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National Operational Hydrologic
Remote Sensing Center

The National Operational Hydrologic
Remote Sensing Center
Snow Hydrology
in the
National Weather Service

Background Material for

Session Five:
Snow Hydrology Breakout Session
2002 December 5, Thursday, 7:45-9:15am and 9:45-11:15am

National Hydrologic Program Managers Conference

Fairmont Hotel
New Orleans, Louisiana
2002 December 3-6


This document provides background information useful for participants at the Snow Hydrology breakout sessions to be held on Thursday morning, December 5, at the National Hydrologic Program Managers Conference. It is not intended to be a definitive discussion on snow hydrology or the National Operational Hydrologic Remote Sensing Center (NOHRSC). The following does provide, however, a brief overview of: (1) the NOHRSC, (2) the requirements for snow data and information to support the NWS Hydrologic Services Program, (3) the Airborne Snow Survey Program, (4) the Satellite Hydrology Program, (5) the Snow Data Assimilation System, and (6) the NOHRSC snow product description and distribution.

Additionally, this document concludes by suggesting a few issues, or discussion topics, that may, or may not, be useful during the Snow Hydrology breakout session. Please have a look at the suggested questions and discussion topics for consideration. Also, you should make a note of any other questions or discussion topics that you would like to raise, or hear discussed, at the Snow Hydrology breakout sessions.

NOHRSC Overview

The National Operational Hydrologic Remote Sensing Center (NOHRSC) is managed by the Hydrologic Service Division in the Office of Climate, Water, and Weather Services. The NOHRSC is collocated with the North Central River Forecast Center (NCRFC) and the Chanhassen Weather Forecast Office (WFO) in Minneapolis, Minnesota. The NOHRSC provides remotely-sensed and modeled hydrology products for the coterminous U.S. and Alaska for the protection of life and property and the enhancement of the national economy. NOHRSC airborne, satellite, and modeled snow data and products are used by the NWS, other government agencies, the private sector, and the public to support operational and research hydrology programs across the nation.

The primary effort of the NOHRSC is to provide a variety of ground-based, airborne, and satellite snow observations and products in map format and in Standard Hydrologic Exchange Format (SHEF). Additionally, the office generates a variety of modeled snowpack products for the coterminous U.S., in near real-time, for use by the NWS River Forecast Centers (RFC) and Weather Forecast Offices (WFO) to support the NWS Hydrologic Services Program. The NWS Instruction 10-931 (2002 August) describes the NOHRSC policy and provides details of the office operation.

Requirements for Snow Information and Products in the NWS

Over the years, requirements for snow information and products to support the NWS Hydrologic Services Program have been articulated and documented in a wide variety of desperate reports and publications. Recently, a white paper titled Requirement for Snow Data, Products, and Information in the Hydrologic Services Program National Weather Service, NOAA, was collated from findings, requirements, and information documented in the 1993, 1996, and 1997 NOAA Disaster Survey Reports and the NWS Assessment of Hydrologic and Hydrometeorological Operations and Services by the National Research Council. The 1996 and 1997 floods were severe snow melt floods; consequently, the survey reports clearly document much of the RFC and WFO snow data, products, and information requirement. Additionally, the snow requirements document includes requirements articulated by NWS regional, RFC, and WFO personnel who attended the Eastern Region snow workshop held at the MARFC on December 1-4, 1998; the Western/Alaska Regions snow workshop held at the NWRFC on July 26-30, 1999; and the Eastern Region snow workshop held at Ithaca, NY, on July 18-19, 2000. Lastly, the snow requirements document also includes input and requirements articulated at the 4th NWS Cold Region Hydrology Workshopheld at the NWS Training Center in Kansas City on November 14-17, 2000. All NWS Regions have had the opportunity to review, to comment on, and to provide input to the snow requirements document.

Airborne Snow Survey Program

The NOHRSC uses low-flying aircraft to make airborne snow water equivalent measurements over a network of 2000 flight lines covering 26 states and 7 Canadian provinces. Airborne snow survey missions are scheduled upon request by RFC and WFO hydrologists when snow is significant in the region. The Airborne Snow Survey Program User's Guide provides details of: (1) the Airborne Snow Survey Program, (2) an explanation of the measurement technique, (3) how to access maps of airborne snow water equivalent, (4) how to interpret the SHEF message containing airborne snow water equivalent data, and (5) how to generate interactive, web-based flight line maps for your CWA or RFC along with other information.

Typical Airborne Snow Survey Program products include: (1) color contour maps of airborne snow water measurements, (2) the associated SHEF message that gives airborne snow water equivalent data by flight line and (3) the associated SHEF message that gives mean areal snow water equivalent over RFC hydrologic basins. The snow-water-equivalent-by-flight-line SHEF message is sent to AWIPS automatically and immediately upon NOHRSC receipt from the survey aircraft (sometimes three times each day) and posted to the NOHRSC web site. The snow- water-equivalent-by-basin SHEF message, for the entire survey area, is sent to AWIPS and the NOHRSC web site at the conclusion of each survey. The snow water equivalent map is posted to the NOHRSC web site at the conclusion of each survey; it is not sent to AWIPS./P>

Satellite Hydrology Program

The NOHRSC Satellite Hydrology Program uses image data from the NOAA GOES and NOAA POES to generate near real-time, satellite-derived areal extent of snow cover for the country. Satellite snow cover image products are generated daily at US scale (including Alaska), RFC scale, and at CWA scale. Additionally, weekly composite satellite snow cover images are produced to minimize the impact of cloud cover. Associated with each RFC scale satellite areal extent of snow cover image is a SHEF message that gives the percent of snow cover by RFC hydrologic basin and by elevation zone in the West. The NOHRSC has compared other satellite snow covering mapping techniques used by NESDIS and NASA with those used by the NOHRSC and found similar results.

Snow Data Assimilation System

The Snow Data Assimilation System (SNODAS) is a software system that uses input from the NWS numerical weather prediction (NWP) models to drive the NOHRSC energy-and-mass-balance snow model for the coterminous U.S. The NOHRSC snow model uses hourly forcing data from the Rapid Update Cycle 2 NWP model to simulate near real-time, hourly snowpack state variables for the country at 1 km resolution. Ground-based, airborne, and satellite snow observations are assimilated into the simulated snowpack state variables to produce a "best estimate" of snowpack characteristics. The resulting snowpack state variable estimates use all available NWP modeled and observed data sets as well as all available snow observations for the country. The NOHRSC snow model is described in detail on the NOHRSC Technology web page. SNODAS products and output will soon be provided to NWS field offices, over AWIPS and the Internet, in a variety of formats and spatial scales to best support the requirement for snow data in the NWS hydrology program. Image examples of SNODAS state variables include: snow water equivalent, sublimation/condensation, mean snow pack temperature, snow depth, and snow melt. Additional snow products, at various spatial scales, generated by the NOHRSC snow model can be found on the NOHRSC experimental web page.

NOHRSC Products Distributed to the Web and to AWIPS

This document describes only selected products and formats currently generated by the NOHRSC. The office posts all image and alphanumeric products to the NOHRSC web site in near real-time. Descriptions and examples of all NOHRSC products can be found on the NOHRSC web site. Additionally, the NOHRSC sends AWIPS products in SHEF and GRIB to the Satellite Broadcast Network for distribution, in near real-time, to the NWS field offices for viewing on AWIPS and on D2D. In the near future, additional NOHRSC snow model products and associated data, in a variety of formats, will be available on a new interactive NOHRSC web site.

Potential Snow Hydrology Breakout Session Discussion Topics

The following is a limited suggestion of potential topics for discussion at the Snow Hydrology breakout sessions. What other questions, topics, or issues would you like to discuss? Make a note of the snow hydrology issues that are important to you and your program and plan to raise them with other hydrologic program managers at the Snow Hydrology breakout session Thursday morning.

  • What are the primary snow hydrology problems in your CWA?
  • What are the potential solutions to said problems?
  • How can RFCs better address your snow hydrology problems?
  • How can the NOHRSC help to address your snow hydrology issues?
  • What NOHRSC products are most useful?
  • What formats are most useful?
  • What snow products would you like to see that are not currently available?
  • Would ArcView shapefiles of NOHRSC products be useful?
  • How would you use ArcView to address your snow issues?
  • What types of NOHRSC snow model products and displays would you like to see on an interactive NOHRSC web site?

Snow Hydrology Breakout Session Contact

If you have any questions, thoughts, or suggestions on the Snow Hydrology breakout session planned for the forthcoming National Hydrologic Program Managers Conference, give me a call.

Tom Carroll

National Operational Hydrologic Remote Sensing Center

Chanhassen, Minnesota

(952) 361-6610 ex 225

Tom DOT Carroll AT noaa DOT gov


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National Operational Hydrologic Remote Sensing Center
Office of Water Prediction
1735 Lake Drive W.
Chanhassen, MN 55317

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