Estimating the snowfall limit in alpine and pre-alpine valleys: A local evaluation of operational approaches

Fehlmann, Michaël; Gascón, Estíbaliz; Rohrer, Mario; Schwarb, Manfred; Stoffel, Markus

doi:10.1016/j.atmosres.2018.01.016

Cited by 13 publications

(13 citation statements)

References 35 publications

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“…When comparing precipitation phase forecasts to local observations, the difference in elevation between the model and the true orography at observation sites can be an important source of uncertainty in the verification process (Gascón et al, ). For this reason, we consider a model grid point located at a similar elevation and at a distance of 25 km to the disdrometer for both the HRES and the ENS model (Fehlmann et al, ). For this grid point, the variables of instantaneous precipitation type and instantaneous precipitation rate are processed according to Gascón et al () and aggregated to the categories of rain and snow (including wet snow) with a temporal resolution of 3 hr.…”

Section: Datamentioning

confidence: 99%

“…Since early 2017, a Thies disdrometer is installed in the study area at 1,060 m a.s.l. (see Figure ), which provides information about the precipitation type at the ground surface with a high temporal resolution of 1 min (Fehlmann et al, ). The disdrometer measures the attenuation of a laser beam (785 nm) by precipitation particles with an optical sensor.…”

Section: Datamentioning

confidence: 99%

“…First, we evaluate the forecasts of rain and snowfall of ECMWF IFS with local disdrometer observations. In particular, we compare the high‐resolution (HRES) forecast with a newly developed ensemble‐based product at ECMWF (Gascón et al, ), as improvements of precipitation type forecasts are expected from ensemble (ENS) forecasts in recent studies (Gascón et al, ; Fehlmann et al, ; Reeves et al, ). Second, weather forecasts of ECMWF IFS are used as input to a conceptual hydrological model to forecast the occurrence of RoS events up to 7 days ahead.…”

Section: Introductionmentioning

confidence: 99%

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Improving Medium‐Range Forecasts of Rain‐on‐Snow Events in Prealpine Areas

Fehlmann

Gascón

Rohrer

et al. 2019

Water Resources Research

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Rain‐on‐snow (RoS) events have caused severe floods in mountainous catchments in the recent past. Challenges in forecasting such events are uncertainties in meteorological input variables, the accurate estimation of snow cover and deficits in process understanding during runoff formation. Here, we evaluate the potential of the European Centre for Medium‐Range Weather Forecasts Integrated Forecasting System (ECMWF IFS) to forecast RoS disposition (i.e., minimum rainfall amounts, initial snow cover, and meltwater contribution) several days ahead. We thereby evaluate forecasts of rain and snowfall with disdrometer observations and show that ensemble‐based forecasts have larger potential than the high‐resolution forecast of ECMWF IFS. Then, we use ECMWF IFS weather forecasts as input to a conceptual hydrological model, which is calibrated using estimates of snow‐covered area (SCA), snow water equivalent (SWE), and discharge observations. We show that the forecast skill of this model chain is reasonably high with respect to SCA and SWE, even several days ahead. However, a number of RoS events are missed in the forecast, mainly due to an underestimation of rainfall amounts. These misses can be reduced by lowering the rainfall amount threshold for the forecast as compared to the analysis, being accompanied by only a moderate increase in false alarm rates. In contrast, the forecast of RoS disposition is found to be less sensitive to thresholds of initial snow cover and meltwater contribution. We conclude that valuable disposition warnings for RoS events can be issued several days ahead, and we illustrate this idea with a case study.

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Section: Datamentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Improving Medium‐Range Forecasts of Rain‐on‐Snow Events in Prealpine Areas

Fehlmann

Gascón

Rohrer

et al. 2019

Water Resources Research

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“…Last not least, both precipitation intensity and its phase (i.e. rain or snowfall) are decisive for runoff formation and the occurrence of flash floods in (pre-)alpine catchments (e.g., Fehlmann et al, 2018;Tobin et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Whereas precipitation intensities measured by the OTT pluviometer were of interest during missed events, precipitation intensities indicated by the Thies disdrometer were analysed during false alarms. To investigate whether the phase of precipitation could be relevant for missed events or false alarms, observations were separated according to a temperature threshold of 1.2°C (Fehlmann et al, 2018). The resulting distributions of precipitation intensities and phase during missed events and false alarms are shown in Fig.…”

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confidence: 99%

Automated precipitation monitoring with the Thies disdrometer: Biases and ways for improvement

Fehlmann¹,

Rohrer²,

Lerber³

et al. 2020

Preprint

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Abstract. The intensity and phase of precipitation at the ground surface can have important implications for meteorological and hydrological situations, but also in terms of hazards and risks. In the field, Thies disdrometers are sometimes used to monitor the quantity and nature of precipitation with high temporal resolution and very low maintenance and thus provide valuable information for the management of meteorological and hydrological risks. Here, we evaluate the Thies disdrometer with respect to precipitation detection as well as the estimation of precipitation intensity and phase at a pre-alpine site in Switzerland (1060 m a.s.l.), using a weighing precipitation gauge (OTT pluviometer) as well as a two-dimensional video disdrometer (2DVD) as a reference. We show that the Thies disdrometer is well suited to detect even light precipitation, reaching a hit rate of around 95 %. However, the instrument tends to systematically underestimate rainfall intensities by 16.5 %, which can be related to a systematic underestimation of the number of raindrops with diameters between 0.5 and 3.5 mm. During snowfall episodes, a similar underestimation is observed in the particle size distribution (PSD), which is, however, not reflected in intensity estimates, probably due to a compensation by snow density assumptions. To improve intensity estimates, we test PSD adjustments (to the 2DVD) as well as direct adjustments of the resulting intensity estimates (to the OTT pluviometer), which are both able to reduce the systematic deviations during rainfall. For snowfall, the combination of the 2DVD and the OTT pluviometer seems promising as it allows improvement of snow density estimates, which poses a challenge to all optical precipitation measurements. Finally, we show that the Thies disdrometer and the 2DVD agree well insofar as the distinction between rain and snowfall is concerned, such that an important prerequisite for the proposed correction methods is fulfilled. Uncertainties mainly persist during mixed phased precipitation or low precipitation intensities, where the assignment of precipitation phase is technically challenging, but less relevant for practical applications. We conclude that the Thies disdrometer is not only suitable to estimate precipitation intensity, but also to distinguish between rain and snowfall. The Thies disdrometer therefore seems promising for the improvement of precipitation monitoring and the nowcasting of discharge in pre-alpine areas, where considerable uncertainties with respect to these quantities are still posing a challenge to decision making.

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The ANYWHERE Paradigm Shift in Responding to Weather and Climate Emergencies

Sempere‐Torres,

Berenguer

2024

Responding to Extreme Weather Events

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Estimating the snowfall limit in alpine and pre-alpine valleys: A local evaluation of operational approaches

Cited by 13 publications

References 35 publications

Improving Medium‐Range Forecasts of Rain‐on‐Snow Events in Prealpine Areas

Improving Medium‐Range Forecasts of Rain‐on‐Snow Events in Prealpine Areas

Automated precipitation monitoring with the Thies disdrometer: Biases and ways for improvement

The ANYWHERE Paradigm Shift in Responding to Weather and Climate Emergencies

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