inst/data-sources.md

In BigelowLab/namanl: nam218

NAM218 data-sources: forecasts, archived-forecast and analyses

NCEI provides multiple data access methods: thredds, FTP, HTTPS and HAS. We use the thredds catalog to access OpeNDAP resources using the ncdf4 R package.

NOTE as of this writing top level urls and variable names have changed twice since we started using NAM in 2016. It's not really possible (or meaningful) to maintain backwards compatibility since the server-side offerings change all served data. We skirt this issue by storing local subsets of the resources for select variable, and by separate packages for accessing online data and for accessing locally stored data.

Analyses aka namanl

An example

Note that these grids are projected Lamber Conformal Conic lcc. Data covers 2004-03 through present - typically lagging 'current' by 2 days. Forecasts are available for forecast statement times ftime = 0000, 0600, 1200, 1800 with look-ahead times ahead = 000, 001, 002, 002, 006

Y = NAM218('https://www.ncei.noaa.gov/thredds/dodsC/namanl/201802/20180219/namanl_218_20180219_0600_000.grb2')
Y
Reference Class: "NAM218RefClass"
  state: open
 file:  https://www.ncei.noaa.gov/thredds/dodsC/namanl/201802/20180219/namanl_218_20180219_0600_000.grb2
 VARS:
    LambertConformal_Projection
    reftime
    height_above_ground_layer_bounds [height_above_ground_layer_bounds_1,height_above_ground_layer]
    ...
    Dewpoint_temperature_height_above_ground [x,y,height_above_ground,time]
    Geopotential_height_isobaric [x,y,isobaric1,time]
    ...
    v-component_of_wind_tropopause [x,y,time]
    v-component_of_wind_planetary_boundary [x,y,time]
    v-component_of_wind_pressure_difference_layer [x,y,pressure_difference_layer2,time]
  DIMS:
    depth_below_surface[1]
    depth_below_surface_layer[4]
    ...
    sigma_layer[1]
    sigma_layer_bounds_1[2]
    time[1]
    x[614]
    y[428]

Forecasts aka nam218 come in two forms: archived and current

Archived Forecasts

An example

Note that these grids are projected Lamber Conformal Conic lcc. Data covers 2016-06 through present - typically lagging 'current' by 2 days. Forecasts are available for forecast statement times ftime = 0000, 0600, 1200, 1800 with look-ahead times ahead = (hourly) 000-036, (3 hourly) 039-084

Contents accessed using the NAM218 reference class and are arranged as shown above for Analyses

Current Forecasts

An example and more specifically we typically use the NAM every 3 hours fcst staring from 00Z

Grid node locations are given by lat,lon coordinates. We use the NAMcast reference object to handle this data source. Note that the variable names and content organization are different than for Analyses ans Archived Forecasts

uri = format(Sys.Date(),"http://nomads.ncep.noaa.gov/dods/nam/nam%Y%m%d/nam_00z" )
Z = NAMcast(uri)
Z
Reference Class: "NAMcastRefClass"
  state: open
file:  http://nomads.ncep.noaa.gov/dods/nam/nam20180221/nam_00z

 VARS:
    absvprs [lon,lat,lev,time]
    no4lftx180_0mb [lon,lat,time]
    acpcpsfc [lon,lat,time]
    ...
    weasdsfc [lon,lat,time]
    wiltsfc [lon,lat,time]

  DIMS:
    lat[443]
    lev[42]
    lon[913]
    time[29]

BigelowLab/namanl documentation built on Nov. 15, 2021, 3:11 p.m.