Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
711
UXUS97 KBOU 171343
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0735 MDT Thursday, April 17, 2025
This forecast is for Thursday, April 17, 2025:
If the trigger temperature of 68.0 F/20.0 C is reached...then
Thermal Soaring Index....................... Good
Maximum rate of lift........................ 848 ft/min (4.3 m/s)
Maximum height of thermals.................. 16272 ft MSL (10982 ft AGL)
Forecast maximum temperature................... 72.0 F/22.7 C
Time of trigger temperature.................... 1045 MDT
Time of overdevelopment........................ 1900 MDT
Middle/high clouds during soaring window....... Broken/overcast thin middle
Surface winds during soaring window............ Between 20 mph and 30 mph
Height of the -3 thermal index................. 8451 ft MSL (3160 ft AGL)
Thermal soaring outlook for Friday 04/18....... Poor
Wave Soaring Index............................. Fair
Wave Soaring Index trend (to 1800 MDT)......... Little change
Height of stable layer (12-18K ft MSL)......... None
Weak PVA/NVA (through 1800 MDT)................ Weak NVA
Potential height of wave....................... 14386 ft MSL (9096 ft AGL)
Wave soaring outlook for Friday 04/18.......... Poor
Remarks...
Sunrise/Sunset.................... 06:18:01 / 19:39:49 MDT
Total possible sunshine........... 13 hr 21 min 48 sec (801 min 48 sec)
Altitude of sun at 12:58:55 MDT... 61.00 degrees
Upper air data from numerical model forecast valid on 04/17/2025 at 0600 MDT
Freezing level.................. 12301 ft MSL (7011 ft AGL)
Convective condensation level... 15326 ft MSL (10036 ft AGL)
Lifted condensation level....... 15538 ft MSL (10248 ft AGL)
Lifted index.................... +0.1
K index......................... +10.6
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 -58.1 -72.6 245 57 29 -2.0 -1.1 M M M M M
45000 -61.1 -78.0 240 82 42 -2.1 -1.2 M M M M M
40000 -61.3 -78.3 245 99 51 -0.0 -0.0 M M M M M
38000 -59.2 -74.6 245 99 51 6.3 3.4 M M M M M
36000 -55.4 -67.7 245 94 49 6.3 3.5 M M M M M
34000 -51.5 -60.7 245 89 46 7.8 4.3 M M M M M
32000 -46.9 -52.4 245 85 44 7.7 4.2 M M M M M
30000 -42.1 -43.8 245 80 41 8.5 4.6 33.8 92.8 8.7 M M
29000 -39.0 -38.2 245 78 40 8.5 4.7 33.1 91.5 8.3 M M
28000 -36.4 -33.5 245 76 39 8.5 4.7 32.6 90.7 8.0 M M
27000 -33.9 -29.0 245 74 38 8.0 4.4 32.2 90.0 7.8 M M
26000 -31.6 -24.9 245 71 37 7.9 4.3 31.4 88.5 7.2 M M
25000 -29.2 -20.6 245 69 36 7.9 4.3 30.7 87.2 6.8 M M
24000 -26.9 -16.4 245 67 34 8.0 4.4 30.1 86.2 6.4 M M
23000 -24.4 -11.9 245 62 32 8.4 4.6 29.5 85.1 5.9 M M
22000 -21.9 -7.4 240 58 30 8.4 4.6 29.0 84.2 5.6 M M
21000 -19.4 -2.9 240 53 28 6.8 3.7 28.5 83.4 5.2 M M
20000 -17.6 0.3 245 53 27 5.9 3.3 27.1 80.8 4.1 M M
19500 -16.7 1.9 245 53 27 5.9 3.3 26.4 79.6 3.6 M M
19000 -15.8 3.6 245 52 27 5.9 3.3 25.8 78.4 3.0 M M
18500 -14.9 5.2 250 52 27 5.8 3.2 25.2 77.4 2.5 M M
18000 -14.1 6.6 245 48 25 5.4 3.0 24.5 76.0 1.9 M M
17500 -13.3 8.1 245 44 23 5.4 3.0 23.7 74.7 1.2 M M
17000 -12.4 9.7 245 41 21 7.3 4.0 23.1 73.6 0.7 M M
16500 -11.4 11.5 240 38 20 7.4 4.1 22.7 72.9 0.3 M M
16000 -10.3 13.5 240 36 19 8.3 4.5 22.3 72.2 -0.1 1032 5.2
15500 -8.9 16.0 235 33 17 9.0 5.0 22.2 72.0 -0.3 977 5.0
15000 -6.9 19.6 235 30 15 8.9 4.9 22.0 71.7 -0.4 894 4.5
14500 -5.6 21.9 240 32 16 8.9 4.9 21.9 71.4 -0.6 840 4.3
14000 -4.3 24.3 245 35 18 8.8 4.8 21.8 71.2 -0.7 785 4.0
13500 -3.0 26.6 250 33 17 8.7 4.8 21.6 70.8 -0.9 732 3.7
13000 -1.7 28.9 250 32 17 8.8 4.9 21.4 70.5 -1.0 679 3.4
12500 -0.3 31.5 255 33 17 9.3 5.1 21.3 70.3 -1.1 623 3.2
12000 1.1 34.0 255 33 17 9.3 5.1 21.2 70.2 -1.2 567 2.9
11500 2.4 36.3 255 31 16 9.1 5.0 21.1 70.0 -1.3 511 2.6
11000 3.7 38.7 255 29 15 9.0 4.9 21.0 69.9 -1.5 457 2.3
10500 5.0 41.0 255 26 14 8.2 4.5 20.8 69.5 -1.7 404 2.1
10250 5.6 42.1 255 26 13 9.1 5.0 20.7 69.3 -1.8 378 1.9
10000 6.3 43.3 255 24 12 9.8 5.4 20.7 69.3 -1.8 350 1.8
9750 7.0 44.6 255 22 11 8.5 4.7 20.7 69.3 -1.9 322 1.6
9500 7.6 45.7 250 21 11 7.9 4.3 20.6 69.0 -2.0 297 1.5
9250 8.2 46.8 250 20 10 8.2 4.5 20.4 68.8 -2.2 272 1.4
9000 8.7 47.7 250 19 10 6.9 3.8 20.3 68.5 -2.3 247 1.3
8750 9.2 48.6 250 19 10 5.8 3.2 20.0 68.0 -2.6 227 1.2
8500 9.6 49.3 250 17 9 6.2 3.4 19.7 67.5 -3.0 207 1.0
8250 10.0 50.0 245 16 8 5.8 3.2 19.4 67.0 -3.3 186 0.9
8000 10.5 50.9 245 14 7 7.0 3.9 19.2 66.5 -3.6 166 0.8
7750 11.0 51.8 245 12 6 6.4 3.5 19.0 66.1 -3.8 143 0.7
7500 11.3 52.3 240 11 6 4.7 2.6 18.6 65.5 -4.2 125 0.6
7250 11.7 53.1 240 10 5 5.2 2.8 18.2 64.8 -4.6 107 0.5
7000 12.0 53.6 240 9 5 4.1 2.2 17.9 64.2 -5.0 90 0.5
6750 12.2 54.0 240 9 4 2.3 1.3 17.4 63.3 -5.5 77 0.4
6500 12.4 54.3 240 8 4 2.8 1.5 16.8 62.2 -6.1 65 0.3
6250 12.5 54.5 235 8 4 -0.3 -0.1 16.2 61.2 -6.7 54 0.3
6000 12.2 54.0 230 7 4 -6.8 -3.8 15.2 59.3 -7.8 56 0.3
5750 11.5 52.7 225 8 4 -7.0 -3.8 13.9 57.0 -9.2 67 0.3
5500 10.8 51.4 210 7 3 -15.6 -8.6 12.5 54.4 -10.7 82 0.4
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
04/17/2025 at 0900 MDT | 04/17/2025 at 1200 MDT
|
CAPE... 0.0 LI... +3.4 | CAPE... +5.0 LI... +1.0
CINH... 0.0 K Index... +4.4 | CINH... -5.3 K Index... +11.5
|
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 -59.6 -75.3 245 67 34 -1.6 -0.9 | -58.3 -72.9 245 67 34 -2.6 -1.4
45000 -62.0 -79.6 240 80 41 -1.7 -0.9 | -62.1 -79.8 240 77 40 -2.6 -1.5
40000 -60.8 -77.4 235 96 49 0.8 0.4 | -59.2 -74.6 235 90 46 2.1 1.1
38000 -58.4 -73.1 235 97 50 6.7 3.7 | -56.9 -70.4 230 93 48 5.4 3.0
36000 -54.3 -65.7 235 95 49 6.7 3.7 | -53.6 -64.5 230 94 49 5.4 3.0
34000 -50.2 -58.4 235 92 47 7.4 4.1 | -50.2 -58.4 230 95 49 7.3 4.0
32000 -45.8 -50.4 235 88 45 7.4 4.0 | -45.9 -50.6 230 93 48 7.1 3.9
30000 -41.4 -42.5 235 84 43 7.8 4.3 | -41.6 -42.9 235 90 47 7.6 4.2
29000 -38.4 -37.1 235 81 42 7.8 4.3 | -38.7 -37.7 235 88 45 7.6 4.2
28000 -36.1 -33.0 235 79 41 7.8 4.3 | -36.5 -33.7 235 85 44 7.6 4.2
27000 -33.7 -28.7 235 77 40 7.9 4.3 | -34.2 -29.6 235 83 43 7.8 4.3
26000 -31.4 -24.5 240 76 39 7.9 4.3 | -31.8 -25.2 235 81 42 8.0 4.4
25000 -29.0 -20.2 240 75 39 7.9 4.3 | -29.4 -20.9 235 80 41 8.0 4.4
24000 -26.6 -15.9 240 74 38 7.9 4.3 | -27.0 -16.6 235 78 40 8.0 4.4
23000 -24.3 -11.7 240 71 37 7.7 4.2 | -24.8 -12.6 235 77 39 7.3 4.0
22000 -22.0 -7.6 240 68 35 7.7 4.2 | -22.6 -8.7 235 75 39 7.3 4.0
21000 -19.8 -3.6 245 64 33 6.8 3.7 | -20.4 -4.7 235 74 38 6.7 3.7
20000 -18.0 -0.4 245 63 32 6.0 3.3 | -18.7 -1.7 240 69 35 5.7 3.1
19500 -17.1 1.2 245 62 32 6.0 3.3 | -17.9 -0.2 240 66 34 5.7 3.1
19000 -16.2 2.8 245 61 31 6.0 3.3 | -17.0 1.4 240 63 32 5.7 3.1
18500 -15.3 4.5 245 60 31 6.2 3.4 | -16.2 2.8 245 60 31 5.8 3.2
18000 -14.3 6.3 245 55 28 7.1 3.9 | -15.3 4.5 245 55 28 6.4 3.5
17500 -13.2 8.2 245 48 25 7.0 3.9 | -14.3 6.3 245 50 26 6.3 3.5
17000 -12.1 10.2 245 42 21 8.2 4.5 | -13.3 8.1 245 45 23 7.7 4.2
16500 -10.9 12.4 245 37 19 8.3 4.5 | -12.2 10.0 240 39 20 8.1 4.4
16000 -9.7 14.5 245 33 17 8.0 4.4 | -11.0 12.2 240 33 17 7.7 4.2
15500 -8.5 16.7 240 30 16 7.5 4.1 | -9.5 14.9 240 31 16 6.6 3.6
15000 -6.9 19.6 235 26 14 7.3 4.0 | -8.6 16.5 240 31 16 7.4 4.1
14500 -5.8 21.6 225 26 13 7.3 4.0 | -7.4 18.7 240 29 15 8.2 4.5
14000 -4.7 23.5 220 26 13 7.8 4.3 | -6.2 20.8 235 27 14 8.4 4.6
13500 -3.4 25.9 220 25 13 8.6 4.7 | -4.9 23.2 235 26 14 9.1 5.0
13000 -2.1 28.2 220 24 12 8.5 4.7 | -3.5 25.7 235 26 13 9.1 5.0
12500 -1.0 30.2 230 25 13 7.7 4.2 | -2.1 28.2 240 24 13 9.8 5.4
12000 0.2 32.4 235 28 14 7.8 4.3 | -0.7 30.7 240 23 12 9.8 5.4
11500 1.3 34.3 245 29 15 7.7 4.2 | 0.8 33.4 240 21 11 9.2 5.1
11000 2.5 36.5 250 31 16 7.7 4.2 | 2.1 35.8 240 20 10 9.3 5.1
10500 3.7 38.7 255 32 16 9.3 5.1 | 3.5 38.3 240 17 9 9.0 5.0
10250 4.4 39.9 255 33 17 8.7 4.8 | 4.2 39.6 235 16 8 8.6 4.7
10000 5.0 41.0 260 33 17 8.3 4.5 | 4.8 40.6 235 14 7 8.0 4.4
9750 5.7 42.3 260 32 16 8.8 4.9 | 5.4 41.7 235 12 6 8.9 4.9
9500 6.3 43.3 260 30 16 9.1 5.0 | 6.1 43.0 235 10 5 9.7 5.3
9250 7.0 44.6 260 28 15 9.3 5.1 | 6.7 44.1 230 8 4 9.2 5.0
9000 7.7 45.9 260 27 14 6.9 3.8 | 7.3 45.1 225 5 3 6.6 3.6
8750 8.1 46.6 260 25 13 5.9 3.3 | 7.8 46.0 225 4 2 8.6 4.7
8500 8.6 47.5 265 23 12 7.3 4.0 | 8.6 47.5 225 4 2 11.4 6.3
8250 9.1 48.4 265 21 11 7.0 3.8 | 9.4 48.9 225 3 2 11.5 6.3
8000 9.6 49.3 265 19 10 7.1 3.9 | 10.2 50.4 225 3 2 8.4 4.6
7750 10.1 50.2 265 16 8 5.2 2.9 | 10.7 51.3 225 3 1 7.7 4.2
7500 10.4 50.7 270 13 7 3.8 2.1 | 11.5 52.7 230 3 1 10.5 5.8
7250 10.6 51.1 270 11 6 4.3 2.4 | 12.2 54.0 230 2 1 9.5 5.2
7000 10.9 51.6 275 8 4 3.3 1.8 | 12.9 55.2 230 2 1 10.6 5.8
6750 11.1 52.0 275 6 3 2.8 1.5 | 13.7 56.7 235 2 1 10.8 5.9
6500 11.3 52.3 285 4 2 3.0 1.7 | 14.5 58.1 240 2 1 10.0 5.5
6250 11.5 52.7 300 3 1 3.5 1.9 | 15.3 59.5 240 2 1 10.4 5.7
6000 11.7 53.1 325 1 1 5.0 2.8 | 16.0 60.8 245 2 1 10.3 5.7
5750 12.1 53.8 355 1 0 5.3 2.9 | 17.0 62.6 250 2 1 16.3 8.9
5500 12.5 54.5 030 1 0 9.1 5.0 | 18.6 65.5 255 2 1 26.8 14.7
04/17/2025 at 1500 MDT | 04/17/2025 at 1800 MDT
|
CAPE... +16.4 LI... -0.0 | CAPE... +108.3 LI... -0.9
CINH... -3.5 K Index... +16.9 | CINH... -17.8 K Index... +17.8
|
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 -57.8 -72.0 240 60 31 -1.3 -0.7 | -55.5 -67.9 240 56 29 -1.7 -1.1
45000 -59.8 -75.6 240 75 39 -1.7 -0.9 | -58.1 -72.6 235 74 38 -2.0 -1.1
40000 -57.3 -71.1 235 90 46 1.7 0.9 | -56.6 -69.9 240 88 45 1.2 0.6
38000 -55.7 -68.3 235 95 49 3.9 2.1 | -55.4 -67.7 240 92 47 3.0 1.7
36000 -53.3 -63.9 235 100 51 3.9 2.1 | -53.6 -64.5 240 97 50 3.0 1.7
34000 -50.9 -59.6 235 103 53 6.4 3.5 | -51.6 -60.9 240 101 52 5.3 2.9
32000 -47.1 -52.8 235 98 51 6.3 3.5 | -48.1 -54.6 235 95 49 5.9 3.2
30000 -42.7 -44.9 235 92 48 7.1 3.9 | -44.5 -48.1 235 89 46 6.9 3.8
29000 -40.6 -41.1 235 89 46 7.1 3.9 | -42.4 -44.3 235 84 43 7.0 3.8
28000 -38.5 -37.3 235 85 44 7.1 3.9 | -39.8 -39.6 235 78 40 7.0 3.8
27000 -36.4 -33.5 235 81 42 7.5 4.1 | -37.7 -35.9 235 73 38 7.2 4.0
26000 -33.8 -28.8 235 78 40 8.6 4.7 | -35.3 -31.5 235 69 36 8.0 4.4
25000 -31.3 -24.3 235 76 39 8.6 4.7 | -32.9 -27.2 235 65 33 8.0 4.4
24000 -28.7 -19.7 235 73 38 8.6 4.7 | -30.5 -22.9 235 60 31 8.0 4.4
23000 -26.0 -14.8 235 69 36 9.0 4.9 | -28.2 -18.8 235 57 29 7.7 4.2
22000 -23.3 -9.9 235 65 33 9.0 4.9 | -26.0 -14.8 235 53 27 7.7 4.2
21000 -20.6 -5.1 235 60 31 7.7 4.2 | -23.7 -10.7 240 49 25 7.7 4.2
20000 -19.2 -2.6 235 53 27 4.5 2.5 | -21.4 -6.5 240 42 21 7.8 4.3
19500 -18.6 -1.5 240 50 26 4.6 2.5 | -20.3 -4.5 240 38 19 7.8 4.3
19000 -17.9 -0.2 240 46 24 4.7 2.6 | -19.1 -2.4 240 34 17 7.9 4.3
18500 -17.3 0.9 245 43 22 4.8 2.6 | -18.0 -0.4 240 30 15 8.0 4.4
18000 -16.4 2.5 245 39 20 7.5 4.1 | -16.7 1.9 240 28 14 9.0 4.9
17500 -15.3 4.5 245 35 18 7.3 4.0 | -15.4 4.3 240 27 14 8.9 4.9
17000 -14.2 6.4 245 31 16 8.4 4.6 | -14.1 6.6 235 26 13 9.2 5.0
16500 -12.9 8.8 245 29 15 8.8 4.8 | -12.7 9.1 235 25 13 9.2 5.1
16000 -10.9 12.4 240 26 13 9.3 5.1 | -11.3 11.7 235 25 13 9.3 5.1
15500 -9.6 14.7 240 25 13 9.3 5.1 | -9.9 14.2 230 24 12 9.4 5.1
15000 -8.2 17.2 235 24 12 9.3 5.1 | -8.5 16.7 230 23 12 9.4 5.1
14500 -6.8 19.8 230 22 11 9.3 5.1 | -7.1 19.2 230 21 11 9.2 5.1
14000 -5.4 22.3 230 21 11 9.3 5.1 | -5.7 21.7 225 20 10 9.3 5.1
13500 -4.0 24.8 230 19 10 9.3 5.1 | -4.3 24.3 225 19 10 9.2 5.0
13000 -2.6 27.3 230 18 9 9.3 5.1 | -3.0 26.6 225 17 9 9.2 5.0
12500 -1.2 29.8 225 17 9 9.7 5.3 | -0.9 30.4 225 14 7 9.3 5.1
12000 0.2 32.4 225 16 8 9.7 5.3 | 0.5 32.9 230 12 6 9.3 5.1
11500 1.7 35.1 230 15 8 9.6 5.3 | 1.8 35.2 230 10 5 9.3 5.1
11000 3.1 37.6 230 15 8 9.4 5.2 | 3.2 37.8 240 8 4 9.3 5.1
10500 4.7 40.5 230 14 7 11.8 6.5 | 4.5 40.1 245 7 4 8.3 4.6
10250 5.5 41.9 230 14 7 9.8 5.4 | 5.2 41.4 255 6 3 9.5 5.2
10000 6.1 43.0 230 14 7 7.7 4.2 | 5.9 42.6 260 6 3 10.5 5.8
9750 6.8 44.2 230 14 7 10.1 5.6 | 6.7 44.1 265 6 3 10.0 5.5
9500 7.6 45.7 230 14 7 12.3 6.8 | 7.4 45.3 280 5 3 9.8 5.4
9250 8.5 47.3 230 13 7 11.1 6.1 | 8.1 46.6 290 5 3 9.9 5.4
9000 9.2 48.6 230 13 7 7.3 4.0 | 8.9 48.0 300 5 3 10.1 5.6
8750 9.7 49.5 230 13 7 8.9 4.9 | 9.6 49.3 305 6 3 9.8 5.4
8500 10.6 51.1 230 13 7 11.9 6.5 | 10.3 50.5 310 6 3 9.4 5.2
8250 11.5 52.7 230 13 7 12.3 6.7 | 11.0 51.8 320 6 3 9.7 5.3
8000 12.3 54.1 230 13 7 7.8 4.3 | 11.8 53.2 325 7 3 9.0 4.9
7750 12.7 54.9 230 13 6 6.7 3.7 | 12.4 54.3 325 7 4 9.2 5.0
7500 13.4 56.1 230 12 6 10.9 6.0 | 13.1 55.6 330 8 4 9.8 5.4
7250 14.2 57.6 230 12 6 9.4 5.2 | 13.9 57.0 330 8 4 10.2 5.6
7000 14.9 58.8 230 12 6 11.1 6.1 | 14.6 58.3 330 8 4 7.9 4.3
6750 15.8 60.4 235 12 6 10.9 6.0 | 15.1 59.2 335 8 4 8.8 4.8
6500 16.5 61.7 235 12 6 9.5 5.2 | 16.0 60.8 335 8 4 12.0 6.6
6250 17.3 63.1 235 11 6 9.8 5.4 | 16.8 62.2 335 9 4 10.6 5.8
6000 18.0 64.4 235 11 6 10.5 5.8 | 17.5 63.5 335 9 4 7.7 4.2
5750 19.0 66.2 235 10 5 17.1 9.4 | 18.1 64.6 335 9 4 10.2 5.6
5500 20.6 69.1 235 10 5 25.9 14.2 | 19.2 66.6 335 8 4 19.1 10.5
________________________________________________________________________________
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:
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.
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