547  
UXUS97 KBOU 141326  
SRGBOU  
 
SOARING FORECAST  
NATIONAL WEATHER SERVICE DENVER/BOULDER, COLORADO  
0626 MST THURSDAY, DECEMBER 14, 2017  
 
THIS FORECAST IS FOR THURSDAY, DECEMBER 14, 2017:  
 
IF THE TRIGGER TEMPERATURE OF 38.9 F/3.8 C IS REACHED...THEN  
THERMAL SOARING INDEX....................... POOR  
MAXIMUM RATE OF LIFT........................ 0 FT/MIN (0.0 M/S)  
MAXIMUM HEIGHT OF THERMALS.................. 9362 FT MSL (4077 FT AGL)  
 
FORECAST MAXIMUM TEMPERATURE................... 38.0 F/3.8 C  
TIME OF TRIGGER TEMPERATURE.................... 1300 MST  
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................. 6975 FT MSL (1689 FT AGL)  
THERMAL SOARING OUTLOOK FOR FRIDAY 12/15....... POOR  
 
WAVE SOARING INDEX............................. POOR  
WAVE SOARING INDEX TREND (TO 1700 MST)......... NO CHANGE  
HEIGHT OF STABLE LAYER (12-18K FT MSL)......... 16924 FT MSL (11639 FT AGL)  
WEAK PVA/NVA (THROUGH 1700 MST)................ WEAK PVA  
POTENTIAL HEIGHT OF WAVE....................... 33688 FT MSL (28403 FT AGL)  
WAVE SOARING OUTLOOK FOR FRIDAY 12/15.......... POOR  
 
REMARKS...  
 
SUNRISE/SUNSET.................... 07:13:09 / 16:35:37 MST  
TOTAL POSSIBLE SUNSHINE........... 9 HR 22 MIN 28 SEC (562 MIN 28 SEC)  
ALTITUDE OF SUN AT 11:54:23 MST... 26.97 DEGREES  
 
UPPER AIR DATA FROM RAWINSONDE OBSERVATION TAKEN ON 12/14/2017 AT 0500 MST  
 
FREEZING LEVEL.................. ENTIRE AIRMASS BELOW 32 F / 0 C  
CONVECTIVE CONDENSATION LEVEL... 11581 FT MSL (6296 FT AGL)  
LIFTED CONDENSATION LEVEL....... 11011 FT MSL (5726 FT AGL)  
LIFTED INDEX.................... +11.3  
K INDEX......................... -2.8  
 
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  
--------------------------------------------------------------------------------  
 
* * * * * * NUMERICAL WEATHER PREDICTION MODEL FORECAST DATA VALID * * * * * *  
 
12/14/2017 AT 0800 MST | 12/14/2017 AT 1100 MST  
|  
CAPE... 0.0 LI... +4.6 | CAPE... +8.7 LI... +4.5  
CINH... 0.0 K INDEX... +10.3 | CINH... -3.5 K INDEX... +4.7  
|  
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 -56.2 -69.2 320 14 7 1.9 1.0 | -55.8 -68.4 325 13 7 1.8 1.0  
45000 -53.3 -63.9 315 17 9 2.0 1.1 | -53.1 -63.6 320 16 8 1.9 1.0  
40000 -53.1 -63.6 310 17 9 0.0 0.0 | -52.4 -62.3 325 20 10 0.4 0.2  
38000 -52.9 -63.2 305 18 9 1.2 0.6 | -52.0 -61.6 330 21 11 1.3 0.7  
36000 -52.1 -61.8 300 18 9 1.2 0.7 | -51.2 -60.2 335 21 11 1.3 0.7  
34000 -51.4 -60.5 300 18 9 2.2 1.2 | -50.4 -58.7 340 21 11 1.9 1.0  
32000 -49.1 -56.4 295 19 10 3.9 2.1 | -48.3 -54.9 350 24 12 3.6 2.0  
30000 -46.8 -52.2 290 19 10 4.8 2.6 | -46.2 -51.2 355 27 14 3.9 2.2  
29000 -45.1 -49.2 290 19 10 5.7 3.1 | -44.8 -48.6 355 28 14 4.7 2.6  
28000 -43.4 -46.1 290 19 10 5.7 3.1 | -43.4 -46.1 355 28 14 4.7 2.6  
27000 -41.6 -42.9 290 19 10 5.7 3.1 | -42.0 -43.6 355 29 15 4.7 2.6  
26000 -39.7 -39.5 290 18 9 6.9 3.8 | -40.5 -40.9 350 28 15 5.5 3.0  
25000 -37.6 -35.7 295 18 9 7.0 3.8 | -38.8 -37.8 350 27 14 5.5 3.0  
24000 -35.5 -31.9 295 17 9 7.0 3.8 | -37.2 -35.0 350 26 13 5.5 3.0  
23000 -33.6 -28.5 300 17 9 6.2 3.4 | -35.4 -31.7 345 25 13 6.5 3.6  
22000 -31.7 -25.1 310 17 9 6.1 3.4 | -33.4 -28.1 345 24 12 6.5 3.6  
21000 -29.9 -21.8 315 17 9 6.2 3.4 | -31.5 -24.7 345 23 12 6.5 3.6  
20000 -27.7 -17.9 320 16 8 5.9 3.3 | -28.9 -20.0 340 22 12 7.2 3.9  
19500 -26.8 -16.2 325 16 8 6.0 3.3 | -27.8 -18.0 340 22 11 7.2 3.9  
19000 -25.9 -14.6 325 16 8 5.9 3.3 | -26.7 -16.1 340 22 11 7.2 3.9  
18500 -25.0 -13.0 330 16 8 5.8 3.2 | -25.6 -14.1 340 22 11 6.9 3.8  
18000 -24.2 -11.6 330 16 8 5.5 3.0 | -24.6 -12.3 335 21 11 6.4 3.5  
17500 -23.4 -10.1 330 15 8 5.5 3.0 | -23.7 -10.7 335 21 11 6.5 3.6  
17000 -22.5 -8.5 330 15 8 6.3 3.4 | -22.8 -9.0 335 21 11 5.8 3.2  
16500 -21.6 -6.9 330 15 8 6.2 3.4 | -21.9 -7.4 335 20 10 5.9 3.2  
16000 -20.6 -5.1 330 15 8 6.8 3.7 | -21.0 -5.8 335 20 10 5.6 3.1  
15500 -19.6 -3.3 330 15 8 7.0 3.8 | -20.2 -4.4 330 19 10 5.6 3.0  
15000 -18.6 -1.5 330 14 7 6.7 3.7 | -19.4 -2.9 330 18 9 5.6 3.1  
14500 -17.6 0.3 330 14 7 6.3 3.5 | -18.6 -1.5 330 18 9 5.6 3.1  
14000 -16.7 1.9 330 14 7 6.1 3.4 | -17.8 -0.0 330 17 9 5.9 3.2  
13500 -15.8 3.6 335 13 7 5.7 3.1 | -16.8 1.8 330 17 9 6.4 3.5  
13000 -15.0 5.0 335 13 6 5.8 3.2 | -15.9 3.4 330 16 8 6.4 3.5  
12500 -14.1 6.6 340 12 6 6.0 3.3 | -14.9 5.2 330 16 8 6.4 3.5  
12000 -13.2 8.2 340 11 6 5.9 3.3 | -14.0 6.8 330 15 8 6.5 3.6  
11500 -12.4 9.7 345 11 6 5.8 3.2 | -13.0 8.6 330 14 7 6.6 3.6  
11000 -11.5 11.3 345 12 6 5.8 3.2 | -12.1 10.2 330 14 7 7.0 3.8  
10500 -10.7 12.7 350 12 6 5.9 3.3 | -11.0 12.2 335 13 7 7.3 4.0  
10250 -10.2 13.6 350 12 6 6.0 3.3 | -10.4 13.3 335 13 7 7.4 4.1  
10000 -9.8 14.4 350 12 6 6.0 3.3 | -9.9 14.2 335 12 6 8.2 4.5  
9750 -9.3 15.3 355 12 6 5.8 3.2 | -9.3 15.3 335 12 6 7.9 4.3  
9500 -8.9 16.0 355 12 6 5.7 3.1 | -8.7 16.3 340 12 6 7.2 4.0  
9250 -8.5 16.7 355 11 6 5.9 3.2 | -8.2 17.2 340 11 6 7.3 4.0  
9000 -8.1 17.4 360 11 6 5.8 3.2 | -7.7 18.1 340 11 6 6.7 3.7  
8750 -7.6 18.3 360 11 6 6.8 3.7 | -7.1 19.2 345 11 6 7.3 4.0  
8500 -7.1 19.2 360 11 5 7.5 4.1 | -6.6 20.1 345 10 5 8.1 4.4  
8250 -6.5 20.3 360 10 5 7.9 4.3 | -6.0 21.2 350 9 5 7.5 4.1  
8000 -5.9 21.4 360 9 5 8.9 4.9 | -5.4 22.3 350 8 4 7.5 4.1  
7750 -5.3 22.5 360 9 4 7.7 4.2 | -4.9 23.2 355 8 4 6.9 3.8  
7500 -4.8 23.4 360 8 4 6.7 3.7 | -4.4 24.1 355 6 3 7.0 3.9  
7250 -4.3 24.3 360 7 3 6.8 3.7 | -3.8 25.2 355 5 3 8.4 4.6  
7000 -3.7 25.3 360 5 3 7.4 4.0 | -3.2 26.2 355 4 2 8.6 4.7  
6750 -3.2 26.2 355 4 2 5.3 2.9 | -2.6 27.3 355 4 2 8.4 4.6  
6500 -2.9 26.8 345 3 2 4.5 2.5 | -2.0 28.4 355 3 1 9.0 5.0  
6250 -2.5 27.5 315 2 1 5.8 3.2 | -1.2 29.8 355 3 1 9.8 5.4  
6000 -2.1 28.2 265 2 1 5.7 3.2 | -0.5 31.1 355 2 1 9.2 5.0  
5750 -1.7 28.9 235 3 1 4.5 2.5 | 0.2 32.4 355 2 1 11.4 6.3  
5500 -1.5 29.3 225 2 1 1.5 0.8 | 1.2 34.2 355 1 1 16.3 8.9  
 
12/14/2017 AT 1400 MST | 12/14/2017 AT 1700 MST  
|  
CAPE... +35.0 LI... +2.9 | CAPE... +1.0 LI... +7.1  
CINH... -2.2 K INDEX... +6.2 | CINH... -3.7 K INDEX... -2.8  
|  
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 -55.8 -68.4 325 12 6 1.7 1.0 | -56.2 -69.2 335 13 7 1.8 1.0  
45000 -53.2 -63.8 330 15 7 1.8 1.0 | -53.4 -64.1 335 16 8 1.9 1.1  
40000 -52.1 -61.8 335 21 11 0.6 0.3 | -52.4 -62.3 355 25 13 0.6 0.3  
38000 -51.7 -61.1 340 24 12 1.3 0.7 | -52.0 -61.6 360 30 15 0.4 0.2  
36000 -50.8 -59.4 350 28 14 1.3 0.7 | -51.8 -61.2 005 37 19 0.4 0.2  
34000 -50.0 -58.0 360 33 17 1.7 0.9 | -51.5 -60.7 010 44 22 1.2 0.7  
32000 -48.2 -54.8 005 37 19 3.1 1.7 | -49.9 -57.8 010 45 23 2.8 1.5  
30000 -46.4 -51.5 005 41 21 3.7 2.0 | -48.2 -54.8 015 46 23 4.5 2.5  
29000 -44.8 -48.6 005 42 22 5.6 3.0 | -46.3 -51.3 015 46 24 6.6 3.6  
28000 -43.1 -45.6 005 43 22 5.5 3.0 | -44.3 -47.7 015 47 24 6.6 3.6  
27000 -41.5 -42.7 005 44 23 5.6 3.0 | -42.3 -44.1 015 47 24 6.6 3.6  
26000 -39.8 -39.6 005 44 22 5.8 3.2 | -40.1 -40.2 015 47 24 8.0 4.4  
25000 -38.0 -36.4 005 42 22 5.8 3.2 | -37.7 -35.9 015 47 24 8.0 4.4  
24000 -36.3 -33.3 005 41 21 5.8 3.2 | -35.3 -31.5 015 46 24 8.0 4.4  
23000 -34.6 -30.3 005 39 20 5.6 3.1 | -33.0 -27.4 015 45 23 7.4 4.0  
22000 -32.9 -27.2 360 37 19 5.6 3.1 | -30.8 -23.4 015 43 22 7.4 4.0  
21000 -31.2 -24.2 355 34 18 5.6 3.1 | -28.6 -19.5 015 42 22 7.6 4.1  
20000 -29.6 -21.3 355 31 16 5.2 2.8 | -26.4 -15.5 015 39 20 5.5 3.0  
19500 -28.5 -19.3 350 29 15 5.2 2.8 | -25.5 -13.9 010 37 19 5.5 3.0  
19000 -27.7 -17.9 350 28 14 5.2 2.8 | -24.7 -12.5 010 35 18 5.5 3.0  
18500 -26.9 -16.4 345 27 14 5.2 2.8 | -23.9 -11.0 010 34 17 5.2 2.9  
18000 -26.1 -15.0 345 26 13 5.2 2.8 | -23.2 -9.8 005 32 17 4.6 2.6  
17500 -25.4 -13.7 345 25 13 5.1 2.8 | -22.5 -8.5 005 31 16 4.8 2.7  
17000 -24.6 -12.3 340 24 12 5.5 3.0 | -21.9 -7.4 005 29 15 3.0 1.6  
16500 -23.8 -10.8 340 24 12 5.5 3.0 | -21.4 -6.5 360 27 14 3.2 1.7  
16000 -22.9 -9.2 340 23 12 6.1 3.4 | -20.9 -5.6 360 26 13 3.2 1.8  
15500 -22.0 -7.6 335 22 11 6.4 3.5 | -20.5 -4.9 355 24 12 3.3 1.8  
15000 -21.0 -5.8 335 21 11 6.9 3.8 | -20.0 -4.0 350 23 12 3.6 2.0  
14500 -20.0 -4.0 335 20 10 7.4 4.1 | -19.4 -2.9 350 21 11 3.9 2.2  
14000 -18.9 -2.0 330 19 10 7.5 4.1 | -18.8 -1.8 345 20 10 4.6 2.5  
13500 -17.7 0.1 330 18 9 7.8 4.3 | -18.0 -0.4 340 19 10 5.7 3.2  
13000 -16.6 2.1 330 16 8 7.8 4.3 | -17.2 1.0 340 17 9 6.5 3.6  
12500 -15.4 4.3 325 16 8 7.9 4.3 | -16.1 3.0 335 16 8 7.9 4.3  
12000 -14.3 6.3 325 15 8 7.8 4.3 | -14.9 5.2 330 15 8 8.0 4.4  
11500 -13.2 8.2 325 14 7 7.6 4.2 | -13.7 7.3 330 14 7 8.2 4.5  
11000 -12.1 10.2 325 13 7 7.8 4.3 | -12.5 9.5 325 13 7 8.5 4.7  
10500 -10.9 12.4 330 12 6 8.0 4.4 | -11.2 11.8 330 13 7 8.7 4.8  
10250 -10.3 13.5 330 12 6 8.1 4.4 | -10.6 12.9 330 13 7 9.0 5.0  
10000 -9.7 14.5 335 11 6 8.6 4.7 | -9.8 14.4 330 13 6 10.1 5.5  
9750 -9.0 15.8 335 11 6 7.6 4.2 | -9.1 15.6 330 13 6 8.9 4.9  
9500 -8.5 16.7 340 10 5 6.6 3.6 | -8.5 16.7 335 12 6 7.4 4.1  
9250 -8.0 17.6 340 10 5 7.0 3.8 | -7.9 17.8 335 12 6 8.1 4.5  
9000 -7.5 18.5 345 9 5 7.0 3.8 | -7.3 18.9 335 12 6 8.6 4.7  
8750 -7.0 19.4 345 9 5 7.9 4.3 | -6.7 19.9 340 12 6 8.7 4.8  
8500 -6.3 20.7 350 9 4 8.6 4.7 | -6.0 21.2 340 12 6 8.7 4.7  
8250 -5.7 21.7 350 8 4 8.7 4.8 | -5.4 22.3 345 11 6 8.8 4.8  
8000 -5.1 22.8 355 8 4 9.0 4.9 | -4.7 23.5 350 11 6 9.3 5.1  
7750 -4.4 24.1 355 8 4 9.0 5.0 | -4.0 24.8 350 12 6 7.9 4.3  
7500 -3.7 25.3 355 7 4 9.4 5.2 | -3.5 25.7 355 11 6 7.4 4.1  
7250 -3.0 26.6 355 7 4 9.7 5.3 | -2.9 26.8 360 10 5 8.6 4.7  
7000 -2.3 27.9 360 7 4 9.9 5.4 | -2.3 27.9 360 10 5 9.2 5.0  
6750 -1.6 29.1 360 7 3 9.3 5.1 | -1.6 29.1 005 10 5 7.3 4.0  
6500 -0.9 30.4 360 6 3 9.3 5.1 | -1.1 30.0 005 9 5 7.1 3.9  
6250 -0.1 31.8 360 6 3 10.1 5.6 | -0.5 31.1 010 8 4 8.9 4.9  
6000 0.6 33.1 360 6 3 9.3 5.1 | 0.1 32.2 010 8 4 8.3 4.5  
5750 1.3 34.3 360 6 3 11.8 6.5 | 0.7 33.3 015 7 4 6.4 3.5  
5500 2.4 36.3 360 5 3 17.7 9.7 | 1.0 33.8 020 5 3 3.6 2.0  
________________________________________________________________________________  
 
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.  
 
042613  
 
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