Soaring Guidance
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
019
UXUS97 KBOU 181328
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
0727 MDT Friday, April 18, 2025
This forecast is for Friday, April 18, 2025:
If the trigger temperature of 38.6 F/3.7 C is reached...then
Thermal Soaring Index....................... Poor
Maximum rate of lift........................ 0 ft/min (0.0 m/s)
Maximum height of thermals.................. 7760 ft MSL (2452 ft AGL)
Forecast maximum temperature................... 35.0 F/2.1 C
Time of trigger temperature.................... None
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... Broken/overcast opaque middle
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. None
Thermal soaring outlook for Saturday 04/19..... Poor
Wave Soaring Index............................. Fair
Wave Soaring Index trend (to 1800 MDT)......... No change
Height of stable layer (12-18K ft MSL)......... 11968 ft MSL (6660 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Neither
Potential height of wave....................... 15175 ft MSL (9867 ft AGL)
Wave soaring outlook for Saturday 04/19........ Poor
Remarks...
Sunrise/Sunset.................... 06:16:34 / 19:40:49 MDT
Total possible sunshine........... 13 hr 24 min 16 sec (804 min 16 sec)
Altitude of sun at 12:58:42 MDT... 61.35 degrees
Upper air data from numerical model forecast valid on 04/18/2025 at 0600 MDT
Freezing level.................. 5383 ft MSL (75 ft AGL)
Convective condensation level... 8225 ft MSL (2917 ft AGL)
Lifted condensation level....... 8085 ft MSL (2777 ft AGL)
Lifted index.................... +10.1
K index......................... +13.8
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 -54.1 -65.4 230 54 28 0.4 0.2 M M M M M
45000 -53.4 -64.1 225 65 33 0.4 0.2 M M M M M
40000 -52.5 -62.5 225 70 36 0.6 0.3 M M M M M
38000 -52.0 -61.6 225 73 37 1.7 0.9 M M M M M
36000 -50.9 -59.6 225 80 41 1.7 0.9 M M M M M
34000 -49.9 -57.8 225 87 45 1.8 1.0 M M M M M
32000 -48.5 -55.3 225 85 44 2.3 1.3 M M M M M
30000 -47.2 -53.0 225 82 42 3.3 1.8 M M M M M
29000 -45.4 -49.7 225 78 40 6.4 3.5 28.0 82.3 19.9 M M
28000 -43.4 -46.1 225 73 38 6.4 3.5 26.6 79.9 19.1 M M
27000 -41.5 -42.7 225 69 35 6.4 3.5 25.4 77.7 18.4 M M
26000 -39.4 -38.9 225 64 33 7.5 4.1 24.3 75.8 17.8 M M
25000 -37.2 -35.0 225 60 31 7.5 4.1 23.4 74.1 17.3 M M
24000 -34.9 -30.8 230 56 29 7.5 4.1 22.6 72.7 16.8 M M
23000 -32.6 -26.7 230 52 27 8.0 4.4 21.9 71.3 16.4 M M
22000 -30.3 -22.5 230 48 25 8.0 4.4 21.2 70.1 16.0 M M
21000 -27.9 -18.2 235 44 23 8.0 4.4 20.6 69.1 15.7 M M
20000 -25.5 -13.9 235 42 22 7.9 4.4 19.9 67.9 15.3 M M
19500 -24.3 -11.7 235 41 21 8.0 4.4 19.6 67.3 15.1 M M
19000 -23.1 -9.6 235 41 21 8.0 4.4 19.3 66.7 14.9 M M
18500 -21.4 -6.5 235 40 21 8.0 4.4 18.9 66.0 14.7 M M
18000 -20.2 -4.4 235 40 21 7.7 4.2 18.5 65.4 14.4 M M
17500 -19.1 -2.4 235 42 21 7.7 4.2 18.2 64.7 14.2 M M
17000 -17.9 -0.2 235 42 22 8.4 4.6 17.9 64.2 14.0 M M
16500 -16.6 2.1 235 40 21 8.6 4.7 17.7 63.8 13.9 M M
16000 -15.4 4.3 230 39 20 8.5 4.7 17.5 63.5 13.8 M M
15500 -14.1 6.6 230 39 20 8.3 4.6 17.2 63.0 13.6 M M
15000 -12.9 8.8 230 40 21 8.3 4.5 17.0 62.6 13.4 M M
14500 -11.8 10.8 225 40 21 7.0 3.8 16.6 61.9 13.2 M M
14000 -10.8 12.6 225 40 20 7.5 4.1 16.2 61.1 12.8 M M
13500 -10.0 14.0 220 38 19 3.2 1.8 15.5 59.8 12.2 M M
13000 -9.5 14.9 215 33 17 4.1 2.2 14.4 58.0 11.3 M M
12500 -9.4 15.1 210 28 15 -3.4 -1.9 13.0 55.4 10.0 M M
12000 -9.9 14.2 205 22 11 -4.1 -2.2 10.8 51.4 8.1 M M
11500 -10.2 13.6 190 16 8 1.3 0.7 8.9 48.1 6.4 M M
11000 -9.9 14.2 175 14 7 1.3 0.7 7.6 45.7 5.2 M M
10500 -9.5 14.9 155 12 6 4.8 2.6 6.5 43.8 4.2 M M
10250 -9.1 15.6 150 11 6 4.9 2.7 6.1 43.1 3.8 M M
10000 -8.8 16.2 145 11 5 4.1 2.3 5.8 42.4 3.4 M M
9750 -8.6 16.5 140 9 5 2.5 1.4 5.2 41.4 3.0 M M
9500 -8.4 16.9 125 9 5 2.2 1.2 4.6 40.3 2.4 M M
9250 -8.2 17.2 110 9 5 2.0 1.1 4.0 39.3 1.8 M M
9000 -8.1 17.4 100 10 5 2.9 1.6 3.4 38.2 1.3 M M
8750 -7.8 18.0 095 10 5 5.9 3.2 3.0 37.4 0.8 M M
8500 -7.2 19.0 090 11 6 7.3 4.0 2.8 37.0 0.6 M M
8250 -6.7 19.9 090 12 6 6.7 3.7 2.6 36.6 0.4 M M
8000 -6.2 20.8 085 12 6 7.7 4.2 2.4 36.3 0.2 M M
7750 -5.7 21.7 085 13 7 7.1 3.9 2.2 36.0 0.0 M M
7500 -5.2 22.6 080 12 6 5.7 3.1 1.9 35.5 -0.3 134 0.7
7250 -4.8 23.4 075 11 6 5.9 3.2 1.6 35.0 -0.6 114 0.6
7000 -4.4 24.1 070 10 5 5.8 3.2 1.3 34.4 -0.9 94 0.5
6750 -4.0 24.8 055 9 5 5.6 3.1 1.0 33.9 -1.2 74 0.4
6500 -3.6 25.5 040 8 4 5.3 2.9 0.7 33.3 -1.5 55 0.3
6250 -3.1 26.4 020 8 4 8.1 4.4 0.4 32.8 -1.8 34 0.2
6000 -2.4 27.7 015 8 4 10.6 5.8 0.4 32.8 -1.8 5 0.0
5750 -1.7 28.9 005 7 4 8.8 4.8 0.4 32.8 -1.9 M M
5500 -1.0 30.2 360 7 3 10.8 5.9 0.4 32.7 -1.9 M M
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
04/18/2025 at 0900 MDT | 04/18/2025 at 1200 MDT
|
CAPE... +27.2 LI... +7.1 | CAPE... +27.7 LI... +7.5
CINH... -1.0 K Index... +12.3 | CINH... -0.0 K Index... +12.3
|
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 -52.5 -62.5 235 47 24 0.5 0.3 | -51.8 -61.2 230 49 25 0.4 0.2
45000 -51.8 -61.2 230 67 34 0.5 0.3 | -51.1 -60.0 230 61 32 0.4 0.2
40000 -51.8 -61.2 220 68 35 -0.1 -0.0 | -51.8 -61.2 220 68 35 -0.6 -0.3
38000 -51.6 -60.9 220 71 36 1.2 0.6 | -51.9 -61.4 215 71 37 1.3 0.7
36000 -50.9 -59.6 220 79 40 1.2 0.7 | -51.1 -60.0 220 77 40 1.3 0.7
34000 -50.2 -58.4 225 86 44 1.1 0.6 | -50.3 -58.5 220 83 43 1.3 0.7
32000 -49.0 -56.2 225 85 44 2.1 1.1 | -49.3 -56.7 220 81 42 1.7 0.9
30000 -47.8 -54.0 225 83 43 1.6 0.9 | -48.3 -54.9 220 77 40 1.3 0.7
29000 -45.9 -50.6 220 76 39 6.1 3.3 | -46.5 -51.7 220 69 36 5.7 3.1
28000 -44.0 -47.2 220 69 36 6.1 3.3 | -44.8 -48.6 220 61 32 5.7 3.1
27000 -42.2 -44.0 220 63 32 6.1 3.3 | -43.1 -45.6 220 54 28 5.8 3.2
26000 -40.1 -40.2 220 56 29 8.1 4.4 | -40.9 -41.6 220 48 25 8.9 4.9
25000 -37.6 -35.7 220 51 26 8.2 4.5 | -38.2 -36.8 220 45 23 9.0 4.9
24000 -35.2 -31.4 225 45 23 8.2 4.5 | -35.5 -31.9 220 41 21 9.0 4.9
23000 -32.7 -26.9 225 41 21 8.8 4.8 | -32.9 -27.2 220 39 20 8.7 4.8
22000 -30.0 -22.0 225 40 20 8.8 4.8 | -30.3 -22.5 220 38 20 8.7 4.8
21000 -27.4 -17.3 225 38 20 8.9 4.9 | -27.7 -17.9 220 37 19 8.8 4.9
20000 -25.0 -13.0 230 36 19 7.7 4.2 | -25.3 -13.5 220 35 18 7.3 4.0
19500 -23.9 -11.0 230 35 18 7.7 4.2 | -24.3 -11.7 220 34 18 7.3 4.0
19000 -22.8 -9.0 230 34 18 7.7 4.2 | -23.2 -9.8 220 33 17 7.3 4.0
18500 -21.6 -6.9 230 33 17 7.7 4.2 | -22.1 -7.8 220 32 16 7.4 4.1
18000 -20.5 -4.9 230 32 17 7.1 3.9 | -21.1 -6.0 220 31 16 5.9 3.2
17500 -19.5 -3.1 230 32 16 6.9 3.8 | -20.3 -4.5 220 30 15 5.4 3.0
17000 -18.5 -1.3 230 31 16 6.9 3.8 | -19.5 -3.1 220 29 15 5.6 3.1
16500 -17.5 0.5 225 31 16 6.8 3.7 | -18.6 -1.5 220 28 14 6.5 3.6
16000 -16.5 2.3 225 31 16 6.9 3.8 | -17.6 0.3 220 27 14 6.4 3.5
15500 -15.6 3.9 220 31 16 6.1 3.3 | -16.6 2.1 215 27 14 7.3 4.0
15000 -14.7 5.5 220 31 16 6.2 3.4 | -15.6 3.9 215 26 13 7.3 4.0
14500 -13.5 7.7 215 31 16 4.8 2.6 | -14.3 6.3 215 24 12 4.8 2.6
14000 -12.8 9.0 210 30 15 5.1 2.8 | -13.5 7.7 215 22 11 5.0 2.7
13500 -12.3 9.9 210 27 14 1.7 0.9 | -13.1 8.4 215 19 10 0.7 0.4
13000 -12.0 10.4 205 22 11 2.4 1.3 | -13.0 8.6 210 15 8 1.3 0.7
12500 -11.9 10.6 200 18 9 -2.2 -1.2 | -13.0 8.6 210 11 6 -1.4 -0.8
12000 -12.2 10.0 190 14 7 -2.8 -1.5 | -13.1 8.4 205 8 4 -1.9 -1.1
11500 -11.9 10.6 175 11 6 6.9 3.8 | -12.7 9.1 205 6 3 6.9 3.8
11000 -11.0 12.2 165 9 5 6.8 3.7 | -11.9 10.6 205 4 2 6.1 3.3
10500 -10.4 13.3 155 8 4 1.6 0.9 | -11.1 12.0 205 3 2 4.4 2.4
10250 -10.2 13.6 155 8 4 2.0 1.1 | -10.8 12.6 205 3 1 4.0 2.2
10000 -10.1 13.8 150 7 4 2.9 1.6 | -10.5 13.1 205 2 1 6.2 3.4
9750 -9.8 14.4 140 7 3 6.1 3.3 | -9.9 14.2 160 2 1 7.5 4.1
9500 -9.3 15.3 125 7 4 7.0 3.8 | -9.4 15.1 120 3 2 6.2 3.4
9250 -8.7 16.3 110 8 4 7.4 4.0 | -8.9 16.0 110 5 3 7.0 3.8
9000 -8.2 17.2 095 9 5 5.1 2.8 | -8.5 16.7 105 7 4 5.3 2.9
8750 -8.0 17.6 090 10 5 4.4 2.4 | -8.1 17.4 100 10 5 5.0 2.7
8500 -7.5 18.5 085 11 6 6.2 3.4 | -7.7 18.1 090 11 6 6.3 3.5
8250 -7.1 19.2 075 13 7 5.7 3.1 | -7.3 18.9 080 12 6 6.0 3.3
8000 -6.7 19.9 070 14 7 6.2 3.4 | -6.8 19.8 075 14 7 5.7 3.1
7750 -6.2 20.8 060 14 7 6.2 3.4 | -6.4 20.5 070 16 8 5.8 3.2
7500 -5.8 21.6 050 14 7 5.6 3.1 | -6.0 21.2 065 17 9 6.0 3.3
7250 -5.4 22.3 045 14 7 6.5 3.6 | -5.5 22.1 060 19 10 6.7 3.7
7000 -4.8 23.4 040 13 7 7.9 4.3 | -5.0 23.0 055 18 9 7.5 4.1
6750 -4.3 24.3 030 13 7 7.6 4.2 | -4.5 23.9 050 16 8 8.0 4.4
6500 -3.7 25.3 020 13 7 7.5 4.1 | -3.8 25.2 045 15 8 9.3 5.1
6250 -3.1 26.4 015 13 7 9.2 5.0 | -3.1 26.4 045 14 7 10.1 5.5
6000 -2.4 27.7 010 12 6 10.1 5.5 | -2.4 27.7 040 13 6 10.5 5.8
5750 -1.7 28.9 005 11 6 9.6 5.3 | -1.6 29.1 040 12 6 10.2 5.6
5500 -0.9 30.4 005 10 5 12.3 6.7 | -0.8 30.6 035 11 5 12.3 6.7
04/18/2025 at 1500 MDT | 04/18/2025 at 1800 MDT
|
CAPE... +32.4 LI... +7.9 | CAPE... +29.5 LI... +8.2
CINH... -0.1 K Index... +10.6 | CINH... 0.0 K Index... +9.1
|
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 -51.4 -60.5 225 44 23 0.4 0.2 | -52.4 -62.3 225 41 21 0.7 0.4
45000 -50.8 -59.4 225 52 27 0.4 0.2 | -51.3 -60.3 230 48 24 0.7 0.4
40000 -50.3 -58.5 225 62 32 0.3 0.2 | -50.6 -59.1 230 53 27 0.4 0.2
38000 -50.3 -58.5 220 65 34 -0.6 -0.3 | -50.6 -59.1 230 55 28 -1.4 -0.8
36000 -50.6 -59.1 225 69 36 -0.6 -0.3 | -51.5 -60.7 230 59 30 -1.4 -0.8
34000 -51.0 -59.8 225 73 37 -0.6 -0.3 | -52.4 -62.3 230 62 32 -1.6 -0.9
32000 -51.4 -60.5 225 65 33 -0.7 -0.4 | -52.3 -62.1 230 59 31 0.5 0.3
30000 -51.8 -61.2 225 55 28 -1.6 -0.9 | -52.0 -61.6 230 55 29 -0.5 -0.3
29000 -49.3 -56.7 225 48 25 9.0 5.0 | -50.1 -58.2 230 52 27 8.9 4.9
28000 -46.6 -51.9 225 43 22 9.0 5.0 | -46.7 -52.1 225 47 24 8.9 4.9
27000 -43.9 -47.0 220 38 20 9.0 5.0 | -44.1 -47.4 225 43 22 8.9 4.9
26000 -41.3 -42.3 220 35 18 9.0 4.9 | -41.3 -42.3 225 40 21 9.5 5.2
25000 -38.6 -37.5 220 33 17 9.0 4.9 | -38.4 -37.1 230 38 19 9.6 5.2
24000 -35.9 -32.6 215 32 16 9.0 4.9 | -35.6 -32.1 230 35 18 9.5 5.2
23000 -33.3 -27.9 215 30 16 8.4 4.6 | -33.1 -27.6 230 34 18 7.5 4.1
22000 -30.8 -23.4 215 29 15 8.4 4.6 | -30.8 -23.4 235 35 18 7.5 4.1
21000 -28.3 -18.9 215 28 15 8.4 4.6 | -28.6 -19.5 240 35 18 7.4 4.1
20000 -25.9 -14.6 215 28 14 7.9 4.4 | -26.2 -15.2 245 34 18 8.4 4.6
19500 -24.7 -12.5 220 27 14 7.9 4.4 | -25.0 -13.0 245 33 17 8.4 4.6
19000 -23.6 -10.5 220 27 14 8.0 4.4 | -23.7 -10.7 245 32 17 8.4 4.6
18500 -22.4 -8.3 220 27 14 8.0 4.4 | -22.5 -8.5 245 31 16 8.4 4.6
18000 -21.2 -6.2 220 27 14 7.0 3.8 | -21.3 -6.3 245 30 16 7.9 4.3
17500 -20.2 -4.4 220 26 14 6.8 3.7 | -20.1 -4.2 245 29 15 7.8 4.3
17000 -19.2 -2.6 220 26 13 6.8 3.7 | -19.0 -2.2 245 27 14 7.6 4.2
16500 -18.2 -0.8 220 26 13 6.8 3.7 | -17.9 -0.2 245 26 14 7.2 4.0
16000 -17.2 1.0 220 25 13 6.9 3.8 | -16.8 1.8 240 25 13 7.2 4.0
15500 -16.3 2.7 225 25 13 6.2 3.4 | -15.9 3.4 240 24 12 5.9 3.2
15000 -15.3 4.5 225 24 12 6.4 3.5 | -15.0 5.0 235 22 12 6.2 3.4
14500 -14.1 6.6 220 21 11 5.1 2.8 | -13.9 7.0 230 19 10 4.1 2.2
14000 -13.3 8.1 225 19 10 5.0 2.8 | -13.3 8.1 230 17 9 3.7 2.0
13500 -12.9 8.8 225 16 8 1.3 0.7 | -13.0 8.6 230 13 7 0.9 0.5
13000 -12.7 9.1 230 12 6 1.9 1.0 | -12.9 8.8 225 9 5 1.0 0.5
12500 -12.7 9.1 235 8 4 -2.7 -1.5 | -12.8 9.0 235 6 3 -0.5 -0.3
12000 -13.0 8.6 255 5 3 -2.8 -1.5 | -12.9 8.8 260 4 2 -0.2 -0.1
11500 -12.7 9.1 285 5 2 6.3 3.5 | -12.6 9.3 290 4 2 3.9 2.1
11000 -11.9 10.6 300 6 3 5.5 3.0 | -12.0 10.4 315 5 3 3.8 2.1
10500 -11.2 11.8 310 5 3 4.8 2.6 | -11.3 11.7 325 6 3 5.4 3.0
10250 -10.8 12.6 310 4 2 5.3 2.9 | -10.9 12.4 330 6 3 5.8 3.2
10000 -10.5 13.1 315 3 2 3.6 2.0 | -10.5 13.1 330 6 3 4.1 2.2
9750 -10.2 13.6 330 2 1 5.1 2.8 | -10.3 13.5 335 6 3 5.5 3.0
9500 -9.7 14.5 060 2 1 7.7 4.2 | -9.7 14.5 355 5 2 8.1 4.4
9250 -9.2 15.4 095 4 2 7.4 4.0 | -9.2 15.4 020 4 2 7.7 4.2
9000 -8.7 16.3 105 7 4 6.0 3.3 | -8.6 16.5 050 4 2 6.0 3.3
8750 -8.3 17.1 100 9 5 5.6 3.1 | -8.3 17.1 075 5 2 5.8 3.2
8500 -7.8 18.0 095 11 6 7.0 3.8 | -7.7 18.1 090 6 3 7.6 4.2
8250 -7.3 18.9 090 13 7 6.5 3.6 | -7.2 19.0 095 7 4 6.7 3.7
8000 -6.9 19.6 085 16 8 5.7 3.1 | -6.8 19.8 100 9 5 5.9 3.2
7750 -6.5 20.3 080 18 9 5.6 3.0 | -6.3 20.7 095 10 5 5.7 3.1
7500 -6.0 21.2 080 19 10 5.5 3.0 | -5.9 21.4 090 12 6 5.8 3.2
7250 -5.6 21.9 075 20 10 6.8 3.7 | -5.5 22.1 090 13 7 6.1 3.4
7000 -5.0 23.0 070 18 9 8.4 4.6 | -5.0 23.0 090 14 7 6.6 3.6
6750 -4.5 23.9 065 16 8 7.6 4.1 | -4.6 23.7 085 15 8 6.1 3.3
6500 -3.9 25.0 065 15 8 8.1 4.4 | -4.1 24.6 085 15 8 7.8 4.3
6250 -3.3 26.1 060 14 7 9.7 5.3 | -3.4 25.9 080 13 7 10.3 5.6
6000 -2.6 27.3 060 12 6 9.8 5.4 | -2.7 27.1 080 12 6 10.1 5.5
5750 -1.8 28.8 060 11 6 10.4 5.7 | -1.9 28.6 080 11 6 10.8 5.9
5500 -0.9 30.4 060 10 5 15.1 8.3 | -1.0 30.2 075 10 5 14.5 8.0
________________________________________________________________________________
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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