Mn/DOT Agreement No. 74708

"Climatological Characterization of Snowfall
and Snowdrift in Minnesota"

Summary Report for Task 1 of Project

Task 1:  Complete entry of daily snowfall data sets prior to 1948 and merge with

               Post-1948 database.

               Duration:  9 months (actual 16 months)

               Deliverable: Task summary report describing data sets available

Contents:
Comment
  Disclaimer
  Procedures
  Status of the Work Plan
  Conclusions
  References
  Appendix

Comment: Upon initiation of this project in May 1999, the task of digitizing the pre-1948 daily climate observations for Minnesota was cost-shared with a grant from the Midwest Climate Center.  The data entry software was written by Jim Zandlo of the DNR-State Climatology Office, and each student worker was trained in its use. Nine different undergraduate students worked on this phase of the project.  The daily maximum and minimum temperatures, precipitation, snowfall, and snow depth were entered when available for over 370 locations.  Data sources included the paper and microfilm records stored in the Kuehnast Library of the University of Minnesota.  The source of these original observational records was variable depending on the time frame.  Three types of  governmental voluntary observational networks have existed over the past 160 years: the Smithsonian Network (prior to 1880); the U.S. Army Signal Corps Network (1870-1890) and the cooperative observer program of the National Weather Service whose data are archived and managed by the National Climatic Data Center (NCDC).  Some records as far back to the 1840s were discovered and utilized.  In all, nearly 60 megabytes of pre-1948 data were entered and merged with the post-1948 records, comprising a data record of over 120 megabytes.  Where appropriate, metadata were carefully annotated.  An annotated index of all data used in this project is available as a Foxpro or Excel data file, a sample of which is attached to the Task 1 report.

Disclaimer:  The Minnesota Department of Transportation (MN/DOT), in cooperation with the University of Minnesota (UMN) and the Minnesota Department of Natural Resources State Climatology Office (SCO) provide these data for informational purposes only.  As with most government services, these data exist in the public domain, but users are encouraged to pay special attention to the conditions and provisions under which the data were collected, as there were some variations in method of observation.  The user assumes the entire risk related to use of this database.  Data are provided on an "as is" basis and MN/DOT,  UMN, and the SCO disclaims any and all warranties, whether express or implied, including (without limitation) any implied warranties of merchantability or fitness for a particular purpose.  In no event will MN/DOT, UMN, or the SCO be liable to users or to any third party for any direct, indirect, incidental, consequential, special or exemplary damages or lost profit resulting from any use or misuse of this data.

Procedures:  Data were entered in a Foxpro database structure following the National Climatic Data Center (NCDC) guidelines for summary of the day (SOD) statistical reporting.  This conforms to existing CD ROM data sets of the post-1948 data.  Data quality controls included notations on a variety of metadata, including time of day, instrumentation, exposure, and method of observation.  With respect to snowfall and liquid equivalent precipitation, two observational practices were noted.  Some observers followed National Weather Service guidelines which equate liquid equivalent precipitation as 1/10 of the snowfall recorded.  Other observers melted the snowfall and measured the liquid equivalent in the rain gage.  The latter records will be used in this project to evaluate the variability in snow density.  Another difference in observational practice was noted in recording snow depth.  Some measurements were made daily throughout the snow season, while some were only made following each snowfall event.  Still, other observers made a practice of recording snow depth only on the 15th and the last day of the month.  Trace amounts of snowfall were entered in the database and assumed to represent a measurement which yielded less than 0.1 inches.  This conforms to the assumptions used by NCDC in formatting the post-1948 data.

Priority was given to entering continuous, unbroken data time series.  However, numerous locations with limited time series were also utilized and incorporated into the database.  Though these may not be useful for deriving meaningful statistics, they will be used in the analysis of extremes and perhaps in case studies for Task 3 of the project.  In addition they will enhance the spatial resolution in some MN/DOT Districts with relatively few climate stations.

Pre-1948 data sets were merged with post-1948 data and stored as a Microsoft Foxpro relational database.  In addition, the data were made available on the Minnesota Climatology Working Group web site (http://www.climate.umn.edu) and can be viewed or downloaded for analysis.  The database format includes the following descriptors:

Standard location attributes include station name (alphabetic characters), universal coordinates, latitude and longitude, elevation, county, township, range and section number.  The NAD83 (North American Datum) serves as a basis for these descriptors. Legal descriptors (county, township, range, and section) and geographic descriptors (latitude, longitude, UTM) are translated via the conventions established by the Minnesota Land Management Information Center (LMIC) and the use of SECTIC.EXE software.  County numbers range from 1 to 87 (alphabetically).  Township, range and section numbers conform to the standards used by LIMIC and designate east, west, or north from baseline values.  The NCDC station numbers are six digits, with the first two digits (21 for Minnesota) designating a state identity.  In some cases two NCDC station numbers may be used for a single location because the local observer moved from one residence to another.

Elevation is given in feet above mean sea level (MSL).  Dates are noted as numeric (year=4 digits, month=2 digits, day=2 digits).   The individual climate elements in the database are entirely numeric, with the exception of trace amounts of precipitation which are noted as T.  Maximum daily temperature (Tmx) and minimum daily temperature (Tmn) are given in whole degrees F.  Liquid precipitation (pre) is given as inches, tenths, or Trace (T).  Snowfall (sno) is given as inches and tenths.  Snow depth on the ground (snD) is rounded to the nearest whole inch.  The distance factor (dis) for geographical interpretation represents the linear distance from the climate station to a point of interest  and is rounded to the nearest mile.

The numeric identifiers for township, range, and section are taken from the public land survey for Minnesota.  In addition to the above, monthly average maximum and minimum temperature, monthly average snow depth, monthly total precipitation and monthly total snowfall are provided.  See Appendix I for further description of the data sources for this database. A sample from the web site (http://www.climate.umn.edu)  showing the screen format of the data is attached to the Task 1 report.

Status of the Work Plan:  The web based data will be dynamic, and therefore periodically updated with quality controlled data from the National Climatic Data Center. The Foxpro database in its present form is being used to generate the statistical summaries, maps, and tables noted as deliverables in Task 2.   Visual Basic (version 6.0) software library is being utilized to derive these summary statistics.  All data are being grouped by Mn/DOT District, including ancillary climate data to assess wind vector fields needed in calculating some of the Tabler parameters.  The analysis mandated in Task 2 will lead to a more informed perspective on utilization of the RWIS data network deployed recently by MN/DOT to measure conditions at strategic points along Minnesota roads.

Conclusions:  With Task 1 completion, the project work plan (Tasks 2-4) will progress more rapidly now.  We presuppose that utilization of the full snow climatology database will provide greater geographic and  temporal resolution of important statistical distributions, including those of the Tabler parameters; a better appreciation for and definition of extreme events; and a better range of conditions from which to make particular case studies within the MN/DOT districts.

References:

(1)   Tabler, Ronald D., "Design Guidelines for Control of Blowing and Drifting Snow", SHRP-H-381, Strategic Highway Research Program, National Research Council, Washington, D.C., 1994.

(2)   Microsoft Visual Basic Professional 6.0 Step by Step by Microsoft Press (1997)

(3)   Microsoft Visual Foxpro Relational Database Management System for Windows 

(version 6.0), Microsoft Press (1999)

Appendix I

Description of Source Data for Climatic Database Derived in Task 1