Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
607
UXUS97 KBOU 271230
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0629 MDT Wednesday, August 27, 2025
This forecast is for Wednesday, August 27, 2025:
If the trigger temperature of 75.8 F/24.3 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 289 ft/min (1.5 m/s)
Maximum height of thermals.................. 11796 ft MSL (6462 ft AGL)
Forecast maximum temperature................... 81.0 F/27.7 C
Time of trigger temperature.................... 1200 MDT
Time of overdevelopment........................ 1430 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................. 9223 ft MSL (3889 ft AGL)
Thermal soaring outlook for Thursday 08/28..... 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....................... 20583 ft MSL (15249 ft AGL)
Wave soaring outlook for Thursday 08/28........ Poor
Remarks... Stratus and areas of fog until 0900. Then broken mid clouds til 1400,
then scattered to numerous storms.
Sunrise/Sunset.................... 06:23:28 / 19:38:15 MDT
Total possible sunshine........... 13 hr 14 min 47 sec (794 min 47 sec)
Altitude of sun at 13:00:52 MDT... 60.00 degrees
Upper air data from numerical model forecast valid on 08/27/2025 at 0600 MDT
Freezing level.................. 15561 ft MSL (10227 ft AGL)
Convective condensation level... 11277 ft MSL (5943 ft AGL)
Lifted condensation level....... 11532 ft MSL (6197 ft AGL)
Lifted index.................... -4.0
K index......................... +30.2
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 -64.3 -83.7 280 23 12 2.6 1.4 M M M M M
45000 -58.7 -73.7 270 37 19 5.4 3.0 M M M M M
40000 -50.6 -59.1 265 49 25 5.6 3.1 M M M M M
38000 -47.3 -53.1 260 38 19 5.6 3.1 M M M M M
36000 -43.9 -47.0 255 27 14 5.6 3.1 M M M M M
34000 -38.7 -37.7 255 27 14 8.9 4.9 M M M M M
32000 -32.7 -26.9 255 28 14 9.2 5.1 M M M M M
30000 -28.1 -18.6 260 31 16 7.7 4.2 48.2 118.8 16.0 M M
29000 -25.8 -14.4 265 33 17 7.7 4.2 47.5 117.5 15.6 M M
28000 -23.5 -10.3 265 34 17 6.7 3.7 46.8 116.2 15.2 M M
27000 -21.5 -6.7 265 32 17 6.7 3.7 45.5 113.9 14.3 M M
26000 -19.6 -3.3 260 31 16 6.8 3.7 44.4 111.8 13.5 M M
25000 -17.6 0.3 260 30 15 6.8 3.7 43.4 110.1 12.8 M M
24000 -15.7 3.7 260 28 14 6.5 3.6 42.1 107.8 11.9 M M
23000 -13.8 7.2 255 26 13 6.5 3.6 40.9 105.6 11.0 M M
22000 -11.8 10.8 255 23 12 6.5 3.6 39.8 103.7 10.2 M M
21000 -10.0 14.0 255 22 11 6.5 3.6 38.6 101.5 9.2 M M
20000 -8.1 17.4 250 20 10 6.6 3.6 37.5 99.5 8.2 M M
19500 -7.1 19.2 250 19 10 6.6 3.6 37.0 98.6 7.8 M M
19000 -6.2 20.8 250 18 9 6.5 3.6 36.5 97.6 7.3 M M
18500 -5.3 22.5 250 17 9 6.5 3.6 35.9 96.6 6.9 M M
18000 -3.9 25.0 240 15 8 5.3 2.9 35.0 95.0 6.1 M M
17500 -3.2 26.2 235 13 7 5.2 2.9 34.2 93.6 5.3 M M
17000 -2.5 27.5 225 12 6 5.5 3.0 33.4 92.2 4.6 M M
16500 -1.6 29.1 225 11 6 6.2 3.4 32.8 91.1 4.1 M M
16000 -0.7 30.7 220 10 5 6.1 3.3 32.2 90.0 3.6 M M
15500 0.3 32.5 215 10 5 7.3 4.0 31.7 89.1 3.1 M M
15000 1.4 34.5 220 9 5 7.2 3.9 31.3 88.3 2.7 M M
14500 2.4 36.3 220 9 5 7.2 4.0 30.9 87.6 2.3 M M
14000 3.4 38.1 225 9 4 7.3 4.0 30.4 86.8 1.9 M M
13500 4.5 40.1 225 8 4 7.2 3.9 30.1 86.1 1.5 M M
13000 5.5 41.9 230 8 4 7.1 3.9 29.6 85.3 1.1 M M
12500 6.5 43.7 235 8 4 7.1 3.9 29.2 84.5 0.6 M M
12000 7.5 45.5 240 7 4 7.2 4.0 28.8 83.8 0.2 M M
11500 8.5 47.3 240 7 4 7.2 4.0 28.4 83.1 -0.3 461 2.3
11000 9.5 49.1 245 6 3 7.1 3.9 28.0 82.3 -0.7 415 2.1
10500 10.5 50.9 245 6 3 5.3 2.9 27.6 81.6 -1.2 370 1.9
10250 10.8 51.4 245 5 3 3.6 2.0 27.1 80.8 -1.6 355 1.8
10000 11.1 52.0 250 5 3 6.3 3.4 26.7 80.1 -2.0 337 1.7
9750 11.6 52.9 255 4 2 7.2 4.0 26.5 79.7 -2.2 315 1.6
9500 12.1 53.8 260 4 2 6.0 3.3 26.3 79.3 -2.5 292 1.5
9250 12.4 54.3 270 4 2 3.6 2.0 25.9 78.6 -2.9 276 1.4
9000 12.6 54.7 280 4 2 3.3 1.8 25.4 77.7 -3.4 262 1.3
8750 12.9 55.2 290 4 2 3.8 2.1 24.9 76.8 -4.0 249 1.3
8500 13.1 55.6 295 4 2 3.5 1.9 24.4 76.0 -4.5 235 1.2
8250 13.3 55.9 300 4 2 3.1 1.7 23.9 75.1 -5.0 221 1.1
8000 13.5 56.3 310 4 2 3.2 1.8 23.4 74.2 -5.6 208 1.1
7750 13.7 56.7 315 3 2 3.7 2.1 22.9 73.3 -6.1 194 1.0
7500 13.9 57.0 320 3 2 3.2 1.8 22.5 72.5 -6.6 180 0.9
7250 14.1 57.4 325 4 2 2.7 1.5 21.9 71.5 -7.2 168 0.9
7000 14.2 57.6 330 5 3 2.7 1.5 21.4 70.5 -7.8 156 0.8
6750 14.4 57.9 330 6 3 2.8 1.5 20.9 69.6 -8.4 144 0.7
6500 14.6 58.3 330 6 3 3.7 2.0 20.4 68.7 -8.9 130 0.7
6250 14.9 58.8 330 6 3 4.7 2.6 20.0 67.9 -9.4 114 0.6
6000 15.1 59.2 325 6 3 2.7 1.5 19.5 67.2 -9.8 99 0.5
5750 15.3 59.5 325 7 4 3.7 2.0 19.0 66.1 -10.4 87 0.4
5500 15.8 60.4 320 5 3 10.8 5.9 18.8 65.8 -10.7 65 0.3
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/27/2025 at 0900 MDT | 08/27/2025 at 1200 MDT
|
CAPE... +40.8 LI... -0.4 | CAPE... +264.4 LI... -0.5
CINH... -126.6 K Index... +29.6 | CINH... -31.8 K Index... +25.3
|
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 -64.2 -83.6 280 27 14 2.6 1.4 | -64.0 -83.2 280 30 15 2.4 1.3
45000 -58.7 -73.7 270 43 22 5.3 2.9 | -58.6 -73.5 275 45 23 5.8 3.2
40000 -50.3 -58.5 265 52 27 7.4 4.1 | -49.6 -57.3 265 52 27 7.1 3.9
38000 -45.9 -50.6 260 45 23 7.4 4.0 | -45.3 -49.5 265 48 25 7.1 3.9
36000 -41.5 -42.7 255 39 20 7.4 4.1 | -41.1 -42.0 265 45 23 7.1 3.9
34000 -37.8 -36.0 245 33 17 6.1 3.3 | -37.0 -34.6 255 40 21 6.0 3.3
32000 -33.6 -28.5 230 29 15 6.8 3.8 | -33.4 -28.1 250 37 19 6.3 3.4
30000 -29.4 -20.9 240 26 13 7.3 4.0 | -29.4 -20.9 245 33 17 6.8 3.7
29000 -27.2 -17.0 245 25 13 7.3 4.0 | -27.4 -17.3 240 32 16 6.8 3.7
28000 -25.0 -13.0 250 24 13 8.6 4.7 | -25.3 -13.5 240 30 16 8.4 4.6
27000 -22.4 -8.3 255 24 13 8.7 4.8 | -22.8 -9.0 240 29 15 8.5 4.7
26000 -19.9 -3.8 260 24 13 8.7 4.8 | -20.3 -4.5 245 28 14 8.5 4.7
25000 -17.3 0.9 265 25 13 8.1 4.5 | -17.8 -0.0 250 26 14 8.1 4.4
24000 -15.3 4.5 270 25 13 6.5 3.6 | -15.8 3.6 255 26 14 6.8 3.7
23000 -13.5 7.7 275 25 13 6.5 3.6 | -13.7 7.3 260 27 14 6.8 3.7
22000 -11.6 11.1 275 26 13 6.5 3.6 | -11.7 10.9 265 27 14 6.9 3.8
21000 -9.6 14.7 280 27 14 6.5 3.6 | -9.6 14.7 270 26 14 7.2 4.0
20000 -7.7 18.1 280 28 15 6.5 3.6 | -7.4 18.7 270 25 13 7.2 4.0
19500 -6.8 19.8 280 29 15 6.6 3.6 | -6.3 20.7 275 24 13 7.3 4.0
19000 -5.9 21.4 280 29 15 5.5 3.0 | -5.3 22.5 275 23 12 7.2 3.9
18500 -5.1 22.8 280 28 14 5.5 3.0 | -4.2 24.4 280 22 11 7.2 4.0
18000 -4.3 24.3 280 27 14 5.3 2.9 | -3.2 26.2 280 21 11 6.8 3.7
17500 -3.6 25.5 280 25 13 4.9 2.7 | -2.0 28.4 285 19 10 5.6 3.1
17000 -2.9 26.8 280 23 12 4.8 2.6 | -1.2 29.8 290 19 10 5.3 2.9
16500 -1.7 28.9 275 20 10 6.0 3.3 | -0.6 30.9 295 18 9 4.8 2.6
16000 -0.9 30.4 270 18 9 6.0 3.3 | 0.1 32.2 300 17 9 4.8 2.7
15500 -0.0 32.0 270 17 9 6.5 3.5 | 0.7 33.3 305 16 8 4.7 2.6
15000 0.9 33.6 265 16 8 6.4 3.5 | 1.4 34.5 310 15 8 4.6 2.5
14500 1.8 35.2 265 15 7 6.3 3.5 | 2.1 35.8 315 15 8 5.8 3.2
14000 2.7 36.9 265 14 7 6.3 3.5 | 3.0 37.4 320 14 7 6.0 3.3
13500 3.7 38.7 265 13 7 6.7 3.7 | 3.9 39.0 320 14 7 6.6 3.6
13000 4.7 40.5 265 12 6 7.0 3.9 | 4.9 40.8 320 13 7 7.0 3.8
12500 5.7 42.3 270 11 6 7.0 3.8 | 5.9 42.6 320 13 6 7.1 3.9
12000 6.6 43.9 275 10 5 6.9 3.8 | 7.0 44.6 320 12 6 7.2 4.0
11500 7.6 45.7 285 9 5 6.7 3.7 | 8.1 46.6 325 12 6 7.1 3.9
11000 8.5 47.3 295 9 5 6.1 3.3 | 9.1 48.4 325 11 6 6.6 3.6
10500 9.4 48.9 300 9 5 4.0 2.2 | 10.1 50.2 325 11 6 4.3 2.3
10250 9.6 49.3 305 9 5 3.5 1.9 | 10.3 50.5 325 11 5 4.7 2.6
10000 10.1 50.2 305 9 5 7.8 4.3 | 10.9 51.6 325 10 5 9.2 5.0
9750 10.7 51.3 310 10 5 9.0 4.9 | 11.5 52.7 325 10 5 9.2 5.0
9500 11.4 52.5 315 10 5 7.2 4.0 | 12.2 54.0 325 10 5 8.3 4.5
9250 11.8 53.2 315 11 5 4.9 2.7 | 12.7 54.9 325 9 5 6.9 3.8
9000 12.2 54.0 320 11 6 5.9 3.2 | 13.2 55.8 325 9 5 7.7 4.2
8750 12.6 54.7 320 11 6 7.1 3.9 | 13.8 56.8 320 9 5 8.3 4.6
8500 13.1 55.6 320 12 6 5.5 3.0 | 14.4 57.9 320 9 5 8.1 4.4
8250 13.4 56.1 325 12 6 4.0 2.2 | 15.0 59.0 320 9 5 8.3 4.5
8000 13.8 56.8 325 12 6 4.7 2.6 | 15.6 60.1 315 9 5 7.6 4.2
7750 14.1 57.4 325 12 6 5.1 2.8 | 16.1 61.0 310 9 5 6.5 3.5
7500 14.4 57.9 325 12 6 3.8 2.1 | 16.5 61.7 310 9 4 6.4 3.5
7250 14.6 58.3 325 12 6 2.8 1.6 | 16.9 62.4 305 8 4 6.6 3.6
7000 14.8 58.6 325 13 6 3.1 1.7 | 17.3 63.1 300 7 3 6.2 3.4
6750 14.9 58.8 325 13 7 2.0 1.1 | 17.6 63.7 295 5 3 7.2 4.0
6500 15.0 59.0 320 11 6 1.7 0.9 | 18.2 64.8 285 4 2 9.8 5.4
6250 15.0 59.0 320 9 5 1.1 0.6 | 19.0 66.2 285 4 2 10.0 5.5
6000 15.1 59.2 315 7 3 4.2 2.3 | 19.7 67.5 280 3 2 11.2 6.2
5750 15.6 60.1 310 6 3 10.8 5.9 | 20.7 69.3 275 3 2 18.0 9.9
5500 16.5 61.7 305 5 3 12.5 6.9 | 22.4 72.3 275 3 2 24.8 13.6
08/27/2025 at 1500 MDT | 08/27/2025 at 1800 MDT
|
CAPE... +159.4 LI... -0.4 | CAPE... +248.6 LI... -2.1
CINH... -22.9 K Index... +27.4 | CINH... -14.1 K Index... +31.4
|
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 -64.2 -83.6 275 29 15 2.1 1.1 | -64.0 -83.2 275 29 15 2.0 1.1
45000 -58.9 -74.0 270 45 23 6.2 3.4 | -58.7 -73.7 270 48 25 6.3 3.4
40000 -49.3 -56.7 265 55 28 7.0 3.9 | -49.2 -56.6 270 63 32 6.8 3.7
38000 -45.1 -49.2 270 53 27 7.0 3.9 | -45.1 -49.2 275 60 31 6.8 3.7
36000 -40.9 -41.6 270 50 26 7.0 3.9 | -41.1 -42.0 275 56 29 6.8 3.7
34000 -36.9 -34.4 270 44 23 5.9 3.2 | -36.7 -34.1 270 47 24 6.5 3.6
32000 -33.3 -27.9 265 38 20 6.2 3.4 | -32.8 -27.0 265 38 19 6.5 3.6
30000 -28.9 -20.0 270 32 16 7.5 4.1 | -29.0 -20.2 270 30 16 6.3 3.5
29000 -26.7 -16.1 270 29 15 7.5 4.1 | -27.1 -16.8 270 27 14 6.4 3.5
28000 -24.4 -11.9 275 26 13 7.5 4.1 | -25.1 -13.2 270 23 12 8.3 4.6
27000 -22.2 -8.0 265 26 13 7.5 4.1 | -22.6 -8.7 270 22 12 8.4 4.6
26000 -19.9 -3.8 260 26 13 7.5 4.1 | -20.0 -4.0 265 21 11 8.4 4.6
25000 -17.7 0.1 255 26 13 7.2 4.0 | -17.5 0.5 265 21 11 7.9 4.3
24000 -15.8 3.6 255 27 14 6.4 3.5 | -15.6 3.9 265 21 11 6.3 3.5
23000 -13.9 7.0 250 27 14 6.6 3.6 | -13.7 7.3 260 22 11 6.4 3.5
22000 -12.1 10.2 250 28 14 7.2 3.9 | -11.9 10.6 260 23 12 6.3 3.5
21000 -9.8 14.4 250 27 14 7.6 4.2 | -10.2 13.6 260 23 12 6.1 3.4
20000 -7.6 18.3 255 26 14 7.6 4.2 | -8.4 16.9 260 23 12 6.3 3.5
19500 -6.5 20.3 255 26 13 7.8 4.3 | -7.6 18.3 260 22 11 6.4 3.5
19000 -5.5 22.1 255 25 13 6.0 3.3 | -6.7 19.9 265 22 11 6.4 3.5
18500 -4.6 23.7 260 24 12 6.0 3.3 | -5.8 21.6 270 22 11 6.4 3.5
18000 -3.7 25.3 260 22 11 5.8 3.2 | -4.4 24.1 270 22 11 6.1 3.4
17500 -2.5 27.5 260 20 10 5.5 3.0 | -3.6 25.5 270 21 11 6.1 3.4
17000 -1.7 28.9 260 19 10 5.8 3.2 | -2.7 27.1 270 20 10 6.3 3.5
16500 -0.9 30.4 265 18 9 6.3 3.5 | -1.7 28.9 270 20 10 6.6 3.6
16000 -0.1 31.8 270 17 9 6.4 3.5 | -0.8 30.6 275 21 11 6.6 3.6
15500 0.8 33.4 275 16 8 5.9 3.2 | 0.2 32.4 275 20 10 6.9 3.8
15000 1.7 35.1 275 15 8 5.9 3.2 | 1.1 34.0 275 20 10 6.8 3.7
14500 2.6 36.7 280 14 7 6.8 3.7 | 2.1 35.8 280 19 10 7.2 3.9
14000 3.6 38.5 285 14 7 6.9 3.8 | 3.2 37.8 280 18 9 7.2 4.0
13500 4.6 40.3 290 13 7 7.3 4.0 | 4.2 39.6 280 17 9 7.7 4.2
13000 5.7 42.3 295 13 7 7.6 4.2 | 5.4 41.7 285 15 8 8.1 4.4
12500 6.8 44.2 300 12 6 7.6 4.2 | 6.5 43.7 285 14 7 8.4 4.6
12000 7.9 46.2 305 11 6 7.5 4.1 | 7.8 46.0 290 12 6 8.8 4.8
11500 9.1 48.4 310 11 5 7.4 4.1 | 9.0 48.2 290 10 5 8.7 4.8
11000 10.1 50.2 320 9 5 7.0 3.8 | 10.4 50.7 295 7 4 8.2 4.5
10500 11.2 52.2 330 8 4 4.0 2.2 | 11.7 53.1 300 4 2 3.4 1.9
10250 11.4 52.5 330 8 4 5.2 2.9 | 11.7 53.1 300 4 2 4.3 2.4
10000 12.0 53.6 335 7 4 10.1 5.5 | 12.5 54.5 305 3 2 11.5 6.3
9750 12.6 54.7 345 6 3 8.9 4.9 | 13.2 55.8 310 3 1 9.7 5.3
9500 13.3 55.9 355 6 3 8.8 4.8 | 13.9 57.0 315 2 1 9.9 5.4
9250 13.9 57.0 360 5 3 8.5 4.6 | 14.6 58.3 320 2 1 9.4 5.1
9000 14.5 58.1 005 4 2 9.9 5.4 | 15.3 59.5 325 2 1 9.7 5.3
8750 15.2 59.4 010 4 2 10.9 6.0 | 16.1 61.0 325 2 1 9.9 5.4
8500 16.0 60.8 015 4 2 10.1 5.5 | 16.8 62.2 330 2 1 9.8 5.4
8250 16.7 62.1 015 4 2 9.4 5.1 | 17.5 63.5 330 2 1 9.9 5.4
8000 17.4 63.3 015 4 2 9.7 5.3 | 18.2 64.8 330 2 1 9.7 5.3
7750 18.2 64.8 015 4 2 10.0 5.5 | 19.0 66.2 330 2 1 9.3 5.1
7500 18.9 66.0 015 4 2 10.1 5.6 | 19.7 67.5 330 2 1 10.0 5.5
7250 19.7 67.5 015 4 2 10.4 5.7 | 20.4 68.7 330 2 1 10.5 5.8
7000 20.4 68.7 015 4 2 9.9 5.4 | 21.2 70.2 330 2 1 10.1 5.6
6750 21.2 70.2 015 4 2 9.5 5.2 | 21.9 71.4 330 2 1 9.7 5.3
6500 21.9 71.4 015 4 2 10.5 5.7 | 22.7 72.9 330 2 1 10.0 5.5
6250 22.7 72.9 015 3 2 11.9 6.5 | 23.4 74.1 330 2 1 10.5 5.8
6000 23.6 74.5 015 3 2 8.9 4.9 | 24.2 75.6 325 2 1 9.5 5.2
5750 24.3 75.7 015 3 2 14.6 8.0 | 24.9 76.8 325 2 1 11.1 6.1
5500 26.0 78.8 020 3 2 32.5 17.8 | 25.9 78.6 330 2 1 16.4 9.0
________________________________________________________________________________
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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