Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
926 UXUS97 KBOU 251240 SRGBOU Soaring Forecast National Weather Service Denver/Boulder, Colorado 0639 MDT Wednesday, September 25, 2024 This forecast is for Wednesday, September 25, 2024: If the trigger temperature of 78.1 F/25.6 C is reached...then Thermal Soaring Index....................... Good Maximum rate of lift........................ 642 ft/min (3.3 m/s) Maximum height of thermals.................. 13510 ft MSL (8213 ft AGL) Forecast maximum temperature................... 87.0 F/31.0 C Time of trigger temperature.................... 1145 MDT 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................. 10604 ft MSL (5307 ft AGL) Thermal soaring outlook for Thursday 09/26..... 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)................ Neither Potential height of wave....................... 19831 ft MSL (14534 ft AGL) Wave soaring outlook for Thursday 09/26........ Fair Remarks... Sunrise/Sunset.................... 06:50:48 / 18:51:00 MDT Total possible sunshine........... 12 hr 0 min 12 sec (720 min 12 sec) Altitude of sun at 12:50:54 MDT... 48.91 degrees Upper air data from numerical model forecast valid on 09/25/2024 at 0600 MDT Freezing level.................. 16525 ft MSL (11228 ft AGL) Convective condensation level... 18282 ft MSL (12985 ft AGL) Lifted condensation level....... 16399 ft MSL (11102 ft AGL) Lifted index.................... +2.5 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 -66.4 -87.5 315 15 8 1.9 1.1 M M M M M 45000 -61.9 -79.4 335 14 7 5.3 2.9 M M M M M 40000 -53.5 -64.3 045 20 10 7.2 4.0 M M M M M 38000 -49.2 -56.6 035 21 11 7.2 4.0 M M M M M 36000 -44.9 -48.8 030 22 11 7.3 4.0 M M M M M 34000 -39.7 -39.5 020 20 10 8.6 4.7 M M M M M 32000 -33.9 -29.0 010 18 9 8.7 4.8 M M M M M 30000 -28.8 -19.8 010 16 8 8.5 4.6 47.1 116.8 12.6 M M 29000 -26.3 -15.3 010 15 8 8.5 4.6 46.7 116.0 12.4 M M 28000 -23.8 -10.8 010 13 7 8.2 4.5 46.2 115.2 12.2 M M 27000 -21.3 -6.3 360 12 6 8.2 4.5 45.5 113.9 11.8 M M 26000 -18.8 -1.8 345 11 6 8.2 4.5 45.0 112.9 11.5 M M 25000 -16.4 2.5 330 11 6 7.6 4.2 44.5 112.1 11.3 M M 24000 -14.4 6.1 325 12 6 6.5 3.6 43.2 109.8 10.4 M M 23000 -12.4 9.7 325 12 6 6.5 3.6 42.1 107.7 9.5 M M 22000 -10.5 13.1 320 12 6 6.4 3.5 41.0 105.8 8.7 M M 21000 -8.6 16.5 330 11 6 6.2 3.4 39.7 103.4 7.6 M M 20000 -6.8 19.8 340 11 6 6.3 3.4 38.4 101.2 6.7 M M 19500 -5.9 21.4 345 11 6 6.3 3.5 37.9 100.2 6.2 M M 19000 -4.9 23.2 355 11 6 6.2 3.4 37.3 99.1 5.7 M M 18500 -4.0 24.8 005 11 6 6.3 3.4 36.7 98.0 5.2 M M 18000 -3.1 26.4 015 11 6 6.4 3.5 36.1 97.0 4.6 M M 17500 -2.2 28.0 020 11 6 6.7 3.7 35.5 96.0 4.2 M M 17000 -1.2 29.8 025 11 6 6.7 3.7 35.0 95.0 3.7 M M 16500 0.3 32.5 030 11 6 6.7 3.7 34.2 93.6 3.0 M M 16000 1.3 34.3 030 11 6 6.7 3.7 33.7 92.7 2.5 M M 15500 2.2 36.0 030 11 5 6.8 3.7 33.2 91.8 2.0 M M 15000 3.2 37.8 030 10 5 6.9 3.8 32.7 90.9 1.6 M M 14500 4.2 39.6 025 9 5 6.0 3.3 32.2 90.0 1.1 M M 14000 5.1 41.2 015 9 5 5.8 3.2 31.5 88.8 0.5 M M 13500 5.9 42.6 010 9 4 5.9 3.2 30.9 87.7 -0.1 635 3.2 13000 6.8 44.2 360 9 5 6.0 3.3 30.3 86.5 -0.7 595 3.0 12500 7.6 45.7 350 9 5 6.6 3.6 29.7 85.4 -1.4 555 2.8 12000 8.7 47.7 350 10 5 7.5 4.1 29.3 84.7 -1.8 508 2.6 11500 9.7 49.5 350 10 5 7.4 4.0 29.0 84.1 -2.2 461 2.3 11000 10.7 51.3 350 10 5 6.9 3.8 28.5 83.3 -2.6 416 2.1 10500 11.7 53.1 350 10 5 5.1 2.8 28.1 82.6 -3.1 372 1.9 10250 12.0 53.6 350 10 5 4.3 2.3 27.6 81.7 -3.6 356 1.8 10000 12.4 54.3 345 9 5 7.0 3.9 27.3 81.2 -3.9 337 1.7 9750 12.9 55.2 345 8 4 7.7 4.2 27.1 80.8 -4.2 315 1.6 9500 13.4 56.1 340 8 4 6.5 3.6 27.0 80.5 -4.4 293 1.5 9250 13.7 56.7 340 7 3 4.8 2.6 26.6 79.9 -4.8 275 1.4 9000 14.1 57.4 335 6 3 5.2 2.8 26.2 79.2 -5.2 257 1.3 8750 14.5 58.1 320 4 2 5.7 3.1 25.9 78.6 -5.6 238 1.2 8500 14.9 58.8 300 3 2 5.2 2.8 25.6 78.0 -5.9 218 1.1 8250 15.2 59.4 275 3 1 4.6 2.5 25.2 77.3 -6.3 200 1.0 8000 15.6 60.1 245 3 1 5.1 2.8 24.8 76.7 -6.7 182 0.9 7750 16.0 60.8 215 3 2 5.7 3.1 24.5 76.1 -7.0 162 0.8 7500 16.5 61.7 200 4 2 5.4 3.0 24.2 75.5 -7.3 141 0.7 7250 16.9 62.4 195 4 2 4.6 2.5 23.8 74.8 -7.7 122 0.6 7000 17.3 63.1 190 4 2 6.0 3.3 23.4 74.2 -8.0 102 0.5 6750 17.7 63.9 185 3 2 2.3 1.2 23.1 73.6 -8.3 82 0.4 6500 17.5 63.5 190 3 2 -5.6 -3.1 22.2 71.9 -9.3 81 0.4 6250 16.9 62.4 205 4 2 -7.2 -4.0 20.9 69.7 -10.6 90 0.5 6000 16.4 61.5 215 4 2 -6.9 -3.8 19.7 67.4 -11.9 99 0.5 5750 15.6 60.1 215 5 3 -15.5 -8.5 18.2 64.7 -13.4 115 0.6 5500 13.9 57.0 205 5 3 -28.4 -15.6 15.8 60.4 -15.9 159 0.8 * * * * * * Numerical weather prediction model forecast data valid * * * * * * 09/25/2024 at 0900 MDT | 09/25/2024 at 1200 MDT | CAPE... 0.0 LI... +4.2 | CAPE... 0.0 LI... +4.0 CINH... 0.0 K Index... +6.2 | CINH... 0.0 K Index... +5.6 | 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 -66.3 -87.3 315 17 9 2.2 1.2 | -66.2 -87.2 305 15 7 2.0 1.1 45000 -61.5 -78.7 330 13 7 5.3 2.9 | -61.6 -78.9 305 12 6 5.4 3.0 40000 -53.2 -63.8 075 14 7 6.9 3.8 | -52.7 -62.9 140 7 4 7.0 3.9 38000 -49.0 -56.2 055 14 7 6.9 3.8 | -48.5 -55.3 105 7 3 7.0 3.8 36000 -44.9 -48.8 040 15 8 7.0 3.8 | -44.3 -47.7 075 9 5 7.8 4.3 34000 -39.1 -38.4 025 13 7 8.6 4.7 | -39.1 -38.4 050 6 3 8.7 4.8 32000 -33.9 -29.0 010 12 6 8.7 4.8 | -33.9 -29.0 005 6 3 8.8 4.8 30000 -29.0 -20.2 010 11 6 8.3 4.5 | -29.0 -20.2 360 6 3 8.2 4.5 29000 -26.5 -15.7 010 10 5 8.3 4.5 | -26.5 -15.7 355 5 3 8.2 4.5 28000 -24.0 -11.2 010 10 5 8.4 4.6 | -24.0 -11.2 350 5 3 8.4 4.6 27000 -21.4 -6.5 360 10 5 8.4 4.6 | -20.9 -5.6 355 6 3 8.4 4.6 26000 -18.9 -2.0 355 10 5 8.4 4.6 | -18.4 -1.1 360 6 3 8.4 4.6 25000 -16.4 2.5 350 11 6 7.6 4.2 | -15.9 3.4 005 6 3 7.4 4.1 24000 -14.4 6.1 340 11 6 6.6 3.6 | -13.8 7.2 005 7 4 7.0 3.8 23000 -12.4 9.7 335 11 6 6.6 3.6 | -11.8 10.8 005 8 4 7.0 3.8 22000 -10.4 13.3 330 12 6 6.5 3.6 | -9.7 14.5 005 8 4 6.1 3.4 21000 -8.5 16.7 335 11 6 6.4 3.5 | -8.0 17.6 355 8 4 5.8 3.2 20000 -6.6 20.1 335 10 5 6.4 3.5 | -6.3 20.7 350 8 4 5.8 3.2 19500 -5.7 21.7 335 10 5 6.4 3.5 | -5.4 22.3 345 8 4 5.9 3.3 19000 -4.8 23.4 340 9 5 6.2 3.4 | -4.5 23.9 340 8 4 6.7 3.7 18500 -3.8 25.2 345 8 4 6.3 3.4 | -3.5 25.7 335 7 3 6.6 3.6 18000 -2.9 26.8 355 7 4 6.9 3.8 | -2.5 27.5 330 6 3 6.8 3.7 17500 -1.8 28.8 360 6 3 7.4 4.1 | -1.5 29.3 325 5 3 6.9 3.8 17000 -0.7 30.7 010 5 3 7.6 4.1 | -0.5 31.1 315 5 2 7.0 3.8 16500 0.3 32.5 015 4 2 6.5 3.6 | 0.5 32.9 305 4 2 6.9 3.8 16000 1.3 34.3 020 3 2 6.7 3.6 | 1.5 34.7 290 5 2 6.9 3.8 15500 2.7 36.9 025 3 1 6.8 3.7 | 2.5 36.5 285 5 3 6.9 3.8 15000 3.7 38.7 025 2 1 6.8 3.7 | 3.5 38.3 275 6 3 6.8 3.8 14500 4.7 40.5 005 2 1 6.7 3.7 | 4.5 40.1 270 6 3 6.8 3.7 14000 5.7 42.3 340 3 1 6.8 3.7 | 5.5 41.9 275 7 4 6.7 3.7 13500 6.7 44.1 330 3 2 6.1 3.3 | 6.9 44.4 280 7 4 6.0 3.3 13000 7.5 45.5 330 4 2 5.9 3.2 | 7.8 46.0 285 7 3 5.9 3.2 12500 8.4 47.1 330 5 3 6.2 3.4 | 8.6 47.5 290 6 3 5.9 3.2 12000 9.3 48.7 335 5 3 6.5 3.5 | 9.4 48.9 290 4 2 6.0 3.3 11500 10.2 50.4 345 5 3 6.7 3.7 | 10.2 50.4 285 3 1 6.3 3.4 11000 11.2 52.2 350 5 3 6.9 3.8 | 11.2 52.2 270 2 1 6.3 3.4 10500 12.2 54.0 360 5 2 3.9 2.1 | 12.1 53.8 200 1 1 2.3 1.3 10250 12.3 54.1 360 5 2 3.8 2.1 | 12.1 53.8 190 1 1 4.0 2.2 10000 12.9 55.2 005 4 2 9.0 4.9 | 12.8 55.0 165 2 1 10.4 5.7 9750 13.5 56.3 010 4 2 9.7 5.3 | 13.4 56.1 155 3 2 9.4 5.1 9500 14.1 57.4 015 4 2 6.9 3.8 | 14.1 57.4 150 4 2 7.2 3.9 9250 14.4 57.9 020 3 2 3.4 1.9 | 14.5 58.1 155 5 2 4.7 2.6 9000 14.7 58.5 020 3 1 6.5 3.5 | 14.9 58.8 155 5 3 7.6 4.2 8750 15.3 59.5 030 2 1 8.5 4.7 | 15.5 59.9 155 6 3 8.9 4.9 8500 15.8 60.4 070 1 0 6.2 3.4 | 16.1 61.0 155 7 3 7.6 4.2 8250 16.2 61.2 155 1 1 4.6 2.5 | 16.6 61.9 150 7 4 6.5 3.6 8000 16.6 61.9 175 2 1 5.6 3.1 | 17.1 62.8 150 7 4 7.9 4.3 7750 17.0 62.6 180 3 2 6.2 3.4 | 17.7 63.9 145 7 4 9.3 5.1 7500 17.5 63.5 180 4 2 5.3 2.9 | 18.4 65.1 145 7 4 9.0 4.9 7250 17.8 64.0 180 5 2 4.6 2.5 | 19.0 66.2 140 7 4 8.8 4.8 7000 18.2 64.8 175 5 3 5.0 2.7 | 19.7 67.5 140 7 3 9.0 4.9 6750 18.6 65.5 175 6 3 2.8 1.5 | 20.4 68.7 140 7 3 10.2 5.6 6500 18.7 65.7 175 6 3 0.1 0.1 | 21.2 70.2 140 6 3 10.8 5.9 6250 18.7 65.7 180 7 4 1.7 0.9 | 22.0 71.6 135 6 3 10.9 6.0 6000 18.7 65.7 185 8 4 -3.5 -1.9 | 22.8 73.0 135 6 3 10.3 5.7 5750 18.2 64.8 185 6 3 -7.3 -4.0 | 23.6 74.5 135 6 3 14.8 8.1 5500 17.9 64.2 185 5 3 1.6 0.9 | 25.1 77.2 135 6 3 23.8 13.1 09/25/2024 at 1500 MDT | 09/25/2024 at 1800 MDT | CAPE... 0.0 LI... +2.8 | CAPE... 0.0 LI... +1.8 CINH... 0.0 K Index... +6.2 | CINH... 0.0 K Index... +16.9 | 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 -66.0 -86.8 280 12 6 2.0 1.1 | -66.5 -87.7 275 16 8 2.1 1.2 45000 -61.5 -78.7 275 11 6 5.2 2.8 | -61.8 -79.2 255 15 8 5.1 2.8 40000 -52.7 -62.9 205 14 7 7.4 4.1 | -53.6 -64.5 200 16 8 7.6 4.1 38000 -48.3 -54.9 195 9 5 7.4 4.1 | -49.0 -56.2 205 13 7 7.6 4.1 36000 -43.9 -47.0 170 6 3 8.0 4.4 | -44.5 -48.1 205 10 5 7.8 4.3 34000 -38.7 -37.7 190 3 2 8.7 4.8 | -38.4 -37.1 210 8 4 9.0 4.9 32000 -33.5 -28.3 250 2 1 8.8 4.8 | -33.0 -27.4 220 7 3 8.8 4.9 30000 -28.5 -19.3 275 3 2 8.2 4.5 | -28.1 -18.6 230 6 3 8.1 4.5 29000 -26.0 -14.8 280 4 2 8.2 4.5 | -25.6 -14.1 230 6 3 8.2 4.5 28000 -23.0 -9.4 285 4 2 8.1 4.4 | -23.2 -9.8 235 6 3 8.0 4.4 27000 -20.5 -4.9 295 3 1 8.1 4.4 | -20.8 -5.4 230 5 3 8.0 4.4 26000 -18.1 -0.6 305 2 1 8.1 4.4 | -18.4 -1.1 225 4 2 8.0 4.4 25000 -15.7 3.7 335 1 1 7.5 4.1 | -16.0 3.2 220 4 2 7.6 4.2 24000 -13.6 7.5 025 2 1 7.2 3.9 | -13.9 7.0 205 3 2 7.1 3.9 23000 -11.4 11.5 050 3 1 7.2 3.9 | -11.7 10.9 190 3 2 7.1 3.9 22000 -9.3 15.3 055 4 2 6.0 3.3 | -9.6 14.7 170 4 2 6.2 3.4 21000 -7.7 18.1 035 4 2 5.5 3.0 | -8.0 17.6 205 2 1 5.2 2.9 20000 -6.1 21.0 015 4 2 5.5 3.0 | -6.5 20.3 265 2 1 5.2 2.9 19500 -5.3 22.5 005 4 2 5.6 3.1 | -5.7 21.7 280 3 2 5.1 2.8 19000 -4.4 24.1 355 4 2 6.9 3.8 | -4.8 23.4 290 4 2 7.3 4.0 18500 -3.4 25.9 345 5 2 6.8 3.8 | -3.7 25.3 295 5 3 7.1 3.9 18000 -2.4 27.7 330 5 2 6.9 3.8 | -2.7 27.1 295 6 3 7.2 3.9 17500 -1.3 29.7 320 5 3 6.9 3.8 | -1.6 29.1 295 7 3 7.3 4.0 17000 -0.3 31.5 310 6 3 6.9 3.8 | -0.0 32.0 300 8 4 7.5 4.1 16500 0.7 33.3 305 6 3 7.2 4.0 | 1.0 33.8 300 9 5 7.8 4.3 16000 1.8 35.2 295 7 4 7.2 3.9 | 2.1 35.8 300 10 5 7.9 4.3 15500 2.8 37.0 295 8 4 7.4 4.1 | 3.2 37.8 305 10 5 8.1 4.5 15000 3.9 39.0 290 9 4 7.5 4.1 | 4.3 39.7 305 11 6 8.3 4.6 14500 5.0 41.0 285 9 5 7.5 4.1 | 5.4 41.7 310 12 6 8.1 4.4 14000 6.1 43.0 285 10 5 7.5 4.1 | 6.6 43.9 310 11 6 8.1 4.4 13500 7.6 45.7 285 10 5 6.9 3.8 | 7.7 45.9 310 11 5 7.5 4.1 13000 8.6 47.5 285 9 5 6.7 3.7 | 8.8 47.8 305 8 4 7.2 3.9 12500 9.5 49.1 280 9 4 6.3 3.5 | 9.8 49.6 295 6 3 6.6 3.6 12000 10.3 50.5 270 7 3 6.0 3.3 | 10.7 51.3 260 4 2 5.9 3.2 11500 11.1 52.0 255 5 3 6.1 3.4 | 11.6 52.9 210 5 2 5.9 3.2 11000 12.0 53.6 210 4 2 6.0 3.3 | 12.5 54.5 180 6 3 5.8 3.2 10500 12.9 55.2 175 6 3 2.1 1.2 | 13.4 56.1 165 9 5 3.1 1.7 10250 13.0 55.4 170 6 3 4.6 2.5 | 13.6 56.5 160 10 5 6.2 3.4 10000 13.7 56.7 160 6 3 11.5 6.3 | 14.4 57.9 160 9 5 12.0 6.6 9750 14.4 57.9 155 7 3 10.2 5.6 | 15.2 59.4 160 9 5 10.7 5.9 9500 15.1 59.2 145 7 4 8.5 4.7 | 16.0 60.8 155 9 5 10.1 5.5 9250 15.6 60.1 145 7 4 7.2 3.9 | 16.6 61.9 155 9 5 8.9 4.9 9000 16.3 61.3 145 7 4 10.5 5.8 | 17.3 63.1 155 9 5 9.9 5.4 8750 17.1 62.8 145 7 4 12.1 6.7 | 18.1 64.6 155 9 5 10.3 5.7 8500 18.0 64.4 145 7 4 10.2 5.6 | 18.9 66.0 150 9 5 10.2 5.6 8250 18.7 65.7 140 7 4 8.4 4.6 | 19.7 67.5 150 9 5 10.5 5.7 8000 19.3 66.7 140 7 4 9.8 5.4 | 20.4 68.7 150 9 5 10.0 5.5 7750 20.1 68.2 140 7 4 10.7 5.9 | 21.1 70.0 145 9 5 9.5 5.2 7500 20.9 69.6 140 7 3 10.2 5.6 | 21.9 71.4 145 9 4 9.9 5.5 7250 21.6 70.9 140 7 3 10.0 5.5 | 22.6 72.7 145 9 4 10.4 5.7 7000 22.4 72.3 140 7 3 10.1 5.5 | 23.4 74.1 145 8 4 10.0 5.5 6750 23.1 73.6 140 7 3 10.3 5.6 | 24.1 75.4 140 8 4 9.2 5.1 6500 23.9 75.0 140 6 3 10.4 5.7 | 24.8 76.6 140 8 4 9.4 5.2 6250 24.7 76.5 140 6 3 11.1 6.1 | 25.5 77.9 140 8 4 9.8 5.4 6000 25.5 77.9 140 6 3 8.9 4.9 | 26.3 79.3 140 7 4 9.8 5.4 5750 26.2 79.2 140 6 3 13.1 7.2 | 27.0 80.6 135 7 4 9.3 5.1 5500 27.7 81.9 135 6 3 26.7 14.6 | 27.6 81.7 135 6 3 7.8 4.3 ________________________________________________________________________________ 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. 042613