Operationnal use of high resolution Operationnal use of high resolution model AROMEmodel AROME

image source: Sander Tijm, KNMI

AbstractAbstract

Advantages of AROME versus global model ARPEGE Examples of mesoscale structures: see breeze, precipitation

features, fog and low clouds, etc… Orography: precipitations and winds Resolution of strong convection

Some problems of false alert Gust and thunderstorm Heavy rainfall

Sea breeze: example in the gulf of ValenciaSea breeze: example in the gulf of Valencia

05 utc14 utc14.45 utc

Precipitation feature: example of a narrow band of cold front

Fog and low cloudsFog and low clouds

Thanks to its high density levels close to the surface and its microphysics, AROME forecast of fog/low clouds is often better than ARPEGE

Orography and rainfall: example of storm Dirk

1. synoptic background

2. Continuous rain over Britanny during 18 hours with intensity about 3-4 mm/h

3. Comparison between models ECMWF/ARP/AROME

Orogrophic wave and foehn storm: example of storm Xynthia 27th February 2010 (synoptic background)

AROME 2.5km

ALADIN

ZOOMVent 10m

(km/h)21H

Max=129km/hPic du Midi = 124km/h

Source C.Lac et all CNRM Meteo France

Max=104km/h

Max=110 km/h=Pic du Midi

10m wind (km/h)

21H

Relief

Strong winds downstream of relief

Gust 10m (km/h) 21H AROME 2.5km

OBS

Max=209km/hMax=213km/hPic du Midi=195km/h

Source C.Lac et all CNRM Meteo France

Strong convection

When deep convection is prevailing, AROME is

able to produce forecast that differ from its global

model ARPEGE

Example 1: ZT 500 hPa from 18th July to 21th July 2014

Pmer and Wet Bulb Température 850 hPa

A stormy front moves to the SE of France

RR03 forecast by ARPEGE from 03 to 18 UTC on 20th

RR03 forecast by AROME from 03 to 18 UTC

1818

3 hours

rainfall from 03 to 18Z

comparison

Mesoscale structure: bow echo

Mesoscale structure: bow echo

Mesoscale structure: bow echo (zoom)

Strong convection example 2 :heavy rains and strong convection on the SW France 25/7/14

24 hours rainfall forecast by ARPEGE

24 hours rainfall forecast by AROME

24 hours rainfall by radar

Gusts under thunderstormsGusts under thunderstorms

5.34110

ou

TKEURafales erNiveaum

Formula is ok most of the time

But what happen under strong convection?

Thunderstorm and gusts, example1 18/7/14

Strong convective structure (bow echo) forecast between 18/19UTC

Gust and wind forecast by AROME between 18/19 UTC

Gust= max during previous hour

Wind=at the time step

Observation: strong convection OK but smaller structures than forecast

Observed gusts

Example 2 case 28/6/2014

Forecast of gusts by three successive runs of AROME

Last run before the event!

False alert of heavy rainfall

At 12 utc, more than 40 mm in 3 hours forecast, 3.4 mm observed

Example of 28/7/14 on the Pyrénéees

At 14 UTC, more than 60 mm in 3 hours forecast, 5 mm observed

ConclusionConclusion

Positive balance sheet of AROME use by forecasters (previous synoptic study still required!)

Wishes Extending the forecast period to 48 hours More realistic convection (could be achieved with lower

resolution?)

Next challenge for forecasters: work with the ensemble forecast AROME