Scheduled Downtime
On Friday 21 April 2023 @ 5pm MT, this website will be down for maintenance and expected to return online the morning of 24 April 2023 at the latest


This post was from a previous version of the WRF&MPAS-A Support Forum. New replies have been disabled and if you have follow up questions related to this post, then please start a new thread from the forum home page.


Dear Sir/Madam,

I am interested in how the two WRF variables of hail size, namely HAIL_MAXK1:description = "MAX HAIL DIAMETER K=1" and HAIL_MAX2D:description = "MAX HAIL DIAMETER ENTIRE COLUMN" are estimated in the WRF model? What methodology is used and where can I find relevant description? Was the maximum estimated size of hail (MESH) method applied? I am using WRF V3.9 and NSSL 2-moment scheme mp scheme (option 22).

Best regards,
You can take a look in the phys/module_diag_misc.F file to see how these are calculated.
Dear Colleges,

I am still interested in the difference between the HAIL_MAXK1 and HAIL_MAX2D WRF variables.
I have looked the the phys/module_diag_misc.F file as you suggested. However, the fortran code is quite difficult, and I was not able to understand the difference of estimation hail size by the two variables. In my simulation results the hail size estimated by the HAIL_MAX2D is strongly overestimated compared to that estimated from the HAIL_MAXK1 variable.

Can I ask you to provide more simple explanation why this does occur?

Best regards,
Can you attach the namelist.input file you're using, and some plots to show the problem you're seeing?
Please, find attached the maps for 11 hour forecasts of the HAIL_MAXK1 and HAIL_MAX2D at 3 km spatial resolution (d02). I am using the NSSL microphysics (namelist.input is attached).

Best regards,


  • HAIL_MAX2D.jpg
    354.6 KB · Views: 1,209
  • HAIL_MAXK1.jpg
    275.5 KB · Views: 1,208
  • namelist.input.txt
    6.2 KB · Views: 84
According to the code (phys/module_diag_misc.F), it looks like both of these variables are initialized to zero, and then the code loops over all tiles in the i/j/k directions, setting hail_max2d for every tile, all the way through the column, while hail_max1k is only calculated at the surface. We expect hail_max2d to be larger because this is the largest value found in the full column, which would be the value before any melting occurs. hail_max1k is the value taken at the surface, after a great deal of melting has taken place.
Thank you very much for the valuable and helpful clarifications! Then, I assume that it is better to consider hail_max1k when making comparisons with the ground-based hail observations (station observations).

Best regards,