From time to time, NCEP upgrades GFS products and this may have effects on running WRF in forecast or analysis mode.
For example, NCEP upgraded GFS products from version 14 to 15.1 beginning with the 1200 UTC run on June 12, 2019. A similar change happened May 11, 2016 when vertical levels changed from 27 to 32.
Such upgrades do not affect forecasts when they happen if WPS/WRF 4.0 or higher is used. Using WRF 3.9 or older, requires to upgrade ungrib binary to v4.0 or higher.
However, a problem still exists if these products are used for analysis runs (i.e. on periods in the past), for example using the FNL (Final) Operational Global Analysis dataset at 1deg resolution. In fact, such changes typically happen in the middle of the day and this prevents to run WRF across the day when the change happens.
Analysis runs are the basis for the production of meteorological inputs for air quality models.
The solution to run WRF for the day when the GFS product changes is to prepare a set of grib files that are consistent for the whole simulation period (spin-up hours + day of change).
For example, in order to run WFR with FNL data to simulate May 11, 2016 when the vertical levels changed fron 27 to 32 at 12 UTC (new upper isobaric surfaces 7, 5, 3, 2, 1 mb), it is necessary to have all the files with 27 levels from - say - 18 UTC of May 10, 2016 to 00 UTC of May 13, 2016. This allows to make a 30-hour run (6 hours spin-up to be discarded + 24 hours analysis).
In order to run WFR with FNL data to simulate June 12, 2019 when the vertical levels changed fron 32 to 34 at 12 UTC, it is necessary to have all the files with 32 levels from - say - 18 UTC of June 11, 2019 to 00 UTC of June 13, 2019. This allows to make a 30-hour run (6 hours spin-up to be discarded + 24 hours analysis).
For this specific update of June 12, 2019, it is necessary to exclude the new lowest isobaric surface 0.2 mb and the new intermediate isobaric surfaces 40 mb and 15 mb.
This requires to create a dataset with the same number of vertical levels making a "Customizable data request" on NCEP website.
The Customizable data request form allows to select all vertical levels but the three levels 40, 15, and 0.2 mb.
Once the request is processed a download link is made available via email and it is then possible to download a tar file with the GRIB2 files to be used with WPS.