We thank the reviewer for their helpful comments in improving the manuscript. Our
responses are below. The reviewer’s original comments are in blue.
1. line 43: Ref. to Fig. 1. It would be helpful if Duanesburg and Delanson, NY were
indicated on the map.
The location of Duanesburg, NY has been added to the map. Delanson, NY is adjacent to
Duanesburg, NY.
2. Line 96: It would be helpful if the magnitude of the differential velocity were
converted into vertical vorticity, subject to the appropriate assumptions about the
symmetry of the wind field. Differential velocities without a horizontal scale are more
difficult to interpret.
We agree with the potential advantages of using vertical vorticity since it factors in a
horizontal scale. However, the reason for using differential velocity is largely operational,
since it is what NWS forecasters commonly use to diagnose mesocyclone strength. My
strong preference is to use differential velocity due to the collaborative nature of this
work with the NWS. The differential velocity is also a prevalent metric in existing
literature on supercells and tornadoes.
3. Line 104: How do we reconcile the statement that the “cell strengthened as it
descended off the higher terrain…” with the earlier statement in lines 59 – 60 that
“…weakening occurs in regions of downslope flow.” I gather that the motion of the
storm in the downslope direction is not the same as downslope motion at the surface. Was
there not any ground-relative downslope motion in the storm?
The ground-relative flow is the important aspect here (Markowski and Dotzek 2011), not
whether the storm is moving from higher terrain to lower terrain. “Descended” has been
replaced with “moved” in order to avoid confusion.
4. Line 123: “subtle” is a word commonly used euphemistically. How about “virtually
nonexistent”? I am trying to be subtle…
“Virtual nonexistent” sounds strange. I replaced “subtle” with “ambiguous.” It matches
with the “unexpected” nature of the event from a predictive skill standpoint.
5. Line 126: It would be useful to mark the axis of the trough with a dashed line in the
figure.
Done.
6. Lines 151 – 153: This statement needs to be backed up by the observational data. How
was the EML modified? Please be more specific. How do you know that weak warm
advection triggered the earlier convection? This seems like a hypothesis rather than a
conclusion.
Since evidence is not shown in any of the figures and this statement is a minor point, it
has been removed.
7. Line 161: “remained in place” is jargon. How about “was stationary”?
The sentence was modified to, “To the east of the boundary, low clouds inhibited surface
heating.”
8. Line 217: “lift ahead of the upper-level shortwave” conflicts with the trajectory
analysis, which shows descending air or only very slowly ascending air (Fig. 6).
Comment? If trajectories were computed beginning farther east, would the result over
NY State have shown rising air parcels?
The trajectories in Fig. 6 do show lift ahead of the shortwave trough. From Michigan
eastward, the lower trajectory rose from 850 hPa to 780 hPa, and the upper trajectory rose
from 590 hPa to 550 hPa. By no means was the lift tremendous, but it was present.
HYSPLIT trajectories initiated farther east also showed the same pattern.
9. Lines 223 – 228: So the deviate motion could not have been due to storm rotation?
The authors have presented hypotheses that they cannot test. This reviewer, however,
thinks that deviate motion due to rotation, even if it were small, is also a possible
hypothesis.
Agreed. We have added this possibility: “One possible mechanism for the deviate motion
is dynamic pressure perturbation gradients.” Additionally, we have added hodographs
(Fig. 9) with the Bunkers et al. (2014) and observed storm motion to support this
hypothesis.
10. Line 246: It should be noted how the streamwise vorticity was generated:
baroclinally.
Done.
11. Line 262: Upslope of only 0.2 m s-1 is pretty miniscule. How can this very small
upslope component be significant? What effect could it have?
The magnitude of upslope is similar to the idealized study of Markowski and Dotzek
(2011), which had upslope flow magnitudes around 0.1 m s-1. Still, these values are small
compared to a convective updraft. The main effect of the upslope flow is to increase the
relative humidity in the lower troposphere. This effect is now discussed in the
manuscript. A time series of the upslope flow and 850 hPa relative humidity is given in
Fig. 10b.
121. Line 297: A reference for a ZDR column belongs here.
Added the Conway and Zrnic (1993) reference here
13. Lines 327 – 329: What is the false alarm rate for the reduction in lightning flashes
just prior to tornadogeneis? I. e., are there many instances when there is a reduction in
flashes in a rip-snorting supercell but no tornadogenesis?
This is a good question. The Perez et al. (1997) study only focuses on probability of
detection and limits the cases to F4 and F5 tornadoes. No study, as far as we know, has
been conducted to assess the false alarm rate, but it probably would be quite high. As
Perez et al. (1997) states, using lightning alone as a predictor for tornadogenesis is not a
good idea.
14. Line 337: Here and in a few other places: A statement is given, followed by several
sentences, at least, before the statement is backed up with evidence. It is stated that there
was a rear-to-front surge, but the evidence for this is not mentioned until lines 343 – 344,
and at that, no Doppler wind data are presented. This structure of the paragraph can
confound the reader. I suggest it be re-written and Doppler wind data shown to back up
the statement.
Since the DRC is not the focus of the paper and an expansion of the analysis would
require substantial work, we have opted to remove this paragraph and the corresponding
figure from the manuscript. This action was also based off a comment from another
reviewer.
15. Line 345: Nothing is shown to indicate that a TVS (tornadic vortex signature) was
indeed present.
This sentence has been removed. “Tornadic debris signature” is more appropriate.
16. Line 349: What is the evidence that there was a rear-flank downdraft? Was vertical
velocity computed?
No vertical velocities were computed, but we infer the presence of a RFD from the
reflectivity signatures and evolution of the storm structure. The final two sentences have
been modified to not be as definitive given the lack of vertical velocity data: “Convection
along the inferred rear flank downdraft appeared as a leading arc of >40 dBZ echos
extending from the east side of the hook echo back toward the west. Soon after, the arc of
convection surged toward the southeast, occluding the tornado. The tornado finally
dissipated at 1955 UTC.”
17. Lines 364 – 368: This section perhaps raises a more major issue: The authors should
make a back-of-the envelope estimate of how much the surface pressure might fall given
the observed/estimated changes in temperature. Also, the contribution to the ageostrophic
wind should also be estimated.
The surface pressure change due to the observed change in virtual temperature from 1530
to 1830 UTC at KNY0 is estimated using the following formula derived from hydrostatic
balance and the ideal gas law, including virtual effects:
𝑝! = 𝑝! exp !! !!
𝑇! 𝑑𝑧
! !
!
,
where ps is the surface pressure, po is the pressure at some given level, g is the
gravitational acceleration, R is the gas constant for dry air, zo is the height of po, and Tv is
the virtual temperature. We assume a range of lapse rates from 6.5° to 10°C km-1 in order
to express Tv as a linear function of height, fixed by the observed surface Tv at KNY0. po
and zo are chosen to either be 850 hPa or 900 hPa, with the height of the pressure surface
given by the 1200 UTC KALB sounding.
Tv at KNY0 is 17.8°C at 1530 UTC and 22.0°C at 1830 UTC. Given the possible
combinations of parameters above, we estimate that the change in pressure due to the rise
in virtual temperature is approximately -1.5 to -2.5 hPa, which is consistent with the
pressure fall noted at KNY0. One caveat is that we assume zo does not change, but it
should increase as the temperature rises, so the pressure falls calculated using the formula
above are likely too large in magnitude. Since there is a lot of uncertainty in this
calculation and it requires some strong assumptions, we prefer to leave this calculation to
the response here. In the manuscript, we note, “The pressure drop at KNY0 was
consistent with what would be expected from hydrostatic balance adjustment due to the
observed temperature change, assuming the thermal and mass profiles above the
boundary layer were steady.”
We also attempted to calculate the ageostrophic wind response to the horizontal gradient
in pressure tendency using Eq. 4.1.103 from Bluestein (1991):
!
𝑣! = − !!! ∇
!"
!"
,
where va is the ageostrophic wind, ρ is the density, f is the Coriolis parameter. The values
obtained from the observed pressure tendencies between KNY0 and KALB/KSCH were 40 to -67 m s-1, which is of course absurd. The simple explanation for the large
discrepancy is that the equation above is valid for the synoptic scale and does not
consider frictional and turbulent effects, which are large in the boundary layer. Hence,
there is no simple way to calculate the ageostrophic wind contribution in this case from
traditional synoptic-scale tools. However, qualitatively, the equation above does indicate
there must be a tendency for the ageostrophic wind to be directed up the Mohawk Valley.
18. Same as my comment #4: “subtle” is a bit cagy! How about, again, “virtually
nonexistent”?
“Subtle” has been not so subtly stricken from the manuscript.
19. Line 392: As the cool air flowed up Mohawk Valley, it slowed, as noted. A Froude
number analysis might be in order here.
Froude numbers at 1800 UTC are calculated using HRRR data at KSCH. Given a
specified depth, h, we calculate the static stability, N, and mean zonal wind, u, over this
layer. The Froude number is estimated from these three variables. The Froude number
was supercritical (>1) for depths less than 500 m and subcritical (<1) for depths greater
than 500 m, indicating that the cool, moist air would be able to spread up the Mohawk
River and adjacent lowlands all the way east to the boundary, but would be blocked by
the higher terrain of the Catskills and Adirondacks. We have added this analysis to the
manuscript.
20. Line 405: I may have missed it, but if not, please provide a reference for the RTMA.
Added the De Pondeca et al. (2011) reference
21. Line 420: “…allowing moisture to pool below it.” Again, jargon. Please be more
specific.
Replaced with “…allowing the horizontal moisture flux convergence to increase the
moisture below the cap.”
22. Line 421: Suggest changing “…EML that was…” to “…EML as was …” This looks
like a typo.
Done.
23. Line 450: It is not good form, in my opinion, to begin a sentence with a number. At
least I was taught not to do this! Also, is “values” really necessary? I suggest deleting it
and changing “were” to “was.”
Changed to, “The 0--1 km storm relative helicity was generally…”
24. n Fig. 10, is the reflectivity core really descending, or instead is just
precipitation dumping out of the new, nearby cell?
The old Fig. 10 has been removed from the manuscript.