Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
380
UXUS97 KBOU 081317
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0617 MST Monday, December 8, 2025
This forecast is for Monday, December 8, 2025:
If the trigger temperature of 54.6 F/12.6 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 250 ft/min (1.3 m/s)
Maximum height of thermals.................. 8806 ft MSL (3545 ft AGL)
Forecast maximum temperature................... 53.0 F/12.1 C
Time of trigger temperature.................... None
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................. 7323 ft MSL (2062 ft AGL)
Thermal soaring outlook for Tuesday 12/09...... Fair
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1700 MST)......... No change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1700 MST)................ Neither
Potential height of wave....................... 27136 ft MSL (21875 ft AGL)
Wave soaring outlook for Tuesday 12/09......... Fair
Remarks...
Sunrise/Sunset.................... 07:08:31 / 16:34:43 MST
Total possible sunshine........... 9 hr 26 min 12 sec (566 min 12 sec)
Altitude of sun at 11:51:37 MST... 27.40 degrees
Upper air data from numerical model forecast valid on 12/08/2025 at 0500 MST
Freezing level.................. 5456 ft MSL (195 ft AGL)
Additional freezing level....... 9590 ft MSL (4329 ft AGL)
Convective condensation level... 15270 ft MSL (10009 ft AGL)
Lifted condensation level....... 13601 ft MSL (8340 ft AGL)
Lifted index.................... +4.1
K index......................... +10.4
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 -63.2 -81.8 295 60 31 2.0 1.1 M M M M M
45000 -60.2 -76.4 290 55 28 2.0 1.1 M M M M M
40000 -58.1 -72.6 300 48 25 1.3 0.7 M M M M M
38000 -56.6 -69.9 300 46 24 4.2 2.3 M M M M M
36000 -54.0 -65.2 305 43 22 4.2 2.3 M M M M M
34000 -51.5 -60.7 305 40 21 4.3 2.4 M M M M M
32000 -48.9 -56.0 305 45 23 4.4 2.4 M M M M M
30000 -46.2 -51.2 305 50 26 5.4 3.0 30.7 87.2 14.2 M M
29000 -44.6 -48.3 305 52 27 5.6 3.1 28.9 84.0 13.0 M M
28000 -42.9 -45.2 300 54 28 5.6 3.1 27.2 81.0 11.9 M M
27000 -40.8 -41.4 300 56 29 6.1 3.4 25.4 77.7 10.7 M M
26000 -38.6 -37.5 300 55 28 7.4 4.0 24.3 75.7 9.9 M M
25000 -36.4 -33.5 300 54 28 7.4 4.1 23.4 74.1 9.3 M M
24000 -34.2 -29.6 300 53 27 7.5 4.1 22.6 72.7 8.8 M M
23000 -31.8 -25.2 300 51 26 8.2 4.5 21.9 71.5 8.3 M M
22000 -29.4 -20.9 300 48 25 8.2 4.5 21.3 70.4 7.9 M M
21000 -27.0 -16.6 300 44 23 7.6 4.2 20.9 69.5 7.6 M M
20000 -24.8 -12.6 295 37 19 7.4 4.0 19.9 67.9 6.9 M M
19500 -23.7 -10.7 295 34 17 7.4 4.0 19.5 67.1 6.6 M M
19000 -22.6 -8.7 290 30 16 7.4 4.0 19.1 66.4 6.3 M M
18500 -21.5 -6.7 285 27 14 7.4 4.0 18.8 65.8 6.0 M M
18000 -20.4 -4.7 280 24 12 7.3 4.0 18.3 65.0 5.6 M M
17500 -19.3 -2.7 280 21 11 7.3 4.0 17.9 64.2 5.3 M M
17000 -18.2 -0.8 275 18 9 7.7 4.2 17.5 63.6 5.0 M M
16500 -17.1 1.2 275 16 8 7.7 4.2 17.2 62.9 4.7 M M
16000 -15.9 3.4 275 14 7 8.0 4.4 16.9 62.3 4.4 M M
15500 -14.7 5.5 275 12 6 8.1 4.5 16.6 61.8 4.2 M M
15000 -13.5 7.7 280 10 5 9.0 5.0 16.3 61.3 4.0 M M
14500 -12.0 10.4 290 11 5 9.8 5.4 16.3 61.4 4.0 M M
14000 -10.5 13.1 295 11 6 9.7 5.3 16.3 61.4 4.0 M M
13500 -9.1 15.6 300 12 6 9.5 5.2 16.3 61.3 4.0 M M
13000 -7.0 19.4 305 14 7 9.1 5.0 16.2 61.2 4.0 M M
12500 -5.7 21.7 310 17 9 9.1 5.0 16.1 61.0 3.9 M M
12000 -4.4 24.1 310 20 10 7.9 4.3 15.9 60.7 3.7 M M
11500 -3.3 26.1 310 24 13 7.5 4.1 15.6 60.0 3.4 M M
11000 -2.2 28.0 310 28 15 7.2 4.0 15.2 59.3 3.0 M M
10500 -1.1 30.0 310 33 17 7.9 4.3 14.8 58.6 2.6 M M
10250 -0.6 30.9 310 35 18 4.2 2.3 14.5 58.2 2.4 M M
10000 -0.5 31.1 310 36 18 2.3 1.3 13.9 57.1 1.9 M M
9750 -0.2 31.6 305 38 19 5.3 2.9 13.5 56.3 1.4 M M
9500 0.2 32.4 305 40 21 5.6 3.1 13.2 55.7 1.1 M M
9250 0.6 33.1 305 43 22 4.5 2.5 12.8 55.1 0.8 M M
9000 0.9 33.6 300 44 23 3.0 1.6 12.3 54.2 0.3 M M
8750 1.1 34.0 300 45 23 2.9 1.6 11.8 53.2 -0.2 244 1.2
8500 1.3 34.3 300 45 23 2.9 1.6 11.3 52.3 -0.8 231 1.2
8250 1.5 34.7 295 45 23 3.3 1.8 10.7 51.3 -1.3 217 1.1
8000 1.7 35.1 295 43 22 3.7 2.1 10.3 50.5 -1.8 202 1.0
7750 2.0 35.6 290 40 21 3.3 1.8 9.8 49.6 -2.2 187 1.0
7500 2.2 36.0 290 37 19 3.6 2.0 9.3 48.7 -2.7 173 0.9
7250 2.5 36.5 290 34 17 4.7 2.6 8.9 48.0 -3.2 156 0.8
7000 2.9 37.2 290 30 16 4.7 2.6 8.5 47.3 -3.6 138 0.7
6750 3.3 37.9 290 27 14 5.3 2.9 8.1 46.6 -3.9 120 0.6
6500 3.5 38.3 285 23 12 -0.0 -0.0 7.7 45.8 -4.4 104 0.5
6250 3.2 37.8 280 19 10 -5.4 -3.0 6.6 43.9 -5.4 106 0.5
6000 3.0 37.4 275 15 8 -1.5 -0.9 5.6 42.1 -6.5 107 0.5
5750 2.7 36.9 260 11 6 -11.7 -6.4 4.6 40.2 -7.5 109 0.6
5500 0.7 33.3 235 7 4 -41.8 -22.9 1.9 35.4 -10.2 160 0.8
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
12/08/2025 at 0800 MST | 12/08/2025 at 1100 MST
|
CAPE... 0.0 LI... +2.5 | CAPE... 0.0 LI... +7.0
CINH... 0.0 K Index... +9.0 | CINH... 0.0 K Index... -1.9
|
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 -62.5 -80.5 295 57 29 1.9 1.0 | -62.0 -79.6 295 51 26 1.4 0.7
45000 -59.7 -75.5 290 55 28 2.0 1.1 | -59.9 -75.8 295 60 31 1.4 0.8
40000 -59.6 -75.3 300 51 26 -0.1 -0.0 | -60.7 -77.3 305 55 29 -0.6 -0.3
38000 -58.4 -73.1 305 49 25 4.6 2.5 | -60.0 -76.0 310 51 26 3.2 1.7
36000 -55.7 -68.3 305 45 23 4.6 2.5 | -58.2 -72.8 325 44 23 3.2 1.7
34000 -52.9 -63.2 310 42 22 6.0 3.3 | -55.9 -68.6 335 41 21 8.8 4.8
32000 -49.2 -56.6 325 42 22 6.1 3.3 | -50.8 -59.4 340 43 22 8.5 4.7
30000 -45.4 -49.7 335 44 23 8.1 4.4 | -45.1 -49.2 345 44 23 8.7 4.8
29000 -42.4 -44.3 335 44 23 8.1 4.4 | -42.5 -44.5 345 42 22 8.7 4.8
28000 -40.0 -40.0 335 43 22 8.1 4.4 | -39.9 -39.8 345 40 21 8.7 4.8
27000 -37.5 -35.5 340 43 22 7.2 4.0 | -37.3 -35.1 345 39 20 7.5 4.1
26000 -35.8 -32.4 335 39 20 5.7 3.1 | -35.3 -31.5 345 39 20 6.7 3.7
25000 -34.1 -29.4 330 36 19 5.7 3.1 | -33.3 -27.9 340 40 21 6.7 3.6
24000 -32.4 -26.3 325 33 17 5.7 3.1 | -31.3 -24.3 340 41 21 7.0 3.8
23000 -30.6 -23.1 320 32 16 6.2 3.4 | -29.0 -20.2 340 41 21 7.8 4.3
22000 -28.7 -19.7 320 32 16 6.2 3.4 | -26.7 -16.1 340 41 21 7.8 4.3
21000 -26.9 -16.4 315 32 16 6.0 3.3 | -24.4 -11.9 340 40 21 7.3 4.0
20000 -25.1 -13.2 310 28 14 5.9 3.2 | -22.2 -8.0 335 37 19 7.2 3.9
19500 -24.3 -11.7 305 26 13 5.9 3.2 | -21.1 -6.0 335 35 18 7.2 3.9
19000 -23.4 -10.1 300 25 13 6.0 3.3 | -20.1 -4.2 330 33 17 7.1 3.9
18500 -22.5 -8.5 295 23 12 6.7 3.7 | -19.0 -2.2 330 32 16 5.8 3.2
18000 -21.4 -6.5 295 21 11 7.6 4.2 | -18.3 -0.9 330 29 15 4.5 2.5
17500 -20.3 -4.5 295 19 10 7.6 4.2 | -17.7 0.1 325 26 14 4.4 2.4
17000 -19.1 -2.4 300 18 9 7.9 4.3 | -17.0 1.4 325 23 12 4.8 2.6
16500 -18.0 -0.4 305 16 8 7.9 4.3 | -16.3 2.7 325 20 10 4.7 2.6
16000 -16.8 1.8 310 15 8 8.0 4.4 | -15.2 4.6 320 15 8 5.8 3.2
15500 -15.6 3.9 305 14 7 8.0 4.4 | -14.3 6.3 305 12 6 5.7 3.1
15000 -13.8 7.2 310 13 7 8.2 4.5 | -13.4 7.9 295 10 5 6.7 3.7
14500 -12.6 9.3 315 14 7 8.2 4.5 | -12.4 9.7 275 10 5 6.7 3.7
14000 -11.4 11.5 320 15 8 8.2 4.5 | -11.5 11.3 265 10 5 6.1 3.4
13500 -10.2 13.6 325 16 8 8.2 4.5 | -10.6 12.9 270 10 5 6.0 3.3
13000 -8.9 16.0 330 17 9 8.1 4.5 | -9.7 14.5 285 10 5 7.1 3.9
12500 -7.7 18.1 330 20 10 8.1 4.4 | -8.6 16.5 310 10 5 7.4 4.0
12000 -6.5 20.3 330 22 11 7.9 4.3 | -7.5 18.5 330 13 7 7.3 4.0
11500 -5.4 22.3 330 26 13 7.8 4.3 | -6.4 20.5 335 16 8 7.2 3.9
11000 -4.2 24.4 330 29 15 7.4 4.1 | -5.3 22.5 340 20 10 7.9 4.3
10500 -3.2 26.2 325 30 15 8.0 4.4 | -4.1 24.6 335 21 11 8.6 4.7
10250 -2.6 27.3 325 30 16 4.7 2.6 | -3.6 25.5 330 21 11 5.7 3.1
10000 -2.4 27.7 325 31 16 4.0 2.2 | -3.3 26.1 330 22 11 4.8 2.6
9750 -1.9 28.6 320 32 17 7.8 4.3 | -2.8 27.0 325 24 12 7.8 4.3
9500 -1.3 29.7 320 34 17 8.7 4.8 | -2.2 28.0 320 25 13 8.2 4.5
9250 -0.8 30.6 315 35 18 6.2 3.4 | -1.6 29.1 320 27 14 6.7 3.7
9000 -0.5 31.1 315 36 19 3.4 1.9 | -1.2 29.8 315 28 14 5.0 2.8
8750 -0.2 31.6 310 37 19 4.7 2.6 | -0.8 30.6 310 29 15 5.4 3.0
8500 0.2 32.4 310 37 19 5.1 2.8 | -0.4 31.3 305 30 16 5.5 3.0
8250 0.6 33.1 310 37 19 4.4 2.4 | -0.1 31.8 305 31 16 5.6 3.1
8000 0.8 33.4 305 36 18 3.9 2.1 | 0.4 32.7 305 29 15 5.8 3.2
7750 1.1 34.0 305 35 18 4.3 2.4 | 0.8 33.4 300 28 15 5.7 3.1
7500 1.5 34.7 305 32 17 4.8 2.6 | 1.2 34.2 300 26 14 7.1 3.9
7250 1.8 35.2 305 30 15 5.0 2.7 | 1.8 35.2 300 24 13 8.7 4.8
7000 2.2 36.0 305 27 14 4.9 2.7 | 2.4 36.3 300 22 11 9.1 5.0
6750 2.6 36.7 305 24 12 5.2 2.8 | 3.1 37.6 300 20 10 7.6 4.2
6500 2.9 37.2 305 21 11 4.7 2.6 | 3.6 38.5 300 18 9 5.2 2.8
6250 3.2 37.8 305 17 9 2.0 1.1 | 3.9 39.0 295 15 8 4.8 2.6
6000 3.5 38.3 305 14 7 8.5 4.7 | 4.3 39.7 290 11 6 5.0 2.7
5750 3.7 38.7 300 10 5 -14.8 -8.1 | 4.7 40.5 280 9 4 8.0 4.4
5500 0.5 32.9 265 4 2 -66.8 -36.7 | 5.4 41.7 275 7 4 12.1 6.6
12/08/2025 at 1400 MST | 12/08/2025 at 1700 MST
|
CAPE... 0.0 LI... +8.1 | CAPE... 0.0 LI... +8.9
CINH... 0.0 K Index... -19.0 | CINH... 0.0 K Index... -25.7
|
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 -62.4 -80.3 295 49 25 1.7 1.0 | -62.8 -81.0 300 45 23 1.3 0.7
45000 -59.8 -75.6 305 55 28 1.9 1.1 | -60.9 -77.6 310 53 27 1.5 0.8
40000 -61.7 -79.1 315 63 32 -1.4 -0.8 | -63.0 -81.4 330 65 34 -1.5 -0.8
38000 -61.1 -78.0 315 63 32 4.0 2.2 | -61.9 -79.4 335 67 35 5.3 2.9
36000 -58.7 -73.7 320 58 30 4.0 2.2 | -58.8 -73.8 335 65 34 5.3 2.9
34000 -55.9 -68.6 325 54 28 8.7 4.8 | -55.2 -67.4 340 64 33 8.7 4.8
32000 -51.0 -59.8 325 50 26 8.2 4.5 | -50.1 -58.2 340 63 33 8.5 4.7
30000 -45.9 -50.6 330 47 24 9.4 5.1 | -45.0 -49.0 340 62 32 8.8 4.8
29000 -42.5 -44.5 330 46 24 9.3 5.1 | -42.4 -44.3 335 59 30 8.8 4.8
28000 -39.7 -39.5 325 45 23 9.3 5.1 | -39.0 -38.2 330 56 29 8.8 4.9
27000 -36.9 -34.4 325 45 23 8.1 4.5 | -36.4 -33.5 325 54 28 8.6 4.7
26000 -34.6 -30.3 325 46 24 7.8 4.3 | -33.9 -29.0 325 54 28 8.5 4.7
25000 -32.3 -26.1 330 47 24 7.8 4.3 | -31.3 -24.3 320 54 28 8.5 4.7
24000 -30.0 -22.0 330 48 25 7.8 4.3 | -28.8 -19.8 320 53 27 8.0 4.4
23000 -27.6 -17.7 330 46 24 7.9 4.3 | -26.6 -15.9 320 51 26 7.5 4.1
22000 -25.3 -13.5 330 44 23 7.9 4.3 | -24.4 -11.9 320 48 25 7.5 4.1
21000 -23.0 -9.4 330 42 21 7.5 4.1 | -22.1 -7.8 320 45 23 7.3 4.0
20000 -20.7 -5.3 325 36 18 7.5 4.1 | -20.0 -4.0 315 41 21 7.3 4.0
19500 -19.6 -3.3 325 33 17 7.5 4.1 | -18.9 -2.0 315 39 20 7.3 4.0
19000 -18.4 -1.1 320 30 16 7.5 4.1 | -17.8 -0.0 315 37 19 7.3 4.0
18500 -17.3 0.9 315 28 14 7.9 4.3 | -16.7 1.9 315 35 18 7.3 4.0
18000 -16.1 3.0 315 27 14 8.1 4.5 | -15.6 3.9 315 33 17 7.3 4.0
17500 -14.9 5.2 310 26 13 8.2 4.5 | -14.5 5.9 310 31 16 7.2 4.0
17000 -13.9 7.0 310 24 12 5.1 2.8 | -13.4 7.9 310 30 15 6.8 3.7
16500 -13.1 8.4 300 22 11 5.5 3.0 | -12.4 9.7 310 28 14 6.9 3.8
16000 -12.4 9.7 295 21 11 3.0 1.6 | -11.4 11.5 310 26 14 5.4 3.0
15500 -11.9 10.6 285 19 10 2.5 1.4 | -10.6 12.9 305 25 13 5.2 2.8
15000 -11.6 11.1 280 18 9 1.6 0.9 | -9.9 14.2 300 24 13 3.5 1.9
14500 -11.3 11.7 275 16 8 1.5 0.8 | -9.4 15.1 295 21 11 1.8 1.0
14000 -11.0 12.2 275 14 7 4.2 2.3 | -9.1 15.6 295 19 10 2.6 1.4
13500 -10.3 13.5 275 12 6 4.5 2.4 | -8.7 16.3 295 16 8 2.5 1.4
13000 -9.5 14.9 280 10 5 7.4 4.1 | -8.2 17.2 300 13 7 6.6 3.6
12500 -8.3 17.1 285 9 5 8.3 4.6 | -7.0 19.4 305 12 6 7.6 4.2
12000 -7.0 19.4 290 9 5 9.3 5.1 | -5.9 21.4 310 11 5 7.8 4.3
11500 -5.5 22.1 295 11 6 9.8 5.4 | -4.7 23.5 315 12 6 7.9 4.3
11000 -4.2 24.4 300 14 7 7.8 4.3 | -3.6 25.5 315 14 7 7.4 4.1
10500 -3.1 26.4 300 19 10 7.8 4.3 | -2.5 27.5 310 18 9 7.9 4.3
10250 -2.6 27.3 300 22 11 5.1 2.8 | -2.0 28.4 305 20 10 4.8 2.6
10000 -2.4 27.7 300 23 12 3.1 1.7 | -1.8 28.8 305 20 11 3.0 1.6
9750 -2.1 28.2 300 26 13 4.6 2.5 | -1.5 29.3 300 23 12 5.2 2.8
9500 -1.8 28.8 295 29 15 5.1 2.8 | -1.1 30.0 300 25 13 5.5 3.0
9250 -1.4 29.5 295 32 16 3.7 2.0 | -0.7 30.7 295 28 14 4.3 2.3
9000 -1.3 29.7 290 31 16 3.0 1.6 | -0.5 31.1 290 29 15 3.0 1.6
8750 -1.0 30.2 290 30 15 5.8 3.2 | -0.3 31.5 290 29 15 4.1 2.3
8500 -0.5 31.1 290 28 14 7.0 3.9 | 0.0 32.0 285 28 15 4.6 2.5
8250 0.0 32.0 285 26 13 8.2 4.5 | 0.4 32.7 285 27 14 5.2 2.8
8000 0.7 33.3 285 24 12 9.5 5.2 | 0.7 33.3 280 25 13 5.6 3.0
7750 1.4 34.5 285 22 11 8.6 4.7 | 1.2 34.2 280 22 12 7.2 3.9
7500 2.0 35.6 290 21 11 8.4 4.6 | 1.8 35.2 280 20 11 8.4 4.6
7250 2.6 36.7 290 19 10 8.7 4.8 | 2.3 36.1 275 18 10 7.7 4.2
7000 3.3 37.9 290 17 9 8.7 4.8 | 2.9 37.2 275 16 8 7.5 4.1
6750 3.9 39.0 285 14 7 8.7 4.8 | 3.5 38.3 275 14 7 8.4 4.6
6500 4.6 40.3 285 13 6 8.7 4.7 | 4.1 39.4 270 12 6 8.4 4.6
6250 5.2 41.4 285 11 6 8.6 4.7 | 4.7 40.5 265 10 5 7.3 4.0
6000 5.8 42.4 285 10 5 8.6 4.7 | 5.2 41.4 260 9 4 8.6 4.7
5750 6.4 43.5 280 8 4 8.6 4.7 | 5.8 42.4 250 7 3 4.6 2.5
5500 7.0 44.6 280 7 4 9.6 5.2 | 5.7 42.3 230 5 3 -5.2 -2.9
________________________________________________________________________________
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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