Experiences with 0-36 h Explicit Convective Forecasting

with the WRF-ARW Model

Morris Weisman

(Wei Wang, Chris Davis)

NCAR/MMM

WSN05

September 8, 2005

Composite NEXRAD Radar 00 UTC 6/10/03 - 12 UTC 6/11/03

WRF Realtime Convective Forecasting

May 1 – July 31 4 km 00 UTC -- 36h

2003, 2004, 2005

WRF Real-time Forecasts: 2004, 2005

4-km from 0000 UTC - 36 h

Version 1.3 (2.0.3.1)

Eta initial and boundary conditions (40 km)

Physics:

Lin et al. (5 cat.) microphysics (WSM6)

YSU PBL (first-order closure)

Noah LSM (HRLDAS)

2000 km X 2000 km domain / 2800 km X 2600 km domain

5.0h (6.5h) on 128 (192) IBM Power-4 processors

Real-time WRF 4 km Forecast

Composite NEXRAD RadarReflectivity forecast

Initialized 00 UTC 9 June 03

Real-time WRF 4 km Forecast

Initialized 00 UTC 10 June 03

Reflectivity forecast Composite NEXRAD Radar

Consider the 24-30 h forecast challenge (i.e., the next diurnal cycle).

How does the 4 km WRF-ARW ‘’guidance’’ compare to the 12 km operational ETA?

Radar 03 GMT

May 30, 2004

03 GMT 27 hr 06 GMT prec. 30 hr4 km WRF-ARW

12 km ETA

Overall Forecast

Good:

OK:

Bad:

WRF RADAR

How well does 4-km WRF represent the climatological behavior of convection? (e.g., diurnal cycle, episodes)

Longitudinal 1 hr Precip. May 10-31, 2004

Stage IV WRF

Diurnal Average Frequency: May 10-July 31 2004

Stage IV 4 km WRF

12 km ETA4 km WRF

Stage IV

Diurnal Average 3 hr Precip.

Initialized 04 June 2005 00 UTC

Reflectivity forecast Composite NEXRAD Radar

24 h forecast Valid 00 UTC 06/05/05

4-km ARW

2-km ARW

4-km NMM

Nexrad

ARW2 BREF

NMM4ARW4

0500 UTC 29 April 2005: 1 km model reflectivity, NEXRAD BREF

Progress

4 km WRF-ARW simulations exhibit:

A surprising ability to forecast mesoscale convective systems (MCS) out to 36 h ( strongly

controlled by 12-km ETA forcing)

A demonstrated skill at depicting MCS mode (bow echoes, mesoscale convective vortices, supercell lines)

A more accurate depiction of diurnal cycle and precipitation episodes

An ability to spin-up convective systems within 3-4 h from a cold start.

• QPF problematic (too much convective precip)• Stratiform regions appear too small (microphysics?)• Convective systems often fail to decay (BL

evolution?)• Initialization (data assimilation)• Verification methods

Challenge:

WRF-ARW 2005 real-time forecasts can be found at:

http://box.mmm.ucar.edu/projects/wrf_spring/

http://rain.mmm.ucar.edu/mm5/

Also archived at:

http://www.joss.ucar.edu/wrf-2004/catalog/http://www.joss.ucar.edu/wrf-2005/catalog/

24 hr precipitation verification

Valid 6/10/03 12 UTC

OBS

10 km WRF4 km WRF 12 km ETA

4 km WRF 12 h Precipitation Forecast

NCEP Stage 4 Data

Reisner Scheme SB2004 Scheme

WSM-6 SchemeLin, et al. Scheme

Valid 10 June 2003 12 Z

Total Precipitation (mm)

(Axel Seifert, 2004)

4 km WRF 12 h Reflectivity Forecast

NEXRAD Composite

Reisner Scheme SB2004 Scheme

WSM-6 SchemeLin, et al. Scheme

Valid 10 June 2003 12 Z

Column Max Reflectivity (dBZ )

(Axel Seifert, 2004)

Reisner

Lin WSM-6

SB2004

12 h Surface Theta

Sounding comparison: 24h forecast valid 00Z 24 May at DDC

ARW4

NMM4

Good forecast…

PBL too shallow, cold, & moist…clouds just broke up!

Model Raob

Model Raob

Sounding comparison: 24h forecast valid 00Z 18 May at DDC

ARW4

NMM4

Too dry in PBL, too moist above; Where is the PBL top?

Good forecast…

Model Raob

Model Raob

Sounding comparison: 24h forecast valid 00Z 28 April at OUN

ARW4

NMM4

Good in PBL, but CIN layer is washed out

PBL too shallow and moist, but CIN layer looks good

Model

Raob

Model

Raob

24 h Reflectivity Forecast valid 4-30-05 00Z

Radar

4 km WRF-ARW

2 km WRF-ARW

4 km WRF-NMM

Diurnal Average (2003)

4 km 10 km

1 10 100 km

Cumulus ParameterizationResolved Convection

LES PBL Parameterization

Two Stream Radiation3-D Radiation

Model Physics in High Resolution NWP

Physics“No Man’s Land”

CAT 3: severe, well organized (> 1 in)

CAT 2: some organization (.25-1.0 in)

CAT 1: weak, disorganized (< .25 in)

Convective Mode/Intensity WRF ETA