NOUS41 KWBC 091900 AAA



Technical Implementation Notice 15-05: Updated

National Weather Service Headquarters Silver Spring, MD

300 PM EST Thu Mar 9 2017


To:      Subscribers:

         -NOAA Weather Wire Service

         -Emergency Managers Weather Information Network


         Other NWS Partners, Users and Employees


From:     Edward P. Clark

          Director, National Water Center

          Deputy Director, Office of Water Prediction

          NOAA National Weather Service


Subject:  Updated: Modification of the National Operational

          Hydrologic Remote Sensing Center, (now the Office of

          Water Prediction (OWP)) prototype gridded

          Snowfall Analysis product effective March 15, 2017


Updated to amend the 2015 Technical Information Notice to

reflect the modified OWP gridded Snowfall Analysis


Effective 1200 Coordinated Universal Time (UTC) Wednesday, March

15, 2017, the OWP in Chanhassen, MN, will change the prototype

analysis of snowfall observations displayed on its interactive



These products are currently viewable at:


Beginning March 15, they may also be viewed by connecting to the

NOHRSC Interactive Snow Information page at:

and selecting from the "Select Physical Element" drop-down item

"Interpolated SF (24 hrs)," "Interpolated SF (48 hrs)" or

"Interpolated SF (72 hrs)."


The current version of the analysis is generated by

interpolating observations of 24-hour snowfall accumulations at

point locations over the coterminous United States (CONUS),

taken primarily from Cooperative observers, CoCoRaHS observers

and NWS spotter reports. The interpolation method is a Barnes 

2-pass analysis performed for 1200 UTC each day at a resolution

of 0.04 degrees (144 arc sec). The products originally included

a 0000 UTC analysis, but this was discontinued due to its 

poor quality.


The modified products are built upon a 24-hour background

analysis based on Stage IV quantitative precipitation estimates

(QPE), with contributions from High Resolution Rapid Refresh

(HRRR) and Rapid Refresh (RAP) quantitative precipitation

forecasts, National Snow Analysis (NSA) 2-meter air temperature

grids, and a new gridded snowfall-to-liquid ratio climatology.

Snowfall observations are assimilated into this background

analysis via ordinary kriging. The addition of a background

analysis produces a spatial distribution of snowfall that

improves upon the previous version, particularly in the 

Western United States.


Improved automated quality control of station reports has been

implemented for the modified analysis, and a new method for

accurately subdividing snowfall observations into hourly amounts

has made a 0000 UTC analysis possible. Consequently, the

modified analysis is performed for 24-hour periods ending on

both 0000 UTC and 1200 UTC each day. The first issuance of the

analysis is generated about an hour after a given analysis time,

then repeated hourly for at least 72 hours following the

analysis time so the products can benefit from late-arriving

observations and improvements in the QPE input to the background



The modified analysis uses the same 0.04 degree (144 arc sec)

spatial resolution as the previous version. The same file

formats (NetCDF, GeoTIFF, and GRIB2), projections and

accumulation periods (24-, 48-, and 72-hour, plus seasonal) that

were available previously will be available for the modified

analysis; however, some changes to file naming conventions will

occur. As before, all accumulations for periods exceeding 

24 hours are produced by aggregating 24-hour analyses; i.e., no

independent 48- or 72-hour-or seasonal-analyses are performed.


For questions regarding these changes, please contact:


Greg Fall

Office of Water Prediction - Chanhassen, MN



David Soroka

NWS Winter Weather Program Leader

Severe, Fire, Public and Winter Weather Services Branch

Silver Spring, MD



NWS National Technical Implementation Notices are online at: