Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
391
UXUS97 KBOU 140118
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
1917 MDT Sunday, September 13, 2026
This forecast is for Monday, September 14, 2026:
If the trigger temperature of 83.1 F/28.4 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 824 ft/min (4.2 m/s)
Maximum height of thermals.................. 14576 ft MSL (9216 ft AGL)
Forecast maximum temperature................... 88.0 F/31.6 C
Time of trigger temperature.................... 1145 MDT
Time of overdevelopment........................ None
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................. 8887 ft MSL (3527 ft AGL)
Thermal soaring outlook for Tuesday 09/15...... Fair
Wave Soaring Index............................. Fair
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....................... 17177 ft MSL (11817 ft AGL)
Wave soaring outlook for Tuesday 09/15......... Poor
Remarks... Cold front should move through Tuesday morning.
Sunrise/Sunset.................... 06:40:01 / 19:09:55 MDT
Total possible sunshine........... 12 hr 29 min 54 sec (749 min 54 sec)
Altitude of sun at 12:54:58 MDT... 53.40 degrees
Upper air data from numerical model forecast valid on 09/14/2026 at 0600 MDT
Freezing level.................. 16425 ft MSL (11065 ft AGL)
Convective condensation level... 15457 ft MSL (10097 ft AGL)
Lifted condensation level....... 15149 ft MSL (9789 ft AGL)
Lifted index.................... -2.1
K index......................... +28.5
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 -65.8 -86.4 255 42 21 2.7 1.5 M M M M M
45000 -60.3 -76.5 245 55 28 5.8 3.2 M M M M M
40000 -51.5 -60.7 245 59 30 5.9 3.2 M M M M M
38000 -48.0 -54.4 240 57 29 5.9 3.2 M M M M M
36000 -44.0 -47.2 240 55 28 6.5 3.6 M M M M M
34000 -38.9 -38.0 235 50 26 8.5 4.7 M M M M M
32000 -33.8 -28.8 235 45 23 8.4 4.6 M M M M M
30000 -29.0 -20.2 235 44 22 8.0 4.4 46.7 116.1 11.8 M M
29000 -26.6 -15.9 235 43 22 8.0 4.4 46.1 115.0 11.4 M M
28000 -24.3 -11.7 235 42 22 7.5 4.1 45.6 114.0 11.1 M M
27000 -22.1 -7.8 235 40 20 7.2 3.9 44.4 112.0 10.3 M M
26000 -20.0 -4.0 240 38 19 7.2 3.9 43.5 110.2 9.6 M M
25000 -17.9 -0.2 240 35 18 7.2 4.0 42.6 108.7 9.0 M M
24000 -15.8 3.6 240 34 17 7.1 3.9 41.6 106.9 8.2 M M
23000 -13.8 7.2 240 32 17 7.1 3.9 40.6 105.1 7.4 M M
22000 -11.7 10.9 235 31 16 7.1 3.9 39.7 103.5 6.7 M M
21000 -9.7 14.5 235 31 16 6.8 3.7 38.6 101.6 5.8 M M
20000 -7.2 19.0 240 30 16 6.8 3.7 37.4 99.2 4.8 M M
19500 -6.2 20.8 240 30 16 6.8 3.7 36.9 98.4 4.4 M M
19000 -5.1 22.8 240 30 16 7.2 3.9 36.4 97.6 4.0 M M
18500 -4.1 24.6 240 31 16 7.2 3.9 36.0 96.8 3.6 M M
18000 -3.0 26.6 245 31 16 7.1 3.9 35.6 96.0 3.2 M M
17500 -2.0 28.4 245 32 16 7.0 3.8 35.1 95.1 2.8 M M
17000 -1.0 30.2 245 32 17 7.0 3.8 34.6 94.3 2.4 M M
16500 -0.0 32.0 245 32 17 6.4 3.5 34.1 93.4 1.9 M M
16000 0.9 33.6 250 32 17 6.5 3.6 33.5 92.4 1.4 M M
15500 1.9 35.4 250 32 16 6.8 3.7 33.0 91.4 0.9 M M
15000 2.8 37.0 245 30 15 6.9 3.8 32.5 90.5 0.4 M M
14500 3.8 38.8 245 28 15 7.3 4.0 32.1 89.7 -0.1 814 4.1
14000 5.0 41.0 245 27 14 8.1 4.4 31.7 89.1 -0.4 765 3.9
13500 6.2 43.2 240 25 13 8.1 4.4 31.5 88.7 -0.7 714 3.6
13000 7.3 45.1 240 24 12 8.2 4.5 31.2 88.2 -1.0 664 3.4
12500 8.5 47.3 235 22 11 8.1 4.5 31.0 87.7 -1.2 614 3.1
12000 9.8 49.6 235 20 10 8.7 4.8 30.8 87.4 -1.5 562 2.9
11500 11.0 51.8 240 19 10 8.8 4.8 30.6 87.1 -1.7 509 2.6
11000 12.2 54.0 240 18 9 7.7 4.2 30.4 86.6 -1.9 458 2.3
10500 13.4 56.1 245 18 9 8.5 4.7 30.0 86.1 -2.2 409 2.1
10250 14.1 57.4 245 17 9 10.0 5.5 30.0 86.0 -2.3 381 1.9
10000 14.8 58.6 245 17 9 9.1 5.0 30.0 86.0 -2.3 353 1.8
9750 15.4 59.7 245 17 9 8.3 4.6 29.9 85.8 -2.4 327 1.7
9500 16.0 60.8 250 17 9 8.8 4.8 29.8 85.7 -2.5 300 1.5
9250 16.6 61.9 250 17 9 7.9 4.3 29.7 85.5 -2.6 274 1.4
9000 17.2 63.0 255 17 9 7.2 3.9 29.5 85.2 -2.9 251 1.3
8750 17.7 63.9 255 16 8 7.4 4.1 29.3 84.8 -3.1 228 1.2
8500 18.2 64.8 260 16 8 7.5 4.1 29.2 84.5 -3.3 204 1.0
8250 18.8 65.8 260 15 8 6.8 3.7 29.0 84.2 -3.5 181 0.9
8000 19.2 66.6 265 13 7 6.1 3.4 28.7 83.7 -3.7 160 0.8
7750 19.7 67.5 265 12 6 6.5 3.6 28.5 83.2 -4.0 138 0.7
7500 20.2 68.4 270 11 6 6.4 3.5 28.2 82.8 -4.3 117 0.6
7250 20.6 69.1 275 10 5 5.6 3.0 27.9 82.3 -4.6 96 0.5
7000 21.0 69.8 280 9 5 4.6 2.5 27.6 81.6 -4.9 78 0.4
6750 21.3 70.3 280 8 4 4.7 2.6 27.2 80.9 -5.3 60 0.3
6500 21.6 70.9 285 8 4 3.1 1.7 26.8 80.2 -5.8 44 0.2
6250 21.7 71.1 280 7 3 -0.1 -0.1 26.1 79.0 -6.4 34 0.2
6000 21.6 70.9 275 5 3 -1.3 -0.7 25.3 77.6 -7.3 29 0.1
5750 21.5 70.7 265 4 2 -0.8 -0.4 24.5 76.1 -8.1 25 0.1
5500 21.4 70.5 250 4 2 -3.6 -2.0 23.6 74.6 -9.0 22 0.1
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/14/2026 at 0900 MDT | 09/14/2026 at 1200 MDT
|
CAPE... +91.6 LI... +0.5 | CAPE... +208.1 LI... -0.9
CINH... -70.8 K Index... +26.1 | CINH... -28.4 K Index... +29.7
|
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 -64.9 -84.8 245 42 22 2.4 1.3 | -64.6 -84.3 240 48 24 2.6 1.4
45000 -59.8 -75.6 250 62 32 5.5 3.0 | -59.7 -75.5 245 66 34 5.0 2.7
40000 -51.5 -60.7 245 67 35 5.9 3.3 | -52.0 -61.6 245 73 38 6.2 3.4
38000 -47.9 -54.2 240 65 34 6.0 3.3 | -48.3 -54.9 240 70 36 6.2 3.4
36000 -44.3 -47.7 235 64 33 5.9 3.2 | -44.6 -48.3 240 67 35 6.1 3.4
34000 -39.2 -38.6 235 58 30 7.8 4.3 | -39.4 -38.9 235 62 32 8.1 4.4
32000 -34.5 -30.1 235 51 26 7.7 4.2 | -34.5 -30.1 235 57 29 7.9 4.4
30000 -30.0 -22.0 235 46 24 7.5 4.1 | -30.0 -22.0 235 52 27 7.5 4.1
29000 -27.8 -18.0 235 43 22 7.5 4.1 | -27.7 -17.9 235 50 26 7.5 4.1
28000 -25.5 -13.9 235 41 21 7.6 4.2 | -25.5 -13.9 230 47 24 7.6 4.2
27000 -23.2 -9.8 235 39 20 7.7 4.2 | -23.2 -9.8 235 45 23 7.6 4.2
26000 -20.9 -5.6 235 38 19 7.7 4.2 | -20.9 -5.6 235 43 22 7.6 4.2
25000 -18.6 -1.5 235 36 19 7.8 4.3 | -18.7 -1.7 235 41 21 7.6 4.2
24000 -16.4 2.5 240 35 18 7.5 4.1 | -16.5 2.3 240 39 20 7.5 4.1
23000 -14.2 6.4 240 33 17 7.5 4.1 | -14.2 6.4 240 39 20 7.5 4.1
22000 -12.0 10.4 240 32 16 7.5 4.1 | -12.0 10.4 245 38 20 7.6 4.1
21000 -9.9 14.2 240 31 16 7.3 4.0 | -10.1 13.8 245 38 19 6.0 3.3
20000 -7.8 18.0 245 31 16 7.3 4.0 | -8.4 16.9 250 37 19 6.1 3.3
19500 -6.2 20.8 250 31 16 7.3 4.0 | -7.1 19.2 250 37 19 6.1 3.3
19000 -5.2 22.6 250 32 16 6.7 3.7 | -6.2 20.8 255 36 18 5.8 3.2
18500 -4.2 24.4 250 32 16 6.8 3.7 | -5.4 22.3 255 34 18 5.9 3.2
18000 -3.2 26.2 255 32 17 6.6 3.6 | -4.6 23.7 255 33 17 6.6 3.6
17500 -2.3 27.9 255 32 17 6.4 3.5 | -3.6 25.5 255 31 16 7.1 3.9
17000 -1.3 29.7 255 32 17 6.4 3.5 | -2.6 27.3 255 29 15 7.2 3.9
16500 -0.4 31.3 255 32 16 6.0 3.3 | -1.7 28.9 255 27 14 6.5 3.6
16000 0.4 32.7 255 31 16 6.1 3.3 | -0.7 30.7 255 25 13 6.6 3.6
15500 1.3 34.3 255 29 15 6.5 3.6 | 0.2 32.4 255 23 12 6.6 3.6
15000 2.3 36.1 255 28 14 6.6 3.6 | 1.2 34.2 255 21 11 6.7 3.7
14500 3.2 37.8 255 26 13 6.9 3.8 | 2.2 36.0 255 19 10 7.2 4.0
14000 4.3 39.7 255 24 13 7.2 4.0 | 3.3 37.9 250 17 9 7.9 4.3
13500 5.3 41.5 255 23 12 7.3 4.0 | 4.5 40.1 250 16 8 8.1 4.4
13000 6.4 43.5 255 22 11 7.9 4.3 | 5.7 42.3 245 15 8 8.9 4.9
12500 7.6 45.7 255 20 11 7.9 4.3 | 7.0 44.6 245 15 8 8.9 4.9
12000 8.7 47.7 255 20 10 7.4 4.0 | 8.3 46.9 250 15 8 8.2 4.5
11500 9.8 49.6 265 20 10 7.5 4.1 | 9.5 49.1 260 17 9 8.4 4.6
11000 10.8 51.4 265 20 10 6.2 3.4 | 10.6 51.1 265 16 8 6.5 3.6
10500 11.7 53.1 270 21 11 7.9 4.3 | 11.5 52.7 260 14 7 9.4 5.2
10250 12.4 54.3 270 21 11 10.2 5.6 | 12.3 54.1 260 13 7 11.0 6.0
10000 13.0 55.4 270 21 11 8.3 4.6 | 13.0 55.4 260 12 6 8.3 4.5
9750 13.6 56.5 270 21 11 7.2 4.0 | 13.6 56.5 260 11 6 9.0 4.9
9500 14.1 57.4 270 21 11 7.9 4.3 | 14.3 57.7 260 10 5 8.8 4.8
9250 14.7 58.5 265 21 11 6.4 3.5 | 14.9 58.8 260 10 5 8.2 4.5
9000 15.1 59.2 265 19 10 7.0 3.9 | 15.5 59.9 260 9 5 9.2 5.0
8750 15.7 60.3 265 18 9 8.9 4.9 | 16.3 61.3 260 9 5 10.4 5.7
8500 16.3 61.3 265 17 9 8.5 4.7 | 17.0 62.6 260 9 4 10.1 5.5
8250 16.9 62.4 265 16 8 8.1 4.4 | 17.8 64.0 260 9 4 9.1 5.0
8000 17.5 63.5 265 15 8 8.0 4.4 | 18.4 65.1 260 8 4 9.2 5.1
7750 18.1 64.6 260 14 7 8.5 4.7 | 19.2 66.6 265 8 4 10.4 5.7
7500 18.8 65.8 260 13 7 8.2 4.5 | 19.9 67.8 265 8 4 9.8 5.4
7250 19.3 66.7 260 12 6 6.8 3.7 | 20.6 69.1 265 7 4 8.4 4.6
7000 19.8 67.6 260 11 5 6.3 3.5 | 21.2 70.2 265 7 4 8.5 4.7
6750 20.3 68.5 255 9 5 7.5 4.1 | 21.9 71.4 270 7 4 10.8 5.9
6500 20.9 69.6 255 8 4 7.8 4.3 | 22.8 73.0 270 6 3 11.0 6.1
6250 21.4 70.5 250 7 4 7.6 4.2 | 23.5 74.3 270 6 3 10.2 5.6
6000 22.0 71.6 245 6 3 7.6 4.1 | 24.3 75.7 270 6 3 10.0 5.5
5750 22.5 72.5 240 6 3 7.3 4.0 | 25.1 77.2 275 6 3 10.7 5.9
5500 23.1 73.6 235 5 3 10.4 5.7 | 26.0 78.8 275 6 3 17.8 9.8
09/14/2026 at 1500 MDT | 09/14/2026 at 1800 MDT
|
CAPE... +383.8 LI... -2.2 | CAPE... +245.1 LI... -1.8
CINH... -10.9 K Index... +31.9 | CINH... -68.4 K Index... +28.0
|
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 -64.2 -83.6 245 52 27 2.1 1.2 | -63.9 -83.0 250 52 27 2.6 1.4
45000 -59.7 -75.5 245 69 35 4.9 2.7 | -59.3 -74.7 250 69 35 4.2 2.3
40000 -52.1 -61.8 240 76 39 6.9 3.8 | -52.5 -62.5 240 78 40 7.4 4.1
38000 -47.9 -54.2 240 73 38 6.9 3.8 | -48.0 -54.4 240 76 39 7.5 4.1
36000 -43.3 -45.9 240 71 36 7.0 3.9 | -42.9 -45.2 240 72 37 7.5 4.1
34000 -38.7 -37.7 240 64 33 7.7 4.2 | -38.4 -37.1 240 65 34 7.5 4.1
32000 -34.1 -29.4 240 58 30 7.5 4.1 | -33.8 -28.8 245 58 30 7.4 4.1
30000 -29.5 -21.1 240 54 28 7.8 4.3 | -29.4 -20.9 245 52 27 7.4 4.0
29000 -27.1 -16.8 240 53 27 7.8 4.3 | -27.2 -17.0 250 50 26 7.4 4.1
28000 -24.8 -12.6 240 51 26 7.5 4.1 | -25.0 -13.0 250 48 25 7.2 3.9
27000 -22.7 -8.9 245 49 25 7.3 4.0 | -23.0 -9.4 250 46 24 7.0 3.8
26000 -20.5 -4.9 245 47 24 7.3 4.0 | -20.9 -5.6 255 44 23 7.0 3.8
25000 -18.3 -0.9 245 45 23 7.3 4.0 | -18.8 -1.8 255 43 22 7.0 3.9
24000 -16.2 2.8 250 43 22 7.1 3.9 | -16.7 1.9 255 41 21 7.1 3.9
23000 -14.1 6.6 250 42 22 7.1 3.9 | -14.6 5.7 255 40 21 7.1 3.9
22000 -12.1 10.2 250 41 21 7.3 4.0 | -12.5 9.5 255 39 20 7.2 4.0
21000 -10.3 13.5 250 39 20 5.8 3.2 | -10.7 12.7 255 36 19 6.1 3.4
20000 -8.2 17.2 250 35 18 5.9 3.2 | -8.5 16.7 255 33 17 6.2 3.4
19500 -7.4 18.7 250 34 17 5.9 3.2 | -7.6 18.3 255 32 16 6.2 3.4
19000 -6.5 20.3 255 32 17 6.9 3.8 | -6.6 20.1 255 30 16 7.3 4.0
18500 -5.5 22.1 255 31 16 6.9 3.8 | -5.6 21.9 255 29 15 7.3 4.0
18000 -4.6 23.7 255 29 15 6.7 3.7 | -4.5 23.9 255 28 14 7.5 4.1
17500 -3.6 25.5 260 28 15 6.5 3.6 | -3.4 25.9 255 26 14 7.7 4.2
17000 -2.7 27.1 260 27 14 6.5 3.6 | -2.3 27.9 260 25 13 7.8 4.3
16500 -1.7 28.9 260 26 13 7.1 3.9 | -1.1 30.0 260 24 12 8.3 4.5
16000 -0.7 30.7 260 23 12 7.0 3.8 | 0.1 32.2 260 23 12 8.2 4.5
15500 0.4 32.7 260 20 11 7.8 4.3 | 1.3 34.3 260 22 11 8.4 4.6
15000 1.5 34.7 255 17 9 8.6 4.4 | 2.5 36.5 260 20 10 8.5 4.7
14500 2.7 36.9 245 14 7 8.1 4.4 | 3.8 38.8 260 19 10 8.5 4.7
14000 3.9 39.0 240 13 7 8.2 4.5 | 5.0 41.0 260 18 9 8.6 4.7
13500 5.1 41.2 235 11 6 8.3 4.6 | 6.3 43.3 260 17 9 8.6 4.7
13000 6.3 43.3 230 10 5 9.0 5.0 | 7.6 45.7 260 16 8 8.8 4.8
12500 7.7 45.9 225 9 5 9.0 4.9 | 8.9 48.0 260 15 8 8.8 4.8
12000 9.0 48.2 220 8 4 9.3 5.1 | 10.2 50.4 260 14 7 8.8 4.8
11500 10.4 50.7 215 7 4 9.5 5.2 | 11.5 52.7 260 13 7 9.0 4.9
11000 11.7 53.1 210 6 3 8.2 4.5 | 12.7 54.9 255 12 6 7.7 4.2
10500 12.9 55.2 210 5 3 9.6 5.3 | 13.9 57.0 255 11 6 9.4 5.2
10250 13.7 56.7 210 5 2 10.9 6.0 | 14.7 58.5 255 11 6 10.7 5.9
10000 14.4 57.9 205 4 2 9.8 5.4 | 15.4 59.7 255 10 5 8.8 4.8
9750 15.2 59.4 205 4 2 9.7 5.3 | 16.0 60.8 255 10 5 8.5 4.7
9500 15.9 60.6 200 4 2 10.0 5.5 | 16.6 61.9 255 9 5 8.8 4.8
9250 16.6 61.9 200 4 2 8.9 4.9 | 17.3 63.1 255 9 5 8.0 4.4
9000 17.2 63.0 195 4 2 9.0 4.9 | 17.8 64.0 255 8 4 8.0 4.4
8750 18.0 64.4 195 4 2 10.2 5.6 | 18.5 65.3 255 8 4 8.7 4.8
8500 18.7 65.7 190 3 2 9.9 5.4 | 19.1 66.4 255 8 4 8.8 4.8
8250 19.5 67.1 190 3 2 9.9 5.4 | 19.7 67.5 255 7 4 7.7 4.2
8000 20.2 68.4 185 3 2 9.9 5.4 | 20.2 68.4 255 7 3 7.4 4.0
7750 20.9 69.6 185 3 2 9.9 5.5 | 20.8 69.4 255 6 3 8.3 4.5
7500 21.7 71.1 175 3 1 9.9 5.4 | 21.4 70.5 255 6 3 8.0 4.4
7250 22.4 72.3 170 3 1 9.8 5.4 | 22.0 71.6 255 6 3 7.1 3.9
7000 23.1 73.6 170 2 1 9.6 5.3 | 22.4 72.3 250 5 3 6.8 3.7
6750 23.8 74.8 160 2 1 9.0 5.0 | 22.9 73.2 245 5 3 7.6 4.2
6500 24.5 76.1 150 2 1 9.3 5.1 | 23.5 74.3 240 5 2 8.2 4.5
6250 25.2 77.4 140 2 1 10.1 5.5 | 24.1 75.4 235 4 2 8.9 4.9
6000 26.0 78.8 135 2 1 10.7 5.8 | 24.8 76.6 230 4 2 9.2 5.1
5750 26.7 80.1 125 2 1 8.6 4.7 | 25.4 77.7 225 4 2 9.3 5.1
5500 27.4 81.3 115 2 1 11.6 6.4 | 26.2 79.2 220 4 2 11.2 6.1
________________________________________________________________________________
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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