Issued by NWS Denver/Boulder, CO
000
UXUS97 KBOU 091218
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
618 AM MDT Saturday May 9, 2009
This forecast is for Saturday May 9, 2009:
If the trigger temperature of 48.8 F/9.3 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 481 ft/min (2.4 m/s)
Maximum height of thermals.................. 14268 ft MSL (8983 ft AGL)
Forecast maximum temperature................... 61.0 F/16.6 C
Time of trigger temperature.................... 0830 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Broken/overcast thin middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 11414 ft MSL (6129 ft AGL)
Thermal soaring outlook for Sunday 05/10....... Fair
Wave Soaring Index............................. Good
Wave Soaring Index trend (to 1800 MDT)......... No change
Height of stable layer (12-18K ft MSL)......... 17604 ft MSL (12319 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 40518 ft MSL (35233 ft AGL)
Wave soaring outlook for Sunday 05/10.......... Good
Remarks...
Sunrise/Sunset.................... 05:50:38 / 20:00:58 MDT
Total possible sunshine........... 14 hr 10 min 20 sec (850 min 20 sec)
Altitude of sun at 12:55:59 MDT... 67.76 degrees
Upper air data from rawinsonde observation taken on 05/09/2009 at 0600 MDT
Freezing level.................. 8088 ft MSL (2803 ft AGL)
Convective condensation level... 12598 ft MSL (7313 ft AGL)
Lifted condensation level....... 13334 ft MSL (8049 ft AGL)
Lifted index.................... +6.1
K index......................... +8.1
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 -59.5 -75.1 277 51 26 -3.0 -1.6 99.7 211.4 47.9 M M
45000 -57.2 -71.0 275 91 47 -7.4 -4.1 78.6 173.5 38.4 M M
40000 -62.1 -79.8 274 109 56 -3.1 -1.7 48.1 118.5 21.0 M M
38000 -58.7 -73.7 272 106 54 6.8 3.7 44.2 111.6 19.0 M M
36000 -54.2 -65.6 268 101 52 8.8 4.9 42.4 108.3 18.2 M M
34000 -48.8 -55.8 265 97 50 9.0 4.9 41.6 106.9 18.2 M M
32000 -42.7 -44.9 268 94 49 7.9 4.4 41.0 105.8 18.2 M M
30000 -39.3 -38.7 269 93 48 6.2 3.4 37.7 99.9 16.3 M M
29000 -37.4 -35.3 268 93 48 6.3 3.5 36.3 97.3 15.4 M M
28000 -35.1 -31.2 267 92 47 8.9 4.9 35.4 95.8 14.9 M M
27000 -32.4 -26.3 266 92 47 9.0 5.0 35.1 95.1 14.8 M M
26000 -29.7 -21.5 266 91 47 9.0 5.0 34.8 94.7 14.8 M M
25000 -27.0 -16.6 265 91 47 8.1 4.5 34.7 94.5 14.9 M M
24000 -26.3 -15.3 270 85 44 4.7 2.6 31.9 89.5 12.8 M M
23000 -23.8 -10.8 271 83 43 8.9 4.9 31.3 88.3 12.4 M M
22000 -22.5 -8.5 272 80 41 3.5 1.9 29.5 85.0 11.0 M M
21000 -20.9 -5.6 273 78 40 5.4 3.0 27.8 82.1 9.7 M M
20000 -18.9 -2.0 274 76 39 8.9 4.9 26.9 80.4 9.0 M M
19500 -17.5 0.5 275 76 39 9.0 4.9 26.7 80.1 9.0 M M
19000 -16.3 2.7 275 77 40 4.2 2.3 26.5 79.6 8.8 M M
18500 -16.0 3.2 275 73 37 3.7 2.0 25.0 77.1 7.6 M M
18000 -15.5 4.1 276 68 35 1.9 1.0 23.9 75.1 6.8 M M
17500 -15.2 4.6 277 64 33 1.3 0.7 22.5 72.5 5.6 M M
17000 -15.0 5.0 279 60 31 1.9 1.0 21.1 70.1 4.4 M M
16500 -14.6 5.7 274 56 29 2.4 1.3 19.9 67.8 3.3 M M
16000 -14.1 6.6 265 51 26 6.5 3.6 18.1 64.5 1.6 M M
15500 -13.0 8.6 265 46 23 5.6 3.1 17.7 63.9 1.3 M M
15000 -12.1 10.2 265 40 21 6.3 3.4 17.1 62.8 0.7 M M
14500 -11.2 11.8 265 35 18 6.4 3.5 16.6 61.8 0.1 M M
14000 -10.3 13.5 263 30 16 6.9 3.8 16.0 60.9 -0.4 650 3.3
13500 -9.2 15.4 256 28 14 8.6 4.7 15.8 60.4 -0.7 601 3.1
13000 -8.1 17.4 248 26 13 6.7 3.7 15.4 59.7 -1.2 556 2.8
12500 -7.2 19.0 238 25 13 6.8 3.7 14.9 58.8 -1.7 511 2.6
12000 -6.2 20.8 228 25 13 7.2 4.0 14.4 58.0 -2.1 467 2.4
11500 -5.5 22.1 218 24 12 2.4 1.3 13.6 56.5 -2.9 431 2.2
11000 -5.0 23.0 207 24 12 2.9 1.6 12.5 54.5 -4.0 403 2.0
10500 -4.6 23.7 196 24 12 2.6 1.4 11.4 52.6 -5.0 375 1.9
10250 -4.4 24.1 191 25 13 4.0 2.2 10.9 51.7 -5.5 361 1.8
10000 -3.9 25.0 188 24 12 6.3 3.5 10.6 51.0 -5.8 341 1.7
9750 -3.5 25.7 185 22 11 6.4 3.5 10.3 50.6 -6.1 319 1.6
9500 -3.0 26.6 182 20 10 6.9 3.8 10.1 50.1 -6.3 297 1.5
9250 -2.4 27.7 179 18 9 7.7 4.2 9.9 49.8 -6.5 273 1.4
9000 -1.9 28.6 174 16 8 7.6 4.2 9.7 49.5 -6.7 249 1.3
8750 -1.3 29.7 174 14 7 7.8 4.3 9.6 49.2 -6.9 225 1.1
8500 -0.8 30.6 173 13 7 7.1 3.9 9.4 48.9 -7.1 201 1.0
8250 -0.3 31.5 171 11 6 5.4 2.9 9.1 48.4 -7.4 180 0.9
8000 0.2 32.4 169 10 5 7.2 4.0 8.8 47.9 -7.7 158 0.8
7750 0.8 33.4 159 11 5 9.0 4.9 8.7 47.7 -7.8 131 0.7
7500 1.5 34.7 149 11 6 8.5 4.7 8.7 47.6 -7.9 104 0.5
7250 2.2 36.0 141 13 6 8.6 4.7 8.6 47.4 -7.9 76 0.4
7000 2.8 37.0 135 14 7 8.5 4.7 8.5 47.3 -8.0 49 0.3
6750 3.5 38.3 135 12 6 8.5 4.7 8.4 47.1 -8.2 23 0.1
6500 4.1 39.4 136 11 5 8.4 4.6 8.3 46.9 -8.3 M M
6250 4.7 40.5 137 9 5 8.1 4.5 8.2 46.7 -8.4 M M
6000 5.2 41.4 139 7 4 8.0 4.4 8.1 46.5 -8.7 M M
5750 5.8 42.4 143 6 3 7.8 4.3 7.9 46.3 -8.8 M M
5500 6.4 43.5 147 5 3 8.9 4.9 7.8 46.1 -8.9 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
05/09/2009 at 0900 MDT | 05/09/2009 at 1200 MDT
|
K index... +3.0 | K index... +9.8
|
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 -59.2 -74.6 273 54 28 0.8 0.5 | -59.7 -75.5 274 59 30 0.8 0.5
45000 -58.0 -72.4 279 77 40 0.9 0.5 | -58.4 -73.1 276 76 39 1.0 0.5
40000 -56.6 -69.9 276 98 51 1.0 0.5 | -56.9 -70.4 270 98 50 1.1 0.6
38000 -54.5 -66.1 274 99 51 4.6 2.5 | -54.6 -66.3 270 100 51 4.9 2.7
36000 -51.7 -61.1 272 96 50 4.6 2.5 | -51.7 -61.1 270 100 51 4.9 2.7
34000 -48.6 -55.5 270 93 48 6.9 3.8 | -48.4 -55.1 269 98 50 6.5 3.6
32000 -44.4 -47.9 269 89 46 6.9 3.8 | -44.5 -48.1 268 91 47 6.5 3.6
30000 -39.6 -39.3 270 85 44 7.7 4.2 | -40.5 -40.9 269 85 44 7.3 4.0
29000 -37.3 -35.1 273 84 43 7.7 4.2 | -37.7 -35.9 272 82 42 7.3 4.0
28000 -35.0 -31.0 275 84 43 7.7 4.2 | -35.6 -32.1 274 80 41 7.3 4.0
27000 -32.6 -26.7 278 82 42 8.5 4.7 | -33.2 -27.8 277 78 40 9.1 5.0
26000 -30.1 -22.2 280 80 41 8.5 4.6 | -30.5 -22.9 279 77 39 9.0 4.9
25000 -27.5 -17.5 283 78 40 8.5 4.6 | -27.8 -18.0 282 76 39 9.0 4.9
24000 -25.1 -13.2 285 76 39 6.8 3.7 | -25.3 -13.5 284 74 38 7.0 3.8
23000 -23.1 -9.6 287 72 37 6.6 3.6 | -23.2 -9.8 286 71 37 7.0 3.8
22000 -21.2 -6.2 288 69 36 6.6 3.6 | -21.1 -6.0 289 68 35 7.0 3.8
21000 -19.3 -2.7 288 65 34 5.5 3.0 | -19.0 -2.2 290 65 33 6.6 3.6
20000 -17.6 0.3 285 60 31 5.6 3.1 | -17.0 1.4 285 59 30 6.6 3.6
19500 -16.8 1.8 283 58 30 5.6 3.1 | -16.1 3.0 283 56 29 6.6 3.6
19000 -16.0 3.2 281 55 29 5.7 3.1 | -15.1 4.8 280 53 27 6.8 3.7
18500 -15.2 4.6 279 53 27 4.7 2.6 | -14.1 6.6 277 51 26 5.3 2.9
18000 -14.5 5.9 279 51 26 4.5 2.4 | -13.4 7.9 276 50 26 5.1 2.8
17500 -13.9 7.0 278 50 26 4.5 2.4 | -12.6 9.3 274 49 25 4.4 2.4
17000 -13.2 8.2 276 47 24 4.4 2.4 | -12.2 10.0 274 47 24 2.7 1.5
16500 -12.6 9.3 275 45 23 4.3 2.4 | -11.8 10.8 273 44 23 2.6 1.4
16000 -11.4 11.5 272 42 22 6.2 3.4 | -10.9 12.4 270 39 20 4.7 2.6
15500 -10.4 13.3 271 40 21 6.2 3.4 | -10.2 13.6 268 36 19 5.2 2.9
15000 -9.4 15.1 270 37 19 7.7 4.2 | -9.2 15.4 267 33 17 8.3 4.6
14500 -8.3 17.1 270 34 18 7.9 4.3 | -8.0 17.6 266 30 16 8.5 4.7
14000 -7.3 18.9 269 31 16 5.4 3.0 | -7.1 19.2 265 27 14 4.8 2.6
13500 -6.6 20.1 269 28 14 5.8 3.2 | -6.4 20.5 264 24 13 5.3 2.9
13000 -6.0 21.2 268 25 13 2.6 1.5 | -5.6 21.9 261 22 11 4.8 2.6
12500 -5.7 21.7 266 22 11 2.4 1.3 | -5.0 23.0 257 19 10 4.8 2.6
12000 -5.4 22.3 261 19 10 2.4 1.3 | -4.3 24.3 250 16 8 4.8 2.6
11500 -5.1 22.8 251 17 9 2.4 1.3 | -3.6 25.5 239 14 7 4.8 2.6
11000 -4.8 23.4 237 16 8 2.3 1.3 | -2.9 26.8 223 12 6 5.3 2.9
10500 -4.4 24.1 219 15 8 1.9 1.0 | -2.1 28.2 201 10 5 5.2 2.8
10250 -4.2 24.4 210 15 8 3.9 2.1 | -1.7 28.9 188 10 5 5.8 3.2
10000 -3.8 25.2 204 15 8 7.1 3.9 | -1.2 29.8 180 10 5 6.6 3.6
9750 -3.2 26.2 199 15 8 7.3 4.0 | -0.7 30.7 173 9 5 6.7 3.7
9500 -2.7 27.1 194 15 8 7.4 4.0 | -0.2 31.6 165 9 5 6.4 3.5
9250 -2.1 28.2 188 15 8 6.9 3.8 | 0.3 32.5 156 9 4 7.5 4.1
9000 -1.6 29.1 183 15 7 6.5 3.5 | 0.9 33.6 152 8 4 8.6 4.7
8750 -1.1 30.0 176 14 7 6.6 3.6 | 1.5 34.7 147 7 4 8.3 4.5
8500 -0.6 30.9 169 13 7 6.5 3.6 | 2.1 35.8 141 7 4 8.6 4.7
8250 -0.1 31.8 163 13 7 6.3 3.5 | 2.8 37.0 136 7 3 9.5 5.2
8000 0.3 32.5 156 12 6 6.2 3.4 | 3.5 38.3 135 6 3 10.0 5.5
7750 0.8 33.4 149 11 6 6.1 3.4 | 4.2 39.6 133 6 3 9.9 5.4
7500 1.2 34.2 141 11 6 6.6 3.6 | 5.0 41.0 132 6 3 10.0 5.5
7250 1.7 35.1 135 9 5 7.3 4.0 | 5.7 42.3 131 6 3 10.1 5.6
7000 2.3 36.1 129 8 4 7.1 3.9 | 6.5 43.7 130 5 3 10.1 5.5
6750 2.8 37.0 120 7 4 7.6 4.2 | 7.2 45.0 129 5 3 10.2 5.6
6500 3.4 38.1 114 6 3 9.3 5.1 | 8.0 46.4 129 5 2 10.2 5.6
6250 4.1 39.4 112 6 3 10.1 5.6 | 8.8 47.8 128 4 2 10.8 5.9
6000 4.8 40.6 110 6 3 9.7 5.3 | 9.6 49.3 127 4 2 9.0 4.9
5750 5.6 42.1 108 5 3 12.5 6.8 | 10.3 50.5 127 4 2 15.8 8.7
5500 6.7 44.1 110 5 3 17.6 9.6 | 12.1 53.8 128 4 2 32.5 17.8
05/09/2009 at 1500 MDT | 05/09/2009 at 1800 MDT
|
K index... +14.4 | K index... +20.0
|
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 -60.6 -77.1 271 56 29 1.9 1.0 | -59.6 -75.3 271 55 29 2.0 1.1
45000 -57.9 -72.2 274 72 37 1.1 0.6 | -56.8 -70.2 273 75 39 0.1 0.1
40000 -56.1 -69.0 272 96 49 1.3 0.7 | -56.7 -70.1 270 99 51 0.2 0.1
38000 -54.0 -65.2 271 98 50 4.3 2.3 | -54.8 -66.6 269 101 52 4.4 2.4
36000 -51.4 -60.5 270 97 50 4.3 2.3 | -52.1 -61.8 269 99 51 4.4 2.4
34000 -48.5 -55.3 270 95 49 6.2 3.4 | -49.2 -56.6 270 95 49 6.1 3.3
32000 -44.7 -48.5 272 88 45 6.2 3.4 | -45.5 -49.9 272 84 43 6.1 3.4
30000 -40.2 -40.4 275 81 42 7.3 4.0 | -40.9 -41.6 273 76 39 8.0 4.4
29000 -38.1 -36.6 277 80 41 7.3 4.0 | -38.5 -37.3 272 74 38 8.0 4.4
28000 -35.9 -32.6 278 78 40 7.3 4.0 | -36.1 -33.0 272 73 37 8.0 4.4
27000 -33.6 -28.5 279 76 39 8.1 4.4 | -33.8 -28.8 272 71 37 7.9 4.3
26000 -31.2 -24.2 280 74 38 8.1 4.4 | -31.4 -24.5 272 69 36 7.9 4.3
25000 -28.8 -19.8 280 72 37 8.1 4.4 | -29.1 -20.4 272 67 34 7.9 4.4
24000 -26.4 -15.5 281 70 36 7.7 4.2 | -26.7 -16.1 273 65 33 7.4 4.1
23000 -24.1 -11.4 279 65 34 7.7 4.2 | -24.5 -12.1 272 61 31 7.4 4.1
22000 -21.8 -7.2 278 61 31 7.7 4.2 | -22.3 -8.1 272 57 29 7.4 4.1
21000 -19.5 -3.1 276 57 29 6.9 3.8 | -20.2 -4.4 272 54 28 6.5 3.6
20000 -17.4 0.7 274 55 28 7.0 3.8 | -18.2 -0.8 270 52 27 6.6 3.6
19500 -16.4 2.5 273 54 28 7.0 3.8 | -17.3 0.9 269 51 26 6.6 3.6
19000 -15.4 4.3 272 53 27 7.2 4.0 | -16.3 2.7 268 50 26 6.6 3.6
18500 -14.5 5.9 271 51 26 4.5 2.4 | -15.3 4.5 267 49 25 6.6 3.6
18000 -13.8 7.2 268 49 25 4.6 2.5 | -14.4 6.1 265 45 23 6.6 3.6
17500 -13.2 8.2 265 46 24 5.2 2.9 | -13.4 7.9 263 42 22 7.1 3.9
17000 -12.3 9.9 262 43 22 6.3 3.4 | -12.3 9.9 263 39 20 7.7 4.2
16500 -11.4 11.5 260 41 21 6.2 3.4 | -10.6 12.9 263 35 18 8.2 4.5
16000 -9.6 14.7 258 37 19 8.6 4.7 | -9.4 15.1 263 33 17 8.5 4.6
15500 -8.4 16.9 258 35 18 8.4 4.6 | -8.1 17.4 264 31 16 8.1 4.5
15000 -7.2 19.0 257 33 17 7.5 4.1 | -7.1 19.2 264 28 14 6.4 3.5
14500 -6.1 21.0 256 30 15 7.7 4.2 | -6.2 20.8 263 26 13 6.6 3.6
14000 -5.2 22.6 255 27 14 5.2 2.9 | -5.3 22.5 262 22 12 5.7 3.1
13500 -4.5 23.9 253 24 12 5.7 3.1 | -4.5 23.9 260 19 10 5.9 3.2
13000 -3.9 25.0 248 20 10 3.2 1.8 | -3.7 25.3 257 15 8 5.0 2.8
12500 -3.4 25.9 238 14 7 3.1 1.7 | -3.0 26.6 248 11 5 4.9 2.7
12000 -2.9 26.8 221 10 5 4.6 2.5 | -2.1 28.2 231 7 4 7.2 4.0
11500 -2.2 28.0 200 8 4 4.4 2.4 | -1.0 30.2 205 5 3 7.3 4.0
11000 -1.3 29.7 178 8 4 7.9 4.3 | 0.2 32.4 169 5 2 9.0 4.9
10500 -0.0 32.0 166 7 4 8.0 4.4 | 1.6 34.9 152 5 3 9.1 5.0
10250 0.6 33.1 159 7 3 8.8 4.8 | 2.2 36.0 144 6 3 9.3 5.1
10000 1.3 34.3 155 7 3 9.7 5.3 | 2.9 37.2 141 6 3 9.6 5.3
9750 2.0 35.6 153 6 3 9.8 5.4 | 3.7 38.7 138 6 3 9.6 5.3
9500 2.7 36.9 151 6 3 9.8 5.4 | 4.4 39.9 135 6 3 9.6 5.3
9250 3.5 38.3 149 6 3 9.6 5.3 | 5.1 41.2 133 6 3 9.7 5.3
9000 4.2 39.6 148 6 3 9.5 5.2 | 5.8 42.4 132 6 3 9.8 5.4
8750 4.9 40.8 146 6 3 9.5 5.2 | 6.5 43.7 131 6 3 9.7 5.3
8500 5.6 42.1 145 6 3 9.6 5.2 | 7.3 45.1 130 6 3 9.7 5.3
8250 6.3 43.3 144 6 3 9.9 5.4 | 8.0 46.4 129 6 3 9.8 5.4
8000 7.1 44.8 144 5 3 10.1 5.6 | 8.7 47.7 129 6 3 9.9 5.4
7750 7.8 46.0 144 5 3 10.1 5.5 | 9.5 49.1 128 6 3 9.9 5.4
7500 8.6 47.5 144 5 3 10.0 5.5 | 10.2 50.4 127 6 3 9.9 5.4
7250 9.3 48.7 143 5 3 9.9 5.4 | 10.9 51.6 127 6 3 9.8 5.4
7000 10.1 50.2 143 5 3 9.9 5.4 | 11.7 53.1 126 6 3 9.8 5.4
6750 10.8 51.4 142 5 2 9.9 5.4 | 12.4 54.3 126 6 3 9.8 5.4
6500 11.5 52.7 142 5 2 10.2 5.6 | 13.1 55.6 125 6 3 9.9 5.4
6250 12.3 54.1 142 4 2 10.9 6.0 | 13.9 57.0 124 6 3 10.2 5.6
6000 13.1 55.6 143 4 2 9.4 5.2 | 14.6 58.3 123 5 3 9.6 5.3
5750 13.9 57.0 143 4 2 14.7 8.1 | 15.4 59.7 123 5 3 11.5 6.3
5500 15.5 59.9 141 4 2 28.8 15.8 | 16.4 61.5 123 5 3 17.2 9.5
________________________________________________________________________________
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:
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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