Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
382
UXUS97 KBOU 201251
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0550 MST Thursday, November 20, 2025
This forecast is for Thursday, November 20, 2025:
If the trigger temperature of 59.9 F/15.5 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 0 ft/min (0.0 m/s)
Maximum height of thermals.................. 6962 ft MSL (1646 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....... Broken/overcast opaque middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 6134 ft MSL (818 ft AGL)
Thermal soaring outlook for Friday 11/21....... Poor
Wave Soaring Index............................. Poor
Wave Soaring Index trend (to 1700 MST)......... Little change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1700 MST)................ Weak PVA
Potential height of wave....................... 33088 ft MSL (27772 ft AGL)
Wave soaring outlook for Friday 11/21.......... Poor
Remarks... Rain showers possible this afternoon into tonight
Sunrise/Sunset.................... 06:50:24 / 16:40:00 MST
Total possible sunshine........... 9 hr 49 min 35 sec (589 min 35 sec)
Altitude of sun at 11:45:12 MST... 30.26 degrees
Upper air data from numerical model forecast valid on 11/20/2025 at 0500 MST
Freezing level.................. 10915 ft MSL (5599 ft AGL)
Convective condensation level... 14946 ft MSL (9630 ft AGL)
Lifted condensation level....... 12280 ft MSL (6964 ft AGL)
Lifted index.................... +6.4
K index......................... +20.0
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 -58.4 -73.1 255 26 14 1.9 1.1 M M M M M
45000 -55.4 -67.7 245 34 18 2.5 1.4 M M M M M
40000 -51.8 -61.2 235 36 18 2.4 1.3 M M M M M
38000 -51.6 -60.9 230 43 22 -1.5 -0.8 M M M M M
36000 -52.4 -62.3 230 56 29 -1.5 -0.8 M M M M M
34000 -52.8 -63.0 225 67 35 6.3 3.4 M M M M M
32000 -49.6 -57.3 220 65 33 5.4 2.9 M M M M M
30000 -45.3 -49.5 215 60 31 9.1 5.0 29.8 85.6 13.6 M M
29000 -42.6 -44.7 215 55 28 9.2 5.0 29.4 85.0 13.5 M M
28000 -39.8 -39.6 215 49 25 9.2 5.0 29.2 84.6 13.5 M M
27000 -37.1 -34.8 215 44 23 8.6 4.7 29.1 84.4 13.6 M M
26000 -34.6 -30.3 215 41 21 8.4 4.6 28.5 83.3 13.2 M M
25000 -32.1 -25.8 215 37 19 8.4 4.6 28.0 82.3 13.0 M M
24000 -29.7 -21.5 220 34 18 7.8 4.3 27.6 81.6 12.8 M M
23000 -27.6 -17.7 215 31 16 6.8 3.7 26.4 79.5 12.0 M M
22000 -25.6 -14.1 215 28 14 6.8 3.7 25.3 77.6 11.2 M M
21000 -23.6 -10.5 210 25 13 6.8 3.7 24.3 75.8 10.5 M M
20000 -21.6 -6.9 210 23 12 6.9 3.8 23.2 73.8 9.6 M M
19500 -20.6 -5.1 205 22 11 6.9 3.8 22.7 72.9 9.2 M M
19000 -19.6 -3.3 205 21 11 6.9 3.8 22.2 72.0 8.9 M M
18500 -18.6 -1.5 200 20 10 7.1 3.9 21.8 71.2 8.5 M M
18000 -17.5 0.5 205 18 9 7.2 4.0 21.3 70.4 8.2 M M
17500 -16.4 2.5 205 16 8 7.3 4.0 20.9 69.7 7.8 M M
17000 -15.3 4.5 205 14 7 7.5 4.1 20.5 68.9 7.5 M M
16500 -14.2 6.4 210 13 6 7.5 4.1 20.1 68.2 7.2 M M
16000 -12.5 9.5 210 11 6 7.9 4.3 19.6 67.3 6.7 M M
15500 -11.4 11.5 205 10 5 7.9 4.3 19.3 66.7 6.5 M M
15000 -10.2 13.6 205 10 5 8.1 4.5 19.0 66.2 6.2 M M
14500 -9.0 15.8 200 10 5 8.1 4.4 18.7 65.7 6.0 M M
14000 -7.8 18.0 195 10 5 8.4 4.6 18.5 65.3 5.8 M M
13500 -6.5 20.3 190 10 5 8.4 4.6 18.3 64.9 5.6 M M
13000 -5.3 22.5 185 10 5 8.6 4.7 18.1 64.5 5.4 M M
12500 -4.0 24.8 185 9 5 8.6 4.7 17.9 64.1 5.3 M M
12000 -2.7 27.1 180 9 5 8.7 4.8 17.7 63.8 5.1 M M
11500 -1.4 29.5 180 9 4 8.8 4.8 17.5 63.5 5.0 M M
11000 -0.1 31.8 180 8 4 8.3 4.6 17.4 63.3 4.9 M M
10500 1.1 34.0 180 7 4 8.9 4.9 17.1 62.7 4.6 M M
10250 1.6 34.9 180 7 3 4.4 2.4 16.9 62.5 4.5 M M
10000 1.8 35.2 185 7 3 4.6 2.5 16.4 61.4 4.0 M M
9750 2.4 36.3 190 6 3 9.1 5.0 16.2 61.2 3.8 M M
9500 3.0 37.4 190 6 3 8.2 4.5 16.1 61.0 3.7 M M
9250 3.7 38.7 195 5 3 7.3 4.0 16.0 60.8 3.6 M M
9000 4.1 39.4 200 5 2 5.7 3.1 15.7 60.3 3.4 M M
8750 4.6 40.3 205 4 2 6.4 3.5 15.4 59.8 3.1 M M
8500 5.1 41.2 215 3 2 7.4 4.1 15.2 59.4 2.9 M M
8250 5.6 42.1 220 3 1 5.7 3.1 15.0 59.0 2.7 M M
8000 5.9 42.6 235 2 1 3.6 2.0 14.6 58.2 2.3 M M
7750 6.2 43.2 255 2 1 4.0 2.2 14.1 57.4 1.8 M M
7500 6.5 43.7 285 2 1 4.5 2.5 13.7 56.7 1.4 M M
7250 6.8 44.2 310 3 1 1.5 0.8 13.2 55.8 1.0 M M
7000 6.8 44.2 320 4 2 -0.9 -0.5 12.5 54.4 0.2 M M
6750 6.7 44.1 325 5 3 0.4 0.2 11.7 53.1 -0.5 107 0.5
6500 6.7 44.1 325 5 3 -1.5 -0.8 11.0 51.7 -1.3 100 0.5
6250 6.5 43.7 325 6 3 -4.3 -2.4 10.0 49.9 -2.3 100 0.5
6000 6.1 43.0 325 7 4 -5.3 -2.9 8.9 48.0 -3.4 103 0.5
5750 5.7 42.3 325 8 4 -2.9 -1.6 7.8 46.0 -4.5 107 0.5
5500 5.6 42.1 320 6 3 -0.2 -0.1 7.0 44.6 -5.3 102 0.5
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
11/20/2025 at 0800 MST | 11/20/2025 at 1100 MST
|
CAPE... 0.0 LI... +1.0 | CAPE... 0.0 LI... +1.8
CINH... -0.1 K Index... +21.1 | CINH... 0.0 K Index... +20.6
|
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 -58.4 -73.1 255 19 10 2.4 1.3 | -58.2 -72.8 270 18 9 3.4 1.8
45000 -54.8 -66.6 250 16 8 1.8 1.0 | -53.3 -63.9 255 15 8 1.3 0.7
40000 -51.9 -61.4 225 25 13 1.9 1.0 | -51.0 -59.8 225 27 14 1.5 0.8
38000 -51.7 -61.1 220 33 17 -0.8 -0.5 | -50.8 -59.4 220 32 16 -0.6 -0.3
36000 -52.2 -62.0 220 43 22 -0.8 -0.5 | -51.1 -60.0 215 37 19 -0.6 -0.3
34000 -52.3 -62.1 220 52 27 5.7 3.1 | -50.9 -59.6 215 41 21 4.1 2.2
32000 -48.7 -55.7 210 54 28 5.2 2.9 | -48.5 -55.3 205 42 21 4.1 2.2
30000 -45.1 -49.2 205 52 27 8.5 4.7 | -45.3 -49.5 195 42 22 9.2 5.1
29000 -42.5 -44.5 205 46 24 8.6 4.7 | -42.5 -44.5 195 41 21 9.4 5.1
28000 -39.9 -39.8 205 39 20 8.6 4.7 | -39.7 -39.5 195 39 20 9.4 5.1
27000 -37.3 -35.1 205 33 17 8.3 4.6 | -36.9 -34.4 190 38 19 8.7 4.8
26000 -34.9 -30.8 205 29 15 8.1 4.4 | -34.5 -30.1 190 32 16 8.0 4.4
25000 -32.5 -26.5 210 26 13 8.1 4.4 | -32.1 -25.8 185 26 13 8.0 4.4
24000 -30.1 -22.2 215 22 11 8.0 4.4 | -29.8 -21.6 180 20 10 7.9 4.3
23000 -27.8 -18.0 210 20 10 7.7 4.2 | -27.5 -17.5 180 16 8 7.5 4.1
22000 -25.5 -13.9 205 18 9 7.7 4.2 | -25.3 -13.5 180 14 7 7.5 4.1
21000 -23.2 -9.8 195 16 8 7.2 4.0 | -23.0 -9.4 180 11 6 7.6 4.2
20000 -21.1 -6.0 190 15 8 7.1 3.9 | -20.7 -5.3 175 12 6 7.7 4.2
19500 -20.1 -4.2 185 15 8 7.1 3.9 | -19.6 -3.3 175 12 6 7.7 4.2
19000 -19.0 -2.2 185 15 8 7.1 3.9 | -18.5 -1.3 175 12 6 7.7 4.2
18500 -18.0 -0.4 180 15 8 6.7 3.7 | -17.3 0.9 170 13 7 7.4 4.1
18000 -17.1 1.2 175 15 8 6.3 3.5 | -15.8 3.6 170 14 7 6.7 3.7
17500 -16.1 3.0 175 16 8 6.2 3.4 | -14.8 5.4 170 14 7 6.5 3.6
17000 -14.6 5.7 170 15 8 7.0 3.9 | -13.9 7.0 165 15 8 6.2 3.4
16500 -13.6 7.5 165 14 7 7.1 3.9 | -13.0 8.6 160 16 8 6.2 3.4
16000 -12.5 9.5 165 14 7 7.8 4.3 | -12.1 10.2 160 17 9 6.6 3.6
15500 -11.3 11.7 165 13 7 7.8 4.3 | -11.1 12.0 155 17 9 6.5 3.6
15000 -10.2 13.6 165 12 6 7.6 4.1 | -10.1 13.8 155 17 9 6.8 3.7
14500 -9.1 15.6 170 12 6 7.6 4.2 | -9.1 15.6 150 16 8 6.9 3.8
14000 -8.0 17.6 170 12 6 7.4 4.1 | -8.1 17.4 150 15 8 6.9 3.8
13500 -6.9 19.6 170 12 6 7.4 4.0 | -7.1 19.2 150 15 8 6.9 3.8
13000 -5.8 21.6 170 12 6 7.2 4.0 | -6.1 21.0 150 14 7 6.8 3.7
12500 -4.8 23.4 175 11 6 7.1 3.9 | -5.2 22.6 150 14 7 6.7 3.7
12000 -3.8 25.2 175 11 6 7.0 3.8 | -4.2 24.4 145 13 7 6.8 3.7
11500 -2.8 27.0 170 11 6 6.9 3.8 | -3.2 26.2 145 13 6 6.9 3.8
11000 -1.8 28.8 170 11 5 6.7 3.7 | -2.1 28.2 140 12 6 6.4 3.5
10500 -0.8 30.6 165 10 5 7.3 4.0 | -1.3 29.7 140 11 6 5.3 2.9
10250 -0.3 31.5 165 9 5 3.3 1.8 | -0.9 30.4 140 11 5 7.6 4.1
10000 -0.2 31.6 170 9 5 4.3 2.4 | -0.2 31.6 145 10 5 8.4 4.6
9750 0.4 32.7 165 8 4 9.0 4.9 | 0.3 32.5 145 10 5 6.6 3.6
9500 1.0 33.8 160 7 4 8.0 4.4 | 0.9 33.6 145 10 5 6.9 3.8
9250 1.6 34.9 160 6 3 7.5 4.1 | 1.4 34.5 150 10 5 6.5 3.6
9000 2.1 35.8 155 6 3 6.2 3.4 | 1.8 35.2 150 10 5 5.6 3.1
8750 2.6 36.7 155 5 3 6.8 3.7 | 2.2 36.0 150 9 5 6.2 3.4
8500 3.1 37.6 155 4 2 7.4 4.1 | 2.8 37.0 150 9 5 7.3 4.0
8250 3.7 38.7 150 3 1 7.0 3.8 | 3.3 37.9 145 8 4 6.0 3.3
8000 4.2 39.6 150 2 1 6.5 3.6 | 3.6 38.5 150 8 4 3.8 2.1
7750 4.7 40.5 150 2 1 5.4 3.0 | 3.9 39.0 150 7 4 3.8 2.1
7500 5.0 41.0 140 1 0 4.5 2.5 | 4.2 39.6 140 6 3 4.7 2.6
7250 5.3 41.5 000 0 0 3.0 1.6 | 4.5 40.1 130 6 3 3.3 1.8
7000 5.5 41.9 330 1 1 2.1 1.2 | 4.7 40.5 130 4 2 1.2 0.7
6750 5.7 42.3 330 2 1 1.1 0.6 | 4.9 40.8 125 3 2 6.2 3.4
6500 5.6 42.1 325 2 1 -1.3 -0.7 | 5.6 42.1 115 2 1 10.0 5.5
6250 5.5 41.9 315 3 2 -1.8 -1.0 | 6.3 43.3 100 2 1 8.7 4.8
6000 5.4 41.7 310 5 2 -2.6 -1.4 | 6.9 44.4 090 1 1 8.1 4.5
5750 5.2 41.4 305 6 3 0.1 0.1 | 7.6 45.7 075 1 0 10.8 5.9
5500 5.5 41.9 305 4 2 6.9 3.8 | 8.7 47.7 065 1 1 19.1 10.5
11/20/2025 at 1400 MST | 11/20/2025 at 1700 MST
|
CAPE... +4.1 LI... +1.4 | CAPE... +33.8 LI... +1.5
CINH... 0.0 K Index... +21.9 | CINH... -1.6 K Index... +22.8
|
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 -59.1 -74.4 270 19 10 3.7 2.0 | -59.7 -75.5 275 27 14 5.0 2.7
45000 -53.6 -64.5 260 21 11 3.0 1.6 | -52.3 -62.1 280 34 17 3.7 2.0
40000 -49.0 -56.2 235 22 11 3.1 1.7 | -46.7 -52.1 255 23 12 3.8 2.1
38000 -48.6 -55.5 220 25 13 -1.5 -0.8 | -46.0 -50.8 235 21 11 -1.2 -0.6
36000 -49.5 -57.1 205 31 16 -1.5 -0.8 | -46.8 -52.2 210 23 12 -1.2 -0.6
34000 -49.9 -57.8 200 39 20 3.9 2.1 | -47.2 -53.0 195 29 15 1.4 0.8
32000 -47.6 -53.7 195 48 25 3.8 2.1 | -46.4 -51.5 180 37 19 1.3 0.7
30000 -44.7 -48.5 195 53 27 8.6 4.7 | -44.7 -48.5 175 43 22 9.2 5.0
29000 -42.1 -43.8 195 48 24 8.6 4.7 | -42.0 -43.6 180 40 21 8.9 4.9
28000 -39.6 -39.3 195 42 22 8.6 4.7 | -39.4 -38.9 180 37 19 8.9 4.9
27000 -37.0 -34.6 195 37 19 8.8 4.8 | -36.7 -34.1 185 34 18 8.8 4.8
26000 -34.3 -29.7 195 34 17 9.1 5.0 | -34.1 -29.4 185 29 15 8.5 4.6
25000 -31.5 -24.7 195 31 16 9.1 5.0 | -31.6 -24.9 180 24 12 8.5 4.6
24000 -28.8 -19.8 190 28 14 9.1 5.0 | -29.1 -20.4 175 18 9 8.5 4.7
23000 -26.5 -15.7 180 22 11 7.3 4.0 | -26.8 -16.2 170 17 9 7.6 4.2
22000 -24.4 -11.9 170 17 9 7.3 4.0 | -24.5 -12.1 160 17 9 7.6 4.2
21000 -22.2 -8.0 145 14 7 6.8 3.8 | -22.2 -8.0 155 17 9 7.3 4.0
20000 -20.4 -4.7 135 13 6 6.2 3.4 | -20.2 -4.4 145 16 8 6.7 3.7
19500 -19.5 -3.1 130 12 6 6.2 3.4 | -19.3 -2.7 140 16 8 6.7 3.7
19000 -18.5 -1.3 125 11 6 6.2 3.4 | -17.8 -0.0 130 16 8 6.7 3.7
18500 -17.2 1.0 120 11 6 6.1 3.4 | -16.8 1.8 125 16 8 5.7 3.1
18000 -16.3 2.7 120 11 6 6.1 3.4 | -16.1 3.0 120 15 8 5.3 2.9
17500 -15.4 4.3 120 12 6 6.2 3.4 | -15.3 4.5 115 15 8 5.3 2.9
17000 -14.5 5.9 125 12 6 6.3 3.5 | -14.5 5.9 105 15 8 5.1 2.8
16500 -13.5 7.7 125 13 7 6.3 3.5 | -13.8 7.2 100 15 8 5.0 2.7
16000 -12.6 9.3 125 13 7 6.6 3.6 | -12.9 8.8 095 15 8 6.6 3.6
15500 -11.6 11.1 125 14 7 6.6 3.6 | -12.0 10.4 090 15 8 6.6 3.6
15000 -10.7 12.7 125 14 7 6.9 3.8 | -11.0 12.2 090 16 8 6.7 3.7
14500 -9.6 14.7 125 14 7 7.0 3.8 | -10.0 14.0 090 15 8 6.8 3.7
14000 -8.6 16.5 125 14 7 7.1 3.9 | -9.0 15.8 085 15 8 6.8 3.7
13500 -7.6 18.3 125 14 7 7.2 4.0 | -8.0 17.6 090 14 7 6.8 3.7
13000 -6.5 20.3 130 14 7 7.1 3.9 | -7.0 19.4 090 13 7 6.8 3.7
12500 -5.5 22.1 130 13 7 6.9 3.8 | -6.0 21.2 090 12 6 6.8 3.8
12000 -4.5 23.9 130 13 7 6.7 3.7 | -5.0 23.0 085 11 6 6.7 3.7
11500 -3.6 25.5 130 12 6 6.3 3.4 | -4.1 24.6 085 10 5 6.1 3.3
11000 -2.6 27.3 130 11 6 6.1 3.4 | -3.2 26.2 080 9 4 5.9 3.2
10500 -1.8 28.8 130 10 5 5.4 3.0 | -2.4 27.7 075 8 4 4.9 2.7
10250 -1.3 29.7 125 9 5 6.9 3.8 | -2.1 28.2 075 8 4 5.4 2.9
10000 -0.7 30.7 125 8 4 9.8 5.4 | -1.6 29.1 070 8 4 8.4 4.6
9750 0.0 32.0 125 8 4 8.7 4.8 | -0.9 30.4 065 8 4 7.6 4.2
9500 0.6 33.1 120 8 4 7.0 3.9 | -0.5 31.1 060 8 4 5.1 2.8
9250 1.1 34.0 120 7 4 7.8 4.3 | -0.1 31.8 060 8 4 6.0 3.3
9000 1.6 34.9 115 7 3 5.8 3.2 | 0.3 32.5 055 8 4 5.1 2.8
8750 2.0 35.6 110 6 3 6.2 3.4 | 0.7 33.3 055 8 4 5.9 3.2
8500 2.6 36.7 105 6 3 8.5 4.7 | 1.2 34.2 055 8 4 7.2 4.0
8250 3.2 37.8 105 5 3 7.4 4.1 | 1.7 35.1 060 9 4 6.9 3.8
8000 3.7 38.7 095 5 3 5.5 3.0 | 2.2 36.0 060 9 5 7.5 4.1
7750 4.1 39.4 085 4 2 6.3 3.5 | 2.9 37.2 060 9 5 9.2 5.1
7500 4.7 40.5 075 4 2 7.7 4.2 | 3.6 38.5 060 9 5 10.6 5.8
7250 5.3 41.5 065 4 2 7.5 4.1 | 4.4 39.9 060 10 5 9.2 5.0
7000 5.8 42.4 060 4 2 7.5 4.1 | 5.0 41.0 065 10 5 7.3 4.0
6750 6.5 43.7 055 4 2 10.0 5.5 | 5.6 42.1 065 10 5 9.6 5.2
6500 7.3 45.1 055 5 2 11.9 6.5 | 6.4 43.5 065 10 5 11.1 6.1
6250 8.1 46.6 055 5 2 10.2 5.6 | 7.2 45.0 065 10 5 9.5 5.2
6000 8.9 48.0 055 4 2 9.8 5.4 | 7.8 46.0 065 10 5 8.9 4.9
5750 9.6 49.3 050 4 2 9.5 5.2 | 8.5 47.3 065 9 5 9.2 5.0
5500 10.4 50.7 050 4 2 11.1 6.1 | 9.2 48.6 060 8 4 8.2 4.5
________________________________________________________________________________
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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