Issued by NWS Denver/Boulder, CO
000
UXUS97 KBOU 211155
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
555 AM MDT Sunday September 21, 2008
This forecast is for Sunday September 21, 2008:
If the trigger temperature of 73.6 F/23.1 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 1061 ft/min (5.4 m/s)
Maximum height of thermals.................. 15876 ft MSL (10553 ft AGL)
Forecast maximum temperature................... 80.0 F/27.1 C
Time of trigger temperature.................... 1130 MDT
Time of overdevelopment........................ 1600 MDT
Middle/high clouds during soaring window....... Overcast thin high
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 13475 ft MSL (8152 ft AGL)
Thermal soaring outlook for Monday 09/22....... 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....................... 35390 ft MSL (30067 ft AGL)
Wave soaring outlook for Monday 09/22.......... Poor
Remarks... Isolated showers and thunderstorms
Sunrise/Sunset.................... 06:46:35 / 18:58:58 MDT
Total possible sunshine........... 12 hr 12 min 22 sec (732 min 22 sec)
Altitude of sun at 12:52:17 MDT... 50.58 degrees
Upper air data from numerical model forecast valid on 09/21/2008 at 0600 MDT
Freezing level.................. 13136 ft MSL (7813 ft AGL)
Convective condensation level... 13264 ft MSL (7941 ft AGL)
Lifted condensation level....... 14649 ft MSL (9326 ft AGL)
Lifted index.................... -1.5
K index......................... +29.9
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 -62.3 -80.1 278 17 9 1.5 0.8 89.2 192.6 36.4 M M
45000 -59.8 -75.6 273 25 13 2.6 1.4 70.4 158.7 27.2 M M
40000 -55.9 -68.6 253 31 16 3.3 1.8 54.1 129.3 18.2 M M
38000 -52.9 -63.2 255 36 19 5.1 2.8 49.3 120.8 15.5 M M
36000 -49.5 -57.1 257 43 22 5.1 2.8 44.9 112.9 12.9 M M
34000 -45.2 -49.4 256 43 22 8.2 4.5 42.8 109.0 11.6 M M
32000 -40.2 -40.4 255 40 21 8.3 4.5 41.6 106.9 11.0 M M
30000 -35.4 -31.7 254 39 20 8.2 4.5 40.3 104.6 10.3 M M
29000 -32.9 -27.2 253 39 20 8.2 4.5 39.7 103.5 10.0 M M
28000 -30.5 -22.9 253 39 20 8.2 4.5 39.3 102.7 9.7 M M
27000 -28.1 -18.6 252 37 19 8.0 4.4 38.5 101.4 9.2 M M
26000 -25.7 -14.3 249 35 18 8.0 4.4 37.8 100.1 8.7 M M
25000 -23.3 -9.9 247 32 17 8.0 4.4 37.2 99.0 8.3 M M
24000 -21.0 -5.8 246 31 16 7.9 4.3 36.6 97.8 7.8 M M
23000 -18.7 -1.7 247 30 16 7.9 4.3 35.8 96.5 7.3 M M
22000 -16.4 2.5 248 30 15 8.0 4.4 35.2 95.4 6.8 M M
21000 -14.3 6.3 248 28 15 6.3 3.4 34.2 93.5 6.0 M M
20000 -12.5 9.5 247 26 13 6.2 3.4 32.9 91.3 4.9 M M
19500 -11.6 11.1 247 25 13 6.3 3.4 32.3 90.2 4.4 M M
19000 -10.2 13.6 246 24 12 6.1 3.3 31.5 88.6 3.6 M M
18500 -9.3 15.3 247 24 12 6.1 3.3 30.8 87.5 3.1 M M
18000 -8.5 16.7 247 24 12 6.0 3.3 30.2 86.4 2.5 M M
17500 -7.6 18.3 247 23 12 5.8 3.2 29.5 85.2 1.9 M M
17000 -6.8 19.8 247 22 11 5.8 3.2 28.9 84.0 1.3 M M
16500 -5.9 21.4 249 22 11 5.8 3.2 28.2 82.8 0.7 M M
16000 -5.1 22.8 252 21 11 5.8 3.2 27.5 81.6 0.1 M M
15500 -4.3 24.3 255 21 11 5.7 3.1 26.9 80.4 -0.6 924 4.7
15000 -3.4 25.9 254 19 10 5.7 3.1 26.2 79.1 -1.2 885 4.5
14500 -2.6 27.3 254 18 9 5.9 3.2 25.5 77.9 -1.9 846 4.3
14000 -1.7 28.9 255 16 8 6.3 3.5 24.9 76.9 -2.5 804 4.1
13500 -0.8 30.6 257 13 7 6.7 3.7 24.4 75.8 -3.0 762 3.9
13000 0.6 33.1 259 12 6 11.3 6.2 24.3 75.7 -3.1 706 3.6
12500 2.2 36.0 261 12 6 11.0 6.0 24.5 76.1 -2.9 641 3.3
12000 3.8 38.8 263 11 6 10.5 5.8 24.6 76.4 -2.8 578 2.9
11500 5.4 41.7 265 11 6 10.7 5.9 24.8 76.6 -2.7 516 2.6
11000 6.9 44.4 267 11 5 8.9 4.9 24.8 76.6 -2.7 458 2.3
10500 8.2 46.8 268 11 5 9.2 5.0 24.7 76.4 -2.8 403 2.0
10250 8.9 48.0 269 11 5 8.7 4.8 24.6 76.4 -2.9 376 1.9
10000 9.5 49.1 268 11 5 8.3 4.6 24.5 76.2 -3.1 350 1.8
9750 10.1 50.2 267 11 5 8.4 4.6 24.4 76.0 -3.2 325 1.6
9500 10.7 51.3 267 10 5 8.4 4.6 24.3 75.8 -3.3 299 1.5
9250 11.3 52.3 266 10 5 8.2 4.5 24.2 75.6 -3.5 274 1.4
9000 11.9 53.4 265 10 5 8.1 4.4 24.1 75.4 -3.6 248 1.3
8750 12.5 54.5 265 10 5 8.1 4.5 24.0 75.1 -3.7 223 1.1
8500 13.1 55.6 264 10 5 8.2 4.5 23.8 74.9 -3.9 198 1.0
8250 13.7 56.7 265 10 5 8.6 4.7 23.7 74.7 -4.0 171 0.9
8000 14.4 57.9 270 10 5 8.7 4.8 23.7 74.6 -4.1 144 0.7
7750 15.0 59.0 274 10 5 8.9 4.9 23.6 74.4 -4.1 117 0.6
7500 15.7 60.3 278 10 5 7.9 4.3 23.5 74.3 -4.2 89 0.5
7250 16.2 61.2 283 11 6 6.2 3.4 23.3 73.9 -4.4 66 0.3
7000 16.7 62.1 286 13 7 5.8 3.2 23.0 73.4 -4.7 45 0.2
6750 17.1 62.8 289 15 8 6.6 3.6 22.7 72.9 -5.0 24 0.1
6500 17.5 63.5 291 16 8 1.3 0.7 22.4 72.3 -5.3 5 0.0
6250 17.3 63.1 288 15 8 -3.9 -2.2 21.4 70.6 -6.3 3 0.0
6000 17.1 62.8 285 14 7 -0.9 -0.5 20.5 68.9 -7.2 2 0.0
5750 16.9 62.4 282 13 7 -7.8 -4.3 19.6 67.2 -8.1 0 0.0
5500 15.6 60.1 271 9 5 -26.6 -14.6 17.5 63.6 -10.3 34 0.2
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
09/21/2008 at 0900 MDT | 09/21/2008 at 1200 MDT
|
K index... +26.6 | K index... +27.3
|
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 -60.9 -77.6 270 15 8 1.6 0.9 | -61.1 -78.0 260 13 7 1.7 0.9
45000 -58.4 -73.1 262 20 10 2.0 1.1 | -58.4 -73.1 259 21 11 1.8 1.0
40000 -55.3 -67.5 254 44 22 3.2 1.7 | -55.7 -68.3 265 42 22 2.1 1.2
38000 -52.8 -63.0 254 50 26 4.1 2.3 | -52.9 -63.2 274 47 24 4.2 2.3
36000 -50.4 -58.7 254 55 29 4.1 2.2 | -50.4 -58.7 281 51 26 4.3 2.3
34000 -46.2 -51.2 255 54 28 8.7 4.8 | -46.1 -51.0 281 51 26 8.5 4.7
32000 -41.0 -41.8 256 47 24 8.7 4.8 | -41.0 -41.8 277 49 25 8.6 4.7
30000 -36.0 -32.8 260 43 22 8.0 4.4 | -36.0 -32.8 274 47 24 8.1 4.4
29000 -33.1 -27.6 263 42 22 8.0 4.4 | -33.6 -28.5 272 46 24 8.1 4.4
28000 -30.7 -23.3 266 42 21 8.0 4.4 | -31.2 -24.2 270 45 23 8.1 4.5
27000 -28.2 -18.8 265 40 21 8.2 4.5 | -28.8 -19.8 268 43 22 8.1 4.4
26000 -25.8 -14.4 262 38 20 8.2 4.5 | -26.4 -15.5 264 41 21 8.1 4.4
25000 -23.4 -10.1 260 37 19 8.2 4.5 | -24.0 -11.2 260 38 20 8.1 4.4
24000 -21.2 -6.2 256 36 18 6.6 3.6 | -21.6 -6.9 258 37 19 7.5 4.1
23000 -19.3 -2.7 252 35 18 6.6 3.6 | -19.4 -2.9 258 38 20 7.5 4.1
22000 -17.4 0.7 248 34 18 6.7 3.6 | -17.2 1.0 257 39 20 7.6 4.2
21000 -15.5 4.1 248 34 18 6.7 3.7 | -15.1 4.8 255 39 20 6.8 3.7
20000 -13.5 7.7 251 34 18 6.8 3.7 | -13.1 8.4 253 37 19 6.8 3.7
19500 -12.5 9.5 252 35 18 6.8 3.7 | -11.6 11.1 250 37 19 6.8 3.8
19000 -11.6 11.1 254 35 18 6.9 3.8 | -10.6 12.9 250 36 18 6.9 3.8
18500 -10.6 12.9 255 34 18 7.0 3.8 | -9.6 14.7 251 34 17 6.9 3.8
18000 -9.5 14.9 256 34 17 7.0 3.8 | -8.5 16.7 252 32 16 6.8 3.7
17500 -8.5 16.7 257 32 17 7.5 4.1 | -7.6 18.3 253 29 15 6.7 3.7
17000 -7.4 18.7 257 30 15 7.5 4.1 | -6.6 20.1 253 26 13 6.7 3.7
16500 -6.4 20.5 258 28 14 7.5 4.1 | -5.6 21.9 253 22 12 6.1 3.4
16000 -4.7 23.5 262 24 12 7.5 4.1 | -4.7 23.5 249 19 10 6.1 3.4
15500 -3.6 25.5 265 21 11 7.3 4.0 | -3.8 25.2 245 16 8 6.7 3.7
15000 -2.6 27.3 267 19 10 7.3 4.0 | -2.8 27.0 244 15 8 7.0 3.9
14500 -1.5 29.3 269 17 9 7.8 4.3 | -1.8 28.8 242 14 7 7.3 4.0
14000 -0.3 31.5 268 16 8 8.4 4.6 | -0.7 30.7 239 13 7 7.8 4.3
13500 1.0 33.8 267 14 7 8.4 4.6 | 0.4 32.7 237 13 6 8.0 4.4
13000 2.2 36.0 267 14 7 8.2 4.5 | 1.7 35.1 235 12 6 9.9 5.4
12500 3.4 38.1 267 14 7 8.3 4.5 | 3.2 37.8 233 12 6 9.7 5.3
12000 4.6 40.3 266 14 7 8.3 4.6 | 4.6 40.3 232 12 6 9.9 5.4
11500 5.9 42.6 264 13 7 8.3 4.6 | 6.1 43.0 231 12 6 10.0 5.5
11000 7.1 44.8 262 14 7 8.5 4.6 | 7.5 45.5 230 12 6 9.3 5.1
10500 8.4 47.1 261 14 7 8.5 4.6 | 8.9 48.0 228 11 6 9.3 5.1
10250 9.0 48.2 260 14 7 8.4 4.6 | 9.6 49.3 227 11 6 9.4 5.1
10000 9.6 49.3 259 14 7 8.4 4.6 | 10.3 50.5 226 11 6 9.4 5.2
9750 10.2 50.4 258 14 7 8.4 4.6 | 11.0 51.8 225 11 6 9.4 5.2
9500 10.8 51.4 256 13 7 8.4 4.6 | 11.7 53.1 223 10 5 9.4 5.2
9250 11.4 52.5 254 13 7 8.1 4.4 | 12.4 54.3 222 10 5 9.2 5.1
9000 12.0 53.6 251 13 6 7.9 4.3 | 13.0 55.4 220 10 5 9.1 5.0
8750 12.6 54.7 247 12 6 8.0 4.4 | 13.7 56.7 218 9 5 9.1 5.0
8500 13.2 55.8 243 12 6 7.7 4.2 | 14.4 57.9 216 9 5 9.2 5.1
8250 13.7 56.7 239 11 6 7.1 3.9 | 15.1 59.2 215 9 4 9.7 5.3
8000 14.2 57.6 234 10 5 6.9 3.8 | 15.8 60.4 214 8 4 10.0 5.5
7750 14.7 58.5 229 10 5 6.8 3.7 | 16.6 61.9 213 8 4 9.9 5.4
7500 15.2 59.4 224 9 5 7.3 4.0 | 17.3 63.1 211 8 4 9.9 5.4
7250 15.8 60.4 225 9 5 7.9 4.4 | 18.0 64.4 211 8 4 9.8 5.4
7000 16.4 61.5 227 9 5 7.9 4.3 | 18.8 65.8 210 7 4 9.8 5.4
6750 17.0 62.6 229 9 5 8.0 4.4 | 19.5 67.1 210 7 4 9.8 5.4
6500 17.5 63.5 231 9 5 4.3 2.4 | 20.2 68.4 210 7 4 9.9 5.4
6250 17.6 63.7 227 8 4 1.9 1.0 | 21.0 69.8 209 7 4 10.2 5.6
6000 17.7 63.9 223 8 4 1.5 0.8 | 21.7 71.1 208 7 3 9.6 5.3
5750 17.9 64.2 218 7 4 5.6 3.1 | 22.5 72.5 207 6 3 11.7 6.4
5500 18.7 65.7 216 6 3 18.2 10.0 | 23.6 74.5 209 6 3 18.6 10.2
09/21/2008 at 1500 MDT | 09/21/2008 at 1800 MDT
|
K index... +26.7 | K index... +30.6
|
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 -61.2 -78.2 267 16 8 1.7 0.9 | -62.0 -79.6 265 21 11 1.9 1.1
45000 -58.9 -74.0 270 27 14 1.1 0.6 | -59.2 -74.6 270 32 17 1.5 0.8
40000 -57.0 -70.6 265 44 23 3.9 2.2 | -57.0 -70.6 271 48 25 2.8 1.5
38000 -53.7 -64.7 271 47 24 5.6 3.1 | -53.4 -64.1 274 49 25 6.1 3.4
36000 -50.3 -58.5 278 50 26 5.6 3.1 | -49.3 -56.7 277 51 26 6.2 3.4
34000 -45.8 -50.4 277 51 26 8.7 4.8 | -44.7 -48.5 276 50 26 8.2 4.5
32000 -40.6 -41.1 273 50 26 8.7 4.8 | -39.8 -39.6 274 48 25 8.3 4.5
30000 -35.6 -32.1 270 47 24 8.2 4.5 | -35.0 -31.0 269 45 23 7.9 4.4
29000 -32.5 -26.5 268 45 23 8.2 4.5 | -32.6 -26.7 266 44 23 7.9 4.4
28000 -30.1 -22.2 267 43 22 8.2 4.5 | -30.2 -22.4 263 43 22 8.0 4.4
27000 -27.8 -18.0 266 42 22 7.7 4.2 | -28.0 -18.4 261 42 22 7.2 3.9
26000 -25.5 -13.9 265 41 21 7.7 4.2 | -25.9 -14.6 260 41 21 7.2 4.0
25000 -23.2 -9.8 264 40 21 7.7 4.2 | -23.7 -10.7 258 41 21 7.2 4.0
24000 -21.0 -5.8 264 40 20 7.5 4.1 | -21.6 -6.9 256 38 20 7.1 3.9
23000 -18.7 -1.7 265 39 20 7.5 4.1 | -19.6 -3.3 255 35 18 7.1 3.9
22000 -16.5 2.3 265 38 20 7.6 4.2 | -17.5 0.5 252 32 17 7.1 3.9
21000 -14.6 5.7 261 36 18 6.0 3.3 | -15.4 4.3 250 30 15 7.0 3.8
20000 -12.9 8.8 254 33 17 6.1 3.3 | -13.4 7.9 248 29 15 7.0 3.8
19500 -12.0 10.4 250 32 17 6.1 3.4 | -11.9 10.6 246 28 14 7.0 3.8
19000 -11.1 12.0 246 31 16 6.4 3.5 | -10.8 12.6 245 27 14 7.3 4.0
18500 -10.2 13.6 246 31 16 6.7 3.7 | -9.8 14.4 246 26 13 7.3 4.0
18000 -9.2 15.4 247 31 16 6.6 3.6 | -8.7 16.3 247 25 13 7.3 4.0
17500 -8.2 17.2 247 30 16 7.6 4.2 | -7.7 18.1 247 24 12 7.2 3.9
17000 -7.0 19.4 248 29 15 7.6 4.2 | -6.6 20.1 248 23 12 7.1 3.9
16500 -5.9 21.4 249 28 14 7.4 4.1 | -5.5 22.1 247 22 12 8.1 4.4
16000 -4.4 24.1 251 25 13 7.3 4.0 | -4.4 24.1 247 21 11 8.0 4.4
15500 -3.3 26.1 251 23 12 7.4 4.1 | -3.2 26.2 247 20 10 8.8 4.8
15000 -2.2 28.0 249 20 10 7.5 4.1 | -1.8 28.8 246 19 10 9.2 5.1
14500 -1.1 30.0 246 17 9 8.0 4.4 | -0.5 31.1 246 17 9 9.6 5.3
14000 0.1 32.2 245 15 8 8.7 4.8 | 1.1 34.0 245 16 8 10.2 5.6
13500 1.3 34.3 243 14 7 8.9 4.9 | 2.6 36.7 245 15 8 10.2 5.6
13000 2.8 37.0 242 13 7 10.0 5.5 | 4.1 39.4 244 14 7 9.5 5.2
12500 4.2 39.6 241 12 6 9.9 5.4 | 5.5 41.9 242 13 6 9.6 5.2
12000 5.7 42.3 240 12 6 9.5 5.2 | 6.9 44.4 239 11 6 9.2 5.0
11500 7.1 44.8 238 11 6 9.5 5.2 | 8.3 46.9 234 10 5 9.2 5.0
11000 8.5 47.3 236 10 5 9.7 5.3 | 9.6 49.3 229 8 4 9.3 5.1
10500 9.9 49.8 232 9 4 9.7 5.3 | 11.0 51.8 222 7 4 9.4 5.1
10250 10.6 51.1 230 8 4 9.6 5.3 | 11.7 53.1 218 6 3 9.1 5.0
10000 11.4 52.5 228 8 4 9.5 5.2 | 12.4 54.3 213 6 3 8.9 4.9
9750 12.1 53.8 227 7 4 9.6 5.2 | 13.1 55.6 208 5 3 9.0 4.9
9500 12.8 55.0 225 7 4 9.5 5.2 | 13.7 56.7 202 5 2 9.0 4.9
9250 13.5 56.3 223 6 3 9.7 5.3 | 14.4 57.9 194 4 2 9.0 5.0
9000 14.2 57.6 222 6 3 9.9 5.4 | 15.1 59.2 186 4 2 9.1 5.0
8750 14.9 58.8 220 6 3 9.8 5.4 | 15.8 60.4 176 3 2 9.1 5.0
8500 15.7 60.3 218 6 3 9.9 5.4 | 16.4 61.5 164 3 2 9.1 5.0
8250 16.4 61.5 217 5 3 9.9 5.4 | 17.1 62.8 150 3 1 9.2 5.0
8000 17.1 62.8 216 5 3 10.0 5.5 | 17.8 64.0 139 3 1 9.2 5.1
7750 17.9 64.2 216 5 3 10.0 5.5 | 18.5 65.3 127 3 1 9.2 5.0
7500 18.6 65.5 215 5 2 10.0 5.5 | 19.2 66.6 116 3 2 9.4 5.1
7250 19.3 66.7 214 5 2 10.0 5.5 | 19.9 67.8 109 3 2 10.0 5.5
7000 20.1 68.2 214 4 2 10.0 5.5 | 20.6 69.1 104 3 2 10.2 5.6
6750 20.8 69.4 213 4 2 10.0 5.5 | 21.4 70.5 099 3 2 10.2 5.6
6500 21.6 70.9 213 4 2 10.1 5.5 | 22.1 71.8 094 3 2 9.9 5.4
6250 22.3 72.1 212 4 2 10.2 5.6 | 22.9 73.2 090 3 2 9.6 5.3
6000 23.1 73.6 211 4 2 9.8 5.3 | 23.6 74.5 085 3 2 9.6 5.3
5750 23.9 75.0 210 4 2 11.5 6.3 | 24.3 75.7 080 3 2 9.5 5.2
5500 24.9 76.8 210 3 2 19.0 10.4 | 25.0 77.0 076 3 2 9.2 5.1
________________________________________________________________________________
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:
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 - 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, cirrostatus, 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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