NOUS41 KWBC 031235



Service Change Notice 16-03

National Weather Service Headquarters, Washington, DC

835 AM EDT Tue May 3 2016


TO:        Subscribers:

           -NOAA Weather Wire Service

           -Emergency Managers Weather Information Network


           -Other NWS partners and NWS employees


FROM:      Robyn Heffernan

           Acting Chief, Severe, Fire, Public and Winter Services



           Eric Christensen

           Acting Chief, Marine, Tropical, and Tsunami Services



SUBJECT:   Improved warning polygons along complex coastal

           boundaries effective May 10, 2016


Effective May 10, 2016, the NWS will complete enhancements to the

product generation software used to draw warning threat areas

(polygons) along complex coastal boundaries. This change allows a

buffer along land-marine boundaries. Small scale details of a

coastline are no longer mapped and fewer polygon vertices are

needed. This change only affects the appearance of the polygon.

There is no change to product formats, and users do not have to

take any actions.


Special Marine Warning (SMW) and the follow-up Marine Weather

Statement (MWS) polygons will be drawn slightly further into land

zones than in the past, particularly along complex coastlines.


Similarly, polygons for Tornado Warnings (TOR), Severe Thunderstorm

Warnings (SVR), Flash Flood Warnings (FFW), Flood Warnings (FLW),

Special Weather Statements (SPS) and the corresponding follow-up

Severe Weather Statements (SVS), Flash Flood Statements (FFS), and

Flood Statements (FLS) will be drawn slightly farther into marine

zones than in the past.


This change will improve warning polygons along complex coastal

boundaries of the Atlantic and Pacific Oceans, Gulf of Mexico and

Great Lakes. This change will not apply to warning polygons along

complex inland County Warning Area boundaries, such as along the

Mississippi River.


More information and several examples can be found at:



For more information, please contact:


  John Ferree

  NWS Severe Storms Services Leader


National Service Change Notices are online at: