SNODAS (SNOw Data Assimilation System) gridded data from NOHRSC (National Operational Hydrologic Remote Sensing Center of NOAA's National Weather Service) are made available by NSIDC (National Snow & Ice Dat Center) as Unix .tar files at ftp site sidads.colorado.edu. Such files are for 24hr periods ending 06 UT which matches the Mountain Daylight Time day (or ends 11pm MST). Gridded values are SWE (Snow Water Equivalent depth), Snow Depth, Snow Melt, Snowpack Tempera- ure, Liquid Precipitation, Snow Precipitation, Snowpack Sublimation, and Blowing Snow Sublimation. For looking at water volumes likely in various river basins and subbasins, SWE is of most interest, projecting future water to flow into river systems, also 24hr Snow Melt. The SNODAS grid is a subdivision of longitudes & latitudes into half minute resolution width and height grid cells. That's under a square kilometer per grid cell. SWE is supplied as integer mm amounts. Higher precision would be unreasonable to ask of the model. No edge of any grid cell lies exactly on any whole integer longitude or latitude. E.g. one edge lies along -110.000416666667 deg. (west) longitude. Another edge lies along 39.9995833333333 deg. (north) latitude. Originally in Autumn 2004 to compare SNODAS basin averages with SNOTEL snow values which are only at specific gage sites, not as well representative of whole basin water availability, just plots were made. Then for import into Microsoft Excel for doing comparative line plots of snow water depths (SWE = Snow Water Equivalent), Steve Hunter of Bureau of Reclamation in the Denver Fed- eral Center (303-445-2478 smhunter@do.usbr.gov) had basin averages accumulated into .csv (comma separated value) files. Computed were basin averages and also subbasin averages, both trimmed at the Colorado state border, and also untrimmed HUC subbasins as exported as digitized longitude, latitude (Lon,Lat as grid X,Y) files from ArcGIS. An enlarged look at a part of such basin boundaries shows that they are a bit coursely drawn on a small scale, not smooth curves. Basin averages are computed by first preparing a file telling the area of each SNODAS half minute resolution Lon,Lat grid cell inside a basin boundary. The whole area of such a grid cell is computed by considering Earth a sphere, with each grid cell of height = circumference/(360*120), and width equal to height times cosine of the latitude at the midpoint of the grid cell. That's more than accurate enough, considering the fine detail courseness of the ArcGIS basin boundaries and also the imprecision of the SNODAS model. If none of the grid cells in a subbasin area have any snow, then SNODAS reports no valid data there, and the .csv file will get not a single character output for the column corresponding to that subbasin, so one will then see there consecutive commas marking the place where that data column belongs. E.g. in NPSnM.csv (North Platte Snow Melt) with top col. heading long line (broken here) "Mo/Da/Yr","101800- Laramie & N. Platte","10180001+10180010- Laramie & N. Platte","101800- NP0","10180002 NP1","10180010 NP2","10180001 NP3" one may find below lines like 10/27/03,0.00,0.00,0.00,,0.00,0.01 10/28/03,,,,,, <---likely a day with no SNODAS snow melt data 10/29/03,,,0.00,0.00,, <---some subbasins lacked any valid grid cell values (Some explanation of the column headings may be found below.) For local convenience, basins were abbreviated down to 2 characters: Ak=Arkansas R., Co=Colorado R., Gn=Gunnison R., NP=N. Platte R., SP=S. Platte R. RG=Rio Grande, SJ=San Juan R., Wt=White R., Yp=Yampa R. Originally as exported from ArcGIS, subbasin boundaries were simply numbered 0,1,2,... starting from the one with the most northerly extent coming first. It became convenient to renumber these 1,2,3,... to then let 0 designate the whole basin sum of the subbasins. In several places, HUC basins include more subbasins than were wanted to compare with SNOTEL readings. In .csv column headings, this might be indicated as "110200- Ak0" to indicate our used Arkansas R. basin is in fact not the entire HUC basin 110200, but in fact includes just some, not all HUC subbasins within HUC basin 110200, which are Ak1=HUC 11020001, Ak2=HUC 11020006, Ak3=HUC 11020007, Ak4=HUC 11020010. Then also for comparing with SNOTEL estimates of basin SWE, these HUC sub- basins were trimmed at the Colorado state border. But the original untrimmed subbasins were also kept as exported from ArcGIS, so output .csv files of daily basin and subbasin averages include both types, trimmed and untrimmed to allow use of whichever one may want. .csv file left col. 1 is Mo/Da/Yr Mtn. Time date of day ending at 06 UT (23 MST or midnight MDT). 2nd column is basin trimmed at Colorado state border. Next are the subbasins included in that basin from HUC subbasins trimmed at Co. state border. Then about the middle column is for basin average NOT trimmed at the Co. state border, then the included HUC subbasins follow on the right. They have column headings which are a 2 char. basin abbreviation and a single digit index to the included subbasins, as in the list at the bottom. Also computed daily for SWE & Snow Melt are basin & subbasin averages subdivided into elevation bands like "Mo/Da/Yr",Basin,"area km^2",ElevFtLo,ElevFtHi,ElevLabel,VarStat,VarType,VarValue ... 02/28/06,Yp02, 78.01,11000,11500,"11-11.5kf",avg,SWE,15.53 02/28/06,Yp02, 24.01,11500,12000,"11.5-12kf",avg,SWE,13.07 02/28/06,Yp02, 0.67,12000,12500,"12-12.5kf",avg,SWE,9.62 02/28/06,Yp02, 0.00,12500,13000,"12.5-13kf",avg,SWE, 02/28/06,Yp02, 0.00,13000,13500,"13-13.5kf",avg,SWE, 02/28/06,Yp02, 0.00,13500,14500,"13.5-14.5kf",avg,SWE, # Yp03 4032.1875km^2 , "lower Yampa, Co", "HUC 14050002" 02/28/06,Yp03, 4032.19, 0,14500," allElevs",avg,SWE,0.15 02/28/06,Yp03, 0.00, 0, 5000," 0-5kf",avg,SWE, 02/28/06,Yp03, 23.55, 5000, 5500," 5-5.5kf",avg,SWE,0.00 02/28/06,Yp03, 268.77, 5500, 6000," 5.5-6kf",avg,SWE,0.00 02/28/06,Yp03, 1432.82, 6000, 6500," 6-6.5kf",avg,SWE,0.00 02/28/06,Yp03, 1201.89, 6500, 7000," 6.5-7kf",avg,SWE,0.02 02/28/06,Yp03, 618.24, 7000, 7500," 7-7.5kf",avg,SWE,0.17 02/28/06,Yp03, 332.30, 7500, 8000," 7.5-8kf",avg,SWE,0.40 02/28/06,Yp03, 122.21, 8000, 8500," 8-8.5kf",avg,SWE,1.17 02/28/06,Yp03, 21.18, 8500, 9000," 8.5-9kf",avg,SWE,5.81 02/28/06,Yp03, 8.28, 9000, 9500," 9-9.5kf",avg,SWE,7.09 02/28/06,Yp03, 2.51, 9500,10000," 9.5-10kf",avg,SWE,10.54 02/28/06,Yp03, 0.43,10000,10500,"10-10.5kf",avg,SWE,14.96 02/28/06,Yp03, 0.00,10500,11000,"10.5-11kf",avg,SWE, 02/28/06,Yp03, 0.00,11000,11500,"11-11.5kf",avg,SWE, 02/28/06,Yp03, 0.00,11500,12000,"11.5-12kf",avg,SWE, 02/28/06,Yp03, 0.00,12000,12500,"12-12.5kf",avg,SWE, 02/28/06,Yp03, 0.00,12500,13000,"12.5-13kf",avg,SWE, 02/28/06,Yp03, 0.00,13000,13500,"13-13.5kf",avg,SWE, 02/28/06,Yp03, 0.00,13500,14500,"13.5-14.5kf",avg,SWE, These elevation banded .csv files are big, hence only a month at a time is put to our SNODAS WWWeb site or the Bureau of Recl. ftp server ftp.usbr.gov. Such a file is CUSWE0602elv.csv where CU indicates this covers Colorado and Utah (& more), 0602 indicates year 2006 Feb. Where you see 0.00 in the "area km^2" column, it means no part of that subbasin reached that elev. Hence the VarValue column there is empty, indicating undefined value at such too high elev. bands. In the above section, the line "# Yp03 ..." is our comment line only kept local- ly, but removed from what a script updates daily to ftp.usbr.gov or to WWWeb to http://www.usbr.gov/pmts/rivers/awards/Co/SNODAS/miscsv/. Co. border trimmed basins and subbasin left columns are (for SWE = snowpack Snow Water Equivalent, or similarly for SnM = Snow Melt): in file AkSWE.csv or AkSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "110200- Arkansas", "-" indicates trimmed, not all of HUC 110200 3 "11020001 Arkansas hdwtr", 4 "11020006 Huerfano", 5 "11020010- Purgatoire", "-" indicates trimmed, not all of HUC 11020010 then the additional columns on the right cover untrimmed HUC subbasins. 6 "110200- Ak0", (all of subbasins Ak1 - Ak4) 7 "11020001 Ak1", 8 "11020006 Ak2", 9 "11020007 Ak3", 10 "11020010 Ak4" in file CoSWE.csv or CoSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "140100- Colorado R", 3 "14010001+14010003 Colorado hdwtr+Eagle", 4 "14010002 Blue", 5 "14010005- Plateau Creek", 6 "14010004 Roaring Fork Co", then the additional columns on the right cover untrimmed HUC subbasins. 7 "140100 Co0", (all of subbasins Co1 - Co6) 8 "14010001 Co1", 9 "14010002 Co2", 10 "14010005 Co3", 11 "14010003 Co4", 12 "14010006 Co5", 13 "14010004 Co6" in file GnSWE.csv or GnSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "140200 Gunnison R.", 3 "14020001+14020002+14020003+14020004 Upper Gunnison", 4 "14020005 Surface Creek", 5 "14020006 Uncompahgre", then the additional columns on the right cover untrimmed HUC subbasins. 6 "140200 Gn0", 7 "14020004 Gn1", 8 "14020005 Gn2", 9 "14020001 Gn3", 10 "14020002 Gn4", 11 "14020006 Gn5", 12 "14020003 Gn6" in file NPSWE.csv or NPSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "101800- Laramie & N. Platte", 3 "10180001+10180010- Laramie & N. Platte", then the additional columns on the right cover untrimmed HUC subbasins. 4 "101800- NP0", 5 "10180002 NP1", 6 "10180010 NP2", 7 "10180001 NP3" in file RGSWE.csv or RGSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "13010001+13010002-+13010005- Upper Rio Grande", 3 "13010001 Upper Rio Grande", 4 "13010002- Alamosa Ck, Culebra & Trinchera Ck", 5 "13010005- Conejos & Rio San Antonio", then the additional columns on the right cover untrimmed HUC subbasins. 6 "130100+130201 RG0", 7 "13010003 RG1", 8 "13010004 RG2", 9 "13010001 RG3", 10 "13010002 RG4", 11 "13010005 RG5", 12 "13020101 RG6", 13 "13020102 RG7" in file SJSWE.csv or SJSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "140300-+140801- SAN MIGUEL/ANIMAS/DOLORES/SAN JUAN", 3 "14030004- San Miguel", 4 "14030002- Animas", 5 "14030003+14080102 Dolores", 6 "14080104- San Juan", then the additional columns on the right cover untrimmed HUC subbasins. 7 "140300-+140801- SJ0", 8 "14030001 SJ1", 9 "14030004 SJ2", 10 "14030003 SJ3", 11 "14030002 SJ4", 12 "14080104 SJ5", 13 "14080101 SJ6", 14 "14080102 SJ7", 15 "14080107 SJ8", 16 "14080105 SJ9" in file SPSWE.csv or SPSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "101900- S. Platte", 3 "10190007- Cache La Poudre", 4 "10190006 Big Thompson Co", 5 "10190005 St. Vrain, Co", 6 "10190004 Clear Creek, Co", 7 "10190001+10190002 S. Platte hdwtr & upper S. Platte", then the additional columns on the right cover untrimmed HUC subbasins. 8 "101900- SP0", 9 "10190007 SP1", 10 "10190006 SP2", 11 "10190005 SP3", 12 "10190004 SP4", 13 "10190002 SP5", 14 "10190001 SP6" in file YpSWE.csv or YpSnM.csv 1 @23MST, YrMoDa Mtn Time date near or at midnight 2 "14050001+14050003-+14050005 YAMPA & WHITE", 3 "14050003- Little Snake", 4 "14050001 Yampa & Elk", 5 "14050005 White", then the additional columns on the right cover untrimmed HUC subbasins. 6 "140500- Yp0", 7 "14050003 Yp1", 8 "14050001 Yp2", 9 "14050002 Yp3", 10 "140500- Wt0", 11 "14050007 Wt1", 12 "14050005 Wt2", 13 "14050006 Wt3" basn,"(sub)basin name" , basin , km^2 areaA, HUC Ak0,"Arkansas R." , Arkansas , 24425.2349,"110200-" Ak1,"Arkansas hdwtr" , Arkansas1, 7900.1475,"11020001" Ak2,"Huerfano Co" , Arkansas2, 4798.4385,"11020006" Ak3,"Apishapa Co" , Arkansas3, 2777.7067,"11020007" Ak4,"Purgatoire, Co" , Arkansas4, 8948.9421,"11020010" Co0,"Colorado R." , Colorado , 25468.1097,"140100" Co1,"Colorado hdwtr" , Colorado1, 7538.0021,"14010001" Co2,"Blue, Co" , Colorado2, 1739.8588,"14010002" Co3,"Plateau Creek" , Colorado3, 8071.3096,"14010005" Co4,"Eagle, Co" , Colorado4, 2520.6554,"14010003" Co5,"Parachute-Roan" , Colorado5, 1808.9471,"14010006" Co6,"Roaring Fork,Co" , Colorado6, 3789.3367,"14010004" Gn0,"Gunnison R." , Gunnison , 20817.0082,"140200" Gn1,"N Fork Gunnison" , Gunnison1, 2523.8800,"14020004" Gn2,"lower Gunnison" , Gunnison2, 4316.9406,"14020005" Gn3,"East Taylor" , Gunnison3, 2007.0179,"14020001" Gn4,"upper Gunnison" , Gunnison4, 6240.5374,"14020002" Gn5,"Uncompahgre, Co" , Gunnison5, 2888.5439,"14020006" Gn6,"Tomichi, Co" , Gunnison6, 2840.0884,"14020003" NP0,"N. Platte R." , N_Platte , 16798.6906,"101800-" NP1,"upper N Platte" , N_Platte1, 7424.3578,"10180002" NP2,"upper Laramie" , N_Platte2, 5677.8250,"10180010" NP3,"N. Platte hdwtr" , N_Platte3, 3696.5079,"10180001" RG0,"Rio Grande" ,Rio_Grande , 36452.0013,"130100 & 130201" RG1,"San Luis, Co" ,Rio_Grande1, 4131.3298,"13010003" RG2,"Saguache, Co" ,Rio_Grande2, 3464.6092,"13010004" RG3,"Rio Grande hdwt" ,Rio_Grande3, 3456.3612,"13010001" RG4,"Alamosa-Trinchera",Rio_Grande4, 6662.6652,"13010002" RG5,"Conegos, Co, NM" ,Rio_Grande5, 2095.1211,"13010005" RG6,"uper Rio Grande" ,Rio_Grande6, 8466.9763,"13020101" RG7,"Rio Chama" ,Rio_Grande7, 8174.9385,"13020102" SP0,"S. Platte R." , S_Platte , 20166.8926,"101900-" SP1,"Cache La Poudre" , S_Platte1, 4971.1985,"10190007" SP2,"Big Thompson, Co" , S_Platte2, 2160.7396,"10190006" SP3,"St. Vrain, Co" , S_Platte3, 2569.7027,"10190005" SP4,"Clear Creek, Co" , S_Platte4, 1477.1746,"10190004" SP5,"upper S. Platte" , S_Platte5, 4798.4415,"10190002" SP6,"S. Platte hdwtr" , S_Platte6, 4189.6356,"10190001" SJ0,"San Juan R." , San_Juan , 36942.4402,"140300- & 140801-" SJ1,"Westwater Canyon" , San_Juan1, 3718.3129,"14030001" SJ2,"Lower Dolores" , San_Juan2, 2311.8690,"14030004" SJ3,"San Miguel, Co" , San_Juan3, 4032.2731,"14030003" SJ4,"upper Dolores" , San_Juan4, 5551.0373,"14030002" SJ5,"Animas, Co" , San_Juan5, 3526.1325,"14080104" SJ6,"upper San Juan" , San_Juan6, 8867.9085,"14080101" SJ7,"Piedra, Co" , San_Juan7, 1718.3370,"14080102" SJ8,"Mancos, Co, NM" , San_Juan8, 2087.5346,"14080107" SJ9,"Middle San Juan" , San_Juan9, 5129.0354,"14080105" Wt0,"White R." , White , 12848.8271,"140500-" Wt1,"Lower White, Co" , White1, 6887.4008,"14050007" Wt2,"upper White, Co" , White2, 3576.0998,"14050005" Wt3,"Piceance Yellow" , White3, 2385.3265,"14050006" Yp0,"Yampa R." , Yampa , 18679.9930,"140500-" Yp1,"Little Snake, Co" , Yampa1, 7881.3169,"14050003" Yp2,"upper Yampa, Co" , Yampa2, 6766.4886,"14050001" Yp3,"lower Yampa, Co" , Yampa3, 4032.1875,"14050002"