There are certain important messages that the NWS issues, such as watches and warnings, in which the communication identifier [or] wmo header message header alone does not contain sufficient information for identifying specific geographic areas. To provide this information, text products may contain one or more additional coded lines containing one or more UGC (Universal Geographic Code) groups. These give specific Federal Information Processing Standard county or NWS zone identifier numbers.
A code group consists of 6 alphanumeric characters, consisting of a 3 letter prefix and a 3 number suffix, followed by a dash (-). There are additional format rules, given below. The final UGC element, after all code groups, is the product-purge time (previously called the expiration time) in UTC (Coordinated Universal Time) aka GMT (Greenwich Mean Time). This is the time after which the product should no longer be broadcast or viewed.
A generic UGC line, with some concatenated groups, looks like:
SS = 2-letter state identifier (USPS code).
F = UGC format, either:
= 'C', indicating the nnn following represents a county or
an independent city, or
= 'Z', indicating the nnn following represents an NWS
public-forecast zone (or part or all of the state).
nnn = after 'C', the FIPS country or independent city number, or
= after 'Z', the NWS zone number, or ALL (all zones in the
state), or 000 (an undesignated part of the state).
DDHHMM = the product-purge date's day (DD), hour (HH), and minute (MM).
There are certain conventions or rules for interpreting a UGC series of concatenated groups, in which repeated prefix elements can be omitted.
ILZ001>003-005-IAC045-163-051200- means: the affected areas for the particular message include northern Illinois zones 1, 2, 3, and 5, and the (bordering) counties of southeast Iowa, Clinton and Scott, and the product is to be purged on the 5th day of the month at 1200 UTC.
For most NWS message products, the UGC is placed on the third line of the header, immediately after the wmo header the AWIPS identifier. For messages in the form of a collection of separate information, each affecting a different area but all under one message header, each separate information section begins with its own UGC line and ends with a $$ line as an end-of-section marker.
An NWS UGC with a type 'C' (county) code uses the Federal Information Processing Standard (FIPS) 6-4 3-digit county numbers. A listings of these is available at NIST/FIPS.
An NWS UGC with a type 'Z' (zone) code uses the numbers. Maps and listings of the state zones are available here.
Zone Code Background
Each of the 121 Weather Forecast Office's (WFO) areas of public forecast responsibility is divided into zones. Most zones in the National Weather Service (NWS) Eastern, Southern, and Central Regions (mainly from the Rocky Mountains eastward) were reconfigured effective October 1, 1993, to contain only a single county. Some large and/or topographically diverse counties in the reconfiguration, especially in mountainous and some coastal areas, are further subdivided into separate zones.
Climate and usual weather features anywhere within a zone are similar. This allows a single zone forecast to serve as the local forecast for any community within the area--not just those locations where the NWS has offices. Weather conditions, however, are such that several zones typically can be grouped together under the same forecast.
A zone that contains only a single county uses the county name and, therefore, does not need supplemental county identification. Similarly, a zone that is named by part of one or more counties (e.g., New York State zone 70, "Northern Westchester" [Co.]; New York State zone 71, "Southern Westchester" [Co.]; Minnesota zone 12, "Northern Cook/Northern lake [Cos.]) also does not need supplemental county identification.
A zone, however, that contains part of one or more counties but uses another recognizable geographical name needs supplemental county identification in the list. For example, South Dakota zone 25, "Northern Foot Hills," includes an entry in the supplemental county identification column of "N Lawrence, X SW Butte, part of SW Meade," which means the zone encompasses "north Lawrence Co., extreme southwest Butte Co., and part of southwest Meade Co."
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