Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
581
UXUS97 KBOU 290118
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1917 MDT Monday, September 28, 2026
This forecast is for Tuesday, September 29, 2026:
If the trigger temperature of 68.5 F/20.3 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 58 ft/min (0.3 m/s)
Maximum height of thermals.................. 9102 ft MSL (3742 ft AGL)
Forecast maximum temperature................... 68.0 F/20.5 C
Time of trigger temperature.................... 1415 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Broken/overcast opaque middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 6178 ft MSL (818 ft AGL)
Thermal soaring outlook for Wednesday 09/30.... Poor
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)................ Weak PVA
Potential height of wave....................... 17198 ft MSL (11838 ft AGL)
Wave soaring outlook for Wednesday 09/30....... Poor
Remarks...
Sunrise/Sunset.................... 06:54:10 / 18:45:15 MDT
Total possible sunshine........... 11 hr 51 min 5 sec (711 min 5 sec)
Altitude of sun at 12:49:43 MDT... 47.53 degrees
Upper air data from numerical model forecast valid on 09/29/2026 at 0600 MDT
Freezing level.................. 13305 ft MSL (7945 ft AGL)
Convective condensation level... 11411 ft MSL (6051 ft AGL)
Lifted condensation level....... 10721 ft MSL (5361 ft AGL)
Lifted index.................... +3.0
K index......................... +25.6
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 -61.9 -79.4 255 54 28 1.9 1.0 M M M M M
45000 -58.1 -72.6 250 79 40 4.7 2.6 M M M M M
40000 -50.7 -59.3 235 79 41 4.8 2.6 M M M M M
38000 -47.8 -54.0 225 77 39 4.8 2.6 M M M M M
36000 -44.9 -48.8 215 76 39 4.9 2.7 M M M M M
34000 -40.3 -40.5 220 71 37 8.8 4.8 M M M M M
32000 -35.0 -31.0 225 66 34 8.9 4.9 M M M M M
30000 -30.1 -22.2 225 60 31 7.9 4.3 46.8 116.3 20.3 M M
29000 -27.7 -17.9 225 56 29 7.9 4.3 46.1 115.0 19.9 M M
28000 -25.4 -13.7 225 53 27 8.0 4.4 45.5 113.9 19.7 M M
27000 -23.4 -10.1 225 48 25 6.1 3.3 44.3 111.7 18.9 M M
26000 -21.6 -6.9 230 43 22 6.1 3.3 42.8 109.1 18.0 M M
25000 -19.8 -3.6 240 38 20 6.1 3.3 41.5 106.7 17.1 M M
24000 -17.9 -0.2 240 35 18 7.3 4.0 40.3 104.6 16.3 M M
23000 -15.8 3.6 240 33 17 7.2 4.0 39.3 102.8 15.6 M M
22000 -13.1 8.4 240 31 16 7.4 4.0 38.3 100.9 14.9 M M
21000 -11.3 11.7 240 26 14 5.5 3.0 36.9 98.4 13.9 M M
20000 -9.7 14.5 240 21 11 5.5 3.0 35.4 95.7 12.8 M M
19500 -8.8 16.2 235 18 9 5.4 3.0 34.7 94.4 12.2 M M
19000 -8.0 17.6 235 16 8 4.9 2.7 34.0 93.2 11.7 M M
18500 -7.4 18.7 235 15 8 3.9 2.2 33.0 91.4 10.8 M M
18000 -6.9 19.6 235 14 7 3.8 2.1 32.0 89.6 10.0 M M
17500 -6.2 20.8 240 13 7 5.3 2.9 31.1 88.0 9.3 M M
17000 -5.5 22.1 240 12 6 5.4 2.9 30.3 86.6 8.6 M M
16500 -4.7 23.5 245 12 6 5.4 2.9 29.6 85.3 7.9 M M
16000 -4.0 24.8 250 11 6 5.3 2.9 28.8 83.9 7.2 M M
15500 -3.3 26.1 255 11 5 5.3 2.9 28.1 82.6 6.5 M M
15000 -2.6 27.3 260 10 5 4.6 2.5 27.3 81.1 5.8 M M
14500 -1.9 28.6 265 8 4 4.6 2.5 26.5 79.6 5.0 M M
14000 -1.2 29.8 270 7 3 6.0 3.3 25.7 78.3 4.3 M M
13500 -0.3 31.5 285 5 2 6.0 3.3 25.1 77.2 3.7 M M
13000 0.5 32.9 310 3 2 6.4 3.5 24.5 76.1 3.1 M M
12500 1.5 34.7 335 4 2 6.6 3.6 24.0 75.2 2.6 M M
12000 2.4 36.3 350 5 2 6.9 3.8 23.5 74.3 2.1 M M
11500 3.5 38.3 345 6 3 7.0 3.9 23.0 73.5 1.7 M M
11000 4.5 40.1 340 7 4 7.0 3.8 22.6 72.7 1.3 M M
10500 5.6 42.1 345 8 4 6.5 3.6 22.2 71.9 0.9 M M
10250 6.1 43.0 345 8 4 8.9 4.9 22.0 71.6 0.7 M M
10000 6.8 44.2 345 8 4 9.3 5.1 22.0 71.6 0.7 M M
9750 7.4 45.3 345 8 4 7.1 3.9 21.8 71.3 0.6 M M
9500 7.9 46.2 350 9 4 7.9 4.3 21.7 71.0 0.4 M M
9250 8.5 47.3 350 9 4 7.0 3.8 21.5 70.7 0.2 M M
9000 9.0 48.2 350 9 5 7.2 3.9 21.3 70.3 -0.0 254 1.3
8750 9.5 49.1 350 9 5 8.0 4.4 21.1 70.0 -0.2 229 1.2
8500 10.1 50.2 350 9 5 7.9 4.3 21.0 69.7 -0.4 205 1.0
8250 10.7 51.3 350 10 5 7.7 4.2 20.8 69.5 -0.5 180 0.9
8000 11.2 52.2 350 10 5 7.0 3.8 20.6 69.2 -0.7 157 0.8
7750 11.7 53.1 350 11 5 6.7 3.7 20.4 68.7 -1.0 135 0.7
7500 12.2 54.0 350 11 6 6.8 3.7 20.2 68.3 -1.2 113 0.6
7250 12.7 54.9 350 11 6 6.4 3.5 19.9 67.9 -1.4 91 0.5
7000 13.1 55.6 355 11 6 6.1 3.3 19.7 67.4 -1.7 70 0.4
6750 13.6 56.5 355 12 6 6.0 3.3 19.4 66.9 -2.0 50 0.3
6500 14.0 57.2 355 11 6 5.7 3.2 19.1 66.4 -2.4 30 0.2
6250 14.3 57.7 355 11 6 5.0 2.7 18.8 65.8 -2.7 11 0.1
6000 14.7 58.5 350 10 5 4.4 2.4 18.4 65.1 -3.1 M M
5750 15.0 59.0 350 10 5 5.1 2.8 18.0 64.4 -3.5 M M
5500 15.4 59.7 345 9 4 5.4 3.0 17.7 63.8 -3.9 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/29/2026 at 0900 MDT | 09/29/2026 at 1200 MDT
|
CAPE... +2.9 LI... -1.2 | CAPE... +2.6 LI... +1.3
CINH... -46.4 K Index... +24.8 | CINH... -9.1 K Index... +22.2
|
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 -61.5 -78.7 250 46 24 2.5 1.4 | -61.4 -78.5 245 48 25 2.3 1.2
45000 -56.7 -70.1 250 70 36 4.4 2.4 | -57.1 -70.8 240 71 36 3.9 2.1
40000 -50.2 -58.4 230 81 42 3.8 2.1 | -51.2 -60.2 230 79 41 5.7 3.1
38000 -47.9 -54.2 220 73 38 3.8 2.1 | -47.9 -54.2 220 77 40 5.5 3.0
36000 -45.6 -50.1 210 68 35 3.9 2.2 | -44.6 -48.3 215 76 39 5.5 3.0
34000 -41.0 -41.8 205 64 33 9.4 5.1 | -40.4 -40.7 215 70 36 8.0 4.4
32000 -35.3 -31.5 210 59 30 9.4 5.1 | -35.0 -31.0 220 61 32 8.0 4.4
30000 -29.6 -21.3 210 51 26 8.0 4.4 | -30.4 -22.7 225 54 28 7.7 4.2
29000 -27.2 -17.0 210 47 24 8.1 4.4 | -28.1 -18.6 225 50 26 7.8 4.3
28000 -24.9 -12.8 205 42 22 8.3 4.5 | -25.8 -14.4 225 46 23 7.9 4.4
27000 -23.1 -9.6 215 37 19 5.4 3.0 | -23.7 -10.7 230 42 22 6.4 3.5
26000 -21.5 -6.7 225 33 17 5.4 3.0 | -21.8 -7.2 235 40 21 6.4 3.5
25000 -19.9 -3.8 235 30 15 5.5 3.0 | -19.9 -3.8 245 39 20 6.4 3.5
24000 -18.2 -0.8 245 30 15 5.9 3.2 | -18.0 -0.4 255 36 18 6.8 3.7
23000 -16.5 2.3 255 32 17 5.9 3.2 | -15.9 3.4 255 30 16 6.8 3.7
22000 -14.8 5.4 260 35 18 5.9 3.2 | -13.9 7.0 260 25 13 6.8 3.7
21000 -13.0 8.6 265 33 17 6.0 3.3 | -12.0 10.4 260 20 10 5.5 3.0
20000 -11.2 11.8 270 26 13 6.0 3.3 | -10.4 13.3 260 16 8 5.5 3.0
19500 -10.3 13.5 270 23 12 6.1 3.3 | -9.7 14.5 260 13 7 5.5 3.0
19000 -9.4 15.1 275 19 10 6.2 3.4 | -8.9 16.0 260 11 6 5.5 3.0
18500 -8.3 17.1 275 17 9 7.5 4.1 | -7.6 18.3 265 10 5 5.8 3.2
18000 -7.2 19.0 275 16 8 7.5 4.1 | -6.8 19.8 265 10 5 5.8 3.2
17500 -6.2 20.8 270 15 8 5.9 3.2 | -6.0 21.2 265 10 5 5.5 3.0
17000 -5.4 22.3 270 14 7 5.3 2.9 | -5.2 22.6 270 9 5 5.5 3.0
16500 -4.7 23.5 270 12 6 5.4 2.9 | -4.4 24.1 270 9 5 5.5 3.0
16000 -3.8 25.2 270 11 6 6.2 3.4 | -3.7 25.3 270 8 4 5.4 3.0
15500 -2.5 27.5 270 10 5 6.0 3.3 | -2.9 26.8 275 7 4 5.4 3.0
15000 -1.8 28.8 270 9 5 5.7 3.2 | -2.2 28.0 280 6 3 5.2 2.8
14500 -1.0 30.2 275 8 4 5.8 3.2 | -1.5 29.3 285 5 3 5.2 2.9
14000 -0.3 31.5 275 6 3 5.1 2.8 | -0.8 30.6 290 4 2 5.3 2.9
13500 0.4 32.7 270 5 2 5.1 2.8 | -0.0 32.0 300 3 2 5.3 2.9
13000 1.2 34.2 270 4 2 6.6 3.6 | 0.7 33.3 310 2 1 5.8 3.2
12500 2.2 36.0 280 3 2 6.6 3.6 | 1.5 34.7 335 2 1 5.8 3.2
12000 3.0 37.4 295 4 2 5.7 3.1 | 2.3 36.1 355 3 1 5.3 2.9
11500 3.8 38.8 315 4 2 5.6 3.1 | 3.1 37.6 005 3 2 5.2 2.9
11000 4.6 40.3 330 5 2 5.8 3.2 | 3.8 38.8 015 4 2 5.3 2.9
10500 5.5 41.9 350 5 2 5.3 2.9 | 4.5 40.1 020 5 3 4.8 2.7
10250 5.9 42.6 355 5 3 8.1 4.4 | 4.9 40.8 020 5 3 7.2 4.0
10000 6.5 43.7 355 6 3 8.2 4.5 | 5.5 41.9 025 6 3 7.8 4.3
9750 6.9 44.4 355 6 3 5.3 2.9 | 6.0 42.8 025 6 3 5.8 3.2
9500 7.4 45.3 355 6 3 6.4 3.5 | 6.4 43.5 025 7 3 6.3 3.5
9250 7.8 46.0 355 7 4 4.7 2.6 | 6.8 44.2 025 7 4 6.2 3.4
9000 8.0 46.4 360 7 4 4.4 2.4 | 7.3 45.1 025 7 4 7.3 4.0
8750 8.4 47.1 005 8 4 5.9 3.2 | 7.9 46.2 025 7 4 7.9 4.4
8500 8.8 47.8 005 8 4 5.2 2.9 | 8.5 47.3 025 8 4 8.1 4.4
8250 9.1 48.4 010 8 4 6.5 3.6 | 9.0 48.2 025 8 4 6.9 3.8
8000 9.6 49.3 020 9 5 6.7 3.7 | 9.5 49.1 025 8 4 6.4 3.5
7750 10.0 50.0 030 10 5 4.4 2.4 | 10.1 50.2 025 8 4 8.0 4.4
7500 10.3 50.5 030 12 6 3.7 2.0 | 10.7 51.3 025 8 4 8.5 4.6
7250 10.6 51.1 035 13 7 3.7 2.0 | 11.4 52.5 025 8 4 7.6 4.2
7000 11.0 51.8 030 14 7 3.7 2.0 | 11.9 53.4 020 8 4 7.2 3.9
6750 11.3 52.3 025 14 7 3.4 1.9 | 12.4 54.3 020 8 4 10.0 5.5
6500 11.6 52.9 020 14 7 5.6 3.1 | 13.3 55.9 020 8 4 11.3 6.2
6250 12.1 53.8 015 12 6 8.4 4.6 | 14.0 57.2 020 7 4 10.4 5.7
6000 12.7 54.9 010 10 5 8.2 4.5 | 14.8 58.6 020 7 4 10.5 5.8
5750 13.3 55.9 355 8 4 8.9 4.9 | 15.6 60.1 020 7 4 10.0 5.5
5500 14.0 57.2 350 7 4 12.1 6.7 | 16.4 61.5 020 7 3 13.3 7.3
09/29/2026 at 1500 MDT | 09/29/2026 at 1800 MDT
|
CAPE... +0.6 LI... +1.3 | CAPE... +3.3 LI... +1.8
CINH... -10.0 K Index... +23.7 | CINH... -0.7 K Index... +23.0
|
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 -61.7 -79.1 245 48 25 2.9 1.6 | -62.1 -79.8 245 46 24 2.8 1.5
45000 -56.6 -69.9 245 68 35 4.0 2.2 | -57.1 -70.8 245 62 32 4.4 2.4
40000 -50.5 -58.9 235 79 41 5.3 2.9 | -50.4 -58.7 235 82 42 5.3 2.9
38000 -47.5 -53.5 230 80 41 5.1 2.8 | -47.3 -53.1 230 77 40 5.2 2.9
36000 -44.4 -47.9 225 82 42 5.2 2.8 | -44.1 -47.4 225 73 38 5.3 2.9
34000 -40.0 -40.0 225 76 39 8.5 4.7 | -39.6 -39.3 225 66 34 8.7 4.8
32000 -34.2 -29.6 225 64 33 8.5 4.7 | -33.7 -28.7 225 57 29 8.7 4.8
30000 -29.8 -21.6 225 50 26 6.9 3.8 | -29.3 -20.7 225 45 23 6.9 3.8
29000 -27.8 -18.0 230 43 22 6.9 3.8 | -27.3 -17.1 225 39 20 6.9 3.8
28000 -25.7 -14.3 230 35 18 7.0 3.9 | -25.2 -13.4 220 32 17 7.0 3.8
27000 -23.9 -11.0 235 31 16 5.9 3.2 | -23.2 -9.8 225 27 14 6.6 3.6
26000 -22.1 -7.8 245 29 15 5.9 3.2 | -21.2 -6.2 235 22 12 6.6 3.6
25000 -20.3 -4.5 260 28 14 5.9 3.3 | -19.3 -2.7 250 19 10 6.6 3.6
24000 -18.4 -1.1 265 26 13 7.3 4.0 | -17.3 0.9 260 16 8 6.5 3.6
23000 -16.1 3.0 260 22 11 7.3 4.0 | -15.3 4.5 265 14 7 6.5 3.6
22000 -13.9 7.0 260 18 9 7.3 4.0 | -13.3 8.1 265 12 6 6.5 3.6
21000 -12.0 10.4 255 15 8 5.6 3.1 | -11.4 11.5 265 9 5 6.1 3.4
20000 -10.3 13.5 260 13 7 5.6 3.1 | -9.6 14.7 250 7 4 6.1 3.4
19500 -9.5 14.9 260 12 6 5.6 3.1 | -8.7 16.3 245 6 3 6.1 3.4
19000 -8.7 16.3 265 11 6 5.6 3.1 | -7.8 18.0 230 6 3 6.2 3.4
18500 -7.3 18.9 270 10 5 6.4 3.5 | -6.6 20.1 225 4 2 4.8 2.6
18000 -6.4 20.5 275 9 5 6.6 3.6 | -6.0 21.2 225 3 2 4.8 2.7
17500 -5.6 21.9 280 9 5 4.6 2.5 | -5.3 22.5 230 2 1 4.4 2.4
17000 -5.0 23.0 285 9 5 4.9 2.7 | -4.8 23.4 255 2 1 4.6 2.5
16500 -4.3 24.3 290 8 4 5.4 2.9 | -4.2 24.4 290 2 1 5.3 2.9
16000 -3.6 25.5 295 8 4 5.6 3.1 | -3.4 25.9 305 2 1 5.8 3.2
15500 -2.8 27.0 295 8 4 5.8 3.2 | -2.6 27.3 315 2 1 5.9 3.2
15000 -2.0 28.4 300 8 4 6.0 3.3 | -1.8 28.8 330 3 1 5.4 3.0
14500 -1.2 29.8 305 7 4 6.1 3.4 | -1.1 30.0 340 3 2 5.4 3.0
14000 -0.4 31.3 310 7 4 5.2 2.9 | -0.3 31.5 345 4 2 5.7 3.1
13500 0.4 32.7 310 6 3 5.2 2.9 | 0.5 32.9 350 4 2 5.7 3.1
13000 1.2 34.2 310 6 3 6.3 3.4 | 1.3 34.3 350 4 2 6.0 3.3
12500 2.1 35.8 310 5 3 6.4 3.5 | 2.2 36.0 355 4 2 6.1 3.3
12000 3.0 37.4 315 4 2 5.9 3.2 | 3.0 37.4 355 4 2 5.8 3.2
11500 3.8 38.8 325 4 2 5.7 3.1 | 3.8 38.8 360 3 2 5.7 3.1
11000 4.6 40.3 345 3 2 5.6 3.1 | 4.6 40.3 005 3 2 6.0 3.3
10500 5.4 41.7 360 3 2 5.2 2.8 | 5.5 41.9 010 3 1 5.9 3.2
10250 5.8 42.4 005 3 2 7.2 3.9 | 6.0 42.8 015 3 1 7.7 4.2
10000 6.4 43.5 015 3 2 8.2 4.5 | 6.6 43.9 015 3 1 8.6 4.7
9750 6.9 44.4 015 4 2 6.9 3.8 | 7.1 44.8 015 3 1 7.4 4.0
9500 7.4 45.3 015 4 2 7.3 4.0 | 7.7 45.9 015 3 2 7.8 4.3
9250 7.9 46.2 015 4 2 7.0 3.8 | 8.2 46.8 015 3 2 7.2 3.9
9000 8.4 47.1 015 5 2 7.5 4.1 | 8.8 47.8 015 3 2 8.2 4.5
8750 9.0 48.2 015 5 2 8.0 4.4 | 9.5 49.1 015 3 2 9.5 5.2
8500 9.6 49.3 020 5 3 7.9 4.3 | 10.1 50.2 020 3 2 9.2 5.1
8250 10.2 50.4 020 5 3 7.7 4.2 | 10.8 51.4 020 3 2 9.0 5.0
8000 10.7 51.3 020 5 3 8.0 4.4 | 11.5 52.7 020 3 2 9.1 5.0
7750 11.4 52.5 020 5 3 9.1 5.0 | 12.2 54.0 020 3 1 9.7 5.3
7500 12.0 53.6 020 5 3 9.0 4.9 | 12.9 55.2 020 3 1 9.7 5.3
7250 12.7 54.9 025 5 3 9.8 5.4 | 13.6 56.5 025 3 1 9.8 5.4
7000 13.5 56.3 025 5 3 10.7 5.9 | 14.4 57.9 025 3 1 9.9 5.4
6750 14.3 57.7 025 5 2 10.3 5.7 | 15.1 59.2 025 2 1 9.8 5.4
6500 15.1 59.2 025 5 2 10.3 5.7 | 15.8 60.4 030 2 1 9.8 5.4
6250 15.8 60.4 025 5 2 10.4 5.7 | 16.6 61.9 030 2 1 10.0 5.5
6000 16.6 61.9 025 5 2 10.8 5.9 | 17.3 63.1 035 2 1 10.2 5.6
5750 17.4 63.3 025 4 2 9.7 5.3 | 18.1 64.6 035 2 1 9.5 5.2
5500 18.2 64.8 030 4 2 13.1 7.2 | 18.7 65.7 035 2 1 9.4 5.1
________________________________________________________________________________
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.
042613