This prototype web interface to grads provides support for the dimension environment to be set, an expression to be entered, and a plot produced based on those user entry fields. No control is yet provided over graphics or annotation, nor is multi-step analysis supported. There are plans to implement these enhancements.

The underlying web programming uses an AJAX approach. The code running in the web browser is JavaScript. The code that runs on the server is GrADS, with a small interface that is written in the C language. The information sent to the server is put in the XML format.

For those not familiar with grads, it may be helpful to visit the grads home page and read the documentation on the dimension environment and the use of expressions.

Basically, the web interface allows one to enter a range of longitude, latitude, level, and time. (In grads usage, you are setting lon, lat, lev, and t. Note the use of relative grid time rather than absolute time). If you wish to provide a varying dimension, enter values in boxes for both the minimum and maximum rows. If you want a fixed dimension, enter a value for just the minimum, and leae the maximum blank. If you want the grads default, you may leave both fields blank. If you are displaying a non-level-dependent variable (eg, a surface variable) you may leave both of the level fields blank. You will need to have one or two varying dimensions -- do not try zero or more than two varying dimensions.

Currently the web interface does not handle errors. For most errors you will simply not get a plot produced. Sorry about that. This will be the first thing to get improved upon as work progresses.

The interface currently points to just the GFS model run. This gets updated every six hours -- the 00z run shows up around 05z, etc. See the table at the end of this page for the variables available, listed in the first column.

The entry field labeled "variable" will actually allow you to enter a general grads expression. The way an expression is evaluated is highly dependent on the dimension environment that is set. It is beyond the scope of this short document to explain this; refer to the main grads documentation.

A few examples:

The above entries would give you a map of sea level pressure over the western atlantic at the last time in the data set (about an 7.5 day forecast). Note the sea level pressure is divided by 100 to convert from pascals to mb. The plot will be produced with a contour interval of 2.


The above entries give an example of using the expression capability to calculate the temperature of the air at 850mb lowered dry-adiabaticly to the surface (eg, an application of Poisson's equation). Note the surface pressure is in pascals, so the initial pressure of 850mb is provided as pascals in the equation. Also note the cint field is blank; this tells grads to choose an appropriate value automatically.


The above entries give a vertical cross section. Any slice through the data may be made, and is controlled by the dimension environment. Refer to the grads documentation.

The GFS data set has a global spatial extent, with a half degree lon/lat grid. It has 61 times with a time interval of 3 hours. It has the following levels:
1000,975,950,925,900,850,800,750,700,650,600,550,500,450,400,350,300,250,200,150,100,70,50,30,20,10.

Below is a list of all the variables. The first 8 variables (up to clwmr) are 3D variables; the rest are 2D variables that are non-level-dependent. The first column is the abbreviation for the variable -- this is what is used in the grads expressions.

z 26,100 0,3,5 Geopotential Height [gpm]
t 26,100 0,0,0 Temperature [K]
u 26,100 0,2,2 U-Component of Wind [m/s]
v 26,100 0,2,3 V-Component of Wind [m/s]
vort 26,100 0,2,10 Absolute Vorticity [/s]
vv 21,100 0,2,8 Vertical Velocity (Pressure) [Pa/s]
rh 21,100 0,1,1 Relative Humidity [%]
clwmr 21,100 0,1,22 Cloud Water Mixing Ratio [kg/kg]
ps 0,1,0 0,3,0 Surface Pressure [Pa]
ts 0,1,0 0,0,0 Surface Temperature [K]
t2m 0,103,2 0,0,0 2m Temperature [K]
t2min 0,103,2 0,0,4 2m Minimum Temperature [K]
t2max 0,103,2 0,0,5 2m Maximum Temperature [K]
q2 0,103,2 0,1,0 2m Specific Humidity [kg/kg]
p 0,1,0 0,1,8,1 Total Accumulated Precipitation [kg/m2]
pc 0,1,0 0,1,10,1 Convective Precipitation [kg/m2]
crain 0,1,0 0,1,192,0 Categorical Rain (yes=1; no=0)
cfrzr 0,1,0 0,1,193,0 Categorical Freezing Rain (yes=1; no=0)
cicep 0,1,0 0,1,194,0 Categorical Ice Pellets (yes=1; no=0)
csnow 0,1,0 0,1,195,0 Categorical Snow (yes=1; no=0)
pwat 0,200,0 0,1,3 Entire Atmosphere Precipitable Water [kg/m^2]
rhum 0,200,0 0,1,1 entire Atmosphere Relative Humidity [%]
o3mr100 0,100,10000 0,14,192 100mb Ozone Mixing Ratio [kg/kg]
o3mr70 0,100,7000 0,14,192 70mb Ozone Mixing Ratio [kg/kg]
o3mr50 0,100,5000 0,14,192 50mb Ozone Mixing Ratio [kg/kg]
o3mr30 0,100,3000 0,14,192 30mb Ozone Mixing Ratio [kg/kg]
o3mr20 0,100,2000 0,14,192 20mb Ozone Mixing Ratio [kg/kg]
o3mr10 0,100,1000 0,14,192 10mb Ozone Mixing Ratio [kg/kg]
wavh500 0,100,50000 0,3,193 5-Wave Geopotential Height [gpm]
wava500 0,100,50000 0,3,197 5-Wave Geopotential Height Anomaly [gpm]
soilw1 0,106,0,0.1 2,0,192 Volumetric Soil Moisture,0.0-0.1m below surface [fraction]
soilw2 0,106,0.1,0.4 2,0,192 Volumetric Soil Moisture,0.1-0.4m below surface [fraction]
soilw3 0,106,0.4,1 2,0,192 Volumetric Soil Moisture,0.4-1.0m below surface [fraction]
soilw4 0,106,1,2 2,0,192 Volumetric Soil Moisture,1.0-2.0m below surface [fraction]
soilt1 0,106,0,0.1 0,0,0 Soil Temperature,0.0-0.1m below surface [K]
soilt2 0,106,0.1,0.4 0,0,0 Soil Temperature,0.1-0.4m below surface [K]
soilt3 0,106,0.4,1 0,0,0 Soil Temperature,0.4-1.0m below surface [K]
soilt4 0,106,1,2 0,0,0 Soil Temperature,1.0-2.0m below surface [K]
tb 0,108,3000,0 0,0,0 Bottom 30mb Temperature [K]
rhb 0,108,3000,0 0,1,1 Bottom 30mb Relative Humidity [%]
qb 0,108,3000,0 0,1,0 Bottom 30mb Specific Humidity [kg/kg]
ub 0,108,3000,0 0,2,2 Bottom 30mb U Winds [m/s]
vb 0,108,3000,0 0,2,3 Bottom 30mb V Winds [m/s]
t6000 0,102,1829 0,0,0 Temperature at 6000ft AMSL [K]
t9000 0,102,2743 0,0,0 Temperature at 9000ft AMSL [K]
t12000 0,102,3658 0,0,0 Temperature at 12000ft AMSL [K]
u6000 0,102,1829 0,2,2 U Winds at 6000ft AMSL [m/s]
u9000 0,102,2743 0,2,3 U Winds at 9000ft AMSL [m/s]
u12000 0,102,3658 0,2,2 U Winds at 12000ft AMSL [m/s]
v6000 0,102,1829 0,2,3 V Winds at 6000ft AMSL [m/s]
v9000 0,102,2743 0,2,2 V Winds at 9000ft AMSL [m/s]
v12000 0,102,3658 0,2,3 V Winds at 12000ft AMSL [m/s]
ztrop 0,7,0 0,3,5 Tropopause Geopotential Height [gpm]
ttrop 0,7,0 0,0,0 Tropopause Temperature [K]
ptrop 0,7,0 0,3,0 Tropopause Pressure [Pa]
utrop 0,7,0 0,2,2 Tropopause U Winds [m/s]
vtrop 0,7,0 0,2,3 Tropopause V Winds [m/s]
strop 0,7,0 0,2,192 Tropopause Vertical Speed Shear [/s]
rhl1 0,104,0.33,1 0,1,1 Relative Humidity, Sigma 0.33 to 1 [%]
rhl2 0,104,0.44,1 0,1,1 Relative Humidity, Sigma 0.44 to 1 [%]
rhl3 0,104,0.72,0.94 0,1,1 Relative Humidity, Sigma 0.72 to 0.94 [%]
rhl4 0,104,0.44,0.72 0,1,1 Relative Humidity, Sigma 0.44 to 0.72 [%]
ptls 0,104,0.995 0,0,2 Sigma 0.995 Potential Temperature [K]
tls 0,104,0.995 0,0,0 Sigma 0.995 Temperature [K]
vvls 0,104,0.995 0,2,8 Sigma 0.995 Vertical Velocity [Pa/s]
rhls 0,104,0.995 0,1,1 Sigma 0.995 Relative Humidity [%]
uls 0,104,0.995 0,2,2 Sigma 0.995 U Winds [m/s]
vls 0,104,0.995 0,2,3 Sigma 0.995 V Winds [m/s]
sli 0,1,0 0,7,192 Surface Lifted Index [K]
capes 0,1,0 0,7,6 Convective Available Potential Energy (Surface) [J/kg]
cins 0,1,0 0,7,7 Convective Inhibition (Surface) [J/kg]
li 0,1,0 0,7,193 Best (4 Layer) Lifted Index [K]
cape 0,108,18000,0 0,7,6 Convective Available Potential Energy (Lowest 180mb) [J/kg]
cin 0,108,18000,0 0,7,7 Convective Inhibition (Lowest 180mb) [J/kg]
zwmx 0,6,0 0,3,5 Max Wind Level Geopotential Height [gpm]
twmx 0,6,0 0,0,0 Max Wind Level Temperature [K]
pwmx 0,6,0 0,3,0 Max Wind Level Pressure [Pa]
uwmx 0,6,0 0,2,2 Max Wind Level U Winds [m/s]
vwmx 0,6,0 0,2,3 Max Wind Level V Winds [m/s]
zs 0,1,0 0,3,5 Surface Geopotential Height [gpm]
slp 0,101,0 0,3,1 Sea Level Pressure [Pa]
dlwrfs 0,1,0 0,5,192,0 Surface Downward Long Wave Rad. Flux [W/m^2]
ulwrfs 0,1,0 0,5,193,0 Surface Upward Long Wave Rad. Flux [W/m^2]
ulwrft 0,8,0 0,5,193,0 Top of Atmosphere Upward Long Wave Rad. Flux [W/m^2]
uswrft 0,8,0 0,4,193,0 Top of Atmosphere Upward Short Wave Rad. Flux [W/m^2]
uswrfs 0,1,0 0,4,193,0 Surface Upward Short Wave Rad. Flux [W/m^2]
dswrfs 0,1,0 0,4,192,0 Surface Downward Short Wave Rad. Flux [W/m^2]
z0c 0,4,0 0,3,5 Geopotential Height at 0C Isotherm [gpm]
rh0c 0,4,0 0,1,1 Relative Humidity at 0C Isotherm [%]
shtfls 0,1,0 0,0,11,0 Surface Sensible Heat Net Flux [W/m^2]
lhtfls 0,1,0 0,0,10,0 Surface Latent Heat Net Flux [W/m^2]
weasd 0,1,0 0,1,13 Accumulated Snow Depth (water equivalent) [kg/m^2]
prate 0,1,0 0,1,7,0 Precipitation Rate [kg/m^2 s^1]
cprate 0,1,0 0,1,196,0 Convective Precipitation Rate [kg/m^2 s^1]
gflux 0,1,0 2,0,193,0 Ground Heat Flux [W/m^2]
land 0,1,0 2,0,0 Land Cover (1=land, 0=sea)
icec 0,1,0 10,2,0 Ice Cover [Proportion]
runoff 0,1,0 2,0,5,1 Surface Water Runoff [kg/m^2]
pevpr 0,1,0 0,1,200 Surface Potential Evaporation Rate [W/m^2]
hpbl 0,1,0 0,3,196 Planetary Boundary Layer Height [m]
albedo 0,1,0 0,19,1,0 Surface Albedo [%]
rh2m 0,103,2 0,1,1 2m Relative Humidity [%]
uflx 0,1,0 0,2,17,0 Surface U-Momentum Flux [N/m^2]
vflx 0,1,0 0,2,18,0 Surface v-Momentum Flux [N/m^2]
u10m 0,103,10 0,2,2 10m U Winds [m/s]
v10m 0,103,10 0,2,3 10m V Winds [m/s]
ugwd 0,1,0 0,3,194,0 Zonal Flux of Gravity Wave Stress [N/m^2]
vgwd 0,1,0 0,3,195,0 Meridional Flux of Gravity Wave Stress [N/m^2]
gpa1000 0,100,100000 0,3,9 1000mb Geopotential Height Anomaly [gpm]
gpa500 0,100,50000 0,3,9 500mb Geopotential Height Anomaly [gpm]
ozone 0,200,0 0,14,0 Entire Atmosphere Total Ozone [Dobson]
cwat 0,200,0 0,6,6 Entire Atmosphere Cloud Water [kg/m^2]
cwork 0,200,0 0,6,193,0 Entire Atmosphere Cloud Work Function [J/kg]
ztropfl 0,204,0 0,3,5 Highest Tropospheric Freezing Level Geopotential Height [gpm]
rhtropfl 0,204,0 0,1,1 Highest Tropospheric Freezing Level Relative Humidity [%]
lcbp 0,212,0 0,3,0,0 Low cloud Bottom Pressure [Pa]
lctp 0,213,0 0,3,0,0 Low Cloud Top Pressure [Pa]
mcbp 0,222,0 0,3,0,0 Middle Cloud Bottom Pressure [Pa]
mctp 0,223,0 0,3,0,0 Middle Cloud Top Pressure [Pa]
hcbp 0,232,0 0,3,0,0 High Cloud Bottom Pressure [Pa]
hctp 0,233,0 0,3,0,0 High Cloud Top Pressure [Pa]
ccbp 0,242,0 0,3,0 Convective Cloud Bottom Pressure [Pa]
cctp 0,243,0 0,3,0 Convective Cloud Top Pressure [Pa]
tcc 0,200,0 0,6,1,0 Entire Atmosphere Total Cloud Cover [%]
blcc 0,211,0 0,6,1,0 Boundary Layer Total Cloud Cover [%]
lcc 0,214,0 0,6,1,0 Low Cloud Cover [%]
mcc 0,224,0 0,6,1,0 Middle Cloud Cover [%]
hcc 0,234,0 0,6,1,0 High Cloud Cover [%]
ccc 0,244,0 0,6,1 Convective Cloud Cover [%]
lctt 0,213,0 0,0,0,0 Low Cloud Top Temperature [K]
mctt 0,223,0 0,0,0,0 Middle Cloud Top Temperature [K]
hctt 0,233,0 0,0,0,0 High Cloud Top Temperature [K]
hgt2pv 0,109,2e-6 0,3,5 2PotVortSfc Geopotential Height [gpm]
hgtneg2pv 0,109,-2e-6 0,3,5 neg2PotVortSfc Geopotential Height [gpm]
pres2pv 0,109,2e-6 0,3,0 2PotVortSfc Pressure [Pa]
presneg2pv 0,109,-2e-6 0,3,0 neg2PotVortSfc Pressure [Pa]
t2pv 0,109,2e-6 0,0,0 2PotVortSfc Temperature [K]
tneg2pv 0,109,-2e-6 0,0,0 neg2PotVortSfc Temperature [K]
u2pv 0,109,2e-6 0,2,2 2PotVortSfc U-Component of Wind [m/s]
uneg2pv 0,109,-2e-6 0,2,2 neg2PotVortSfc U-Component of Wind [m/s]
v2pv 0,109,2e-6 0,2,3 2PotVortSfc V-Component of Wind [m/s]
vneg2pv 0,109,-2e-6 0,2,3 neg2PotVortSfc V-Component of Wind [m/s]
vss2pv 0,109,2e-6 0,2,192 2PotVortSfc Vertical speed sheer [1/s]
vssneg2pv 0,109,-2e-6 0,2,192 neg2PotVortSfc Vertical speed sheer [1/s]