Explanation of the Area and Point Forecast Matrices Product


I. What are the Area and Point Forecast Matrices Products?

The Area Forecast Matrices Product, or AFM product displays various forecasted weather parameters for specified NWS  zones, or zone groups in 3-hour, 6-hour, and/or 12-hour intervals. The Point Forecast Matrices Product, or PFM product displays various forecasted weather parameters for bigger cities in the NWS office's geographic area of responsibility. The AFM and PFM are 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 AFM and PFM allow for rapid visual scanning of a large number of forecast parameters/ values. In addition, the forecast data is decodable by computers for those who wish to create derived products. Information in the AFM and PFM are provided to customers and partners as supplemental detail and/ or higher resolution detail than can be found in other standard NWS products. Through the AFM and PFM products, 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 AFM/PFM Product

There are several forecasted parameters which appear in the AFM and PFM products. 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. An example of the AFM product is displayed in Table 1.  An example of the PFM product is displayed in Table 2

Table 1.

KSZ038>040-272230-
WABAUNSEE-SHAWNEE-DOUGLAS-
INCLUDING THE CITIES OF...LAWRENCE...TOPEKA
400 AM CST THU FEB 27 2003

DATE          THU 02/27/03            FRI 02/28/03            SAT 03/01/03
UTC 3HRLY  09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00
CST 3HRLY  03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18

MX/MN                     29          19          30          22          36
TEMP                30 30 27 23 21 20 19 22 27 30 29 25 24 23 22 25 33 36 34
DEWPT               20 21 22 21 20 20 19 21 22 24 24 22 20 18 18 20 23 23 23
RH                  79 73 81 91 94 97100 97 82 76 82 87 84 83 86 81 67 59 63
WIND DIR            NE NE NE NE  N  N NE NE  E  E  E  S SW SW  S SW SW SW SW
WIND SPD             3  3  2  2  2  3  3  4  3  3  3  4  5  5  5  5  6  6  6
CLOUDS              OV OV OV BK BK BK OV OV OV OV OV OV OV BK SC SC SC SC BK
POP 12HR                  80          10          60          50          10
QPF 12HR                0.16           0        0.05        0.04           0
SNOW 12HR                  2       00-00           1                       
SNOW                 O  O              C  C  L  L  C  C  C  C              
WIND CHILL          23                13 16             17 15 15 18 26 30 28
MIN CHILL           12    22    21    13    13    24    16    13    13    27

DATE            SUN 03/02/03  MON 03/03/03  TUE 03/04/03  WED 03/05/03 
UTC 6HRLY  06   12 18 00 06   12 18 00 06   12 18 00 06   12 18 00 06   12
CST 6HRLY  00   06 12 18 00   06 12 18 00   06 12 18 00   06 12 18 00   06

MN/MX           23    36      22    40      24    41      20    38      23
TEMP       26   23 33 34 26   22 36 38 28   24 37 38 26   21 34 35 27   23
DEWPT      21   20 20 20 18   19 26 27 28   28 30 31 26   24 22 22 21   20
PWIND DIR       SW    NW      NW    SW      SW     S       E     N      NE
WIND CHAR       LT    LT      LT    LT      LT    LT      LT    LT      LT
AVG CLOUDS BK   BK SC SC BK   BK SC SC SC   SC SC SC SC   SC SC SC OV   MM
POP 12HR        10    10      10    10      10    10      10    10      20

$$

 

Table 2

KSZ039-102221-
TOPEKA-SHAWNEE KS
39.08N  95.62W
421 AM CST MON NOV 10 2003

DATE             MON 11/10/03            TUE 11/11/03            WED 11/12/03
UTC 3HRLY     09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00
CST 3HRLY     03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18

MAX/MIN                      56          48          63          41          52
TEMP             47 49 54 56 52 50 49 49 48 52 60 63 57 48 44 42 41 44 50 52 48
DEWPT            41 44 47 48 50 48 47 47 47 48 48 48 48 44 40 38 37 35 33 32 31
RH               79 83 77 74 93 93 93 93 96 86 64 58 72 86 86 86 85 70 52 46 51
WIND DIR          S  S  S SW  S SW SW SW  W NW  N NW  W  W SW  W  W NW NW NW NW
WIND SPD          9 13 18 17  9  9  8  3  2  5  4  5  5  6  8  9  8 12 18 13  8
CLOUDS           OV OV OV OV BK BK BK BK BK BK BK BK SC SC SC SC FW FW FW FW FW
POP 12HR                     10          10          20          10          10
QPF 12HR                      0           0           0           0          MM
RAIN SHWRS                                S  S                                
DRIZZLE          AR AR                                                        
OBVIS             F  F                                                        


DATE               THU 11/13/03  FRI 11/14/03  SAT 11/15/03  SUN 11/16/03
UTC 6HRLY     06   12 18 00 06   12 18 00 06   12 18 00 06   12 18 00
CST 6HRLY     00   06 12 18 00   06 12 18 00   06 12 18 00   06 12 18

MIN/MAX            32    49      34    50      34    53      34    51
TEMP          35   32 46 43 36   34 47 44 37   34 49 46 37   34 48 44
DEWPT         29   30 30 31 34   34 37 37 31   30 34 33 35   34 35 35
PWIND DIR          NW     W      SW     S      NE     N      NW    SW
WIND CHAR          LT    LT      GN    GN      LT    GN      LT    LT
AVG CLOUDS    FW   FW SC SC BK   BK BK BK SC   SC SC SC SC   SC SC FW
POP 12HR           10    10      30    30      20    10      10    10
RAIN SHWRS                   C    C  C  C                           
RAIN                                       S    S                   

$$

 

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). 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.
 

3 HOUR FORECASTS

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.

AFM Wind Character Code Wind Character 12 hr Maximum Sustained Wind Speed
LT light < 8 mph
GN gentle 8 - 14 mph
BZ breezy 15 - 22 mph
WY windy 23 -30 mph
VW very windy 31 - 39 mph
SD strong damaging >= 40 mph
HF hurricane force >= 74 mph

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.

Sky Cover Sky Cover Expression Equivalent Percent Sky Cover
CL (Clear) Clear / Sunny 0% <= 6%
FW (Few) Mostly Clear / Mostly Sunny > 6% and <= 31%
SC (Scattered) Partly Cloudy / Partly Sunny > 31% and <= 69 %
BK (Broken) Mostly Cloudy > 69% and <= 94 %
OV (Overcast) Cloudy > 94% and <= 100%


8) PRECIPITATION TYPE - The AFM/PFM may list several types of precipitation. Precipitation types are only shown in the AFM/PFM if they are forecast to occur during the seven day forecast, and are listed in the far left column of the AFM/PFM 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 AFM/PFM 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.

Precipitation Type Code Sensible Weather
RAIN Rain
RAIN SHWRS Rain Showers
SPRINKLES Sprinkles
TSTMS Thunderstorms
DRIZZLE Drizzle
SNOW Snow
SNOWSHWRS Snow Showers
FLURRIES Flurries
SLEET Ice Pellets
FRZNG RAIN Freezing Rain
FRZNG DRZL Freezing Drizzle

 

AFM Probability Code POP Expression Equivalent POP (%)
IS Isolated (< 20 %)
S Slight Chance (< 20 %)
C Chance (30 % - 50 %)
SC Scattered (30 % - 50 %)
L Likely (60 % - 70 %)
NM Numerous (60 % - 70 %)
O Occasional (80 % - 100 %)
D Definite (80 % - 100 %)
WP Widespread (80 % - 100 %)

 

PFM Probability Code POP Expression Equivalent POP (%)
S Slight Chance (< 20 %)
C Chance (30 % - 50 %)
L Likely (60 % - 70 %)
O Occasional (80 % - 100 %)
D Definite (80 % - 100 %)

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.

OBVIS Code Obstruction to Visibility
F Fog
PF Patchy Fog
F+ Dense Fog
PF+ Patchy Dense Fog
H Haze
BS Blowing Snow
K Smoke
BD Blowing Dust

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 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.