Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
919
UXUS97 KBOU 300120
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1919 MDT Tuesday, July 29, 2025
This forecast is for Wednesday, July 30, 2025:
If the trigger temperature of 76.3 F/24.6 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 0 ft/min (0.0 m/s)
Maximum height of thermals.................. 11043 ft MSL (5675 ft AGL)
Forecast maximum temperature................... 82.0 F/28.2 C
Time of trigger temperature.................... 1130 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................. 9391 ft MSL (4023 ft AGL)
Thermal soaring outlook for Thursday 07/31..... Fair
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....................... 19388 ft MSL (14020 ft AGL)
Wave soaring outlook for Thursday 07/31........ Poor
Remarks...
Sunrise/Sunset.................... 05:57:15 / 20:14:36 MDT
Total possible sunshine........... 14 hr 17 min 21 sec (857 min 21 sec)
Altitude of sun at 13:05:55 MDT... 68.50 degrees
Upper air data from numerical model forecast valid on 07/30/2025 at 0600 MDT
Freezing level.................. 16383 ft MSL (11015 ft AGL)
Convective condensation level... 15170 ft MSL (9802 ft AGL)
Lifted condensation level....... 13327 ft MSL (7959 ft AGL)
Lifted index.................... -2.5
K index......................... +19.0
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 -61.8 -79.2 230 25 13 0.9 0.5 M M M M M
45000 -59.1 -74.4 225 41 21 3.6 2.0 M M M M M
40000 -52.9 -63.2 220 49 25 7.3 4.0 M M M M M
38000 -48.5 -55.3 220 48 25 7.3 4.0 M M M M M
36000 -44.1 -47.4 220 47 24 7.3 4.0 M M M M M
34000 -39.0 -38.2 220 41 21 7.7 4.2 M M M M M
32000 -34.4 -29.9 225 36 18 8.4 4.6 M M M M M
30000 -29.8 -21.6 225 31 16 7.7 4.2 46.2 115.1 13.9 M M
29000 -27.5 -17.5 230 29 15 7.8 4.3 45.5 113.8 13.5 M M
28000 -25.2 -13.4 235 26 13 6.5 3.6 44.7 112.4 13.1 M M
27000 -23.2 -9.8 240 22 12 6.6 3.6 43.4 110.0 12.2 M M
26000 -21.2 -6.2 250 19 10 6.6 3.6 42.2 107.9 11.4 M M
25000 -19.2 -2.6 265 17 9 6.6 3.6 41.1 106.1 10.7 M M
24000 -17.2 1.0 280 15 8 6.7 3.6 39.9 103.8 9.8 M M
23000 -15.3 4.5 305 15 8 6.7 3.7 38.8 101.8 9.0 M M
22000 -13.3 8.1 320 17 9 6.9 3.8 37.8 100.0 8.3 M M
21000 -11.2 11.8 325 19 10 7.1 3.9 36.7 98.1 7.4 M M
20000 -8.6 16.5 325 21 11 7.2 3.9 35.6 96.1 6.5 M M
19500 -7.5 18.5 325 21 11 7.7 4.2 35.2 95.4 6.2 M M
19000 -6.4 20.5 325 22 11 8.1 4.4 34.9 94.8 5.9 M M
18500 -5.2 22.6 325 22 11 8.1 4.4 34.6 94.3 5.7 M M
18000 -4.0 24.8 325 22 11 8.8 4.8 34.4 93.9 5.5 M M
17500 -2.7 27.1 325 22 11 8.7 4.8 34.2 93.6 5.3 M M
17000 -1.4 29.5 325 22 11 8.8 4.8 34.1 93.3 5.1 M M
16500 -0.1 31.8 325 21 11 8.8 4.8 33.9 93.0 5.0 M M
16000 1.1 34.0 325 21 11 8.8 4.8 33.7 92.7 4.8 M M
15500 2.4 36.3 320 21 11 8.6 4.7 33.5 92.4 4.6 M M
15000 3.7 38.7 320 20 10 8.7 4.8 33.3 92.0 4.5 M M
14500 4.9 40.8 320 19 10 7.5 4.1 33.1 91.6 4.2 M M
14000 6.0 42.8 320 18 9 7.6 4.2 32.7 90.9 3.9 M M
13500 7.0 44.6 315 17 9 6.5 3.6 32.3 90.2 3.5 M M
13000 7.9 46.2 315 15 8 6.2 3.4 31.7 89.1 2.9 M M
12500 8.7 47.7 315 14 7 5.6 3.1 31.2 88.1 2.3 M M
12000 9.4 48.9 315 12 6 5.1 2.8 30.4 86.7 1.6 M M
11500 10.1 50.2 315 10 5 4.8 2.6 29.7 85.4 0.8 M M
11000 10.7 51.3 310 8 4 4.2 2.3 28.8 83.8 -0.0 388 2.0
10500 11.3 52.3 310 7 4 3.7 2.1 27.9 82.3 -0.9 356 1.8
10250 11.5 52.7 305 6 3 3.7 2.1 27.4 81.4 -1.4 342 1.7
10000 11.8 53.2 305 6 3 4.7 2.6 27.0 80.6 -1.8 325 1.7
9750 12.2 54.0 300 5 3 5.1 2.8 26.6 79.9 -2.3 308 1.6
9500 12.5 54.5 290 4 2 4.2 2.3 26.3 79.3 -2.7 291 1.5
9250 12.7 54.9 290 4 2 3.0 1.6 25.8 78.4 -3.2 277 1.4
9000 12.9 55.2 285 4 2 3.9 2.2 25.3 77.5 -3.7 264 1.3
8750 13.2 55.8 280 4 2 4.7 2.6 24.8 76.7 -4.1 247 1.3
8500 13.5 56.3 275 3 2 4.0 2.2 24.4 76.0 -4.6 231 1.2
8250 13.8 56.8 275 3 2 3.4 1.9 24.0 75.1 -5.1 216 1.1
8000 14.0 57.2 275 3 1 3.9 2.1 23.5 74.3 -5.6 201 1.0
7750 14.3 57.7 280 2 1 4.4 2.4 23.1 73.5 -6.0 185 0.9
7500 14.6 58.3 280 2 1 4.2 2.3 22.7 72.8 -6.5 169 0.9
7250 14.8 58.6 280 2 1 4.1 2.2 22.2 72.0 -7.0 154 0.8
7000 15.1 59.2 280 2 1 3.8 2.1 21.8 71.2 -7.4 139 0.7
6750 15.3 59.5 275 1 1 3.4 1.9 21.3 70.4 -8.0 124 0.6
6500 15.5 59.9 285 1 1 3.7 2.0 20.8 69.5 -8.5 111 0.6
6250 15.8 60.4 305 1 1 4.1 2.3 20.4 68.7 -9.0 97 0.5
6000 16.0 60.8 315 2 1 3.3 1.8 20.0 67.9 -9.5 82 0.4
5750 16.1 61.0 320 2 1 0.6 0.3 19.4 66.9 -10.2 73 0.4
5500 16.0 60.8 300 1 0 -1.6 -0.9 18.6 65.5 -11.1 68 0.3
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
07/30/2025 at 0900 MDT | 07/30/2025 at 1200 MDT
|
CAPE... +781.0 LI... -2.6 | CAPE... +1238.3 LI... -4.0
CINH... -213.8 K Index... +20.9 | CINH... -59.3 K Index... +23.6
|
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 -61.8 -79.2 235 26 13 1.0 0.6 | -61.4 -78.5 235 25 13 1.6 0.9
45000 -59.0 -74.2 230 41 21 3.3 1.8 | -58.3 -72.9 230 42 21 2.8 1.5
40000 -53.2 -63.8 225 45 23 7.1 3.9 | -53.4 -64.1 220 49 25 6.7 3.7
38000 -49.0 -56.2 220 45 23 7.1 3.9 | -49.3 -56.7 225 45 23 6.7 3.7
36000 -44.7 -48.5 220 45 23 7.1 3.9 | -45.3 -49.5 225 41 21 6.7 3.7
34000 -40.3 -40.5 225 40 21 7.5 4.1 | -40.8 -41.4 230 36 18 7.5 4.1
32000 -35.2 -31.4 230 34 18 7.7 4.2 | -35.8 -32.4 235 30 15 7.6 4.2
30000 -30.8 -23.4 235 29 15 7.4 4.1 | -31.4 -24.5 240 24 12 7.3 4.0
29000 -28.5 -19.3 245 27 14 7.4 4.1 | -29.2 -20.6 250 22 11 7.3 4.0
28000 -26.3 -15.3 250 25 13 7.1 3.9 | -27.0 -16.6 255 20 10 7.2 3.9
27000 -24.2 -11.6 250 21 11 7.2 3.9 | -24.8 -12.6 255 19 10 7.2 3.9
26000 -22.0 -7.6 255 18 9 7.2 3.9 | -22.7 -8.9 260 17 9 7.2 4.0
25000 -19.9 -3.8 260 15 8 7.0 3.9 | -20.5 -4.9 265 16 8 7.2 4.0
24000 -17.8 -0.0 270 12 6 6.9 3.8 | -18.4 -1.1 270 15 7 7.2 4.0
23000 -15.8 3.6 290 10 5 6.9 3.8 | -16.3 2.7 275 13 7 7.3 4.0
22000 -13.8 7.2 315 10 5 7.1 3.9 | -14.1 6.6 280 11 6 7.3 4.0
21000 -11.6 11.1 320 12 6 7.3 4.0 | -11.9 10.6 290 12 6 7.4 4.0
20000 -9.5 14.9 325 15 8 7.3 4.0 | -9.8 14.4 300 12 6 7.4 4.0
19500 -8.4 16.9 325 16 8 7.3 4.0 | -8.7 16.3 305 13 7 7.3 4.0
19000 -7.4 18.7 325 17 9 7.1 3.9 | -7.6 18.3 305 14 7 7.0 3.9
18500 -6.4 20.5 325 18 9 7.1 3.9 | -6.6 20.1 310 15 8 7.1 3.9
18000 -5.3 22.5 320 18 9 8.0 4.4 | -5.6 21.9 310 16 8 8.0 4.4
17500 -4.1 24.6 320 18 9 8.3 4.6 | -4.4 24.1 310 16 8 8.3 4.5
17000 -2.3 27.9 320 17 9 8.9 4.9 | -2.6 27.3 315 16 8 9.1 5.0
16500 -0.9 30.4 320 16 8 9.0 5.0 | -1.2 29.8 315 15 8 9.2 5.1
16000 0.4 32.7 325 15 8 9.0 4.9 | 0.2 32.4 315 14 7 9.1 5.0
15500 1.7 35.1 325 14 7 8.9 4.9 | 1.5 34.7 315 12 6 8.8 4.8
15000 3.1 37.6 325 12 6 8.9 4.9 | 2.8 37.0 320 11 6 8.8 4.8
14500 4.3 39.7 325 11 6 8.3 4.6 | 4.1 39.4 320 10 5 8.4 4.6
14000 5.5 41.9 325 10 5 8.4 4.6 | 5.3 41.5 320 8 4 8.5 4.7
13500 6.7 44.1 325 9 5 7.7 4.2 | 6.5 43.7 315 7 4 7.5 4.1
13000 7.8 46.0 325 9 5 7.7 4.2 | 7.6 45.7 315 6 3 7.7 4.2
12500 8.9 48.0 320 8 4 7.1 3.9 | 8.6 47.5 310 5 3 6.1 3.3
12000 9.9 49.8 320 8 4 7.0 3.8 | 9.4 48.9 305 4 2 5.8 3.2
11500 10.9 51.6 315 7 4 6.2 3.4 | 10.1 50.2 300 3 2 4.4 2.4
11000 11.7 53.1 315 6 3 5.8 3.2 | 10.6 51.1 305 2 1 4.0 2.2
10500 12.4 54.3 310 5 2 3.1 1.7 | 11.0 51.8 330 1 0 1.5 0.8
10250 12.6 54.7 315 4 2 3.1 1.7 | 11.0 51.8 005 1 0 2.0 1.1
10000 12.9 55.2 315 4 2 6.7 3.7 | 11.2 52.2 040 1 1 5.1 2.8
9750 13.4 56.1 320 4 2 6.7 3.7 | 11.5 52.7 050 2 1 5.0 2.7
9500 13.7 56.7 320 3 2 3.8 2.1 | 11.8 53.2 050 3 2 4.0 2.2
9250 13.9 57.0 330 3 2 1.5 0.8 | 12.0 53.6 045 4 2 3.0 1.7
9000 14.0 57.2 340 3 2 3.8 2.1 | 12.2 54.0 045 4 2 6.1 3.3
8750 14.3 57.7 345 3 2 4.4 2.4 | 12.7 54.9 045 5 2 7.9 4.4
8500 14.4 57.9 345 3 2 1.8 1.0 | 13.2 55.8 040 5 2 6.8 3.7
8250 14.4 57.9 350 4 2 0.4 0.2 | 13.6 56.5 040 5 2 5.6 3.1
8000 14.4 57.9 355 4 2 2.7 1.5 | 14.1 57.4 035 5 2 9.8 5.4
7750 14.7 58.5 350 4 2 4.6 2.5 | 15.0 59.0 040 5 2 11.1 6.1
7500 14.9 58.8 350 4 2 3.6 2.0 | 15.6 60.1 035 5 3 7.8 4.3
7250 15.1 59.2 355 4 2 2.6 1.4 | 16.2 61.2 035 5 3 6.9 3.8
7000 15.3 59.5 355 4 2 5.1 2.8 | 16.7 62.1 030 5 3 11.5 6.3
6750 15.8 60.4 355 3 2 7.3 4.0 | 17.8 64.0 035 5 3 13.1 7.2
6500 16.2 61.2 360 3 2 6.5 3.6 | 18.5 65.3 035 5 3 9.3 5.1
6250 16.7 62.1 010 4 2 7.1 3.9 | 19.3 66.7 035 6 3 11.0 6.0
6000 17.1 62.8 015 4 2 5.8 3.2 | 20.0 68.0 030 6 3 8.3 4.5
5750 17.6 63.7 015 4 2 10.2 5.6 | 20.7 69.3 030 6 3 13.5 7.4
5500 18.7 65.7 015 4 2 21.1 11.6 | 22.2 72.0 025 6 3 28.9 15.8
07/30/2025 at 1500 MDT | 07/30/2025 at 1800 MDT
|
CAPE... +1273.6 LI... -3.4 | CAPE... +822.6 LI... -4.3
CINH... -6.5 K Index... +27.5 | CINH... -82.5 K Index... +31.1
|
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 -60.7 -77.3 235 25 13 1.5 0.8 | -59.7 -75.5 260 20 10 1.5 0.8
45000 -57.9 -72.2 235 42 21 2.5 1.4 | -57.8 -72.0 260 31 16 0.9 0.5
40000 -53.4 -64.1 230 53 27 6.5 3.6 | -55.1 -67.2 240 40 20 8.5 4.7
38000 -49.5 -57.1 235 46 24 6.5 3.6 | -49.2 -56.6 250 33 17 8.7 4.8
36000 -45.6 -50.1 240 40 21 6.5 3.5 | -44.0 -47.2 260 27 14 8.4 4.6
34000 -41.0 -41.8 245 36 19 7.8 4.3 | -39.1 -38.4 270 25 13 8.2 4.5
32000 -35.7 -32.3 250 33 17 8.1 4.5 | -34.3 -29.7 280 24 12 8.9 4.9
30000 -31.3 -24.3 255 28 15 7.4 4.1 | -29.8 -21.6 285 24 12 7.5 4.1
29000 -29.1 -20.4 260 26 14 7.4 4.1 | -27.6 -17.7 285 24 12 7.5 4.1
28000 -26.9 -16.4 260 24 13 6.6 3.6 | -25.4 -13.7 285 24 12 6.6 3.6
27000 -24.9 -12.8 260 22 11 6.7 3.7 | -23.5 -10.3 290 23 12 6.5 3.6
26000 -22.9 -9.2 265 20 10 6.7 3.7 | -21.6 -6.9 290 21 11 6.5 3.6
25000 -20.8 -5.4 265 17 9 7.4 4.1 | -19.2 -2.6 290 19 10 6.5 3.6
24000 -18.5 -1.3 265 15 8 7.9 4.3 | -17.3 0.9 290 17 9 6.5 3.6
23000 -16.1 3.0 265 13 7 7.9 4.3 | -15.4 4.3 295 14 7 6.5 3.6
22000 -13.8 7.2 265 11 6 8.1 4.4 | -13.5 7.7 300 12 6 6.3 3.4
21000 -11.3 11.7 270 10 5 8.1 4.5 | -11.7 10.9 300 10 5 6.2 3.4
20000 -8.9 16.0 280 9 4 8.1 4.5 | -9.9 14.2 305 8 4 6.3 3.4
19500 -7.7 18.1 285 8 4 8.1 4.4 | -9.0 15.8 310 7 4 6.4 3.5
19000 -6.6 20.1 290 9 4 7.9 4.3 | -8.0 17.6 310 7 3 6.6 3.6
18500 -5.4 22.3 295 9 5 7.9 4.3 | -7.0 19.4 310 6 3 6.6 3.6
18000 -4.3 24.3 300 10 5 8.2 4.5 | -6.1 21.0 310 6 3 6.9 3.8
17500 -3.1 26.4 300 10 5 8.2 4.5 | -5.1 22.8 310 5 3 6.9 3.8
17000 -1.9 28.6 305 10 5 8.2 4.5 | -4.1 24.6 310 5 3 7.2 4.0
16500 -0.7 30.7 305 10 5 8.1 4.5 | -3.0 26.6 305 4 2 7.6 4.2
16000 0.4 32.7 310 9 4 8.3 4.6 | -1.8 28.8 300 4 2 7.6 4.2
15500 1.5 34.7 310 8 4 6.8 3.7 | -0.7 30.7 285 3 2 8.5 4.6
15000 2.5 36.5 310 7 3 7.0 3.8 | 0.6 33.1 270 3 1 8.4 4.6
14500 3.5 38.3 305 5 3 6.2 3.4 | 1.8 35.2 250 3 1 8.0 4.4
14000 4.6 40.3 305 4 2 5.9 3.2 | 2.9 37.2 235 3 2 7.9 4.4
13500 5.5 41.9 310 3 2 7.4 4.1 | 4.0 39.2 225 4 2 7.2 3.9
13000 6.6 43.9 320 2 1 7.6 4.2 | 5.0 41.0 215 5 2 6.7 3.7
12500 7.5 45.5 335 2 1 4.6 2.5 | 5.9 42.6 210 6 3 6.8 3.8
12000 8.1 46.6 350 2 1 4.2 2.3 | 7.4 45.3 210 7 4 7.0 3.8
11500 8.7 47.7 015 2 1 6.4 3.5 | 8.4 47.1 210 7 4 8.0 4.4
11000 9.6 49.3 045 2 1 7.0 3.8 | 9.5 49.1 210 7 4 8.3 4.5
10500 10.5 50.9 060 3 2 3.4 1.9 | 10.5 50.9 210 7 4 5.1 2.8
10250 10.7 51.3 060 3 2 7.7 4.2 | 10.9 51.6 215 7 4 7.1 3.9
10000 11.6 52.9 065 4 2 14.7 8.1 | 11.5 52.7 220 7 4 10.9 6.0
9750 12.5 54.5 065 5 2 11.8 6.5 | 12.3 54.1 225 8 4 8.9 4.9
9500 13.2 55.8 065 5 3 7.3 4.0 | 12.8 55.0 225 8 4 6.1 3.4
9250 13.7 56.7 065 5 3 6.0 3.3 | 13.2 55.8 225 8 4 5.4 3.0
9000 14.3 57.7 065 5 3 13.0 7.1 | 13.7 56.7 230 9 4 10.7 5.9
8750 15.4 59.7 060 5 3 13.3 7.3 | 14.6 58.3 235 10 5 10.3 5.6
8500 16.1 61.0 060 6 3 8.0 4.4 | 15.1 59.2 235 10 5 5.5 3.0
8250 16.7 62.1 060 6 3 6.2 3.4 | 15.5 59.9 240 11 5 5.7 3.1
8000 17.3 63.1 060 6 3 13.0 7.1 | 16.0 60.8 240 11 6 8.4 4.6
7750 18.5 65.3 060 6 3 14.5 8.0 | 16.7 62.1 245 14 7 8.5 4.7
7500 19.3 66.7 060 6 3 8.4 4.6 | 17.1 62.8 245 15 8 5.4 2.9
7250 20.0 68.0 055 6 3 11.2 6.2 | 17.6 63.7 245 16 8 6.5 3.5
7000 20.7 69.3 055 6 3 6.0 3.3 | 18.0 64.4 245 17 9 5.3 2.9
6750 21.1 70.0 055 6 3 7.8 4.3 | 18.4 65.1 250 17 9 5.7 3.2
6500 22.0 71.6 055 6 3 13.3 7.3 | 18.8 65.8 250 17 9 7.0 3.8
6250 22.9 73.2 055 6 3 13.1 7.2 | 19.3 66.7 250 18 9 6.8 3.7
6000 23.8 74.8 055 6 3 8.6 4.7 | 19.8 67.6 250 18 9 6.3 3.4
5750 24.4 75.9 055 6 3 12.4 6.8 | 20.3 68.5 250 17 9 8.7 4.8
5500 26.1 79.0 050 6 3 33.6 18.4 | 21.1 70.0 255 15 8 14.6 8.0
________________________________________________________________________________
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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