Soaring Guidance
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
695
UXUS97 KGJT 171306
SRGGJT
Soaring Forecast
National Weather Service Grand Junction, Colorado
706 AM MDT Friday, October 17, 2025
This forecast is for Friday, October 17, 2025:
If the trigger temperature of 55.1 F/12.8 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 425 ft/min (2.2 m/s)
Maximum height of thermals.................. 11415 ft MSL (5808 ft AGL)
Forecast maximum temperature................... 60.0 F/16.0 C
Time of trigger temperature.................... 1230 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 9335 ft MSL (3729 ft AGL)
Thermal soaring outlook for Saturday 10/18..... Good
Wave Soaring Index............................. Not available
Remarks...
Sunrise/Sunset.................... 07:26:25 / 18:32:17 MDT
Total possible sunshine........... 11 hr 5 min 51 sec (665 min 51 sec)
Altitude of sun at 12:59:21 MDT... 41.33 degrees
Upper air data from rawinsonde observation taken on 10/17/2025 at 0600 MDT
Freezing level.................. 10135 ft MSL (4528 ft AGL)
Convective condensation level... 16683 ft MSL (11076 ft AGL)
Lifted condensation level....... 13873 ft MSL (8267 ft AGL)
Lifted index.................... +9.2
K index......................... +9.7
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 -63.3 -81.9 290 38 20 2.7 1.5 M M M M M
45000 -58.8 -73.8 290 53 27 5.0 2.8 M M M M M
40000 -51.2 -60.2 300 60 31 5.1 2.8 M M M M M
38000 -50.1 -58.2 305 65 33 1.0 0.5 M M M M M
36000 -49.5 -57.1 315 71 37 1.0 0.5 M M M M M
34000 -47.1 -52.8 325 78 40 7.0 3.9 M M M M M
32000 -42.8 -45.0 330 84 43 7.0 3.9 M M M M M
30000 -38.2 -36.8 335 87 45 8.5 4.6 37.1 98.8 16.3 M M
29000 -35.7 -32.3 335 86 44 8.5 4.6 36.6 97.8 16.1 M M
28000 -33.1 -27.6 335 84 43 8.5 4.6 36.1 97.1 16.0 M M
27000 -30.6 -23.1 330 82 42 8.7 4.8 35.7 96.3 15.8 M M
26000 -28.0 -18.4 330 79 41 8.7 4.8 35.2 95.4 15.6 M M
25000 -25.4 -13.7 325 76 39 8.7 4.8 34.9 94.8 15.5 M M
24000 -22.9 -9.2 325 72 37 7.0 3.8 34.5 94.1 15.4 M M
23000 -20.8 -5.4 320 66 34 6.9 3.8 33.3 92.0 14.6 M M
22000 -18.8 -1.8 315 61 31 6.9 3.8 32.3 90.1 13.9 M M
21000 -16.9 1.6 310 56 29 4.8 2.6 31.1 88.1 13.1 M M
20000 -15.4 4.3 310 53 27 5.0 2.8 29.4 84.9 11.7 M M
19500 -14.3 6.3 310 50 26 5.1 2.8 28.2 82.7 10.8 M M
19000 -13.5 7.7 310 49 25 5.0 2.7 27.4 81.4 10.1 M M
18500 -12.9 8.8 305 47 24 4.4 2.4 26.5 79.8 9.4 M M
18000 -12.2 10.0 305 45 23 4.5 2.4 25.6 78.1 8.6 M M
17500 -11.6 11.1 305 43 22 5.2 2.9 24.8 76.6 7.9 M M
17000 -10.8 12.6 305 41 21 5.4 3.0 24.0 75.3 7.2 M M
16500 -10.0 14.0 305 40 21 5.7 3.1 23.3 74.0 6.6 M M
16000 -9.1 15.6 305 39 20 6.2 3.4 22.7 72.8 6.0 M M
15500 -8.3 17.1 305 37 19 6.2 3.4 22.1 71.7 5.5 M M
15000 -7.4 18.7 305 36 18 5.7 3.1 21.4 70.6 4.9 M M
14500 -6.5 20.3 305 34 18 5.8 3.2 20.8 69.4 4.4 M M
14000 -5.7 21.7 305 32 17 5.0 2.7 20.1 68.1 3.8 M M
13500 -4.9 23.2 305 31 16 5.0 2.7 19.3 66.7 3.1 M M
13000 -4.2 24.4 305 29 15 5.0 2.7 18.5 65.3 2.4 M M
12500 -3.4 25.9 305 26 14 5.0 2.8 17.7 63.9 1.6 M M
12000 -2.7 27.1 300 24 12 4.9 2.7 17.0 62.6 0.9 M M
11500 -2.0 28.4 300 22 11 4.9 2.7 16.2 61.1 0.1 M M
11000 -1.3 29.7 295 20 10 4.8 2.6 15.4 59.7 -0.6 397 2.0
10500 -0.7 30.7 290 19 10 4.8 2.6 14.6 58.3 -1.4 362 1.8
10250 -0.3 31.5 290 18 9 6.0 3.3 14.3 57.7 -1.7 343 1.7
10000 0.2 32.4 285 17 9 5.9 3.2 14.0 57.2 -2.0 322 1.6
9750 0.6 33.1 285 16 8 5.2 2.9 13.6 56.5 -2.4 302 1.5
9500 1.0 33.8 285 15 8 5.1 2.8 13.3 55.9 -2.7 283 1.4
9250 1.4 34.5 280 14 7 6.2 3.4 13.0 55.3 -3.1 264 1.3
9000 1.9 35.4 280 12 6 6.9 3.8 12.7 54.9 -3.3 241 1.2
8750 2.4 36.3 275 11 6 6.2 3.4 12.5 54.4 -3.5 220 1.1
8500 2.8 37.0 270 10 5 6.4 3.5 12.2 54.0 -3.8 198 1.0
8250 3.3 37.9 270 8 4 6.4 3.5 12.0 53.5 -4.1 176 0.9
8000 3.8 38.8 265 8 4 6.7 3.7 11.7 53.1 -4.3 154 0.8
7750 4.3 39.7 265 7 4 7.0 3.8 11.5 52.7 -4.5 131 0.7
7500 4.8 40.6 260 6 3 6.7 3.7 11.3 52.3 -4.8 109 0.6
7250 5.3 41.5 250 5 3 5.7 3.1 11.0 51.8 -5.0 87 0.4
7000 5.7 42.3 235 4 2 5.3 2.9 10.7 51.2 -5.4 68 0.3
6750 6.1 43.0 225 3 2 6.2 3.4 10.4 50.6 -5.7 48 0.2
6500 6.5 43.7 210 3 2 3.8 2.1 10.0 50.1 -6.0 28 0.1
6250 6.6 43.9 185 3 2 -0.8 -0.4 9.4 48.9 -6.7 18 0.1
6000 6.7 44.1 165 4 2 6.1 3.4 8.7 47.7 -7.4 9 0.0
5750 7.2 45.0 155 4 2 0.8 0.5 8.5 47.4 -7.6 M M
5500 M M M M M M M M M M M M
5250 M M M M M M M M M M M M
5000 M M M M M M M M M M M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
10/17/2025 at 0900 MDT | 10/17/2025 at 1200 MDT
|
CAPE... 0.0 LI... +4.7 | CAPE... 0.0 LI... +4.2
CINH... -0.0 K Index... +10.1 | CINH... -0.0 K Index... +4.7
|
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 -59.6 -75.3 255 21 11 2.7 1.5 | -59.9 -75.8 260 20 10 2.6 1.4
45000 -55.3 -67.5 250 28 14 3.9 2.2 | -55.8 -68.4 260 26 13 3.7 2.0
40000 -49.3 -56.7 255 32 16 4.0 2.2 | -50.3 -58.5 265 21 11 3.7 2.0
38000 -47.3 -53.1 255 32 16 3.1 1.7 | -48.5 -55.3 285 16 8 2.8 1.5
36000 -45.2 -49.4 250 31 16 3.1 1.7 | -46.6 -51.9 330 16 8 2.8 1.5
34000 -43.3 -45.9 250 31 16 3.2 1.8 | -44.7 -48.5 360 24 12 3.9 2.1
32000 -41.4 -42.5 250 32 17 3.2 1.8 | -42.3 -44.1 015 38 20 3.9 2.1
30000 -39.2 -38.6 255 31 16 4.7 2.6 | -39.5 -39.1 020 48 25 6.3 3.5
29000 -37.8 -36.0 255 29 15 4.7 2.6 | -37.6 -35.7 025 46 24 6.4 3.5
28000 -36.4 -33.5 260 26 13 4.7 2.6 | -35.7 -32.3 025 45 23 6.4 3.5
27000 -34.9 -30.8 265 23 12 4.7 2.6 | -33.8 -28.8 025 43 22 6.9 3.8
26000 -33.6 -28.5 265 22 11 4.7 2.6 | -31.7 -25.1 025 38 20 7.2 3.9
25000 -32.2 -26.0 270 20 10 4.7 2.6 | -29.5 -21.1 025 34 17 7.2 3.9
24000 -30.8 -23.4 270 18 9 5.2 2.8 | -27.4 -17.3 030 29 15 6.6 3.6
23000 -28.5 -19.3 270 17 9 8.0 4.4 | -25.8 -14.4 020 22 11 5.0 2.8
22000 -25.5 -13.9 270 17 9 8.0 4.4 | -23.9 -11.0 355 13 7 5.1 2.8
21000 -23.1 -9.6 270 17 9 8.3 4.5 | -22.2 -8.0 325 11 6 7.5 4.1
20000 -20.7 -5.3 270 17 9 8.2 4.5 | -20.0 -4.0 310 11 6 7.3 4.0
19500 -19.5 -3.1 270 16 8 8.3 4.5 | -18.9 -2.0 305 11 6 7.3 4.0
19000 -18.2 -0.8 275 16 8 8.3 4.6 | -17.9 -0.2 300 11 6 7.2 4.0
18500 -17.1 1.2 275 16 8 7.5 4.1 | -16.8 1.8 295 12 6 7.5 4.1
18000 -16.0 3.2 275 16 8 7.5 4.1 | -15.6 3.9 295 12 6 7.5 4.1
17500 -14.8 5.4 275 16 8 7.2 3.9 | -14.5 5.9 295 12 6 7.2 4.0
17000 -13.9 7.0 275 16 8 6.7 3.7 | -13.5 7.7 290 12 6 6.9 3.8
16500 -12.9 8.8 275 16 8 6.7 3.7 | -12.5 9.5 290 12 6 6.9 3.8
16000 -11.9 10.6 280 16 8 6.1 3.3 | -11.5 11.3 290 12 6 6.1 3.4
15500 -11.0 12.2 280 15 8 6.2 3.4 | -10.6 12.9 290 11 6 6.3 3.4
15000 -10.1 13.8 280 15 8 5.8 3.2 | -9.7 14.5 290 11 6 5.7 3.1
14500 -9.3 15.3 280 14 7 5.7 3.1 | -8.9 16.0 290 11 6 5.7 3.1
14000 -8.5 16.7 280 13 7 5.3 2.9 | -8.1 17.4 290 10 5 5.3 2.9
13500 -7.7 18.1 280 12 6 5.1 2.8 | -7.4 18.7 290 10 5 5.2 2.8
13000 -7.0 19.4 280 11 6 5.0 2.8 | -6.6 20.1 285 10 5 5.1 2.8
12500 -6.3 20.7 275 10 5 5.0 2.8 | -5.9 21.4 285 9 5 5.1 2.8
12000 -5.5 22.1 275 9 4 5.4 2.9 | -5.2 22.6 285 9 4 5.2 2.9
11500 -4.7 23.5 270 8 4 5.9 3.2 | -4.4 24.1 285 8 4 5.4 3.0
11000 -3.9 25.0 270 6 3 6.2 3.4 | -3.6 25.5 280 7 4 5.7 3.1
10500 -2.9 26.8 265 5 3 6.9 3.8 | -2.7 27.1 285 7 4 6.0 3.3
10250 -2.5 27.5 265 5 2 5.1 2.8 | -2.3 27.9 285 7 3 6.8 3.7
10000 -2.2 28.0 265 4 2 5.6 3.1 | -1.8 28.8 285 6 3 7.6 4.1
9750 -1.6 29.1 265 3 2 7.7 4.2 | -1.2 29.8 285 6 3 7.3 4.0
9500 -1.1 30.0 265 3 1 7.2 3.9 | -0.7 30.7 290 6 3 7.4 4.1
9250 -0.6 30.9 270 2 1 7.1 3.9 | -0.2 31.6 290 5 3 7.2 3.9
9000 -0.1 31.8 270 1 1 6.7 3.7 | 0.4 32.7 290 5 3 7.3 4.0
8750 0.4 32.7 270 1 0 7.0 3.8 | 0.9 33.6 295 5 2 7.9 4.3
8500 1.0 33.8 000 0 0 7.5 4.1 | 1.5 34.7 295 4 2 8.5 4.6
8250 1.5 34.7 000 0 0 6.8 3.7 | 2.5 36.5 305 4 2 5.4 3.0
8000 2.4 36.3 070 1 0 6.7 3.7 | 3.0 37.4 305 3 2 8.7 4.8
7750 3.0 37.4 070 1 1 7.4 4.1 | 3.8 38.8 310 3 2 11.2 6.2
7500 3.5 38.3 075 1 1 6.0 3.3 | 4.5 40.1 310 3 1 7.8 4.3
7250 3.9 39.0 080 2 1 4.8 2.6 | 5.0 41.0 310 3 1 4.6 2.5
7000 4.3 39.7 085 2 1 6.2 3.4 | 5.4 41.7 310 3 1 10.6 5.8
6750 4.8 40.6 095 2 1 6.3 3.5 | 6.4 43.5 310 3 1 13.0 7.1
6500 5.2 41.4 100 2 1 4.9 2.7 | 7.2 45.0 310 3 1 9.1 5.0
6250 5.5 41.9 100 2 1 4.7 2.6 | 7.9 46.2 305 3 1 8.4 4.6
6000 5.9 42.6 100 3 1 5.1 2.8 | 8.5 47.3 305 3 1 10.7 5.9
5750 6.2 43.2 115 2 1 4.3 2.3 | 9.6 49.3 305 3 1 18.9 10.4
5500 6.3 43.3 130 2 1 -5.6 -3.1 | 11.2 52.2 305 3 1 23.9 13.1
5250 M M M M M M M | M M M M M M M
5000 M M M M M M M | M M M M M M M
10/17/2025 at 1500 MDT | 10/17/2025 at 1800 MDT
|
CAPE... 0.0 LI... +4.9 | CAPE... 0.0 LI... +6.2
CINH... 0.0 K Index... -1.0 | CINH... 0.0 K Index... -0.9
|
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 -60.3 -76.5 270 19 10 2.3 1.3 | -62.0 -79.6 295 19 10 1.8 1.0
45000 -56.6 -69.9 295 21 11 3.4 1.8 | -58.8 -73.8 340 24 12 3.9 2.1
40000 -51.6 -60.9 330 20 10 3.4 1.8 | -52.9 -63.2 345 34 17 3.9 2.1
38000 -49.8 -57.6 355 25 13 2.8 1.5 | -50.9 -59.6 350 36 19 3.3 1.8
36000 -47.9 -54.2 010 34 18 2.8 1.5 | -48.9 -56.0 360 39 20 3.3 1.8
34000 -45.8 -50.4 015 42 22 4.9 2.7 | -46.1 -51.0 360 43 22 5.5 3.0
32000 -42.8 -45.0 015 46 24 4.9 2.7 | -42.8 -45.0 360 48 25 5.5 3.0
30000 -39.4 -38.9 015 48 25 7.3 4.0 | -39.0 -38.2 360 48 25 7.9 4.3
29000 -37.2 -35.0 015 45 23 7.3 4.0 | -36.6 -33.9 360 45 23 7.9 4.3
28000 -35.0 -31.0 015 43 22 7.3 4.0 | -34.2 -29.6 360 42 21 7.9 4.3
27000 -32.8 -27.0 010 41 21 8.0 4.4 | -31.9 -25.4 360 39 20 8.0 4.4
26000 -30.4 -22.7 010 37 19 8.0 4.4 | -29.5 -21.1 360 37 19 8.0 4.4
25000 -28.0 -18.4 015 34 18 8.0 4.4 | -27.1 -16.8 360 35 18 8.0 4.4
24000 -25.7 -14.3 015 31 16 7.5 4.1 | -24.8 -12.6 360 33 17 7.4 4.1
23000 -23.6 -10.5 010 28 14 7.0 3.8 | -22.6 -8.7 360 30 15 7.1 3.9
22000 -21.0 -5.8 010 23 12 7.0 3.8 | -20.5 -4.9 355 27 14 7.1 3.9
21000 -19.1 -2.4 010 20 10 5.3 2.9 | -17.9 -0.2 355 24 12 6.3 3.4
20000 -17.4 0.7 360 17 9 5.4 3.0 | -16.0 3.2 355 22 11 6.3 3.5
19500 -16.6 2.1 355 15 8 5.4 3.0 | -15.1 4.8 355 21 11 6.3 3.5
19000 -15.8 3.6 350 14 7 5.4 3.0 | -14.2 6.4 350 20 10 6.4 3.5
18500 -15.0 5.0 340 13 7 5.6 3.1 | -13.3 8.1 350 19 10 6.0 3.3
18000 -14.1 6.6 335 12 6 5.6 3.1 | -12.4 9.7 350 19 10 6.1 3.3
17500 -13.3 8.1 325 12 6 5.8 3.2 | -11.5 11.3 345 18 9 5.8 3.2
17000 -12.4 9.7 320 11 6 6.1 3.3 | -10.6 12.9 345 17 9 5.5 3.0
16500 -11.5 11.3 310 11 6 6.1 3.3 | -9.8 14.4 340 16 8 5.5 3.0
16000 -10.6 12.9 305 11 6 6.1 3.3 | -9.0 15.8 340 15 8 4.9 2.7
15500 -9.7 14.5 305 11 6 6.1 3.3 | -8.3 17.1 335 14 7 4.9 2.7
15000 -8.8 16.2 300 11 6 5.8 3.2 | -7.5 18.5 330 13 7 5.1 2.8
14500 -8.0 17.6 295 11 6 5.8 3.2 | -6.8 19.8 325 12 6 5.1 2.8
14000 -7.1 19.2 295 11 6 5.5 3.0 | -6.0 21.2 320 11 6 5.2 2.8
13500 -6.4 20.5 295 10 5 5.4 3.0 | -5.3 22.5 315 10 5 5.2 2.9
13000 -5.6 21.9 290 10 5 5.4 3.0 | -4.5 23.9 310 9 5 5.2 2.8
12500 -4.8 23.4 290 9 5 5.4 3.0 | -3.8 25.2 300 9 4 5.1 2.8
12000 -4.0 24.8 285 9 4 5.5 3.0 | -3.1 26.4 290 8 4 5.4 3.0
11500 -3.2 26.2 285 8 4 5.7 3.1 | -2.3 27.9 290 8 4 5.8 3.2
11000 -2.4 27.7 290 7 4 6.0 3.3 | -1.4 29.5 285 7 4 6.0 3.3
10500 -1.5 29.3 290 7 3 6.2 3.4 | -0.5 31.1 285 7 4 6.2 3.4
10250 -1.0 30.2 290 6 3 7.7 4.2 | -0.0 32.0 285 7 4 7.5 4.1
10000 -0.4 31.3 295 6 3 8.4 4.6 | 0.6 33.1 280 7 3 8.5 4.6
9750 0.2 32.4 295 6 3 7.6 4.2 | 1.1 34.0 285 7 3 7.9 4.3
9500 0.7 33.3 295 6 3 7.9 4.3 | 1.7 35.1 285 7 3 7.9 4.3
9250 1.3 34.3 295 6 3 7.6 4.1 | 2.3 36.1 285 7 3 8.3 4.5
9000 1.9 35.4 295 5 3 7.8 4.3 | 2.9 37.2 285 7 3 8.5 4.7
8750 2.5 36.5 295 5 3 8.4 4.6 | 3.5 38.3 285 7 3 7.7 4.3
8500 3.1 37.6 295 5 3 9.0 4.9 | 4.1 39.4 285 7 3 7.5 4.1
8250 3.7 38.7 295 5 3 7.5 4.1 | 4.6 40.3 290 7 3 7.4 4.1
8000 4.7 40.5 295 5 2 9.2 5.0 | 5.7 42.3 290 6 3 7.8 4.3
7750 5.5 41.9 295 5 3 11.9 6.5 | 6.3 43.3 290 6 3 8.6 4.7
7500 6.3 43.3 300 5 3 8.7 4.8 | 6.9 44.4 295 6 3 7.1 3.9
7250 6.8 44.2 295 5 3 5.9 3.2 | 7.3 45.1 295 6 3 5.3 2.9
7000 7.3 45.1 295 5 3 10.9 6.0 | 7.8 46.0 295 6 3 8.4 4.6
6750 8.3 46.9 295 5 3 12.9 7.1 | 8.5 47.3 295 6 3 10.4 5.7
6500 9.1 48.4 295 5 2 9.6 5.2 | 9.2 48.6 295 5 3 8.9 4.9
6250 9.8 49.6 295 5 3 8.7 4.8 | 9.8 49.6 300 6 3 8.7 4.8
6000 10.5 50.9 295 5 3 9.9 5.4 | 10.5 50.9 300 6 3 8.8 4.8
5750 11.4 52.5 295 4 2 16.6 9.1 | 11.1 52.0 300 5 2 7.7 4.2
5500 13.2 55.8 295 5 2 36.9 20.3 | 11.5 52.7 305 4 2 3.3 1.8
5250 M M M M M M M | M M M M M M M
5000 M M M M M M M | M M M M M M M
________________________________________________________________________________
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 at Walker Field in Grand
Junction, Colorado at
North Latitude: 39 deg 07 min 00.001 sec
West Longitude: 108 deg 31 min 59.998 sec
Elevation: 4839 feet (1475 meters)
and may not be representative of other areas along the Western Slope of
Colorado. 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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