Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
479
UXUS97 KBOU 281252
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0652 MDT Monday, September 28, 2026
This forecast is for Monday, September 28, 2026:
If the trigger temperature of 76.8 F/24.9 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 85 ft/min (0.4 m/s)
Maximum height of thermals.................. 8309 ft MSL (2946 ft AGL)
Forecast maximum temperature................... 75.0 F/24.3 C
Time of trigger temperature.................... None
Time of overdevelopment........................ 1400 MDT
Middle/high clouds during soaring window....... Overcast thin high
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 6549 ft MSL (1186 ft AGL)
Thermal soaring outlook for Tuesday 09/29...... Poor
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... No change
Height of stable layer (12-18K ft MSL)......... 6200 ft MSL (837 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 30400 ft MSL (25037 ft AGL)
Wave soaring outlook for Tuesday 09/29......... Poor
Remarks...
Sunrise/Sunset.................... 06:53:12 / 18:46:53 MDT
Total possible sunshine........... 11 hr 53 min 41 sec (713 min 41 sec)
Altitude of sun at 12:50:03 MDT... 47.92 degrees
Upper air data from numerical model forecast valid on 09/28/2026 at 0600 MDT
Freezing level.................. 14563 ft MSL (9200 ft AGL)
Convective condensation level... 14961 ft MSL (9598 ft AGL)
Lifted condensation level....... 13506 ft MSL (8143 ft AGL)
Lifted index.................... +1.2
K index......................... +23.1
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 -79.2 270 44 23 2.4 1.3 M M M M M
45000 -57.2 -71.0 270 61 31 4.5 2.4 M M M M M
40000 -50.7 -59.3 270 72 37 2.6 1.4 M M M M M
38000 -49.0 -56.2 270 68 35 2.8 1.5 M M M M M
36000 -47.4 -53.3 270 63 32 2.9 1.6 M M M M M
34000 -43.1 -45.6 265 58 30 9.1 5.0 M M M M M
32000 -37.6 -35.7 255 54 28 9.2 5.0 M M M M M
30000 -32.0 -25.6 250 49 25 8.1 4.4 43.8 110.9 15.1 M M
29000 -29.6 -21.3 250 47 24 8.1 4.5 43.2 109.8 14.8 M M
28000 -27.2 -17.0 250 44 23 7.9 4.4 42.7 108.9 14.5 M M
27000 -25.1 -13.2 245 40 21 6.7 3.7 41.5 106.7 13.8 M M
26000 -23.2 -9.8 245 36 19 6.7 3.7 40.3 104.6 12.9 M M
25000 -21.2 -6.2 240 32 16 6.8 3.7 39.3 102.8 12.2 M M
24000 -19.3 -2.7 235 29 15 6.1 3.3 38.0 100.4 11.3 M M
23000 -17.6 0.3 235 26 13 6.1 3.3 36.6 97.9 10.2 M M
22000 -15.8 3.6 230 23 12 6.1 3.4 35.4 95.7 9.3 M M
21000 -14.2 6.4 225 20 10 5.0 2.7 33.8 92.8 8.0 M M
20000 -12.7 9.1 215 19 10 5.0 2.7 32.1 89.8 6.6 M M
19500 -12.0 10.4 210 18 9 5.1 2.8 31.3 88.3 6.0 M M
19000 -11.2 11.8 205 18 9 6.3 3.4 30.5 86.9 5.4 M M
18500 -10.1 13.8 205 18 9 7.9 4.3 30.2 86.3 5.1 M M
18000 -8.3 17.1 210 17 9 7.9 4.3 29.7 85.5 4.7 M M
17500 -7.1 19.2 210 17 9 7.9 4.3 29.4 84.9 4.4 M M
17000 -6.0 21.2 215 17 9 7.8 4.3 29.1 84.3 4.1 M M
16500 -4.8 23.4 215 18 9 8.7 4.8 28.8 83.9 3.9 M M
16000 -3.5 25.7 220 18 9 8.6 4.7 28.6 83.5 3.7 M M
15500 -2.2 28.0 220 18 9 8.7 4.8 28.5 83.2 3.6 M M
15000 -1.0 30.2 220 18 9 8.7 4.8 28.3 82.9 3.4 M M
14500 0.3 32.5 220 18 9 8.6 4.7 28.1 82.6 3.3 M M
14000 1.5 34.7 220 18 9 8.5 4.7 27.9 82.2 3.1 M M
13500 2.8 37.0 220 18 9 8.6 4.7 27.7 81.9 2.9 M M
13000 4.1 39.4 220 18 9 8.9 4.9 27.5 81.6 2.7 M M
12500 5.4 41.7 220 18 9 8.9 4.9 27.4 81.3 2.5 M M
12000 6.6 43.9 220 18 9 8.8 4.8 27.3 81.1 2.4 M M
11500 7.9 46.2 220 17 9 9.0 4.9 27.1 80.8 2.2 M M
11000 9.1 48.4 220 17 9 6.9 3.8 26.8 80.3 1.9 M M
10500 10.1 50.2 225 17 9 6.4 3.5 26.4 79.6 1.5 M M
10250 10.6 51.1 225 16 8 10.1 5.5 26.2 79.2 1.3 M M
10000 11.5 52.7 225 16 8 10.4 5.7 26.4 79.5 1.4 M M
9750 12.0 53.6 225 16 8 6.8 3.7 26.2 79.2 1.3 M M
9500 12.6 54.7 225 16 8 8.2 4.5 26.1 78.9 1.1 M M
9250 13.1 55.6 225 15 8 6.0 3.3 25.9 78.6 0.9 M M
9000 13.5 56.3 230 14 7 6.0 3.3 25.5 78.0 0.6 M M
8750 14.0 57.2 230 14 7 7.9 4.3 25.4 77.6 0.4 M M
8500 14.6 58.3 230 14 7 7.5 4.1 25.2 77.3 0.2 M M
8250 15.1 59.2 230 13 7 5.9 3.2 25.0 77.0 -0.0 185 0.9
8000 15.5 59.9 230 12 6 4.9 2.7 24.6 76.3 -0.4 167 0.8
7750 15.9 60.6 230 12 6 6.0 3.3 24.3 75.7 -0.7 148 0.8
7500 16.3 61.3 230 12 6 5.5 3.0 24.0 75.2 -1.0 127 0.6
7250 16.6 61.9 230 12 6 4.0 2.2 23.6 74.5 -1.4 110 0.6
7000 16.9 62.4 225 12 6 3.2 1.7 23.1 73.6 -1.9 95 0.5
6750 17.1 62.8 225 12 6 3.7 2.0 22.7 72.8 -2.4 81 0.4
6500 17.3 63.1 215 13 7 2.1 1.1 22.2 71.9 -2.9 67 0.3
6250 17.3 63.1 210 13 7 0.1 0.0 21.5 70.7 -3.6 59 0.3
6000 17.3 63.1 200 13 7 0.5 0.3 20.8 69.4 -4.4 52 0.3
5750 17.3 63.1 195 13 7 -1.0 -0.6 20.0 68.1 -5.1 46 0.2
5500 17.0 62.6 190 10 5 -6.3 -3.5 19.1 66.3 -6.2 48 0.2
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/28/2026 at 0900 MDT | 09/28/2026 at 1200 MDT
|
CAPE... +22.7 LI... +0.6 | CAPE... +0.9 LI... +0.9
CINH... -101.3 K Index... +24.8 | CINH... -1.7 K Index... +25.5
|
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 -79.2 265 43 22 2.8 1.6 | -61.6 -78.9 260 39 20 2.9 1.6
45000 -56.9 -70.4 265 60 31 3.9 2.1 | -56.7 -70.1 265 55 28 3.6 2.0
40000 -51.1 -60.0 270 65 33 3.4 1.8 | -51.4 -60.5 265 66 34 3.6 2.0
38000 -49.1 -56.4 265 65 34 3.4 1.9 | -49.2 -56.6 260 65 33 3.6 2.0
36000 -47.0 -52.6 265 66 34 3.5 1.9 | -47.1 -52.8 255 65 33 3.7 2.0
34000 -42.7 -44.9 260 62 32 8.8 4.8 | -42.6 -44.7 250 60 31 9.1 5.0
32000 -37.4 -35.3 260 56 29 8.9 4.9 | -37.2 -35.0 250 54 28 9.1 5.0
30000 -31.7 -25.1 250 49 25 8.3 4.6 | -31.5 -24.7 245 48 25 8.3 4.6
29000 -29.2 -20.6 250 47 24 8.3 4.6 | -29.0 -20.2 245 47 24 8.3 4.6
28000 -26.8 -16.2 245 45 23 8.1 4.5 | -26.5 -15.7 245 45 23 8.2 4.5
27000 -24.6 -12.3 245 43 22 7.1 3.9 | -24.3 -11.7 245 43 22 7.3 4.0
26000 -22.5 -8.5 245 42 22 7.1 3.9 | -22.2 -8.0 240 42 22 7.3 4.0
25000 -20.4 -4.7 245 41 21 7.1 3.9 | -20.1 -4.2 240 40 21 7.3 4.0
24000 -18.5 -1.3 245 39 20 6.4 3.5 | -18.0 -0.4 240 39 20 6.6 3.6
23000 -16.6 2.1 245 37 19 6.4 3.5 | -16.1 3.0 235 37 19 6.6 3.6
22000 -14.8 5.4 245 34 18 6.5 3.6 | -14.2 6.4 235 36 18 6.6 3.6
21000 -13.0 8.6 240 32 16 5.7 3.2 | -12.4 9.7 235 34 18 6.2 3.4
20000 -11.3 11.7 235 29 15 5.8 3.2 | -10.6 12.9 235 33 17 6.2 3.4
19500 -10.5 13.1 235 28 14 5.8 3.2 | -9.7 14.5 230 33 17 6.2 3.4
19000 -9.7 14.5 235 26 14 5.7 3.1 | -8.8 16.2 230 32 16 6.2 3.4
18500 -8.9 16.0 230 25 13 5.5 3.0 | -7.9 17.8 230 31 16 6.1 3.4
18000 -7.7 18.1 225 23 12 5.4 3.0 | -6.6 20.1 235 30 15 6.2 3.4
17500 -6.9 19.6 220 22 11 5.4 2.9 | -5.6 21.9 235 29 15 6.6 3.6
17000 -6.1 21.0 220 21 11 5.3 2.9 | -4.7 23.5 235 29 15 6.5 3.6
16500 -5.2 22.6 215 21 11 6.5 3.6 | -3.7 25.3 235 28 14 6.7 3.7
16000 -4.3 24.3 215 21 11 6.5 3.6 | -2.8 27.0 230 27 14 6.7 3.7
15500 -3.3 26.1 210 20 10 7.4 4.0 | -1.8 28.8 230 26 14 6.7 3.7
15000 -2.1 28.2 210 20 10 7.9 4.3 | -0.8 30.6 230 25 13 6.6 3.6
14500 -1.0 30.2 210 19 10 8.1 4.5 | 0.2 32.4 230 24 12 6.6 3.6
14000 0.3 32.5 210 19 10 8.7 4.8 | 1.1 34.0 225 23 12 6.3 3.4
13500 1.5 34.7 210 18 9 8.7 4.8 | 2.0 35.6 225 22 11 6.2 3.4
13000 2.8 37.0 210 17 9 9.0 4.9 | 3.0 37.4 225 21 11 7.0 3.9
12500 4.2 39.6 215 17 9 9.0 4.9 | 4.0 39.2 220 21 11 6.9 3.8
12000 5.5 41.9 215 16 8 9.2 5.0 | 5.1 41.2 220 20 10 8.2 4.5
11500 6.8 44.2 215 15 8 9.3 5.1 | 6.4 43.5 220 20 10 8.2 4.5
11000 8.1 46.6 220 15 8 7.2 3.9 | 7.5 45.5 220 19 10 7.2 4.0
10500 9.2 48.6 220 15 8 6.3 3.5 | 8.6 47.5 220 19 10 6.9 3.8
10250 9.7 49.5 225 15 8 11.4 6.2 | 9.2 48.6 220 18 10 10.9 6.0
10000 10.7 51.3 225 15 8 12.2 6.7 | 10.1 50.2 220 19 10 11.1 6.1
9750 11.4 52.5 225 15 8 7.6 4.2 | 10.7 51.3 220 19 10 7.8 4.3
9500 12.0 53.6 225 15 8 9.5 5.2 | 11.4 52.5 220 19 10 9.1 5.0
9250 12.7 54.9 225 15 8 6.7 3.7 | 12.0 53.6 220 18 9 7.2 3.9
9000 13.1 55.6 230 14 7 6.8 3.7 | 12.5 54.5 215 17 9 7.7 4.2
8750 13.7 56.7 230 14 7 9.2 5.0 | 13.2 55.8 215 17 9 9.5 5.2
8500 14.4 57.9 230 14 7 8.7 4.8 | 13.8 56.8 215 17 9 9.4 5.2
8250 15.0 59.0 230 14 7 6.9 3.8 | 14.5 58.1 215 17 9 8.0 4.4
8000 15.4 59.7 235 13 7 5.6 3.1 | 15.1 59.2 215 16 8 7.5 4.1
7750 15.9 60.6 235 13 7 6.7 3.7 | 15.7 60.3 210 16 8 9.1 5.0
7500 16.3 61.3 235 12 6 5.9 3.2 | 16.3 61.3 215 15 8 9.0 4.9
7250 16.7 62.1 230 12 6 3.4 1.9 | 17.0 62.6 210 15 8 7.7 4.2
7000 16.8 62.2 235 10 5 2.3 1.3 | 17.5 63.5 210 14 7 7.4 4.1
6750 17.0 62.6 235 9 5 4.3 2.4 | 18.1 64.6 205 13 6 10.0 5.5
6500 17.3 63.1 225 9 5 3.5 1.9 | 18.9 66.0 205 12 6 11.0 6.0
6250 17.5 63.5 225 8 4 1.6 0.9 | 19.7 67.5 205 11 6 10.6 5.8
6000 17.5 63.5 220 7 4 1.4 0.7 | 20.5 68.9 200 11 6 10.8 5.9
5750 17.6 63.7 215 6 3 3.1 1.7 | 21.3 70.3 200 10 5 9.8 5.4
5500 18.0 64.4 210 5 3 8.9 4.9 | 22.0 71.6 200 9 5 13.2 7.2
09/28/2026 at 1500 MDT | 09/28/2026 at 1800 MDT
|
CAPE... +6.9 LI... +0.9 | CAPE... +84.4 LI... -0.2
CINH... -3.9 K Index... +28.1 | CINH... -38.9 K Index... +26.9
|
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 -62.4 -80.3 260 41 21 2.6 1.4 | -62.4 -80.3 260 40 20 2.6 1.4
45000 -57.7 -71.9 260 56 29 3.8 2.1 | -57.6 -71.7 260 56 29 4.1 2.3
40000 -51.9 -61.4 265 68 35 4.6 2.5 | -51.4 -60.5 255 63 33 4.9 2.7
38000 -49.2 -56.6 255 65 33 4.6 2.5 | -48.5 -55.3 245 56 29 4.9 2.7
36000 -46.4 -51.5 250 62 32 4.7 2.6 | -45.6 -50.1 235 51 26 5.0 2.7
34000 -41.7 -43.1 245 57 29 9.2 5.0 | -40.9 -41.6 235 52 27 9.0 5.0
32000 -35.6 -32.1 240 50 26 9.0 4.9 | -34.8 -30.6 235 56 29 8.8 4.8
30000 -30.5 -22.9 240 47 24 8.2 4.5 | -29.8 -21.6 235 58 30 8.2 4.5
29000 -28.1 -18.6 240 47 24 8.2 4.5 | -27.4 -17.3 235 58 30 8.2 4.5
28000 -25.7 -14.3 240 46 24 8.1 4.5 | -25.0 -13.0 235 58 30 8.1 4.5
27000 -23.5 -10.3 240 47 24 7.4 4.0 | -22.8 -9.0 235 57 29 7.2 4.0
26000 -21.3 -6.3 240 47 24 7.4 4.1 | -20.7 -5.3 235 55 28 7.2 4.0
25000 -19.1 -2.4 240 48 24 7.4 4.1 | -18.6 -1.5 235 53 27 7.2 4.0
24000 -17.1 1.2 240 47 24 6.6 3.6 | -16.7 1.9 235 50 26 6.1 3.3
23000 -15.2 4.6 240 46 24 6.6 3.6 | -14.9 5.2 235 45 23 6.1 3.3
22000 -13.3 8.1 240 45 23 6.6 3.6 | -13.1 8.4 235 41 21 6.1 3.3
21000 -11.5 11.3 235 43 22 6.0 3.3 | -11.4 11.5 235 37 19 5.8 3.2
20000 -9.7 14.5 235 42 21 6.0 3.3 | -9.7 14.5 235 33 17 5.8 3.2
19500 -8.8 16.2 235 41 21 6.0 3.3 | -8.9 16.0 235 31 16 5.8 3.2
19000 -8.0 17.6 235 40 20 5.9 3.3 | -8.1 17.4 235 29 15 5.8 3.2
18500 -7.2 19.0 235 39 20 5.5 3.0 | -7.2 19.0 235 28 15 5.7 3.1
18000 -6.0 21.2 235 37 19 5.5 3.0 | -6.0 21.2 240 28 14 5.7 3.2
17500 -5.2 22.6 235 35 18 5.5 3.0 | -5.2 22.6 240 27 14 5.6 3.1
17000 -4.4 24.1 230 34 17 5.5 3.0 | -4.4 24.1 240 26 13 5.7 3.1
16500 -3.6 25.5 230 32 16 5.3 2.9 | -3.5 25.7 240 24 13 5.5 3.0
16000 -2.9 26.8 230 30 16 5.2 2.9 | -2.8 27.0 240 24 12 5.5 3.0
15500 -2.1 28.2 230 28 15 5.2 2.9 | -2.0 28.4 240 23 12 5.5 3.0
15000 -1.4 29.5 230 27 14 5.3 2.9 | -1.2 29.8 240 22 12 5.6 3.1
14500 -0.6 30.9 230 26 13 5.3 2.9 | -0.4 31.3 235 22 11 5.6 3.1
14000 0.2 32.4 225 24 13 5.9 3.2 | 0.4 32.7 235 21 11 5.5 3.0
13500 1.0 33.8 225 23 12 5.7 3.1 | 1.2 34.2 235 20 11 5.4 2.9
13000 2.0 35.6 225 22 11 7.8 4.3 | 2.1 35.8 235 20 10 6.9 3.8
12500 3.2 37.8 225 21 11 7.6 4.2 | 3.1 37.6 235 19 10 6.9 3.8
12000 4.3 39.7 220 21 11 8.5 4.7 | 4.1 39.4 230 18 9 7.7 4.2
11500 5.6 42.1 220 20 10 8.6 4.7 | 5.3 41.5 230 18 9 7.9 4.3
11000 6.8 44.2 220 20 10 7.1 3.9 | 6.4 43.5 230 18 9 6.9 3.8
10500 7.8 46.0 220 21 11 6.1 3.3 | 7.4 45.3 225 19 10 6.0 3.3
10250 8.3 46.9 220 21 11 10.5 5.8 | 7.8 46.0 225 19 10 9.1 5.0
10000 9.2 48.6 220 20 10 11.3 6.2 | 8.6 47.5 225 18 9 9.6 5.2
9750 9.9 49.8 220 20 10 7.4 4.1 | 9.2 48.6 225 18 9 6.6 3.6
9500 10.5 50.9 220 21 11 9.1 5.0 | 9.7 49.5 220 18 9 7.8 4.3
9250 11.1 52.0 215 21 11 6.5 3.5 | 10.2 50.4 220 19 10 6.1 3.4
9000 11.5 52.7 220 22 11 6.9 3.8 | 10.6 51.1 220 20 10 6.5 3.6
8750 12.1 53.8 215 21 11 9.2 5.0 | 11.2 52.2 220 20 10 8.1 4.4
8500 12.8 55.0 215 21 11 9.2 5.0 | 11.8 53.2 215 20 11 7.9 4.4
8250 13.4 56.1 215 21 11 7.0 3.8 | 12.3 54.1 215 21 11 7.0 3.9
8000 13.8 56.8 215 22 11 6.4 3.5 | 12.8 55.0 215 22 11 6.4 3.5
7750 14.4 57.9 215 22 11 8.9 4.9 | 13.3 55.9 210 22 11 7.3 4.0
7500 15.1 59.2 215 21 11 9.2 5.0 | 13.8 56.8 210 22 11 7.8 4.3
7250 15.7 60.3 210 21 11 7.4 4.1 | 14.3 57.7 210 21 11 6.0 3.3
7000 16.2 61.2 210 21 11 6.8 3.7 | 14.7 58.5 205 22 11 4.9 2.7
6750 16.8 62.2 210 21 11 10.9 6.0 | 15.1 59.2 205 22 11 8.2 4.5
6500 17.7 63.9 210 20 10 12.0 6.6 | 15.7 60.3 200 20 11 9.2 5.1
6250 18.5 65.3 210 19 10 9.9 5.4 | 16.3 61.3 200 19 10 7.7 4.2
6000 19.2 66.6 210 19 10 9.3 5.1 | 16.8 62.2 195 18 9 7.0 3.8
5750 19.9 67.8 210 19 10 10.1 5.5 | 17.3 63.1 190 17 9 9.0 4.9
5500 20.8 69.4 210 16 8 13.3 7.3 | 18.1 64.6 190 14 7 11.6 6.4
________________________________________________________________________________
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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