Soaring Guidance
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
057
UXUS97 KGJT 171306
SRGGJT
Soaring Forecast
National Weather Service Grand Junction, Colorado
706 AM MDT Sunday, August 17, 2025
This forecast is for Sunday, August 17, 2025:
If the trigger temperature of 81.7 F/27.6 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1255 ft/min (6.4 m/s)
Maximum height of thermals.................. 19025 ft MSL (13417 ft AGL)
Forecast maximum temperature................... 92.0 F/33.8 C
Time of trigger temperature.................... 1045 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................. 16040 ft MSL (10432 ft AGL)
Thermal soaring outlook for Monday 08/18....... Excellent
Wave Soaring Index............................. Not available
Remarks...
Sunrise/Sunset.................... 06:29:48 / 20:06:24 MDT
Total possible sunshine........... 13 hr 36 min 36 sec (816 min 36 sec)
Altitude of sun at 13:18:06 MDT... 63.72 degrees
Upper air data from rawinsonde observation taken on 08/17/2025 at 0600 MDT
Freezing level.................. 15554 ft MSL (9946 ft AGL)
Convective condensation level... 20544 ft MSL (14936 ft AGL)
Lifted condensation level....... 20238 ft MSL (14630 ft AGL)
Lifted index.................... -0.1
K index......................... +15.1
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 -64.5 -84.1 235 26 13 1.5 0.8 M M M M M
45000 -59.6 -75.3 245 33 17 6.2 3.4 M M M M M
40000 -49.9 -57.8 250 39 20 7.6 4.2 M M M M M
38000 -45.4 -49.7 255 40 20 7.6 4.2 M M M M M
36000 -40.8 -41.4 255 40 21 7.7 4.2 M M M M M
34000 -36.8 -34.2 255 41 21 6.5 3.6 M M M M M
32000 -32.5 -26.5 250 41 21 6.5 3.6 M M M M M
30000 -29.0 -20.2 250 37 19 5.6 3.1 46.2 115.2 9.8 M M
29000 -27.3 -17.1 245 35 18 5.6 3.1 44.7 112.4 8.8 M M
28000 -25.7 -14.3 245 32 17 5.5 3.0 43.2 109.8 7.7 M M
27000 -24.0 -11.2 245 29 15 5.5 3.0 41.4 106.6 6.4 M M
26000 -22.4 -8.3 245 26 14 5.5 3.0 39.8 103.7 5.2 M M
25000 -20.8 -5.4 240 23 12 6.0 3.3 38.4 101.1 4.1 M M
24000 -18.5 -1.3 240 22 11 7.9 4.3 37.5 99.5 3.4 M M
23000 -16.1 3.0 240 20 10 7.9 4.3 36.8 98.3 2.9 M M
22000 -13.8 7.2 240 19 10 7.7 4.2 36.3 97.3 2.4 M M
21000 -11.6 11.1 230 19 10 7.4 4.0 35.3 95.6 1.6 M M
20000 -9.4 15.1 225 19 10 7.4 4.1 34.5 94.1 0.9 M M
19500 -8.3 17.1 220 19 10 7.6 4.2 34.1 93.5 0.6 M M
19000 -6.9 19.6 215 19 10 6.4 3.5 33.4 92.0 -0.2 1242 6.3
18500 -6.0 21.2 215 19 10 6.4 3.5 32.8 91.0 -0.7 1201 6.1
18000 -5.1 22.8 210 19 10 6.1 3.4 32.2 89.9 -1.3 1159 5.9
17500 -4.2 24.4 215 18 9 6.2 3.4 31.6 88.8 -1.9 1118 5.7
17000 -3.3 26.1 215 17 9 7.2 3.9 31.0 87.8 -2.5 1077 5.5
16500 -2.1 28.2 215 16 8 8.1 4.5 30.7 87.2 -2.8 1027 5.2
16000 -0.9 30.4 220 14 7 8.2 4.5 30.4 86.8 -3.1 976 5.0
15500 0.3 32.5 220 13 7 8.6 4.7 30.2 86.4 -3.3 924 4.7
15000 1.6 34.9 225 11 6 8.6 4.7 30.0 86.0 -3.5 872 4.4
14500 2.8 37.0 225 10 5 8.8 4.8 29.8 85.7 -3.7 819 4.2
14000 4.1 39.4 225 9 5 8.8 4.8 29.7 85.4 -3.9 764 3.9
13500 5.5 41.9 220 8 4 8.8 4.9 29.5 85.2 -4.0 710 3.6
13000 6.8 44.2 220 7 3 8.9 4.9 29.4 84.9 -4.2 656 3.3
12500 8.1 46.6 215 6 3 8.9 4.9 29.3 84.7 -4.4 602 3.1
12000 9.4 48.9 215 5 2 8.8 4.8 29.1 84.4 -4.5 547 2.8
11500 10.7 51.3 210 4 2 8.3 4.6 29.0 84.2 -4.7 493 2.5
11000 11.9 53.4 210 4 2 7.3 4.0 28.6 83.6 -5.0 444 2.3
10500 13.1 55.6 210 3 2 10.8 5.9 28.5 83.2 -5.2 391 2.0
10250 14.0 57.2 215 3 1 9.8 5.4 28.5 83.4 -5.2 360 1.8
10000 14.6 58.3 215 3 1 7.9 4.4 28.4 83.2 -5.3 333 1.7
9750 15.2 59.4 215 2 1 8.9 4.9 28.3 83.0 -5.4 307 1.6
9500 15.8 60.4 215 2 1 6.8 3.8 28.2 82.8 -5.5 281 1.4
9250 16.3 61.3 210 2 1 7.1 3.9 27.9 82.3 -5.8 261 1.3
9000 16.9 62.4 200 2 1 8.9 4.9 27.9 82.1 -5.9 234 1.2
8750 17.6 63.7 190 2 1 9.0 4.9 27.8 82.0 -6.0 207 1.1
8500 18.2 64.8 180 2 1 6.9 3.8 27.7 81.8 -6.1 181 0.9
8250 18.6 65.5 165 3 1 5.2 2.9 27.4 81.2 -6.5 162 0.8
8000 19.0 66.2 155 3 2 6.5 3.5 27.1 80.7 -6.8 142 0.7
7750 19.5 67.1 150 4 2 6.4 3.5 26.8 80.3 -7.1 120 0.6
7500 19.9 67.8 145 4 2 4.2 2.3 26.5 79.7 -7.4 101 0.5
7250 20.1 68.2 140 5 3 2.2 1.2 26.0 78.7 -8.0 87 0.4
7000 20.3 68.5 135 6 3 2.9 1.6 25.4 77.8 -8.5 74 0.4
6750 20.4 68.7 130 6 3 0.4 0.2 24.8 76.7 -9.1 62 0.3
6500 20.3 68.5 125 6 3 -4.1 -2.2 24.0 75.1 -10.0 60 0.3
6250 19.9 67.8 120 6 3 -7.5 -4.1 22.8 73.0 -11.2 65 0.3
6000 19.5 67.1 115 6 3 1.7 0.9 21.7 71.0 -12.3 68 0.3
5750 19.7 67.5 110 6 3 -4.9 -2.7 21.2 70.1 -12.8 54 0.3
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 * * * * * *
08/17/2025 at 0900 MDT | 08/17/2025 at 1200 MDT
|
CAPE... +4.8 LI... -0.1 | CAPE... +22.6 LI... +0.4
CINH... -34.4 K Index... +19.4 | CINH... -3.8 K Index... +18.8
|
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 -63.7 -82.7 220 20 10 1.4 0.8 | -63.8 -82.8 215 20 10 1.5 0.8
45000 -58.8 -73.8 225 31 16 6.2 3.4 | -58.9 -74.0 225 29 15 6.3 3.4
40000 -49.3 -56.7 225 40 20 7.0 3.8 | -49.4 -56.9 230 38 19 6.6 3.6
38000 -45.0 -49.0 230 44 23 7.0 3.8 | -45.4 -49.7 230 42 21 6.6 3.6
36000 -40.8 -41.4 230 49 25 7.0 3.9 | -41.5 -42.7 235 45 23 6.6 3.6
34000 -37.0 -34.6 230 48 25 6.4 3.5 | -37.6 -35.7 230 45 23 6.5 3.6
32000 -33.1 -27.6 230 47 24 6.4 3.5 | -33.7 -28.7 230 45 23 6.5 3.6
30000 -29.5 -21.1 230 45 23 5.8 3.2 | -30.2 -22.4 230 42 22 5.5 3.0
29000 -27.8 -18.0 230 44 22 5.8 3.2 | -28.6 -19.5 230 41 21 5.6 3.0
28000 -26.1 -15.0 235 42 22 6.0 3.3 | -26.9 -16.4 230 39 20 6.2 3.4
27000 -23.6 -10.5 235 40 21 6.7 3.7 | -24.2 -11.6 230 38 19 7.3 4.0
26000 -21.6 -6.9 240 39 20 6.7 3.7 | -22.0 -7.6 235 36 19 7.3 4.0
25000 -19.6 -3.3 240 37 19 6.4 3.5 | -19.8 -3.6 240 35 18 7.2 3.9
24000 -17.8 -0.0 245 34 18 5.8 3.2 | -17.7 0.1 240 34 17 6.9 3.8
23000 -16.1 3.0 245 32 16 5.8 3.2 | -15.6 3.9 240 32 16 6.9 3.8
22000 -14.3 6.3 245 29 15 5.8 3.2 | -13.5 7.7 240 30 15 6.2 3.4
21000 -12.6 9.3 245 26 14 5.7 3.1 | -11.9 10.6 245 26 14 5.6 3.1
20000 -10.9 12.4 250 24 12 5.8 3.2 | -10.2 13.6 245 23 12 5.6 3.1
19500 -10.1 13.8 250 23 12 5.8 3.2 | -9.4 15.1 250 21 11 5.7 3.1
19000 -9.2 15.4 250 22 11 6.0 3.3 | -8.5 16.7 250 20 10 6.3 3.4
18500 -8.3 17.1 250 21 11 6.0 3.3 | -7.6 18.3 250 19 10 6.3 3.4
18000 -7.5 18.5 250 21 11 6.0 3.3 | -6.7 19.9 250 17 9 6.3 3.4
17500 -6.6 20.1 250 20 10 6.0 3.3 | -5.9 21.4 245 17 9 6.3 3.5
17000 -5.8 21.6 250 19 10 6.2 3.4 | -5.0 23.0 245 16 8 6.4 3.5
16500 -4.8 23.4 250 18 9 7.6 4.1 | -4.0 24.8 245 15 8 7.0 3.8
16000 -3.7 25.3 250 17 9 7.4 4.1 | -3.0 26.6 245 15 8 6.9 3.8
15500 -2.6 27.3 250 17 9 8.4 4.6 | -1.9 28.6 240 14 7 8.2 4.5
15000 -1.3 29.7 250 16 8 8.5 4.7 | -0.7 30.7 245 14 7 8.3 4.6
14500 -0.1 31.8 250 16 8 8.9 4.9 | 0.5 32.9 245 14 7 8.8 4.8
14000 1.3 34.3 250 15 8 9.1 5.0 | 1.8 35.2 245 14 7 9.0 4.9
13500 2.6 36.7 250 15 8 9.3 5.1 | 3.1 37.6 245 14 7 9.1 5.0
13000 4.0 39.2 250 14 7 9.4 5.2 | 4.5 40.1 245 13 7 9.3 5.1
12500 5.4 41.7 250 13 7 9.3 5.1 | 5.9 42.6 245 13 7 9.3 5.1
12000 6.7 44.1 250 12 6 9.0 4.9 | 7.3 45.1 250 12 6 9.4 5.2
11500 8.0 46.4 245 12 6 9.0 4.9 | 8.7 47.7 250 12 6 9.4 5.2
11000 9.3 48.7 245 11 6 8.8 4.8 | 10.1 50.2 250 11 6 9.1 5.0
10500 10.6 51.1 245 10 5 7.4 4.1 | 11.5 52.7 250 10 5 5.9 3.2
10250 11.1 52.0 240 9 5 7.0 3.9 | 11.8 53.2 250 10 5 6.7 3.7
10000 11.7 53.1 240 9 5 9.3 5.1 | 12.6 54.7 250 9 5 11.6 6.4
9750 12.4 54.3 240 8 4 9.4 5.1 | 13.3 55.9 250 9 5 10.5 5.7
9500 13.1 55.6 235 8 4 9.0 4.9 | 14.1 57.4 250 8 4 10.1 5.5
9250 13.7 56.7 235 7 4 8.0 4.4 | 14.8 58.6 255 8 4 8.4 4.6
9000 14.3 57.7 230 7 3 7.8 4.3 | 16.1 61.0 255 7 4 10.3 5.6
8750 15.4 59.7 220 6 3 7.5 4.1 | 16.9 62.4 255 7 3 9.2 5.1
8500 15.9 60.6 215 6 3 6.1 3.3 | 17.4 63.3 260 6 3 7.0 3.8
8250 16.4 61.5 205 5 3 6.4 3.5 | 18.0 64.4 265 6 3 9.0 5.0
8000 16.9 62.4 195 5 3 8.1 4.4 | 18.8 65.8 260 5 3 13.0 7.2
7750 17.4 63.3 185 5 3 6.2 3.4 | 19.7 67.5 260 5 3 10.2 5.6
7500 17.8 64.0 180 5 3 3.8 2.1 | 20.3 68.5 265 5 3 6.9 3.8
7250 18.1 64.6 175 5 3 5.0 2.7 | 20.9 69.6 270 5 3 8.7 4.8
7000 18.5 65.3 170 5 3 8.1 4.4 | 21.7 71.1 270 5 2 13.2 7.2
6750 19.2 66.6 160 5 2 7.4 4.1 | 22.7 72.9 265 5 2 12.1 6.6
6500 19.6 67.3 155 4 2 5.4 3.0 | 23.5 74.3 270 5 2 9.7 5.3
6250 20.0 68.0 150 4 2 5.2 2.9 | 24.2 75.6 275 4 2 9.0 4.9
6000 20.5 68.9 145 4 2 9.8 5.4 | 24.9 76.8 280 4 2 14.5 7.9
5750 21.6 70.9 140 3 2 20.4 11.2 | 26.6 79.9 275 4 2 30.2 16.6
5500 22.8 73.0 130 3 1 1.9 1.0 | 28.6 83.5 290 4 2 13.0 7.2
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
08/17/2025 at 1500 MDT | 08/17/2025 at 1800 MDT
|
CAPE... +2.2 LI... +0.6 | CAPE... 0.0 LI... +0.9
CINH... -0.3 K Index... +21.5 | CINH... -0.1 K Index... +20.4
|
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 -63.5 -82.3 215 22 12 1.7 1.0 | -63.4 -82.1 215 22 11 1.4 0.8
45000 -58.7 -73.7 220 31 16 5.7 3.2 | -58.8 -73.8 225 32 16 5.9 3.2
40000 -49.9 -57.8 230 37 19 7.0 3.8 | -49.8 -57.6 235 34 17 6.8 3.8
38000 -45.7 -50.3 230 40 21 7.0 3.8 | -45.8 -50.4 235 37 19 6.8 3.8
36000 -41.5 -42.7 235 44 23 7.0 3.9 | -41.7 -43.1 235 41 21 6.9 3.8
34000 -37.3 -35.1 235 45 23 6.2 3.4 | -37.4 -35.3 235 43 22 6.3 3.4
32000 -33.6 -28.5 230 46 23 6.3 3.5 | -33.6 -28.5 235 44 23 6.4 3.5
30000 -30.2 -22.4 230 43 22 5.7 3.1 | -30.2 -22.4 230 41 21 5.6 3.1
29000 -28.5 -19.3 230 42 21 5.7 3.1 | -28.5 -19.3 230 40 20 5.6 3.1
28000 -26.8 -16.2 225 40 21 6.8 3.7 | -26.8 -16.2 230 38 20 6.7 3.7
27000 -24.6 -12.3 230 38 20 7.3 4.0 | -24.7 -12.5 230 36 18 7.1 3.9
26000 -22.4 -8.3 230 36 19 7.3 4.0 | -22.5 -8.5 235 34 17 7.1 3.9
25000 -20.3 -4.5 235 34 18 7.3 4.0 | -20.4 -4.7 235 32 16 7.2 4.0
24000 -18.1 -0.6 235 33 17 7.3 4.0 | -18.1 -0.6 235 30 16 7.8 4.3
23000 -15.9 3.4 235 31 16 7.3 4.0 | -15.7 3.7 235 29 15 7.8 4.3
22000 -13.7 7.3 235 30 15 7.0 3.8 | -13.4 7.9 235 28 14 7.4 4.1
21000 -11.6 11.1 235 25 13 5.6 3.1 | -11.2 11.8 230 24 12 5.8 3.2
20000 -10.0 14.0 235 21 11 5.7 3.1 | -9.5 14.9 225 20 10 6.0 3.3
19500 -9.2 15.4 235 19 10 6.2 3.4 | -8.7 16.3 225 19 10 6.4 3.5
19000 -8.2 17.2 230 17 9 7.2 3.9 | -7.7 18.1 220 17 9 7.1 3.9
18500 -7.2 19.0 230 16 8 7.2 3.9 | -6.7 19.9 215 16 8 7.1 3.9
18000 -6.1 21.0 230 15 8 7.9 4.3 | -5.7 21.7 210 15 8 8.2 4.5
17500 -5.0 23.0 225 15 7 8.0 4.4 | -4.5 23.9 210 15 8 8.4 4.6
17000 -3.9 25.0 225 14 7 8.2 4.5 | -3.3 26.1 210 14 7 8.6 4.7
16500 -2.7 27.1 225 13 7 8.5 4.6 | -2.0 28.4 210 13 7 9.0 4.9
16000 -1.4 29.5 220 13 7 8.5 4.7 | -0.7 30.7 210 13 7 9.0 4.9
15500 -0.2 31.6 220 12 6 8.4 4.6 | 0.6 33.1 210 12 6 8.9 4.9
15000 1.0 33.8 220 12 6 8.4 4.6 | 2.0 35.6 210 12 6 8.9 4.9
14500 2.3 36.1 225 11 6 9.0 4.9 | 3.3 37.9 215 11 6 9.2 5.0
14000 3.6 38.5 225 11 6 9.1 5.0 | 4.7 40.5 215 10 5 9.3 5.1
13500 5.0 41.0 230 11 5 9.2 5.0 | 6.1 43.0 220 10 5 9.3 5.1
13000 6.3 43.3 230 10 5 9.2 5.0 | 7.4 45.3 225 9 5 9.3 5.1
12500 7.7 45.9 235 10 5 9.2 5.0 | 8.8 47.8 230 9 5 9.3 5.1
12000 9.1 48.4 235 9 5 9.1 5.0 | 10.2 50.4 235 9 5 9.3 5.1
11500 10.4 50.7 240 9 5 9.1 5.0 | 11.6 52.9 240 9 4 9.2 5.0
11000 11.8 53.2 245 9 5 9.0 4.9 | 12.9 55.2 245 8 4 8.4 4.6
10500 13.2 55.8 255 9 5 6.8 3.7 | 14.1 57.4 255 8 4 10.5 5.8
10250 13.6 56.5 260 9 5 7.5 4.1 | 15.0 59.0 255 8 4 11.1 6.1
10000 14.4 57.9 260 9 5 11.0 6.0 | 15.7 60.3 255 8 4 8.7 4.8
9750 15.1 59.2 265 9 5 10.2 5.6 | 16.4 61.5 260 8 4 9.4 5.1
9500 15.9 60.6 265 9 5 9.8 5.4 | 17.1 62.8 260 8 4 9.0 4.9
9250 16.6 61.9 270 9 5 9.0 4.9 | 17.8 64.0 265 9 4 8.8 4.8
9000 17.3 63.1 270 10 5 9.7 5.3 | 18.4 65.1 270 9 5 9.0 5.0
8750 18.0 64.4 270 10 5 10.3 5.6 | 19.1 66.4 270 9 5 9.4 5.1
8500 18.8 65.8 270 10 5 9.7 5.3 | 19.8 67.6 275 9 4 8.9 4.9
8250 19.4 66.9 275 10 5 8.3 4.6 | 20.4 68.7 275 9 5 6.7 3.7
8000 20.1 68.2 280 10 5 9.7 5.3 | 21.7 71.1 280 9 5 11.0 6.0
7750 21.7 71.1 275 10 5 9.9 5.4 | 22.5 72.5 280 9 5 9.6 5.3
7500 22.4 72.3 280 10 5 7.9 4.3 | 23.1 73.6 285 9 5 8.2 4.5
7250 23.0 73.4 285 11 6 9.2 5.1 | 23.7 74.7 285 10 5 9.0 4.9
7000 23.8 74.8 285 11 5 12.5 6.9 | 24.5 76.1 285 10 5 11.8 6.5
6750 24.7 76.5 280 10 5 11.7 6.4 | 25.4 77.7 285 9 5 11.2 6.1
6500 25.5 77.9 285 10 5 10.4 5.7 | 26.2 79.2 285 9 5 9.7 5.3
6250 26.3 79.3 285 11 6 9.3 5.1 | 26.9 80.4 290 10 5 9.6 5.3
6000 27.0 80.6 290 11 5 13.9 7.6 | 27.6 81.7 290 10 5 10.7 5.9
5750 28.7 83.7 285 9 5 30.1 16.5 | 28.6 83.5 290 8 4 17.4 9.6
5500 31.0 87.8 290 10 5 23.8 13.0 | 30.2 86.4 295 9 4 24.9 13.7
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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