Issued by NWS Denver/Boulder, CO
000
UXUS97 KBOU 220018
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
618 PM MDT Tuesday October 21, 2008
This forecast is for Wednesday October 22, 2008:
If the trigger temperature of 38.9 F/3.8 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 752 ft/min (3.8 m/s)
Maximum height of thermals.................. 16144 ft MSL (10821 ft AGL)
Forecast maximum temperature................... 48.0 F/9.3 C
Time of trigger temperature.................... 0915 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................. 11041 ft MSL (5718 ft AGL)
Thermal soaring outlook for Thursday 10/23..... Good
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 NVA
Potential height of wave....................... 42298 ft MSL (36975 ft AGL)
Wave soaring outlook for Thursday 10/23........ Poor
Remarks... None
Sunrise/Sunset.................... 07:17:45 / 18:10:56 MDT
Total possible sunshine........... 10 hr 53 min 11 sec (653 min 11 sec)
Altitude of sun at 12:43:56 MDT... 38.88 degrees
Upper air data from numerical model forecast valid on 10/22/2008 at 0600 MDT
Freezing level.................. 6148 ft MSL (825 ft AGL)
Convective condensation level... 11821 ft MSL (6498 ft AGL)
Lifted condensation level....... 12888 ft MSL (7565 ft AGL)
Lifted index.................... +3.3
K index......................... +5.7
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 -56.3 -69.3 321 22 11 1.8 1.0 105.2 221.4 55.2 M M
45000 -53.6 -64.5 321 36 19 2.1 1.2 87.0 188.6 47.6 M M
40000 -49.9 -57.8 336 38 20 2.5 1.4 69.2 156.5 39.3 M M
38000 -48.4 -55.1 338 38 20 2.3 1.3 62.8 145.0 36.0 M M
36000 -46.8 -52.2 336 35 18 2.3 1.3 55.1 131.2 31.9 M M
34000 -45.5 -49.9 333 33 17 2.3 1.3 49.2 120.5 28.4 M M
32000 -44.0 -47.2 333 32 16 2.3 1.3 42.6 108.7 24.5 M M
30000 -42.6 -44.7 332 31 16 2.3 1.2 36.9 98.4 20.8 M M
29000 -42.0 -43.6 337 30 16 2.2 1.2 33.7 92.6 18.7 M M
28000 -41.3 -42.3 342 30 16 2.2 1.2 30.6 87.1 16.6 M M
27000 -40.7 -41.3 347 30 16 2.2 1.2 27.8 82.0 14.6 M M
26000 -39.9 -39.8 350 30 16 2.7 1.5 25.0 76.9 12.6 M M
25000 -39.1 -38.4 350 30 15 2.7 1.5 22.2 72.0 10.6 M M
24000 -38.3 -36.9 351 30 15 2.8 1.5 19.7 67.4 8.6 M M
23000 -37.3 -35.1 352 30 15 3.9 2.1 17.3 63.1 6.8 M M
22000 -36.1 -33.0 353 31 16 3.9 2.1 15.0 59.1 5.0 M M
21000 -35.0 -31.0 355 32 16 3.7 2.0 13.0 55.4 3.4 M M
20000 -32.9 -27.2 355 32 17 7.7 4.2 11.9 53.5 2.5 M M
19500 -31.8 -25.2 354 32 17 7.7 4.2 11.6 52.8 2.2 M M
19000 -30.1 -22.2 354 32 17 7.7 4.2 11.1 51.9 1.8 M M
18500 -28.9 -20.0 354 33 17 7.5 4.1 10.7 51.3 1.5 M M
18000 -27.8 -18.0 354 33 17 7.3 4.0 10.3 50.5 1.1 M M
17500 -26.7 -16.1 354 33 17 7.4 4.1 9.9 49.8 0.8 M M
17000 -25.6 -14.1 355 33 17 7.8 4.3 9.5 49.1 0.4 M M
16500 -24.4 -11.9 355 34 17 7.7 4.2 9.2 48.5 0.1 M M
16000 -23.2 -9.8 356 34 17 8.6 4.7 8.9 48.0 -0.1 928 4.7
15500 -21.9 -7.4 356 34 17 8.5 4.7 8.7 47.7 -0.3 875 4.4
15000 -20.6 -5.1 357 34 17 8.5 4.6 8.5 47.3 -0.5 821 4.2
14500 -19.3 -2.7 358 34 17 8.5 4.7 8.3 46.9 -0.7 768 3.9
14000 -18.1 -0.6 359 34 17 8.2 4.5 8.1 46.5 -0.9 716 3.6
13500 -16.9 1.6 001 35 18 8.1 4.5 7.8 46.0 -1.1 665 3.4
13000 -15.7 3.7 002 35 18 7.6 4.2 7.5 45.5 -1.4 614 3.1
12500 -14.6 5.7 002 36 19 7.5 4.1 7.1 44.8 -1.8 566 2.9
12000 -13.5 7.7 003 37 19 7.1 3.9 6.7 44.1 -2.1 518 2.6
11500 -12.4 9.7 003 38 19 7.2 3.9 6.3 43.3 -2.6 472 2.4
11000 -11.4 11.5 003 38 20 6.1 3.4 5.8 42.5 -3.1 427 2.2
10500 -10.5 13.1 002 38 20 6.0 3.3 5.2 41.4 -3.7 386 2.0
10250 -10.1 13.8 002 38 20 6.4 3.5 4.9 40.9 -3.9 365 1.9
10000 -9.6 14.7 001 38 20 6.9 3.8 4.7 40.4 -4.2 343 1.7
9750 -9.1 15.6 001 38 19 6.8 3.7 4.5 40.0 -4.5 321 1.6
9500 -8.6 16.5 360 37 19 7.2 3.9 4.2 39.6 -4.7 299 1.5
9250 -8.0 17.6 359 37 19 8.9 4.9 4.1 39.4 -4.9 274 1.4
9000 -7.3 18.9 359 37 19 9.9 5.4 4.1 39.4 -4.9 245 1.2
8750 -6.6 20.1 359 36 19 9.7 5.3 4.1 39.4 -4.9 216 1.1
8500 -5.9 21.4 358 36 19 9.6 5.2 4.1 39.4 -4.9 187 0.9
8250 -5.2 22.6 358 36 18 9.3 5.1 4.1 39.3 -5.0 159 0.8
8000 -4.5 23.9 358 35 18 9.3 5.1 4.0 39.2 -5.1 131 0.7
7750 -3.8 25.2 358 35 18 9.2 5.1 4.0 39.2 -5.1 103 0.5
7500 -3.1 26.4 358 34 18 8.8 4.8 3.9 39.1 -5.2 75 0.4
7250 -2.5 27.5 358 33 17 8.5 4.7 3.8 38.9 -5.3 49 0.2
7000 -1.9 28.6 359 32 16 8.9 4.9 3.8 38.8 -5.4 22 0.1
6750 -1.2 29.8 359 31 16 7.5 4.1 3.7 38.6 -5.5 M M
6500 -0.8 30.6 360 28 14 6.0 3.3 3.4 38.1 -5.8 M M
6250 -0.3 31.5 001 25 13 7.0 3.8 3.2 37.7 -6.1 M M
6000 0.2 32.4 002 22 11 4.7 2.6 2.9 37.2 -6.4 M M
5750 0.3 32.5 002 18 9 1.3 0.7 2.3 36.2 -7.0 M M
5500 0.4 32.7 002 13 7 2.1 1.2 1.7 35.0 -7.7 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
10/22/2008 at 0900 MDT | 10/22/2008 at 1200 MDT
|
K index... +7.6 | K index... +9.9
|
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 -56.8 -70.2 326 20 10 1.8 1.0 | -56.3 -69.3 335 21 11 1.3 0.7
45000 -54.0 -65.2 334 31 16 2.2 1.2 | -54.4 -65.9 340 35 18 2.0 1.1
40000 -49.7 -57.5 353 43 22 2.8 1.6 | -50.0 -58.0 002 48 25 3.0 1.6
38000 -47.9 -54.2 354 50 26 2.6 1.4 | -48.1 -54.6 005 56 29 2.4 1.3
36000 -46.4 -51.5 351 55 28 2.6 1.4 | -46.7 -52.1 004 65 33 2.4 1.3
34000 -44.9 -48.8 349 60 31 1.7 0.9 | -45.3 -49.5 003 73 37 1.7 0.9
32000 -44.0 -47.2 349 58 30 1.4 0.7 | -44.4 -47.9 360 72 37 1.5 0.8
30000 -43.2 -45.8 350 57 29 2.4 1.3 | -43.5 -46.3 356 72 37 2.8 1.5
29000 -42.2 -44.0 351 52 27 3.2 1.8 | -42.4 -44.3 357 65 34 3.6 2.0
28000 -41.3 -42.3 352 48 25 3.2 1.8 | -41.3 -42.3 358 59 30 3.6 2.0
27000 -40.3 -40.5 354 44 22 3.2 1.8 | -40.2 -40.4 359 52 27 3.6 2.0
26000 -39.4 -38.9 355 40 21 3.1 1.7 | -39.0 -38.2 359 47 24 4.2 2.3
25000 -38.4 -37.1 357 37 19 3.1 1.7 | -37.7 -35.9 360 44 23 4.3 2.3
24000 -37.5 -35.5 359 34 18 3.1 1.7 | -36.5 -33.7 001 40 21 4.2 2.3
23000 -36.7 -34.1 359 32 16 2.5 1.4 | -35.5 -31.9 359 36 19 2.1 1.2
22000 -35.9 -32.6 358 30 16 2.5 1.4 | -34.9 -30.8 354 33 17 2.0 1.1
21000 -35.2 -31.4 357 29 15 2.3 1.3 | -34.3 -29.7 347 31 16 2.0 1.1
20000 -33.2 -27.8 357 29 15 7.8 4.3 | -32.2 -26.0 346 29 15 6.4 3.5
19500 -31.4 -24.5 358 30 15 7.8 4.3 | -31.2 -24.2 346 29 15 6.4 3.5
19000 -30.3 -22.5 358 30 16 7.8 4.3 | -30.3 -22.5 346 29 15 6.4 3.5
18500 -29.1 -20.4 359 31 16 7.9 4.3 | -29.3 -20.7 346 28 15 7.5 4.1
18000 -27.9 -18.2 359 31 16 7.9 4.3 | -28.1 -18.6 346 28 14 7.9 4.4
17500 -26.8 -16.2 360 31 16 7.9 4.3 | -26.9 -16.4 347 28 14 8.0 4.4
17000 -25.6 -14.1 001 30 16 7.9 4.3 | -25.7 -14.3 347 28 14 8.1 4.4
16500 -24.4 -11.9 001 30 16 7.9 4.3 | -24.5 -12.1 348 28 14 8.1 4.5
16000 -23.2 -9.8 002 31 16 8.7 4.8 | -23.3 -9.9 348 28 15 7.8 4.3
15500 -21.9 -7.4 002 31 16 8.7 4.8 | -22.2 -8.0 349 29 15 7.9 4.3
15000 -20.6 -5.1 002 31 16 8.0 4.4 | -21.0 -5.8 349 29 15 7.6 4.1
14500 -19.4 -2.9 002 32 17 8.0 4.4 | -19.9 -3.8 349 30 15 7.6 4.1
14000 -18.2 -0.8 002 33 17 7.8 4.3 | -18.8 -1.8 349 31 16 7.7 4.2
13500 -17.1 1.2 001 33 17 7.9 4.3 | -17.6 0.3 349 31 16 7.7 4.2
13000 -15.9 3.4 001 34 18 7.0 3.9 | -16.5 2.3 349 32 17 7.8 4.3
12500 -14.9 5.2 360 34 18 6.9 3.8 | -15.3 4.5 348 33 17 7.8 4.3
12000 -13.9 7.0 359 35 18 6.8 3.7 | -14.1 6.6 348 33 17 8.0 4.4
11500 -12.9 8.8 359 34 18 6.9 3.8 | -12.9 8.8 348 33 17 8.0 4.4
11000 -11.9 10.6 359 34 18 6.4 3.5 | -11.7 10.9 348 32 17 8.2 4.5
10500 -11.0 12.2 359 34 18 6.4 3.5 | -10.5 13.1 349 31 16 8.3 4.6
10250 -10.5 13.1 359 34 18 5.9 3.2 | -9.9 14.2 349 30 15 7.3 4.0
10000 -10.1 13.8 360 34 18 5.5 3.0 | -9.4 15.1 352 28 14 6.6 3.6
9750 -9.7 14.5 001 34 18 5.5 3.0 | -9.0 15.8 354 26 13 6.7 3.7
9500 -9.3 15.3 001 34 18 5.9 3.2 | -8.5 16.7 357 24 12 7.3 4.0
9250 -8.8 16.2 002 34 18 7.6 4.2 | -7.9 17.8 360 22 12 9.0 4.9
9000 -8.2 17.2 001 34 17 8.4 4.6 | -7.2 19.0 001 22 11 9.6 5.2
8750 -7.6 18.3 360 34 17 8.0 4.4 | -6.5 20.3 002 21 11 9.3 5.1
8500 -7.0 19.4 360 33 17 8.7 4.8 | -5.8 21.6 003 21 11 9.6 5.3
8250 -6.3 20.7 359 33 17 9.3 5.1 | -5.0 23.0 004 20 11 9.9 5.4
8000 -5.7 21.7 358 32 17 9.2 5.0 | -4.3 24.3 004 20 10 9.8 5.4
7750 -5.0 23.0 357 31 16 9.2 5.0 | -3.6 25.5 004 20 10 9.9 5.4
7500 -4.3 24.3 356 31 16 9.0 5.0 | -2.8 27.0 004 20 10 10.0 5.5
7250 -3.6 25.5 356 29 15 9.0 4.9 | -2.1 28.2 005 20 10 10.1 5.5
7000 -2.9 26.8 355 28 15 9.0 4.9 | -1.3 29.7 005 19 10 10.1 5.5
6750 -2.3 27.9 355 27 14 8.7 4.8 | -0.5 31.1 005 19 10 10.1 5.6
6500 -1.6 29.1 355 24 12 8.8 4.8 | 0.2 32.4 005 19 10 10.6 5.8
6250 -1.0 30.2 355 21 11 8.0 4.4 | 1.0 33.8 005 18 10 9.2 5.0
6000 -0.4 31.3 355 19 10 11.0 6.0 | 1.8 35.2 005 18 9 14.5 7.9
5750 0.6 33.1 355 16 8 15.0 8.2 | 3.2 37.8 006 17 9 21.5 11.8
5500 1.7 35.1 354 14 7 12.6 6.9 | 4.7 40.5 007 16 8 17.2 9.5
10/22/2008 at 1500 MDT | 10/22/2008 at 1800 MDT
|
K index... +10.7 | K index... +4.3
|
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 -56.8 -70.2 345 19 10 0.8 0.4 | -57.3 -71.1 346 22 11 1.6 0.9
45000 -55.6 -68.1 351 36 19 1.3 0.7 | -55.0 -67.0 349 41 21 1.1 0.6
40000 -52.6 -62.7 007 66 34 2.0 1.1 | -54.4 -65.9 008 81 42 0.4 0.2
38000 -50.9 -59.6 008 76 39 4.0 2.2 | -52.8 -63.0 008 94 49 4.6 2.5
36000 -48.2 -54.8 006 85 44 4.0 2.2 | -50.0 -58.0 006 105 54 4.6 2.5
34000 -45.8 -50.4 004 92 48 3.3 1.8 | -47.3 -53.1 004 115 59 4.6 2.5
32000 -43.8 -46.8 003 94 49 3.3 1.8 | -44.5 -48.1 005 114 59 4.6 2.5
30000 -41.8 -43.2 003 95 49 4.2 2.3 | -41.2 -42.2 006 113 58 6.0 3.3
29000 -40.5 -40.9 003 89 46 4.4 2.4 | -39.4 -38.9 006 110 57 5.9 3.3
28000 -39.2 -38.6 003 83 42 4.4 2.4 | -37.7 -35.9 007 108 55 5.9 3.3
27000 -37.9 -36.2 002 76 39 4.4 2.4 | -35.9 -32.6 007 105 54 5.9 3.3
26000 -36.5 -33.7 002 70 36 4.5 2.4 | -34.1 -29.4 007 98 50 5.9 3.2
25000 -35.2 -31.4 002 64 33 4.5 2.4 | -32.3 -26.1 006 90 46 5.9 3.2
24000 -33.9 -29.0 001 58 30 4.5 2.4 | -30.6 -23.1 005 82 42 6.1 3.4
23000 -32.9 -27.2 360 53 27 2.3 1.3 | -29.2 -20.6 005 73 37 3.9 2.2
22000 -32.2 -26.0 357 49 25 2.3 1.3 | -28.0 -18.4 005 64 33 4.0 2.2
21000 -31.5 -24.7 354 46 24 2.3 1.3 | -26.9 -16.4 004 55 28 3.4 1.8
20000 -30.5 -22.9 349 43 22 3.7 2.0 | -26.3 -15.3 004 51 26 1.8 1.0
19500 -30.0 -22.0 345 42 21 3.7 2.0 | -26.0 -14.8 003 49 25 1.8 1.0
19000 -29.2 -20.6 339 40 21 3.7 2.0 | -25.7 -14.3 003 47 24 1.7 1.0
18500 -28.6 -19.5 336 39 20 6.1 3.3 | -25.5 -13.9 002 45 23 1.7 0.9
18000 -27.5 -17.5 336 38 20 7.3 4.0 | -25.3 -13.5 359 43 22 1.0 0.6
17500 -26.3 -15.3 336 37 19 7.4 4.1 | -25.1 -13.2 353 42 21 0.8 0.5
17000 -25.3 -13.5 336 36 19 7.3 4.0 | -24.8 -12.6 347 40 20 3.9 2.1
16500 -24.2 -11.6 336 36 18 7.3 4.0 | -24.3 -11.7 340 37 19 4.1 2.2
16000 -23.1 -9.6 336 34 18 6.9 3.8 | -23.2 -9.8 330 34 18 7.1 3.9
15500 -22.1 -7.8 336 33 17 6.9 3.8 | -22.2 -8.0 326 32 17 6.8 3.7
15000 -21.0 -5.8 335 31 16 7.6 4.1 | -21.1 -6.0 323 31 16 7.9 4.4
14500 -19.9 -3.8 335 30 15 7.6 4.2 | -19.9 -3.8 323 30 15 7.9 4.3
14000 -18.7 -1.7 334 29 15 7.6 4.2 | -18.7 -1.7 323 29 15 8.2 4.5
13500 -17.6 0.3 335 28 14 7.6 4.2 | -17.5 0.5 324 28 14 8.2 4.5
13000 -16.5 2.3 336 27 14 7.8 4.3 | -16.3 2.7 325 27 14 8.3 4.6
12500 -15.3 4.5 338 26 13 7.8 4.3 | -15.1 4.8 326 26 14 8.3 4.6
12000 -14.1 6.6 341 25 13 7.9 4.4 | -13.8 7.2 328 26 13 8.5 4.7
11500 -13.0 8.6 346 24 12 7.9 4.3 | -12.5 9.5 330 25 13 8.5 4.7
11000 -11.7 10.9 351 22 12 8.9 4.9 | -11.3 11.7 333 25 13 8.5 4.7
10500 -10.4 13.3 356 21 11 8.8 4.9 | -10.0 14.0 337 25 13 8.6 4.7
10250 -9.8 14.4 359 20 10 9.4 5.2 | -9.4 15.1 338 25 13 8.1 4.5
10000 -9.0 15.8 360 20 10 10.0 5.5 | -8.8 16.2 341 24 13 7.7 4.2
9750 -8.3 17.1 360 20 10 9.9 5.4 | -8.2 17.2 343 24 12 7.8 4.3
9500 -7.6 18.3 360 20 10 9.9 5.4 | -7.6 18.3 346 24 12 7.9 4.4
9250 -6.8 19.8 001 20 10 9.6 5.3 | -7.0 19.4 348 24 12 8.7 4.8
9000 -6.1 21.0 001 20 10 9.5 5.2 | -6.4 20.5 350 23 12 9.1 5.0
8750 -5.4 22.3 002 20 10 9.5 5.2 | -5.7 21.7 353 23 12 8.9 4.9
8500 -4.7 23.5 002 20 10 9.7 5.3 | -5.0 23.0 355 23 12 9.2 5.1
8250 -3.9 25.0 003 19 10 10.0 5.5 | -4.3 24.3 356 22 12 9.5 5.2
8000 -3.2 26.2 003 19 10 10.0 5.5 | -3.6 25.5 357 22 11 9.5 5.2
7750 -2.4 27.7 003 19 10 10.0 5.5 | -2.9 26.8 359 22 11 9.5 5.2
7500 -1.7 28.9 004 19 10 10.1 5.5 | -2.2 28.0 360 22 11 9.7 5.3
7250 -0.9 30.4 004 19 10 10.1 5.5 | -1.5 29.3 360 21 11 9.8 5.4
7000 -0.2 31.6 004 19 10 10.1 5.5 | -0.8 30.6 001 21 11 9.7 5.3
6750 0.6 33.1 005 19 10 10.0 5.5 | -0.0 32.0 002 21 11 9.7 5.3
6500 1.3 34.3 005 19 10 10.1 5.6 | 0.7 33.3 002 20 10 9.8 5.4
6250 2.1 35.8 005 18 9 9.5 5.2 | 1.4 34.5 003 20 10 9.6 5.3
6000 2.8 37.0 005 18 9 11.9 6.5 | 2.1 35.8 004 19 10 10.3 5.6
5750 3.9 39.0 006 17 9 16.0 8.8 | 3.0 37.4 004 18 9 11.6 6.3
5500 5.1 41.2 007 16 8 15.9 8.7 | 3.8 38.8 004 15 8 11.5 6.3
________________________________________________________________________________
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:
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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