Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
047
UXUS97 KBOU 301244
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0644 MDT Wednesday, September 30, 2026
This forecast is for Wednesday, September 30, 2026:
If the trigger temperature of 67.6 F/19.8 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 0 ft/min (0.0 m/s)
Maximum height of thermals.................. 6601 ft MSL (1242 ft AGL)
Forecast maximum temperature................... 63.0 F/17.7 C
Time of trigger temperature.................... None
Time of overdevelopment........................ None
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................. 5430 ft MSL (71 ft AGL)
Thermal soaring outlook for Thursday 10/01..... Poor
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....................... 17651 ft MSL (12292 ft AGL)
Wave soaring outlook for Thursday 10/01........ Poor
Remarks...
Sunrise/Sunset.................... 06:55:08 / 18:43:38 MDT
Total possible sunshine........... 11 hr 48 min 30 sec (708 min 30 sec)
Altitude of sun at 12:49:23 MDT... 47.13 degrees
Upper air data from numerical model forecast valid on 09/30/2026 at 0600 MDT
Freezing level.................. 12828 ft MSL (7469 ft AGL)
Convective condensation level... 12258 ft MSL (6899 ft AGL)
Lifted condensation level....... 10445 ft MSL (5085 ft AGL)
Lifted index.................... +7.5
K index......................... +19.1
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 -62.2 -80.0 240 45 23 3.1 1.7 M M M M M
45000 -56.8 -70.2 220 58 30 4.5 2.5 M M M M M
40000 -50.0 -58.0 210 56 29 5.2 2.9 M M M M M
38000 -46.9 -52.4 205 48 25 5.2 2.8 M M M M M
36000 -43.8 -46.8 200 40 21 5.2 2.9 M M M M M
34000 -39.3 -38.7 195 35 18 8.5 4.7 M M M M M
32000 -33.6 -28.5 200 31 16 8.6 4.7 M M M M M
30000 -28.8 -19.8 195 26 13 7.8 4.3 48.2 118.7 23.4 M M
29000 -26.5 -15.7 195 23 12 7.8 4.3 47.4 117.4 23.1 M M
28000 -24.2 -11.6 195 21 11 7.9 4.4 46.8 116.2 22.8 M M
27000 -22.2 -8.0 190 17 9 6.6 3.6 45.6 114.1 22.2 M M
26000 -20.2 -4.4 180 14 7 6.6 3.6 44.4 111.9 21.4 M M
25000 -18.3 -0.9 165 11 6 6.6 3.6 43.3 109.9 20.7 M M
24000 -16.5 2.3 150 10 5 5.4 3.0 42.0 107.5 19.8 M M
23000 -14.9 5.2 145 11 5 5.5 3.0 40.3 104.6 18.7 M M
22000 -13.3 8.1 140 11 6 5.5 3.0 38.8 101.9 17.6 M M
21000 -11.9 10.6 130 10 5 4.6 2.5 37.2 98.9 16.3 M M
20000 -10.5 13.1 110 9 5 4.6 2.5 35.3 95.6 14.9 M M
19500 -9.8 14.4 095 9 5 4.6 2.5 34.5 94.0 14.3 M M
19000 -8.8 16.2 080 10 5 4.7 2.6 33.2 91.8 13.3 M M
18500 -8.0 17.6 075 11 6 4.9 2.7 32.3 90.2 12.6 M M
18000 -7.3 18.9 075 12 6 4.9 2.7 31.5 88.7 12.0 M M
17500 -6.6 20.1 075 13 7 4.5 2.5 30.7 87.2 11.3 M M
17000 -5.9 21.4 080 13 7 4.6 2.5 29.8 85.6 10.6 M M
16500 -5.2 22.6 080 14 7 4.1 2.3 28.9 84.1 9.9 M M
16000 -4.7 23.5 085 14 7 3.8 2.1 27.9 82.2 9.0 M M
15500 -4.2 24.4 085 14 7 3.9 2.2 26.9 80.4 8.1 M M
15000 -3.5 25.7 085 13 7 5.1 2.8 26.0 78.9 7.4 M M
14500 -2.8 27.0 085 13 7 5.0 2.7 25.3 77.5 6.7 M M
14000 -2.0 28.4 085 13 7 5.5 3.0 24.5 76.2 6.0 M M
13500 -1.2 29.8 080 13 7 5.4 3.0 23.8 74.9 5.4 M M
13000 -0.3 31.5 070 13 7 6.9 3.8 23.2 73.8 4.8 M M
12500 0.7 33.3 065 14 7 7.1 3.9 22.8 73.0 4.4 M M
12000 1.8 35.2 060 14 7 7.8 4.3 22.4 72.3 4.0 M M
11500 2.9 37.2 055 13 7 8.0 4.4 22.1 71.8 3.8 M M
11000 4.0 39.2 055 13 6 7.2 3.9 21.8 71.3 3.5 M M
10500 5.0 41.0 050 12 6 6.3 3.5 21.4 70.5 3.0 M M
10250 5.5 41.9 050 11 6 8.9 4.9 21.2 70.1 2.8 M M
10000 6.3 43.3 045 10 5 9.8 5.4 21.2 70.2 2.8 M M
9750 6.9 44.4 045 9 5 7.8 4.3 21.1 70.0 2.7 M M
9500 7.5 45.5 040 9 4 8.5 4.7 21.0 69.7 2.6 M M
9250 8.1 46.6 040 8 4 7.7 4.2 20.9 69.5 2.4 M M
9000 8.6 47.5 035 7 4 8.2 4.5 20.7 69.2 2.3 M M
8750 9.3 48.7 035 7 4 9.2 5.0 20.6 69.1 2.2 M M
8500 9.9 49.8 030 7 4 9.0 5.0 20.6 69.0 2.1 M M
8250 10.6 51.1 030 7 3 8.7 4.8 20.5 68.9 2.1 M M
8000 11.2 52.2 025 6 3 7.8 4.3 20.4 68.7 2.0 M M
7750 11.7 53.1 020 6 3 7.2 3.9 20.2 68.4 1.8 M M
7500 12.3 54.1 015 7 3 7.7 4.2 20.0 68.1 1.6 M M
7250 12.8 55.0 005 7 4 5.3 2.9 19.8 67.7 1.4 M M
7000 13.0 55.4 005 8 4 3.0 1.6 19.4 66.8 0.9 M M
6750 13.3 55.9 360 8 4 4.3 2.4 18.9 66.0 0.4 M M
6500 13.6 56.5 360 8 4 3.8 2.1 18.5 65.3 -0.0 28 0.1
6250 13.7 56.7 355 9 4 1.7 0.9 18.0 64.3 -0.6 16 0.1
6000 13.8 56.8 355 9 4 0.2 0.1 17.3 63.1 -1.3 7 0.0
5750 13.8 56.8 355 9 4 3.6 2.0 16.6 61.9 -1.9 M M
5500 14.2 57.6 355 7 4 6.6 3.6 16.4 61.4 -2.3 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/30/2026 at 0900 MDT | 09/30/2026 at 1200 MDT
|
CAPE... +4.7 LI... +3.0 | CAPE... +52.0 LI... +2.6
CINH... -40.8 K Index... +18.7 | CINH... -3.9 K Index... +12.5
|
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 -61.5 -78.7 225 41 21 4.2 2.3 | -60.8 -77.4 220 39 20 3.9 2.1
45000 -55.2 -67.4 215 55 29 4.2 2.3 | -55.0 -67.0 210 50 26 4.0 2.2
40000 -48.8 -55.8 210 59 30 3.6 2.0 | -49.0 -56.2 200 51 26 3.4 1.9
38000 -46.6 -51.9 205 43 22 3.7 2.0 | -46.9 -52.4 190 33 17 3.4 1.9
36000 -44.4 -47.9 195 27 14 3.7 2.0 | -44.9 -48.8 165 18 9 3.4 1.9
34000 -39.7 -39.5 185 19 10 8.4 4.6 | -40.0 -40.0 140 13 7 8.9 4.9
32000 -34.6 -30.3 180 15 8 8.5 4.7 | -34.6 -30.3 125 11 6 9.0 4.9
30000 -29.7 -21.5 175 14 7 8.1 4.4 | -29.7 -21.5 135 13 7 8.0 4.4
29000 -27.3 -17.1 170 14 7 8.1 4.5 | -27.3 -17.1 145 15 8 8.0 4.4
28000 -24.9 -12.8 165 14 7 8.2 4.5 | -25.0 -13.0 150 17 9 8.1 4.4
27000 -22.7 -8.9 165 14 7 7.2 4.0 | -22.8 -9.0 150 17 9 7.2 3.9
26000 -20.6 -5.1 160 14 7 7.3 4.0 | -20.7 -5.3 145 17 9 7.2 3.9
25000 -18.5 -1.3 155 14 7 7.3 4.0 | -18.6 -1.5 145 17 9 7.2 4.0
24000 -16.5 2.3 150 14 7 6.1 3.4 | -16.6 2.1 145 17 9 6.3 3.5
23000 -14.7 5.5 140 13 7 6.2 3.4 | -14.7 5.5 140 17 9 6.3 3.5
22000 -12.9 8.8 130 13 6 6.1 3.4 | -12.9 8.8 135 17 9 6.3 3.5
21000 -11.3 11.7 115 13 6 4.7 2.6 | -11.3 11.7 125 17 9 4.4 2.4
20000 -9.9 14.2 100 13 7 4.7 2.6 | -10.0 14.0 115 18 9 4.4 2.4
19500 -8.8 16.2 090 14 7 4.7 2.6 | -9.0 15.8 110 18 9 4.3 2.4
19000 -8.1 17.4 080 15 8 3.9 2.1 | -8.4 16.9 105 19 10 3.4 1.9
18500 -7.7 18.1 075 17 9 3.0 1.6 | -8.1 17.4 095 19 10 2.1 1.1
18000 -7.3 18.9 075 18 9 2.8 1.6 | -7.7 18.1 085 20 10 1.9 1.0
17500 -6.8 19.8 070 19 10 3.7 2.0 | -7.3 18.9 075 21 11 3.7 2.0
17000 -6.2 20.8 070 20 10 3.6 2.0 | -6.7 19.9 070 22 11 3.8 2.1
16500 -5.7 21.7 070 20 10 4.0 2.2 | -6.2 20.8 060 23 12 4.6 2.5
16000 -5.0 23.0 065 19 10 4.2 2.3 | -5.3 22.5 055 23 12 5.4 3.0
15500 -4.4 24.1 065 18 9 4.4 2.4 | -4.5 23.9 055 23 12 5.5 3.0
15000 -3.6 25.5 060 17 8 5.6 3.1 | -3.6 25.5 050 23 12 6.1 3.3
14500 -2.8 27.0 060 16 8 5.5 3.0 | -2.7 27.1 050 22 11 6.2 3.4
14000 -2.0 28.4 055 15 8 5.6 3.0 | -1.9 28.6 050 21 11 4.5 2.5
13500 -1.1 30.0 055 15 8 5.6 3.1 | -1.2 29.8 050 19 10 4.6 2.5
13000 -0.3 31.5 050 16 8 5.3 2.9 | -0.6 30.9 045 18 9 4.8 2.6
12500 0.4 32.7 050 17 9 5.2 2.9 | 0.1 32.2 045 16 8 4.8 2.7
12000 1.2 34.2 050 17 9 6.9 3.8 | 0.8 33.4 040 15 8 6.7 3.7
11500 2.2 36.0 045 17 9 7.5 4.1 | 1.9 35.4 035 14 7 7.5 4.1
11000 3.2 37.8 045 17 9 7.2 4.0 | 2.9 37.2 035 14 7 6.7 3.7
10500 4.2 39.6 045 16 8 6.3 3.5 | 3.9 39.0 030 13 7 5.8 3.2
10250 4.7 40.5 045 15 8 10.3 5.7 | 4.3 39.7 030 13 6 8.6 4.7
10000 5.7 42.3 040 13 7 10.9 6.0 | 5.0 41.0 030 12 6 9.6 5.3
9750 6.2 43.2 040 12 6 7.3 4.0 | 5.6 42.1 030 12 6 7.5 4.1
9500 6.8 44.2 040 11 6 8.5 4.6 | 6.1 43.0 030 11 6 8.1 4.4
9250 7.4 45.3 035 10 5 7.3 4.0 | 6.7 44.1 030 11 6 8.0 4.4
9000 7.9 46.2 035 10 5 7.4 4.1 | 7.2 45.0 025 11 6 8.4 4.6
8750 8.5 47.3 035 9 5 8.2 4.5 | 7.8 46.0 025 10 5 8.6 4.7
8500 9.1 48.4 030 9 5 8.2 4.5 | 8.4 47.1 020 10 5 8.6 4.7
8250 9.7 49.5 030 8 4 7.6 4.2 | 9.1 48.4 020 9 5 8.7 4.8
8000 10.2 50.4 025 8 4 6.7 3.7 | 9.7 49.5 020 9 5 8.9 4.9
7750 10.7 51.3 020 8 4 6.5 3.6 | 10.3 50.5 015 9 5 9.0 4.9
7500 11.1 52.0 015 8 4 6.6 3.6 | 11.0 51.8 015 9 4 9.2 5.0
7250 11.6 52.9 015 8 4 4.9 2.7 | 11.6 52.9 010 8 4 8.2 4.5
7000 11.9 53.4 010 8 4 3.4 1.9 | 12.2 54.0 005 8 4 7.5 4.1
6750 12.2 54.0 005 8 4 5.4 3.0 | 12.8 55.0 360 8 4 9.6 5.3
6500 12.6 54.7 005 8 4 5.6 3.1 | 13.6 56.5 360 7 4 10.6 5.8
6250 12.9 55.2 360 7 4 3.9 2.2 | 14.3 57.7 360 7 4 10.0 5.5
6000 13.1 55.6 360 6 3 3.1 1.7 | 15.1 59.2 360 7 4 10.1 5.6
5750 13.4 56.1 355 5 3 5.8 3.2 | 15.8 60.4 355 7 3 9.6 5.2
5500 14.1 57.4 345 4 2 12.7 7.0 | 16.6 61.9 355 6 3 12.7 7.0
09/30/2026 at 1500 MDT | 09/30/2026 at 1800 MDT
|
CAPE... +40.6 LI... +3.3 | CAPE... +20.2 LI... +3.1
CINH... -5.2 K Index... +17.1 | CINH... -17.8 K Index... +16.8
|
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 -60.6 -77.1 220 36 19 4.1 2.2 | -60.1 -76.2 220 31 16 4.2 2.3
45000 -54.6 -66.3 210 42 22 3.2 1.8 | -53.9 -65.0 205 33 17 3.1 1.7
40000 -49.7 -57.5 190 41 21 4.2 2.3 | -49.2 -56.6 180 34 17 3.4 1.9
38000 -47.1 -52.8 175 26 13 4.2 2.3 | -47.1 -52.8 155 21 11 3.4 1.9
36000 -44.6 -48.3 135 15 8 4.2 2.3 | -45.0 -49.0 100 19 10 3.4 1.9
34000 -39.7 -39.5 115 17 9 8.6 4.7 | -40.6 -41.1 085 21 11 8.2 4.5
32000 -34.6 -30.3 115 19 10 8.6 4.7 | -35.7 -32.3 090 19 10 8.2 4.5
30000 -30.0 -22.0 130 19 10 7.2 3.9 | -31.3 -24.3 095 14 7 7.1 3.9
29000 -27.9 -18.2 140 19 10 7.2 3.9 | -29.1 -20.4 100 10 5 7.2 3.9
28000 -25.8 -14.4 150 20 10 7.2 4.0 | -27.0 -16.6 105 7 4 7.1 3.9
27000 -23.7 -10.7 155 18 10 6.9 3.8 | -24.8 -12.6 115 5 3 7.8 4.3
26000 -21.6 -6.9 160 16 8 6.9 3.8 | -22.5 -8.5 115 4 2 7.8 4.3
25000 -19.6 -3.3 165 14 7 6.9 3.8 | -20.2 -4.4 110 3 1 7.8 4.3
24000 -17.5 0.5 170 13 7 7.2 3.9 | -18.0 -0.4 115 3 1 6.6 3.6
23000 -15.4 4.3 165 12 6 7.2 4.0 | -16.1 3.0 120 5 3 6.6 3.6
22000 -13.3 8.1 160 12 6 7.2 4.0 | -14.2 6.4 125 7 4 6.6 3.6
21000 -11.6 11.1 150 11 6 4.4 2.4 | -12.5 9.5 105 9 5 4.2 2.3
20000 -10.3 13.5 130 10 5 4.5 2.5 | -11.2 11.8 080 12 6 4.2 2.3
19500 -9.3 15.3 115 11 6 4.5 2.4 | -10.6 12.9 070 15 8 4.2 2.3
19000 -8.6 16.5 105 12 6 3.6 2.0 | -9.7 14.5 060 19 10 3.8 2.1
18500 -8.3 17.1 090 14 7 2.2 1.2 | -9.2 15.4 055 22 11 3.2 1.8
18000 -7.9 17.8 075 16 8 2.2 1.2 | -8.7 16.3 050 25 13 3.2 1.7
17500 -7.5 18.5 065 19 10 3.1 1.7 | -8.2 17.2 050 28 14 3.2 1.8
17000 -7.0 19.4 060 22 11 3.1 1.7 | -7.7 18.1 045 29 15 3.2 1.8
16500 -6.5 20.3 055 26 13 3.9 2.1 | -7.2 19.0 040 31 16 3.4 1.9
16000 -5.8 21.6 050 26 13 4.8 2.7 | -6.7 19.9 040 31 16 3.6 2.0
15500 -5.1 22.8 045 26 14 4.9 2.7 | -6.1 21.0 035 30 16 3.7 2.1
15000 -4.4 24.1 045 26 13 4.4 2.4 | -5.4 22.3 035 30 15 5.7 3.1
14500 -3.7 25.3 040 24 13 4.4 2.4 | -4.6 23.7 035 28 14 5.4 3.0
14000 -3.0 26.6 040 23 12 5.2 2.8 | -3.7 25.3 035 26 14 6.7 3.7
13500 -2.3 27.9 035 21 11 5.1 2.8 | -2.8 27.0 030 24 13 6.6 3.6
13000 -1.4 29.5 035 19 10 7.3 4.0 | -1.8 28.8 030 22 12 7.5 4.1
12500 -0.3 31.5 030 17 9 7.8 4.3 | -0.7 30.7 025 21 11 7.7 4.2
12000 0.8 33.4 025 16 8 7.7 4.3 | 0.4 32.7 025 20 10 7.8 4.3
11500 1.9 35.4 025 16 8 7.8 4.3 | 1.5 34.7 025 18 10 7.8 4.3
11000 2.9 37.2 020 15 8 7.0 3.8 | 2.6 36.7 020 17 9 7.3 4.0
10500 3.9 39.0 015 15 8 5.9 3.3 | 3.6 38.5 020 17 9 6.4 3.5
10250 4.3 39.7 010 15 8 9.4 5.2 | 4.1 39.4 020 16 8 10.2 5.6
10000 5.1 41.2 010 14 7 10.6 5.8 | 5.0 41.0 015 16 8 11.2 6.2
9750 5.7 42.3 010 14 7 7.8 4.3 | 5.7 42.3 015 15 8 8.1 4.4
9500 6.3 43.3 010 14 7 8.7 4.8 | 6.3 43.3 015 15 8 9.1 5.0
9250 7.0 44.6 010 14 7 8.0 4.4 | 7.0 44.6 015 15 8 8.0 4.4
9000 7.6 45.7 010 14 7 8.8 4.8 | 7.6 45.7 015 15 8 8.6 4.7
8750 8.3 46.9 010 14 7 9.9 5.4 | 8.3 46.9 015 15 8 9.7 5.3
8500 9.0 48.2 010 13 7 9.6 5.3 | 9.0 48.2 015 15 8 9.5 5.2
8250 9.7 49.5 010 13 7 9.5 5.2 | 9.7 49.5 015 14 7 9.1 5.0
8000 10.4 50.7 010 13 7 9.3 5.1 | 10.4 50.7 015 14 7 8.6 4.7
7750 11.1 52.0 005 13 7 9.2 5.1 | 11.0 51.8 015 14 7 8.9 4.9
7500 11.8 53.2 005 12 6 9.4 5.2 | 11.7 53.1 015 13 7 9.0 4.9
7250 12.5 54.5 005 12 6 8.8 4.8 | 12.3 54.1 015 12 6 7.7 4.2
7000 13.1 55.6 005 12 6 8.4 4.6 | 12.8 55.0 010 12 6 6.8 3.7
6750 13.8 56.8 005 12 6 10.0 5.5 | 13.4 56.1 010 11 6 8.7 4.8
6500 14.5 58.1 005 11 6 10.8 5.9 | 14.1 57.4 010 10 5 9.4 5.2
6250 15.3 59.5 005 11 6 10.1 5.5 | 14.7 58.5 005 9 5 8.8 4.8
6000 16.1 61.0 360 10 5 10.2 5.6 | 15.4 59.7 005 9 4 8.8 4.8
5750 16.8 62.2 360 10 5 9.2 5.1 | 16.0 60.8 005 8 4 8.5 4.7
5500 17.5 63.5 360 9 5 10.2 5.6 | 16.6 61.9 005 6 3 8.6 4.7
________________________________________________________________________________
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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