Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
563
UXUS97 KBOU 180033
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1832 MDT Thursday, September 17, 2026
This forecast is for Friday, September 18, 2026:
If the trigger temperature of 77.2 F/25.1 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 360 ft/min (1.8 m/s)
Maximum height of thermals.................. 12483 ft MSL (7122 ft AGL)
Forecast maximum temperature................... 83.0 F/28.8 C
Time of trigger temperature.................... 1100 MDT
Time of overdevelopment........................ 1400 MDT
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................. 9450 ft MSL (4089 ft AGL)
Thermal soaring outlook for Saturday 09/19..... 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....................... 17156 ft MSL (11795 ft AGL)
Wave soaring outlook for Saturday 09/19........ Poor
Remarks...
Sunrise/Sunset.................... 06:43:45 / 19:03:20 MDT
Total possible sunshine........... 12 hr 19 min 35 sec (739 min 35 sec)
Altitude of sun at 12:53:32 MDT... 51.84 degrees
Upper air data from numerical model forecast valid on 09/18/2026 at 0600 MDT
Freezing level.................. 16147 ft MSL (10786 ft AGL)
Convective condensation level... 14299 ft MSL (8938 ft AGL)
Lifted condensation level....... 13663 ft MSL (8302 ft AGL)
Lifted index.................... -1.4
K index......................... +23.4
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 -65.3 -85.5 220 26 13 2.7 1.5 M M M M M
45000 -59.6 -75.3 220 34 18 5.4 3.0 M M M M M
40000 -51.1 -60.0 225 46 24 7.2 4.0 M M M M M
38000 -46.8 -52.2 220 49 25 7.2 4.0 M M M M M
36000 -42.5 -44.5 215 53 27 7.3 4.0 M M M M M
34000 -37.9 -36.2 215 50 26 7.7 4.2 M M M M M
32000 -32.7 -26.9 220 45 23 8.3 4.6 M M M M M
30000 -28.3 -18.9 220 42 22 7.4 4.1 47.8 118.0 14.8 M M
29000 -26.0 -14.8 220 41 21 7.4 4.1 47.0 116.5 14.3 M M
28000 -23.9 -11.0 220 39 20 6.7 3.7 46.1 115.0 13.8 M M
27000 -21.9 -7.4 225 36 18 6.7 3.7 44.8 112.7 12.9 M M
26000 -19.9 -3.8 230 33 17 6.8 3.7 43.7 110.7 12.1 M M
25000 -17.9 -0.2 230 30 16 6.7 3.7 42.7 108.9 11.5 M M
24000 -15.9 3.4 235 27 14 6.6 3.6 41.5 106.6 10.5 M M
23000 -14.0 6.8 235 24 12 6.6 3.6 40.3 104.5 9.7 M M
22000 -12.1 10.2 240 21 11 7.1 3.9 39.3 102.7 8.9 M M
21000 -9.7 14.5 240 19 10 7.7 4.2 38.5 101.2 8.3 M M
20000 -7.4 18.7 240 18 9 7.8 4.3 37.8 100.0 7.8 M M
19500 -6.2 20.8 245 17 9 8.0 4.4 37.5 99.5 7.6 M M
19000 -5.2 22.6 245 16 8 6.0 3.3 37.0 98.6 7.3 M M
18500 -3.8 25.2 250 14 7 6.3 3.5 36.1 97.0 6.5 M M
18000 -3.0 26.6 255 13 7 6.0 3.3 35.5 95.9 5.9 M M
17500 -2.1 28.2 260 12 6 6.0 3.3 34.8 94.7 5.3 M M
17000 -1.3 29.7 270 10 5 5.9 3.3 34.2 93.6 4.8 M M
16500 -0.4 31.3 275 10 5 5.8 3.2 33.5 92.4 4.1 M M
16000 0.4 32.7 280 9 5 5.8 3.2 32.9 91.2 3.5 M M
15500 1.2 34.2 285 9 4 6.5 3.6 32.3 90.1 2.9 M M
15000 2.1 35.8 290 8 4 6.5 3.6 31.7 89.1 2.3 M M
14500 3.0 37.4 295 8 4 6.6 3.6 31.2 88.2 1.8 M M
14000 4.0 39.2 295 7 4 6.7 3.7 30.7 87.3 1.3 M M
13500 4.9 40.8 300 7 4 7.0 3.8 30.2 86.4 0.8 M M
13000 6.0 42.8 300 7 4 7.1 3.9 29.8 85.6 0.4 M M
12500 7.0 44.6 300 7 3 7.2 3.9 29.4 84.9 0.0 M M
12000 8.0 46.4 305 6 3 7.2 3.9 29.0 84.1 -0.4 514 2.6
11500 9.1 48.4 305 6 3 7.1 3.9 28.6 83.4 -0.9 469 2.4
11000 10.1 50.2 305 5 3 6.9 3.8 28.1 82.6 -1.3 424 2.2
10500 11.1 52.0 305 5 3 5.1 2.8 27.7 81.9 -1.8 379 1.9
10250 11.4 52.5 305 4 2 4.9 2.7 27.3 81.1 -2.2 363 1.8
10000 11.8 53.2 305 4 2 7.7 4.2 27.0 80.6 -2.5 341 1.7
9750 12.4 54.3 305 3 2 7.6 4.2 26.8 80.3 -2.7 318 1.6
9500 12.9 55.2 305 2 1 6.7 3.7 26.7 80.0 -2.9 295 1.5
9250 13.3 55.9 300 2 1 5.3 2.9 26.4 79.5 -3.2 275 1.4
9000 13.7 56.7 290 1 1 6.7 3.7 26.1 78.9 -3.5 256 1.3
8750 14.2 57.6 275 1 0 8.1 4.4 25.9 78.6 -3.7 232 1.2
8500 14.8 58.6 235 1 0 6.9 3.8 25.7 78.3 -3.9 209 1.1
8250 15.2 59.4 215 1 0 5.9 3.2 25.5 77.8 -4.2 188 1.0
8000 15.7 60.3 205 1 1 6.6 3.6 25.2 77.3 -4.5 167 0.8
7750 16.2 61.2 205 1 1 7.6 4.1 25.0 77.0 -4.7 144 0.7
7500 16.7 62.1 215 1 1 7.1 3.9 24.8 76.7 -4.9 121 0.6
7250 17.2 63.0 245 2 1 6.5 3.5 24.6 76.2 -5.2 99 0.5
7000 17.7 63.9 265 3 1 7.1 3.9 24.3 75.8 -5.4 77 0.4
6750 18.2 64.8 270 4 2 6.2 3.4 24.1 75.5 -5.7 54 0.3
6500 18.6 65.5 270 5 2 3.8 2.1 23.8 74.8 -6.1 36 0.2
6250 18.7 65.7 265 5 3 1.7 0.9 23.2 73.8 -6.6 24 0.1
6000 18.9 66.0 265 6 3 6.2 3.4 22.7 72.9 -7.2 11 0.1
5750 19.4 66.9 265 7 4 0.2 0.1 22.5 72.4 -7.5 M M
5500 18.4 65.1 245 5 3 -21.9 -12.0 20.9 69.6 -9.2 11 0.1
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/18/2026 at 0900 MDT | 09/18/2026 at 1200 MDT
|
CAPE... +165.2 LI... +0.1 | CAPE... +292.2 LI... -1.7
CINH... -109.4 K Index... +25.4 | CINH... -43.6 K Index... +25.7
|
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 -85.2 225 29 15 2.2 1.2 | -64.6 -84.3 220 31 16 2.2 1.2
45000 -59.7 -75.5 220 40 21 5.8 3.2 | -59.3 -74.7 215 42 22 5.7 3.1
40000 -50.9 -59.6 220 48 25 6.5 3.6 | -50.7 -59.3 215 49 25 6.0 3.3
38000 -47.0 -52.6 215 51 26 6.5 3.6 | -47.2 -53.0 215 53 27 6.0 3.3
36000 -43.2 -45.8 215 54 28 6.6 3.6 | -43.6 -46.5 215 58 30 6.1 3.4
34000 -38.7 -37.7 215 52 27 7.6 4.2 | -38.9 -38.0 215 56 29 7.9 4.4
32000 -33.5 -28.3 215 48 25 8.4 4.6 | -33.6 -28.5 215 53 27 8.6 4.7
30000 -29.0 -20.2 220 43 22 7.6 4.2 | -29.1 -20.4 220 46 24 7.5 4.1
29000 -26.8 -16.2 225 40 21 7.6 4.2 | -26.9 -16.4 220 42 22 7.5 4.1
28000 -24.6 -12.3 225 37 19 6.6 3.6 | -24.7 -12.5 220 39 20 6.8 3.8
27000 -22.6 -8.7 225 34 17 6.6 3.6 | -22.7 -8.9 220 35 18 6.9 3.8
26000 -20.7 -5.3 225 31 16 6.6 3.6 | -20.7 -5.3 215 32 17 6.9 3.8
25000 -18.7 -1.7 220 27 14 6.7 3.7 | -18.6 -1.5 215 29 15 6.7 3.7
24000 -16.7 1.9 220 25 13 6.7 3.7 | -16.8 1.8 210 28 14 6.2 3.4
23000 -14.7 5.5 220 23 12 6.7 3.7 | -14.9 5.2 210 26 14 6.2 3.4
22000 -12.7 9.1 225 21 11 6.9 3.8 | -13.1 8.4 210 25 13 6.5 3.6
21000 -10.6 12.9 225 19 10 7.2 4.0 | -11.0 12.2 210 23 12 7.0 3.8
20000 -8.4 16.9 230 17 9 7.2 4.0 | -9.0 15.8 210 21 11 7.0 3.8
19500 -7.3 18.9 230 17 9 7.3 4.0 | -7.9 17.8 210 20 10 7.0 3.9
19000 -6.3 20.7 230 15 8 6.4 3.5 | -6.9 19.6 210 18 10 6.5 3.6
18500 -4.9 23.2 235 13 7 6.5 3.5 | -5.5 22.1 215 15 8 6.5 3.6
18000 -4.0 24.8 240 12 6 6.7 3.7 | -4.5 23.9 215 14 7 7.1 3.9
17500 -3.0 26.6 240 10 5 6.7 3.7 | -3.5 25.7 215 13 6 7.1 3.9
17000 -2.1 28.2 240 9 5 6.6 3.6 | -2.5 27.5 220 11 6 7.0 3.8
16500 -1.2 29.8 245 8 4 6.5 3.6 | -1.5 29.3 220 10 5 6.9 3.8
16000 -0.3 31.5 250 7 4 6.6 3.6 | -0.5 31.1 220 9 5 6.9 3.8
15500 0.7 33.3 250 6 3 7.1 3.9 | 0.4 32.7 225 8 4 7.0 3.9
15000 1.7 35.1 255 5 3 7.1 3.9 | 1.4 34.5 225 7 4 7.0 3.8
14500 2.7 36.9 265 5 2 7.2 3.9 | 2.5 36.5 230 7 3 7.5 4.1
14000 3.7 38.7 270 4 2 7.2 3.9 | 3.6 38.5 230 6 3 7.6 4.2
13500 4.7 40.5 280 4 2 7.2 4.0 | 4.6 40.3 230 6 3 7.6 4.2
13000 5.8 42.4 285 3 2 7.3 4.0 | 5.7 42.3 230 5 3 7.7 4.2
12500 6.8 44.2 290 3 2 7.2 3.9 | 6.9 44.4 230 5 2 7.6 4.2
12000 7.8 46.0 290 3 1 7.1 3.9 | 8.0 46.4 230 5 2 7.6 4.1
11500 8.9 48.0 285 3 1 6.9 3.8 | 9.0 48.2 225 4 2 7.4 4.1
11000 9.8 49.6 275 2 1 6.6 3.6 | 10.1 50.2 220 4 2 7.0 3.9
10500 10.8 51.4 255 2 1 4.1 2.3 | 11.1 52.0 215 4 2 4.2 2.3
10250 11.0 51.8 240 2 1 4.7 2.6 | 11.3 52.3 215 5 2 5.2 2.8
10000 11.6 52.9 230 2 1 9.0 4.9 | 12.0 53.6 210 4 2 9.7 5.3
9750 12.2 54.0 220 2 1 8.9 4.9 | 12.6 54.7 200 4 2 8.9 4.9
9500 12.8 55.0 215 2 1 7.2 4.0 | 13.2 55.8 190 4 2 7.6 4.1
9250 13.2 55.8 210 3 2 5.2 2.8 | 13.7 56.7 190 4 2 5.9 3.2
9000 13.7 56.7 205 4 2 7.6 4.2 | 14.2 57.6 190 4 2 8.3 4.5
8750 14.3 57.7 200 4 2 9.3 5.1 | 14.8 58.6 180 4 2 9.7 5.3
8500 14.9 58.8 200 4 2 7.6 4.2 | 15.5 59.9 175 4 2 8.5 4.6
8250 15.4 59.7 200 4 2 6.2 3.4 | 16.1 61.0 170 4 2 7.2 4.0
8000 15.9 60.6 205 5 2 7.6 4.1 | 16.6 61.9 170 4 2 8.8 4.8
7750 16.5 61.7 205 5 2 8.6 4.7 | 17.3 63.1 165 4 2 10.3 5.7
7500 17.1 62.8 210 5 2 6.9 3.8 | 18.0 64.4 155 3 2 9.2 5.0
7250 17.5 63.5 215 5 2 5.3 2.9 | 18.6 65.5 155 3 2 8.0 4.4
7000 17.9 64.2 225 5 2 7.1 3.9 | 19.3 66.7 155 3 2 9.6 5.3
6750 18.5 65.3 230 5 2 7.6 4.2 | 20.1 68.2 150 3 2 11.9 6.5
6500 18.9 66.0 240 5 2 4.6 2.5 | 20.9 69.6 145 3 2 10.9 6.0
6250 19.2 66.6 240 5 3 4.0 2.2 | 21.7 71.1 145 3 2 10.0 5.5
6000 19.5 67.1 240 6 3 2.6 1.4 | 22.4 72.3 145 3 2 9.8 5.4
5750 19.6 67.3 235 6 3 3.7 2.0 | 23.2 73.8 140 3 2 14.7 8.1
5500 20.0 68.0 225 5 2 10.6 5.8 | 24.7 76.5 140 3 1 24.4 13.4
09/18/2026 at 1500 MDT | 09/18/2026 at 1800 MDT
|
CAPE... +155.1 LI... -1.5 | CAPE... +70.3 LI... -1.3
CINH... -22.3 K Index... +28.7 | CINH... -127.3 K Index... +29.5
|
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 -64.7 -84.5 225 32 16 2.2 1.2 | -64.8 -84.6 230 31 16 1.8 1.0
45000 -59.6 -75.3 220 46 23 5.3 2.9 | -60.0 -76.0 220 44 23 5.6 3.1
40000 -51.3 -60.3 215 52 27 6.8 3.7 | -51.3 -60.3 215 49 25 6.6 3.6
38000 -47.2 -53.0 215 53 27 6.8 3.7 | -47.4 -53.3 215 53 27 6.6 3.6
36000 -43.1 -45.6 215 54 28 6.9 3.8 | -43.4 -46.1 215 58 30 6.6 3.6
34000 -38.3 -36.9 220 51 26 8.2 4.5 | -38.7 -37.7 215 56 29 8.1 4.4
32000 -32.8 -27.0 220 48 25 8.6 4.7 | -33.2 -27.8 220 53 27 8.6 4.7
30000 -28.5 -19.3 220 44 22 7.1 3.9 | -28.8 -19.8 220 47 24 7.5 4.1
29000 -26.4 -15.5 220 41 21 7.1 3.9 | -26.6 -15.9 220 44 23 7.5 4.1
28000 -24.3 -11.7 220 39 20 7.4 4.1 | -24.3 -11.7 225 41 21 7.5 4.1
27000 -22.1 -7.8 220 35 18 7.4 4.1 | -22.1 -7.8 220 38 19 7.5 4.1
26000 -19.9 -3.8 220 31 16 7.5 4.1 | -19.9 -3.8 220 34 18 7.5 4.1
25000 -17.7 0.1 220 27 14 7.3 4.0 | -17.7 0.1 220 31 16 7.4 4.1
24000 -15.8 3.6 220 25 13 6.6 3.6 | -15.7 3.7 220 29 15 6.8 3.7
23000 -13.8 7.2 215 24 12 6.6 3.6 | -13.8 7.2 215 28 14 6.8 3.7
22000 -11.9 10.6 215 22 11 6.3 3.5 | -11.8 10.8 215 26 13 6.5 3.6
21000 -10.2 13.6 215 20 10 5.7 3.1 | -10.1 13.8 210 24 12 5.6 3.1
20000 -8.5 16.7 210 18 9 5.7 3.1 | -8.5 16.7 215 22 12 5.6 3.1
19500 -7.7 18.1 210 17 9 5.7 3.1 | -7.7 18.1 215 22 11 5.7 3.1
19000 -6.9 19.6 210 16 8 6.1 3.3 | -6.9 19.6 215 20 10 5.6 3.1
18500 -5.5 22.1 205 15 8 6.1 3.3 | -6.1 21.0 215 18 9 5.6 3.1
18000 -4.7 23.5 200 14 7 6.2 3.4 | -4.8 23.4 215 14 7 6.3 3.4
17500 -3.8 25.2 200 13 7 6.2 3.4 | -3.9 25.0 215 12 6 6.4 3.5
17000 -2.9 26.8 195 12 6 6.4 3.5 | -3.0 26.6 215 9 5 6.4 3.5
16500 -2.0 28.4 190 11 6 6.6 3.6 | -2.1 28.2 220 7 4 6.6 3.6
16000 -1.0 30.2 190 10 5 6.6 3.6 | -1.1 30.0 230 5 3 6.6 3.6
15500 0.0 32.0 185 10 5 7.2 3.9 | -0.2 31.6 235 3 2 6.8 3.7
15000 1.0 33.8 185 9 5 7.1 3.9 | 0.8 33.4 245 2 1 6.8 3.7
14500 2.1 35.8 185 8 4 7.6 4.2 | 1.8 35.2 255 1 1 7.0 3.8
14000 3.2 37.8 185 7 4 7.7 4.2 | 2.8 37.0 270 1 1 7.0 3.9
13500 4.3 39.7 185 7 4 7.6 4.1 | 3.8 38.8 300 1 0 7.5 4.1
13000 5.4 41.7 185 6 3 7.5 4.1 | 4.9 40.8 335 1 0 8.0 4.4
12500 6.4 43.5 185 6 3 7.6 4.2 | 6.1 43.0 015 1 0 8.3 4.5
12000 7.6 45.7 180 5 3 7.9 4.3 | 7.4 45.3 060 1 0 8.9 4.9
11500 8.7 47.7 170 5 2 8.0 4.4 | 8.7 47.7 085 1 1 8.8 4.8
11000 9.9 49.8 165 4 2 8.1 4.4 | 9.9 49.8 075 2 1 8.2 4.5
10500 11.0 51.8 160 4 2 5.4 2.9 | 11.2 52.2 065 2 1 5.7 3.1
10250 11.3 52.3 160 4 2 6.5 3.6 | 11.5 52.7 055 2 1 5.5 3.0
10000 12.1 53.8 160 4 2 10.9 6.0 | 12.1 53.8 040 3 1 9.1 5.0
9750 12.8 55.0 160 4 2 10.0 5.5 | 12.7 54.9 030 3 2 8.7 4.8
9500 13.5 56.3 165 4 2 9.2 5.1 | 13.4 56.1 020 4 2 8.0 4.4
9250 14.1 57.4 165 4 2 7.8 4.3 | 13.9 57.0 010 4 2 6.3 3.5
9000 14.7 58.5 165 4 2 9.1 5.0 | 14.4 57.9 360 5 3 6.8 3.7
8750 15.5 59.9 170 4 2 10.1 5.5 | 14.9 58.8 355 6 3 7.9 4.3
8500 16.2 61.2 175 4 2 9.5 5.2 | 15.5 59.9 350 7 3 6.4 3.5
8250 16.8 62.2 180 4 2 9.1 5.0 | 15.8 60.4 340 8 4 4.6 2.5
8000 17.5 63.5 180 4 2 9.0 4.9 | 16.1 61.0 335 9 5 4.6 2.5
7750 18.2 64.8 185 4 2 8.8 4.8 | 16.5 61.7 330 10 5 5.2 2.8
7500 18.8 65.8 190 4 2 9.2 5.1 | 16.8 62.2 325 11 6 3.6 2.0
7250 19.5 67.1 195 4 2 9.7 5.3 | 17.0 62.6 320 12 6 2.2 1.2
7000 20.2 68.4 195 4 2 9.3 5.1 | 17.1 62.8 315 14 7 2.1 1.2
6750 20.9 69.6 200 4 2 9.0 4.9 | 17.2 63.0 310 15 8 1.5 0.8
6500 21.6 70.9 200 5 2 9.6 5.3 | 17.3 63.1 310 16 8 5.0 2.8
6250 22.3 72.1 200 5 2 10.7 5.8 | 17.8 64.0 310 16 8 7.6 4.2
6000 23.1 73.6 200 5 2 8.9 4.9 | 18.3 64.9 305 16 8 6.3 3.4
5750 23.8 74.8 200 5 2 13.0 7.1 | 18.7 65.7 305 16 8 8.9 4.9
5500 25.2 77.4 195 4 2 25.0 13.7 | 19.6 67.3 305 14 7 14.9 8.2
________________________________________________________________________________
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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