Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
605
UXUS97 KBOU 081226
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0625 MDT Tuesday, September 8, 2026
This forecast is for Tuesday, September 8, 2026:
If the trigger temperature of 77.3 F/25.1 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 989 ft/min (5.0 m/s)
Maximum height of thermals.................. 14918 ft MSL (9556 ft AGL)
Forecast maximum temperature................... 87.0 F/31.0 C
Time of trigger temperature.................... 1045 MDT
Time of overdevelopment........................ 1600 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 11125 ft MSL (5763 ft AGL)
Thermal soaring outlook for Wednesday 09/09.... Excellent
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... Trending downwards
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 41298 ft MSL (35936 ft AGL)
Wave soaring outlook for Wednesday 09/09....... Poor
Remarks... Afternoon and evening thunderstorms possible along the palmer divide
and eastern plains today
Sunrise/Sunset.................... 06:34:26 / 19:19:43 MDT
Total possible sunshine........... 12 hr 45 min 17 sec (765 min 17 sec)
Altitude of sun at 12:57:04 MDT... 55.69 degrees
Upper air data from numerical model forecast valid on 09/08/2026 at 0600 MDT
Freezing level.................. 15791 ft MSL (10429 ft AGL)
Convective condensation level... 13100 ft MSL (7738 ft AGL)
Lifted condensation level....... 13758 ft MSL (8396 ft AGL)
Lifted index.................... -3.8
K index......................... +26.7
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 -65.0 -85.0 240 47 24 3.7 2.0 80.7 177.2 29.5 M M
45000 -57.8 -72.0 240 60 31 6.6 3.6 69.2 156.5 24.3 M M
40000 -48.0 -54.4 240 65 34 6.1 3.4 62.1 143.8 21.2 M M
38000 -44.4 -47.9 230 63 32 6.1 3.4 58.7 137.7 19.4 M M
36000 -40.2 -40.4 220 63 32 6.4 3.5 55.7 132.2 17.8 M M
34000 -36.4 -33.5 220 59 30 6.5 3.5 52.6 126.7 16.0 M M
32000 -32.5 -26.5 220 55 28 6.6 3.6 50.2 122.4 14.6 M M
30000 -28.2 -18.8 225 52 27 7.3 4.0 48.0 118.4 13.3 M M
29000 -26.0 -14.8 230 51 26 7.3 4.0 47.1 116.8 12.7 M M
28000 -23.9 -11.0 230 49 25 7.0 3.9 46.3 115.3 12.2 M M
27000 -21.8 -7.2 230 47 24 7.0 3.9 45.1 113.2 11.4 M M
26000 -19.7 -3.5 235 45 23 7.1 3.9 44.1 111.4 10.7 M M
25000 -17.6 0.3 235 43 22 7.0 3.8 43.2 109.8 10.0 M M
24000 -15.6 3.9 235 41 21 6.6 3.6 42.0 107.6 9.1 M M
23000 -13.7 7.3 235 39 20 6.6 3.6 40.8 105.5 8.2 M M
22000 -11.8 10.8 235 36 19 6.5 3.6 39.8 103.7 7.4 M M
21000 -10.0 14.0 230 34 17 6.0 3.3 38.4 101.1 6.2 M M
20000 -7.8 18.0 230 31 16 6.1 3.4 36.8 98.3 4.9 M M
19500 -7.0 19.4 225 30 15 6.2 3.4 36.2 97.2 4.3 M M
19000 -6.1 21.0 225 29 15 6.3 3.4 35.6 96.1 3.8 M M
18500 -5.2 22.6 225 28 15 6.3 3.4 35.0 95.0 3.2 M M
18000 -4.3 24.3 225 27 14 6.5 3.6 34.4 94.0 2.7 M M
17500 -3.3 26.1 225 27 14 6.5 3.6 33.9 93.0 2.2 M M
17000 -2.4 27.7 225 26 13 6.7 3.7 33.3 92.0 1.7 M M
16500 -1.4 29.5 225 24 12 7.1 3.9 32.9 91.2 1.3 M M
16000 -0.3 31.5 230 23 12 7.1 3.9 32.4 90.4 0.8 M M
15500 0.7 33.3 230 21 11 7.1 3.9 32.0 89.6 0.4 M M
15000 1.8 35.2 235 19 10 7.1 3.9 31.5 88.8 0.0 M M
14500 2.8 37.0 240 18 9 7.5 4.1 31.1 88.0 -0.3 746 3.8
14000 3.9 39.0 245 16 8 7.5 4.1 30.8 87.4 -0.7 698 3.5
13500 5.1 41.2 250 15 8 7.6 4.2 30.4 86.7 -1.1 650 3.3
13000 6.2 43.2 260 14 7 7.7 4.2 30.1 86.1 -1.4 602 3.1
12500 7.3 45.1 265 13 7 7.6 4.2 29.7 85.5 -1.8 555 2.8
12000 8.3 46.9 275 13 6 7.4 4.1 29.4 84.8 -2.2 508 2.6
11500 9.4 48.9 285 13 6 7.2 3.9 29.0 84.2 -2.6 461 2.3
11000 10.3 50.5 295 13 6 6.4 3.5 28.5 83.3 -3.1 418 2.1
10500 11.3 52.3 305 13 7 3.8 2.1 28.0 82.5 -3.6 375 1.9
10250 11.5 52.7 310 14 7 3.7 2.0 27.4 81.4 -4.2 361 1.8
10000 11.9 53.4 315 13 7 8.1 4.4 27.2 81.0 -4.5 340 1.7
9750 12.4 54.3 320 12 6 8.2 4.5 27.1 80.7 -4.7 318 1.6
9500 13.0 55.4 330 11 6 7.1 3.9 26.9 80.5 -4.9 295 1.5
9250 13.3 55.9 335 11 6 5.1 2.8 26.6 79.9 -5.3 276 1.4
9000 13.7 56.7 340 11 6 6.5 3.6 26.3 79.3 -5.7 258 1.3
8750 14.2 57.6 350 9 5 8.2 4.5 26.1 79.0 -5.9 234 1.2
8500 14.8 58.6 010 9 4 6.9 3.8 26.0 78.7 -6.1 211 1.1
8250 15.2 59.4 020 8 4 5.8 3.2 25.7 78.2 -6.4 191 1.0
8000 15.6 60.1 035 8 4 6.1 3.4 25.4 77.7 -6.7 172 0.9
7750 16.1 61.0 035 7 4 6.8 3.7 25.1 77.3 -7.0 150 0.8
7500 16.6 61.9 030 7 3 5.2 2.9 24.9 76.8 -7.3 128 0.7
7250 16.9 62.4 030 6 3 3.8 2.1 24.5 76.0 -7.7 112 0.6
7000 17.2 63.0 030 5 3 4.4 2.4 24.0 75.2 -8.2 95 0.5
6750 17.5 63.5 015 5 3 5.3 2.9 23.7 74.6 -8.6 78 0.4
6500 17.9 64.2 350 5 3 5.6 3.1 23.3 74.0 -8.9 58 0.3
6250 18.2 64.8 345 5 3 4.0 2.2 23.0 73.3 -9.3 40 0.2
6000 18.6 65.5 340 5 3 7.9 4.3 22.6 72.7 -9.7 23 0.1
5750 19.1 66.4 340 5 3 1.4 0.8 22.4 72.4 -9.9 M M
5500 18.3 64.9 320 3 2 -20.0 -11.0 21.0 69.8 -11.5 15 0.1
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/08/2026 at 0900 MDT | 09/08/2026 at 1200 MDT
|
CAPE... +150.1 LI... -0.9 | CAPE... +4.3 LI... +1.3
CINH... -43.0 K Index... +22.9 | CINH... -0.8 K Index... +23.6
|
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 -65.3 -85.5 240 43 22 3.7 2.0 | -65.3 -85.5 235 46 24 2.9 1.6
45000 -57.9 -72.2 245 57 29 6.8 3.7 | -58.7 -73.7 240 59 30 6.7 3.7
40000 -47.8 -54.0 240 63 32 6.5 3.6 | -48.5 -55.3 240 62 32 7.4 4.0
38000 -43.9 -47.0 235 62 32 6.5 3.6 | -44.1 -47.4 235 62 32 7.4 4.0
36000 -39.5 -39.1 230 61 32 6.5 3.6 | -39.2 -38.6 235 61 31 6.3 3.5
34000 -35.6 -32.1 230 60 31 6.5 3.5 | -35.6 -32.1 235 60 31 6.0 3.3
32000 -31.7 -25.1 230 58 30 6.4 3.5 | -32.0 -25.6 235 58 30 6.2 3.4
30000 -27.9 -18.2 230 54 28 6.4 3.5 | -27.9 -18.2 235 55 28 6.9 3.8
29000 -26.0 -14.8 230 52 27 6.4 3.5 | -25.8 -14.4 235 53 27 6.9 3.8
28000 -24.1 -11.4 225 50 26 6.9 3.8 | -23.8 -10.8 235 52 27 6.6 3.6
27000 -22.1 -7.8 230 48 25 6.9 3.8 | -21.8 -7.2 235 50 26 6.6 3.6
26000 -20.0 -4.0 230 46 24 6.9 3.8 | -19.9 -3.8 235 48 25 6.6 3.6
25000 -18.0 -0.4 230 44 22 6.9 3.8 | -18.0 -0.4 230 47 24 6.5 3.6
24000 -15.9 3.4 230 42 21 6.9 3.8 | -16.0 3.2 230 44 23 6.4 3.5
23000 -13.9 7.0 235 40 20 6.9 3.8 | -14.1 6.6 230 42 22 6.5 3.5
22000 -11.9 10.6 235 38 19 6.7 3.7 | -12.2 10.0 235 40 20 6.4 3.5
21000 -10.0 14.0 235 36 18 6.4 3.5 | -10.4 13.3 235 38 19 6.4 3.5
20000 -7.7 18.1 230 34 17 6.4 3.5 | -8.1 17.4 235 35 18 6.4 3.5
19500 -6.8 19.8 230 33 17 6.3 3.5 | -7.2 19.0 235 34 18 6.5 3.6
19000 -5.9 21.4 230 32 17 6.2 3.4 | -6.2 20.8 235 34 17 6.6 3.6
18500 -5.0 23.0 235 31 16 6.2 3.4 | -5.2 22.6 235 33 17 6.6 3.6
18000 -4.1 24.6 235 31 16 6.3 3.4 | -4.3 24.3 235 32 17 6.9 3.8
17500 -3.2 26.2 235 30 15 6.3 3.5 | -3.3 26.1 240 32 16 6.9 3.8
17000 -2.3 27.9 235 29 15 6.6 3.6 | -2.3 27.9 240 31 16 6.9 3.8
16500 -1.2 29.8 240 28 15 6.9 3.8 | -1.2 29.8 245 30 16 6.9 3.8
16000 -0.2 31.6 240 28 14 6.9 3.8 | -0.2 31.6 245 29 15 6.9 3.8
15500 0.8 33.4 245 26 14 6.8 3.7 | 0.7 33.3 250 28 15 6.6 3.6
15000 1.8 35.2 245 25 13 6.8 3.7 | 1.7 35.1 250 27 14 6.6 3.6
14500 2.8 37.0 250 24 12 6.4 3.5 | 2.7 36.9 255 26 13 6.6 3.6
14000 3.8 38.8 255 22 11 6.4 3.5 | 3.6 38.5 255 24 12 6.6 3.6
13500 4.7 40.5 260 20 10 6.4 3.5 | 4.6 40.3 260 22 11 6.5 3.6
13000 5.6 42.1 260 18 9 6.3 3.5 | 5.5 41.9 260 19 10 6.5 3.6
12500 6.5 43.7 265 15 8 6.3 3.4 | 6.5 43.7 260 17 9 6.6 3.6
12000 7.3 45.1 270 13 6 6.2 3.4 | 7.4 45.3 260 13 7 6.7 3.7
11500 8.1 46.6 280 10 5 6.4 3.5 | 8.4 47.1 255 10 5 6.7 3.7
11000 9.0 48.2 285 7 3 6.3 3.5 | 9.3 48.7 250 6 3 6.5 3.6
10500 9.8 49.6 295 4 2 2.1 1.2 | 10.3 50.5 235 3 2 2.0 1.1
10250 9.8 49.6 305 3 2 2.1 1.2 | 10.3 50.5 235 4 2 2.8 1.5
10000 10.3 50.5 325 1 1 9.9 5.4 | 10.9 51.6 210 2 1 10.4 5.7
9750 11.1 52.0 070 1 1 10.9 6.0 | 11.6 52.9 160 2 1 10.0 5.5
9500 11.9 53.4 095 3 2 7.5 4.1 | 12.3 54.1 125 3 2 7.8 4.3
9250 12.2 54.0 100 5 2 3.2 1.8 | 12.7 54.9 120 4 2 5.1 2.8
9000 12.5 54.5 105 6 3 6.8 3.8 | 13.2 55.8 115 5 2 8.3 4.6
8750 13.1 55.6 090 5 2 9.5 5.2 | 14.0 57.2 110 5 2 10.4 5.7
8500 13.7 56.7 075 4 2 6.9 3.8 | 14.7 58.5 100 5 3 8.0 4.4
8250 14.0 57.2 070 4 2 5.1 2.8 | 15.2 59.4 100 5 3 5.4 3.0
8000 14.4 57.9 065 3 2 6.8 3.8 | 15.7 60.3 095 6 3 9.1 5.0
7750 15.0 59.0 045 3 2 7.9 4.3 | 16.6 61.9 090 6 3 12.4 6.8
7500 15.5 59.9 030 4 2 5.7 3.1 | 17.4 63.3 090 6 3 8.5 4.7
7250 15.8 60.4 035 4 2 3.4 1.9 | 17.9 64.2 090 6 3 5.0 2.7
7000 16.2 61.2 040 4 2 6.9 3.8 | 18.4 65.1 090 7 3 10.0 5.5
6750 16.9 62.4 040 5 2 11.2 6.1 | 19.4 66.9 085 7 3 15.6 8.6
6500 17.7 63.9 035 5 3 8.7 4.8 | 20.4 68.7 085 7 3 12.0 6.6
6250 18.3 64.9 035 5 2 7.8 4.3 | 21.2 70.2 080 7 3 10.3 5.6
6000 18.8 65.8 040 5 2 5.3 2.9 | 22.0 71.6 080 7 3 8.8 4.8
5750 19.0 66.2 065 4 2 7.9 4.4 | 22.8 73.0 080 7 4 15.5 8.5
5500 20.0 68.0 070 4 2 21.2 11.6 | 24.6 76.3 080 7 3 33.4 18.3
09/08/2026 at 1500 MDT | 09/08/2026 at 1800 MDT
|
CAPE... +9.3 LI... -0.9 | CAPE... +179.0 LI... -2.3
CINH... -58.9 K Index... +28.8 | CINH... -43.5 K Index... +32.1
|
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 -65.3 -85.5 240 46 24 2.5 1.4 | -65.6 -86.1 240 45 23 3.3 1.8
45000 -58.9 -74.0 240 57 30 7.2 4.0 | -58.4 -73.1 240 54 28 7.2 3.9
40000 -48.0 -54.4 240 59 30 7.2 3.9 | -47.7 -53.9 245 62 32 6.8 3.8
38000 -43.7 -46.7 240 58 30 7.2 3.9 | -43.6 -46.5 250 65 33 6.9 3.8
36000 -38.9 -38.0 240 58 30 6.5 3.6 | -39.0 -38.2 250 68 35 6.1 3.4
34000 -35.1 -31.2 240 58 30 6.3 3.5 | -35.5 -31.9 250 66 34 5.9 3.2
32000 -31.3 -24.3 240 57 30 6.4 3.5 | -32.0 -25.6 250 64 33 6.1 3.3
30000 -27.3 -17.1 245 57 29 6.9 3.8 | -27.8 -18.0 250 60 31 7.0 3.9
29000 -25.2 -13.4 245 57 29 6.9 3.8 | -25.7 -14.3 250 58 30 7.0 3.9
28000 -23.2 -9.8 245 56 29 5.8 3.2 | -23.7 -10.7 250 56 29 5.1 2.8
27000 -21.5 -6.7 245 53 27 5.9 3.2 | -22.2 -8.0 250 54 28 5.1 2.8
26000 -19.8 -3.6 245 50 26 5.9 3.2 | -20.7 -5.3 250 52 27 5.2 2.8
25000 -18.0 -0.4 245 47 24 5.9 3.2 | -19.2 -2.6 250 50 26 5.3 2.9
24000 -16.3 2.7 245 46 24 5.8 3.2 | -17.6 0.3 245 46 24 5.6 3.1
23000 -14.6 5.7 240 45 23 5.8 3.2 | -15.9 3.4 245 43 22 5.7 3.1
22000 -12.9 8.8 240 45 23 5.9 3.3 | -14.3 6.3 245 40 21 6.4 3.5
21000 -11.2 11.8 240 43 22 6.2 3.4 | -11.6 11.1 245 36 19 7.6 4.1
20000 -9.0 15.8 245 40 21 6.3 3.4 | -9.4 15.1 250 34 17 7.6 4.2
19500 -8.1 17.4 245 39 20 6.7 3.6 | -8.3 17.1 255 33 17 7.7 4.2
19000 -7.1 19.2 245 38 19 7.0 3.9 | -7.2 19.0 255 31 16 7.7 4.2
18500 -6.1 21.0 245 37 19 7.0 3.9 | -6.1 21.0 255 30 15 7.7 4.2
18000 -5.1 22.8 245 35 18 7.5 4.1 | -5.0 23.0 260 29 15 7.9 4.3
17500 -4.0 24.8 245 34 17 7.5 4.1 | -3.8 25.2 260 27 14 7.9 4.3
17000 -2.9 26.8 245 32 16 7.6 4.2 | -2.7 27.1 260 26 13 8.0 4.4
16500 -1.8 28.8 245 30 16 7.7 4.2 | -1.6 29.1 260 24 12 8.0 4.4
16000 -0.7 30.7 245 28 15 7.7 4.2 | -0.4 31.3 260 21 11 8.1 4.4
15500 0.5 32.9 245 26 13 8.3 4.5 | 0.8 33.4 255 19 10 8.2 4.5
15000 1.7 35.1 245 24 12 8.3 4.5 | 2.0 35.6 250 17 9 8.2 4.5
14500 2.9 37.2 245 21 11 8.0 4.4 | 3.1 37.6 245 14 7 8.1 4.4
14000 4.0 39.2 240 18 10 8.0 4.4 | 4.3 39.7 230 13 6 8.1 4.4
13500 5.2 41.4 240 16 8 7.5 4.1 | 5.5 41.9 215 11 6 8.2 4.5
13000 6.2 43.2 235 13 7 7.3 4.0 | 6.7 44.1 205 11 6 8.2 4.5
12500 7.3 45.1 225 10 5 7.4 4.1 | 7.9 46.2 190 11 6 8.2 4.5
12000 8.5 47.3 210 7 4 7.5 4.1 | 9.2 48.6 180 11 6 8.3 4.5
11500 9.6 49.3 185 6 3 7.8 4.3 | 10.4 50.7 175 12 6 8.5 4.6
11000 10.9 51.6 170 5 3 7.9 4.3 | 11.7 53.1 170 12 6 8.4 4.6
10500 12.1 53.8 160 5 3 2.1 1.2 | 13.1 55.6 165 12 6 2.5 1.4
10250 12.1 53.8 165 6 3 4.5 2.5 | 13.0 55.4 160 13 7 5.1 2.8
10000 13.0 55.4 155 6 3 13.9 7.6 | 14.0 57.2 160 13 7 14.6 8.0
9750 13.9 57.0 140 6 3 12.2 6.7 | 14.9 58.8 155 13 7 12.9 7.1
9500 14.8 58.6 125 6 3 9.5 5.2 | 15.9 60.6 155 13 7 10.1 5.5
9250 15.3 59.5 125 6 3 6.4 3.5 | 16.5 61.7 155 13 7 7.2 3.9
9000 15.9 60.6 120 6 3 10.1 5.5 | 17.1 62.8 150 14 7 10.6 5.8
8750 16.8 62.2 115 7 3 11.9 6.5 | 18.0 64.4 150 13 7 11.9 6.5
8500 17.6 63.7 115 7 4 9.8 5.4 | 18.8 65.8 150 13 7 10.0 5.5
8250 18.3 64.9 110 7 4 7.7 4.2 | 19.5 67.1 150 13 7 8.0 4.4
8000 18.9 66.0 110 7 4 10.1 5.5 | 20.1 68.2 150 14 7 9.9 5.4
7750 19.7 67.5 110 7 4 11.8 6.5 | 20.9 69.6 145 13 7 11.0 6.0
7500 20.5 68.9 110 7 4 8.8 4.8 | 21.7 71.1 145 13 6 8.5 4.7
7250 21.1 70.0 105 7 4 6.1 3.3 | 22.2 72.0 145 13 7 6.3 3.4
7000 21.6 70.9 105 7 4 9.7 5.3 | 22.8 73.0 145 13 7 9.4 5.2
6750 22.6 72.7 105 7 4 14.4 7.9 | 23.6 74.5 145 13 7 13.3 7.3
6500 23.6 74.5 105 7 4 11.8 6.5 | 24.6 76.3 145 12 6 11.0 6.0
6250 24.3 75.7 100 7 4 9.9 5.4 | 25.3 77.5 145 12 6 9.2 5.1
6000 25.1 77.2 100 7 4 9.2 5.1 | 26.0 78.8 145 12 6 9.3 5.1
5750 25.9 78.6 100 7 4 15.7 8.6 | 26.7 80.1 140 11 5 10.2 5.6
5500 27.6 81.7 095 7 3 30.5 16.8 | 27.6 81.7 140 10 5 13.4 7.4
________________________________________________________________________________
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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