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WHAT ARE THE POINT FORECAST MATRICES?
The PFM displays forecast weather parameters in 3, 6, and 12 hour intervals out to 7 days in the future.
HOW TO READ/INTERPRET THE PFM PRODUCT
There are several forecast parameters which appear in the PFM product. Some of these values are forecast in 12 hour intervals while others are forecast in 3 and 6 hour intervals. Listed below is an example of an PFM product and a description of each of its parameters.

 

DCZ001-VAZ054-072000-
ARLINGTON-DISTRICT OF COLUMBIA-
INCLUDING THE CITIES OF...ALEXANDRIA AND FALLS CHURCH...WASHINGTON
355 AM EDT FRI MAY 7 2004


DATE             FRI 05/07/04            SAT 05/08/04            SUN 05/09/04
UTC 3HRLY     07 10 13 16 19 22 01 04 07 10 13 16 19 22 01 04 07 10 13 16 19 22
EDT 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                      81          58          63          56          81
TEMP             60 65 76 81 80 75 67 61 59 60 62 63 62 59 58 57 56 67 76 81 79
DEWPT            58 55 59 60 58 56 55 54 52 45 46 48 48 51 51 53 53 55 58 59 58
RH               93 70 56 49 47 52 65 78 78 58 56 58 60 75 77 86 90 65 54 47 49
WIND DIR          W SW  W NW NW  N  N NE NE  E  E  E  E  E  E  E  E SE  S SW SW
WIND SPD          6  6  9 10  8  6  6  6 10 13 14 14 14 12 12  9  9  9  9  9  9
CLOUDS           SC SC SC SC SC SC SC SC BK BK BK BK BK BK BK BK BK SC SC BK BK
POP 12HR                     30          30          20          10          30
QPF 12HR                   0.06        0.04        0.04           0        0.01
SNOW 12HR                 00-00       00-00       00-00
RAIN SHWRS        S  S  C  C  C  C  S        S  S  S                       S  S
TSTMS             S  S  C  C  C  C  S        S  S  S                       S  S


DATE               MON 05/10/04  TUE 05/11/04  WED 05/12/04  THU 05/13/04
UTC 6HRLY     04   10 16 22 04   10 16 22 04   10 16 22 04   10 16 22
EDT 6HRLY     00   06 12 18 00   06 12 18 00   06 12 18 00   06 12 18

MIN/MAX            62    81      65    83      63    83      67    86
TEMP          66   62 77 79 68   65 79 80 67   63 79 81 70   67 82 84
DEWPT         59   58 57 57 58   58 56 56 56   56 56 56 56   56 60 60
PWIND DIR          SW    SW       W     W      SE     S       S    SW
WIND CHAR          GN    GN      GN    LT      LT    GN      GN    GN
AVG CLOUDS    BK   SC SC SC SC   SC SC SC SC   SC SC SC SC   SC SC SC
POP 12HR           30    20      20    20      20    20      20    20
RAIN SHWRS     S    S  S  S  S    S  S  S  S    S  S  S  S    S  S  S
TSTMS          S    S  S  S  S    S  S  S  S    S  S  S  S    S  S  S


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.
TEMP
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.
DEWPT
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.
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.
WIND DIR
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.
WIND SPD
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.

See Wind Speed Table for list of categories.
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.
CLOUDS
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.

See Table for list of cloud codes and equivalent skycover definitions.
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 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.
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.

MAX QPF (optional)
The value for MAX QPF value is the estimated maximum amount of precipitation, in inches occurring at any point
within the zone(s) during the12-hour period ending at 6:00 a.m. or 6:00 p.m. local time. This amount is presented
as either a single value or a range, and is based upon a 75% confidence level of the QPF forecaster(s). MAX QPF
is right justified below the hour defining the ending time of the expected precipitation, and is available out to 60
hours.
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.
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 at any point within the zones(s) 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.

See Table for types of precipitation and probabilities of preciptation.
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. In the Figure 19 example, “K” implies that smoke is restricting visibility during the 6-hour period from
3:00 a.m. - 9:00 a.m. EST on Monday 2/12/01. OBVIS is forecast at 3-hour intervals through 60 hours.

See Table for list of OBVIS codes.
WIND CHILL
Wind Chill is 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 is forecast out to 60 hours.
MIN CHILL 6HR
When WIND CHILL values appear in the PFM, a 6-hour minimum wind chill may appear on the following row.
These values indicate the minimum wind chill index forecast to occur during the 6-hour period ending at the time
indicated at the top of the column. MIN CHILL 6HR is forecast out to 60 hours.

Definitions of the PFM Codes

Wind Speed Table

Wind Char - 12HR Max 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

Clouds

Sky Cover
CL Clear/Sunny 0%= 6%
FW Mostly Clear/Mostly Sunny > 6% and = 31%
SC Partly Cloudy/Partly Sunny >31% and = 69%
BK Mostly Cloudy >69% and = 94%
OV Cloudy >94% and = 100%

Precipitation Type

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

Probablility of Precipitation Codes

Stratiform or Convective
S Slight Chance (= 20%)
C Chance (30%-50%)
L Likely (60%-70%)
O Occasional/Periods of (80%-100%)
D None (80%-100%)

Convective Only
IS Isolated (= 20%)
SC Scattered (30%-50%)
NM Numerous (60%-70%)
EX None (80%-100%)

OBVIS

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


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Page last modified: January 24, 2006 3:50 PM
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