Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
365
UXUS97 KBOU 191311
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0710 MDT Wednesday, August 19, 2026
This forecast is for Wednesday, August 19, 2026:
If the trigger temperature of 82.1 F/27.9 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1218 ft/min (6.2 m/s)
Maximum height of thermals.................. 16544 ft MSL (11248 ft AGL)
Forecast maximum temperature................... 90.0 F/32.7 C
Time of trigger temperature.................... 1130 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 10930 ft MSL (5633 ft AGL)
Thermal soaring outlook for Thursday 08/20..... Excellent
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 NVA
Potential height of wave....................... 22510 ft MSL (17214 ft AGL)
Wave soaring outlook for Thursday 08/20........ Poor
Remarks... Isolated afternoon storms possible.
Sunrise/Sunset.................... 06:15:44 / 19:50:22 MDT
Total possible sunshine........... 13 hr 34 min 39 sec (814 min 39 sec)
Altitude of sun at 13:03:03 MDT... 62.80 degrees
Upper air data from numerical model forecast valid on 08/19/2026 at 0600 MDT
Freezing level.................. 15903 ft MSL (10607 ft AGL)
Convective condensation level... 14024 ft MSL (8728 ft AGL)
Lifted condensation level....... 14611 ft MSL (9315 ft AGL)
Lifted index.................... -4.4
K index......................... +31.3
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 -64.2 -83.6 295 41 21 -0.2 -0.1 M M M M M
45000 -61.7 -79.1 285 47 24 5.3 2.9 M M M M M
40000 -53.2 -63.8 285 53 28 7.8 4.3 M M M M M
38000 -48.5 -55.3 280 48 25 7.8 4.3 M M M M M
36000 -43.8 -46.8 280 42 22 8.0 4.4 M M M M M
34000 -38.7 -37.7 285 40 21 8.6 4.7 M M M M M
32000 -33.5 -28.3 285 38 20 8.6 4.7 M M M M M
30000 -28.2 -18.8 285 37 19 7.9 4.3 47.7 117.8 11.8 M M
29000 -25.8 -14.4 285 37 19 7.9 4.3 47.0 116.7 11.4 M M
28000 -23.6 -10.5 285 37 19 6.4 3.5 46.2 115.2 10.9 M M
27000 -21.7 -7.1 290 39 20 6.6 3.6 44.9 112.9 10.0 M M
26000 -19.7 -3.5 290 41 21 6.7 3.7 43.8 110.8 9.1 M M
25000 -17.8 -0.0 295 43 22 6.7 3.7 42.7 108.9 8.3 M M
24000 -15.8 3.6 295 44 23 6.7 3.7 41.5 106.7 7.3 M M
23000 -13.9 7.0 295 45 23 6.7 3.7 40.4 104.7 6.5 M M
22000 -11.9 10.6 295 46 24 6.5 3.6 39.4 102.9 5.6 M M
21000 -10.1 13.8 295 44 23 6.4 3.5 38.1 100.6 4.6 M M
20000 -8.2 17.2 295 42 21 6.4 3.5 36.9 98.5 3.5 M M
19500 -7.3 18.9 295 41 21 6.4 3.5 36.4 97.5 3.1 M M
19000 -6.4 20.5 295 39 20 6.0 3.3 35.8 96.4 2.5 M M
18500 -5.5 22.1 295 38 20 6.0 3.3 35.1 95.3 1.9 M M
18000 -4.7 23.5 295 37 19 6.7 3.7 34.5 94.2 1.3 M M
17500 -3.7 25.3 300 36 19 7.0 3.9 34.1 93.3 0.9 M M
17000 -2.7 27.1 300 35 18 7.1 3.9 33.6 92.5 0.4 M M
16500 -1.6 29.1 300 34 18 7.7 4.2 33.2 91.8 0.0 M M
16000 -0.5 31.1 300 33 17 7.6 4.2 32.9 91.2 -0.3 976 5.0
15500 1.3 34.3 305 32 17 8.7 4.8 32.5 90.5 -0.7 901 4.6
15000 2.6 36.7 305 31 16 8.7 4.8 32.3 90.2 -0.9 848 4.3
14500 3.8 38.8 305 30 16 8.8 4.8 32.1 89.9 -1.1 795 4.0
14000 5.1 41.2 305 29 15 8.8 4.8 32.0 89.6 -1.3 742 3.8
13500 6.4 43.5 305 28 14 8.4 4.6 31.8 89.3 -1.5 689 3.5
13000 7.6 45.7 310 26 13 8.3 4.6 31.6 88.8 -1.7 638 3.2
12500 8.8 47.8 310 25 13 8.3 4.5 31.4 88.4 -2.0 587 3.0
12000 10.0 50.0 310 23 12 8.2 4.5 31.1 88.0 -2.3 536 2.7
11500 11.2 52.2 315 21 11 7.7 4.2 30.9 87.6 -2.5 486 2.5
11000 12.2 54.0 315 18 9 6.9 3.8 30.5 86.8 -3.0 441 2.2
10500 13.2 55.8 320 16 8 2.9 1.6 30.1 86.1 -3.4 395 2.0
10250 13.3 55.9 325 16 8 5.2 2.9 29.4 84.9 -4.1 385 2.0
10000 14.1 57.4 325 15 8 12.0 6.6 29.5 85.0 -4.0 355 1.8
9750 14.8 58.6 330 14 7 11.0 6.0 29.5 85.2 -4.0 325 1.6
9500 15.6 60.1 330 14 7 8.3 4.6 29.6 85.3 -4.0 295 1.5
9250 16.1 61.0 330 14 7 5.4 3.0 29.3 84.8 -4.3 273 1.4
9000 16.6 61.9 330 14 7 9.0 4.9 29.1 84.4 -4.4 249 1.3
8750 17.4 63.3 325 14 7 10.6 5.8 29.1 84.5 -4.4 219 1.1
8500 18.1 64.6 325 14 7 8.3 4.6 29.1 84.5 -4.4 189 1.0
8250 18.7 65.7 315 14 7 6.8 3.7 28.9 84.1 -4.6 166 0.8
8000 19.2 66.6 310 15 8 7.2 4.0 28.7 83.7 -4.8 143 0.7
7750 19.7 67.5 305 15 8 6.2 3.4 28.5 83.3 -5.1 121 0.6
7500 20.0 68.0 295 16 8 3.4 1.9 28.2 82.7 -5.5 104 0.5
7250 20.1 68.2 285 15 8 1.7 0.9 27.6 81.6 -6.1 93 0.5
7000 20.2 68.4 280 16 8 2.7 1.5 27.0 80.6 -6.8 83 0.4
6750 20.3 68.5 270 16 8 -0.8 -0.4 26.4 79.5 -7.5 74 0.4
6500 19.9 67.8 260 16 8 -5.0 -2.8 25.4 77.7 -8.6 77 0.4
6250 19.4 66.9 245 16 8 -5.5 -3.0 24.2 75.6 -9.8 84 0.4
6000 19.0 66.2 235 16 8 -4.1 -2.3 23.1 73.6 -11.0 91 0.5
5750 18.7 65.7 225 15 8 -2.6 -1.4 22.2 71.9 -12.1 92 0.5
5500 18.3 64.9 220 10 5 -4.0 -2.2 21.2 70.2 -13.1 94 0.5
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
08/19/2026 at 0900 MDT | 08/19/2026 at 1200 MDT
|
CAPE... +803.3 LI... -3.2 | CAPE... +1086.4 LI... -3.4
CINH... -132.1 K Index... +30.1 | CINH... -26.5 K Index... +27.3
|
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 -63.5 -82.3 290 42 22 -0.4 -0.2 | -63.5 -82.3 290 42 21 -0.7 -0.4
45000 -61.6 -78.9 285 52 27 4.7 2.6 | -61.9 -79.4 285 57 29 4.8 2.6
40000 -53.8 -64.8 285 57 29 7.7 4.2 | -54.1 -65.4 285 64 33 7.8 4.3
38000 -49.3 -56.7 290 57 29 7.6 4.2 | -49.4 -56.9 290 62 32 7.8 4.3
36000 -44.7 -48.5 295 57 29 7.9 4.3 | -44.7 -48.5 290 60 31 8.1 4.4
34000 -39.3 -38.7 290 54 28 9.1 5.0 | -39.3 -38.7 290 57 29 9.1 5.0
32000 -33.9 -29.0 285 50 26 9.1 5.0 | -33.2 -27.8 290 53 27 8.7 4.8
30000 -28.3 -18.9 285 48 25 8.1 4.4 | -28.5 -19.3 295 55 28 7.8 4.3
29000 -25.9 -14.6 285 47 24 8.1 4.4 | -26.1 -15.0 295 56 29 7.8 4.3
28000 -23.7 -10.7 285 46 24 5.0 2.8 | -23.9 -11.0 300 57 29 6.0 3.3
27000 -22.1 -7.8 290 45 23 5.4 3.0 | -22.1 -7.8 300 55 28 6.2 3.4
26000 -20.6 -5.1 295 45 23 5.5 3.0 | -20.2 -4.4 300 54 28 6.2 3.4
25000 -19.0 -2.2 295 45 23 6.3 3.5 | -18.4 -1.1 300 52 27 6.5 3.6
24000 -16.9 1.6 300 43 22 7.1 3.9 | -16.4 2.5 300 50 26 6.9 3.8
23000 -14.8 5.4 300 42 22 7.1 3.9 | -14.3 6.3 300 47 24 6.9 3.8
22000 -12.8 9.0 305 41 21 6.9 3.8 | -12.3 9.9 300 45 23 7.0 3.8
21000 -10.8 12.6 305 41 21 6.6 3.6 | -10.3 13.5 300 43 22 7.0 3.8
20000 -8.8 16.2 300 41 21 6.6 3.6 | -8.2 17.2 305 41 21 7.0 3.8
19500 -7.9 17.8 300 41 21 6.6 3.6 | -7.2 19.0 305 40 20 6.9 3.8
19000 -7.0 19.4 300 41 21 5.8 3.2 | -6.3 20.7 305 38 20 5.4 3.0
18500 -6.1 21.0 300 41 21 5.9 3.3 | -5.5 22.1 300 37 19 5.5 3.0
18000 -5.3 22.5 300 40 21 6.8 3.8 | -4.7 23.5 300 36 19 6.4 3.5
17500 -4.3 24.3 300 39 20 7.4 4.1 | -3.8 25.2 305 35 18 6.8 3.7
17000 -3.2 26.2 300 38 19 7.6 4.2 | -2.8 27.0 305 34 17 7.0 3.9
16500 -2.0 28.4 300 36 18 9.3 5.1 | -1.7 28.9 305 33 17 8.7 4.8
16000 0.0 32.0 305 32 16 8.9 4.9 | 0.2 32.4 305 31 16 8.4 4.6
15500 1.2 34.2 305 29 15 7.7 4.2 | 1.3 34.3 305 29 15 7.9 4.3
15000 2.4 36.3 305 27 14 7.7 4.2 | 2.5 36.5 305 27 14 7.8 4.3
14500 3.5 38.3 305 24 13 8.1 4.5 | 3.7 38.7 305 25 13 8.9 4.9
14000 4.7 40.5 310 23 12 8.1 4.4 | 5.0 41.0 310 23 12 8.8 4.8
13500 5.9 42.6 310 21 11 8.8 4.8 | 6.3 43.3 310 21 11 8.7 4.8
13000 7.2 45.0 315 19 10 8.9 4.9 | 7.6 45.7 310 20 10 8.7 4.8
12500 8.5 47.3 315 18 9 8.4 4.6 | 9.0 48.2 315 19 10 8.6 4.7
12000 9.7 49.5 315 16 8 8.2 4.5 | 10.2 50.4 315 18 9 8.5 4.7
11500 10.9 51.6 315 15 8 8.1 4.4 | 11.5 52.7 315 17 9 8.3 4.5
11000 12.1 53.8 320 13 7 7.8 4.3 | 12.6 54.7 310 14 7 7.9 4.3
10500 13.2 55.8 320 12 6 4.1 2.3 | 13.7 56.7 310 12 6 3.5 1.9
10250 13.4 56.1 320 12 6 5.4 3.0 | 13.9 57.0 310 12 6 5.3 2.9
10000 14.1 57.4 325 11 6 11.0 6.0 | 14.6 58.3 310 10 5 11.6 6.3
9750 14.8 58.6 325 10 5 9.9 5.5 | 15.3 59.5 310 9 5 10.2 5.6
9500 15.5 59.9 325 10 5 7.6 4.2 | 16.0 60.8 305 8 4 8.0 4.4
9250 15.9 60.6 330 9 5 5.2 2.9 | 16.4 61.5 310 7 4 6.1 3.4
9000 16.3 61.3 330 9 5 7.5 4.1 | 17.0 62.6 310 6 3 8.7 4.8
8750 16.9 62.4 330 9 4 8.2 4.5 | 17.6 63.7 310 5 2 9.3 5.1
8500 17.4 63.3 330 8 4 6.8 3.7 | 18.2 64.8 315 3 2 7.9 4.3
8250 17.8 64.0 335 8 4 5.6 3.1 | 18.7 65.7 325 2 1 6.8 3.7
8000 18.3 64.9 335 7 4 6.7 3.7 | 19.2 66.6 350 2 1 8.3 4.6
7750 18.8 65.8 335 6 3 7.0 3.9 | 19.8 67.6 010 2 1 9.9 5.4
7500 19.2 66.6 335 6 3 5.5 3.0 | 20.4 68.7 015 2 1 9.9 5.4
7250 19.6 67.3 335 6 3 4.6 2.5 | 21.2 70.2 020 2 1 10.0 5.5
7000 19.9 67.8 330 6 3 5.8 3.2 | 21.9 71.4 020 2 1 9.7 5.3
6750 20.3 68.5 330 6 3 4.2 2.3 | 22.6 72.7 020 2 1 9.8 5.4
6500 20.4 68.7 325 5 3 1.7 0.9 | 23.4 74.1 020 2 1 10.6 5.8
6250 20.5 68.9 320 5 2 0.8 0.5 | 24.2 75.6 020 2 1 10.4 5.7
6000 20.5 68.9 315 4 2 4.4 2.4 | 24.9 76.8 020 2 1 11.0 6.0
5750 21.1 70.0 315 4 2 12.5 6.9 | 26.0 78.8 020 2 1 17.5 9.6
5500 22.1 71.8 310 3 2 15.3 8.4 | 27.6 81.7 020 2 1 26.5 14.5
08/19/2026 at 1500 MDT | 08/19/2026 at 1800 MDT
|
CAPE... +808.3 LI... -2.7 | CAPE... +660.1 LI... -2.8
CINH... -18.9 K Index... +31.3 | CINH... -29.2 K Index... +30.6
|
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 -63.3 -81.9 295 41 21 -0.5 -0.3 | -64.2 -83.6 300 38 20 0.2 0.1
45000 -61.6 -78.9 295 59 30 4.5 2.5 | -61.6 -78.9 305 54 28 4.6 2.5
40000 -54.1 -65.4 295 59 30 7.7 4.2 | -53.8 -64.8 310 58 30 7.9 4.3
38000 -49.5 -57.1 295 56 29 7.7 4.2 | -49.1 -56.4 305 52 27 7.9 4.3
36000 -44.9 -48.8 295 53 28 8.0 4.4 | -44.3 -47.7 305 45 23 8.1 4.4
34000 -39.6 -39.3 295 53 27 8.9 4.9 | -38.5 -37.3 300 44 23 8.6 4.7
32000 -33.6 -28.5 295 53 27 8.6 4.7 | -33.4 -28.1 295 43 22 8.6 4.7
30000 -28.8 -19.8 305 52 27 8.1 4.4 | -28.4 -19.1 295 42 22 8.3 4.5
29000 -26.4 -15.5 305 52 27 8.1 4.4 | -25.9 -14.6 300 42 21 8.3 4.5
28000 -24.1 -11.4 305 50 26 6.7 3.7 | -23.6 -10.5 300 41 21 7.1 3.9
27000 -22.1 -7.8 310 47 24 6.8 3.7 | -21.4 -6.5 305 39 20 7.2 4.0
26000 -20.0 -4.0 310 43 22 6.8 3.7 | -19.2 -2.6 305 38 19 7.2 4.0
25000 -18.0 -0.4 310 40 20 6.9 3.8 | -17.1 1.2 310 36 19 7.0 3.8
24000 -15.9 3.4 305 40 21 7.1 3.9 | -15.0 5.0 310 35 18 6.9 3.8
23000 -13.8 7.2 305 41 21 7.1 3.9 | -13.0 8.6 310 34 17 6.9 3.8
22000 -11.7 10.9 305 41 21 6.7 3.7 | -11.0 12.2 305 33 17 6.0 3.3
21000 -9.8 14.4 300 41 21 6.6 3.6 | -9.4 15.1 305 33 17 5.6 3.1
20000 -7.9 17.8 300 40 21 6.7 3.7 | -7.7 18.1 300 33 17 5.7 3.1
19500 -7.0 19.4 300 40 20 6.8 3.7 | -6.9 19.6 300 34 17 6.1 3.3
19000 -6.0 21.2 300 39 20 6.7 3.7 | -5.9 21.4 300 33 17 8.3 4.6
18500 -5.1 22.8 295 37 19 6.7 3.7 | -4.7 23.5 300 32 17 8.3 4.5
18000 -4.2 24.4 295 36 19 7.3 4.0 | -3.6 25.5 295 32 16 8.1 4.4
17500 -3.1 26.4 295 34 18 7.5 4.1 | -2.4 27.7 295 31 16 8.0 4.4
17000 -2.0 28.4 290 32 17 7.6 4.2 | -1.3 29.7 295 30 15 8.2 4.5
16500 -0.9 30.4 290 30 16 8.2 4.5 | 0.6 33.1 290 27 14 9.1 5.0
16000 0.9 33.6 285 27 14 8.5 4.6 | 1.9 35.4 290 25 13 8.9 4.9
15500 2.1 35.8 285 26 13 9.1 5.0 | 3.1 37.6 290 23 12 8.2 4.5
15000 3.4 38.1 285 24 12 9.1 5.0 | 4.2 39.6 290 21 11 8.3 4.5
14500 4.7 40.5 285 21 11 9.0 4.9 | 5.4 41.7 295 18 9 8.3 4.6
14000 6.0 42.8 285 19 10 9.0 4.9 | 6.7 44.1 295 16 8 8.3 4.6
13500 7.3 45.1 285 17 9 8.4 4.6 | 7.9 46.2 300 13 7 8.0 4.4
13000 8.5 47.3 285 14 7 8.4 4.6 | 9.0 48.2 305 10 5 8.0 4.4
12500 9.7 49.5 285 11 6 8.2 4.5 | 10.2 50.4 315 7 4 7.6 4.2
12000 10.9 51.6 285 7 4 8.1 4.4 | 11.2 52.2 340 5 3 7.5 4.1
11500 12.1 53.8 290 4 2 8.1 4.4 | 12.3 54.1 015 5 2 8.1 4.5
11000 13.3 55.9 310 2 1 7.9 4.3 | 13.6 56.5 020 5 3 8.4 4.6
10500 14.5 58.1 015 1 1 4.2 2.3 | 14.9 58.8 020 6 3 4.4 2.4
10250 14.7 58.5 015 1 1 6.5 3.6 | 15.1 59.2 020 6 3 6.5 3.5
10000 15.5 59.9 015 1 1 12.6 6.9 | 16.0 60.8 020 6 3 13.3 7.3
9750 16.3 61.3 020 2 1 11.4 6.3 | 16.8 62.2 020 6 3 12.0 6.6
9500 17.2 63.0 020 2 1 9.4 5.1 | 17.7 63.9 020 6 3 9.9 5.4
9250 17.7 63.9 020 2 1 8.0 4.4 | 18.3 64.9 020 6 3 8.2 4.5
9000 18.5 65.3 020 2 1 10.5 5.8 | 19.0 66.2 020 6 3 10.5 5.8
8750 19.3 66.7 020 2 1 10.9 6.0 | 19.8 67.6 020 6 3 10.8 5.9
8500 20.1 68.2 020 2 1 10.4 5.7 | 20.6 69.1 020 6 3 10.1 5.5
8250 20.8 69.4 020 2 1 10.0 5.5 | 21.4 70.5 020 6 3 9.4 5.2
8000 21.6 70.9 020 2 1 10.2 5.6 | 22.1 71.8 020 7 3 10.0 5.5
7750 22.3 72.1 020 2 1 10.3 5.6 | 22.8 73.0 020 7 3 10.4 5.7
7500 23.1 73.6 020 2 1 10.1 5.5 | 23.6 74.5 020 7 3 10.1 5.5
7250 23.8 74.8 020 2 1 10.2 5.6 | 24.3 75.7 020 7 3 9.9 5.5
7000 24.6 76.3 020 2 1 9.5 5.2 | 25.1 77.2 020 7 3 10.1 5.5
6750 25.3 77.5 015 2 1 9.6 5.3 | 25.8 78.4 015 7 3 10.4 5.7
6500 26.0 78.8 015 2 1 10.9 6.0 | 26.6 79.9 015 7 3 10.2 5.6
6250 26.9 80.4 015 2 1 11.9 6.5 | 27.4 81.3 015 7 3 10.9 6.0
6000 27.7 81.9 015 2 1 9.3 5.1 | 28.2 82.8 015 7 3 8.4 4.6
5750 28.5 83.3 015 2 1 14.8 8.1 | 28.8 83.8 015 7 3 10.7 5.9
5500 30.2 86.4 015 3 1 31.0 17.0 | 29.9 85.8 015 7 3 21.9 12.0
________________________________________________________________________________
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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