Issued by NWS Denver/Boulder, CO
000
UXUS97 KBOU 090058
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
658 PM MDT Friday May 8, 2009
This forecast is for Saturday May 9, 2009:
If the trigger temperature of 47.8 F/8.8 C is reached...then
Thermal Soaring Index....................... Fair
Maximum rate of lift........................ 258 ft/min (1.3 m/s)
Maximum height of thermals.................. 12310 ft MSL (6987 ft AGL)
Forecast maximum temperature................... 59.0 F/15.5 C
Time of trigger temperature.................... 0815 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Overcast opaque high
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 10974 ft MSL (5651 ft AGL)
Thermal soaring outlook for Sunday 05/10....... Poor
Wave Soaring Index............................. Excellent
Wave Soaring Index trend (to 1800 MDT)......... Decreasing
Height of stable layer (12-18K ft MSL)......... 12689 ft MSL (7366 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Weak PVA
Potential height of wave....................... 39452 ft MSL (34129 ft AGL)
Wave soaring outlook for Sunday 05/10.......... Fair
Remarks... None
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 numerical model forecast valid on 05/09/2009 at 0600 MDT
Freezing level.................. 7981 ft MSL (2658 ft AGL)
Convective condensation level... 14602 ft MSL (9279 ft AGL)
Lifted condensation level....... 12901 ft MSL (7578 ft AGL)
Lifted index.................... +6.8
K index......................... +8.4
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 -59.9 -75.8 276 55 28 1.2 0.7 96.9 206.4 47.2 M M
45000 -58.2 -72.8 282 82 42 0.5 0.3 77.2 170.9 38.1 M M
40000 -57.3 -71.1 278 98 50 0.7 0.4 54.3 129.7 25.9 M M
38000 -54.5 -66.1 277 98 51 6.0 3.3 49.5 121.0 23.3 M M
36000 -51.0 -59.8 275 97 50 6.0 3.3 46.2 115.2 21.7 M M
34000 -47.2 -53.0 274 95 49 7.0 3.8 43.5 110.2 20.3 M M
32000 -43.0 -45.4 273 91 47 7.0 3.8 41.1 105.9 19.1 M M
30000 -38.8 -37.8 272 87 45 7.0 3.8 39.0 102.1 18.0 M M
29000 -36.2 -33.2 273 85 44 7.0 3.8 37.5 99.5 17.1 M M
28000 -34.2 -29.6 273 83 43 7.0 3.8 36.5 97.7 16.6 M M
27000 -32.1 -25.8 274 81 42 6.8 3.7 35.5 95.8 16.0 M M
26000 -30.1 -22.2 274 80 41 6.8 3.7 34.2 93.6 15.2 M M
25000 -28.0 -18.4 274 78 40 6.8 3.7 33.2 91.7 14.5 M M
24000 -26.0 -14.8 274 76 39 6.7 3.7 32.2 89.9 13.8 M M
23000 -24.0 -11.2 275 75 38 6.7 3.7 30.9 87.7 13.0 M M
22000 -22.0 -7.6 275 73 38 6.7 3.7 29.8 85.7 12.2 M M
21000 -20.1 -4.2 276 71 36 5.6 3.1 28.7 83.7 11.4 M M
20000 -18.4 -1.1 276 65 34 5.7 3.1 27.2 81.0 10.2 M M
19500 -17.6 0.3 275 63 32 5.7 3.1 26.5 79.7 9.7 M M
19000 -16.7 1.9 275 60 31 5.8 3.2 25.8 78.5 9.2 M M
18500 -15.9 3.4 275 58 30 4.3 2.4 25.1 77.2 8.6 M M
18000 -15.4 4.3 273 54 28 4.0 2.2 24.1 75.4 7.8 M M
17500 -14.8 5.4 272 51 26 4.5 2.4 23.1 73.6 6.9 M M
17000 -13.9 7.0 270 48 25 6.7 3.7 22.4 72.4 6.4 M M
16500 -13.0 8.6 268 45 23 6.4 3.5 21.9 71.4 5.9 M M
16000 -11.3 11.7 266 42 22 8.4 4.6 21.4 70.5 5.4 M M
15500 -10.0 14.0 265 40 21 8.4 4.6 21.2 70.1 5.3 M M
15000 -9.0 15.8 263 39 20 6.1 3.4 20.7 69.3 4.8 M M
14500 -8.1 17.4 262 37 19 6.6 3.6 20.1 68.3 4.3 M M
14000 -7.3 18.9 260 35 18 3.8 2.1 19.4 67.0 3.6 M M
13500 -6.8 19.8 257 33 17 4.1 2.2 18.5 65.2 2.7 M M
13000 -6.4 20.5 254 30 16 1.6 0.9 17.4 63.3 1.7 M M
12500 -6.3 20.7 247 28 14 1.2 0.6 16.0 60.8 0.4 M M
12000 -6.1 21.0 239 26 13 2.6 1.4 14.7 58.4 -0.9 443 2.2
11500 -5.7 21.7 229 25 13 2.9 1.6 13.6 56.4 -1.9 416 2.1
11000 -5.2 22.6 219 24 12 2.6 1.4 12.5 54.4 -3.0 389 2.0
10500 -4.9 23.2 208 23 12 2.3 1.3 11.3 52.4 -4.1 363 1.8
10250 -4.7 23.5 202 23 12 3.4 1.9 10.7 51.3 -4.7 350 1.8
10000 -4.4 24.1 197 22 11 5.2 2.9 10.3 50.6 -5.1 332 1.7
9750 -3.9 25.0 193 21 11 5.5 3.0 10.0 50.0 -5.4 313 1.6
9500 -3.5 25.7 188 21 11 5.0 2.8 9.7 49.4 -5.7 293 1.5
9250 -3.1 26.4 183 20 10 6.8 3.7 9.3 48.8 -6.1 274 1.4
9000 -2.5 27.5 181 19 10 8.5 4.7 9.2 48.5 -6.2 248 1.3
8750 -1.9 28.6 179 19 10 8.1 4.4 9.1 48.3 -6.3 223 1.1
8500 -1.3 29.7 177 18 9 8.1 4.5 8.9 48.1 -6.5 197 1.0
8250 -0.7 30.7 174 17 9 7.8 4.3 8.8 47.8 -6.6 171 0.9
8000 -0.1 31.8 170 16 8 7.7 4.2 8.6 47.6 -6.8 146 0.7
7750 0.5 32.9 166 15 8 7.8 4.3 8.5 47.3 -6.9 121 0.6
7500 1.1 34.0 162 14 7 7.5 4.1 8.3 47.0 -7.1 96 0.5
7250 1.6 34.9 157 13 7 7.2 3.9 8.1 46.7 -7.3 72 0.4
7000 2.2 36.0 152 12 6 7.2 4.0 7.9 46.3 -7.5 48 0.2
6750 2.7 36.9 146 12 6 7.1 3.9 7.8 46.0 -7.7 25 0.1
6500 3.2 37.8 140 11 6 6.7 3.7 7.5 45.6 -7.9 2 0.0
6250 3.7 38.7 135 10 5 6.5 3.6 7.3 45.1 -8.2 M M
6000 4.1 39.4 128 9 5 6.5 3.6 7.1 44.7 -8.5 M M
5750 4.6 40.3 121 8 4 7.4 4.1 6.8 44.3 -8.8 M M
5500 5.2 41.4 117 6 3 9.2 5.0 6.7 44.0 -9.1 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
05/09/2009 at 0900 MDT | 05/09/2009 at 1200 MDT
|
K index... +6.1 | K index... +10.8
|
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 -59.7 -75.5 274 53 27 0.8 0.4 | -60.4 -76.7 273 55 28 0.5 0.2
45000 -58.5 -73.3 283 78 40 0.7 0.4 | -59.6 -75.3 274 71 36 1.5 0.8
40000 -57.5 -71.5 277 97 50 0.9 0.5 | -57.3 -71.1 270 89 46 1.4 0.8
38000 -54.7 -66.5 276 97 50 5.9 3.2 | -54.4 -65.9 270 90 46 6.0 3.3
36000 -51.2 -60.2 275 94 49 5.9 3.2 | -50.8 -59.4 270 89 46 6.0 3.3
34000 -47.5 -53.5 274 91 47 6.4 3.5 | -47.1 -52.8 270 87 45 6.5 3.6
32000 -43.7 -46.7 273 85 44 6.4 3.5 | -43.2 -45.8 269 81 42 6.5 3.6
30000 -39.1 -38.4 272 79 41 7.6 4.2 | -39.3 -38.7 269 76 39 6.8 3.7
29000 -36.8 -34.2 273 77 40 7.6 4.2 | -36.8 -34.2 269 73 37 6.8 3.7
28000 -34.5 -30.1 274 75 39 7.6 4.2 | -34.7 -30.5 270 70 36 6.8 3.7
27000 -32.3 -26.1 274 73 38 7.2 3.9 | -32.5 -26.5 271 68 35 8.5 4.6
26000 -30.1 -22.2 274 72 37 7.2 4.0 | -30.0 -22.0 272 67 35 8.4 4.6
25000 -28.0 -18.4 274 71 37 7.2 4.0 | -27.5 -17.5 272 67 34 8.4 4.6
24000 -25.8 -14.4 274 70 36 7.2 4.0 | -25.1 -13.2 273 66 34 6.6 3.6
23000 -23.7 -10.7 274 70 36 7.3 4.0 | -23.1 -9.6 273 65 34 6.6 3.6
22000 -21.5 -6.7 274 69 35 7.3 4.0 | -21.2 -6.2 273 64 33 6.6 3.6
21000 -19.5 -3.1 275 67 35 5.7 3.1 | -19.2 -2.6 274 64 33 6.9 3.8
20000 -17.7 0.1 276 63 32 5.9 3.2 | -17.2 1.0 276 64 33 6.9 3.8
19500 -16.8 1.8 277 61 31 5.9 3.2 | -16.1 3.0 277 64 33 6.9 3.8
19000 -16.0 3.2 278 59 30 5.9 3.3 | -15.1 4.8 278 64 33 7.1 3.9
18500 -15.2 4.6 278 57 29 4.6 2.5 | -14.2 6.4 279 63 32 4.6 2.5
18000 -14.5 5.9 278 53 27 4.4 2.4 | -13.6 7.5 280 61 31 4.5 2.5
17500 -13.9 7.0 277 50 26 4.6 2.5 | -12.9 8.8 280 59 30 4.6 2.5
17000 -13.1 8.4 276 47 24 5.1 2.8 | -12.2 10.0 280 55 28 4.9 2.7
16500 -12.4 9.7 274 44 23 4.8 2.6 | -11.5 11.3 279 50 26 4.7 2.6
16000 -10.9 12.4 271 41 21 7.6 4.1 | -10.2 13.6 277 43 22 6.2 3.4
15500 -9.8 14.4 269 39 20 7.6 4.2 | -9.3 15.3 275 39 20 6.4 3.5
15000 -8.7 16.3 268 36 19 7.4 4.1 | -8.3 17.1 274 35 18 8.0 4.4
14500 -7.6 18.3 267 34 18 7.7 4.2 | -7.1 19.2 274 32 17 8.4 4.6
14000 -6.7 19.9 267 32 16 5.1 2.8 | -6.3 20.7 274 29 15 3.3 1.8
13500 -5.9 21.4 266 29 15 5.5 3.0 | -5.8 21.6 272 25 13 3.9 2.1
13000 -5.3 22.5 265 27 14 3.4 1.9 | -5.3 22.5 270 22 11 3.0 1.7
12500 -4.8 23.4 263 24 12 3.5 1.9 | -4.9 23.2 267 19 10 3.0 1.7
12000 -4.6 23.7 260 21 11 0.4 0.2 | -4.5 23.9 262 16 8 3.4 1.9
11500 -4.6 23.7 253 19 10 -0.2 -0.1 | -4.0 24.8 249 11 6 3.4 1.9
11000 -4.6 23.7 243 17 9 3.0 1.6 | -3.4 25.9 228 8 4 5.3 2.9
10500 -4.1 24.6 229 16 8 3.1 1.7 | -2.6 27.3 200 6 3 5.1 2.8
10250 -3.8 25.2 222 15 8 4.6 2.6 | -2.2 28.0 183 6 3 6.8 3.7
10000 -3.3 26.1 216 16 8 6.8 3.7 | -1.6 29.1 176 6 3 9.0 4.9
9750 -2.8 27.0 210 16 8 6.9 3.8 | -0.9 30.4 172 6 3 9.1 5.0
9500 -2.3 27.9 205 17 9 6.9 3.8 | -0.2 31.6 168 5 3 8.9 4.9
9250 -1.8 28.8 200 18 9 6.9 3.8 | 0.5 32.9 163 5 3 9.5 5.2
9000 -1.3 29.7 195 17 9 6.9 3.8 | 1.2 34.2 163 5 3 10.1 5.5
8750 -0.8 30.6 189 16 8 6.8 3.7 | 1.9 35.4 162 5 3 9.9 5.4
8500 -0.3 31.5 183 16 8 7.1 3.9 | 2.7 36.9 161 5 2 10.0 5.5
8250 0.3 32.5 178 15 8 8.2 4.5 | 3.4 38.1 160 5 2 10.0 5.5
8000 0.9 33.6 174 14 7 8.8 4.9 | 4.2 39.6 159 4 2 10.0 5.5
7750 1.6 34.9 170 13 7 8.6 4.7 | 4.9 40.8 158 4 2 10.0 5.5
7500 2.2 36.0 165 12 6 9.2 5.0 | 5.7 42.3 157 4 2 10.0 5.5
7250 2.9 37.2 163 11 6 9.9 5.4 | 6.4 43.5 156 4 2 10.0 5.5
7000 3.6 38.5 162 10 5 9.8 5.4 | 7.2 45.0 156 4 2 10.0 5.5
6750 4.4 39.9 160 10 5 9.9 5.4 | 7.9 46.2 155 4 2 10.1 5.5
6500 5.1 41.2 158 9 5 10.0 5.5 | 8.7 47.7 154 3 2 10.4 5.7
6250 5.8 42.4 157 9 4 10.2 5.6 | 9.5 49.1 153 3 2 11.1 6.1
6000 6.6 43.9 156 8 4 9.6 5.3 | 10.3 50.5 152 3 2 9.4 5.1
5750 7.4 45.3 154 8 4 13.5 7.4 | 11.1 52.0 150 3 1 15.7 8.6
5500 8.7 47.7 154 7 4 21.3 11.7 | 12.8 55.0 156 3 2 31.3 17.2
05/09/2009 at 1500 MDT | 05/09/2009 at 1800 MDT
|
K index... +16.7 | K index... +24.0
|
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 -60.9 -77.6 267 50 26 1.7 0.9 | -59.9 -75.8 272 47 24 2.5 1.4
45000 -58.5 -73.3 268 67 34 1.3 0.7 | -56.2 -69.2 270 71 36 0.9 0.5
40000 -56.4 -69.5 266 90 46 1.4 0.8 | -54.9 -66.8 262 89 46 0.9 0.5
38000 -53.8 -64.8 266 93 48 5.4 3.0 | -53.3 -63.9 266 93 48 3.4 1.9
36000 -50.5 -58.9 266 95 49 5.4 3.0 | -51.3 -60.3 271 96 49 3.4 1.9
34000 -47.2 -53.0 267 94 48 5.9 3.2 | -48.6 -55.5 275 98 50 6.7 3.7
32000 -43.7 -46.7 267 88 45 5.9 3.2 | -44.6 -48.3 275 95 49 6.7 3.7
30000 -39.4 -38.9 268 81 42 7.1 3.9 | -40.0 -40.0 274 90 46 7.1 3.9
29000 -37.3 -35.1 269 78 40 7.1 3.9 | -37.8 -36.0 273 87 45 7.1 3.9
28000 -35.2 -31.4 269 75 39 7.1 3.9 | -35.7 -32.3 271 84 43 7.1 3.9
27000 -33.0 -27.4 269 73 38 7.7 4.2 | -33.6 -28.5 270 81 42 6.8 3.7
26000 -30.7 -23.3 270 72 37 7.7 4.2 | -31.6 -24.9 269 79 40 6.8 3.8
25000 -28.4 -19.1 270 71 37 7.7 4.2 | -29.6 -21.3 269 76 39 6.9 3.8
24000 -26.2 -15.2 271 70 36 7.2 4.0 | -27.5 -17.5 269 74 38 6.9 3.8
23000 -24.1 -11.4 271 69 35 7.2 4.0 | -25.5 -13.9 270 71 36 6.9 3.8
22000 -21.9 -7.4 271 67 35 7.2 4.0 | -23.5 -10.3 272 68 35 6.9 3.8
21000 -19.9 -3.8 271 65 34 5.6 3.1 | -21.4 -6.5 274 64 33 7.5 4.1
20000 -18.2 -0.8 273 63 32 5.8 3.2 | -19.2 -2.6 273 60 31 7.5 4.1
19500 -17.4 0.7 274 61 32 5.8 3.2 | -18.1 -0.6 273 57 30 7.5 4.1
19000 -16.5 2.3 275 60 31 5.7 3.1 | -17.0 1.4 273 55 28 7.5 4.1
18500 -15.6 3.9 275 58 30 6.4 3.5 | -15.9 3.4 273 53 27 7.5 4.1
18000 -14.7 5.5 273 54 28 6.5 3.6 | -14.8 5.4 272 50 26 7.5 4.1
17500 -13.7 7.3 272 50 25 7.0 3.8 | -13.7 7.3 272 47 24 7.3 4.0
17000 -12.6 9.3 270 46 24 7.8 4.3 | -12.7 9.1 272 44 23 6.8 3.8
16500 -11.4 11.5 268 43 22 7.8 4.3 | -11.2 11.8 272 40 21 6.7 3.7
16000 -9.7 14.5 267 39 20 8.2 4.5 | -10.2 13.6 272 37 19 6.4 3.5
15500 -8.4 16.9 267 36 19 8.0 4.4 | -9.3 15.3 272 33 17 6.4 3.5
15000 -7.4 18.7 266 34 17 6.7 3.7 | -8.4 16.9 272 29 15 6.4 3.5
14500 -6.4 20.5 266 31 16 7.0 3.9 | -7.5 18.5 271 25 13 6.4 3.5
14000 -5.6 21.9 265 27 14 4.7 2.6 | -6.6 20.1 270 21 11 5.8 3.2
13500 -4.9 23.2 263 24 12 5.1 2.8 | -5.8 21.6 267 16 8 5.9 3.2
13000 -4.3 24.3 260 19 10 3.0 1.7 | -5.0 23.0 261 12 6 4.7 2.6
12500 -3.9 25.0 252 13 7 2.8 1.6 | -4.3 24.3 245 7 4 4.4 2.4
12000 -3.4 25.9 236 8 4 4.9 2.7 | -3.5 25.7 205 4 2 7.7 4.2
11500 -2.7 27.1 206 5 2 4.9 2.7 | -2.2 28.0 169 4 2 8.2 4.5
11000 -1.7 28.9 157 4 2 8.4 4.6 | -0.9 30.4 145 5 3 9.6 5.3
10500 -0.4 31.3 137 4 2 8.8 4.8 | 0.5 32.9 137 5 3 9.9 5.4
10250 0.3 32.5 127 5 2 9.2 5.0 | 1.3 34.3 134 6 3 9.9 5.4
10000 1.0 33.8 123 5 2 9.6 5.3 | 2.0 35.6 132 6 3 9.8 5.4
9750 1.7 35.1 121 5 2 9.7 5.3 | 2.7 36.9 130 6 3 9.8 5.4
9500 2.4 36.3 119 5 2 9.6 5.3 | 3.5 38.3 129 6 3 9.8 5.4
9250 3.1 37.6 117 5 2 9.8 5.4 | 4.2 39.6 127 6 3 9.7 5.3
9000 3.9 39.0 116 5 2 10.1 5.5 | 4.9 40.8 126 6 3 9.7 5.3
8750 4.6 40.3 115 5 2 10.0 5.5 | 5.7 42.3 124 6 3 9.7 5.3
8500 5.4 41.7 114 4 2 10.0 5.5 | 6.4 43.5 122 6 3 9.7 5.3
8250 6.1 43.0 112 4 2 10.0 5.5 | 7.1 44.8 121 6 3 9.8 5.4
8000 6.9 44.4 112 4 2 10.1 5.5 | 7.8 46.0 119 6 3 9.9 5.4
7750 7.6 45.7 111 4 2 10.1 5.5 | 8.6 47.5 118 6 3 9.9 5.4
7500 8.4 47.1 110 4 2 10.0 5.5 | 9.3 48.7 117 6 3 9.9 5.4
7250 9.1 48.4 109 4 2 9.9 5.4 | 10.1 50.2 115 6 3 9.8 5.4
7000 9.9 49.8 108 4 2 9.9 5.4 | 10.8 51.4 114 6 3 9.8 5.4
6750 10.6 51.1 106 4 2 9.9 5.4 | 11.5 52.7 113 6 3 9.8 5.4
6500 11.3 52.3 105 4 2 10.3 5.6 | 12.2 54.0 111 6 3 9.9 5.4
6250 12.1 53.8 104 4 2 11.0 6.1 | 13.0 55.4 110 6 3 10.1 5.6
6000 12.9 55.2 103 4 2 9.6 5.3 | 13.7 56.7 109 6 3 9.7 5.3
5750 13.7 56.7 102 4 2 14.6 8.0 | 14.5 58.1 107 5 3 11.1 6.1
5500 15.3 59.5 104 4 2 28.5 15.6 | 15.4 59.7 107 6 3 15.6 8.6
________________________________________________________________________________
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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