Soaring Guidance
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
387
UXUS97 KGJT 171306
SRGGJT
Soaring Forecast
National Weather Service Grand Junction, Colorado
706 AM MDT Thursday, April 17, 2025
This forecast is for Thursday, April 17, 2025:
If the trigger temperature of 41.2 F/5.1 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 1940 ft/min (9.9 m/s)
Maximum height of thermals.................. 26993 ft MSL (21385 ft AGL)
Forecast maximum temperature................... 70.0 F/21.6 C
Time of trigger temperature.................... None
Time of overdevelopment........................ 1800 MDT
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ Between 20 mph and 30 mph
Height of the -3 thermal index................. 21823 ft MSL (16216 ft AGL)
Thermal soaring outlook for Friday 04/18....... Excellent
Wave Soaring Index............................. Not available
Remarks...
Sunrise/Sunset.................... 06:33:33 / 19:53:35 MDT
Total possible sunshine........... 13 hr 20 min 2 sec (800 min 2 sec)
Altitude of sun at 13:13:34 MDT... 61.49 degrees
Upper air data from rawinsonde observation taken on 04/17/2025 at 0600 MDT
Freezing level.................. 6796 ft MSL (1188 ft AGL)
Convective condensation level... 11679 ft MSL (6071 ft AGL)
Lifted condensation level....... 17647 ft MSL (12040 ft AGL)
Lifted index.................... -5.2
K index......................... +6.4
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 -53.2 -63.8 230 45 23 1.4 0.8 M M M M M
45000 -51.0 -59.8 230 49 25 1.4 0.8 M M M M M
40000 -49.7 -57.5 230 51 26 0.8 0.5 M M M M M
38000 -49.2 -56.6 230 53 27 0.3 0.2 M M M M M
36000 -49.0 -56.2 235 59 30 0.4 0.2 M M M M M
34000 -48.7 -55.7 235 66 34 0.4 0.2 M M M M M
32000 -49.4 -56.9 230 71 36 -1.4 -0.8 M M M M M
30000 -50.2 -58.4 220 77 39 -2.0 -1.1 M M M M M
29000 -49.0 -56.2 220 76 39 7.3 4.0 23.0 73.4 1.4 M M
28000 -46.7 -52.1 215 74 38 7.4 4.1 22.0 71.6 0.7 M M
27000 -44.5 -48.1 215 71 37 7.4 4.1 21.1 70.1 0.0 M M
26000 -42.2 -44.0 210 69 36 8.9 4.9 20.5 68.8 -0.5 1843 9.4
25000 -39.6 -39.3 215 68 35 8.7 4.8 20.0 68.0 -0.9 1735 8.8
24000 -37.0 -34.6 220 66 34 8.8 4.8 19.6 67.3 -1.2 1627 8.3
23000 -34.5 -30.1 225 64 33 6.5 3.6 19.2 66.5 -1.6 1523 7.7
22000 -32.6 -26.7 225 61 31 6.4 3.5 17.9 64.2 -2.7 1436 7.3
21000 -30.6 -23.1 230 57 29 6.4 3.5 16.7 62.1 -3.7 1348 6.8
20000 -28.7 -19.7 235 53 28 6.7 3.7 15.6 60.1 -4.7 1260 6.4
19500 -27.2 -17.0 240 50 26 6.7 3.7 14.8 58.6 -5.5 1193 6.1
19000 -26.2 -15.2 240 49 25 6.7 3.7 14.2 57.6 -6.0 1148 5.8
18500 -25.2 -13.4 245 47 24 6.7 3.7 13.7 56.7 -6.4 1103 5.6
18000 -24.2 -11.6 245 45 23 6.0 3.3 13.2 55.8 -6.9 1059 5.4
17500 -23.3 -9.9 250 41 21 5.8 3.2 12.5 54.5 -7.6 1019 5.2
17000 -22.5 -8.5 250 38 20 5.8 3.2 11.9 53.3 -8.2 978 5.0
16500 -21.6 -6.9 250 34 18 5.8 3.2 11.2 52.1 -8.9 937 4.8
16000 -20.8 -5.4 255 31 16 5.8 3.2 10.5 50.9 -9.5 897 4.6
15500 -19.8 -3.6 260 27 14 6.7 3.7 9.9 49.9 -10.1 854 4.3
15000 -18.9 -2.0 260 25 13 6.5 3.6 9.4 48.9 -10.7 810 4.1
14500 -17.8 -0.0 265 23 12 7.3 4.0 8.9 48.1 -11.2 765 3.9
14000 -16.8 1.8 265 21 11 7.3 4.0 8.5 47.3 -11.6 718 3.6
13500 -15.7 3.7 260 19 10 6.7 3.7 8.1 46.5 -12.1 672 3.4
13000 -14.7 5.5 260 18 9 6.6 3.6 7.6 45.6 -12.7 627 3.2
12500 -13.7 7.3 255 16 8 7.0 3.8 7.1 44.7 -13.2 583 3.0
12000 -12.7 9.1 250 15 8 7.1 3.9 6.7 44.0 -13.7 536 2.7
11500 -11.6 11.1 245 14 7 8.1 4.4 6.3 43.3 -14.1 489 2.5
11000 -10.3 13.5 240 13 7 8.4 4.6 6.1 42.9 -14.4 437 2.2
10500 -9.1 15.6 240 12 6 7.0 3.9 5.8 42.4 -14.8 386 2.0
10250 -8.6 16.5 240 12 6 8.2 4.5 5.6 42.1 -15.0 363 1.8
10000 -7.9 17.8 240 11 6 9.8 5.4 5.6 42.0 -15.1 335 1.7
9750 -7.2 19.0 235 11 6 8.7 4.8 5.5 41.9 -15.2 307 1.6
9500 -6.7 19.9 235 11 5 7.7 4.2 5.4 41.7 -15.4 282 1.4
9250 -6.1 21.0 235 10 5 8.0 4.4 5.2 41.4 -15.6 257 1.3
9000 -5.5 22.1 230 10 5 8.7 4.8 5.1 41.2 -15.7 231 1.2
8750 -4.8 23.4 230 9 5 8.6 4.7 5.0 41.1 -15.8 204 1.0
8500 -4.2 24.4 230 9 5 8.3 4.5 4.9 40.9 -16.0 179 0.9
8250 -3.6 25.5 235 9 5 8.3 4.5 4.8 40.7 -16.2 153 0.8
8000 -3.0 26.6 240 9 5 7.7 4.2 4.7 40.5 -16.3 128 0.6
7750 -2.4 27.7 240 8 4 7.9 4.4 4.5 40.2 -16.6 103 0.5
7500 -1.8 28.8 240 8 4 8.2 4.5 4.4 39.9 -16.7 78 0.4
7250 -1.2 29.8 240 8 4 8.4 4.6 4.3 39.7 -16.9 53 0.3
7000 -0.6 30.9 240 7 3 8.1 4.5 4.2 39.6 -17.1 28 0.1
6750 -0.1 31.8 240 6 3 7.6 4.2 4.0 39.3 -17.3 4 0.0
6500 0.5 32.9 240 5 2 7.9 4.3 3.9 39.0 -17.6 M M
6250 1.0 33.8 240 4 2 7.4 4.0 3.7 38.7 -17.8 M M
6000 1.5 34.7 245 3 1 6.1 3.4 3.5 38.3 -18.1 M M
5750 1.9 35.4 245 2 1 5.4 3.0 3.2 37.8 -18.5 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 * * * * * *
04/17/2025 at 0900 MDT | 04/17/2025 at 1200 MDT
|
CAPE... +34.5 LI... -1.2 | CAPE... +68.7 LI... -0.9
CINH... -14.3 K Index... +18.4 | CINH... -1.6 K Index... +17.9
|
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 -55.8 -68.4 245 46 24 -0.4 -0.2 | -55.6 -68.1 240 47 24 0.3 0.2
45000 -56.5 -69.7 245 63 33 -0.4 -0.2 | -55.1 -67.2 235 58 30 0.3 0.2
40000 -56.6 -69.9 240 92 47 -0.1 -0.1 | -54.7 -66.5 235 83 43 0.3 0.1
38000 -55.8 -68.4 235 99 51 3.4 1.9 | -54.3 -65.7 235 91 47 1.4 0.8
36000 -53.7 -64.7 235 102 52 3.4 1.9 | -53.4 -64.1 235 95 49 1.4 0.8
34000 -51.6 -60.9 235 103 53 5.8 3.2 | -52.5 -62.5 235 98 51 3.8 2.1
32000 -47.7 -53.9 235 92 47 6.4 3.5 | -49.0 -56.2 235 86 45 5.8 3.2
30000 -43.8 -46.8 235 81 42 7.6 4.2 | -45.5 -49.9 235 75 38 7.3 4.0
29000 -41.5 -42.7 235 79 41 7.8 4.3 | -43.1 -45.6 235 72 37 8.1 4.5
28000 -39.1 -38.4 235 77 40 7.8 4.3 | -40.6 -41.1 235 70 36 8.2 4.5
27000 -36.2 -33.2 235 75 38 7.6 4.2 | -37.6 -35.7 235 68 35 8.1 4.5
26000 -34.2 -29.6 235 72 37 6.7 3.7 | -35.2 -31.4 235 65 34 8.0 4.4
25000 -32.1 -25.8 235 69 36 6.7 3.7 | -32.8 -27.0 235 63 32 8.0 4.4
24000 -30.1 -22.2 235 66 34 6.9 3.8 | -30.3 -22.5 235 61 31 8.3 4.6
23000 -28.4 -19.1 235 62 32 5.4 2.9 | -28.6 -19.5 235 56 29 5.1 2.8
22000 -26.8 -16.2 235 58 30 5.4 3.0 | -27.0 -16.6 235 49 25 5.2 2.8
21000 -25.2 -13.4 235 54 28 5.9 3.2 | -25.5 -13.9 235 43 22 5.5 3.0
20000 -23.2 -9.8 230 50 26 6.9 3.8 | -23.6 -10.5 230 40 20 6.4 3.5
19500 -22.2 -8.0 230 48 25 6.9 3.8 | -22.7 -8.9 230 38 20 6.4 3.5
19000 -21.2 -6.2 230 46 24 7.0 3.8 | -21.8 -7.2 230 36 19 6.5 3.6
18500 -20.1 -4.2 230 44 23 7.1 3.9 | -20.8 -5.4 230 35 18 6.6 3.6
18000 -19.0 -2.2 225 43 22 8.0 4.4 | -19.7 -3.5 225 34 17 8.9 4.9
17500 -17.8 -0.0 225 41 21 7.9 4.4 | -18.4 -1.1 225 33 17 8.8 4.8
17000 -16.7 1.9 225 39 20 8.2 4.5 | -17.1 1.2 225 33 17 8.8 4.9
16500 -15.4 4.3 225 38 19 8.2 4.5 | -15.8 3.6 225 32 17 8.9 4.9
16000 -14.2 6.4 225 37 19 8.4 4.6 | -14.4 6.1 225 32 17 8.7 4.8
15500 -12.9 8.8 230 36 18 8.6 4.7 | -13.2 8.2 225 31 16 8.5 4.7
15000 -11.6 11.1 230 35 18 8.7 4.8 | -11.9 10.6 225 31 16 8.5 4.7
14500 -10.3 13.5 230 35 18 9.1 5.0 | -10.6 12.9 225 30 16 8.9 4.9
14000 -9.0 15.8 230 34 17 9.1 5.0 | -9.3 15.3 225 30 15 8.8 4.9
13500 -7.6 18.3 235 33 17 9.1 5.0 | -7.9 17.8 225 30 15 9.4 5.2
13000 -6.3 20.7 235 32 16 9.1 5.0 | -6.5 20.3 225 29 15 9.4 5.1
12500 -5.0 23.0 235 31 16 9.0 5.0 | -5.1 22.8 225 29 15 9.5 5.2
12000 -3.6 25.5 240 29 15 9.1 5.0 | -3.7 25.3 225 28 15 9.5 5.2
11500 -2.3 27.9 240 28 14 8.9 4.9 | -2.2 28.0 225 28 14 9.7 5.3
11000 -1.0 30.2 240 27 14 8.9 4.9 | -0.8 30.6 230 28 14 9.8 5.4
10500 0.3 32.5 240 25 13 8.0 4.4 | 0.6 33.1 230 27 14 8.2 4.5
10250 0.9 33.6 240 25 13 8.5 4.7 | 1.2 34.2 230 27 14 9.1 5.0
10000 1.6 34.9 240 24 12 9.8 5.4 | 2.0 35.6 230 27 14 11.0 6.0
9750 2.3 36.1 240 23 12 9.6 5.3 | 2.8 37.0 230 27 14 10.6 5.8
9500 3.0 37.4 240 23 12 8.9 4.9 | 3.6 38.5 230 27 14 9.8 5.4
9250 4.3 39.7 240 22 11 8.2 4.5 | 5.0 41.0 230 26 13 9.9 5.4
9000 4.9 40.8 235 20 11 8.1 4.4 | 5.8 42.4 230 26 14 10.0 5.5
8750 5.5 41.9 235 20 10 8.9 4.9 | 6.5 43.7 230 26 13 9.9 5.4
8500 6.2 43.2 235 19 10 9.0 4.9 | 7.3 45.1 230 26 13 9.9 5.4
8250 6.8 44.2 235 19 10 7.7 4.2 | 8.0 46.4 230 26 13 9.8 5.4
8000 7.3 45.1 230 17 9 7.4 4.1 | 8.7 47.7 230 25 13 10.0 5.5
7750 7.9 46.2 230 16 8 8.4 4.6 | 9.5 49.1 230 25 13 10.0 5.5
7500 8.5 47.3 230 15 8 8.3 4.6 | 10.3 50.5 230 24 13 10.5 5.7
7250 9.2 48.6 230 14 7 7.4 4.1 | 11.0 51.8 230 24 12 8.5 4.7
7000 9.7 49.5 230 15 8 7.7 4.2 | 11.6 52.9 230 24 13 9.0 4.9
6750 10.4 50.7 225 13 7 8.8 4.8 | 12.4 54.3 230 23 12 11.3 6.2
6500 11.0 51.8 225 12 6 8.6 4.7 | 13.2 55.8 230 22 11 10.7 5.9
6250 11.7 53.1 220 11 6 10.1 5.5 | 14.0 57.2 230 21 11 10.8 5.9
6000 12.6 54.7 225 12 6 13.7 7.5 | 15.0 59.0 230 22 11 16.4 9.0
5750 13.7 56.7 220 10 5 16.7 9.2 | 16.6 61.9 230 20 10 26.0 14.3
5500 14.9 58.8 220 8 4 12.1 6.6 | 18.2 64.8 230 18 9 8.9 4.9
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
04/17/2025 at 1500 MDT | 04/17/2025 at 1800 MDT
|
CAPE... +45.5 LI... -0.4 | CAPE... +163.2 LI... -0.8
CINH... -3.1 K Index... +18.2 | CINH... -20.6 K Index... +22.6
|
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 -55.5 -67.9 240 50 26 0.9 0.5 | -54.3 -65.7 240 48 25 -0.2 -0.1
45000 -54.1 -65.4 235 59 31 0.9 0.5 | -54.7 -66.5 235 60 31 -0.3 -0.1
40000 -54.2 -65.6 240 74 38 -0.1 -0.1 | -54.4 -65.9 240 68 35 0.2 0.1
38000 -53.9 -65.0 240 79 41 1.3 0.7 | -54.1 -65.4 240 71 37 1.2 0.7
36000 -53.2 -63.8 235 84 43 1.3 0.7 | -53.3 -63.9 235 76 39 1.2 0.7
34000 -52.4 -62.3 235 89 46 3.1 1.7 | -52.6 -62.7 235 81 42 2.6 1.4
32000 -49.4 -56.9 235 81 42 5.1 2.8 | -49.7 -57.5 235 76 39 4.9 2.7
30000 -46.3 -51.3 235 74 38 6.5 3.6 | -46.8 -52.2 235 71 37 6.2 3.4
29000 -44.0 -47.2 235 70 36 7.5 4.1 | -44.5 -48.1 235 66 34 7.5 4.1
28000 -41.8 -43.2 235 66 34 7.5 4.1 | -42.3 -44.1 235 60 31 7.5 4.1
27000 -39.5 -39.1 235 62 32 7.5 4.1 | -40.0 -40.0 235 54 28 7.5 4.1
26000 -36.6 -33.9 235 57 29 7.9 4.3 | -37.8 -36.0 235 49 25 7.7 4.2
25000 -34.2 -29.6 235 53 27 7.9 4.3 | -34.9 -30.8 235 45 23 7.7 4.2
24000 -31.9 -25.4 235 49 25 8.0 4.4 | -32.6 -26.7 235 42 22 7.7 4.2
23000 -29.8 -21.6 235 44 23 6.7 3.7 | -30.3 -22.5 235 39 20 7.8 4.3
22000 -27.7 -17.9 235 39 20 6.8 3.7 | -27.9 -18.2 230 36 19 7.9 4.3
21000 -25.7 -14.3 235 33 17 7.0 3.8 | -25.6 -14.1 225 34 17 8.0 4.4
20000 -23.5 -10.3 235 32 16 7.7 4.2 | -23.1 -9.6 225 34 17 8.3 4.6
19500 -22.4 -8.3 230 31 16 7.7 4.2 | -21.9 -7.4 225 34 18 8.3 4.6
19000 -21.2 -6.2 230 31 16 7.7 4.2 | -20.7 -5.3 220 34 18 8.4 4.6
18500 -20.1 -4.2 225 30 16 7.8 4.3 | -19.4 -2.9 220 35 18 8.4 4.6
18000 -18.9 -2.0 225 30 16 8.7 4.8 | -18.2 -0.8 220 35 18 8.1 4.5
17500 -17.6 0.3 225 30 16 8.7 4.8 | -17.0 1.4 220 34 18 8.2 4.5
17000 -16.3 2.7 225 30 16 8.7 4.7 | -15.8 3.6 220 34 18 8.0 4.4
16500 -15.0 5.0 225 30 16 8.6 4.7 | -14.6 5.7 220 34 17 8.0 4.4
16000 -13.7 7.3 220 30 15 8.6 4.7 | -13.5 7.7 220 33 17 8.1 4.4
15500 -12.5 9.5 220 30 15 8.6 4.7 | -12.2 10.0 220 33 17 8.3 4.5
15000 -11.2 11.8 220 30 15 8.6 4.7 | -11.0 12.2 220 33 17 8.2 4.5
14500 -9.9 14.2 220 29 15 9.2 5.0 | -9.7 14.5 220 33 17 9.0 4.9
14000 -8.5 16.7 220 29 15 9.1 5.0 | -8.4 16.9 220 32 17 8.9 4.9
13500 -7.1 19.2 225 29 15 9.5 5.2 | -7.1 19.2 220 32 17 9.2 5.1
13000 -5.7 21.7 225 29 15 9.4 5.2 | -5.7 21.7 220 32 16 9.3 5.1
12500 -4.3 24.3 225 29 15 9.6 5.3 | -4.3 24.3 225 31 16 9.2 5.1
12000 -2.8 27.0 225 29 15 9.7 5.3 | -2.9 26.8 225 31 16 9.2 5.1
11500 -1.4 29.5 225 29 15 9.7 5.3 | -1.5 29.3 225 30 16 9.2 5.1
11000 0.1 32.2 225 29 15 9.7 5.3 | -0.2 31.6 230 30 15 9.3 5.1
10500 1.5 34.7 225 28 15 8.9 4.9 | 1.1 34.0 230 29 15 6.8 3.7
10250 2.2 36.0 225 28 14 9.5 5.2 | 1.6 34.9 230 28 14 7.9 4.3
10000 3.0 37.4 225 28 14 10.5 5.7 | 2.3 36.1 235 28 14 10.9 6.0
9750 3.7 38.7 225 28 15 10.3 5.6 | 3.1 37.6 235 28 14 10.4 5.7
9500 4.5 40.1 225 28 15 10.0 5.5 | 3.9 39.0 235 28 14 8.9 4.9
9250 5.2 41.4 230 28 14 10.0 5.5 | 4.5 40.1 235 27 14 8.1 4.4
9000 6.7 44.1 230 28 14 9.7 5.3 | 5.1 41.2 240 26 14 10.0 5.5
8750 7.4 45.3 230 28 14 10.3 5.6 | 6.6 43.9 240 26 13 8.8 4.8
8500 8.2 46.8 230 27 14 10.6 5.8 | 7.2 45.0 240 25 13 8.0 4.4
8250 9.0 48.2 230 27 14 9.4 5.2 | 7.9 46.2 245 25 13 10.2 5.6
8000 9.6 49.3 230 27 14 9.2 5.0 | 8.7 47.7 240 24 12 10.2 5.6
7750 10.4 50.7 230 26 14 10.0 5.5 | 9.3 48.7 245 24 12 8.3 4.5
7500 11.1 52.0 230 26 13 10.2 5.6 | 10.0 50.0 245 23 12 7.4 4.1
7250 11.9 53.4 230 25 13 8.7 4.8 | 10.6 51.1 250 23 12 11.6 6.4
7000 12.5 54.5 230 26 13 9.2 5.0 | 11.6 52.9 245 21 11 12.4 6.8
6750 13.3 55.9 230 25 13 11.1 6.1 | 12.3 54.1 245 20 10 8.6 4.7
6500 14.1 57.4 230 24 12 10.5 5.8 | 13.0 55.4 245 19 10 9.9 5.5
6250 14.9 58.8 235 23 12 11.0 6.0 | 13.7 56.7 245 18 10 8.4 4.6
6000 15.9 60.6 235 23 12 16.7 9.2 | 14.3 57.7 255 19 10 10.1 5.6
5750 17.5 63.5 235 21 11 25.3 13.9 | 15.3 59.5 255 17 9 16.4 9.0
5500 19.0 66.2 235 19 10 10.4 5.7 | 16.3 61.3 255 14 7 4.3 2.4
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
________________________________________________________________________________
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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