The snow storm of 8 March 2010 in Catalonia (Spain): a paradigmatic wet-snow event with a high societal impact

Abstract. A heavy precipitation event swept over Catalonia (NE Spain) on 8 March 2010, with a total amount that exceeded 100 mm locally and snowfall of more than 60 cm near the coast. Unusual for this region and at this time of the year, this snowfall event affected mainly the coastal region and was accompanied by thunderstorms and strong wind gusts in some areas. Most of the damage was due to "wet snow", a kind of snow that favours accretion on power lines and causes line-breaking and subsequent interruption of the electricity supply. This paper conducts an interdisciplinary analysis of the event to show its great societal impact and the role played by the recently developed social networks (it has been called the first "Snowfall 2.0"), as well to analyse the meteorological factors associated with the major damage, and to propose an indicator that could summarise them. With this aim, the paper introduces the event and its societal impact and compares it with other important snowfalls that have affected the Catalan coast, using the PRESSGAMA database. The second part of the paper shows the event's main meteorological features and analyses the near-surface atmospheric variables responsible for the major damage through the application of the SAFRAN (Système d'analyse fournissant des renseignements atmosphériques à la neige) mesoscale analysis, which, together with the proposed "wind, wet-snow index" (WWSI), allows to estimate the severity of the event. This snow storm provides further evidence of our vulnerability to natural hazards and highlights the importance of a multidisciplinary approach in analysing societal impact and the meteorological factors responsible for this kind of event.

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Strong Cross-Barrier Flow under Stable Conditions Producing Intense Winter Orographic Precipitation: A Case Study over the Subtropical Central Andes

Weather and Forecasting ◽

10.1175/2009waf2222168.1 ◽

2009 ◽

Vol 24 (4) ◽

pp. 1009-1031 ◽

Cited By ~ 22

Author(s):

Maximiliano Viale ◽

Federico A. Norte

Keyword(s):

Heavy Precipitation ◽

Stable Stratification ◽

Central Andes ◽

Precipitation Event ◽

Windward Side ◽

Orographic Precipitation ◽

Near Surface ◽

Low Level ◽

Precipitation Enhancement ◽

Subtropical Central Andes

Abstract The most intense orographic precipitation event over the subtropical central Andes (36°–30°S) during winter 2005 was examined using observational data and a regional model simulation. The Eta-Programa Regional de Meteorología (PRM) model forecast was evaluated and used to explore the airflow structure that generated this heavy precipitation event, with a focus on orographic influences. Even though the model did not realistically reproduce any near-surface variables, nor the precipitation shadow in the leeside lowlands, its reliable forecast of heavy precipitation over the windward side and the wind fields suggests that it can be used as a valuable forecasting tool for such events in the region. The synoptic flow of the 26–29 August 2005 storm responded to a well-defined dipole from low to upper levels with anomalous low (high) geopotential heights at midlatitudes (subtropical) latitudes located off the southeast Pacific coast, resulting in a large meridional geopotential height gradient that drove a strong anomalous cross-barrier flow. Precipitation enhancement in the Andes was observed during the entire event; however, the highest rates were in the prefrontal sector under the low-level stable stratification and cross-barrier winds exceeding 2.5 standard deviations (σ) from the climatological monthly mean. The combination of strong cross-mountain winds with the stable stratification in the air mass of a frontal system, impinging on the high Andes range, appears to be the major factor in determining the flow structure that produced the pattern of precipitation enhancement, with uplift maximized near mountaintops and low-level blocking upwindleading to the formation of a low-level along-barrier jet. Additionally, only the upstream wind anomalies for the 15 heaviest events over a 10-yr (1967–76) period were investigated. They exhibited strong anomalous northwesterly winds for 14 of the 15 events, whereas for the remaining event there were no available observations to evaluate. Thus, these anomalies may also be exploited for forecasting capabilities.

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Dependence of Predictability of Precipitation in the Northwestern Mediterranean Coastal Region on the Strength of Synoptic Control

10.5194/acp-2020-508 ◽

2020 ◽

Author(s):

Christian Keil ◽

Lucie Chabert ◽

Olivier Nuissier ◽

Laure Raynaud

Keyword(s):

Coastal Region ◽

Heavy Precipitation ◽

Forecast Model ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Precipitation Characteristics ◽

Synoptic Forcing ◽

Convective Adjustment ◽

Forecast Quality

Abstract. The weather regime dependent predictability of precipitation in the convection permitting kilometric scale AROME-EPS is examined for the entire HyMeX SOP1 employing the convective adjustment timescale. This diagnostic quantifies variations in synoptic forcing on precipitation and is associated with different precipitation characteristics, forecast skill and predictability. During strong synoptic control, which is dominating the weather on 80 % of the days in the 2-months period, the domain integrated precipitation predictability assessed with the normalized ensemble standard deviation is above average, the wet bias is smaller and the forecast quality is generally better. In contrast, the spatial forecast quality of most intense precipitation in the afternoon, as quantified with its 95th percentiles, is superior during weakly forced synoptic regimes. The study also considers a prominent heavy precipitation event that occurred during the NAWDEX field campaign in the same region, and the predictability during this event is compared with the events that occurred during HyMeX. It is shown that the unconditional evaluation of precipitation widely parallels the strongly forced weather type evaluation and obscures forecast model characteristics typical for weak control.

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Effects of weather events on X-SAR returns from ice fields: case-study of Hielo Patagónico Sur, South America

Annals of Glaciology ◽

10.3189/s0260305500012465 ◽

1997 ◽

Vol 24 ◽

pp. 367-374 ◽

Cited By ~ 1

Author(s):

Richard R. Forster ◽

Laurence C. Smith ◽

Bryan L. Isacks

Keyword(s):

South America ◽

Space Shuttle ◽

Temperature Drop ◽

Precipitation Event ◽

Glacier Surface ◽

Abrupt Decrease ◽

Near Surface ◽

Surface Conditions ◽

Southern Patagonia ◽

Wet Snow

The space-shuttle-based SIR-C/X-SAR synthetic aperture radar (SAR) imaged part of Hielo Patagónico Sur (HPS; southern Patagonia ice field, South America) for five successive days during missions in April and October 1994. A significant meteorological event occurred during each mission, including a major storm in April and a sharp temperature decrease in October. Changes in backscatter are observed for both episodes in X-SAR returns from the mid-portions of one of the two large outlet glaciers in the study area. Ground-station and satellite meteorological, and hydrological data are combined with the daily X-SAR images to interpret changes in glacier surface conditions caused by meteorological events. Effects interpreted from the April storm are (1) wind- and precipitation-influenced surface roughening of a wet snowpack, and (2) the deposition of new wet snow at lower elevation and its subsequent retreat up-glacier. An abrupt decrease in regional temperature during October is thought to reduce the snow wetness and increase grain-size. The changes in the radar-defined glacier zones due to the April precipitation event are subtle, while the October temperature drop causes significant backscatter increases. Our results suggest that trends in HPS glacier surface and near-surface conditions observable from spaceborne SARs are not significantly masked by precipitation events.

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Effects of weather events on X-SAR returns from ice fields: case-study of Hielo Patagónico Sur, South America

Annals of Glaciology ◽

10.1017/s0260305500012465 ◽

1997 ◽

Vol 24 ◽

pp. 367-374 ◽

Cited By ~ 8

Author(s):

Richard R. Forster ◽

Laurence C. Smith ◽

Bryan L. Isacks

Keyword(s):

South America ◽

Space Shuttle ◽

Temperature Drop ◽

Precipitation Event ◽

Glacier Surface ◽

Abrupt Decrease ◽

Near Surface ◽

Surface Conditions ◽

Southern Patagonia ◽

Wet Snow

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Improving the detailing of atmospheric processes modelling using the Polar WRF model: a case study of a heavy rainfall event at the Akademik Vernadsky station

Ukrainian Antarctic Journal ◽

10.33275/1727-7485.2.2020.650 ◽

2020 ◽

pp. 26-41

Author(s):

D. Pishniak ◽

◽

B. Beznoshchenko ◽

Keyword(s):

Surface Temperature ◽

Antarctic Peninsula ◽

Precipitation Amount ◽

Heavy Precipitation ◽

Horizontal Resolution ◽

Precipitation Event ◽

Heavy Rainfall Event ◽

In Situ Observation ◽

Near Surface ◽

The Antarctic

The Antarctic Peninsula region is of growing interest due to the regional climate change features and related atmospheric circulation patterns. The regional mesoscale atmospheric model Polar Weather Research and Forecasting (WRF) v4.1.1 was used in this research to study a heavy precipitation event over the Ukrainian Antarctic Akademik Vernadsky station region (Antarctic Peninsula). The passage of the cyclone over the Antarctic Peninsula as a typical synoptic process as well as a case of the daily precipitation maximum amount of 2018 were chosen for investigation in this research. The estimation of the modelling quality and downscaling was done by comparing the obtained results with in-situ observation at the Akademik Vernadsky station and cross-domain tracking of average meteorological values and their deviation. The concept of the nested domains allowed to increase the horizontal resolution of the simulated atmosphere up to 1 km and to reproduce the wind regime of this region with high quality. Comparison with measured data showed a significant improvement in wind simulation with increasing of resolution, but worse representation of surface temperature and humidity. The Polar WRF made a general cooling of near surface temperature of 2 °C during the period of simulation and increased precipitation amount by 4.6–8.4 mm (12–21%) on average over the territory relative to the initial data from Global Data Assimilation System. This can be explained by the contribution of noise and imperfection of the model (including static input data of the terrain description). Based on the modelled results, the interaction of wind flow with the mountainous terrain of the Antarctic Peninsula creates a range of complex dynamic effects in the atmosphere. These effects cause local precipitation maxima both over the Peninsula and over the adjacent ocean. These are, respectively, bay-valley areas of increased precipitation and increased precipitation on the crests of shock waves from orographic obstacles. Under certain background wind conditions, the influence of the latter effect can reach the Akademik Vernadsky station and cause the formation of heavy precipitation here.

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A numerical study to investigate the roles of former hurricane Leslie, orography, and evaporative cooling in the 2018 Aude heavy precipitation event

10.5194/wcd-2020-54 ◽

2020 ◽

Author(s):

Marc Mandement ◽

Olivier Caumont

Keyword(s):

Mediterranean Sea ◽

Cold Front ◽

Evaporative Cooling ◽

Heavy Precipitation ◽

Precipitation Event ◽

Maximum Rainfall ◽

Near Surface ◽

Low Level ◽

Mesoscale Convective ◽

The Mediterranean

Abstract. In southeastern France, the Mediterranean coast is regularly affected by heavy precipitation events. On 14–15 October 2018, in the Aude department, a back-building quasi-stationary mesoscale convective system produced up to about 300 mm of rain in 11 h. The synoptic situation was perturbed by the former hurricane Leslie, involved in the formation of a Mediterranean surface low that focused the convective activity. At mesoscale, convective cells focused west of a quasi-stationary cold front and downwind of the terrain. To investigate the roles of Leslie, orography and evaporative cooling in the processes that led to the observed rainfall, numerical simulations are run and evaluated with near-surface analyses comprising standard and personal weather stations. Simulations show that, in a first part of the event, low-level conditionally unstable air parcels found inside strong updrafts mainly originate from the Mediterranean Sea, east of 4.5° E, whereas in a second part, an increasing number originates from Leslie's remnants. Air masses from east of 4.5° E appear as the first supplier of moisture over the entire event. Still, Leslie contributed to substantially moisten mid-levels over the Aude department, diminishing evaporation processes. Thus, the evaporative cooling over the Aude department does not play any substantial role in the stationarity of the cold front. Regarding lifting mechanisms, most of the air parcels found inside strong updrafts near the location of the maximum rainfall are lifted above the cold front, attesting its key role in focusing convection. Downwind of the Albera Massif, mountains bordering the Mediterranean Sea, cells formed by orographic lifting seem to be maintained by low-level leeward convergence, mountain lee waves and a favourable directional wind shear; when terrain is flattened, rainfall is substantially reduced. The location of the exceptional precipitation appears to be driven primarily by the location of the quasi-stationary cold front and secondarily by the location of convective bands downwind of the orography.

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First observation of significant long-lasting Thunderstorm Ground Enhancements on the Milešovka peak (altitude 837 m) in Czechia

10.5194/egusphere-egu21-3141 ◽

2021 ◽

Author(s):

Ivana Kolmašová ◽

Ondřej Santolík ◽

Ondřej Ploc ◽

Ronald Langer ◽

Jana Popová ◽

...

Keyword(s):

Electric Field ◽

Electric Fields ◽

Background Radiation ◽

Heavy Precipitation ◽

Cloud Base ◽

Squall Line ◽

Strong Wind ◽

Particle Detector ◽

Near Surface ◽

Cloud Radar

Bursts of gamma rays observed on the Earth&#8217;s surface &#8211; so called Thunderstorm Ground Enhancements (TGE) were detected by a plastic scintillator (disassembled from the particle detector SEVAN) located in the observatory building on the Mile&#353;ovka peak (50.6N, 13.9E, altitude 837 m) in Czechia. The TGEs observed during two thunderstorms on 23 April 2018 respectively lasted 65 and 15 minutes and exceeded the background radiation levels by 30 and 40 percent.The first storm was a part of an evolving squall line which crossed the Mile&#353;ovka peak. The second storm was probably a supercell, which moved near Mile&#353;ovka but did not hit its top. Both storms caused heavy precipitation and strong wind gusts. The onset of the TGEs preceded the onset of precipitation by approximately 8 minutes. During the increases of TGE radiation, the European lightning detection network EUCLID detected numerous predominantly negative intracloud lightning discharges at distances closer than 5 km from the particle detector.To understand the conditions for the TGE observation we investigated the data collected during the enhancements by a Ka-band cloud radar, an electric field mill, and a broadband electromagnetic receiver installed in the Mile&#353;ovka peak observatory. Using the cloud radar measurements, we estimated the vertical extent of the thunderclouds. The cloud base was found at about 500 m above the observatory. Estimated heights of the cloud tops for the two storms were 12 and 8 km, respectively, indicating that the storm center of the second storm was not directly above the cloud radar. The updraft velocities reached 10 m/s.&#160; A composition of hydrometeors suggested good conditions for cloud electrification.We have found that the increases of TGE radiation corresponded to the large negative electric fields (up to &#8211; 20 kV/m) measured by the electric field mill rather than to individual discharges. We also identified numerous microsecond-scale pulses in the broadband magnetic field records, which can be attributed to corona-type discharges occurring near the receiving antenna in high local electric fields below the thunderstorm.Based on our analysis we assume that observed TGEs corresponded to the bremsstrahlung generated during collisions of electrons accelerated in the thunderstorm electric field with the air molecules. Because of a very small number of cloud-to-ground lighting discharges we hypothesize that the electrons might have been accelerated by a strong lower positive charge center at the bottom of the thundercloud. As the TGE radiation increases were unusually long, we speculate that their later part might have been assigned to the radon progeny which was lifted to the atmosphere by a near-surface electric field and returned back to the ground with the rain precipitation.

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Dependence of predictability of precipitation in the northwestern Mediterranean coastal region on the strength of synoptic control

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-15851-2020 ◽

2020 ◽

Vol 20 (24) ◽

pp. 15851-15865

Author(s):

Christian Keil ◽

Lucie Chabert ◽

Olivier Nuissier ◽

Laure Raynaud

Keyword(s):

Coastal Region ◽

Heavy Precipitation ◽

Forecast Model ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Precipitation Characteristics ◽

Synoptic Forcing ◽

Convective Adjustment ◽

Forecast Quality

Abstract. The weather-regime-dependent predictability of precipitation in the convection-permitting kilometric-scale AROME-EPS is examined for the entire HyMeX-SOP1 employing the convective adjustment timescale. This diagnostic quantifies variations in synoptic forcing on precipitation and is associated with different precipitation characteristics, forecast skill and predictability. During strong synoptic control, which dominates the weather on 80 % of the days in the 2-month period, the domain-integrated precipitation predictability assessed with the normalized ensemble standard deviation is above average, the wet bias is smaller and the forecast quality is generally better. In contrast, the pure spatial forecast quality of the most intense precipitation in the afternoon, as quantified with its 95th percentile, is superior during weakly forced synoptic regimes. The study also considers a prominent heavy-precipitation event that occurred during the NAWDEX field campaign in the same region, and the predictability during this event is compared with the events that occurred during HyMeX. It is shown that the unconditional evaluation of precipitation widely parallels the strongly forced weather type evaluation and obscures forecast model characteristics typical for weak control.

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A numerical study to investigate the roles of former Hurricane Leslie, orography and evaporative cooling in the 2018 Aude heavy-precipitation event

Weather and Climate Dynamics ◽

10.5194/wcd-2-795-2021 ◽

2021 ◽

Vol 2 (3) ◽

pp. 795-818

Author(s):

Marc Mandement ◽

Olivier Caumont

Keyword(s):

Mediterranean Sea ◽

Evaporative Cooling ◽

Heavy Precipitation ◽

Balearic Islands ◽

Precipitation Event ◽

Near Surface ◽

Low Level ◽

Stationary Front ◽

Mesoscale Convective ◽

The Mediterranean

Abstract. In south-eastern France, the Mediterranean coast is regularly affected by heavy-precipitation events. On 14–15 October 2018, in the Aude department, a back-building quasi-stationary mesoscale convective system produced up to about 300 mm of rain in 11 h. At synoptic scale, the former Hurricane Leslie was involved in the formation of a Mediterranean surface low that channelled conditionally unstable air towards the coast. At mesoscale, convective cells focused west of a decaying cold front that became quasi-stationary and downwind of the terrain. To investigate the roles of the moisture provided by Leslie, orography and evaporative cooling among the physical processes that led to the location and intensity of the observed rainfall, numerical simulations are run at 1 km and 500 m horizontal grid spacing and evaluated with independent near-surface analyses including novel crowd-sourced observations of personal weather stations. Simulations show that, in a first part of the event, low-level conditionally unstable air parcels found inside strong updraughts mainly originated from areas east of the Balearic Islands, over the Mediterranean Sea, whereas in a second part, an increasing number originated from Leslie's remnants. Air masses from areas east of the Balearic Islands appeared as the first supplier of moisture over the entire event. Still, Leslie contributed to substantially moistening mid-levels over the Aude department, diminishing evaporation processes. Thus, the evaporative cooling over the Aude department did not play any substantial role in the stationarity of the quasi-stationary front. Regarding lifting mechanisms, the advection of conditionally unstable air by a low-level jet towards the quasi-stationary front, confined to altitudes below 2 km, reactivated convection along and downwind of the front. Most of the air parcels found inside strong updraughts near the location of the maximum rainfall were lifted above the quasi-stationary front. Downwind of the Albera Massif, mountains bordering the Mediterranean Sea, cells formed by orographic lifting were maintained by low-level leeward convergence, mountain lee waves and a favourable directional wind shear; when terrain is flattened, rainfall is substantially reduced. The location of the exceptional precipitation was primarily driven by the location of the quasi-stationary front and secondarily by the location of convective bands downwind of orography.

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Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽

10.3390/w13131727 ◽

2021 ◽

Vol 13 (13) ◽

pp. 1727

Author(s):

Valerio Capecchi ◽

Andrea Antonini ◽

Riccardo Benedetti ◽

Luca Fibbi ◽

Samantha Melani ◽

...

Keyword(s):

Extreme Event ◽

Wrf Model ◽

Heavy Precipitation ◽

Radar Data ◽

Flash Floods ◽

Precipitation Event ◽

Weather Research And Forecasting ◽

Limited Area ◽

Heavy Precipitation Event ◽

The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

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