Soaring Guidance
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
449
UXUS97 KGJT 281305
SRGGJT
Soaring Forecast
National Weather Service Grand Junction, Colorado
705 AM MDT Thursday, August 28, 2025
This forecast is for Thursday, August 28, 2025:
If the trigger temperature of 73.8 F/23.2 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1193 ft/min (6.1 m/s)
Maximum height of thermals.................. 16847 ft MSL (11238 ft AGL)
Forecast maximum temperature................... 84.0 F/29.3 C
Time of trigger temperature.................... 0945 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................. 14370 ft MSL (8761 ft AGL)
Thermal soaring outlook for Friday 08/29....... Excellent
Wave Soaring Index............................. Not available
Remarks...
Sunrise/Sunset.................... 06:39:50 / 19:50:36 MDT
Total possible sunshine........... 13 hr 10 min 46 sec (790 min 46 sec)
Altitude of sun at 13:15:13 MDT... 60.10 degrees
Upper air data from rawinsonde observation taken on 08/28/2025 at 0600 MDT
Freezing level.................. 14141 ft MSL (8532 ft AGL)
Convective condensation level... 14205 ft MSL (8596 ft AGL)
Lifted condensation level....... 15606 ft MSL (9996 ft AGL)
Lifted index.................... +0.2
K index......................... +26.1
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 -65.3 -85.5 260 30 15 2.8 1.5 M M M M M
45000 -58.5 -73.3 260 45 23 7.2 3.9 M M M M M
40000 -48.1 -54.6 260 56 29 5.4 2.9 M M M M M
38000 -44.9 -48.8 250 59 31 5.4 2.9 M M M M M
36000 -41.7 -43.1 250 64 33 5.3 2.9 M M M M M
34000 -37.6 -35.7 245 59 30 7.0 3.8 M M M M M
32000 -32.9 -27.2 240 52 27 7.8 4.3 M M M M M
30000 -28.5 -19.3 245 46 24 7.5 4.1 47.1 116.9 13.8 M M
29000 -26.3 -15.3 245 43 22 7.5 4.1 46.3 115.4 13.3 M M
28000 -24.1 -11.4 245 41 21 6.7 3.7 45.5 114.0 12.8 M M
27000 -22.2 -8.0 245 40 20 6.5 3.6 44.2 111.5 11.9 M M
26000 -20.3 -4.5 245 39 20 6.5 3.6 42.9 109.3 11.0 M M
25000 -18.4 -1.1 240 38 19 6.5 3.6 41.9 107.3 10.2 M M
24000 -16.6 2.1 240 37 19 6.3 3.4 40.5 104.9 9.2 M M
23000 -14.7 5.5 240 36 18 6.3 3.4 39.2 102.6 8.2 M M
22000 -12.9 8.8 240 35 18 6.2 3.4 38.1 100.5 7.2 M M
21000 -11.2 11.8 235 32 16 5.9 3.2 36.6 97.9 6.1 M M
20000 -9.5 14.9 230 28 14 5.9 3.2 35.3 95.5 4.9 M M
19500 -8.7 16.3 225 26 14 5.9 3.3 34.6 94.3 4.3 M M
19000 -7.8 18.0 225 24 13 5.4 3.0 34.0 93.1 3.8 M M
18500 -6.7 19.9 225 20 10 5.5 3.0 32.8 91.1 2.8 M M
18000 -6.0 21.2 225 17 9 3.6 2.0 32.0 89.6 2.0 M M
17500 -5.5 22.1 225 14 7 3.4 1.8 30.9 87.6 1.1 M M
17000 -5.0 23.0 225 11 6 3.9 2.1 29.8 85.7 0.1 M M
16500 -4.3 24.3 230 9 5 5.3 2.9 29.0 84.2 -0.7 961 4.9
16000 -3.5 25.7 235 8 4 5.1 2.8 28.3 82.9 -1.3 923 4.7
15500 -2.6 27.3 240 7 4 6.7 3.7 27.6 81.7 -1.9 882 4.5
15000 -1.7 28.9 245 6 3 6.6 3.6 27.1 80.8 -2.5 839 4.3
14500 -0.7 30.7 255 6 3 7.4 4.1 26.6 79.9 -2.9 795 4.0
14000 0.4 32.7 255 5 3 7.6 4.2 26.3 79.3 -3.3 747 3.8
13500 1.5 34.7 260 5 3 8.1 4.4 25.9 78.7 -3.7 698 3.5
13000 2.8 37.0 260 5 3 8.5 4.7 25.7 78.3 -3.9 646 3.3
12500 4.0 39.2 260 6 3 8.5 4.7 25.5 78.0 -4.1 593 3.0
12000 5.3 41.5 260 6 3 8.6 4.7 25.3 77.6 -4.3 541 2.7
11500 6.6 43.9 255 6 3 8.2 4.5 25.2 77.3 -4.5 488 2.5
11000 7.7 45.9 250 6 3 7.6 4.2 24.8 76.7 -4.9 440 2.2
10500 8.8 47.8 250 6 3 10.5 5.8 24.5 76.0 -5.3 392 2.0
10250 9.7 49.5 245 6 3 11.0 6.1 24.7 76.4 -5.1 357 1.8
10000 10.3 50.5 245 7 3 7.3 4.0 24.5 76.2 -5.2 332 1.7
9750 10.9 51.6 245 7 3 8.7 4.8 24.4 76.0 -5.4 306 1.6
9500 11.5 52.7 245 7 4 6.8 3.7 24.3 75.7 -5.5 281 1.4
9250 11.9 53.4 245 7 3 7.0 3.8 24.0 75.2 -5.8 260 1.3
9000 12.6 54.7 245 7 3 8.7 4.8 23.9 75.0 -5.9 235 1.2
8750 13.2 55.8 245 7 3 8.3 4.6 23.8 74.8 -6.0 209 1.1
8500 13.8 56.8 245 7 3 8.3 4.5 23.7 74.7 -6.2 183 0.9
8250 14.4 57.9 245 6 3 8.0 4.4 23.6 74.4 -6.3 158 0.8
8000 15.0 59.0 245 6 3 7.9 4.3 23.4 74.2 -6.5 133 0.7
7750 15.5 59.9 250 6 3 7.9 4.3 23.3 73.9 -6.6 108 0.6
7500 16.1 61.0 250 5 3 7.1 3.9 23.1 73.6 -6.8 84 0.4
7250 16.6 61.9 250 5 2 6.6 3.6 22.9 73.2 -7.1 62 0.3
7000 17.1 62.8 250 4 2 7.1 3.9 22.7 72.8 -7.3 39 0.2
6750 17.6 63.7 255 3 2 5.9 3.3 22.5 72.4 -7.5 17 0.1
6500 18.0 64.4 255 2 1 4.1 2.2 22.1 71.7 -7.9 M M
6250 18.2 64.8 255 1 1 3.5 1.9 21.6 70.9 -8.4 M M
6000 18.5 65.3 000 0 0 5.3 2.9 21.2 70.2 -8.9 M M
5750 18.9 66.0 000 0 0 2.6 1.4 20.9 69.5 -9.2 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 * * * * * *
08/28/2025 at 0900 MDT | 08/28/2025 at 1200 MDT
|
CAPE... +135.8 LI... -0.5 | CAPE... +208.3 LI... -1.3
CINH... -56.1 K Index... +25.1 | CINH... -3.4 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 -64.2 -83.6 250 40 20 2.1 1.2 | -64.2 -83.6 250 41 21 1.4 0.8
45000 -59.3 -74.7 250 58 30 5.7 3.1 | -59.9 -75.8 250 61 32 6.2 3.4
40000 -50.2 -58.4 255 60 31 6.0 3.3 | -50.2 -58.4 255 59 30 5.9 3.2
38000 -46.6 -51.9 265 63 32 6.0 3.3 | -46.7 -52.1 260 60 31 5.9 3.2
36000 -43.0 -45.4 270 66 34 6.3 3.5 | -43.1 -45.6 270 62 32 6.3 3.4
34000 -38.4 -37.1 265 60 31 7.8 4.3 | -38.4 -37.1 265 55 29 8.0 4.4
32000 -33.7 -28.7 260 54 28 7.6 4.2 | -33.6 -28.5 255 49 25 7.8 4.3
30000 -28.8 -19.8 255 50 26 8.2 4.5 | -28.8 -19.8 250 45 23 8.0 4.4
29000 -26.3 -15.3 255 48 25 8.2 4.5 | -26.4 -15.5 250 44 23 8.0 4.4
28000 -23.9 -11.0 255 46 24 7.3 4.0 | -24.1 -11.4 245 42 22 7.4 4.0
27000 -21.9 -7.4 250 43 22 6.6 3.6 | -21.5 -6.7 245 41 21 6.9 3.8
26000 -19.4 -2.9 245 38 20 6.6 3.6 | -19.4 -2.9 240 40 20 6.9 3.8
25000 -17.4 0.7 240 35 18 6.1 3.3 | -17.3 0.9 240 39 20 6.2 3.4
24000 -15.7 3.7 245 33 17 5.5 3.0 | -15.6 3.9 240 36 19 5.5 3.0
23000 -14.1 6.6 245 32 16 5.5 3.0 | -14.0 6.8 245 34 18 5.5 3.0
22000 -12.5 9.5 250 30 16 5.4 3.0 | -12.3 9.9 250 32 16 5.3 2.9
21000 -10.9 12.4 250 25 13 5.4 3.0 | -10.8 12.6 250 27 14 5.2 2.8
20000 -9.3 15.3 250 20 10 5.5 3.0 | -9.3 15.3 255 21 11 5.2 2.9
19500 -8.5 16.7 250 17 9 5.5 3.0 | -8.5 16.7 255 19 10 5.2 2.8
19000 -7.8 18.0 250 15 8 4.9 2.7 | -7.8 18.0 255 17 9 4.3 2.4
18500 -7.1 19.2 250 14 7 5.0 2.7 | -7.2 19.0 250 15 8 4.5 2.5
18000 -6.4 20.5 245 12 6 4.9 2.7 | -6.6 20.1 250 14 7 4.9 2.7
17500 -5.7 21.7 250 12 6 4.8 2.7 | -5.9 21.4 245 13 7 5.2 2.9
17000 -5.1 22.8 250 11 6 5.0 2.7 | -5.2 22.6 240 13 6 5.5 3.0
16500 -4.3 24.3 250 11 6 5.9 3.2 | -4.4 24.1 240 12 6 6.5 3.6
16000 -3.5 25.7 255 12 6 5.8 3.2 | -3.5 25.7 240 12 6 6.5 3.5
15500 -2.6 27.3 255 12 6 6.6 3.6 | -2.5 27.5 240 12 6 7.0 3.9
15000 -1.7 28.9 255 12 6 6.6 3.6 | -1.5 29.3 245 12 6 7.1 3.9
14500 -0.8 30.6 260 12 6 7.2 3.9 | -0.5 31.1 245 12 6 7.4 4.1
14000 0.3 32.5 260 12 6 7.5 4.1 | 0.6 33.1 245 11 6 7.6 4.2
13500 1.3 34.3 260 11 6 7.8 4.3 | 1.7 35.1 245 11 6 8.0 4.4
13000 2.5 36.5 260 11 6 8.1 4.5 | 2.9 37.2 250 11 6 8.4 4.6
12500 3.7 38.7 255 11 5 8.2 4.5 | 4.1 39.4 250 10 5 8.4 4.6
12000 4.9 40.8 255 10 5 8.5 4.7 | 5.3 41.5 250 10 5 8.4 4.6
11500 6.1 43.0 250 10 5 8.5 4.7 | 6.5 43.7 250 10 5 8.4 4.6
11000 7.3 45.1 250 9 5 8.4 4.6 | 7.7 45.9 250 9 5 8.3 4.5
10500 8.6 47.5 245 8 4 7.7 4.2 | 8.9 48.0 250 8 4 7.9 4.3
10250 9.1 48.4 245 7 4 7.4 4.0 | 9.5 49.1 250 8 4 8.4 4.6
10000 9.7 49.5 245 7 4 8.6 4.7 | 10.2 50.4 255 7 4 9.6 5.2
9750 10.3 50.5 240 6 3 9.0 4.9 | 10.8 51.4 255 7 3 9.5 5.2
9500 10.9 51.6 240 6 3 8.6 4.7 | 11.5 52.7 255 6 3 9.3 5.1
9250 11.5 52.7 235 5 3 7.9 4.3 | 12.2 54.0 255 6 3 8.9 4.9
9000 12.7 54.9 220 4 2 7.6 4.2 | 13.5 56.3 255 5 2 9.0 5.0
8750 13.2 55.8 215 4 2 7.4 4.1 | 14.2 57.6 255 4 2 8.8 4.9
8500 13.7 56.7 205 4 2 7.1 3.9 | 14.8 58.6 260 4 2 8.3 4.5
8250 14.3 57.7 195 4 2 7.2 3.9 | 15.4 59.7 260 4 2 9.3 5.1
8000 14.8 58.6 185 4 2 7.3 4.0 | 16.1 61.0 260 3 2 10.8 6.0
7750 15.3 59.5 180 4 2 6.5 3.5 | 16.9 62.4 260 3 2 9.7 5.3
7500 15.7 60.3 175 5 2 5.7 3.1 | 17.6 63.7 265 3 2 8.4 4.6
7250 16.2 61.2 170 5 3 6.2 3.4 | 18.2 64.8 265 3 2 9.3 5.1
7000 16.6 61.9 165 5 3 7.1 3.9 | 19.0 66.2 265 3 2 11.3 6.2
6750 17.1 62.8 160 5 2 6.6 3.6 | 19.8 67.6 265 3 1 10.8 5.9
6500 17.6 63.7 155 5 2 5.7 3.1 | 20.6 69.1 270 3 1 10.1 5.5
6250 18.0 64.4 150 4 2 6.8 3.7 | 21.3 70.3 270 3 1 9.1 5.0
6000 18.6 65.5 150 4 2 10.3 5.6 | 22.1 71.8 270 3 1 15.2 8.3
5750 19.4 66.9 140 3 2 13.5 7.4 | 23.7 74.7 270 2 1 29.0 15.9
5500 20.3 68.5 130 3 1 8.6 4.7 | 25.4 77.7 275 2 1 3.7 2.0
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
08/28/2025 at 1500 MDT | 08/28/2025 at 1800 MDT
|
CAPE... +120.0 LI... -1.5 | CAPE... +23.3 LI... -0.1
CINH... -10.2 K Index... +25.1 | CINH... -3.0 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 -64.6 -84.3 255 40 21 1.7 0.9 | -64.4 -83.9 255 38 19 2.7 1.5
45000 -59.7 -75.5 255 61 31 5.9 3.2 | -59.1 -74.4 255 60 31 4.7 2.6
40000 -50.8 -59.4 260 59 30 6.3 3.4 | -51.5 -60.7 260 61 31 7.5 4.1
38000 -47.0 -52.6 260 55 28 6.3 3.4 | -47.1 -52.8 260 61 31 7.5 4.1
36000 -43.3 -45.9 260 51 26 6.2 3.4 | -42.6 -44.7 260 60 31 7.5 4.1
34000 -37.8 -36.0 255 51 26 8.3 4.5 | -37.3 -35.1 255 56 29 7.9 4.3
32000 -32.9 -27.2 250 51 26 8.8 4.8 | -32.6 -26.7 255 51 26 8.3 4.6
30000 -28.3 -18.9 245 49 25 7.7 4.2 | -28.0 -18.4 250 49 25 7.7 4.2
29000 -26.0 -14.8 245 48 25 7.8 4.3 | -25.8 -14.4 250 47 24 7.8 4.3
28000 -23.7 -10.7 240 47 24 7.3 4.0 | -23.5 -10.3 245 46 24 6.7 3.7
27000 -21.6 -6.9 240 44 23 7.2 3.9 | -21.6 -6.9 245 44 23 6.5 3.6
26000 -19.4 -2.9 240 42 21 7.2 3.9 | -19.7 -3.5 245 42 21 6.5 3.6
25000 -17.3 0.9 240 39 20 7.0 3.9 | -17.8 -0.0 245 40 20 6.5 3.5
24000 -15.6 3.9 245 37 19 5.1 2.8 | -16.1 3.0 245 37 19 5.2 2.9
23000 -14.0 6.8 245 35 18 5.2 2.8 | -14.5 5.9 250 33 17 5.3 2.9
22000 -12.5 9.5 250 33 17 5.0 2.8 | -12.5 9.5 250 30 15 5.1 2.8
21000 -10.9 12.4 250 26 13 4.0 2.2 | -10.9 12.4 250 24 13 5.1 2.8
20000 -9.8 14.4 250 20 10 4.1 2.2 | -9.4 15.1 250 19 10 5.1 2.8
19500 -9.2 15.4 250 17 9 4.3 2.4 | -8.7 16.3 250 17 9 5.3 2.9
19000 -8.5 16.7 250 15 8 5.3 2.9 | -7.9 17.8 245 15 8 5.9 3.2
18500 -7.8 18.0 245 14 7 5.3 2.9 | -7.0 19.4 245 14 7 5.9 3.2
18000 -7.0 19.4 240 12 6 6.8 3.7 | -6.2 20.8 240 13 7 6.4 3.5
17500 -6.0 21.2 240 12 6 7.1 3.9 | -5.3 22.5 235 13 7 6.6 3.6
17000 -5.0 23.0 235 11 6 7.3 4.0 | -4.4 24.1 235 13 7 6.9 3.8
16500 -3.9 25.0 235 11 6 7.8 4.3 | -3.4 25.9 235 12 6 7.4 4.1
16000 -2.8 27.0 235 11 6 7.8 4.3 | -2.3 27.9 235 12 6 7.4 4.1
15500 -1.7 28.9 240 11 6 7.9 4.3 | -1.2 29.8 235 12 6 7.9 4.3
15000 -0.6 30.9 240 11 5 7.9 4.3 | -0.1 31.8 240 11 6 7.8 4.3
14500 0.6 33.1 245 10 5 8.1 4.4 | 1.0 33.8 245 11 6 8.2 4.5
14000 1.7 35.1 245 10 5 8.2 4.5 | 2.3 36.1 250 10 5 8.4 4.6
13500 2.9 37.2 250 10 5 8.4 4.6 | 3.5 38.3 255 10 5 8.7 4.8
13000 4.2 39.6 250 10 5 8.7 4.7 | 4.8 40.6 255 10 5 9.1 5.0
12500 5.4 41.7 250 10 5 8.7 4.8 | 6.2 43.2 260 9 5 9.2 5.0
12000 6.7 44.1 255 9 5 8.9 4.9 | 7.5 45.5 265 9 5 9.2 5.1
11500 8.0 46.4 255 9 5 8.8 4.9 | 8.9 48.0 270 9 5 9.2 5.1
11000 9.3 48.7 255 9 5 8.7 4.7 | 10.2 50.4 270 9 5 9.1 5.0
10500 10.6 51.1 260 9 5 7.3 4.0 | 11.6 52.9 275 9 5 7.0 3.9
10250 11.1 52.0 265 9 4 8.0 4.4 | 12.0 53.6 275 9 5 7.6 4.1
10000 11.8 53.2 265 9 4 10.4 5.7 | 12.8 55.0 275 9 4 10.7 5.9
9750 12.5 54.5 265 9 4 9.8 5.4 | 13.5 56.3 280 8 4 9.9 5.4
9500 13.3 55.9 265 8 4 9.7 5.3 | 14.3 57.7 280 8 4 10.1 5.5
9250 13.9 57.0 265 8 4 9.2 5.0 | 15.0 59.0 285 8 4 9.6 5.3
9000 14.6 58.3 265 8 4 9.2 5.1 | 15.7 60.3 285 8 4 9.2 5.0
8750 15.3 59.5 265 8 4 9.4 5.2 | 16.4 61.5 285 8 4 9.1 5.0
8500 16.0 60.8 265 8 4 9.1 5.0 | 17.0 62.6 290 7 4 8.8 4.8
8250 16.6 61.9 270 8 4 8.1 4.4 | 18.2 64.8 295 7 4 8.9 4.9
8000 18.1 64.6 270 8 4 12.1 6.6 | 19.0 66.2 295 7 3 11.0 6.0
7750 18.9 66.0 270 8 4 9.9 5.4 | 19.7 67.5 295 6 3 9.6 5.3
7500 19.5 67.1 270 8 4 7.6 4.2 | 20.4 68.7 295 6 3 8.3 4.5
7250 20.1 68.2 275 8 4 9.3 5.1 | 21.0 69.8 295 7 3 9.1 5.0
7000 20.9 69.6 275 8 4 12.2 6.7 | 21.7 71.1 295 6 3 10.8 5.9
6750 21.9 71.4 270 7 4 11.4 6.3 | 22.6 72.7 295 6 3 10.8 5.9
6500 22.6 72.7 275 7 4 10.3 5.6 | 23.3 73.9 295 6 3 10.4 5.7
6250 23.4 74.1 275 7 4 8.9 4.9 | 24.1 75.4 300 6 3 9.6 5.3
6000 24.1 75.4 275 7 4 13.6 7.5 | 24.8 76.6 300 6 3 10.3 5.7
5750 25.6 78.1 275 7 3 28.4 15.6 | 25.7 78.3 300 5 3 16.3 9.0
5500 27.4 81.3 280 6 3 9.4 5.2 | 27.1 80.8 300 6 3 16.3 9.0
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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