Review of “Effect of secondary ice production processes on the simulation of ice pellets using the predicted particle properties microphysics scheme” by Lachapelle et al.

Recommendation: Accept with minor edits

Summary: This paper addresses advances to an NWP microphysics scheme that may allow for better prediction of ice pellets (PL).  Specifically, it shows that secondary ice production (SIP) appears to have been pivotal for transitioning falling hydrometeors from all liquid to all ice, thus resulting in PL.  Two processes that enhance the conversion from liquid to ice are parameterized in this paper (fragmentation of freezing drops FFD and Hallet-Mossep HM).  Additional modifications were made to the FFD code to yield more representative results.  This is a strong paper. It’s clear and concise and the science is compelling.  I have only minor thoughts below.    

1. Line 134: It says the two SIP processes are studied independently (as opposed to simultaneously including both FFD and HM in the same experiment) because that requires the default implementation of HM to be modified. I don’t understand why HM would have to be modified. It is described as being a different physical process than FFD, so up to this point I thought these were 2 separate processes.  Can the authors clarify?
2. Line 138: The paper describes the number of ice splinters produced per unit of rain at a certain temperature range and how it changes outward from there. Is there a citation for this is or is this something the authors of this paper prescribed?  If the latter, how sensitive are the results to the number of ice splinters?
3. I’m confused by the Appendices. It’s not clear to me why they’re included in the paper as appendices.  I think Appendix A could be moved into Section 2.  I struggled with Appendix B since its first referenced on line 155, before we know anything about the case study or experiments.  I think the sensitivity tests in appendix B give some broader context to the results of this paper that merit putting this in the main body of the paper.  And, like above, I think the content in Appendix C could just be put in the main part of the paper as well.  Both Appendices B and C include good content, but having them as appendices confuses me as a reader.  Moving that content into the main body of the paper will strengthen the story line and give greater import to the creative work presented in these parts of the paper. 
4. Paragraph starting at line 220: I like the air parcel trajectory approach, but I’d like to know to what degree that trajectory bobs up and down in the vertical. I think a simple way to address this is to add an inset to Fig. 1 that shows a vertical cross section along the trajectory that shows the position of the parcels from each experiment as a function of time/location.  That way the reader can assess whether the changes made to the microphysics scheme impact the rate at which the parcels are advected and whether their vertical ascent/descent differs. 
5. I find Figs. 3,4,5 difficult to read. It’s a lot of skinny lines and some colors are difficult to distinguish and some of the lines overlay each other enough to make it hard for the reader. I wonder if the authors would consider converting this to a “chicklet plot” for the ptype forecasts.  This would be a lot easier for the reader to interpret.  It would require putting the rates in a separate panel, but I think it’s worth the extra real estate to make a clearer graphic.
6. It’s interesting to me that in Fig. 6 the precip rate varies between the experiments (this is also evident in Figs. 3-5). Can the authors add some thoughts to the paper on why this is?
7. I see there’s MMR data that shows the vertical level at which the transition from FZRA to PL occurs (line 291). Out of curiosity, have the authors tried to reproduce synthetic MMR data from the simulation to see if the transition from FZRA to PL in the vertical is accurately handled by the FFD experiments?