Decoding the Point and Area Forecast Matrices

WMO : FOUS54 KMEG
AWIPS: MEMPFMMEG and MEMAFMMEG

Latest Tabular  PFM and AFM

WHAT IS THE POINT FORECAST MATRIX AND THE AREA FORECAST MATRIX? The Point Forecast Matrix( PFM) and the Area Forecast Matrix(AFM) displays forecasted weather parameters in 3 and 12 hour intervals out to 7 days in the future.  The PFM displays forecast weather parameters for 4 point sites including Memphis(MEM), Jackson(MKL), Jonesboro(JBR), and Tupelo(TUP). The AFM displays forecast weather parameters averaged for a particular zone group. The AFM/PFM replaces the Revised Digital Zone Forecast (RDF). The products are issued daily at 4:00 am and 4:00 pm local time.

HOW TO READ/INTERPRET THE AFM/PFM PRODUCTS There are several forecasted parameters which appear in the PFM/AFM product. Some of these values are forecasted in 12 hour intervals while others are forecasted in 3 and 6 hour intervals. Listed below is an example of an PFM/AFM product and a description of each of its parameters.

DATE         FRI 07/19/02            SAT 07/20/02            SUN 07/21/02 UTC 3HRLY 08 11 14 17 20 23 02 05 08 11 14 17 20 23 02 05 08 11 14 17 20 23 CDT 3HRLY  03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 1. MX/MN                   98          66          98          64          98 2. TEMP        74 85 93 97 92 83 74 67 70 79 90 96 95 89 79 68 73 84 93 96 92 3. DEWPT      59 56 48 47 49 51 53 54 54 53 50 49 49 50 50 51 53 58 60 57 56 4. RH         59 37 21 18 23 33 47 63 56 40 25 20 21 26 36 54 49 41 33 27 29 5. WND DIR SW SW  S  S  S  S  S  S  S  S  S  S  S  S  S  S SW  S  S  S  S 6. WND SPD    7  8  8  9  8  7  7  7  6  8 11 11 10  9  9  7  7  8  9 11 14 6a.WND GUST 7. CLOUDS     OV OV OV OV BK SC SC SC SC SC SC SC SC SC BK BK BK BK BK BK FW 8. POP 12HR               65           0           0           0           0 9. QPF 12HR 0.07-0.23 0 0 0 0 10.SNOW 12HR 00-00 00-00 00-00 00-00 00-00 11.RAIN SHWRS L 12.TSTMS L IS IS IS IS 13.RAIN L L L L 14.OBVIS DATE       MON 07/22/02 TUE 07/23/02 WED 07/24/02 THU 07/25/02 UTC 6HRLY 05 11 17 23 05 11 17 23 05 11 17 23 05 11 17 23 05 CDT 6HRLY 00  06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00 MN/MX       64    90      64    92      65    93      64    91 TEMP 62 49 65 77 62 49 63 74 60 49 63 73 59 47 61 72 61 DEWPT 48 46 48 48 42 39 43 48 48 46 45 45 46 47 49 50 49 PWIND DIR NE NE SW SW SW SW SW SW WIND CHAR BZ BZ GN GN GN BZ BZ BZ AVG CLOUDS    SC    SC      SC    SC      SC    SC     SC    SC POP 12HR 0 0 0 0 0 0 0 0 See Table for list of equivalent definitions.

1. MAX/MIN. (Alternatively labeled as MIN/MAX for afternoon issuance) A forecast of maximum or minimum temperatures in degrees Fahrenheit (F)The MAX temperature is valid for the period 7:00 a.m. through 7:00 p.m. local standard time, and “MIN” is valid for 7:00 p.m. through 8:00 a.m. local standard 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). The nighttime MIN and daytime MAX may be displayed as single integer (e.g., -2, 8, 53, 102) as a range (e.g., 54 56 60) if the MAX/MIN temperatures are expected to vary across the area. In area forecasts, the middle number within the range is the representative single digit value for that area. MAX/MIN is forecast out through Day 7.

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

3. 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.

4. RH The relative humidity (RH) is a snapshot of the expected RH for the same time periods as its corresponding temperature and dew point forecast. The RH row is located directly below the “DEWPT” row. RH is available at 3-hour increments through 60 hours.

5. WIND DIR WIND DIR is a snapshot of the expected wind direction forecast to occur at the indicated hour, using the 8 points of a compass (i.e., N, NE, E, SE, S, SW, W, NW). If a calm wind is forecast, double zeros (00) will be listed in place of a wind direction. WIND DIR is located below the hour to which it refers. WIND DIR is available in 3-hour increments out to 60 hours. Note special exception to wind direction for tropical cyclones in section 4.3.4.4.) 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. local time. PWIND DIR is valid beyond 60 hours through Day 7.

6.WIND SPD WIND SPD is a snapshot of the sustained wind speed in miles per hour (MPH) forecast to occur at the indicated hour. If a calm wind is forecast, double zeros (00) will be listed in place of a wind speed. (Note special exception to wind speed for tropical cyclones in section 4.3.4.4.) WIND SPD is valid in 3-hour increments out to 60 hours. WIND CHAR codes are used beyond 60 hours through Day 7 of the forecast and denote the character of the wind for 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 range categories used in conjunction with deterministic wind speeds. Each range category is equated to a descriptive wind term, i.e., a “wind character” to best describe the MAXIMUM SUSTAINED wind speed during the period.

6A. 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 snapshot of gusts of wind occurring at the indicated hour and is valid in 3-hour increments through 60 hours. (Note special exception to wind gust for tropical cyclones in section 4.3.4.4.)

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 included in 3-hour time intervals out to 60 hours. In the 6HOURLY section, AVG CLOUDS is valid for 6-hour increments beyond 60 hours through Day 7 and indicates the average amount of all clouds during the 6-hour period ending on the hour indicated at the top of the column.

8. 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 forecast area(s) covered by the AFM/PFM. 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.

9. 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.

10. 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 one or two digit number (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 forecast out to 36 hours.

11, 12, and 13. PRECIPITATION TYPE AND CATEGORY The AFM/PFM may list several types of precipitation. Precipitation types only appear in the AFM/PFM if they are forecast to occur at any point within the zones(s) during the seven day forecast. Precipitation type codes are listed in the far left column of the AFM/PFM. For each type of precipitation that is forecast, an associated POP. category is specified within the body of the product. The POP. expression for the indicated precipitation type is valid at the hour specified by the column header. Precipitation type expressions are forecast at three hour time intervals out to 60 hours, then 12-hour time intervals beyond 60 hours through Day 7.

14. 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. OBVIS is forecast at 3-hour intervals through 60 hours.

WIND CHILL and HEAT INDEX Wind Chill and Heat Index are included seasonally based upon locally defined criteria. The decision on whether to include or exclude these parameters is determined by the local WFO criteria. The Wind Chill and Heat Index are forecast out to 60 hours.

MIN CHILL 6HR and MAX HEAT 6HR When WIND CHILL or HEAT INDEX values appear in the AFM/PFM, 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.

This page adapted from the Amarillo, TX office of the National Weather Service.