ineedsnow Posted September 4, 2012 Share Posted September 4, 2012 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. Link to comment Share on other sites More sharing options...
WestMichigan Posted September 5, 2012 Share Posted September 5, 2012 It is about time they try to address this problem. Link to comment Share on other sites More sharing options...
Sunny and Warm Posted September 5, 2012 Share Posted September 5, 2012 The thread title is misleading at best. A table within the entire GFS model scheme was incorrect, and which led to faulty BL temps during drought conditions. That is a very far cry from "upgrade". Link to comment Share on other sites More sharing options...
Ellinwood Posted September 5, 2012 Share Posted September 5, 2012 The thread title is misleading at best. A table within the entire GFS model scheme was incorrect, and which led to faulty BL temps during drought conditions. That is a very far cry from "upgrade". The update improves the output, so it is in fact a textbook definition of an upgrade. Link to comment Share on other sites More sharing options...
Sunny and Warm Posted September 5, 2012 Share Posted September 5, 2012 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. Link to comment Share on other sites More sharing options...
isohume Posted September 5, 2012 Share Posted September 5, 2012 It is about time they try to address this problem. No doubt. I heard they were ignoring it, hoping it would just go away. Link to comment Share on other sites More sharing options...
Ed Lizard Posted September 5, 2012 Share Posted September 5, 2012 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. Link to comment Share on other sites More sharing options...
dtk Posted September 5, 2012 Share Posted September 5, 2012 No doubt. I heard they were ignoring it, hoping it would just go away. +1. It's actually amazing we were able to get it in when we did given our very strict, complicated implementation procedures. Link to comment Share on other sites More sharing options...
meteorologist Posted September 5, 2012 Share Posted September 5, 2012 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.). Link to comment Share on other sites More sharing options...
CoastalWx Posted September 5, 2012 Share Posted September 5, 2012 I've actually been happy with the GFS as of late, in terms of its prediction with sensible wx. Link to comment Share on other sites More sharing options...
Mike.Ventrice Posted September 5, 2012 Share Posted September 5, 2012 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/ Link to comment Share on other sites More sharing options...
ohleary Posted September 5, 2012 Share Posted September 5, 2012 No doubt. I heard they were ignoring it, hoping it would just go away. Link to comment Share on other sites More sharing options...
Rainshadow Posted September 5, 2012 Share Posted September 5, 2012 +1. It's actually amazing we were able to get it in when we did given our very strict, complicated implementation procedures. Thank-you. Link to comment Share on other sites More sharing options...
das Posted September 5, 2012 Share Posted September 5, 2012 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?) Link to comment Share on other sites More sharing options...
trapperman Posted September 5, 2012 Share Posted September 5, 2012 LaCrosse mentioned it today in their afternoon AFD and said it looks a lot better... fwiw. Link to comment Share on other sites More sharing options...
aljareer Posted September 6, 2012 Share Posted September 6, 2012 hi GFS upgrade Will be launched in 2013 year . from T574 (27 km) to T1148 (18 km almost ) . http://www.emc.ncep.noaa.gov/GFS/impl.php CHANGES TO NCEP MODELS NCWCP : http://www.nco.ncep.noaa.gov/pmb/changes/ Link to comment Share on other sites More sharing options...
aljareer Posted September 6, 2012 Share Posted September 6, 2012 GFS upgrade of Resolution : 2/2000: T126L28 to T170L42 (70km) 11/2002: T170L42 to T254L64 (55km) 6/2005: T254L64 to T382L64 (38km) 7/2010: T382L64 to T574L64 (27km) Link to comment Share on other sites More sharing options...
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