The GRIB 1.25 degree data set is sourced from the US NOAA/NWS GFS Model. The ‘thinned’ dataset means that the longitudinal points on the grid are ‘thinned’ as the polar regions are approached.
Forecast Content
Below is a summary of the flight planning data content provided for each forecast period and for each grid, where:
-
Level – Pressure level (hPa)
-
FL – Flight Level (100’s of feet AMSL unless otherwise noted)
-
U Wind – North component of wind (m/sec)
-
V Wind – West component of wind (m/sec)
-
Temp – Air Temperature (Degrees K)
-
RH – Relative Humidity (%)
-
Press – Air Pressure (hPa)
-
Hgt – Geopotential height (meters AMSL)
| Level | FL | U Wind | V Wind | Temp | RH | Press | Hgt |
|---|---|---|---|---|---|---|---|
|
MSL |
0 |
|
|
|
|
X |
|
|
SFC |
0 |
X |
X |
X |
X |
X |
|
|
1000 |
001 |
X |
X |
X |
X |
|
X |
Grid Resolution: 1.25 degree Latitude/Longitude grid in ICAO thinned format
Forecast Interval: 3 hours
Forecast Length: 36 hours (6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36 hour forecasts)
File Counts 1 file for each parameter
11 files for each forecast interval
11 forecast intervals
Total 121 files for each forecast update
Update Period:Every 6 hours
File Packaging and Bundling
The flight planning data is packaged as individual GRIB1 files named with the WMO Header that each has. Therefore, each file contains one parameter for one particular forecast period and atmospheric level. These files are then bundled into TGZ files for distribution.
File Bundle Naming Convention
The individual GRIB1 files are tar’ed together and then compressed by standard zip utility application for distribution. The naming convention of the tar’ed, zip file is:
Filename definition: KWBC<DD><HH>_<FF>.TGZ
Where: DD= Model Run Date Code
HH= Model Run Hour
FF= Forecast Code
Model Run-time Code:
00z ( Filename Code= 00 )
06z ( Filename Code= 06 )
12z ( Filename Code= 12 )
18z ( Filename Code= 18 )
There is one TGZ file for each each forecast hour.
Individual GRIB File Naming Convention
File Names and Packaging
The flight planning data is packaged in individual files, with one file for each GRIB bulletin. This means that the same filenames are reused with every 6 hourly update.
File Naming Convention
The flight planning files use a WMO Header file naming convention:
Filename definition: <M><P><G><I><LL>
Where: M= Model Code
P = Parameter Code
G= Grid Code
I = Forecast Interval Code
LL = Level Code
Model Code: H (always)
Grid Code: X
| Parameter Code (P) | Forecast Interval Code (I) | Level Code (LL) | |||
|---|---|---|---|---|---|
| Code | Description | Code | Description | Code | Description |
|
H |
Height (Geopotential) |
C |
6 hour forecast |
89 |
Mean Sea Level (MSL) |
|
R |
Relative Humidity |
D |
9 hour forecast |
98 |
Surface of the Earth |
|
T |
Temperature |
E |
12 hour forecast |
99 |
1000hPa |
|
U |
U (North) Wind Component |
F |
15 hour forecast |
|
|
|
V |
V (West) Wind Component |
G |
18 hour forecast |
|
|
|
P |
Pressure |
H |
21 hour forecast |
|
|
|
|
|
I |
24 hour forecast |
|
|
|
|
|
J |
27 hour forecast |
|
|
|
|
|
K |
30 hour forecast |
|
|
|
|
|
L |
33 hour forecast |
|
|
|
|
|
M |
36 hour forecast |
|
|
Each file is a single GRIB1 bulletin, with a marker at the head and at the end. The head marker is the ASCII text “GRIB”; the tail marker is a sequence of four ASCII 7’s, as in “7777”. See below. File structure
[start of file]
…..
“GRIB” … [GRIB content] … “7777”
…
“GRIB” … [GRIB content] … “7777”
…
[end of file]