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.
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.
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.
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.
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.
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
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.
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
See Wind Speed Table for list of categories.
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.
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.
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.
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
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
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
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.
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 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
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
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%
RAIN SHWRS Rain Showers
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%)
IS Isolated (= 20%)
SC Scattered (30%-50%)
NM Numerous (60%-70%)
EX None (80%-100%)
PF Patchy Fog
F+ Dense Fog
PF+ Patchy Dense Fog
BS Blowing Snow
BD Blowing Dust
VA Volcanic Ash