230 34 18 5.9 3.2 32.1 89.8 8.2 M M
17000 -4.6 23.7 235 34 17 4.7 2.6 31.3 88.4 7.5 M M
16500 -3.9 25.0 240 34 18 4.6 2.5 30.5 86.9 6.8 M M
16000 -2.7 27.1 240 32 17 6.5 3.6 29.5 85.0 5.9 M M
15500 -1.7 28.9 240 29 15 6.3 3.5 28.9 84.0 5.4 M M
15000 -0.6 30.9 235 26 13 8.6 4.7 28.5 83.4 5.1 M M
14500 0.6 33.1 225 23 12 8.5 4.7 28.3 83.0 4.8 M M
14000 1.8 35.2 220 21 11 7.8 4.3 28.1 82.5 4.6 M M
13500 2.9 37.2 220 20 10 7.6 4.2 27.7 81.9 4.3 M M
13000 4.0 39.2 220 19 10 6.5 3.6 27.4 81.3 3.9 M M
12500 4.7 40.5 210 17 9 5.5 3.0 26.7 80.0 3.2 M M
12000 5.4 41.7 200 16 8 6.4 3.5 26.0 78.8 2.4 M M
11500 6.6 43.9 200 15 8 8.2 4.5 25.7 78.2 2.1 M M
11000 7.8 46.0 205 15 8 8.0 4.4 25.4 77.8 1.9 M M
10500 8.9 48.0 215 14 7 7.5 4.1 25.1 77.2 1.6 M M
10250 9.4 48.9 220 13 7 8.5 4.7 25.0 76.9 1.4 M M
10000 10.1 50.2 230 13 7 7.9 4.3 24.9 76.8 1.3 M M
9750 10.6 51.1 240 15 8 5.3 2.9 24.6 76.3 1.1 M M
9500 10.9 51.6 245 17 9 4.6 2.5 24.2 75.6 0.7 M M
9250 11.2 52.2 255 20 10 5.4 3.0 23.8 74.9 0.3 M M
9000 11.6 52.9 255 23 12 4.0 2.2 23.5 74.3 -0.1 256 1.3
8750 11.8 53.2 260 25 13 1.2 0.7 22.9 73.2 -0.7 244 1.2
8500 11.8 53.2 265 26 13 1.0 0.5 22.2 72.0 -1.4 236 1.2
8250 11.8 53.2 265 28 14 0.5 0.2 21.5 70.8 -2.1 228 1.2
8000 11.8 53.2 265 29 15 3.0 1.7 20.9 69.6 -2.8 220 1.1
7750 12.2 54.0 265 26 13 5.6 3.1 20.5 68.9 -3.2 202 1.0
7500 12.5 54.5 265 24 12 4.8 2.6 20.1 68.3 -3.6 185 0.9
7250 12.8 55.0 265 22 11 5.2 2.9 19.8 67.6 -4.0 167 0.8
7000 13.3 55.9 265 20 10 7.5 4.1 19.5 67.1 -4.3 147 0.7
6750 13.9 57.0 265 18 9 7.9 4.3 19.4 66.9 -4.4 121 0.6
6500 14.5 58.1 265 16 8 8.2 4.5 19.2 66.6 -4.6 97 0.5
6250 15.0 59.0 265 14 7 3.8 2.1 19.0 66.3 -4.8 72 0.4
6000 15.0 59.0 260 12 6 -2.7 -1.5 18.3 64.9 -5.6 66 0.3
5750 14.6 58.3 250 10 5 -7.6 -4.2 17.2 63.0 -6.7 70 0.4
5500 13.4 56.1 225 7 3 -24.3 -13.4 15.4 59.6 -8.6 99 0.5
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
10/12/2025 at 0900 MDT | 10/12/2025 at 1200 MDT
|
CAPE... 0.0 LI... +3.6 | CAPE... 0.0 LI... +6.1
CINH... 0.0 K Index... +7.8 | CINH... 0.0 K Index... -9.0
|
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 -66.3 -87.3 235 74 38 2.4 1.3 | -67.0 -88.6 235 92 47 3.0 1.6
45000 -61.6 -78.9 235 101 52 6.5 3.6 | -61.7 -79.1 240 107 55 6.3 3.4
40000 -51.4 -60.5 235 116 60 6.8 3.7 | -51.8 -61.2 230 123 63 6.6 3.6
38000 -47.2 -53.0 235 113 58 6.9 3.8 | -47.7 -53.9 230 119 61 6.8 3.8
36000 -43.1 -45.6 230 111 57 6.9 3.8 | -43.6 -46.5 230 116 60 6.8 3.8
34000 -39.5 -39.1 230 104 54 5.5 3.0 | -40.0 -40.0 230 107 55 5.3 2.9
32000 -36.1 -33.0 230 95 49 5.5 3.0 | -36.9 -34.4 230 93 48 5.3 2.9
30000 -32.5 -26.5 225 87 45 6.8 3.8 | -32.9 -27.2 230 85 44 8.1 4.4
29000 -29.9 -21.8 225 82 42 6.9 3.8 | -30.5 -22.9 230 85 44 8.1 4.4
28000 -27.8 -18.0 230 78 40 6.9 3.8 | -28.1 -18.6 230 84 43 8.1 4.4
27000 -25.8 -14.4 230 75 39 7.0 3.8 | -25.4 -13.7 230 82 42 6.1 3.3
26000 -23.7 -10.7 230 72 37 7.0 3.8 | -23.6 -10.5 230 80 41 6.0 3.3
25000 -21.6 -6.9 230 69 36 7.0 3.8 | -21.8 -7.2 230 79 40 6.1 3.3
24000 -19.5 -3.1 230 66 34 6.8 3.7 | -20.0 -4.0 230 77 39 6.7 3.7
23000 -17.5 0.5 230 64 33 6.8 3.7 | -18.0 -0.4 235 75 38 6.6 3.6
22000 -15.4 4.3 235 62 32 6.8 3.7 | -16.0 3.2 235 73 37 6.6 3.6
21000 -13.5 7.7 235 60 31 5.6 3.1 | -14.0 6.8 235 70 36 6.7 3.6
20000 -11.8 10.8 235 55 28 5.8 3.2 | -12.0 10.4 240 66 34 6.7 3.7
19500 -11.0 12.2 240 53 27 5.9 3.2 | -11.0 12.2 240 65 33 6.7 3.7
19000 -10.2 13.6 240 51 26 6.1 3.3 | -10.0 14.0 240 63 32 6.7 3.7
18500 -9.4 15.1 240 49 25 4.5 2.5 | -9.0 15.8 245 61 31 5.9 3.2
18000 -8.8 16.2 245 45 23 4.3 2.3 | -8.2 17.2 245 59 30 5.8 3.2
17500 -8.2 17.2 245 42 22 4.5 2.5 | -7.3 18.9 245 56 29 5.8 3.2
17000 -7.4 18.7 245 39 20 5.5 3.0 | -6.4 20.5 245 54 28 5.5 3.0
16500 -6.6 20.1 245 37 19 5.3 2.9 | -5.6 21.9 245 53 27 5.6 3.0
16000 -5.7 21.7 245 34 17 6.9 3.8 | -4.8 23.4 245 51 26 5.3 2.9
15500 -4.6 23.7 245 31 16 7.0 3.8 | -4.0 24.8 245 49 25 5.3 2.9
15000 -3.6 25.5 240 28 15 7.5 4.1 | -3.3 26.1 245 48 25 4.6 2.5
14500 -2.4 27.7 235 27 14 7.9 4.3 | -2.7 27.1 245 46 24 4.2 2.3
14000 -0.7 30.7 235 24 12 8.3 4.5 | -2.1 28.2 245 44 23 4.3 2.3
13500 0.6 33.1 235 23 12 8.3 4.6 | -1.6 29.1 240 41 21 4.1 2.3
13000 1.8 35.2 235 21 11 8.2 4.5 | -0.8 30.6 240 36 19 5.0 2.8
12500 3.0 37.4 240 21 11 8.0 4.4 | -0.0 32.0 240 35 18 5.4 2.9
12000 4.1 39.4 245 22 11 7.7 4.2 | 0.7 33.3 240 33 17 5.5 3.0
11500 5.2 41.4 245 23 12 7.2 4.0 | 1.5 34.7 240 31 16 5.5 3.0
11000 6.2 43.2 250 24 12 5.6 3.1 | 2.2 36.0 240 29 15 4.6 2.5
10500 6.7 44.1 255 26 14 2.7 1.5 | 2.7 36.9 245 27 14 3.5 1.9
10250 6.8 44.2 260 28 14 3.7 2.1 | 3.0 37.4 250 26 13 4.6 2.5
10000 7.1 44.8 260 27 14 4.6 2.5 | 3.3 37.9 250 20 10 5.9 3.2
9750 7.4 45.3 265 27 14 3.9 2.2 | 3.8 38.8 260 18 9 5.7 3.1
9500 7.6 45.7 265 27 14 4.4 2.4 | 4.2 39.6 265 16 8 5.5 3.0
9250 7.9 46.2 270 27 14 2.8 1.5 | 4.6 40.3 275 15 8 6.5 3.6
9000 8.0 46.4 270 27 14 4.1 2.2 | 5.2 41.4 285 14 7 8.1 4.4
8750 8.5 47.3 270 24 13 7.1 3.9 | 5.8 42.4 290 14 7 8.2 4.5
8500 9.0 48.2 270 22 11 6.6 3.6 | 6.4 43.5 295 13 7 8.0 4.4
8250 9.4 48.9 275 20 10 6.8 3.7 | 7.0 44.6 305 13 7 8.6 4.7
8000 10.0 50.0 275 18 9 7.6 4.2 | 7.7 45.9 310 13 7 9.9 5.4
7750 10.5 50.9 275 15 8 7.8 4.3 | 8.4 47.1 310 13 7 10.1 5.5
7500 11.1 52.0 275 14 7 7.5 4.1 | 9.2 48.6 310 13 7 9.7 5.3
7250 11.6 52.9 275 12 6 7.4 4.1 | 9.9 49.8 310 13 7 10.3 5.6
7000 12.2 54.0 280 10 5 7.1 3.9 | 10.7 51.3 310 13 7 10.9 6.0
6750 12.7 54.9 280 8 4 6.3 3.5 | 11.5 52.7 310 13 7 10.1 5.5
6500 13.1 55.6 285 5 3 6.6 3.6 | 12.2 54.0 315 13 7 9.7 5.3
6250 13.6 56.5 295 3 2 4.0 2.2 | 13.0 55.4 315 13 7 10.4 5.7
6000 13.7 56.7 300 2 1 1.6 0.9 | 13.8 56.8 315 13 6 11.0 6.0
5750 13.8 56.8 000 0 0 0.9 0.5 | 14.6 58.3 315 12 6 10.2 5.6
5500 13.7 56.7 115 2 1 -1.5 -0.8 | 15.4 59.7 315 12 6 15.2 8.3
10/12/2025 at 1500 MDT | 10/12/2025 at 1800 MDT
|
CAPE... 0.0 LI... +3.4 | CAPE... 0.0 LI... +1.5
CINH... 0.0 K Index... -6.0 | CINH... 0.0 K Index... -1.5
|
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 -85.4 240 91 47 3.4 1.9 | -63.7 -82.7 240 84 43 3.7 2.0
45000 -59.7 -75.5 235 109 56 5.2 2.9 | -58.0 -72.4 235 104 54 4.0 2.2
40000 -51.5 -60.7 230 128 66 5.5 3.0 | -52.0 -61.6 235 133 68 4.0 2.2
38000 -48.0 -54.4 235 125 65 5.9 3.2 | -49.1 -56.4 235 127 65 4.8 2.6
36000 -44.5 -48.1 235 122 63 5.9 3.2 | -45.9 -50.6 235 117 60 4.8 2.6
34000 -41.0 -41.8 235 116 60 5.7 3.1 | -42.5 -44.5 235 109 56 6.3 3.5
32000 -37.6 -35.7 235 105 54 5.7 3.1 | -38.7 -37.7 240 104 53 6.3 3.5
30000 -33.9 -29.0 235 97 50 6.9 3.8 | -35.0 -31.0 240 96 49 6.2 3.4
29000 -31.8 -25.2 235 94 49 6.9 3.8 | -33.1 -27.6 240 91 47 6.2 3.4
28000 -29.8 -21.6 235 92 47 6.9 3.8 | -31.3 -24.3 240 86 44 6.2 3.4
27000 -27.3 -17.1 235 88 45 6.1 3.4 | -29.4 -20.9 245 81 42 6.9 3.8
26000 -25.4 -13.7 235 85 44 6.1 3.4 | -27.3 -17.1 245 78 40 6.9 3.8
25000 -23.6 -10.5 235 81 42 6.1 3.4 | -25.3 -13.5 245 74 38 6.9 3.8
24000 -21.9 -7.4 240 77 40 4.8 2.6 | -23.3 -9.9 245 70 36 5.0 2.8
23000 -20.4 -4.7 240 72 37 4.9 2.7 | -21.9 -7.4 245 64 33 4.5 2.5
22000 -18.9 -2.0 240 67 35 4.9 2.7 | -20.6 -5.1 250 57 29 4.4 2.4
21000 -17.3 0.9 245 62 32 7.2 4.0 | -19.1 -2.4 250 51 26 7.5 4.1
20000 -15.2 4.6 245 55 28 7.0 3.9 | -16.9 1.6 245 45 23 7.3 4.0
19500 -14.1 6.6 245 52 27 7.0 3.9 | -15.7 3.7 245 42 22 7.3 4.0
19000 -13.1 8.4 245 48 25 7.0 3.8 | -14.6 5.7 245 39 20 7.3 4.0
18500 -12.0 10.4 245 45 23 7.9 4.3 | -13.5 7.7 245 36 19 8.1 4.4
18000 -10.8 12.6 245 43 22 8.0 4.4 | -12.3 9.9 245 36 18 8.3 4.5
17500 -9.6 14.7 245 41 21 7.7 4.2 | -10.4 13.3 240 35 18 8.1 4.5
17000 -8.5 16.7 240 40 21 6.9 3.8 | -9.2 15.4 245 36 18 8.1 4.4
16500 -7.5 18.5 240 39 20 7.1 3.9 | -8.0 17.6 245 36 19 7.7 4.2
16000 -6.5 20.3 240 39 20 5.3 2.9 | -7.0 19.4 245 35 18 6.4 3.5
15500 -5.8 21.6 240 39 20 5.3 2.9 | -6.0 21.2 245 34 18 6.7 3.7
15000 -5.0 23.0 245 39 20 4.6 2.5 | -5.2 22.6 240 33 17 4.8 2.6
14500 -4.4 24.1 245 38 19 4.2 2.3 | -4.5 23.9 240 30 16 5.2 2.8
14000 -3.9 25.0 245 37 19 4.5 2.5 | -3.7 25.3 235 28 15 6.1 3.4
13500 -2.8 27.0 245 32 17 5.1 2.8 | -2.9 26.8 230 26 13 6.3 3.4
13000 -2.1 28.2 240 29 15 5.5 3.0 | -1.9 28.6 225 24 12 8.2 4.5
12500 -1.4 29.5 235 26 13 5.7 3.1 | -0.6 30.9 220 23 12 9.0 4.9
12000 -0.6 30.9 230 22 11 7.4 4.1 | 0.6 33.1 215 22 11 8.0 4.4
11500 0.6 33.1 230 19 10 8.3 4.5 | 1.6 34.9 210 18 9 7.2 4.0
11000 1.8 35.2 230 16 8 7.1 3.9 | 2.6 36.7 200 15 8 5.6 3.0
10500 2.7 36.9 230 11 6 5.4 3.0 | 3.2 37.8 190 11 6 3.8 2.1
10250 3.2 37.8 235 9 5 9.9 5.5 | 3.5 38.3 180 9 5 5.8 3.2
10000 4.1 39.4 245 6 3 12.0 6.6 | 4.1 39.4 165 7 3 7.5 4.1
9750 4.8 40.6 250 5 3 8.8 4.8 | 4.6 40.3 150 5 3 6.6 3.6
9500 5.5 41.9 265 5 2 9.9 5.4 | 5.2 41.4 125 4 2 7.0 3.8
9250 6.2 43.2 280 4 2 8.5 4.6 | 5.7 42.3 095 4 2 6.4 3.5
9000 6.8 44.2 295 4 2 8.9 4.9 | 6.2 43.2 070 5 3 7.7 4.2
8750 7.6 45.7 300 4 2 10.4 5.7 | 6.9 44.4 060 6 3 9.3 5.1
8500 8.3 46.9 305 4 2 9.9 5.4 | 7.6 45.7 055 7 4 8.8 4.8
8250 9.1 48.4 310 4 2 10.4 5.7 | 8.3 46.9 050 8 4 9.3 5.1
8000 9.9 49.8 310 4 2 10.4 5.7 | 9.0 48.2 050 9 5 9.5 5.2
7750 10.6 51.1 315 4 2 9.8 5.4 | 9.7 49.5 045 10 5 9.1 5.0
7500 11.3 52.3 315 4 2 9.4 5.2 | 10.4 50.7 045 10 5 8.6 4.7
7250 12.0 53.6 320 4 2 10.1 5.5 | 11.0 51.8 045 10 5 9.8 5.4
7000 12.8 55.0 320 4 2 10.6 5.8 | 11.8 53.2 045 11 6 10.9 6.0
6750 13.6 56.5 325 5 2 9.8 5.4 | 12.6 54.7 045 11 6 9.4 5.2
6500 14.3 57.7 325 5 2 9.7 5.3 | 13.3 55.9 040 11 6 9.0 4.9
6250 15.1 59.2 325 5 2 10.3 5.6 | 14.0 57.2 040 11 6 9.7 5.3
6000 15.8 60.4 330 5 2 10.8 5.9 | 14.7 58.5 040 11 6 10.0 5.5
5750 16.6 61.9 330 5 2 9.9 5.5 | 15.5 59.9 040 11 6 9.5 5.2
5500 17.4 63.3 335 5 2 14.2 7.8 | 16.1 61.0 040 11 5 8.0 4.4
________________________________________________________________________________
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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