Decoding the Point
Forecast Matrices
WMO : FOUS54 KHUN
AWIPS: HUNPFMHUN
Latest Tabular PFM
INTRODUCTION
An increasing number of National Weather Service offices are now
providing detailed digital forecast data products known as the Point
Forecast Matrices (PFM) and the Area Forecast Matrices (AFM). This
document will explain how to read and interpret the PFM. An example
of a complete PFM is also included.
WHAT IS THE POINT FORECAST MATRICES?
The Point Forecast Matrices (PFM) displays various forecasted
weather parameters at a specific point or geographic location in
3-hour and 6-hour intervals. These intervals combined with a matrix
format create a detailed forecast, allowing quick procurement of
forecast parameters. The PFM is available to disseminators of National
Weather Service products,
and is available on the internet.
Currently, the PFM provides 3-hourly and 12-hourly forecasts up
to 60 hours into the future. An extended portion of the PFM provides
6-hourly and 12-hourly forecasts 7 days into the future.
HOW TO READ AND INTERPRET THE PFM PRODUCT
An example of the PFM product is displayed below in Table 1. There
are several forecast parameters which appear in the PFM. At the
top of each product is the time and date that the PFM was issued.
In the case of Table 1, the forecast was issued on Monday, March
24th, and the issuance time was 9:40 a.m. Central Standard Time
(CST). Below the time and date, two forecast time lines are provided
in 3 hour increments for 60 hours (2 and one half days) into the
future. Listed on the far left of the first time line is UTC (the
abbreviation for Universal Coordinated Time). Below that line and
more familiar to most users, the local time zone that the PFM is
created in is displayed. In this example, CST is listed, which means
the hours in the time line are in Central Standard Time. Note that
in the bottom segment of the PFM, there are similar time lines displayed.
This forecast time line is broken down into 6 hour increments, providing
an extended forecast 3 to 7 days into the future. Reference dates
are located above each time line.
940 AM CST MON MAR 24 2003
DATE MON 03/24/03 TUE 03/25/03 WED 03/26/03
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 77 49 76 51 62
TEMP 56 66 75 73 66 59 53 50 58 67 75 73 67 62 56 51
DEWPT 47 46 45 47 47 47 47 48 50 50 49 49 50 50 51 50
RH 71 48 34 39 50 64 79 92 74 54 39 42 54 64 83 96
WIND DIR S SW SW S S SE SE SE S SW SW SW SW SW W NW
WIND SPD 3 5 5 5 5 5 4 5 6 11 12 9 6 6 6 8
CLOUDS FW FW FW FW FW FW FW FW SC SC BK BK BK BK BK BK BK SC SC SC
POP 12HR 0 0 10 50 50
QPF 12HR 0 0 0 0.39 0.25
SNOW 12HR MM MM MM
RAIN SHWRS C C C C
TSTMS C C C C
DATE THU 03/27/03 FRI 03/28/03 SAT 03/29/03 SUN 03/30/03
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 41 68 49 72 49 58 35 58 35
CLOUDS SC FW FW FW FW SC SC BK BK BK BK BK BK SC SC SC SC SC
POP 12HR 0 0 0 0 40 50 30 0 0
RAIN SHWRS C C C
TSTMS C C C
RAIN C C
Table 1. Sample PFM Product Output
PFM FORECAST PARAMETERS
Below are forecast parameters in the PFM.
1) MX/MN - A forecast of maximum or minimum temperatures
during the daytime or nighttime hours, respectively. The maximum temperatures
are forecast from 6:00 a.m. to 6:00 p.m. Local Time. Minimum temperatures
are forecast from 6:00 p.m. to 6:00 a.m. Local Time. The overnight
lows and daytime highs are displayed as a single number for the specific
point or geographic location.
MX/MN is forecast out to 7 days. MX/MN is located near the ending
time of each 12 hour period forecasted out to day 7.
2) TEMP - The temperature is forecast in 3 hour
intervals. It is an average temperature within the specific geographic
location for the time in question. The TEMP is generally forecasted
48 hours into the future.
3) DEWPT - The expected dewpoint temperature forecast
for the same time period as its corresponding forecast temperature,
forecast out to 48 hours.
4) RH - The relative humidity is based on the expected
temperature and dewpoint. The RH is forecast for the same time as
its corresponding temperature, and is forecast out to 48 hours.
5) WIND DIR - The expected wind direction forecast
for the corresponding time using the 8 points of a compass (e.g.,
W, NW, N. . . etc.). WIND DIR is available out to 48 hours into
the future.
6) WIND SPD - The expected average wind speed
in miles per hour for the time in question.
7) CLOUDS - The expected cloud cover forecast for
every 3-hour time period out to 60 hours. Cloud cover is then forecast
in 6 hour time periods out to day 7. The contractions used and their
meanings are as follows:
CL - Clear FW - Mostly Clear
SC - Partly Cloudy
BK - Mostly Cloudy OV - Cloudy
8) POP 12HR- This parameter is forecast for all 7
days of the PFM. The probability of precipitation is for a 12-hour
period ending at 6:00 a.m. or 6:00 p.m. Local Time. This percentage
probability is listed towards the ending time of each period out to
day 7.
9)QPF 12HR- This parameter is forecast out to 60
hours in the PFM. A quantitative precipitation forecast, QPF 12HR
lists the average precipitation expected if precipitation falls.
QPF 12HR is listed under POP 12HR, and is forecast in 12 hour periods
ending at 6:00 a.m. or 6:00 p.m. Local Time. QPF 12HR is located
towards the ending time of each 12 hour period, and amounts are
given in a range.
10) SNOW 12HR- Seasonal element. The expected
range of snowfall accumulation (in whole inches) during a 12-hour
period ending at 6:00 a.m. or 6:00 p.m. Local Time. SNOW 12HR is
available out to 36 hours, located near the ending time of each
12 hour period for which it is forecast.
11) PRECIPITATION- The PFM may list several types
of precipitation. Precipitation types are only shown in the PFM
if they are forecast to occur at any point in the 7 day forecast,
and are listed in the far left column of the RDF underneath CLOUDS.
For each type of precipitation that is forecast, a probability
of precipitation is specified for 3-hour time periods out to 60
hours, then in 6 hour increments ending at 6 a.m. or 6 p.m. Local
Time out to 7 days. The types of precipitation that may be forecast
in the PFM are listed below.
RAIN- Rain
RAIN SHWRS- Rain showers
TSTMS- Thunderstorms
DRIZZLE- Drizzle
SNOW- Snow
SNOW SHWRS- Snow showers
FLURRIES- Flurries
SLEET- Sleet (ice pellets)
FRZNG RAIN- Freezing rain
FRZNG DRZL- Freezing drizzle
The probability contractions and their meanings are as follows:
S - Slight Chance (< 20%)
C - Chance (30%-50%)
L - Likely (60%-70%)
O - Occasional (80%-100%)
D - Definite (80%-100%)
12) OBVIS- An obstruction to visibility. If this
is forecast at any point out to 48 hours, a row titled OBVIS will
be listed underneath any forecast precipitation. If no precipitation
is forecast, then OBVIS will be listed under the row titled QPF
12HR. OBVIS is forecasted in 3 hour intervals. The contractions
used and their meanings are as follows:
F - Fog PF - Patchy Fog F+ - Dense Fog PF+ - Patchy Dense Fog
H - Haze BS - Blowing Snow K - Smoke BD - Blowing Dust
13) WIND CHILL and HEAT INDEX
When the Wind Chill Index is forecast to be 20 degrees F or lower
with a 5 mph or greater wind speed, a row titled WIND CHILL will
be listed under any forecast precipitation types, OBVIS or QPF 12HR.
The Wind Chill Index is forecast out to 48 hours.
When the heat index is forecast to be 100 degrees F or higher, a
row titled HEAT INDEX will be listed under any forecast precipitation
types. Like Wind Chill, the Heat Index is forecast up to 48 hours
into the future.
This page adapted from similar pages at the Memphis,
TN and Charleston,
WV offices of the National Weather Service.
|