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GFS upgrade tomorrow september 5th


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Technical Implementation Notice 12-42

National Weather Service Headquarters Washington DC

330 PM EDT Tue Sep 4 2012

To: Subscribers:

-Family of Services

-NOAA Weather Wire Service

-Emergency Managers Weather Information Network

-NOAAPORT

-Other NWS Partners, Users and Employees

From: Tim McClung

Science Plans Branch Chief

Office of Science and Technology

Subject: Change in Land Surface Model in Global Forecast

System and Associated Cool and Moist Bias in Near

Surface Temperature and Moisture Fields

Beginning with the 1200 Coordinated Universal Time (UTC) model

run on Wednesday, September 5, 2012, the National Centers for

Environmental Prediction (NCEP) Central Operations will implement

a fix to the Land Surface Model used to drive the Global Forecast

System (GFS). This correction is expected to improve the cool

and moist bias in the near surface air temperature and moisture

fields during the warm season.

Starting in mid-June 2012, NCEP confirmed a problem with the GFS

near-surface temperature and moisture simulations. The model was

not verifying in the late afternoon over the central United

States when drought conditions existed. Specifically, users noted

a significant 2m cold and wet bias in both the MOS and GFS

gridded products. The NCEP Environmental Modeling Center (EMC)

traced the problem to a look-up table used in the land surface

scheme that modulates evapotranspiration based on vegetation type

and root zone depth. Current settings allowed for excessive

transpiration and plant-extraction of soil moisture from deeper

soil layers, which caused the lower atmospheric boundary layer to

become too moist and cool.

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The update improves the output, so it is in fact a textbook definition of an upgrade.

I guess you're right that technically every change to a software output is an upgrade, but I've always felt that a true upgrade was a wholesale change in parameterization with the intended effect of upgrading the output in a number of areas, not just one tiny change leading to a change in one type of output under one set of conditions. For example, when a computer software company creates a fix to a package, they call it 2.1 or 2.2. However, when they make an upgrade, it becomes 3.0.

Edit to add that NCEP calls it is fix and not an upgrade too.

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I heard corn was a special case as far as evapotranspiration went. Whereas most places see dew points drop during the day with mixing, Iowa and places with corn see the dewpoints rise because of the super powers of corn.

Resisted temptation to insert a YouTube of Gordon Macrae riding a horse in tall corn from the movie adaptation of Rodgers and Hammerstein's "Oklahoma!".

FWIW- one of the better GFS improvement threads ever.

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Beginning with the 1200 Coordinated Universal Time (UTC) model run on

Wednesday, September 5, 2012, the National Centers for Environmental

Prediction (NCEP) Central Operations will implement a correction to the

Land Surface Model used to drive the Global Forecast System (GFS). This

correction is expected to improve the cool and moist bias in the near

surface air temperature and moisture fields during the warm season. Starting

in mid-June 2012 NCEP was informed about a problem with the GFS near

surface temperature and moisture simulations verifying in the late

afternoon over the central US where drought conditions existed.

Specifically, customers noted that a significant 2m cold and wet bias

existed in both the MOS and GFS gridded products. Modelers at the NCEP

Environmental Modeling Center (EMC) responsible for development of the GFS

and scientists at the Meteorological Development Laboratory (MDL)

identified the cause in late June. The problem was traced to a look-up

table used in the land surface scheme that modulates evapotranspiration

based on vegetation type and root zone depth. Current * *settings allowed

for excessive transpiration and plant-extraction of soil moisture from

deeper soil layers causing the lower atmospheric boundary layer to become

too moist and cool.

EMC conducted a parallel test of the GFS with corrected land surface

parameters starting in early June and running through late August, to

determine if appropriate modifications to the LSM look-up table would

provide a correction to the cold/wet bias without having an unexpected

negative impact on other meteorological fields over the US and the globe.

EMC conducted an assessment of the GFS parallel and found the change to

the land surface model significantly reduced the cold/wet bias over the US

and improved the 0-3 day precipitation forecasts. An analysis of the

parallel test results can be viewed here:

http://www.emc.ncep.noaa.gov/GFS/ppt/gfs_lsm_analysis_090412_final.pptx

*

*

*

*In addition, MDL conducted an objective evaluation of the GFS MOS guidance

generated from the GFS parallel output. MDL concluded that the corrections

in the GFS parallel output had the desired effect of reducing the cold/wet

bias resulting in improved bias and error scores in the GFS MOS temperature

and dewpoint guidance. Slight improvement was also noted in the GFS MOS

probability of precipitation guidance generated from the GFS parallel

output. A summary of MDL’s evaluation and comparisons of GFS MOS text

bulletins generated from the GFS parallel output can be viewed at

http://www.mdl.nws.noaa.gov/~mos/mos/gfs_coolfix/comp_mavmex.php*

*

NCEP (and MDL) also conducted a 1.5 month GFS parallel evaluation for the

period Jan-Feb 2012 to test the land surface model correction during the US

cold season. As expected, analysis of results indicate that the change in

the land surface model had little impact on the simulated 2m temperature

and dewpoint given the low solar forcing during the winter months. MDL’s

analysis of the MOS guidance from the GFS parallel during the cool season

sample also indicated minimal impact on the 2m temperature **and dewpoint.*

*

Based on the positive results of the GFS parallel tests and the severity of

the cold and wet bias in the near surface air temperature, the NCEP

Director has approved implementation of the correction to the land surface

model. NCEP Central Operations plans to implement the change beginning

with the 1200 UTC cycle on 5 September 2012.

We want to express or thanks to those customers who brought this problem to

our attention in June. NCEP also appreciates your patience as we needed

time to adequately test the GFS to ensure that correcting the land surface

model did not have adverse and unexpected negative impacts on other

forecast guidance (i.e., precipitation, hurricane track, hemispheric wave

patterns, etc.).

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Huge difference in the Guinea Highlands diurnal cycle with respect to the 00 and 06Z 9/5 run from the most recent 12Z run. The diuranl cycle of convection there is now actually pretty well represented with respect to to the 9/6 6Z forecast of rain rates relative to the AEW trough axis. I'm not sure if this is just chance or the update had something to do with it- but I'm definately encouraged.

http://www.atmos.albany.edu/student/abrammer/GFS_forecast/

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Huge difference in the Guinea Highlands diurnal cycle with respect to the 00 and 06Z 9/5 run from the most recent 12Z run. The diuranl cycle of convection there is now actually pretty well represented with respect to to the 9/6 6Z forecast of rain rates relative to the AEW trough axis. I'm not sure if this is just chance or the update had something to do with it- but I'm definately encouraged.

http://www.atmos.alb...r/GFS_forecast/

I read your paper on the role of Guinea Highlands convection on trop. cyclogenesis (Eaton Prize winner for those reading, btw). Interesting, good stuff. Too bad the MJO is going into a supressed phase this week for those two pouches on the continent now (although, would you consider P25L too far east to be a Guinea Highland cluster?)

current_Atlantic_pouch_image.png

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