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## Introduction

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**VAPOR**NUvc, VDvc NUvi, VDvi VDvr VDvs CLci, MLic, FZci CLOUD ICE CLcs CNig CNis, CLis CNcr, CLcr self- collection self- collection VDvh VDvg MLsr, CLsr RAIN SNOW CLsr CLrs CLcg CLri CLir CLrh, MLhr,SHhr CLih MLgr CLsh CLch CNsg CLsr-h CLsr-g GRAUPEL HAIL CLir-g CLir-g CNgh SEDIMENTATION SEDIMENTATION Thompson et al. (2008) ρs Ds 1.0 a) 0.5 0.0 20 30 10 0 SLR 1.0 b) 0.5 0.0 30 20 10 0 SLR SNOW-TO-LIQUID RATIO FROM THE MICROPHYSICS SCHEME USED IN THE HIGH-RESOLUTION NUMERICAL WEATHER PREDICTION SYSTEM FOR THE 2010 WINTER OLYMPICSAnna Glazer and Jason A. MilbrandtMeteorological Research Division / Environment Canada Introduction SLR parameterization High-resolution NWP system for 2010 winter Olympics SLR for Whistler Mountain • SNOW-TO-LIQUID RATIO (SLR) = depth of new snowfall:depth of melted liquid equivalent • necessary to forecast snow amount from a NWP model (precipitation from model in liquid equivalent amount, multiplied by SLR gives snow depth) • 10 : 1 used traditionally, but not representative for all snow conditions • other values based on climatology, statistics and physical principles (e.g. artificial neural networks, decision tree algorithm) are recently used • new technique - prediction of SLR explicitly from a microphysics scheme (= direct snow depth forecast) SNOW Direct comparison Limited area version of the Canadian Global Environmental Multiscale Model (GEM LAM), run twice daily, starting from 0000 and 1200 UTC GEM Regional forecasts: 15 km → 2.5 km → 1 km • Snow measurements at 2PM and 6AM LT • Mark Barton’s report on snow density (1990-2010) Observed snow is represented by 3 model categories: ICE (pristine crystals) ρi= 500 kg m-3 GRAUPEL (rimed crystals) ρg = 400 kg m-3 SNOW (large crystals, aggregates) ρs (Ds)= e Dsf • SLR from GEM LAM 1 km at the same hours 34 events (2010) Whistler 15 km 15 km Brandes et al. (2007) J. Appl. Meteor. and Clim. 15 km 2.5 km 2.5 km 1 km 1 km SLR distribution 2.5 km • Snow measurements from Mark Barton’s report 1 km Vancouver • SLR from GEM LAM 2.5 km M-Y Microphysics Scheme • SLR from both 2.5 and 1 km GEM LAM (January 2010 – March 2011) • Snow events satisfying criteria: • SLR > 2 • QPF (SWE) > 2.8 mm / 24 hrs • Snow depth > 50 mm / 24 hrs SNOW-TO-LIQUID RATIO formula For each model category x = i, s, g representing observed snow: R E L A T I V E F R E Q U E N C Y Mean = 12.6 Volume flux • Six hydrometeor categories: • liquid: cloud, rain • frozen: ice, snow • graupel,hail Mass flux SLR for LAM domain Mean = 12.2 • Two prognostic variables for each hydrometeor (double-moment scheme) • mass mixing ratio • total number concentration Total volume flux for observed snow Total precipitation rate 2.5 km Conclusion SLR = Fv / Fv_liq Mean = 12.0 • New technique to forecast SLR from • microphysics scheme is proposed • It gives realistic probability distribution of SLR for accumulated snowfall events Instantaneous SLR Size distribution function for each hydrometeor x = c, r, i, s, g, h Vx(D), volx(D) and mx(D) are the terminal velocity, volume and mass of a particle of dimension D Future Plans SLR for a snow that has precipitated over a given period of time is computed as the ratio of total unmelted to liquid-equivalent quantity: • SLR parameterization is implemented • and under evaluation in Canadian NWP • deterministic system at 2.5 km resolution • SLR sensitivity to microphysics scheme • parameters will be documented • SLR parameterization will be improved • (e.g. compaction, melting, fragmentation) 1 km Mean=10.69 M-Y Milbrandt & Yau (2005) J. Atmos. Sci. SLR = Fv / Fv_liq sum over the time