Q: Why do the observed data differ?

A: The algorithm used to determine the previous day's high and low temperatures is different from the algorithm used to create the legacy/operational SCS. The old method used only the 6-hourly synoptic high/low temperature reports from the METAR observations. The TPEX method uses hourly METAR temperatures in addition to those values. This allows the TPEX software to more frequently sample the daytime and nighttime periods for each city in the SCS.

Q: Why do the forecast high and low temperatures differ?

A: The data that feed the legacy/operational SCS can be up to 6 hours older than the data that feed the Tabular Product Evolution in eXtensible Markup Language (TPEX) SCS. In rapidly changing forecast scenarios, a Weather Forecast Office's (WFO's) forecast can change quite a bit during this timeframe. For this reason, the TPEX SCS may contain some last minute updates that are not found in the official SCS products. See Table 1 for details.

Q: Why does the predominant weather forecast differ?

A: There are two primary answers to this question.

First, similar to the answer given above regarding temperature differences, the forecast data used to determine the TPEX predominant weather may be up to 6.5 hours fresher than the data in the legacy/operational SCS. See Table 1 for details.

Second, the forecast data that feed the legacy/operational SCS originate from over 100 WFOs. Many of those WFOs have tailored the way their forecast data are input into the legacy/operational SCS. In order to provide a more consistent method of presenting the forecast data in the SCS, TPEX uses a single set of algorithms when determining the predominant weather. These algorithms are designed to closely mimic other digital forecast algorithms used within the NWS and also to comply with the NWS Policy.

Data Format

• Logical separation of Forecast and Observation products.

Introduction of new product information

• As a part of the Observations in XML (ObX) product, users and partners have access to the High and Low Temperatures “so far”.
• The Forecasts in XML (FoX3 and FoX7) forecast products contain both daytime and nighttime weather summaries out to 3 and 7 days, respectively.  This differs from the legacy SCS text product, which only included daytime weather summaries and forecast projections for just 2 days.
• The FoX3 and FoX7 forecast products also contain a link to the associated weather summary icons.

Flexibility

• XML makes it easier for our users and partners to choose the output and amount of data they want.  Extensible Stylesheet Language (XSLT) style sheets can be used as starting points to tailor the exact output of desired products.
• New cities, weather elements, and times can be added to National Weather Service (NWS) products with little impact to our users and partners software.  This is the beauty of moving to XML-based products.

Accuracy

• XML products will be issued more frequently.  They will be more in tune with today’s 24x7 news cycle.
• This increased temporal frequency allows us to addresses the “West Coast” observation timing issue for reporting of High and Low Temperatures.  The “west coast” issue arises because the issuance times of the current operational SCS products (0035Z and 1235Z) do not correlate well with the natural timing of the high and low temperature of the day for West Coast cities.