Reply to reviews

							Reply to Reviewer #1

We thank reviewer #1 for their favorable review and comments that have helped improve
the manuscript. Responses to specific comments are provided below.

Major Comments

1. A summary figure comprised of surface and 700-hPa analyses at 1200 UTC 25 Mar
and 0000 UTC 26 Mar has been added.

2. Surface sensible heat flux difference plots for 1800 and 2100 UTC have been added.

3. I don’t think we need these, but we need to come up with a good explanation for why.

Minor Comments

1. All times in the paper are presented in UTC, which we believe is acceptable.

2. There is considerable spatial detail in the Intermountain orography, some of which is
evident in Fig. 2b. Thus, the smoothing does help to isolate scales that we wish to
emphasize. For examples of the impact of the boxcar filter, see Barnes et al. (1996).

3. Changed to “terrain following lowest η level” for clarity.

4. Given variations in topographic elevations, it is simply not possible to choose a
pressure level that best summarizes the processes in this case.

5. Changed to “net latent heating.”

6. Done.

7. Greg – I think here and elsewhere we need to better and consistently summarize the
processes contributing to the orographic warm pool, based in part on our more
comprehensive analysis.

8. Done. Greg-Let me know if the phrasing in each of the two trajectory sections makes
sense.

9. Added “with trajectories grouped based ending location and trajectory history.”

Reply to Reviewer #2

I don’t have the stomach to work on this yet. Suggest we get through the other 3 reviews,
write a response to Dave’s summary letter, and perhaps blow off a point by point reply.
In my view, his specific comments are petty and unprofessional.
Reply to Reviewer #3

We thank reviewer #3 for their constructive review and suggestions for improvements,
which we believe have led to an improved manuscript. Responses to specific comments
are below.

Major comments

1. Roughly half a page of material has now been added to address items requested.
GREG—Address and respond to the construction of the NOSIERRA terrain.

2. Changes in the height of the η surfaces are quite small except where the terrain as
changed. Interpolating to pressure or height surface has numerous disadvantages in
complex terrain. GEMPAK, Grads, and other software packages used to do this nearly
always smooth out the terrain and create artifacts that are not desirable. The technique
used here appears to be the best option conveniently available.

3. Substantial improvements have been made to the paper to address the deficiencies
noted here including discussion and figures examining: (a) diabatic heating rates from the
explicit moisture and cumulus parameterizations both in the orographic precipitation
region and downstream of the Sierra Nevada, (b) thermodynamic budgets and vertical
positioning of trajectories, etc. With regards to turbulent mixing in downslope winds, it
is highly localized to very near the Sierra Nevada (see cross section figures) and we have
opted not to emphasize it in the text.

Minor comments

1. Done (see above).

2. GREG…ADD THIS SEE 1 ABOVE.

3. I’ve forgotten what this was. I think you discovered it Greg. Can you recall?

4. A major section describing the airflow has now been added.

5. This section has been beefed up substantially and includes discussion of diabatic
temperature tendencies.

6. It was not a goal of this study to detail out the airmass transformation process in this
case. Here and elsewhere we mention airmass scrambling as a component of airmass
transformation so its definition is clear. Nevertheless, we have added a bit more
discussion of the thermodynamic history of trajectories that traverse the Sierra and
terminate at 2100 UTC.
7. See response to major comment 2 above. The bottom line is that there are problems
that arise from this approach as well. We believe the current approach is the best option
available.

8. Additional information with regards to the pressure and thermodynamic history of the
parcels is now presented and compared.

9. Additional information with regards to surface heat fluxes and precipitation-related
diabatic heating tendencies has now been included.

10. This issue is now addressed with the newly added trajectory section.

11. Greg: We didn’t do this. I’m not sure I want to add this, but we need to respond. Can
you look into it?

12. 850-hPa. Added to figure caption. Great catch!

13. Greg: Provide a response to this once you’ve updated the trajectories.

14. Thoughts Greg? If we do this, it has to be done really well. You might respond that
we hesitate to use such a figure because this is a single event and such figures are often
used as a generalized conceptual model.
Reply to Reviewer C

Thanks Dave for finding the time to perform a full review of this manuscript. Please see
the responses to your comments below.

MAJOR COMMENTS:

1. Frontal speeds in m/s added in parentheses throughout the manuscript.

2. Comment is unclear. Shafer et al. (2006) is cited in the text and the reference list, but
neither Hoffman (1995) nor Reynolds and Kuciauskas (1988) are cited anywhere in the
paper or included in the reference list. As such, the paper appears to be fine.

3. Reference cited.

4. This is a good idea. We have added a sentence on Schumacher et al.

5. Dickinson and Knight (1999) is the relevant reference, and this sentence is part of the
discussion of that paper, which begins a few lines above. We’ve decided to not make a
change as it seems OK as is.

6. “and” changed to “and/or.”

7. With such a well developed confluence zone, the axis of dilatation can be inferred
from the wind barbs. Other authors have done this previously in the literature (e.g.,
Bracken and Bosart 2000, sec. 4d). Hence, we’ve left as is in part to keep the figure
presentation straightforward without excessive annotation.

8. We have included the Martin reference because it is readily accessible and easier for
the younger generation to access. In turn, Martin references the relevant early work by
Bergeron and Petterssen.

9. Discussion of the apparent forward slope is relevant to the structure of the DT, which
is located above 500 hPa. The occlusion, which extends only to 500 hPa, is “nearly
vertically stacked” as noted in the text. The text is consistent with the analyzed occlusion
in Fig. 11d.

10. We are familiar with Reeder and Tory (2005) and Tory and Reeder (2005) but have
chosen not to reference it here, primarily because our main emphasis is on the discrete
propagation rather than the influence of the CBL.

11. As noted in the text, the tilting frontogenesis does not appear to contribute
significantly to the observed frontal development, which is why we have called the sum
of the horizontal deformation and divergence the kinematic frontogenesis.

12. Yes it can be estimated, but it is a difficult problem fraught with uncertainty. We
could use estimates from the NAM or NARR, but those are also model derived and only
as good as their precipitation forecast or analysis. We use surface observations and/or
gridded analyses, but such estimates are also problematic and we can only estimate the
net diabatic heating, not separate it into its individual components. Given these problems
and the desire to keep the paper on track, we have not included this estimate.

13. Reference to Palmén and Newton (1969) added.

14. Shafer and Steenburgh (2008) is referenced because it is the first and only
comprehensive climatology of cold fronts over the Intermountain West. It in turn
references other relevant Intermountain cold front papers. We are inclined not to make
changes.

15. Winds are not included with the soundings because they are not discussed in the text.

MINOR COMMENTS:

1. This sounds like a good idea, but is a difficult comparison to make, simply because of
the wind shear that exists in the post frontal environment and the inherent spatial and
temporal variability. For example, the 0Z 26 Mar Reno sounding is the closest in the
post-frontal environment. Wind speeds varied from 15 m/s near the surface to 25 m/s at
700 hPa. Which level are we to use for comparison? Do we use the mean? Is the Reno
sounding the best to use? The selection is somewhat arbitrary. Instead, we have included
a comparison with the speed of the upper-level trough as this is less arbitrary, more
dynamically relevant, and enables us to clearly illustrate the discrete nature. For these
reasons, we have elected not to include a comparison with wind speed aloft in the paper.

2. Good catch. This is the Nevada-Oregon border. Figure 12c is now referenced.

3. This sentence was very unclear. We have added changed “baroclinic zone” to “pre-
occlusion baroclinic zone” for lucidity.

4. Changed to “without a sharp temperature transition.”
5. Corrected.

6. The acknowledgements as written at the end of the manuscript are phrased as
requested by the University of Wyoming.