Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
107
UXUS97 KBOU 251315
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0714 MDT Wednesday, June 25, 2025
This forecast is for Wednesday, June 25, 2025:
If the trigger temperature of 79.8 F/26.5 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 346 ft/min (1.8 m/s)
Maximum height of thermals.................. 10063 ft MSL (4722 ft AGL)
Forecast maximum temperature................... 81.0 F/27.7 C
Time of trigger temperature.................... 1400 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Overcast opaque high
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 8090 ft MSL (2750 ft AGL)
Thermal soaring outlook for Thursday 06/26..... Excellent
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... No change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 14448 ft MSL (9107 ft AGL)
Wave soaring outlook for Thursday 06/26........ Poor
Remarks...
Sunrise/Sunset.................... 05:32:55 / 20:31:38 MDT
Total possible sunshine........... 14 hr 58 min 43 sec (898 min 43 sec)
Altitude of sun at 13:02:16 MDT... 73.59 degrees
Upper air data from numerical model forecast valid on 06/25/2025 at 0600 MDT
Freezing level.................. 15157 ft MSL (9816 ft AGL)
Convective condensation level... 13379 ft MSL (8038 ft AGL)
Lifted condensation level....... 12752 ft MSL (7411 ft AGL)
Lifted index.................... -3.4
K index......................... +25.5
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 -64.4 -83.9 215 49 25 1.9 1.0 M M M M M
45000 -59.9 -75.8 215 67 34 5.4 3.0 M M M M M
40000 -51.5 -60.7 210 77 40 6.9 3.8 M M M M M
38000 -47.3 -53.1 205 72 37 7.0 3.8 M M M M M
36000 -43.1 -45.6 200 68 35 6.9 3.8 M M M M M
34000 -37.8 -36.0 200 63 33 8.1 4.5 M M M M M
32000 -32.9 -27.2 200 60 31 8.0 4.4 M M M M M
30000 -28.7 -19.7 205 53 27 6.7 3.7 47.8 118.0 15.6 M M
29000 -26.7 -16.1 205 50 26 6.7 3.7 46.6 115.9 14.9 M M
28000 -24.7 -12.5 210 47 24 6.0 3.3 45.6 114.1 14.2 M M
27000 -23.1 -9.6 210 42 22 5.3 2.9 43.8 110.8 12.9 M M
26000 -21.5 -6.7 215 38 20 5.3 2.9 42.1 107.7 11.7 M M
25000 -19.9 -3.8 220 34 18 5.1 2.8 40.5 104.9 10.6 M M
24000 -18.0 -0.4 220 30 15 7.3 4.0 39.3 102.8 9.7 M M
23000 -15.8 3.6 220 24 13 7.3 4.0 38.4 101.2 9.0 M M
22000 -13.7 7.3 220 19 10 7.5 4.1 37.6 99.8 8.4 M M
21000 -11.9 10.6 215 14 7 6.1 3.3 36.4 97.5 7.3 M M
20000 -10.1 13.8 210 9 5 6.2 3.4 35.1 95.2 6.2 M M
19500 -9.3 15.3 205 7 4 6.2 3.4 34.5 94.1 5.7 M M
19000 -7.9 17.8 190 4 2 6.5 3.6 33.6 92.5 5.0 M M
18500 -6.9 19.6 170 3 1 6.5 3.6 33.1 91.5 4.5 M M
18000 -6.0 21.2 140 2 1 6.6 3.6 32.5 90.5 4.0 M M
17500 -5.0 23.0 120 2 1 6.7 3.7 32.0 89.6 3.5 M M
17000 -4.0 24.8 100 2 1 6.8 3.7 31.5 88.6 3.1 M M
16500 -3.0 26.6 090 2 1 7.5 4.1 31.0 87.9 2.7 M M
16000 -1.9 28.6 080 1 1 7.4 4.1 30.7 87.2 2.3 M M
15500 -0.7 30.7 000 0 0 8.4 4.6 30.3 86.6 2.1 M M
15000 0.6 33.1 295 1 0 8.5 4.7 30.1 86.2 1.9 M M
14500 1.8 35.2 280 2 1 9.0 4.9 30.0 85.9 1.7 M M
14000 3.2 37.8 275 3 2 9.3 5.1 29.9 85.8 1.6 M M
13500 4.6 40.3 275 4 2 9.2 5.1 29.8 85.6 1.6 M M
13000 6.0 42.8 275 6 3 9.0 4.9 29.7 85.4 1.5 M M
12500 7.3 45.1 280 7 4 9.0 4.9 29.6 85.2 1.4 M M
12000 8.7 47.7 280 9 4 8.8 4.8 29.4 85.0 1.3 M M
11500 10.0 50.0 280 10 5 8.8 4.8 29.3 84.7 1.1 M M
11000 11.2 52.2 280 11 6 7.8 4.3 29.1 84.3 0.9 M M
10500 12.3 54.1 280 12 6 6.3 3.4 28.8 83.8 0.6 M M
10250 12.7 54.9 280 13 7 5.0 2.7 28.4 83.1 0.2 M M
10000 13.1 55.6 280 13 7 7.3 4.0 28.1 82.6 -0.1 343 1.7
9750 13.7 56.7 280 13 6 7.8 4.3 28.0 82.3 -0.3 319 1.6
9500 14.2 57.6 280 12 6 7.5 4.1 27.8 82.0 -0.5 296 1.5
9250 14.7 58.5 280 12 6 5.1 2.8 27.6 81.6 -0.7 275 1.4
9000 14.9 58.8 280 13 6 4.8 2.6 27.1 80.8 -1.2 259 1.3
8750 15.3 59.5 280 12 6 6.5 3.5 26.8 80.3 -1.5 240 1.2
8500 15.7 60.3 280 11 6 5.3 2.9 26.6 79.8 -1.9 222 1.1
8250 15.9 60.6 280 10 5 2.4 1.3 26.1 79.0 -2.4 208 1.1
8000 15.9 60.6 280 10 5 1.6 0.9 25.5 77.9 -3.1 200 1.0
7750 16.0 60.8 285 9 4 3.6 2.0 24.9 76.9 -3.8 189 1.0
7500 16.2 61.2 285 8 4 1.7 1.0 24.4 76.0 -4.3 177 0.9
7250 16.1 61.0 290 7 4 -1.3 -0.7 23.7 74.6 -5.2 173 0.9
7000 15.9 60.6 295 7 3 -1.4 -0.8 22.8 73.1 -6.1 172 0.9
6750 15.8 60.4 300 6 3 1.4 0.8 22.0 71.7 -7.0 168 0.9
6500 15.9 60.6 300 6 3 2.1 1.1 21.5 70.7 -7.6 157 0.8
6250 15.9 60.6 305 6 3 1.1 0.6 20.8 69.5 -8.4 149 0.8
6000 15.9 60.6 305 5 3 0.9 0.5 20.2 68.4 -9.1 141 0.7
5750 15.9 60.6 310 5 2 3.4 1.9 19.6 67.2 -9.8 133 0.7
5500 16.4 61.5 310 4 2 9.3 5.1 19.3 66.8 -10.1 112 0.6
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
06/25/2025 at 0900 MDT | 06/25/2025 at 1200 MDT
|
CAPE... +738.4 LI... -4.2 | CAPE... +695.5 LI... -4.0
CINH... -128.0 K Index... +23.7 | CINH... -46.5 K Index... +26.7
|
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 -64.3 -83.7 215 51 26 1.7 0.9 | -63.4 -82.1 215 49 25 0.9 0.5
45000 -60.0 -76.0 210 70 36 5.5 3.0 | -59.9 -75.8 205 72 37 5.5 3.0
40000 -51.5 -60.7 205 82 42 7.3 4.0 | -51.4 -60.5 205 83 43 7.3 4.0
38000 -47.1 -52.8 205 80 41 7.4 4.1 | -47.0 -52.6 205 82 42 7.4 4.1
36000 -42.6 -44.7 205 79 41 7.4 4.1 | -42.5 -44.5 205 82 42 7.4 4.1
34000 -37.8 -36.0 205 74 38 7.0 3.9 | -38.5 -37.3 205 76 39 6.5 3.6
32000 -33.6 -28.5 205 69 35 7.0 3.8 | -34.1 -29.4 210 68 35 6.4 3.5
30000 -29.7 -21.5 210 60 31 6.5 3.5 | -29.9 -21.8 210 62 32 7.0 3.9
29000 -27.7 -17.9 210 55 28 6.5 3.5 | -27.8 -18.0 210 59 31 7.0 3.9
28000 -25.8 -14.4 215 51 26 6.3 3.5 | -25.7 -14.3 215 57 29 6.4 3.5
27000 -24.0 -11.2 215 46 24 6.1 3.4 | -24.0 -11.2 215 52 27 5.7 3.1
26000 -22.1 -7.8 220 41 21 6.2 3.4 | -22.3 -8.1 215 48 24 5.7 3.1
25000 -20.3 -4.5 220 37 19 6.2 3.4 | -20.6 -5.1 215 43 22 5.8 3.2
24000 -18.5 -1.3 220 31 16 5.9 3.2 | -19.0 -2.2 215 37 19 5.5 3.0
23000 -16.8 1.8 215 25 13 6.1 3.3 | -17.4 0.7 215 30 16 5.6 3.1
22000 -15.1 4.8 215 19 10 6.3 3.4 | -15.8 3.6 215 24 12 5.6 3.1
21000 -13.1 8.4 215 16 8 7.2 4.0 | -13.7 7.3 215 21 11 7.8 4.3
20000 -11.0 12.2 215 13 7 7.3 4.0 | -11.5 11.3 220 19 10 7.8 4.3
19500 -10.0 14.0 215 12 6 7.3 4.0 | -10.3 13.5 220 18 9 7.8 4.3
19000 -9.0 15.8 215 11 6 6.9 3.8 | -9.2 15.4 225 17 9 7.5 4.1
18500 -7.5 18.5 215 9 5 6.7 3.7 | -8.1 17.4 225 16 8 7.5 4.1
18000 -6.5 20.3 210 8 4 6.8 3.8 | -6.5 20.3 225 15 8 7.0 3.8
17500 -5.5 22.1 210 8 4 6.9 3.8 | -5.5 22.1 230 14 7 6.8 3.7
17000 -4.5 23.9 215 7 3 7.0 3.9 | -4.5 23.9 235 13 7 6.8 3.7
16500 -3.3 26.1 220 6 3 7.9 4.3 | -3.6 25.5 240 12 6 6.4 3.5
16000 -2.1 28.2 230 6 3 7.8 4.3 | -2.7 27.1 250 11 6 6.3 3.5
15500 -0.9 30.4 240 5 3 8.4 4.6 | -1.6 29.1 255 10 5 7.6 4.2
15000 0.3 32.5 260 6 3 8.4 4.6 | -0.5 31.1 265 9 4 7.6 4.2
14500 1.5 34.7 270 6 3 8.7 4.8 | 0.6 33.1 275 8 4 8.4 4.6
14000 2.9 37.2 280 6 3 8.8 4.9 | 1.9 35.4 285 7 4 8.8 4.8
13500 4.2 39.6 290 7 4 8.9 4.9 | 3.2 37.8 295 7 4 9.0 4.9
13000 5.5 41.9 295 7 4 8.9 4.9 | 4.6 40.3 300 7 4 9.3 5.1
12500 6.8 44.2 305 8 4 8.9 4.9 | 6.0 42.8 305 7 4 9.3 5.1
12000 8.1 46.6 305 8 4 9.0 4.9 | 7.4 45.3 310 8 4 9.3 5.1
11500 9.5 49.1 310 9 5 8.9 4.9 | 8.8 47.8 315 8 4 9.2 5.1
11000 10.7 51.3 315 10 5 8.1 4.4 | 10.1 50.2 320 8 4 8.7 4.8
10500 12.0 53.6 320 10 5 4.8 2.6 | 11.5 52.7 325 8 4 4.1 2.2
10250 12.2 54.0 320 11 6 4.8 2.6 | 11.6 52.9 325 9 4 5.1 2.8
10000 12.8 55.0 320 11 6 10.0 5.5 | 12.4 54.3 330 9 4 12.1 6.6
9750 13.5 56.3 320 12 6 9.5 5.2 | 13.2 55.8 330 9 5 10.5 5.8
9500 14.2 57.6 320 12 6 8.9 4.9 | 13.9 57.0 330 9 5 9.8 5.4
9250 14.8 58.6 320 12 6 6.2 3.4 | 14.6 58.3 330 9 5 6.9 3.8
9000 15.2 59.4 325 13 7 6.6 3.6 | 15.1 59.2 335 10 5 8.1 4.5
8750 15.8 60.4 320 13 7 8.4 4.6 | 15.8 60.4 335 10 5 10.4 5.7
8500 16.3 61.3 320 13 7 7.2 4.0 | 16.5 61.7 340 10 5 8.4 4.6
8250 16.8 62.2 320 13 7 6.1 3.3 | 17.0 62.6 345 10 5 5.6 3.0
8000 17.2 63.0 320 14 7 5.0 2.7 | 17.4 63.3 350 10 5 5.3 2.9
7750 17.5 63.5 320 13 7 5.2 2.9 | 17.7 63.9 355 9 5 6.3 3.5
7500 17.7 63.9 315 12 6 2.2 1.2 | 18.1 64.6 360 9 5 5.3 2.9
7250 17.6 63.7 315 11 6 -1.3 -0.7 | 18.3 64.9 005 8 4 3.9 2.2
7000 17.4 63.3 320 9 5 -0.8 -0.5 | 18.5 65.3 015 8 4 5.2 2.8
6750 17.2 63.0 320 8 4 -0.2 -0.1 | 18.9 66.0 020 7 4 9.6 5.2
6500 17.1 62.8 320 6 3 2.5 1.4 | 19.6 67.3 030 7 3 10.9 6.0
6250 17.3 63.1 320 4 2 4.4 2.4 | 20.3 68.5 035 6 3 9.9 5.5
6000 17.5 63.5 320 3 2 3.2 1.7 | 21.1 70.0 035 6 3 9.2 5.1
5750 17.7 63.9 320 2 1 8.4 4.6 | 21.8 71.2 035 6 3 13.4 7.4
5500 18.7 65.7 325 1 1 19.1 10.5 | 23.2 73.8 035 6 3 24.8 13.6
06/25/2025 at 1500 MDT | 06/25/2025 at 1800 MDT
|
CAPE... +697.0 LI... -4.0 | CAPE... +350.4 LI... -1.8
CINH... -28.4 K Index... +28.0 | CINH... -49.7 K Index... +29.6
|
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 -62.8 -81.0 205 48 25 -0.4 -0.2 | -63.0 -81.4 205 43 22 0.7 0.4
45000 -60.5 -76.9 205 76 39 6.0 3.3 | -59.7 -75.5 205 70 36 5.8 3.2
40000 -51.4 -60.5 205 84 43 7.1 3.9 | -51.0 -59.8 205 78 40 6.5 3.6
38000 -47.2 -53.0 205 83 43 7.1 3.9 | -47.0 -52.6 210 77 40 6.5 3.6
36000 -42.4 -44.3 205 83 43 7.1 3.9 | -43.1 -45.6 210 77 40 6.5 3.6
34000 -38.5 -37.3 210 76 39 6.4 3.5 | -38.8 -37.8 210 73 38 6.3 3.5
32000 -34.6 -30.3 210 68 35 6.4 3.5 | -35.0 -31.0 215 69 36 6.3 3.4
30000 -30.4 -22.7 215 62 32 7.1 3.9 | -31.5 -24.7 215 62 32 5.9 3.2
29000 -28.3 -18.9 215 60 31 7.1 3.9 | -29.7 -21.5 215 57 30 5.9 3.2
28000 -26.2 -15.2 220 58 30 6.7 3.7 | -28.0 -18.4 220 53 27 6.1 3.4
27000 -24.5 -12.1 220 53 27 5.7 3.1 | -26.1 -15.0 220 47 24 6.5 3.6
26000 -22.8 -9.0 220 49 25 5.7 3.1 | -24.1 -11.4 225 41 21 6.5 3.6
25000 -21.1 -6.0 220 45 23 5.7 3.1 | -22.2 -8.0 225 35 18 6.5 3.6
24000 -19.3 -2.7 225 40 21 6.5 3.6 | -20.1 -4.2 225 32 16 7.6 4.1
23000 -17.3 0.9 225 35 18 6.5 3.6 | -17.9 -0.2 230 29 15 7.6 4.2
22000 -15.4 4.3 225 30 15 6.5 3.6 | -15.6 3.9 230 26 13 7.6 4.2
21000 -13.4 7.9 225 27 14 6.9 3.8 | -13.5 7.7 235 24 12 7.3 4.0
20000 -10.9 12.4 230 24 12 7.0 3.8 | -11.3 11.7 240 22 11 7.4 4.0
19500 -9.9 14.2 230 22 11 7.0 3.8 | -10.2 13.6 240 21 11 7.4 4.1
19000 -8.9 16.0 230 21 11 7.2 4.0 | -9.2 15.4 245 21 11 7.1 3.9
18500 -7.8 18.0 230 20 10 7.2 4.0 | -7.7 18.1 245 19 10 7.0 3.8
18000 -6.8 19.8 235 19 10 7.3 4.0 | -6.7 19.9 250 18 9 6.9 3.8
17500 -5.7 21.7 240 17 9 7.4 4.0 | -5.7 21.7 255 17 9 6.8 3.8
17000 -4.6 23.7 240 15 8 7.4 4.1 | -4.7 23.5 255 16 8 6.8 3.8
16500 -3.5 25.7 245 13 7 7.7 4.3 | -3.7 25.3 260 15 8 6.7 3.7
16000 -2.4 27.7 250 12 6 7.7 4.2 | -2.7 27.1 260 14 7 6.7 3.7
15500 -1.3 29.7 260 10 5 7.8 4.3 | -1.7 28.9 260 13 7 6.9 3.8
15000 -0.1 31.8 265 9 5 7.8 4.3 | -0.7 30.7 265 12 6 6.9 3.8
14500 1.0 33.8 275 9 5 8.0 4.4 | 0.3 32.5 265 11 6 7.4 4.1
14000 2.2 36.0 280 8 4 8.3 4.5 | 1.4 34.5 270 10 5 7.7 4.2
13500 3.4 38.1 290 7 4 8.4 4.6 | 2.5 36.5 270 10 5 7.8 4.3
13000 4.7 40.5 295 6 3 8.8 4.8 | 3.7 38.7 275 9 4 8.0 4.4
12500 6.0 42.8 305 6 3 8.8 4.8 | 4.9 40.8 280 8 4 8.0 4.4
12000 7.3 45.1 310 5 3 8.6 4.7 | 6.1 43.0 285 7 4 8.1 4.5
11500 8.5 47.3 320 4 2 8.6 4.7 | 7.3 45.1 290 6 3 8.1 4.4
11000 9.8 49.6 335 4 2 8.2 4.5 | 8.4 47.1 305 6 3 7.7 4.2
10500 11.0 51.8 350 3 2 5.5 3.0 | 9.6 49.3 320 5 3 4.6 2.5
10250 11.3 52.3 340 4 2 6.2 3.4 | 9.8 49.6 320 6 3 4.1 2.3
10000 12.0 53.6 350 4 2 10.6 5.8 | 10.4 50.7 320 6 3 9.6 5.3
9750 12.7 54.9 360 4 2 9.5 5.2 | 11.1 52.0 325 5 3 10.1 5.5
9500 13.4 56.1 010 4 2 9.4 5.2 | 11.8 53.2 330 5 3 8.7 4.8
9250 14.0 57.2 015 5 2 6.9 3.8 | 12.3 54.1 330 5 2 5.4 3.0
9000 14.5 58.1 015 5 3 7.2 3.9 | 12.7 54.9 330 5 2 7.6 4.2
8750 15.1 59.2 020 5 3 8.9 4.9 | 13.4 56.1 330 4 2 10.7 5.9
8500 15.7 60.3 025 6 3 8.1 4.4 | 14.1 57.4 330 4 2 8.4 4.6
8250 16.3 61.3 030 6 3 6.8 3.7 | 14.6 58.3 325 3 2 5.9 3.2
8000 16.7 62.1 035 7 4 6.8 3.8 | 15.1 59.2 320 3 2 7.0 3.8
7750 17.2 63.0 040 7 4 7.8 4.3 | 15.7 60.3 315 3 2 9.8 5.4
7500 17.7 63.9 045 7 4 7.7 4.2 | 16.4 61.5 315 3 2 7.6 4.1
7250 18.2 64.8 050 7 4 7.5 4.1 | 16.8 62.2 305 3 1 4.8 2.6
7000 18.7 65.7 055 7 4 7.9 4.3 | 17.2 63.0 295 3 1 6.5 3.6
6750 19.3 66.7 060 7 4 9.3 5.1 | 17.8 64.0 290 3 2 10.0 5.5
6500 20.0 68.0 065 7 4 10.3 5.7 | 18.5 65.3 285 3 2 8.7 4.8
6250 20.7 69.3 065 8 4 10.7 5.9 | 19.0 66.2 280 3 2 6.0 3.3
6000 21.5 70.7 065 8 4 9.6 5.2 | 19.4 66.9 270 3 1 6.9 3.8
5750 22.2 72.0 065 8 4 12.5 6.9 | 20.0 68.0 265 3 2 10.9 6.0
5500 23.5 74.3 070 7 4 24.1 13.2 | 21.0 69.8 265 3 1 17.2 9.4
________________________________________________________________________________
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 near the old Stapleton
Airport site in Denver, Colorado at
North Latitude: 39 deg 46 min 5.016 sec
West Longitude: 104 deg 52 min 9.984 sec
Elevation: 5285 feet (1611 meters)
and may not be representative of other areas along the Front Range of the
Colorado Rocky Mountains. 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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