Revision as of 11:23, 31 May 2012

NOAA GFS winds in VR and VORG games

Winds used in the VR and VORG games are from NOAA's Global Forecast System

NOAA GFS winds can be obtained from application:
http://nomads.ncep.noaa.gov/cgi-bin/filter_gfs.pl

This is a 1 degree resolution forecast, with numerous weather variables, spaced 3 hours and up to 384h. This data is fabricated by a of weather simulation program, using laws of physics and inputs from instruments [which?]. Server responses are in grib 2 format. Variable "wind at 10m" is used. Winds are given by its two U and V components, in latitude/longitude directions. Winds at 10m altitude are used.

VORG 11-12 winds for 06Z are extracted from folder YYYYDDMM00, forecast 06.
Time 0 comes from file gfs.t00z.pgrbf06.grib2, time 12 from gfs.t00z.pgrbf18.grib2 and so on.
Winds for 18Z are extracted from folder YYYYDDMM12. Time 0 comes from file gfs.t12z.pgrbf06.grib2, time 12 from gfs.t12z.pgrbf18.grib2 and so on.

Note that a new folder is created by NOAA every 6 hours. Only two of the four daily simulations are used in the game. GFS files are added gradually to latest folder during publication. Publication schedule is:

 forecast      pub time
      
  00         03:30 - 04:30Z    <-- used 

  06         09:30 - 10:30Z

  12         15:30 - 16:30Z    <-- used 

  18         21:30 - 22:30Z

This means forecast 0 is already history when published, and is meant to be used as an interpolation point (in time). Game wind updates are at 6Z and 18Z, approx 2 hours after GFS release.

NOAA game wind downloads in vrtool

Current wind (forecast 00) is the same as the game's ( file 06 from folders 00Z and 12Z ). Future winds (12,24,36 etc) are taken from the latest file available from NOAA at the time of the download. Note that vrtool future winds (12,24,etc) are different from game's most of the time, because they are taken from a newer predictions (probably better).

The table below shows which files are downloaded for each forecast:

 time        NOAA folder    file	   
 0Z-4Z  - latest=18z of previous day (Dt-1)
   00        (Dt-1)12z      file=06 
   12        (Dt-1)18z      file=12   
   24        (Dt-1)18z      file=24   
 4Z-6Z  - forecast 00z becomes available
   00        (Dt-1)12z      file=06 
   12        (Dt  )00z      file=06   
   24        (Dt  )00z      file=18   
 6Z-10Z - Game publication 1
   00        (Dt  )00z      file=06 
   12        (Dt  )00z      file=18   
   24        (Dt  )00z      file=30   
 10Z-16Z - forecast 06z available
   00        (Dt  )00z      file=06 
   12        (Dt  )06z      file=12   
   24        (Dt  )06z      file=24   
 16Z-18Z - forecast 12z available
   00        (Dt  )00z      file=06 
   12        (Dt  )12z      file=06   
   24        (Dt  )12z      file=18   
 18Z-22Z - Game publication 2
   00        (Dt  )12z      file=06 
   12        (Dt  )12z      file=18   
   24        (Dt  )12z      file=30   
 22Z-24Z- forecast 18z available
   00        (Dt  )12z      file=06 
   12        (Dt  )18z      file=12   
   24        (Dt  )18z      file=24   

If you are using weather routing or the track designer, you should update NOAA winds right after the following times: 4Z, 6Z, 10Z, 16Z, 18Z, 22Z (Z=GMT) and recalculate your route. Winds for 4Z and 16Z are particularly important, because the 12h forecast is an accurate preview of winds that will be used in the game two hours latter.

Tip: This 2 hour advance in relation to game wind shift can be even larger. This is because NOAA file publication is gradual. Files start to be published 30 minutes before those times, and the folder is completed (up to 384h) about one hour later. So one could advance the computer clock some 20 minutes and get a peek in the next winds.