Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
124
UXUS97 KBOU 131339
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0738 MDT Sunday, September 13, 2026
This forecast is for Sunday, September 13, 2026:
If the trigger temperature of 84.1 F/29.0 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1102 ft/min (5.6 m/s)
Maximum height of thermals.................. 17394 ft MSL (12035 ft AGL)
Forecast maximum temperature................... 93.0 F/34.3 C
Time of trigger temperature.................... 1130 MDT
Time of overdevelopment........................ 1800 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 13716 ft MSL (8357 ft AGL)
Thermal soaring outlook for Monday 09/14....... Excellent
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... Decreasing
Height of stable layer (12-18K ft MSL)......... 8000 ft MSL (2641 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 46676 ft MSL (41317 ft AGL)
Wave soaring outlook for Monday 09/14.......... Poor
Remarks...
Sunrise/Sunset.................... 06:39:05 / 19:11:33 MDT
Total possible sunshine........... 12 hr 32 min 29 sec (752 min 29 sec)
Altitude of sun at 12:55:19 MDT... 53.78 degrees
Upper air data from numerical model forecast valid on 09/13/2026 at 0600 MDT
Freezing level.................. 16222 ft MSL (10863 ft AGL)
Convective condensation level... 17420 ft MSL (12061 ft AGL)
Lifted condensation level....... 17568 ft MSL (12210 ft AGL)
Lifted index.................... -1.3
K index......................... +20.4
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 -66.7 -88.1 280 47 24 1.6 0.9 M M M M M
45000 -61.7 -79.1 275 61 31 6.6 3.6 M M M M M
40000 -51.7 -61.1 275 56 29 7.3 4.0 M M M M M
38000 -47.3 -53.1 270 54 28 7.3 4.0 M M M M M
36000 -42.9 -45.2 265 52 27 7.4 4.1 M M M M M
34000 -38.4 -37.1 270 47 24 6.6 3.6 M M M M M
32000 -34.4 -29.9 270 43 22 7.1 3.9 M M M M M
30000 -30.0 -22.0 275 39 20 7.5 4.1 45.5 113.8 8.8 M M
29000 -27.7 -17.9 275 38 19 7.5 4.1 44.6 112.4 8.3 M M
28000 -25.5 -13.9 275 36 18 7.8 4.3 43.9 111.0 7.8 M M
27000 -23.1 -9.6 275 34 17 7.8 4.3 43.0 109.5 7.2 M M
26000 -20.8 -5.4 275 32 17 7.8 4.3 42.3 108.2 6.7 M M
25000 -18.4 -1.1 275 30 16 7.8 4.3 41.7 107.1 6.3 M M
24000 -16.1 3.0 270 28 14 7.9 4.3 41.0 105.7 5.7 M M
23000 -13.7 7.3 270 25 13 7.9 4.3 40.3 104.5 5.2 M M
22000 -11.4 11.5 265 22 11 7.5 4.1 39.7 103.5 4.8 M M
21000 -9.4 15.1 265 19 10 6.5 3.6 38.5 101.3 3.8 M M
20000 -7.4 18.7 265 17 9 6.6 3.6 37.4 99.3 2.9 M M
19500 -6.0 21.2 270 16 8 6.4 3.5 36.6 97.9 2.2 M M
19000 -5.1 22.8 265 15 8 6.2 3.4 36.0 96.8 1.7 M M
18500 -4.2 24.4 265 15 7 6.2 3.4 35.4 95.7 1.1 M M
18000 -3.3 26.1 260 14 7 6.5 3.6 34.8 94.6 0.5 M M
17500 -2.4 27.7 260 14 7 6.6 3.6 34.2 93.6 0.0 M M
17000 -1.4 29.5 255 13 7 6.8 3.7 33.7 92.7 -0.5 1060 5.4
16500 -0.4 31.3 255 13 7 7.1 3.9 33.3 91.9 -1.0 1016 5.2
16000 0.6 33.1 255 13 6 7.1 3.9 32.8 91.1 -1.4 971 4.9
15500 1.6 34.9 255 12 6 7.6 4.2 32.4 90.4 -1.9 925 4.7
15000 2.7 36.9 255 11 6 7.6 4.2 32.1 89.7 -2.3 878 4.5
14500 3.8 38.8 260 11 5 8.3 4.6 31.7 89.1 -2.6 830 4.2
14000 5.0 41.0 260 10 5 8.5 4.7 31.5 88.8 -2.9 778 4.0
13500 6.3 43.3 265 10 5 8.5 4.7 31.4 88.4 -3.1 727 3.7
13000 7.5 45.5 270 10 5 8.5 4.6 31.1 88.0 -3.4 675 3.4
12500 8.7 47.7 275 10 5 8.6 4.7 30.9 87.7 -3.6 624 3.2
12000 10.0 50.0 280 11 6 9.0 4.9 30.8 87.4 -3.8 571 2.9
11500 11.3 52.3 280 11 6 8.9 4.9 30.7 87.2 -4.0 517 2.6
11000 12.6 54.7 285 11 6 8.6 4.7 30.5 86.9 -4.2 463 2.4
10500 13.9 57.0 285 11 6 5.0 2.7 30.4 86.7 -4.3 409 2.1
10250 14.1 57.4 285 11 6 6.1 3.3 29.9 85.8 -4.8 395 2.0
10000 14.9 58.8 285 11 6 11.9 6.5 29.9 85.9 -4.8 363 1.8
9750 15.7 60.3 285 11 5 10.5 5.8 30.0 86.0 -4.7 332 1.7
9500 16.5 61.7 285 10 5 10.1 5.5 30.1 86.2 -4.7 301 1.5
9250 17.2 63.0 285 10 5 7.7 4.2 30.0 86.1 -4.7 274 1.4
9000 17.7 63.9 285 9 5 8.2 4.5 29.9 85.7 -4.9 249 1.3
8750 18.4 65.1 285 9 5 9.7 5.3 29.8 85.7 -5.0 221 1.1
8500 19.1 66.4 280 9 5 8.5 4.7 29.8 85.6 -5.0 193 1.0
8250 19.7 67.5 280 9 5 6.7 3.7 29.6 85.3 -5.2 169 0.9
8000 20.2 68.4 285 8 4 5.7 3.1 29.3 84.8 -5.5 147 0.7
7750 20.6 69.1 280 8 4 6.4 3.5 29.0 84.3 -5.8 127 0.6
7500 21.0 69.8 280 8 4 3.5 1.9 28.7 83.7 -6.1 107 0.5
7250 21.1 70.0 280 8 4 -0.2 -0.1 28.1 82.5 -6.8 98 0.5
7000 21.0 69.8 275 7 4 -0.5 -0.3 27.3 81.1 -7.6 92 0.5
6750 20.9 69.6 275 7 3 -1.6 -0.9 26.5 79.7 -8.4 88 0.4
6500 20.6 69.1 265 7 3 -5.5 -3.0 25.5 77.9 -9.5 89 0.4
6250 20.0 68.0 260 6 3 -8.3 -4.5 24.2 75.5 -10.8 99 0.5
6000 19.4 66.9 255 6 3 -6.1 -3.4 22.9 73.2 -12.2 110 0.6
5750 18.8 65.8 250 5 3 -10.5 -5.8 21.6 70.9 -13.5 120 0.6
5500 17.5 63.5 235 4 2 -25.5 -14.0 19.6 67.2 -15.7 154 0.8
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/13/2026 at 0900 MDT | 09/13/2026 at 1200 MDT
|
CAPE... 0.0 LI... +1.7 | CAPE... +102.8 LI... +1.4
CINH... -0.2 K Index... +21.4 | CINH... -51.2 K Index... +19.7
|
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 -66.6 -87.9 275 43 22 2.0 1.1 | -66.0 -86.8 270 40 20 2.3 1.3
45000 -61.3 -78.3 275 58 30 6.6 3.6 | -60.7 -77.3 270 54 28 6.0 3.3
40000 -51.3 -60.3 270 55 28 6.8 3.7 | -51.5 -60.7 265 57 29 6.7 3.7
38000 -47.2 -53.0 270 53 27 6.8 3.7 | -47.5 -53.5 265 54 28 6.7 3.7
36000 -42.6 -44.7 265 51 26 6.6 3.6 | -43.0 -45.4 260 51 26 6.7 3.7
34000 -38.9 -38.0 265 47 24 6.3 3.5 | -39.0 -38.2 260 47 24 6.7 3.7
32000 -35.1 -31.2 270 43 22 6.9 3.8 | -35.0 -31.0 265 43 22 7.2 4.0
30000 -30.3 -22.5 270 38 19 8.1 4.4 | -30.1 -22.2 260 37 19 8.2 4.5
29000 -27.9 -18.2 270 35 18 8.1 4.4 | -27.7 -17.9 260 34 17 8.2 4.5
28000 -25.5 -13.9 270 32 17 7.8 4.3 | -25.2 -13.4 260 31 16 7.8 4.3
27000 -23.2 -9.8 270 31 16 7.8 4.3 | -22.9 -9.2 255 29 15 7.8 4.3
26000 -20.9 -5.6 270 29 15 7.8 4.3 | -20.6 -5.1 255 27 14 7.8 4.3
25000 -18.5 -1.3 265 28 14 7.9 4.3 | -18.2 -0.8 250 26 13 7.8 4.3
24000 -16.1 3.0 265 26 13 8.1 4.4 | -15.8 3.6 245 24 12 8.1 4.4
23000 -13.7 7.3 260 24 12 8.1 4.4 | -13.4 7.9 240 23 12 8.1 4.4
22000 -11.2 11.8 255 22 11 7.7 4.2 | -11.0 12.2 235 22 11 7.7 4.2
21000 -9.2 15.4 255 21 11 6.9 3.8 | -8.9 16.0 240 20 10 6.9 3.8
20000 -6.6 20.1 255 19 10 6.9 3.8 | -6.3 20.7 245 18 9 6.8 3.8
19500 -5.6 21.9 255 18 9 6.4 3.5 | -5.3 22.5 245 17 9 6.7 3.7
19000 -4.7 23.5 250 17 9 5.8 3.2 | -4.4 24.1 245 17 9 6.5 3.6
18500 -3.9 25.0 250 16 8 5.8 3.2 | -3.4 25.9 245 17 9 6.6 3.6
18000 -3.1 26.4 245 15 8 6.3 3.4 | -2.5 27.5 245 16 8 5.9 3.2
17500 -2.2 28.0 240 15 8 6.3 3.5 | -1.7 28.9 245 16 8 5.9 3.3
17000 -1.3 29.7 240 14 7 6.5 3.5 | -0.8 30.6 245 16 8 6.2 3.4
16500 -0.4 31.3 235 14 7 6.6 3.6 | 0.1 32.2 245 15 8 6.6 3.6
16000 0.6 33.1 230 13 7 6.6 3.6 | 1.0 33.8 245 15 8 6.6 3.6
15500 1.6 34.9 230 12 6 7.5 4.1 | 2.0 35.6 245 14 7 7.3 4.0
15000 2.6 36.7 225 12 6 7.5 4.1 | 3.0 37.4 240 13 7 7.3 4.0
14500 3.7 38.7 225 11 6 7.9 4.3 | 4.1 39.4 240 13 7 7.9 4.3
14000 4.9 40.8 220 10 5 8.0 4.4 | 5.2 41.4 235 12 6 8.1 4.4
13500 6.1 43.0 220 9 5 8.3 4.6 | 6.4 43.5 230 11 6 8.3 4.6
13000 7.3 45.1 220 8 4 8.6 4.7 | 7.6 45.7 225 11 6 8.6 4.7
12500 8.5 47.3 225 7 4 8.7 4.8 | 8.9 48.0 220 10 5 8.6 4.7
12000 9.8 49.6 225 7 3 8.9 4.9 | 10.2 50.4 215 10 5 8.7 4.8
11500 11.1 52.0 235 6 3 8.9 4.9 | 11.5 52.7 210 9 5 8.7 4.8
11000 12.4 54.3 245 6 3 8.5 4.7 | 12.8 55.0 210 8 4 8.7 4.8
10500 13.7 56.7 255 6 3 5.5 3.0 | 14.1 57.4 205 7 4 5.5 3.0
10250 14.0 57.2 255 6 3 6.5 3.5 | 14.4 57.9 205 7 3 6.4 3.5
10000 14.7 58.5 260 6 3 11.2 6.1 | 15.1 59.2 200 6 3 11.3 6.2
9750 15.5 59.9 260 6 3 10.2 5.6 | 15.9 60.6 195 6 3 10.3 5.6
9500 16.2 61.2 265 6 3 9.5 5.2 | 16.6 61.9 195 5 3 9.5 5.2
9250 16.9 62.4 265 6 3 7.7 4.2 | 17.2 63.0 190 5 3 8.0 4.4
9000 17.4 63.3 265 7 3 8.6 4.7 | 17.8 64.0 185 5 2 9.5 5.2
8750 18.1 64.6 265 7 3 9.7 5.3 | 18.6 65.5 185 5 2 10.7 5.9
8500 18.8 65.8 270 7 3 8.8 4.8 | 19.4 66.9 180 4 2 9.8 5.4
8250 19.4 66.9 270 7 4 7.6 4.2 | 20.0 68.0 175 4 2 8.1 4.5
8000 20.0 68.0 270 7 4 7.4 4.0 | 20.6 69.1 180 4 2 9.1 5.0
7750 20.6 69.1 270 7 4 8.2 4.5 | 21.4 70.5 175 4 2 10.8 5.9
7500 21.1 70.0 265 7 4 5.9 3.3 | 22.2 72.0 170 4 2 9.6 5.3
7250 21.4 70.5 265 7 4 3.4 1.9 | 22.8 73.0 170 3 2 8.3 4.5
7000 21.7 71.1 260 7 4 3.8 2.1 | 23.5 74.3 170 3 2 9.2 5.0
6750 22.0 71.6 260 7 4 3.8 2.1 | 24.2 75.6 170 3 2 11.8 6.5
6500 22.2 72.0 250 6 3 0.6 0.4 | 25.1 77.2 165 3 1 11.4 6.2
6250 22.1 71.8 245 6 3 -1.4 -0.8 | 25.9 78.6 165 3 1 10.3 5.7
6000 22.0 71.6 235 6 3 -1.5 -0.8 | 26.7 80.1 165 3 1 9.7 5.3
5750 21.9 71.4 220 6 3 1.2 0.7 | 27.5 81.5 165 2 1 13.0 7.1
5500 22.3 72.1 215 5 3 9.2 5.1 | 28.8 83.8 160 2 1 24.5 13.4
09/13/2026 at 1500 MDT | 09/13/2026 at 1800 MDT
|
CAPE... +128.1 LI... -0.2 | CAPE... +147.4 LI... -0.9
CINH... -23.9 K Index... +26.3 | CINH... -25.3 K Index... +28.2
|
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 -65.8 -86.4 255 40 20 2.5 1.3 | -66.8 -88.2 255 40 20 2.8 1.6
45000 -60.5 -76.9 260 53 27 5.7 3.2 | -60.8 -77.4 250 51 26 6.3 3.5
40000 -51.7 -61.1 260 55 28 6.9 3.8 | -51.3 -60.3 250 51 26 6.8 3.7
38000 -47.0 -52.6 260 52 27 6.9 3.8 | -46.6 -51.9 255 49 25 6.8 3.7
36000 -42.8 -45.0 260 50 26 7.1 3.9 | -42.5 -44.5 255 47 24 7.1 3.9
34000 -38.5 -37.3 260 47 24 7.2 4.0 | -38.1 -36.6 255 43 22 7.4 4.1
32000 -34.1 -29.4 260 43 22 7.7 4.2 | -33.6 -28.5 255 40 21 7.9 4.3
30000 -29.4 -20.9 255 38 20 7.9 4.3 | -28.9 -20.0 250 36 19 7.8 4.3
29000 -27.1 -16.8 255 35 18 7.9 4.3 | -26.6 -15.9 250 35 18 7.8 4.3
28000 -24.7 -12.5 250 33 17 7.7 4.2 | -24.3 -11.7 250 33 17 7.7 4.2
27000 -22.4 -8.3 250 31 16 7.7 4.2 | -22.0 -7.6 250 32 16 7.7 4.2
26000 -20.1 -4.2 245 30 15 7.7 4.2 | -19.7 -3.5 250 30 16 7.7 4.2
25000 -17.8 -0.0 245 28 15 7.6 4.2 | -17.4 0.7 245 29 15 7.5 4.1
24000 -15.7 3.7 240 27 14 7.1 3.9 | -15.6 3.9 245 27 14 5.9 3.2
23000 -13.6 7.5 240 26 13 7.1 3.9 | -13.9 7.0 240 26 13 6.0 3.3
22000 -11.5 11.3 235 25 13 6.9 3.8 | -12.2 10.0 240 24 13 6.3 3.5
21000 -9.2 15.4 240 24 12 6.3 3.5 | -9.7 14.5 235 23 12 7.2 3.9
20000 -7.4 18.7 240 22 12 6.5 3.6 | -7.6 18.3 235 22 12 7.2 4.0
19500 -6.5 20.3 245 22 11 6.7 3.7 | -6.6 20.1 230 22 11 7.4 4.0
19000 -5.5 22.1 245 21 11 7.2 4.0 | -5.5 22.1 230 21 11 7.7 4.2
18500 -4.5 23.9 245 20 10 7.2 4.0 | -4.4 24.1 230 20 11 7.7 4.2
18000 -3.4 25.9 245 19 10 7.9 4.4 | -3.2 26.2 230 20 10 8.1 4.5
17500 -2.3 27.9 245 18 9 8.1 4.4 | -2.0 28.4 225 19 10 8.2 4.5
17000 -1.1 30.0 245 18 9 8.3 4.5 | -0.8 30.6 225 18 9 8.3 4.5
16500 0.2 32.4 245 17 9 8.8 4.8 | 0.4 32.7 220 17 9 8.4 4.6
16000 1.5 34.7 245 16 8 8.8 4.8 | 1.7 35.1 215 17 9 8.3 4.6
15500 2.7 36.9 245 15 8 8.5 4.7 | 2.9 37.2 210 16 8 8.9 4.9
15000 4.0 39.2 240 14 7 8.5 4.7 | 4.2 39.6 205 15 8 8.9 4.9
14500 5.3 41.5 235 13 6 8.5 4.7 | 5.6 42.1 200 15 8 9.1 5.0
14000 6.5 43.7 230 11 6 8.5 4.7 | 6.9 44.4 195 14 7 9.1 5.0
13500 7.7 45.9 220 10 5 8.7 4.8 | 8.3 46.9 190 13 7 9.2 5.0
13000 9.1 48.4 215 9 4 9.0 5.0 | 9.6 49.3 190 13 6 9.2 5.1
12500 10.4 50.7 205 8 4 9.1 5.0 | 11.0 51.8 185 12 6 9.2 5.1
12000 11.8 53.2 200 7 4 9.2 5.1 | 12.4 54.3 180 11 6 9.3 5.1
11500 13.2 55.8 190 7 4 9.2 5.0 | 13.8 56.8 175 11 5 9.3 5.1
11000 14.5 58.1 180 7 3 8.3 4.5 | 15.1 59.2 170 10 5 8.3 4.5
10500 15.7 60.3 175 7 3 11.5 6.3 | 16.3 61.3 160 10 5 10.9 6.0
10250 16.7 62.1 170 7 3 12.4 6.8 | 17.2 63.0 160 9 5 11.6 6.4
10000 17.4 63.3 170 7 3 8.7 4.7 | 17.9 64.2 160 9 5 8.6 4.7
9750 18.1 64.6 165 6 3 9.8 5.4 | 18.6 65.5 155 9 5 9.4 5.2
9500 18.8 65.8 165 6 3 9.1 5.0 | 19.3 66.7 150 9 5 9.1 5.0
9250 19.5 67.1 160 6 3 8.8 4.8 | 20.0 68.0 145 9 4 9.1 5.0
9000 20.2 68.4 155 6 3 9.7 5.3 | 20.7 69.3 140 9 4 9.4 5.1
8750 20.9 69.6 155 6 3 10.2 5.6 | 21.4 70.5 135 8 4 9.6 5.3
8500 21.6 70.9 150 6 3 10.0 5.5 | 22.1 71.8 135 8 4 9.5 5.2
8250 22.4 72.3 150 6 3 9.4 5.1 | 22.8 73.0 130 8 4 9.2 5.0
8000 23.1 73.6 145 6 3 9.7 5.3 | 23.5 74.3 120 8 4 9.2 5.1
7750 23.8 74.8 145 6 3 10.6 5.8 | 24.2 75.6 120 7 4 9.7 5.3
7500 24.6 76.3 145 6 3 9.9 5.5 | 24.9 76.8 120 7 4 9.4 5.1
7250 25.3 77.5 140 6 3 8.5 4.6 | 25.6 78.1 120 7 3 8.1 4.5
7000 26.0 78.8 140 6 3 9.0 4.9 | 26.2 79.2 110 7 3 8.1 4.4
6750 26.7 80.1 135 6 3 11.5 6.3 | 26.8 80.2 105 6 3 9.6 5.3
6500 27.6 81.7 135 6 3 11.5 6.3 | 27.5 81.5 105 6 3 9.3 5.1
6250 28.4 83.1 135 6 3 10.5 5.8 | 28.2 82.8 095 5 3 8.0 4.4
6000 29.2 84.6 130 6 3 10.4 5.7 | 28.7 83.7 090 5 3 8.0 4.4
5750 30.0 86.0 130 6 3 10.7 5.9 | 29.3 84.7 080 5 3 7.2 3.9
5500 31.0 87.8 130 5 3 18.1 9.9 | 29.8 85.6 080 4 2 7.1 3.9
________________________________________________________________________________
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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