Soaring Guidance
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
789
UXUS97 KGJT 051306
SRGGJT
Soaring Forecast
National Weather Service Grand Junction, Colorado
606 AM MST Friday, December 5, 2025
This forecast is for Friday, December 5, 2025:
If the trigger temperature of 46.9 F/8.3 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 182 ft/min (0.9 m/s)
Maximum height of thermals.................. 7772 ft MSL (2165 ft AGL)
Forecast maximum temperature................... 40.0 F/4.9 C
Time of trigger temperature.................... None
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................. 6267 ft MSL (659 ft AGL)
Thermal soaring outlook for Saturday 12/06..... Fair
Wave Soaring Index............................. Not available
Remarks...
Sunrise/Sunset.................... 07:18:39 / 16:51:17 MST
Total possible sunshine........... 9 hr 32 min 38 sec (572 min 38 sec)
Altitude of sun at 12:04:58 MST... 28.40 degrees
Upper air data from rawinsonde observation taken on 12/05/2025 at 0500 MST
Freezing level.................. Entire airmass below 32 F / 0 C
Convective condensation level... 12406 ft MSL (6799 ft AGL)
Lifted condensation level....... 9056 ft MSL (3449 ft AGL)
Lifted index.................... +11.7
K index......................... +17.6
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 -61.6 -78.9 295 66 34 3.1 1.7 M M M M M
45000 -56.8 -70.2 295 76 39 1.7 0.9 M M M M M
40000 -54.6 -66.3 315 94 48 1.4 0.8 M M M M M
38000 -53.1 -63.6 315 102 52 3.7 2.0 M M M M M
36000 -50.9 -59.6 315 109 56 3.7 2.0 M M M M M
34000 -48.0 -54.4 315 114 59 7.1 3.9 M M M M M
32000 -43.7 -46.7 315 112 57 7.1 3.9 M M M M M
30000 -39.8 -39.6 315 106 55 3.9 2.2 36.7 98.1 24.3 M M
29000 -38.6 -37.5 310 98 51 4.2 2.3 34.4 93.9 22.8 M M
28000 -37.3 -35.1 310 90 46 4.2 2.3 32.2 90.0 21.4 M M
27000 -36.1 -33.0 310 82 42 4.4 2.4 30.2 86.4 20.1 M M
26000 -33.9 -29.0 305 78 40 8.0 4.4 29.2 84.6 19.5 M M
25000 -31.6 -24.9 305 74 38 8.0 4.4 28.5 83.3 19.2 M M
24000 -29.2 -20.6 300 71 37 8.1 4.4 27.9 82.3 18.9 M M
23000 -27.0 -16.6 300 70 36 7.2 3.9 27.0 80.7 18.4 M M
22000 -24.9 -12.8 300 69 36 7.2 3.9 26.1 78.9 17.8 M M
21000 -22.7 -8.9 300 68 35 7.1 3.9 25.2 77.4 17.3 M M
20000 -20.9 -5.6 300 66 34 6.1 3.4 24.0 75.1 16.4 M M
19500 -20.0 -4.0 300 66 34 6.2 3.4 23.3 74.0 15.9 M M
19000 -18.6 -1.5 300 64 33 6.1 3.4 22.4 72.3 15.2 M M
18500 -17.7 0.1 300 63 33 5.8 3.2 21.9 71.3 14.8 M M
18000 -16.9 1.6 300 61 31 5.3 2.9 21.1 69.9 14.2 M M
17500 -16.1 3.0 300 58 30 5.2 2.9 20.3 68.6 13.6 M M
17000 -15.3 4.5 300 55 28 6.4 3.5 19.6 67.4 13.1 M M
16500 -14.3 6.3 300 53 27 6.3 3.5 19.1 66.3 12.6 M M
16000 -13.4 7.9 300 50 26 5.9 3.2 18.5 65.2 12.2 M M
15500 -12.6 9.3 300 49 25 5.8 3.2 17.8 64.0 11.6 M M
15000 -11.7 10.9 300 47 24 5.7 3.1 17.1 62.8 11.1 M M
14500 -10.9 12.4 300 46 24 5.6 3.1 16.4 61.6 10.5 M M
14000 -10.1 13.8 300 44 23 5.6 3.1 15.8 60.4 9.9 M M
13500 -9.3 15.3 300 44 23 5.7 3.1 15.1 59.2 9.3 M M
13000 -8.5 16.7 295 44 23 5.7 3.1 14.4 58.0 8.7 M M
12500 -7.6 18.3 295 43 22 5.9 3.2 13.8 56.8 8.1 M M
12000 -6.8 19.8 290 42 21 5.9 3.3 13.2 55.7 7.6 M M
11500 -6.0 21.2 285 41 21 4.2 2.3 12.4 54.3 6.9 M M
11000 -5.4 22.3 275 40 20 4.4 2.4 11.6 52.8 6.1 M M
10500 -4.8 23.4 270 38 20 4.0 2.2 10.7 51.2 5.3 M M
10250 -4.5 23.9 270 38 20 4.1 2.3 10.2 50.4 4.9 M M
10000 -4.2 24.4 265 37 19 4.0 2.2 9.8 49.6 4.5 M M
9750 -3.9 25.0 265 35 18 3.2 1.8 9.3 48.8 4.1 M M
9500 -3.7 25.3 260 34 17 2.7 1.5 8.8 47.8 3.5 M M
9250 -3.5 25.7 260 32 17 3.0 1.6 8.2 46.8 3.0 M M
9000 -3.2 26.2 260 30 16 3.1 1.7 7.7 45.9 2.6 M M
8750 -3.0 26.6 255 28 14 2.9 1.6 7.2 45.0 2.1 M M
8500 -2.8 27.0 255 26 13 2.8 1.5 6.7 44.0 1.5 M M
8250 -2.6 27.3 250 24 12 3.0 1.7 6.1 43.0 1.0 M M
8000 -2.3 27.9 250 21 11 3.5 1.9 5.6 42.1 0.6 M M
7750 -2.1 28.2 250 19 10 3.5 1.9 5.2 41.3 0.1 M M
7500 -1.8 28.8 245 16 8 3.7 2.1 4.7 40.4 -0.4 169 0.9
7250 -1.5 29.3 245 14 7 2.8 1.5 4.2 39.6 -0.8 154 0.8
7000 -1.4 29.5 240 10 5 2.9 1.6 3.7 38.6 -1.4 141 0.7
6750 -1.1 30.0 235 9 4 3.8 2.1 3.2 37.7 -1.9 126 0.6
6500 -0.8 30.6 230 7 3 3.6 2.0 2.7 36.9 -2.3 111 0.6
6250 -0.6 30.9 220 5 3 2.5 1.4 2.2 36.0 -2.8 96 0.5
6000 -0.4 31.3 200 3 2 2.0 1.1 1.7 35.0 -3.4 84 0.4
5750 -0.2 31.6 195 2 1 3.8 2.1 1.1 34.0 -3.9 71 0.4
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 * * * * * *
12/05/2025 at 0800 MST | 12/05/2025 at 1100 MST
|
CAPE... 0.0 LI... +5.4 | CAPE... 0.0 LI... +5.2
CINH... -0.2 K Index... +14.3 | CINH... -0.2 K Index... +14.2
|
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 -59.4 -74.9 310 44 22 4.6 2.5 | -59.1 -74.4 305 43 22 4.7 2.6
45000 -52.5 -62.5 310 48 25 5.1 2.8 | -52.1 -61.8 310 45 23 3.6 2.0
40000 -45.0 -49.0 325 56 29 5.0 2.8 | -46.5 -51.7 320 60 31 3.7 2.0
38000 -43.5 -46.3 325 59 30 -0.5 -0.3 | -45.1 -49.2 325 64 33 0.8 0.4
36000 -43.9 -47.0 325 61 32 -0.5 -0.3 | -44.6 -48.3 330 65 33 0.8 0.4
34000 -44.2 -47.6 330 63 32 -0.3 -0.2 | -44.1 -47.4 335 66 34 1.4 0.8
32000 -44.4 -47.9 330 57 29 -0.3 -0.2 | -43.2 -45.8 340 71 37 1.4 0.8
30000 -44.5 -48.1 325 51 26 2.2 1.2 | -42.4 -44.3 345 76 39 1.6 0.9
29000 -43.5 -46.3 325 48 25 3.2 1.7 | -41.9 -43.4 340 69 36 1.6 0.9
28000 -42.6 -44.7 325 46 24 3.2 1.7 | -41.4 -42.5 340 63 33 1.6 0.9
27000 -41.6 -42.9 325 44 23 2.9 1.6 | -41.0 -41.8 335 57 30 1.3 0.7
26000 -39.6 -39.3 325 44 22 9.0 4.9 | -39.4 -38.9 330 53 27 7.5 4.1
25000 -36.8 -34.2 320 44 23 9.1 5.0 | -37.1 -34.8 330 50 26 7.5 4.1
24000 -34.1 -29.4 320 45 23 9.1 5.0 | -34.9 -30.8 325 47 24 7.5 4.1
23000 -31.5 -24.7 320 45 23 8.7 4.8 | -32.4 -26.3 325 45 23 8.8 4.8
22000 -28.2 -18.8 320 44 23 8.7 4.8 | -29.1 -20.4 315 44 23 8.8 4.8
21000 -25.6 -14.1 320 43 22 8.0 4.4 | -26.5 -15.7 315 44 23 8.3 4.5
20000 -23.5 -10.3 325 42 22 7.3 4.0 | -24.1 -11.4 315 45 23 7.9 4.3
19500 -22.4 -8.3 325 42 21 7.3 4.0 | -23.0 -9.4 315 46 24 7.9 4.3
19000 -21.3 -6.3 325 41 21 7.2 4.0 | -21.8 -7.2 320 47 24 7.8 4.3
18500 -20.3 -4.5 325 40 21 7.0 3.8 | -20.6 -5.1 320 48 25 7.3 4.0
18000 -19.3 -2.7 320 39 20 6.1 3.4 | -19.7 -3.5 320 48 24 6.3 3.5
17500 -18.4 -1.1 320 38 20 6.2 3.4 | -18.8 -1.8 320 47 24 6.4 3.5
17000 -17.6 0.3 320 37 19 5.4 3.0 | -17.9 -0.2 320 46 24 5.4 3.0
16500 -16.8 1.8 320 36 19 5.5 3.0 | -17.1 1.2 325 45 23 5.5 3.0
16000 -16.0 3.2 315 35 18 5.4 2.9 | -16.3 2.7 325 43 22 5.8 3.2
15500 -15.2 4.6 315 34 17 5.3 2.9 | -15.4 4.3 325 40 21 5.9 3.2
15000 -14.4 6.1 315 32 17 5.2 2.9 | -14.6 5.7 325 38 20 6.0 3.3
14500 -13.7 7.3 310 31 16 5.1 2.8 | -13.7 7.3 325 35 18 6.2 3.4
14000 -12.9 8.8 310 30 15 5.1 2.8 | -12.8 9.0 325 32 17 6.1 3.3
13500 -12.2 10.0 310 28 15 5.1 2.8 | -11.9 10.6 325 30 15 5.5 3.0
13000 -11.4 11.5 305 27 14 5.1 2.8 | -11.1 12.0 320 27 14 5.5 3.0
12500 -10.7 12.7 305 26 13 4.7 2.6 | -10.4 13.3 320 25 13 4.6 2.5
12000 -10.0 14.0 300 25 13 4.8 2.6 | -9.7 14.5 315 23 12 4.6 2.5
11500 -9.4 15.1 300 23 12 3.6 2.0 | -9.1 15.6 310 21 11 3.9 2.1
11000 -8.9 16.0 295 22 11 3.7 2.0 | -8.5 16.7 305 20 10 3.8 2.1
10500 -8.4 16.9 295 20 10 2.4 1.3 | -8.1 17.4 300 19 10 2.4 1.3
10250 -8.2 17.2 290 19 10 2.4 1.3 | -7.9 17.8 295 18 9 2.6 1.4
10000 -8.0 17.6 290 18 9 2.9 1.6 | -7.7 18.1 290 17 9 2.3 1.2
9750 -7.8 18.0 285 16 8 3.2 1.8 | -7.6 18.3 290 16 8 2.7 1.5
9500 -7.6 18.3 280 14 7 2.9 1.6 | -7.3 18.9 285 14 7 3.4 1.9
9250 -7.3 18.9 275 13 7 2.8 1.6 | -7.1 19.2 280 13 7 2.8 1.5
9000 -7.1 19.2 270 11 6 3.4 1.9 | -6.8 19.8 270 12 6 4.6 2.5
8750 -6.8 19.8 265 11 6 4.4 2.4 | -6.4 20.5 265 12 6 5.4 2.9
8500 -6.5 20.3 260 10 5 4.5 2.5 | -6.1 21.0 265 11 5 4.1 2.2
8250 -5.8 21.6 245 8 4 4.7 2.6 | -5.7 21.7 260 9 5 4.5 2.5
8000 -5.4 22.3 240 8 4 5.3 2.9 | -5.1 22.8 250 8 4 5.4 3.0
7750 -5.0 23.0 230 7 3 6.0 3.3 | -4.6 23.7 245 7 3 7.0 3.9
7500 -4.5 23.9 220 6 3 5.3 2.9 | -4.1 24.6 240 5 3 5.2 2.9
7250 -4.2 24.4 205 5 3 4.2 2.3 | -3.8 25.2 235 4 2 2.3 1.3
7000 -3.8 25.2 195 5 3 5.3 2.9 | -3.5 25.7 225 3 2 7.0 3.9
6750 -3.4 25.9 185 5 3 5.8 3.2 | -2.8 27.0 210 3 2 10.6 5.8
6500 -3.0 26.6 175 5 3 4.1 2.3 | -2.1 28.2 200 3 1 8.4 4.6
6250 -2.8 27.0 165 5 3 3.6 2.0 | -1.5 29.3 195 2 1 7.8 4.3
6000 -2.5 27.5 155 5 3 3.6 2.0 | -0.9 30.4 185 2 1 9.6 5.2
5750 -2.3 27.9 150 4 2 -0.1 -0.1 | -0.0 32.0 195 2 1 14.8 8.1
5500 -2.8 27.0 125 3 1 -15.0 -8.3 | 1.1 34.0 185 1 1 13.5 7.4
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
12/05/2025 at 1400 MST | 12/05/2025 at 1700 MST
|
CAPE... 0.0 LI... +4.8 | CAPE... 0.0 LI... +5.2
CINH... -0.1 K Index... +6.8 | CINH... -0.1 K Index... +0.8
|
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 -59.2 -74.6 305 45 23 4.1 2.3 | -59.6 -75.3 305 46 24 4.4 2.4
45000 -52.8 -63.0 315 49 25 3.5 1.9 | -53.0 -63.4 315 50 26 3.4 1.9
40000 -47.4 -53.3 320 63 33 3.6 2.0 | -48.3 -54.9 310 59 30 3.0 1.6
38000 -46.3 -51.3 325 69 36 -0.3 -0.1 | -47.6 -53.7 320 70 36 -0.2 -0.1
36000 -46.5 -51.7 335 76 39 -0.3 -0.1 | -47.7 -53.9 340 96 49 -0.2 -0.1
34000 -46.3 -51.3 345 87 45 4.8 2.7 | -47.7 -53.9 345 124 64 3.3 1.8
32000 -43.7 -46.7 345 107 55 4.3 2.4 | -45.4 -49.7 345 125 64 3.8 2.1
30000 -41.1 -42.0 350 123 63 3.8 2.1 | -43.1 -45.6 345 125 64 5.6 3.1
29000 -40.0 -40.0 350 112 58 3.7 2.0 | -41.3 -42.3 345 116 60 5.7 3.1
28000 -38.9 -38.0 350 102 52 3.7 2.0 | -39.6 -39.3 345 107 55 5.7 3.1
27000 -37.8 -36.0 350 91 47 3.6 2.0 | -37.9 -36.2 340 98 50 5.7 3.1
26000 -36.4 -33.5 345 81 42 5.2 2.8 | -35.4 -31.7 340 86 44 7.1 3.9
25000 -34.8 -30.6 345 71 36 5.2 2.9 | -33.3 -27.9 340 77 39 7.1 3.9
24000 -33.3 -27.9 340 61 31 5.2 2.8 | -31.1 -24.0 340 67 35 7.1 3.9
23000 -31.4 -24.5 335 54 28 7.2 3.9 | -29.1 -20.4 340 61 31 6.6 3.6
22000 -29.2 -20.6 335 50 26 7.2 4.0 | -27.1 -16.8 335 55 28 6.6 3.6
21000 -26.5 -15.7 325 45 23 7.7 4.2 | -25.1 -13.2 330 49 25 6.8 3.8
20000 -24.1 -11.4 325 45 23 8.1 4.5 | -23.0 -9.4 330 46 24 7.1 3.9
19500 -22.9 -9.2 325 45 23 8.1 4.5 | -21.9 -7.4 325 45 23 7.1 3.9
19000 -21.7 -7.1 325 45 23 8.1 4.5 | -20.9 -5.6 325 44 23 7.1 3.9
18500 -20.5 -4.9 320 44 23 7.9 4.3 | -19.8 -3.6 325 43 22 7.0 3.9
18000 -19.3 -2.7 320 44 23 7.5 4.1 | -18.8 -1.8 320 42 22 6.7 3.7
17500 -18.2 -0.8 320 44 23 7.6 4.2 | -17.8 -0.0 320 41 21 6.7 3.7
17000 -17.2 1.0 320 44 23 5.7 3.2 | -16.8 1.8 320 40 21 6.5 3.6
16500 -16.3 2.7 320 43 22 5.9 3.2 | -15.8 3.6 320 39 20 6.4 3.5
16000 -15.5 4.1 320 42 22 4.8 2.6 | -14.8 5.4 320 38 19 5.7 3.2
15500 -14.9 5.2 320 40 20 4.4 2.4 | -14.1 6.6 320 37 19 5.1 2.8
15000 -14.3 6.3 320 38 19 4.3 2.4 | -13.3 8.1 320 35 18 4.8 2.6
14500 -13.7 7.3 320 35 18 4.3 2.4 | -12.7 9.1 315 33 17 3.8 2.1
14000 -13.1 8.4 320 32 16 4.5 2.5 | -12.2 10.0 315 31 16 3.9 2.1
13500 -12.4 9.7 320 29 15 5.6 3.1 | -11.6 11.1 315 29 15 4.5 2.5
13000 -11.6 11.1 320 26 14 5.6 3.1 | -11.0 12.2 310 27 14 4.5 2.5
12500 -10.7 12.7 315 24 12 6.3 3.5 | -10.3 13.5 310 25 13 5.0 2.7
12000 -9.8 14.4 315 22 11 6.2 3.4 | -9.6 14.7 305 23 12 5.0 2.7
11500 -8.9 16.0 310 20 10 5.5 3.0 | -8.9 16.0 300 21 11 5.1 2.8
11000 -8.1 17.4 305 18 9 5.4 3.0 | -8.2 17.2 295 19 10 5.2 2.8
10500 -7.5 18.5 300 17 9 3.5 1.9 | -7.5 18.5 285 18 9 4.4 2.4
10250 -7.2 19.0 295 17 9 3.5 1.9 | -7.2 19.0 285 17 9 4.0 2.2
10000 -7.0 19.4 290 16 8 4.1 2.3 | -6.8 19.8 280 16 8 5.9 3.2
9750 -6.6 20.1 285 15 8 4.5 2.5 | -6.3 20.7 270 15 8 6.8 3.7
9500 -6.3 20.7 280 14 7 4.2 2.3 | -5.9 21.4 265 14 7 5.5 3.0
9250 -6.0 21.2 275 13 7 4.0 2.2 | -5.4 22.3 260 14 7 5.8 3.2
9000 -5.7 21.7 270 12 6 5.2 2.9 | -5.0 23.0 255 13 7 5.7 3.1
8750 -5.2 22.6 270 13 7 5.5 3.0 | -4.2 24.4 250 13 7 5.7 3.1
8500 -4.9 23.2 265 11 6 4.4 2.4 | -3.7 25.3 250 12 6 5.8 3.2
8250 -4.5 23.9 260 10 5 4.7 2.6 | -3.3 26.1 245 11 5 4.1 2.2
8000 -4.2 24.4 260 9 5 3.2 1.8 | -3.1 26.4 250 10 5 4.3 2.4
7750 -3.4 25.9 260 7 4 8.2 4.5 | -2.6 27.3 245 8 4 5.8 3.2
7500 -2.9 26.8 255 5 3 6.3 3.5 | -2.2 28.0 240 7 3 5.5 3.0
7250 -2.5 27.5 260 4 2 3.2 1.8 | -1.8 28.8 235 5 3 5.2 2.8
7000 -2.2 28.0 265 3 2 8.7 4.8 | -1.4 29.5 240 4 2 6.4 3.5
6750 -1.2 29.8 260 3 2 13.1 7.2 | -0.8 30.6 225 3 2 7.9 4.3
6500 -0.4 31.3 260 3 1 9.2 5.0 | -0.3 31.5 215 3 1 7.7 4.2
6250 0.2 32.4 265 2 1 7.9 4.3 | 0.3 32.5 210 2 1 8.1 4.5
6000 0.8 33.4 275 2 1 9.8 5.4 | 0.9 33.6 185 1 1 7.1 3.9
5750 1.7 35.1 260 2 1 14.4 7.9 | 1.2 34.2 205 1 1 -1.1 -0.6
5500 2.8 37.0 280 2 1 14.1 7.7 | 0.3 32.5 150 1 1 -25.9 -14.2
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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