[Wrf-users] How to use NESDIS snow cover data in WRF

[Eric Altshuler]

Hello Oli, 


I can only answer your first question. I downloaded the file you mentioned, and it seems to have corrupt and/or missing GRIB2 metadata. It's not viewable in grads. There is another ftp server which has the NESDIS-IMS snow cover/sea ice data: 


ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/dcom/us007003/20121113/wgrbbul/ 


Only the most recent data is kept on the server. In the us007003 directory, there are 3 subdirectories named by date, and data is usually available only for the middle date. There are two files of interest: 


imssnow.grb.grib2 - NESDIS-IMS snow cover/sea ice at 24km resolution 
imssnow96.grb.grib2 - NESDIS-IMS snow cover/sea ice at 4km resolution 


Each dataset is on a north polar stereographic grid. The snow cover looks OK in both files, while the sea ice looks fine in the 24km product but is zero everywhere in the 4km product. I've used WRF before (not recently) and I think WPS can handle the interpolation from the polar stereo grid to the WRF grid. In the Vtable, you need to change the parameter number from 42 to 201 in the GRIB2 section. However, converting the snow cover data into something that WRF can use (such as water equivalent accumulated snow depth) requires an empirical algorithm and is beyond my expertise. 


Best regards, 

Eric L. Altshuler 
Assistant Research Scientist 
Center for Ocean-Land-Atmosphere Studies 
4041 Powder Mill Road, Suite 302 
Calverton, MD 20705-3106 
USA 

E-mail: ela at cola.iges.org 
Phone: (301) 902-1257 
Fax: (301) 595-9793 

----- Original Message -----
From: "Ólafur Rögnvaldsson" <or at belgingur.is> 
To: wrf-users at ucar.edu 
Sent: Wednesday, November 7, 2012 5:21:30 PM 
Subject: [Wrf-users] How to use NESDIS snow cover data in WRF 

Dear fellow WRF-users. 

I was wondering if you could assist me in one matter. We would like to start using the daily (more or less) snow cover updates from NESDIS to improve (hopefully:) our operational forecasts here in Iceland. 

Could you please inform me about how one should make the most of these data? In particular: 

1) Is this the proper ftp-site for downloading the snow-cover (grib) files: ftp://140.90.213.161/autosnow/4kmNH/ ? 
2) What changes should one make to the Vtable file? 
3) Is there some code modification (and/or additions) that need to be done to WRF and/or WPS? 

In particular, I was unable to ungrib this file: 

ftp://140.90.213.161/autosnow/4kmNH/NH4km_autosnow_11042012.grb 

using this Vtable snipped: 

GRIB1| Level| From | To | metgrid | metgrid | metgrid |GRIB2|GRIB2|GRIB2|GRIB2| 
Param| Type |Level1|Level2| Name | Units | Description |Discp|Catgy|Param|Level| 
-----+------+------+------+----------+---------+-----------------------------------------+-----------------------+ 
42 | 1 | 0 | | SNOWCOVER| 0/1 | Snow cover | 0 | 1 | 42 | 1 | 

as I get the following error message: 

or at dofri:~/dofri/wrf/V3.3.1/WPS$ ./ungrib.exe 
*** Starting program ungrib.exe *** 
Start_date = 2012-11-04_08:10:00 , End_date = 2012-11_04_08:20:00 
output format is WPS 
Path to intermediate files is ./ 
ungrib - grib edition num 2 
ERROR: Time unit in ipdtmpl(8), 4 is not suported 
Warning: ieee_inexact is signaling 
FORTRAN STOP 

Looking forward to read your advice. 

Kind regards, Óli. 
-- 
Kveðja/regards, 
Ólafur Rögnvaldsson 
Reiknistofa í veðurfræði - Belgingur 
www.riv.is - www.belgingur.is 


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