Introduction SLR for Whistler Mountain High-resolution NWP system

for 2010 winter Olympics

Future Plans

SNOW-TO-LIQUID RATIO FROM THE MICROPHYSICS SCHEME USED IN THE HIGH-RESOLUTION NUMERICAL WEATHER PREDICTION SYSTEM FOR THE 2010 WINTER OLYMPICS

Anna Glazer and Jason A. MilbrandtMeteorological Research Division / Environment Canada

)3(6

)(6 0

3x

xx

xx MdDDNDq

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)

•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)

M-Y Microphysics Scheme

Six hydrometeor categories:

liquid: cloud, rainfrozen: ice, snow

graupel, hail

Dxx

xxeDNDN 0)(

Size distribution function for each hydrometeorx = c, r, i, s, g, h

M-Y Milbrandt & Yau (2005) J. Atmos. Sci.

Two prognostic variables for each hydrometeor (double-moment scheme)• mass mixing ratio• total number concentration

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 Ds

f

SNOW

Ds

ρs

Thompson et al. (2008)

Brandes et al. (2007) J. Appl. Meteor. and Clim.

Direct comparison• Snow measurements at 2PM and 6AM LT Mark Barton’s report on snow density (1990-2010)• SLR from GEM LAM 1 km at the same hours

b)

a)

0

0SLR

10 20SLR

30

10 20 30

0.5

1.0

0.0

0.5

1.0

0.0

RELATIVE

FREQUENCY

Mean = 12.2

34 events (2010)

SLR parameterization

0

_____ )()()( dDDNDvolDV

FFFFFF sss

g

gm

i

imsvgvivv

SLR = Fv / Fv_liq

0_ )()()( dDDNDvolDVF xxxxv

0_ )()()( dDDNDmDVF xxxxm

L

sm

L

gm

L

imliqv

FFFF

___

_

Volume flux

Mass flux

Total precipitation rate

Total volume flux for observed snow

Instantaneous SLR

SNOW-TO-LIQUID RATIO formula

For each model category x = i, s, g representing observed snow:

Vx(D), volx(D) and mx(D) are the terminal velocity, volume and mass of a particle of dimension D

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:

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

1 km

15 km

2.5 km

• SLR from both 2.5 and 1 km GEM LAM (January 2010 – March 2011)

• Snow events satisfying criteria:SLR > 2QPF (SWE) > 2.8 mm / 24 hrsSnow depth > 50 mm / 24 hrs

SLR distribution

SLR for LAM domain

Mean = 12.0

• Snow measurements from Mark Barton’s report • SLR from GEM LAM 2.5 km

Conclusion • New technique to forecast SLR from microphysics scheme is proposed • It gives realistic probability distribution of

SLR for accumulated snowfall events

Mean=10.69

2.5 km

1 km

SLR = Fv / Fv_liq sum over the time

1 km

15 km

2.5 km

1 km

15 km

2.5 km

WhistlerWhistler

VancouverVancouver

Mean = 12.6

RAIN

GRAUPEL HAIL

SEDIMENTATIONSEDIMENTATION

VAPOR

ICECLOUD

VD

vr

VD

vs

NU

vi,

VD

vi

CLci, MLic, FZci

CLcs

CNig

CN

is,

CL i

s

CLri

CL i

h

CL s

h

CLir-g

CLsr-h

CLir-g

CLsr-g

CLch

CNsg

CNgh

ML

gr

CL c

g

VD

vg

CLir

VD

vhself-collection

self-collection

CLrh,MLhr,SHhr

NU vc, VD vc

CN

cr,

CL c

r

CLsr CLrs

MLsr, CLsrSNOW