GFS MOS Wind Guidance: Problem Solved?

Eric Engle and Kathryn GilbertMDL/Statistical Modeling Branch

15 May 2012

Reason for Refresh Development Sample Predictand Definition Predictors and Equation Development Independent Test Systems Verification Impact on Gridded MOS

Overview

GFS Model “bugfix” implemented in May 2011 Set new thermal roughness length to address a low

level warm bias over land Affected the behavior of the low level wind fields

Usually chosen as predictors (10-m u, v, speed)

Reason for Refresh

GFS Vegetation TypeVegetation Type Description7: Groundcover only (perennial)8: Broadleaf shrubs with perennial groundcover9: Broadleaf shrubs with bare soil11: Bare soil Roughness length

change has most impact in these vegetation type areas.

Verifications show this is true (not shown)

VEGETATION TYPES (DORMAN AND SELLERS, 1989; JAM)

GFS Model “bugfix” implemented in May 2011 Set new thermal roughness length to address a low

level warm bias over land Affected the behavior of the low level wind fields

Usually chosen as predictors (10-m u, v, speed)

Had a direct impact on GFS MOS wind speed guidance Large guidance errors (strong positive biases) Western CONUS (low vegetation/desert areas) Most pronounced in warm season, during daytime hours

Reason for Refresh

Implementation 32.2 knot

error

2009

Credit: Dr. Yun Fan

2010

2011 Jan-Apr

2011 May-July

GFS Model “bugfix” implemented in May 2011 Set new thermal roughness length to address a low level

warm bias over land Affected the behavior of the low level wind fields

Usually chosen as predictors (10-m u, v, speed)

Had a direct impact on GFS MOS wind speed guidance Large forecast busts (strong positive biases) Western CONUS (low vegetation/desert areas) Most pronounced in warm season, during daytime hours

Complaints from NWS forecasters and private sector GFS MOS wind guidance “unusable”

Reason for Refresh

“Our workload has increased due to this problem”

“…we continue to deal with serious fire weather conditions…”“The forecaster

stated that this issue makes the point and gridded MOS…typically used to populate GFE…unusable and times.”

“The situation with the MAV guidance winds has become a source of frustration and a workload issue for our office.”

Responses from Users

Turning off partial inflation (PI) Many stations benefit from PI

Development without boundary layer model predictors Many stations benefit from these

Bias correction Big project…significant MOS production overhead

The solution…collect sufficient mixed sample and redevelop Most timely

Solutions Investigated

Previous two warm seasons available April through September, 2010 and 2011.

Comprised of three different versions of GFS model.

Development Sample

Date Range Version

April – June 2010 Pre-9.0.0 (operational)

July – September 2010 9.0.1 (reforecast)

April – May 9 2011 9.0.0 (operational)

May 10 – September 2011

9.0.1 (operational)

Balance the influence of “new” model data (version 9.0.1) with a sufficient sample size 64% “new” / 36% “old”

Predictands: 10-m U-wind 10-m V-wind 10-m Wind Speed

Derived from hourly observed 10-m wind speed and direction Wind data are quality controlled via MDL software

Regression equations for predictands are developed simultaneously Predictors selected that best fit all 3 predictands

Different coefficient 3-hourly guidance to 192-h 6-hourly guidance from 204-h to 264-h

Predictand Definition

U, V, Speed at 1000, 925, 850, 700, and 500 hPa; and 10-m

Mass divergence, relative vorticity, vertical velocity at 925, 850, 700, and 500 hPa

Mean Layer RH 1000-850; 850-700 hPa; and 1-0.44 sigma

Temperature Difference between 1000-925, 1000-800, and 1000-700 hPa levels

K index Sine and cosine DOY (harmonic functions) PBL mixing parameter Bilinear interpolation Observed predictors offered out to 15-h (persistence)

Predictors Offered

Single station equation development Multiple linear regression (forward selection) Maximum number of predictors: 10 (no

forcing) 100 “cases” required equation to be

developed Three independent test systems were

developed Determine the best mix of “old” and “new” GFS

model sample

Regression and Equation Development

TEST1 Only GFS v9.0.1 “new” used July-Sept. 2010 (reforecast); May 10 – Sept. 2011

TEST2 Same as TEST1, but includes April 1 – May 9, 2011

(GFS v9.0.0) TEST3

All data from previous 2 warm seasons included April-Sept. 2010 and 2011

Independent Test Systems

Cross-validation “leave one out” technique used

Each of the 3 test systems comprised of 8 equation sets 7 out of 8 months of “new” GFS model data

included in each equation set Withheld month is used to verify the equation

set in which it was held back. End up with 8 fully independent months of

guidance to verify against

Independent Testing

Compare Equations for KPHX (24-h)00Z

Operational (as of 5/14/2012)

Predictor Coeff.

10-m U-wind -0.1382

10-m V-wind -0.4141

10-m Wind Speed 1.6432

1-0.44 sigma Mean Layer RH

0.0321

850 hPa Mass Divergence -0.5782

1000-850 hPa Mean Layer RH

0.0209

1000-925 hPa Temp difference

-1.6628

Cosine 2*DOY 0.7597

500 hPa Wind Speed 0.0734

850 hPa Vert. Velocity (GB)

-0.3317

New (awaiting implementation)

Predictor Coeff.

925 hPa U-wind -0.0569

850 hPa Wind Speed 1.2445

10-m V-Wind -0.6657

Cosine DOY -1.8675

700 hPa Wind Speed 0.1448

1000-850 hPa Mean Layer RH

0.0519

PBL Mixing (low) 5.2159

850 hPa Vert. Velocity (GB)

-0.3785

500 hPa Mass Divergence -0.1887

K Index (GB) ( ≥ 40) -1.0493

Verifications show TEST3 being the most accurate/skillful system Attribute this to a longer sample

New equations have similar skill in wind direction guidance as the old equations

Guidance in Alaska degraded with test developments Existing equations will remain in place

Verification Summary

Impact on Gridded MOS

GMOS Example

GMOS Example

GMOS Example

GMOS Example

Change in GFS thermal roughness length Negative impact on GFS MOS

Wind equations redeveloped using previous 2 warm seasons Except for Alaska

Large wind speed guidance errors removed Positive impact on Gridded MOS Future work?

Bias correction Redevelop again with longer sample

Implementation in June 2012

Summary

See the New Equations in Action…

http://www.mdl.nws.noaa.gov/~mos/mos/gfsmos_wind/index.php

Questions?