What is the PFM?
PFM stands for the Point Forecast
Matrices product. It provides another way to view WFO
Charleston’s forecast for various specific locations in our geographic
area of responsibility.
In what format is the PFM written?
The PFM is written in a tabular format. Forecast parameters are
listed down the left hand side of the product and forecasts are provided
for each parameter and each location at 3-hour, 6-hour, and/or 12-hour
Who should use the PFM?
While the PFM was initially designed to support large volume users
of NWS products, the PFM product provides specific weather forecast information
that can be used by everyone.
What are the benefits of using the PFM?
The PFM allows for the user to rapidly scan weather forecast information
and pick out the information that is most important to them. As an example,
many users are interested in relative humidity information. The traditional
NWS forecast does not provide this information. The user can access the
PFM information for a specific city and get forecast relative humidity
information at three-hour intervals. In addition, traditional NWS forecasts
many times provide ranges of temperature and wind forecasts over an area
the size of a county or a number of counties. The PFM provided specific
numeric forecasts for specific locations. Advanced users will be able
to parse out important PFM data and reissue this information in their
When will the PFM data be updated?
While the PFM will have a mandatory issuance twice daily of no
later than 4 am and 4 pm daily, the PFM will be an event-driven, dynamic
product. As weather changes and forecasts change, the PFM product will
also be updated as needed. This means that the PFM product will always
provide fresh information for anyone using it.
What time frame does the PFM cover?
The PFM covers a 7-day period of time from the time of issuance.
When I look on the PFM, I see two different time lines below
the date. What am I looking at?
UTC stands for Universal Time
Coordinate. Depending on the time of year, this time
will differ from the local time by 4 or 5 hours. On the next line below
the UTC line, you will see another line showing either EST or EDT (depending
on the time of year). This will be your local time on a 24-hour clock.
As an example, in local time, “03" would represent 3:00 am, “12"
would represent noon, and “18" would be 6:00 pm.
When I look at the MX/MN line, I only see one number every
12 hours. What am I looking at?
The MX/MN line of the PFM displays the high and low temperature
forecast. The maximum temperature is valid between 7 am and 7 pm local
standard time. The minimum temperature is valid between 7 pm and 8 am
local standard time. The numbers you see indicate the forecast high and
low temperature . The MX/MN temperature forecast is placed in the column
at the end of the valid period, with the maximum or minimum temperature
occurring sometime within the prior 12 hours (for the MaX temp) and 13
hours (for the MiN temp).
What units are used for the wind forecast and how many points
on the compass are used?
Also, what does “00" mean?
Wind information is provided in mph (miles per hour) as opposed
to knots. WIND SPD represents a snapshot of the forecast sustained wind
speed at the indicated hour through the first 2 ½ days. WIND GUST
provides a snapshot of the wind gusts in mph (miles per hour) at the indicated
hour. A gust is only indicated when the wind is expected to exceed the
forecast sustained wind by at least 10 mph. “00" represents calm
Beyond 60 hours, wind character codes (WIND CHAR) are used. Click
here to see a table of Wind Character Codes
What does all this cloud information mean?
During the first 60-hours, the PFM provides 3-hourly forecasts
of opaque sky cover. This is done through a series of different cloud
codes. Click here to access the Cloud Code Table.
After 60 hours, a different parameter, AVG CLOUDS, is used to indicate
the average amount of all clouds during a 6-hour period ending on the
hour indicated at the top of the column.
How does the PFM handle forecast information about precipitation?
POP 12HR is a parameter that is used in the PFM to express the
likelihood of measurable precipitation (1/100th of an inch) during the
12-hour period that ends at 6:00 am or 6:00 pm local time (0600 or 1800).
The POP 12HR parameter is provided through Day 7.
Another parameter, QPF 12HR represents the total amount of precipitation
in inches of liquid equivalent that is forecast at a specific point during
the 12-hour period ending at 6:00 am or 6:00 pm local time (0600 or 1800).
QPF will be provided as a range in hundredths of an inch and will be included
out through the first 60 hours.
During the locally defined winter period defined by WFO Charleston, the PFM will also include the SNOW 12HR parameter which will provide users
with specific total snowfall accumulation 12-hour point forecasts in whole
inches of snowfall ending at 6:00 am and 6:00 pm local time. The SNOW
12HR parameter will appear as a single or double digit, or as a range
(i.e. “2-4" meaning two to four inches of snow in a 12-hour period
ending at the specified time). “00-00" is used to indicate no snowfall.
“T” is used to indicate trace amounts (less than 0.1 inch
of frozen precipitation). The SNOW 12HR is forecast out to 36 hours.
Precipitation types may also appear in the left hand column of the PFM.
At 3-hour time intervals out to 60 hours and then during 6-hour time intervals
between 60 hours and Day 7, specific probability of precipitation codes
will be included when certain precipitation types are forecast.
Click here to access a table of PFM Precipitation types
and Probability of Precipitation Codes.
What other types of information are in the PFM?
Visibility forecasts are provided in the PFM at 3-hour intervals
through 60 hours.
Click here to access a list of Obstruction to Visibility
Codes used in the PFM.
Other information you might see on a PFM include wind chill and heat
index information based on criteria locally defined by WFO Charleston. Six-hour
forecasts of minimum wind chill and maximum heat index may also appear
on the following line, again when local criteria are met.
The traditional NWS Forecast highlights long-fused watches,
warnings, and advisories. Will the PFM provide this information as well?
The answer to this question is “yes”. In the future,
special codes will allow for specific input of long-fused watch, warning,
and advisory information into the PFM product. Special codes for watches
(“A”), warnings (“W”), and advisories (“Y”)
will be applied to 3-hour time spans, matching the valid times of the
event as possible. The specific watch, warning, or advisory will be provided
in the left hand column, with the special codes appearing within the first
60 hours of the PFM.
What does “MM” mean on the PFM product?
“MM” represents missing data in the PFM product.