Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
776
UXUS97 KBOU 081324
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0721 MDT Monday, September 8, 2025
This forecast is for Monday, September 8, 2025:
If the trigger temperature of 77.4 F/25.2 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1371 ft/min (7.0 m/s)
Maximum height of thermals.................. 19852 ft MSL (14530 ft AGL)
Forecast maximum temperature................... 88.0 F/31.6 C
Time of trigger temperature.................... 1000 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................. 15229 ft MSL (9908 ft AGL)
Thermal soaring outlook for Tuesday 09/09...... Good
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1800 MDT)......... Little change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 14438 ft MSL (9116 ft AGL)
Wave soaring outlook for Tuesday 09/09......... Poor
Remarks... Warm today with gusty high based showers and storms
Sunrise/Sunset.................... 06:34:39 / 19:19:19 MDT
Total possible sunshine........... 12 hr 44 min 40 sec (764 min 40 sec)
Altitude of sun at 12:56:59 MDT... 55.60 degrees
Upper air data from numerical model forecast valid on 09/08/2025 at 0600 MDT
Freezing level.................. 14515 ft MSL (9193 ft AGL)
Convective condensation level... 15647 ft MSL (10325 ft AGL)
Lifted condensation level....... 16950 ft MSL (11629 ft AGL)
Lifted index.................... -4.1
K index......................... +23.6
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 -60.7 -77.3 290 36 18 2.6 1.4 M M M M M
45000 -57.4 -71.3 290 50 26 0.8 0.4 M M M M M
40000 -56.1 -69.0 300 63 33 3.2 1.7 M M M M M
38000 -53.4 -64.1 300 62 32 4.5 2.5 M M M M M
36000 -50.7 -59.3 295 61 31 4.5 2.5 M M M M M
34000 -45.6 -50.1 295 55 28 8.9 4.9 M M M M M
32000 -40.3 -40.5 295 49 25 8.9 4.9 M M M M M
30000 -35.3 -31.5 290 44 23 8.1 4.4 40.0 104.1 6.7 M M
29000 -32.9 -27.2 290 42 22 8.1 4.4 39.4 103.0 6.3 M M
28000 -30.5 -22.9 290 41 21 7.9 4.4 38.9 102.1 6.0 M M
27000 -28.2 -18.8 290 38 20 7.3 4.0 37.9 100.3 5.3 M M
26000 -26.1 -15.0 290 35 18 7.4 4.0 37.0 98.6 4.6 M M
25000 -23.9 -11.0 290 33 17 7.4 4.0 36.2 97.2 4.0 M M
24000 -21.7 -7.1 290 30 15 7.2 4.0 35.2 95.4 3.2 M M
23000 -19.6 -3.3 290 27 14 7.3 4.0 34.3 93.7 2.5 M M
22000 -17.4 0.7 290 24 12 7.3 4.0 33.5 92.3 1.8 M M
21000 -15.3 4.5 290 22 11 7.3 4.0 32.5 90.6 1.0 M M
20000 -13.1 8.4 290 20 10 7.4 4.0 31.7 89.0 0.2 M M
19500 -12.0 10.4 290 19 10 7.4 4.0 31.3 88.3 -0.2 1348 6.8
19000 -11.0 12.2 290 18 9 7.5 4.1 30.9 87.7 -0.5 1301 6.6
18500 -9.3 15.3 295 18 9 7.5 4.1 30.3 86.6 -1.1 1229 6.2
18000 -8.2 17.2 295 17 9 7.9 4.3 30.0 86.0 -1.4 1181 6.0
17500 -7.0 19.4 300 17 9 8.0 4.4 29.7 85.4 -1.7 1131 5.7
17000 -5.9 21.4 300 17 9 8.0 4.4 29.4 84.9 -2.0 1081 5.5
16500 -4.7 23.5 305 17 9 8.0 4.4 29.1 84.3 -2.3 1031 5.2
16000 -3.5 25.7 305 17 9 7.9 4.4 28.8 83.8 -2.6 981 5.0
15500 -2.3 27.9 305 17 9 8.4 4.6 28.5 83.3 -2.9 930 4.7
15000 -1.1 30.0 310 18 9 8.3 4.6 28.3 82.9 -3.1 878 4.5
14500 0.2 32.4 310 19 10 8.7 4.8 28.0 82.5 -3.4 826 4.2
14000 1.5 34.7 310 19 10 8.7 4.8 27.9 82.2 -3.6 772 3.9
13500 2.8 37.0 310 20 10 8.7 4.8 27.7 81.9 -3.7 719 3.7
13000 4.1 39.4 310 20 10 8.7 4.8 27.5 81.6 -4.0 666 3.4
12500 5.3 41.5 315 20 10 8.7 4.8 27.4 81.3 -4.2 613 3.1
12000 6.6 43.9 310 21 11 8.8 4.8 27.2 81.0 -4.4 560 2.8
11500 7.9 46.2 310 21 11 8.8 4.8 27.0 80.7 -4.6 507 2.6
11000 9.2 48.6 310 21 11 8.5 4.7 26.9 80.4 -4.8 453 2.3
10500 10.5 50.9 310 21 11 4.9 2.7 26.7 80.1 -5.0 400 2.0
10250 10.7 51.3 310 21 11 4.7 2.6 26.2 79.1 -5.5 387 2.0
10000 11.3 52.3 310 20 11 10.8 5.9 26.1 79.0 -5.6 360 1.8
9750 12.1 53.8 305 20 10 11.4 6.2 26.2 79.2 -5.5 328 1.7
9500 12.9 55.2 305 20 10 9.0 5.0 26.3 79.3 -5.5 297 1.5
9250 13.4 56.1 305 20 10 5.5 3.0 26.1 78.9 -5.7 274 1.4
9000 13.9 57.0 300 20 10 8.4 4.6 25.8 78.5 -6.0 253 1.3
8750 14.7 58.5 300 19 10 11.6 6.4 25.9 78.6 -6.0 222 1.1
8500 15.4 59.7 300 19 10 8.4 4.6 25.9 78.7 -5.9 191 1.0
8250 15.9 60.6 300 19 10 5.3 2.9 25.7 78.2 -6.2 170 0.9
8000 16.3 61.3 295 18 9 7.4 4.1 25.4 77.7 -6.5 150 0.8
7750 17.0 62.6 295 18 9 9.7 5.3 25.3 77.6 -6.6 123 0.6
7500 17.6 63.7 295 17 9 6.7 3.7 25.2 77.4 -6.7 96 0.5
7250 18.0 64.4 290 16 8 3.8 2.1 24.8 76.7 -7.1 79 0.4
7000 18.3 64.9 290 16 8 5.5 3.0 24.5 76.0 -7.6 62 0.3
6750 18.7 65.7 285 16 8 5.5 3.0 24.2 75.5 -7.9 42 0.2
6500 19.0 66.2 280 15 8 2.3 1.3 23.7 74.7 -8.4 26 0.1
6250 19.0 66.2 270 13 7 0.3 0.2 23.1 73.5 -9.1 17 0.1
6000 19.1 66.4 265 12 6 2.2 1.2 22.4 72.3 -9.8 9 0.0
5750 19.0 66.2 250 10 5 -5.8 -3.2 21.7 71.0 -10.6 2 0.0
5500 17.9 64.2 240 8 4 -22.3 -12.3 19.9 67.7 -12.4 27 0.1
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/08/2025 at 0900 MDT | 09/08/2025 at 1200 MDT
|
CAPE... +25.4 LI... +0.1 | CAPE... +62.7 LI... -0.8
CINH... -58.5 K Index... +19.2 | CINH... -4.8 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 -61.4 -78.5 300 34 18 1.7 0.9 | -61.7 -79.1 295 35 18 2.0 1.1
45000 -59.1 -74.4 300 53 28 1.0 0.6 | -59.0 -74.2 300 49 25 0.8 0.4
40000 -57.4 -71.3 305 68 35 5.1 2.8 | -57.6 -71.7 305 65 33 6.3 3.5
38000 -53.4 -64.1 305 65 34 6.7 3.7 | -53.3 -63.9 300 61 31 7.3 4.0
36000 -48.8 -55.8 300 62 32 6.7 3.7 | -48.9 -56.0 300 57 29 7.3 4.0
34000 -44.3 -47.7 300 57 29 7.7 4.2 | -43.8 -46.8 300 52 27 7.5 4.1
32000 -39.7 -39.5 300 50 26 7.7 4.2 | -39.3 -38.7 300 48 25 7.5 4.1
30000 -35.0 -31.0 300 46 24 7.8 4.3 | -34.5 -30.1 295 44 23 8.2 4.5
29000 -32.7 -26.9 300 44 23 7.8 4.3 | -32.0 -25.6 295 43 22 8.2 4.5
28000 -30.3 -22.5 300 42 22 7.7 4.2 | -29.5 -21.1 295 41 21 8.0 4.4
27000 -28.1 -18.6 300 40 21 7.4 4.1 | -27.3 -17.1 295 39 20 7.5 4.1
26000 -25.9 -14.6 295 39 20 7.4 4.1 | -25.1 -13.2 295 37 19 7.5 4.1
25000 -23.6 -10.5 295 37 19 7.4 4.1 | -22.8 -9.0 290 35 18 7.5 4.1
24000 -21.4 -6.5 295 34 18 7.4 4.1 | -20.7 -5.3 295 33 17 7.0 3.8
23000 -19.2 -2.6 295 31 16 7.5 4.1 | -18.6 -1.5 295 30 15 7.0 3.8
22000 -17.0 1.4 295 28 14 7.5 4.1 | -16.5 2.3 295 27 14 7.0 3.9
21000 -14.9 5.2 290 25 13 7.0 3.8 | -14.7 5.5 295 25 13 6.0 3.3
20000 -12.8 9.0 290 22 11 7.0 3.8 | -12.9 8.8 295 23 12 6.1 3.3
19500 -11.8 10.8 290 20 10 7.0 3.8 | -12.0 10.4 290 22 11 6.1 3.3
19000 -10.2 13.6 290 18 9 7.3 4.0 | -11.1 12.0 290 21 11 7.1 3.9
18500 -9.1 15.6 290 17 9 7.4 4.0 | -9.5 14.9 295 20 10 7.3 4.0
18000 -8.0 17.6 295 16 8 7.4 4.0 | -8.4 16.9 295 19 10 7.4 4.1
17500 -7.0 19.4 295 15 8 7.4 4.1 | -7.3 18.9 295 18 9 7.5 4.1
17000 -5.9 21.4 300 14 7 7.5 4.1 | -6.2 20.8 300 18 9 7.6 4.2
16500 -4.7 23.5 305 14 7 7.9 4.3 | -5.1 22.8 300 17 9 8.0 4.4
16000 -3.6 25.5 310 14 7 7.8 4.3 | -3.9 25.0 305 17 9 7.9 4.3
15500 -2.4 27.7 310 13 7 8.3 4.5 | -2.7 27.1 305 17 9 9.1 5.0
15000 -1.2 29.8 315 14 7 8.2 4.5 | -1.3 29.7 310 16 8 9.0 4.9
14500 0.0 32.0 320 14 7 8.4 4.6 | -0.0 32.0 310 16 8 9.3 5.1
14000 1.3 34.3 320 14 7 8.5 4.7 | 1.4 34.5 310 16 8 9.4 5.1
13500 2.5 36.5 320 15 8 8.6 4.7 | 2.8 37.0 310 16 8 9.4 5.1
13000 3.8 38.8 320 15 8 8.7 4.7 | 4.2 39.6 310 16 8 9.4 5.1
12500 5.0 41.0 320 16 8 8.7 4.8 | 5.6 42.1 310 16 8 9.4 5.2
12000 6.3 43.3 320 16 8 8.8 4.8 | 7.0 44.6 310 16 8 9.4 5.2
11500 7.6 45.7 315 16 8 8.8 4.8 | 8.4 47.1 310 16 8 9.4 5.2
11000 8.9 48.0 315 17 9 8.5 4.6 | 9.8 49.6 310 16 8 9.0 5.0
10500 10.2 50.4 315 17 9 4.7 2.6 | 11.2 52.2 310 15 8 3.9 2.1
10250 10.4 50.7 320 17 9 4.9 2.7 | 11.2 52.2 310 15 8 5.5 3.0
10000 11.1 52.0 320 17 9 11.4 6.3 | 12.1 53.8 310 14 7 13.5 7.4
9750 11.9 53.4 315 17 9 11.8 6.5 | 13.0 55.4 305 14 7 12.0 6.6
9500 12.7 54.9 315 18 9 9.2 5.0 | 13.9 57.0 305 14 7 9.8 5.4
9250 13.2 55.8 315 18 9 5.6 3.1 | 14.4 57.9 305 13 7 7.0 3.8
9000 13.7 56.7 315 18 9 8.9 4.9 | 15.0 59.0 305 13 7 10.4 5.7
8750 14.5 58.1 310 17 9 11.6 6.4 | 15.9 60.6 305 13 7 12.7 6.9
8500 15.3 59.5 310 17 9 9.0 4.9 | 16.8 62.2 305 13 7 10.0 5.5
8250 15.9 60.6 310 18 9 6.8 3.7 | 17.4 63.3 305 13 7 7.4 4.1
8000 16.4 61.5 310 18 9 8.5 4.7 | 18.0 64.4 310 13 6 9.9 5.5
7750 17.1 62.8 305 18 9 9.8 5.4 | 18.9 66.0 310 12 6 12.0 6.6
7500 17.8 64.0 305 17 9 7.4 4.1 | 19.7 67.5 310 12 6 9.6 5.3
7250 18.2 64.8 305 17 9 5.5 3.0 | 20.3 68.5 310 12 6 7.7 4.2
7000 18.6 65.5 300 17 9 7.1 3.9 | 21.0 69.8 310 12 6 9.8 5.4
6750 19.2 66.6 300 16 8 7.9 4.3 | 21.8 71.2 310 12 6 12.5 6.9
6500 19.7 67.5 295 13 7 5.6 3.1 | 22.7 72.9 310 11 6 11.2 6.1
6250 20.0 68.0 285 12 6 4.9 2.7 | 23.5 74.3 310 11 6 9.9 5.4
6000 20.4 68.7 275 10 5 4.0 2.2 | 24.2 75.6 310 11 5 10.3 5.6
5750 20.7 69.3 270 9 4 7.9 4.3 | 25.1 77.2 310 10 5 16.1 8.8
5500 21.7 71.1 265 7 4 17.8 9.8 | 26.7 80.1 310 9 5 25.8 14.1
09/08/2025 at 1500 MDT | 09/08/2025 at 1800 MDT
|
CAPE... +69.2 LI... -0.6 | CAPE... +65.5 LI... -1.0
CINH... -6.2 K Index... +21.4 | CINH... -69.5 K Index... +24.8
|
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 -62.4 -80.3 290 40 21 1.6 0.9 | -63.4 -82.1 300 41 21 0.4 0.2
45000 -59.8 -75.6 300 56 29 2.2 1.2 | -61.5 -78.7 300 57 29 4.0 2.2
40000 -56.2 -69.2 310 66 34 6.5 3.6 | -55.4 -67.7 305 59 30 6.3 3.4
38000 -52.3 -62.1 305 59 30 6.5 3.6 | -51.7 -61.1 305 55 28 6.2 3.4
36000 -48.4 -55.1 295 53 27 6.5 3.6 | -47.9 -54.2 300 52 27 6.2 3.4
34000 -43.3 -45.9 295 49 25 7.9 4.3 | -43.0 -45.4 295 48 25 7.8 4.3
32000 -38.6 -37.5 290 46 24 7.8 4.3 | -38.3 -36.9 290 44 23 7.7 4.2
30000 -33.9 -29.0 285 44 23 7.9 4.3 | -33.5 -28.3 285 41 21 8.0 4.4
29000 -31.5 -24.7 285 43 22 7.9 4.3 | -31.2 -24.2 285 40 21 8.0 4.4
28000 -29.1 -20.4 280 42 21 7.8 4.3 | -28.8 -19.8 280 39 20 7.5 4.1
27000 -26.9 -16.4 280 40 20 7.6 4.2 | -26.8 -16.2 280 36 18 6.4 3.5
26000 -24.6 -12.3 280 38 20 7.6 4.2 | -24.9 -12.8 275 32 17 6.5 3.5
25000 -22.3 -8.1 280 36 19 7.8 4.3 | -23.0 -9.4 275 29 15 6.5 3.6
24000 -20.5 -4.9 280 33 17 5.9 3.2 | -21.1 -6.0 270 28 14 6.7 3.7
23000 -18.8 -1.8 280 30 15 5.9 3.2 | -19.1 -2.4 270 27 14 6.8 3.7
22000 -17.0 1.4 280 26 13 6.0 3.3 | -17.1 1.2 270 27 14 6.8 3.7
21000 -15.0 5.0 285 24 12 7.3 4.0 | -15.0 5.0 275 26 13 7.5 4.1
20000 -12.8 9.0 290 23 12 7.3 4.0 | -12.8 9.0 275 25 13 7.5 4.1
19500 -11.7 10.9 290 22 11 7.3 4.0 | -11.7 10.9 275 25 13 7.5 4.1
19000 -10.6 12.9 290 21 11 7.5 4.1 | -9.9 14.2 280 24 12 8.1 4.5
18500 -9.5 14.9 290 20 11 7.6 4.2 | -8.7 16.3 280 23 12 8.1 4.4
18000 -8.4 16.9 295 20 10 7.8 4.3 | -7.5 18.5 280 22 12 8.6 4.7
17500 -6.6 20.1 295 19 10 8.5 4.7 | -6.3 20.7 280 21 11 8.7 4.8
17000 -5.3 22.5 295 18 9 8.6 4.7 | -5.0 23.0 280 20 10 8.7 4.8
16500 -4.1 24.6 295 18 9 8.8 4.8 | -3.7 25.3 280 19 10 8.9 4.9
16000 -2.8 27.0 295 17 9 8.7 4.8 | -2.4 27.7 285 18 9 8.9 4.9
15500 -1.4 29.5 295 16 8 9.3 5.1 | -1.1 30.0 285 17 9 9.2 5.0
15000 -0.1 31.8 300 15 8 9.2 5.1 | 0.3 32.5 285 16 8 9.2 5.0
14500 1.3 34.3 300 15 8 9.4 5.2 | 1.7 35.1 290 15 8 9.1 5.0
14000 2.7 36.9 300 14 7 9.4 5.2 | 3.0 37.4 290 14 7 9.0 5.0
13500 4.1 39.4 305 13 7 9.5 5.2 | 4.3 39.7 290 14 7 9.0 4.9
13000 5.6 42.1 305 13 7 9.6 5.3 | 5.7 42.3 295 13 7 8.9 4.9
12500 7.0 44.6 305 12 6 9.5 5.2 | 7.0 44.6 295 12 6 8.9 4.9
12000 8.4 47.1 305 12 6 9.5 5.2 | 8.3 46.9 295 11 6 9.0 4.9
11500 9.8 49.6 305 11 6 9.4 5.2 | 9.6 49.3 300 10 5 8.9 4.9
11000 11.2 52.2 310 11 6 9.1 5.0 | 11.0 51.8 300 10 5 8.4 4.6
10500 12.6 54.7 310 10 5 4.4 2.4 | 12.3 54.1 300 9 5 4.6 2.5
10250 12.8 55.0 310 11 6 6.1 3.3 | 12.5 54.5 300 9 5 5.8 3.2
10000 13.7 56.7 310 10 5 13.7 7.5 | 13.2 55.8 300 9 5 11.7 6.4
9750 14.6 58.3 310 10 5 12.3 6.7 | 14.0 57.2 305 9 4 10.5 5.8
9500 15.5 59.9 310 10 5 10.3 5.6 | 14.8 58.6 305 8 4 9.5 5.2
9250 16.1 61.0 310 10 5 7.6 4.2 | 15.4 59.7 305 8 4 7.1 3.9
9000 16.8 62.2 310 10 5 10.3 5.6 | 16.0 60.8 300 8 4 8.8 4.8
8750 17.6 63.7 315 10 5 11.9 6.5 | 16.7 62.1 305 8 4 10.5 5.7
8500 18.5 65.3 315 10 5 10.2 5.6 | 17.4 63.3 305 7 4 9.3 5.1
8250 19.1 66.4 315 10 5 8.1 4.4 | 18.1 64.6 305 7 4 7.9 4.3
8000 19.8 67.6 315 10 5 10.0 5.5 | 18.7 65.7 300 8 4 8.6 4.7
7750 20.6 69.1 315 10 5 12.1 6.6 | 19.4 66.9 305 7 4 10.0 5.5
7500 21.5 70.7 315 9 5 9.8 5.4 | 20.1 68.2 310 6 3 8.6 4.7
7250 22.1 71.8 315 10 5 7.7 4.2 | 20.6 69.1 305 6 3 7.0 3.9
7000 22.7 72.9 315 10 5 9.6 5.3 | 21.2 70.2 300 7 3 8.2 4.5
6750 23.5 74.3 315 9 5 12.5 6.9 | 21.9 71.4 300 6 3 10.8 5.9
6500 24.5 76.1 315 9 5 11.3 6.2 | 22.7 72.9 305 5 3 10.1 5.6
6250 25.2 77.4 315 9 5 9.9 5.4 | 23.4 74.1 300 5 3 8.7 4.8
6000 26.0 78.8 315 9 5 9.3 5.1 | 24.0 75.2 295 5 3 8.9 4.9
5750 26.8 80.2 315 8 4 14.7 8.1 | 24.7 76.5 295 5 3 10.1 5.6
5500 28.3 82.9 315 8 4 27.1 14.9 | 25.6 78.1 295 4 2 13.0 7.2
________________________________________________________________________________
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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