Jet Superposition and a Cut-off Low Behind a Rare Heavy Hailfall Episode in the United Arab Emirates (10&ndash;12 February 2024)

AlShamsi, Noor; Weston, Michael; Al Kaabi, Ahmed; VanderMerwe, Andrew; Al Mazrouei, Alya

doi:10.5194/egusphere-2025-6305

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https://doi.org/10.5194/egusphere-2025-6305

Preprints

12 Jan 2026

| 12 Jan 2026

Jet Superposition and a Cut-off Low Behind a Rare Heavy Hailfall Episode in the United Arab Emirates (10–12 February 2024)

Noor AlShamsi, Michael Weston, Ahmed Al Kaabi, Andrew VanderMerwe, and Alya Al Mazrouei

Abstract. Coupling between the polar and subtropical jet streams resulted in jet superposition and attendant upper-tropospheric divergence over the Arabian Peninsula, coincident with a southeastward-advancing Cut-Off Low (COL). On 12 February 2024, the associated convective system generated widespread, surface-verified hailfall across parts of the United Arab Emirates (UAE). This study examines the synoptic- and mesoscale evolution of this event using ECMWF operational analyses, CAMS reanalysis data, radiosonde soundings, satellite remote-sensing products, and radar-derived hail diagnostics. In view of the extensive regional dust plume present in the pre-convective environment, CAMS aerosol fields were analysed to assess the degree to which elevated dust layers modulated thermodynamic stability and moisture transport throughout the event. A COL developed south of Iraq, propagated southeastward, and subsequently interacted with a low-level baroclinic zone. Moisture advection from the Red Sea and the Arabian Sea was mediated by the Red Sea Trough (RST), thereby enhancing atmospheric instability. After an initial weakening stage, associated with mid-tropospheric drying and reduced low-level inflow, the convective system underwent re-intensification over the Arabian Gulf. Radiosonde observations from Abu Dhabi at 0000 UTC on 12 February indicated near-saturated conditions from the surface up to approximately 500 hPa, overlain by a comparatively dry mid-tropospheric layer. Concurrent EUMETSAT RGB composite imagery—optimized to depict dry-air intrusions and jet-related structures—exhibited upper-tropospheric signatures consistent with renewed deep convective development. Radar-derived hail products demonstrated that the period of most prolific hail production coincided with the convective system’s mature stage, during which Hail Mass Aloft (HMA, > 100 kilotons) and Vertically Integrated Hail Mass (VIHM, > 2 kg m⁻²) exceeded operational thresholds typically associated with a high probability of hail reaching the surface. The prevailing thermodynamic and microphysical environment was favourable for substantial hail deposition at the ground, whereas aerosol–radiation interactions appeared to be of secondary importance and did not exert a material influence on storm evolution relative to jet dynamics and moisture transport.

Received: 17 Dec 2025 – Discussion started: 12 Jan 2026

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Noor AlShamsi, Michael Weston, Ahmed Al Kaabi, Andrew VanderMerwe, and Alya Al Mazrouei

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6305', Anonymous Referee #1, 02 Feb 2026
Review of “Jet Superposition and a Cut-off Low Behind a Rare Heavy Hailfall Episode in the United Arab Emirates (10–12 February 2024)” – AlShamsi et al.
This study analyzes the synoptic conditions, environment, and radar-derived hail diagnostics for the 12 Feb 2024 hailstorm event over United Arab Emirates. The radar products indicate strong convection intensity consistent with observed hail on the ground. It is concluded that the storms occurred in an environment with low CAPE, aided by strong synoptic scale forcing, and that dust played a minor role.
An intense hail event in such an arid environment is interesting and worth studying. Unfortunately, I got the impression that the authors understanding of severe convective storms is insufficient, which resulted in several flaws in the analysis and interpretation of the results. Please see the general comments below, followed by some minor comments in case the authors decide to resubmit their study, which I encourage them to do after improving the main analysis.
General comments:
Lines 55-60 and conclusions: The possible roles of dust on hailstorms are highly complex, which seems a bit oversimplified in this study (see e.g., Varble et al. 2023, Brennan and Wilhelm 2024). The authors could solve this by including more literature and discussion. However, this also means that it is not easy to prove whether dust contributed in any way to the event studied here. The coarse dust dataset analyzed here is certainly not enough to conclude that dust was unimportant because microphysical processes cannot be investigated without convection-resolving models. I also have some doubts whether this dataset can accurately capture boundary layer dust concentrations, especially if local small-scale processes like haboobs are involved (lines 182-183).

Varble, A. C., Igel, A. L., Morrison, H., Grabowski, W. W., & Lebo, Z. J. (2023). Opinion: A critical evaluation of the evidence for aerosol invigoration of deep convection. Atmospheric Chemistry and Physics, 23(21), 13791–13808. https://doi.org/10.5194/acp-23-13791-2023

Brennan, K. P., & Wilhelm, L. (2024). Saharan dust linked to European hail events. EGUsphere, 2024, 1–19. https://doi.org/10.5194/egusphere-2024-3924

References are missing in several places: lines 71-73, lines 155-157, lines 181-183, lines 235-236, lines 271 (why is this diagnostic more accurate?), 373-374, Line 427, Lines 508-512

The authors need to be more accurate in their severe convective storm terminology. Most large hail is produced by supercells (e.g., Blair et al. 2017, Feldmann et al. 2025). The single track and rightward storm motion in Fig. 9 suggest that the main hail producer here also was a supercell, although it is hard to say based on the limited data shown. In some places, the authors also mention a single updraft, which would be consistent with a single-celled storm mode (line 625). However, in other places they use “MCS” (lines 534, 627), which implies multiple updraft regions. Elsewhere, the authors even seem to link the hailstorm evolution to the evolution of the whole synoptic system (line 359). I recommend the authors to improve their understanding of severe storm dynamics (e.g., Markowski and Richardson, chapters 7-9). Then, a much deeper analysis seems warranted to investigate the storm structure. For example, radar reflectivity fields every hour would be good to show to give the reader a general impression how the convection was structured and evolved.

Blair, S. F., Laflin, J. M., Cavanaugh, D. E., Sanders, K. J., Currens, S. R., Pullin, J. I., … Mallinson, H. M. (2017). High-resolution hail observations: Implications for NWS warning operations. Weather and Forecasting, 32(3), 1101–1119. https://doi.org/10.1175/WAF-D-16-0203.1

Feldmann, M., Blanc, M., Brennan, K. P., Thurnherr, I., Velasquez, P., Martius, O., & Schär, C. (2025). European supercell thunderstorms—A prevalent current threat and an increasing future hazard. Science Advances , 11(35), 1–12. https://doi.org/10.1126/sciadv.adx0513

Markowski, P., & Richardson, Y. (2010). Mesoscale meteorology in midlatitudes (Vol. 2). John Wiley and Sons.

Lines 401-404: Convection initiation is a complex process which in many cases involves rising thermals, orography, fronts, and upper-level lifting to different degrees. Please provide more evidence or remove such statements.

Line 443: The only sounding analyzed is from 00 UTC, so during the night. So it is not surprising that it shows a stable surface layer and no surface-based CAPE. However, CAPE can also be calculated for parcels originating at higher levels where they can become unstable (often used is most unstable CAPE). This would be more fitting given the assumption that the storms were elevated. It seems your interpretation that CAPE was low in your environment is only based on surface-based CAPE (Line 707-712).

Minor comments:
Lines 45-48: There is repeated content here so these lines could be removed.

Some parts seem a bit out of context or unnecessary in a scientific paper and could perhaps be removed: Lines 38-39, lines 109-115, lines 236-241, lines 373-374

1: There is no red star ; also, does the last sentence refer to (b), then maybe put it earlier

Lines 160-163: does this mean up to 3 day forecast times were used? why not use the closest analysis time which should be more accurate, no?

Lines 167: do you mean “coarse” not “course”?

Lines 253: remove repeated words

Section 2.4: most of this section seems unnecessary and could be incorporated into the previoues subsections. Only the part on hail reports gives a new component, so this could be put in single section maybe? Some ore context on the halsizes would also be insightful (see major comment).

Line 379: Should this method not be explained in the methods section?

Lines 397: I suggest using the symbol for theta instead on PT

Lines 399-401: I don't see a clear front, there is a gradient but not very localized, perhaps indicate with a line.

4: In most plots the like in this Fig. the times and heights don’t align which makes it hard to compare them. Of course this is not always possible so consider this small remark.

Lines 616-621: not sure what you mean, the plot only shows the height of maximum reflectivity, not if there is descent.
Citation: https://doi.org/10.5194/egusphere-2025-6305-RC1
- AC1: 'Reply on RC1', Noor AlShamsi, 05 May 2026
  
  Please see reply in attached pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6305-AC1
RC2:
'Comment on egusphere-2025-6305', Anonymous Referee #2, 25 Feb 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6305/egusphere-2025-6305-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6305-RC2
- AC2: 'Reply on RC2', Noor AlShamsi, 05 May 2026
  
  Please see reply in attached pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6305-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6305', Anonymous Referee #1, 02 Feb 2026
Review of “Jet Superposition and a Cut-off Low Behind a Rare Heavy Hailfall Episode in the United Arab Emirates (10–12 February 2024)” – AlShamsi et al.
This study analyzes the synoptic conditions, environment, and radar-derived hail diagnostics for the 12 Feb 2024 hailstorm event over United Arab Emirates. The radar products indicate strong convection intensity consistent with observed hail on the ground. It is concluded that the storms occurred in an environment with low CAPE, aided by strong synoptic scale forcing, and that dust played a minor role.
An intense hail event in such an arid environment is interesting and worth studying. Unfortunately, I got the impression that the authors understanding of severe convective storms is insufficient, which resulted in several flaws in the analysis and interpretation of the results. Please see the general comments below, followed by some minor comments in case the authors decide to resubmit their study, which I encourage them to do after improving the main analysis.
General comments:
Lines 55-60 and conclusions: The possible roles of dust on hailstorms are highly complex, which seems a bit oversimplified in this study (see e.g., Varble et al. 2023, Brennan and Wilhelm 2024). The authors could solve this by including more literature and discussion. However, this also means that it is not easy to prove whether dust contributed in any way to the event studied here. The coarse dust dataset analyzed here is certainly not enough to conclude that dust was unimportant because microphysical processes cannot be investigated without convection-resolving models. I also have some doubts whether this dataset can accurately capture boundary layer dust concentrations, especially if local small-scale processes like haboobs are involved (lines 182-183).

Varble, A. C., Igel, A. L., Morrison, H., Grabowski, W. W., & Lebo, Z. J. (2023). Opinion: A critical evaluation of the evidence for aerosol invigoration of deep convection. Atmospheric Chemistry and Physics, 23(21), 13791–13808. https://doi.org/10.5194/acp-23-13791-2023

Brennan, K. P., & Wilhelm, L. (2024). Saharan dust linked to European hail events. EGUsphere, 2024, 1–19. https://doi.org/10.5194/egusphere-2024-3924

References are missing in several places: lines 71-73, lines 155-157, lines 181-183, lines 235-236, lines 271 (why is this diagnostic more accurate?), 373-374, Line 427, Lines 508-512

The authors need to be more accurate in their severe convective storm terminology. Most large hail is produced by supercells (e.g., Blair et al. 2017, Feldmann et al. 2025). The single track and rightward storm motion in Fig. 9 suggest that the main hail producer here also was a supercell, although it is hard to say based on the limited data shown. In some places, the authors also mention a single updraft, which would be consistent with a single-celled storm mode (line 625). However, in other places they use “MCS” (lines 534, 627), which implies multiple updraft regions. Elsewhere, the authors even seem to link the hailstorm evolution to the evolution of the whole synoptic system (line 359). I recommend the authors to improve their understanding of severe storm dynamics (e.g., Markowski and Richardson, chapters 7-9). Then, a much deeper analysis seems warranted to investigate the storm structure. For example, radar reflectivity fields every hour would be good to show to give the reader a general impression how the convection was structured and evolved.

Blair, S. F., Laflin, J. M., Cavanaugh, D. E., Sanders, K. J., Currens, S. R., Pullin, J. I., … Mallinson, H. M. (2017). High-resolution hail observations: Implications for NWS warning operations. Weather and Forecasting, 32(3), 1101–1119. https://doi.org/10.1175/WAF-D-16-0203.1

Feldmann, M., Blanc, M., Brennan, K. P., Thurnherr, I., Velasquez, P., Martius, O., & Schär, C. (2025). European supercell thunderstorms—A prevalent current threat and an increasing future hazard. Science Advances , 11(35), 1–12. https://doi.org/10.1126/sciadv.adx0513

Markowski, P., & Richardson, Y. (2010). Mesoscale meteorology in midlatitudes (Vol. 2). John Wiley and Sons.

Lines 401-404: Convection initiation is a complex process which in many cases involves rising thermals, orography, fronts, and upper-level lifting to different degrees. Please provide more evidence or remove such statements.

Line 443: The only sounding analyzed is from 00 UTC, so during the night. So it is not surprising that it shows a stable surface layer and no surface-based CAPE. However, CAPE can also be calculated for parcels originating at higher levels where they can become unstable (often used is most unstable CAPE). This would be more fitting given the assumption that the storms were elevated. It seems your interpretation that CAPE was low in your environment is only based on surface-based CAPE (Line 707-712).

Minor comments:
Lines 45-48: There is repeated content here so these lines could be removed.

Some parts seem a bit out of context or unnecessary in a scientific paper and could perhaps be removed: Lines 38-39, lines 109-115, lines 236-241, lines 373-374

1: There is no red star ; also, does the last sentence refer to (b), then maybe put it earlier

Lines 160-163: does this mean up to 3 day forecast times were used? why not use the closest analysis time which should be more accurate, no?

Lines 167: do you mean “coarse” not “course”?

Lines 253: remove repeated words

Section 2.4: most of this section seems unnecessary and could be incorporated into the previoues subsections. Only the part on hail reports gives a new component, so this could be put in single section maybe? Some ore context on the halsizes would also be insightful (see major comment).

Line 379: Should this method not be explained in the methods section?

Lines 397: I suggest using the symbol for theta instead on PT

Lines 399-401: I don't see a clear front, there is a gradient but not very localized, perhaps indicate with a line.

4: In most plots the like in this Fig. the times and heights don’t align which makes it hard to compare them. Of course this is not always possible so consider this small remark.

Lines 616-621: not sure what you mean, the plot only shows the height of maximum reflectivity, not if there is descent.
Citation: https://doi.org/10.5194/egusphere-2025-6305-RC1
- AC1: 'Reply on RC1', Noor AlShamsi, 05 May 2026
  
  Please see reply in attached pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6305-AC1
RC2:
'Comment on egusphere-2025-6305', Anonymous Referee #2, 25 Feb 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6305/egusphere-2025-6305-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6305-RC2
- AC2: 'Reply on RC2', Noor AlShamsi, 05 May 2026
  
  Please see reply in attached pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6305-AC2

Noor AlShamsi, Michael Weston, Ahmed Al Kaabi, Andrew VanderMerwe, and Alya Al Mazrouei

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Short summary

This study investigates why a rare and damaging hailstorm occurred in the United Arab Emirates in February 2024. By combining weather models, satellite images, radar observations, and balloon measurements, we show that strong winds high in the atmosphere and increased moisture worked together to trigger severe storms in an otherwise dry region. These findings improve understanding of extreme weather risks and support better forecasting and preparedness in arid environments.


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