WHAT IS THE POINT FORECAST MATRIX?

The Point Forecast Matrix (PFM) displays forecasted weather parameters in 3 and 12 hour intervals out to 7 days in the future. It replaces the Revised Digital Zone Forecast (RDF).

We normally issue the PFM twice daily by 4:00 am and 4:00 pm local time for these points:

  • South Dakota:  Brookings, Burke, Chamberlain, Huron, Mitchell, Sioux Falls, Vermillion, Yankton
  • Minnesota:  Marshall, Windom, Worthington
  • Iowa:  Sioux Center, Sioux City, Spencer, Storm Lake

HOW TO READ and INTERPRET THE PFM PRODUCT

There are several forecasted parameters which appear in the PFM product. Some of these values are forecasted in 12 hour intervals while others are forecasted in 3 and 6 hour intervals. Shown below is a partial example of a PFM product and a description of each of its parameters.

POINT FORECAST MATRICES
NATIONAL WEATHER SERVICE SIOUX FALLS SD
305 PM CST MON FEB 13 2006
SDZ062-141215-
SIOUX FALLS-MINNEHAHA SD
43.57N  96.73W
305 PM CST MON FEB 13 2006
DATE                         TUE 02/14/06            WED 02/15/06            THU
UTC 3HRLY     21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12
CST 3HRLY     15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06
MIN/MAX                      24          40          14          19          10
TEMP             33 28 30 29 29 31 39 39 34 26 22 19 16 16 17 18 17 14 12 11 10
DEWPT            26 25 23 23 24 24 24 24 23 20 16 13 11 11 12 11 10  9  8  7  7
RH               75 88 75 78 81 75 54 54 64 78 77 77 80 80 80 73 73 80 84 83 87
WIND DIR         NW  W SW SW SW  W NW NW NW NW NW NW  N  N  N NE NE NE NE NE NE
WIND SPD         11  8  8  8  8 11 13 12  9  6  4  4  6 10 13 16 17 18 17 17 16
CLOUDS           FW FW SC SC SC SC BK BK SC SC SC SC SC BK BK OV OV OV OV OV OV
POP 12HR                      0           5           5          30          70
QPF 12HR                      0           0           0        0.02        0.13
SNOW 12HR                 00-00       00-00       00-00
FLURRIES                                  C  C
SNOW                                                        S  C  L  L  L  L  L
WIND CHILL       26 20 22 22 21 22 31 31 27 18 16 12  7  3  3  3  1 -3 -5 -6 -7
MIN CHILL        24    20    20    20    26    15     5     1    -1    -5    -8
DATE           02/16/06  FRI 02/17/06  SAT 02/18/06  SUN 02/19/06  MON 02/20/06
UTC 6HRLY     18 00 06   12 18 00 06   12 18 00 06   12 18 00 06   12 18 00
CST 6HRLY     12 18 00   06 12 18 00   06 12 18 00   06 12 18 00   06 12 18
MAX/MIN          12      -4     8      -4     9      -5    14       3    20
TEMP          11  9  0   -4  5  5 -1   -4  5  6 -1   -5  9 12  6    3 15 18
DEWPT          5  3 -1   -6 -4 -5 -7   -8 -4 -3 -6   -7 -2 -1 -2   -1  5  9
PWIND DIR         N       N     N      NW     W      SW     S       E    NE
WIND CHAR        BZ      GN    BZ      LT    GN      LT    LT      LT    GN
AVG CLOUDS    BK BK SC   SC SC SC BK   BK BK BK SC   SC SC SC SC   SC BK BK
POP 12HR         60      10    10      20    20       5    10      10    10
SNOW           L  C                S    S  S  S
$$

1. MIN/MAX:
(Alternatively labeled as MAX/MIN for morning issuance) 
A forecast of minimum or maximum 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.

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. 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.

Wind Character 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

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.

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.

Sky Cover Code Sky Cover Expression Equivalent Percent Opaque Sky Cover
CL Clear 0% to 6%
FW Mostly Clear/Mostly Sunny 7% to 31%
SC Partly Cloudy/Partly Sunny 32% to 69%
BK Mostly Cloudy 70% to 94%
OV Cloudy 95% to 100%

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. POP 12HR is forecast through Day 7.

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 location. 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. QPF 12HR is forecast out to 60 hours.

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 PFM may list several types of precipitation. Precipitation types only appear in the PFM if they are forecast to occur during the seven day forecast. Precipitation type codes are listed in the far left column of the 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.

Code Qualifying Term POP (%)
S Slight Chance 15% to 24%
C Chance 25% to 54%
L Likely 55% to 74%
O Occasional/Periods of 75% to 100%
D None 75% to 100%

Code Areal Term Areal Coverage (%)
IS Isolated 15% to 24%
SC Scattered 25% to 54%
NM Numerous 55% to 74%
EC None (extensive coverage) 75% to 100%

Code Areal Term Areal Coverage (%)
PA Patchy 1% to 24%
AR Areas 25% to 54%
WD Widespread 55% to 74%

14. OBVIS:
If an obstruction to visibility (OBVIS) is forecasted, 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.

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

15. 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.

16. MIN CHILL 6HR and MAX HEAT 6HR:
When WIND CHILL or HEAT INDEX values appear in the 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.

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