Explanation of the Detailed Forecast

I. What is the Detailed Forecast?

The Detailed Forecast displays various forecasted weather parameters for specified NWS zones, or zone groups in 3-hour, 6-hour, and/or 12-hour intervals. The Detailed Forecast is intended for use by large volume users of NWS forecast information and for use by the general public. The quasi-static matrix format of the Detailed Forecast allows for rapid visual scanning of a large number of forecast parameters/ values. In addition, the forecast data are decodable by computers for those who wish to create derived products. Information in the Detailed Forecast is provided to customers and partners as supplemental detail and/ or higher resolution detail than can be found in other standard NWS products. Through the Detailed Forecast product, the NWS strives to improve communications to the public and Hazards community, increase forecast resolution, provide customers the information on which they can base their decisions, and increase forecast and warning accessibility by all customers.

II. How to Read/Interpret the Detailed Forecast Product

There are several forecasted parameters which appear in the Detailed Forecast product. Some of these values are forecasted in 12 hour intervals while others are forecasted in 3 hour intervals. Listed below is a description of each of these parameters.

12 HOUR FORECASTS

1) POP 12HR - Probability of Precipitation (POP), is defined as the likelihood, expressed as a percent, of a measurable precipitation event (1/100th of an inch) at any given point within the zone(s) covered by the Detailed Forecast. The “12HR” refers to
the 12-hour valid time ending at 6:00 a.m. or 6:00 p.m. local time (0600 or 1800). The POP 12HR value is right justified in the column beneath the hour defining the ending time of the valid period.

2) QPF 12HR - This parameter, quantitative precipitation forecast (QPF) represents the total amount of liquid precipitation, in inches, expected during a 12-hour period ending at 6:00 a.m., or 6:00 p.m. local time at any point in the forecast area. The QPF is presented in locally defined ranges, (e.g., .10-.24), or single values. The QPF 12HR value is right justified in the column beneath the hour defining the ending time of the expected precipitation.

3) MX/MN - A forecast of maximum or minimum temperatures in degrees Fahrenheit (F) during the daytime or nighttime hours, respectively. “Daytime” is defined as 7:00 a.m. through 7:00 p.m. local time, and “Nighttime” is 7:00 p.m. through 8:00 a.m. local time (note that due to a 3-hour minimum time resolution, this element is right justified in the column beneath the approximate ending time of the MAX/MIN period).

4) SNOW 12HR - The expected range of total snowfall accumulation (in whole inches) forecast to occur at the specific point during a 12-hour period ending at 6:00 a.m. or 6:00 p.m. local time. SNOW 12HR will only appear during the locally defined winter period. The snow parameter contains 1 to 5 alphanumeric characters which are right justified in the column below the hour defining the ending time of the precipitation period. SNOW 12HR may appear as a single digit (1, 4, 12), or as a specified range(2-4, 8-12). When no snowfall is forecast during the locally specified winter period, double zeros (00-00) will appear in the row. Snowfall that is not measurable (less than 0.1 inch of frozen precipitation) is referred to as a trace. A trace of snow is depicted by a "T." SNOW 12HR is available out to 36 hours.
 

1) TEMP - TEMP is a snapshot of the expected temperature in degrees F valid during the indicated hour. The temperature is right justified in the column below the hour to which it refers.  TEMP is forecast in 3-hour intervals through 60 hours, then 6-hour intervals through Day 7.

2) DEWPT - DEWPT is a snapshot of the expected dew point temperature in degrees F for the same time periods as its corresponding temperature forecast. DEWPT is located directly below the temperature line. 

3) RH - The relative humidity in percent (RH) is calculated from the corresponding temperature and dew point valid during for the same hour (same column). The RH row is located directly below the "DEWPT" row.  RH is available in 3-hour increments through 60 hours.

4) WIND DIR - WIND DIR is a snapshot of the expected wind direction forecast to occur during the indicated hour, using the 8 points of a compass (i.e., N, NE, E, SE, S, SW, W, NW).  WIND DIR is available in 3-hour increments out to 60 hours.

In the 6HRLY block, PWIND DIR is the "predominant" wind direction for the zone(s) during the 12-hour period between 6:00 a.m. and 6:00 p.m., or 6:00 p.m. and 6:00 a.m. PWIND DIR is valid beyond 60 hours through Day 7.

5) WIND SPD - WIND SPD is a snapshot of the sustained wind speed in miles per hour (MPH) forecast to occur during the indicated hour.  WIND SPD is available for the same time intervals as WIND DIR.

In the 6HRLY block, WIND CHAR denotes character of the wind for the specified point during the 12-hour period between 6:00 a.m. and 6:00 p.m., or 6:00 p.m. and 6:00 a.m. WIND CHAR is comprised of six range categories of the forecasted maximum sustained winds. Each range category is equated to a descriptive wind term, i.e., a "wind character" to best describe the wind during the 12-hour period.  WIND CHAR is valid beyond 60 hours through Day 7.

6) WIND GUST - A wind gust row will appear in the 3HRLY block whenever forecasted wind gusts exceed the sustained wind speed (WIND SPD) by at least 10 MPH. WIND GUST is a snapshot valid on the hour indicated at the top of the corresponding column.  WIND GUST is a 3-hourly gust snapshot through 60 hours.

7) CLOUDS - The CLOUDS category provides a snapshot of sky coverage during the indicated hour. CLOUDS is divided into five category codes ranging from clear to overcast . Each code represents an equivalent percentage of sky cover in percent. CLOUDS parameter is valid for 3-hour time intervals out to 60 hours. Similarly, in the 6HOURLY section, AVG CLOUDS indicates the average amount of all clouds during the 12-hour period ending on the hour in which the value is placed. AVG CLOUDS is valid for 12-hour intervals beyond 60 hours through Day 7.

8) PRECIPITATION TYPE - The Detailed Forecast may list several types of precipitation. Precipitation types are only shown in the Detailed Forecast if they are forecast to occur at any point in the zone(s) during the seven day forecast, and are listed in the far left column of the Detailed Forecast underneath MAX QPF or SNOW 12HR during the locally defined winter period. For each type of precipitation forecast, an associated PoP category is specified in the body of the Detailed Forecast for the time period the precipitation is expected to occur. Three hour time intervals are forecast out to 60 hours, then 12-hour time intervals continue beyond 60 hours through Day 7.

9) OBVIS - If an obstruction to visibility (OBVIS) is forecast for the zone, a row labeled OBVIS will be listed underneath any forecast of precipitation. If no precipitation is forecast, then OBVIS will be listed under the row labeled AVG CLOUDS.

10) WIND CHILL and HEAT INDEX - Wind Chill and Heat Index are included seasonally based upon locally defined criteria.  The Wind Chill and Heat Index are forecast out to 60 hours.

11) MIN CHILL 6HR and MAX HEAT 6HR - When WIND CHILL or HEAT INDEX values appear in the Detailed Forecast, a 6-hour minimum wind chill or maximum heat index may appear on the following row. These values indicate the minimum wind chill/maximum heat index forecast to occur during the 6-hour period ending at the time indicated at the top of the column. MIN CHILL 6HR and MAX HEAT 6HR are forecast out to 60 hours.