Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
138
UXUS97 KBOU 170029
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1827 MDT Wednesday, September 16, 2026
This forecast is for Thursday, September 17, 2026:
If the trigger temperature of 77.4 F/25.2 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 393 ft/min (2.0 m/s)
Maximum height of thermals.................. 12650 ft MSL (7226 ft AGL)
Forecast maximum temperature................... 82.0 F/28.2 C
Time of trigger temperature.................... 1230 MDT
Time of overdevelopment........................ 1600 MDT
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................. 9062 ft MSL (3637 ft AGL)
Thermal soaring outlook for Friday 09/18....... Good
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)................ Neither
Potential height of wave....................... 15744 ft MSL (10320 ft AGL)
Wave soaring outlook for Friday 09/18.......... Poor
Remarks...
Sunrise/Sunset.................... 06:42:48 / 19:04:59 MDT
Total possible sunshine........... 12 hr 22 min 10 sec (742 min 10 sec)
Altitude of sun at 12:53:54 MDT... 52.23 degrees
Upper air data from numerical model forecast valid on 09/17/2026 at 0600 MDT
Freezing level.................. 15516 ft MSL (10092 ft AGL)
Convective condensation level... 13397 ft MSL (7973 ft AGL)
Lifted condensation level....... 13232 ft MSL (7808 ft AGL)
Lifted index.................... +0.6
K index......................... +28.7
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 -65.5 -85.9 235 28 14 2.6 1.4 79.9 175.8 30.7 M M
45000 -60.6 -77.1 230 39 20 4.3 2.4 64.7 148.5 23.2 M M
40000 -53.1 -63.6 235 49 25 8.9 4.9 54.4 129.9 17.9 M M
38000 -47.8 -54.0 230 44 22 8.9 4.9 53.4 128.2 17.7 M M
36000 -41.9 -43.4 230 38 19 8.4 4.6 52.9 127.2 17.8 M M
34000 -36.9 -34.4 225 37 19 8.4 4.6 51.5 124.7 17.2 M M
32000 -31.9 -25.4 225 36 18 8.2 4.5 50.6 123.2 16.9 M M
30000 -27.2 -17.0 225 32 17 8.0 4.4 49.1 120.3 16.1 M M
29000 -24.8 -12.6 225 31 16 8.0 4.4 48.5 119.2 15.8 M M
28000 -22.4 -8.3 225 29 15 7.7 4.2 47.9 118.1 15.5 M M
27000 -20.2 -4.4 225 30 15 7.7 4.2 47.0 116.5 14.9 M M
26000 -17.9 -0.2 220 30 15 7.7 4.2 46.2 115.2 14.5 M M
25000 -15.6 3.9 220 30 15 7.3 4.0 45.6 114.1 14.1 M M
24000 -13.7 7.3 220 29 15 6.5 3.6 44.3 111.8 13.2 M M
23000 -11.8 10.8 215 28 15 6.5 3.6 43.1 109.6 12.3 M M
22000 -9.4 15.1 210 28 14 5.2 2.9 41.7 107.0 11.2 M M
21000 -7.9 17.8 210 27 14 5.2 2.9 40.0 104.0 9.8 M M
20000 -6.5 20.3 205 26 13 5.2 2.9 38.4 101.2 8.6 M M
19500 -5.7 21.7 205 25 13 5.1 2.8 37.7 99.9 7.9 M M
19000 -5.0 23.0 205 24 13 4.9 2.7 36.9 98.4 7.2 M M
18500 -4.3 24.3 205 24 12 4.9 2.7 36.0 96.9 6.5 M M
18000 -3.6 25.5 200 23 12 4.8 2.7 35.2 95.4 5.8 M M
17500 -2.9 26.8 200 21 11 4.9 2.7 34.4 93.9 5.0 M M
17000 -2.3 27.9 195 20 10 5.0 2.7 33.5 92.4 4.3 M M
16500 -1.5 29.3 190 18 9 5.2 2.8 32.8 91.0 3.5 M M
16000 -0.8 30.6 180 17 9 5.0 2.8 32.0 89.6 2.8 M M
15500 0.0 32.0 170 16 8 6.7 3.7 31.4 88.4 2.2 M M
15000 1.0 33.8 160 16 8 6.5 3.6 30.8 87.5 1.7 M M
14500 2.0 35.6 150 16 8 7.3 4.0 30.3 86.6 1.3 M M
14000 3.1 37.6 145 17 9 7.5 4.1 30.0 85.9 0.9 M M
13500 4.2 39.6 140 18 9 7.5 4.1 29.6 85.3 0.6 M M
13000 5.3 41.5 140 18 9 7.6 4.2 29.2 84.6 0.3 M M
12500 6.4 43.5 135 17 9 7.6 4.1 28.9 84.0 -0.1 583 3.0
12000 7.5 45.5 135 16 8 7.5 4.1 28.5 83.4 -0.4 535 2.7
11500 8.6 47.5 140 15 8 7.7 4.3 28.2 82.7 -0.8 487 2.5
11000 9.8 49.6 140 13 7 8.7 4.8 28.0 82.3 -1.0 437 2.2
10500 11.1 52.0 150 11 6 7.9 4.4 27.8 82.0 -1.3 385 2.0
10250 11.5 52.7 150 10 5 6.8 3.8 27.6 81.7 -1.5 363 1.8
10000 12.0 53.6 155 9 4 7.1 3.9 27.4 81.3 -1.7 341 1.7
9750 12.5 54.5 155 7 4 7.3 4.0 27.2 80.9 -2.0 319 1.6
9500 13.0 55.4 155 6 3 6.6 3.6 27.0 80.6 -2.2 297 1.5
9250 13.4 56.1 155 5 3 5.0 2.7 26.7 80.0 -2.6 277 1.4
9000 13.8 56.8 155 4 2 5.2 2.9 26.3 79.3 -2.9 260 1.3
8750 14.2 57.6 150 3 2 6.0 3.3 26.0 78.8 -3.3 240 1.2
8500 14.6 58.3 145 2 1 5.3 2.9 25.7 78.2 -3.6 220 1.1
8250 14.9 58.8 120 1 1 4.5 2.5 25.3 77.5 -4.0 202 1.0
8000 15.7 60.3 050 2 1 6.4 3.5 24.6 76.3 -4.7 165 0.8
7750 16.1 61.0 035 2 1 5.3 2.9 24.3 75.8 -5.0 144 0.7
7500 16.5 61.7 030 3 2 4.0 2.2 23.9 75.0 -5.4 127 0.6
7250 16.8 62.2 025 4 2 4.6 2.5 23.5 74.3 -5.8 110 0.6
7000 17.1 62.8 025 4 2 4.9 2.7 23.1 73.6 -6.2 92 0.5
6750 17.5 63.5 025 5 2 4.2 2.3 22.7 72.9 -6.6 74 0.4
6500 17.7 63.9 025 5 3 3.2 1.8 22.3 72.1 -7.1 59 0.3
6250 18.0 64.4 030 5 3 4.5 2.5 21.8 71.2 -7.6 44 0.2
6000 18.3 64.9 030 6 3 2.2 1.2 21.4 70.5 -8.0 28 0.1
5750 18.1 64.6 030 5 3 -5.3 -2.9 20.5 69.0 -8.9 25 0.1
5500 17.9 64.2 030 4 2 5.0 2.7 19.6 67.3 -9.9 26 0.1
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/17/2026 at 0900 MDT | 09/17/2026 at 1200 MDT
|
CAPE... 0.0 LI... +1.2 | CAPE... +9.5 LI... -0.5
CINH... -0.0 K Index... +27.8 | CINH... -10.8 K Index... +27.0
|
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 -65.3 -85.5 230 25 13 3.2 1.8 | -66.1 -87.0 220 26 13 3.0 1.6
45000 -59.8 -75.6 230 35 18 4.3 2.4 | -60.4 -76.7 225 36 18 5.3 2.9
40000 -52.3 -62.1 240 43 22 8.4 4.6 | -51.8 -61.2 235 41 21 8.1 4.4
38000 -46.7 -52.1 230 44 22 8.4 4.6 | -46.4 -51.5 225 39 20 8.1 4.4
36000 -41.7 -43.1 225 44 23 8.5 4.6 | -41.5 -42.7 215 38 20 8.8 4.8
34000 -36.7 -34.1 225 39 20 8.5 4.7 | -36.2 -33.2 215 38 20 8.9 4.9
32000 -31.6 -24.9 225 34 18 8.3 4.6 | -30.9 -23.6 215 38 20 8.5 4.7
30000 -26.9 -16.4 220 32 16 8.0 4.4 | -26.2 -15.2 215 35 18 7.9 4.4
29000 -24.5 -12.1 220 31 16 8.0 4.4 | -23.9 -11.0 220 34 17 8.0 4.4
28000 -22.3 -8.1 215 30 15 6.5 3.6 | -21.6 -6.9 220 33 17 6.7 3.7
27000 -20.3 -4.5 210 30 15 6.7 3.7 | -19.6 -3.3 225 33 17 6.9 3.8
26000 -18.3 -0.9 210 29 15 6.7 3.7 | -17.6 0.3 225 34 17 6.9 3.8
25000 -16.4 2.5 205 29 15 6.7 3.7 | -15.6 3.9 230 34 18 6.6 3.6
24000 -14.4 6.1 205 28 14 6.7 3.7 | -13.9 7.0 225 34 18 5.8 3.2
23000 -11.9 10.6 210 27 14 6.8 3.7 | -11.8 10.8 225 34 17 5.8 3.2
22000 -10.0 14.0 210 26 13 6.6 3.6 | -10.1 13.8 220 33 17 5.6 3.1
21000 -8.0 17.6 205 26 13 6.6 3.6 | -8.5 16.7 220 31 16 5.6 3.1
20000 -6.1 21.0 205 25 13 6.6 3.6 | -6.9 19.6 215 30 15 5.7 3.1
19500 -5.1 22.8 205 25 13 6.2 3.4 | -6.1 21.0 215 29 15 5.9 3.2
19000 -4.3 24.3 205 25 13 5.5 3.0 | -5.1 22.8 215 28 14 6.3 3.5
18500 -3.5 25.7 205 25 13 5.6 3.0 | -4.2 24.4 215 27 14 6.3 3.4
18000 -2.8 27.0 205 25 13 4.7 2.6 | -3.3 26.1 215 27 14 7.2 3.9
17500 -2.1 28.2 205 25 13 4.7 2.6 | -2.2 28.0 220 26 14 7.2 4.0
17000 -1.5 29.3 205 25 13 5.3 2.9 | -1.1 30.0 220 26 13 7.2 4.0
16500 -0.6 30.9 205 24 12 6.5 3.6 | -0.1 31.8 220 26 13 7.2 3.9
16000 0.3 32.5 205 23 12 6.6 3.6 | 1.0 33.8 225 26 13 7.4 4.0
15500 1.2 34.2 205 23 12 5.5 3.0 | 1.9 35.4 225 26 14 5.3 2.9
15000 2.0 35.6 205 22 11 5.6 3.1 | 2.7 36.9 225 27 14 5.5 3.0
14500 2.9 37.2 205 22 11 6.3 3.4 | 3.4 38.1 225 27 14 4.9 2.7
14000 3.8 38.8 205 21 11 6.5 3.6 | 4.1 39.4 220 27 14 4.8 2.6
13500 4.8 40.6 210 20 10 6.9 3.8 | 4.7 40.5 220 27 14 5.6 3.1
13000 5.8 42.4 210 19 10 7.3 4.0 | 5.6 42.1 215 26 13 6.6 3.6
12500 6.9 44.4 210 19 10 7.4 4.0 | 6.6 43.9 210 26 13 7.1 3.9
12000 8.0 46.4 205 18 9 7.4 4.1 | 7.7 45.9 210 25 13 8.2 4.5
11500 9.1 48.4 205 17 9 7.4 4.0 | 8.9 48.0 205 25 13 8.2 4.5
11000 10.1 50.2 205 15 8 7.1 3.9 | 10.1 50.2 205 24 12 8.2 4.5
10500 11.2 52.2 200 13 7 6.9 3.8 | 11.4 52.5 205 23 12 6.6 3.6
10250 11.6 52.9 200 12 6 6.5 3.6 | 11.8 53.2 205 23 12 7.0 3.8
10000 12.1 53.8 195 11 6 6.4 3.5 | 12.4 54.3 205 22 11 9.2 5.0
9750 12.5 54.5 195 10 5 6.6 3.6 | 13.1 55.6 205 21 11 8.9 4.9
9500 13.0 55.4 190 9 5 5.9 3.3 | 13.7 56.7 200 20 10 7.8 4.3
9250 13.3 55.9 190 8 4 4.3 2.4 | 14.1 57.4 200 19 10 4.6 2.5
9000 13.6 56.5 190 8 4 5.0 2.8 | 14.5 58.1 200 17 9 5.6 3.1
8750 14.0 57.2 190 7 3 6.3 3.5 | 15.0 59.0 195 16 8 7.6 4.2
8500 14.5 58.1 190 6 3 5.2 2.8 | 15.5 59.9 195 14 7 6.1 3.3
8250 15.1 59.2 205 4 2 3.9 2.1 | 15.8 60.4 195 13 7 3.2 1.8
8000 15.3 59.5 215 3 2 4.4 2.4 | 16.7 62.1 190 10 5 9.6 5.3
7750 15.7 60.3 230 3 1 3.8 2.1 | 17.4 63.3 185 9 5 9.2 5.0
7500 15.9 60.6 250 3 1 3.3 1.8 | 18.0 64.4 185 8 4 8.6 4.7
7250 16.2 61.2 265 3 1 3.3 1.8 | 18.7 65.7 185 7 4 9.0 4.9
7000 16.4 61.5 280 3 1 3.7 2.0 | 19.4 66.9 185 7 3 10.0 5.5
6750 16.7 62.1 295 3 2 5.4 3.0 | 20.1 68.2 180 6 3 10.1 5.6
6500 17.2 63.0 300 3 2 6.3 3.5 | 20.9 69.6 180 5 3 10.0 5.5
6250 17.6 63.7 305 3 2 5.7 3.1 | 21.6 70.9 180 5 2 9.1 5.0
6000 18.1 64.6 315 3 2 9.1 5.0 | 22.4 72.3 175 4 2 13.6 7.4
5750 19.0 66.2 320 3 2 15.5 8.5 | 23.8 74.8 165 3 2 24.4 13.4
5500 19.9 67.8 325 3 2 3.3 1.8 | 25.3 77.5 155 2 1 10.1 5.5
09/17/2026 at 1500 MDT | 09/17/2026 at 1800 MDT
|
CAPE... +25.6 LI... -0.6 | CAPE... +40.5 LI... -1.0
CINH... -9.0 K Index... +30.5 | CINH... -52.5 K Index... +32.7
|
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 -66.8 -88.2 225 28 14 2.1 1.2 | -66.1 -87.0 225 26 13 2.0 1.1
45000 -61.3 -78.3 225 36 19 6.3 3.5 | -60.8 -77.4 225 33 17 6.1 3.4
40000 -51.5 -60.7 225 43 22 8.0 4.4 | -51.2 -60.2 220 43 22 7.8 4.3
38000 -46.7 -52.1 220 41 21 8.0 4.4 | -46.0 -50.8 215 44 23 7.8 4.3
36000 -41.2 -42.2 215 38 20 8.5 4.7 | -41.3 -42.3 210 45 23 8.3 4.6
34000 -36.1 -33.0 215 39 20 8.6 4.7 | -36.3 -33.3 210 43 22 8.4 4.6
32000 -31.0 -23.8 215 39 20 8.3 4.5 | -31.3 -24.3 210 41 21 8.2 4.5
30000 -26.4 -15.5 220 31 16 7.8 4.3 | -26.6 -15.9 215 38 20 7.9 4.3
29000 -24.1 -11.4 225 28 14 7.8 4.3 | -24.3 -11.7 215 37 19 7.9 4.3
28000 -21.9 -7.4 225 25 13 6.9 3.8 | -22.0 -7.6 220 36 18 6.2 3.4
27000 -19.8 -3.6 230 26 14 7.0 3.8 | -20.2 -4.4 225 33 17 6.3 3.5
26000 -17.8 -0.0 230 28 14 7.0 3.8 | -18.3 -0.9 225 31 16 6.4 3.5
25000 -15.7 3.7 235 29 15 6.6 3.6 | -16.4 2.5 230 29 15 6.7 3.7
24000 -14.0 6.8 230 30 16 5.9 3.2 | -14.3 6.3 230 28 14 7.4 4.0
23000 -12.2 10.0 230 32 16 5.9 3.2 | -11.6 11.1 230 27 14 7.4 4.1
22000 -10.1 13.8 230 32 17 6.3 3.5 | -9.5 14.9 235 26 14 5.5 3.0
21000 -8.2 17.2 230 30 15 6.4 3.5 | -8.0 17.6 235 25 13 5.4 3.0
20000 -6.4 20.5 230 27 14 6.4 3.5 | -6.5 20.3 240 23 12 5.4 3.0
19500 -5.5 22.1 230 26 13 6.2 3.4 | -5.7 21.7 240 23 12 5.2 2.8
19000 -4.6 23.7 235 24 13 5.9 3.2 | -5.0 23.0 240 22 11 4.7 2.6
18500 -3.8 25.2 235 23 12 5.9 3.3 | -4.4 24.1 245 21 11 4.6 2.5
18000 -2.9 26.8 235 22 11 5.7 3.1 | -3.7 25.3 245 20 10 5.7 3.1
17500 -2.1 28.2 240 20 11 5.7 3.2 | -2.8 27.0 245 18 9 5.8 3.2
17000 -1.3 29.7 245 19 10 6.0 3.3 | -2.0 28.4 250 16 8 6.2 3.4
16500 -0.4 31.3 245 18 9 6.6 3.6 | -1.1 30.0 245 14 7 7.1 3.9
16000 0.6 33.1 250 17 9 6.7 3.7 | -0.1 31.8 240 13 6 7.1 3.9
15500 1.4 34.5 250 16 8 5.5 3.0 | 1.0 33.8 235 12 6 7.5 4.1
15000 2.2 36.0 245 15 8 5.6 3.1 | 2.0 35.6 225 12 6 7.4 4.1
14500 3.0 37.4 235 14 7 7.2 3.9 | 3.1 37.6 220 13 7 8.1 4.4
14000 4.2 39.6 225 14 7 7.7 4.2 | 4.4 39.9 220 14 7 8.3 4.6
13500 5.3 41.5 215 14 7 8.0 4.4 | 5.6 42.1 220 14 7 8.7 4.8
13000 6.5 43.7 215 15 8 8.3 4.5 | 7.0 44.6 220 14 7 9.2 5.1
12500 7.7 45.9 210 15 8 8.6 4.7 | 8.3 46.9 220 14 7 9.3 5.1
12000 9.1 48.4 210 16 8 9.5 5.2 | 9.7 49.5 220 14 7 9.2 5.1
11500 10.5 50.9 205 16 8 9.4 5.2 | 11.1 52.0 220 13 6 9.1 5.0
11000 11.8 53.2 210 15 8 9.0 4.9 | 12.4 54.3 225 11 6 8.3 4.6
10500 13.2 55.8 210 15 8 8.5 4.7 | 13.6 56.5 230 9 5 7.6 4.2
10250 13.8 56.8 210 15 8 9.0 4.9 | 14.1 57.4 235 8 4 7.9 4.3
10000 14.5 58.1 210 15 7 10.0 5.5 | 14.8 58.6 240 7 4 9.1 5.0
9750 15.3 59.5 210 14 7 9.8 5.4 | 15.5 59.9 250 7 3 8.9 4.9
9500 16.0 60.8 210 14 7 9.4 5.2 | 16.1 61.0 255 6 3 8.6 4.7
9250 16.6 61.9 215 14 7 8.3 4.6 | 16.7 62.1 265 6 3 7.9 4.3
9000 17.2 63.0 215 14 7 8.7 4.8 | 17.3 63.1 280 6 3 8.5 4.7
8750 17.9 64.2 215 14 7 9.3 5.1 | 18.0 64.4 285 6 3 9.2 5.1
8500 18.6 65.5 220 13 7 8.9 4.9 | 18.6 65.5 295 6 3 8.6 4.7
8250 19.8 67.6 225 13 7 8.8 4.8 | 19.7 67.5 310 8 4 7.6 4.2
8000 20.5 68.9 225 13 7 11.2 6.1 | 20.4 68.7 315 8 4 9.4 5.2
7750 21.3 70.3 230 13 6 9.9 5.4 | 21.0 69.8 320 9 5 8.4 4.6
7500 22.0 71.6 230 12 6 8.6 4.7 | 21.6 70.9 325 10 5 7.4 4.1
7250 22.6 72.7 230 12 6 9.0 5.0 | 22.2 72.0 325 11 6 7.7 4.2
7000 23.4 74.1 235 12 6 11.1 6.1 | 22.8 73.0 330 12 6 8.8 4.8
6750 24.2 75.6 235 12 6 10.8 5.9 | 23.4 74.1 330 12 6 8.7 4.8
6500 25.0 77.0 240 11 6 9.8 5.4 | 24.0 75.2 330 13 6 8.1 4.4
6250 25.7 78.3 240 11 6 9.6 5.3 | 24.6 76.3 335 13 7 8.2 4.5
6000 26.5 79.7 245 11 6 11.4 6.2 | 25.2 77.4 335 13 7 8.2 4.5
5750 27.5 81.5 250 10 5 17.5 9.6 | 25.8 78.4 335 12 6 8.4 4.6
5500 28.9 84.0 250 8 4 19.0 10.4 | 26.4 79.5 330 9 4 8.1 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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